Bone is one of the most sophisticated mineralized tissues, and the most widely used by vertebrates. At the nanometer level, the basic building block of bone is the mineralized collagen fibril, where type I collagen is the scaffold onto which the mineral phase, composed of carbonated hydroxyapatite (HA) crystals, are deposited. In our group, we have been interested in investigating how the collagen fibrils can template the formation of minerals, resulting in crystals with well defined orientation and morphology. To study the interaction between the organic (collagen) and inorganic (mineral) phases, we have been employing high resolution cryo-transmission electron microscopy (cryoTEM) and tomography (cryoET). The fast0freezing of the sample, coupled to high-resolution transmission electron microscopy, allows the visualization of the molecular structures and their 3-dimensional organization with nanometer resolution. Employing cryoTEM and cryoET, we have recently demonstrated that the supramolecular assembly and charge distribution along the collagen fibril actively controls the formation of hydroxyapatite in the collagen (figure 1).
We are now interested in using the collagen fibril and its properties to template the formation of other types of minerals, in particular magnetite. There is great technological and biomedical interest in producing magnetite crystals with well controlled sizes and morphologies, and the ability of collagen to template the formation of hydroxyapatite may be used to control magnetite as well. In addition, the reaction conditions in which magnetite is formed can be precisely controlled to produce other types of iron oxides, such as lepodicrocite, goethite, hematite, etc. Thus, we can use our system to produce a variety of different minerals controllable sizes and morphologies, ultimately forming an organic-inorganic composite material with tunable properties. See: Nudelman, F and Sommerdijk, N. A. J. M. et al., Nature Materials., 2010, 9, 1004-1009.
dr. Nico Sommerdijk (STO 2.44, Tel: 5870, Email: n.sommerdijk@ ) tue.nl
In nature, organisms are able to produce minerals with well-defined size, shape and structure through the direction of and interaction with biopolymers (figure 1a) and b)). The mineralization of calcium carbonate is controlled in such a manner, and its growth has been found to be facilitated by the presence of acidic residues (such as those present in poly aspartic acid and poly glutamic acid) which are known to act as nucleation points for the calcium carbonate crystal growth. It is of particular interest to be able to mimic these processes through the use of synthetic organic matrices, to produce structures with similar tailored design and ultimately, specified functionality.
Recently, we have observed micelles with complex internal bicontinuous and multi-lamellar structure in aqueous solutions of semi-crystalline, amphiphilic “comb-like” block copolymers of poly(ethylene oxide) and poly(octadecyl methacrylate) (PEO-PODMA) (figure 1c) and d)). Remarkably, the internal structure of these micelles is tuneable by altering the temperature and the relative block composition.
The bicontinuous micelles show promise as templates for the organization of inorganic material; for example, the biomimetic mineralization of calcium carbonate (CaCO3). However, as it stands the polymeric structure is inefficient for the mineral growth due to the lack of crystallization-promoting nucleation points.
This project will involve the modification of PEO-methacrylic block copolymers with amino acids such as glutamic and aspartic acid (Scheme 1) to incorporate acidic residues into the structure that will facilitate the mineralization of CaCO3 in the subsequent micelles. A method will then be designed to promote mineral infiltration into the micellar internal aqueous channels with the exciting prospect of forming porous CaCO3 with well-defined size and structure. The mineralized micelles will be investigated through techniques such as cryoTEM and electron tomography (ET).
Many structural biomaterials, biopolymers as well as biominerals, derive their mechanical properties from a complex hierarchical fibrillar organization. An intriguing example is the Stomatopod Dactyl club that consists of an impact resistant calcium phosphate-chitin composite structure. The chitin matrix has a highly expanded helicoidal organization, which is shown in Figure 1.
Aspects of bone, nacre, and crab shell formation have been mimicked by the mineralization ordered assemblies of collagen, chitin, and chitosan, respectively. However, mimicking the hierarchical structure of biominerals is still very challenging, and no design rules are known. On the other hand, biominerals often grow at controlled reacting conditions, such certain pH value, temperature, concentrations of reactants and also reaction rate. However, most bio-inspired mineralization studies cannot control those parameters during the reaction.
Hence, in this project, we will investigate self-assembly process of chitosan and chitosan derivatives in water solution, control the reaction parameters, and try to obtain ordered structures in a controlled biomimetic way. In addition, we want to investigate the interaction rules between biopolymers and minerals during assembly and mineralization process on the molecular level, which will be very helpful for biomineralization research and biomaterials synthesis. According to this aim, we need to build up a controlled reaction system assisted by Tiamo titration setup, to investigate the assembly process of chitosan, the nucleation and growth of calcium phosphate, and the formation process of chitosan/calcium phosphate biocomposites by the cryo-transmission electron microscopy (cryoTEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) etc.
In Nature several examples can be found of the use of biosilica, but probably the most well-known examples are the diatom algae. These eukaryotic species are able to form very dense and highly structured silica-based exoskeletons at physiological pH and ambient temperature. Understanding of this highly accurate and controllable mechanism is of great interest in both the scientific and industrial field.
In the last decades different protein families have been identified in the frustus of these species and the combination of polypeptides enriched in (phosphorylated) serines and lysines with long chain poly amines (LCPA’s) are found to be active in the silica precipitation process. Although electrostatic interactions are suspected to play a key role, the mechanism and the influence of other interactions are poorly understood.
In this project, the main aim is to gain insight in the function of the interplay between charges and the charge distribution on a surface in the silica formation mechanism. We will use a range of different randomly sequenced poly(amino acid)s with different compositions in terms of hydrophilicity/hydrophobicity and positive/negative charges in order to study the fundamentals and role of charge distribution in the peptide chain on the (bio)silicification process. These poly(amino acid)s on an emulsion droplet can act as a mineralization template for silica deposition, but also block copolymers or the combination of both can be used.
In order to get insight on the molecular level we will use solid state 29Si NMR combined with Raman and infrared spectroscopy to determine the degree of mineralization. The morphology and growth of the formed silica can be characterized in solution with cryoTEM.
In the next 20 years, energy consumption will rise by 40 %, mostly in developing countries, where 1.6 billion people still lack access to electricity, and where 3 billion people rely on traditional biomass fuels for cooking, heating, and other basic household needs. Satisfying the energy need for all of humanity will be one of the most challenging problems of the coming decades. Between the economic crisis and the problem of global warming the world calls out of a green, durable and cheap solution to this energy demand.
Solar energy could solve part of this problem. Photovoltaics are becoming more and more competitive as more investment in the energy sector in recent years has produced major advances in automation, manufacturing efficiencies and throughput. One of these advances is the improvement of the polymer solar cells, which attract attention as possible competitors for crystalline silicon solar cells, with the low cost, flexibility, light weight and fast roll-to-roll production as major advantages.
A polymer solar cell contains an electron donor and acceptor material. As donor component we use poly-(3-hexylthiophene), a conjugated polymer and as acceptor a fullerene. By mixing these components and depositing those on a substrate a photoactive layer can be made. To make sure the plastic can convert light into power, the intermixing of these compounds needs to be simplified. We make our conjugated polymer into nanostructures in solution to print them later as an ink. This way the solar cell will have the optimal internal structure.
This is a versatile project with a more fundamental part where you will investigate the formation and creation of these nanoparticles in more detail. You will use wide range of experimental techniques for materials research, to create more understanding so nanoparticles can be tailored to the needs of the solar cell. Secondly there is a characterization part where you will use spectrometry and electron and scanning probe microscopy to investigate the nanoparticles you create. In the end we intend to make working solar cell devices from these nanoparticles and evaluate their performance.
In Nature several examples can be found of the use of biosilica, but probably the most well-known examples are the diatom algae. These eukaryotic species are able to form very well organized and highly cross linked silica-based exoskeletons at physiological pH and, moreover, low temperature and pressure conditions. Understanding of this highly accurate and controllable mechanism is of great scientific interest.
Amphiphilic block copolymers are able to self-assemble in aqueous solutions to form discrete particles of various morphologies. In our laboratory, we have observed micelles with complex internal bicontinuous and multi-lamellar morphology from block copolymers of poly(ethylene oxide) and poly(octadecyl methacrylate) (PEO-b-PODMA). We can also direct the micellar internal morphology through changes to the relative block composition. Their significance is highlighted by their potential for use as templates to direct the size and form of inorganic materials; specifically, the biomimetic mineralization of silica.
Although in nature different protein families have been identified to be active in the silica precipitation process, ethylene oxide blocks in polymers are also known to have a catalytic effect. Although electrostatic interactions are suspected to play a key role, the mechanism and the influence of other interactions are poorly understood. By varying the morphology of the polymeric micelles, i.e. the mineralization template, we gain insights into the polymerization process of silicate ions.
Goal of this study:
In this project, the main aim is to gain insight into the silica formation mechanism in/on these polymeric micelles. This involves obtaining control over the behaviour of these micelles under different conditions (e.g. ionic strength and pH) as well as the silicification process. In order to gain insight on the molecular level, we will use solid state 29Si NMR combined with Raman and infrared spectroscopy to determine the degree of mineralization. The growth of the formed silica can be characterized in solution with cryoTEM. Together with tomographic studies to reveal morphological changes, the role of non-electrostatic interactions on the silicification process can be unravelled.
MSc Marcel van de Put (STO 2.40, Tel: 3053, Email: m.w.p.v.d.put@ ); tue.nl
dr. Beulah MCKenzie (STO 2.29, Tel: 2405, Email: b.e.mckenzie@ ); tue.nl
dr. Nico Sommerdijk (STO 2.44, Tel: 5870, Email: n.sommerdijk@) tue.nl
Polymers are generally electrically insulating, which is a useful property when you want to insulate copper wires in an electricity cable with a polymer film. However, it can lead to the build-up of static electricity, resulting in small discomforts such as dust on television screens, small electric shocks when turning on the light, and exploding chemical factories.
To avoid such inconveniencies, conductive polymers can be used and an interesting option for making polymeric materials conductive is by mixing the polymer with electrically conductive nanoparticles (making a polymer nanocomposite). When the particles are randomly distributed through the polymer matrix without touching each other, the composite will still be an insulator. At certain conditions, however, the particles will organize themselves in such a way that conductive 3-D fractal networks are formed, resulting in a dramatic increase of the conductivity of the material. This type of materials can be used in a large number of applications, for instance in displays, light emitting diodes, and solar cells.
In this graduation project you will be making and characterizing such conductive polymer nano-composites. Nanoparticles of antimony-doped tin oxide (ATO) with a diameter of 7 nm will be used as conductive filler. The particles have a surface that has been modified with a so-called silane-coupling agent to make the particles well dispersible in an acrylate-based polymer matrix. The objective is to make conductive composites with a low filler amount. This is desirable because the filler material is relatively expensive, but this way also the polymer material and processing properties are best retained. However, we would not only like to make the materials, we also want to be able to understand and explain at what conditions formation of a 3-D network occurs.
We expect this to be a versatile project where a number of experimental techniques will be used, e.g., dynamic light scattering, XPS, FT-IR spectroscopy, electron microscopy, and four-point conductivity measurements You will be working in a field of materials science which is not only fascinating from a scientific point of view, but which also attracts a lot of attention from industry. Cooperation with industrial partners will therefore be an important part of the project.
Interested? Contact us and we’ll talk about what you would like to do and what we had in mind.
Carbon based nanofillers like carbon nanotubes, carbon fibers, graphene possess exceptional physical properties such as electrical conductivity, strength, hardness, thermal conductivity. These functional properties can be introduced to a conventional polymer by homogenously dispersing the nanofillers in polymer matrix by suitable processing method and subsequently they form polymer nanocomposites. Besides the dependence of the intrinsic properties of carbon nanofillers, the macroscopic functional properties of the polymer nanocomposites also depend on the formation of mesoscopic networks of the nanofillers. Despite the fact that 3D network structure of nanofillers exist which can be inferred from the significant increase in the functional properties, so far, there are very few studies which explains the influence of 3D networks on functional properties based on electron microscopy imaging and image analysis.
In this project we study about the structure-property relation between the nanofiller networks and the functional properties of polymer nanocomposites. Incremental increase in filler concentration of polymer nanocomposites improves the functional properties. For instance, adding carbon nanotubes incrementally, at certain specific concentration, the so called insulating polymer behaves like a conducting polymer by forming the first network pathway. This specific filler concentration is called electrical percolation threshold. Similar kind of effects is also noticed in mechanical properties called as rheological threshold usually at different filler concentration. Our objective is to understand the fundamental requirements for these percolation thresholds. At first, we start with the preparation of the nanofiller dispersions and composites followed by characterization and image analysis. Experimental techniques and characterization will include but not limited to compression molding, tensile test, DMA, DSC, TGA, transmission electron microscopy.
Interested? Contact us and we’ll talk about what you would like to do and what we have in mind.
Nanocomposites, consisting of nano-sized filler particles embedded in a polymer matrix, can have unique properties for high-tech functional applications. Because a thin layer of material is sufficient for many of these applications, the field of nanocomposite coatings represents a relevant topic that is studied intensively. The key to the successful preparation of nanocomposites is dispersion: how to separate the individual filler particles and how to keep them separated throughout the matrix? In nanocomposite coatings, however, there is another aspect to keep in mind. In previous studies it was observed that, even if the particle distribution is homogeneous in the bulk of the coating, an inhomogeneous distribution can be observed close to the interfaces of the coating. There appears to be an interaction between the filler particles and the coating interface that leads to layers in the coating where filler particles are no longer present: so-called depletion layers (fig. 1).
The occurrence of depletion layers can have a huge impact on the performance of nanocomposite coatings. Despite of this large practical relevance, the cause of the phenomenon is not well understood. One of the present hypotheses is that van der Waals (vdW) interactions are of primary importance. In previous work, we have constructed a theoretical framework to calculate these vdW interactions and to predict the size of the depletion layer that would result from them. In addition, we have experimentally made some nanocomposite coatings and investigated the particle distribution near the coating interfaces by means of Scanning Electron Microscopy (SEM) (fig. 2).
The results of these experiments correspond reasonably well to the calculations, but the system that we used might not have been the optimal choice. More experiments with different systems are required to elucidate this mystery … and this is where you come in!
After proper sample preparation, a variety of properties can be investigated. One can distinguish between chemical properties and physical properties. Chemical properties refer to the chemical composition of the coating that can be characterized by micro-IR and confocal Raman spectroscopy. Changes in composition are caused by the radical chemistry that causes weathering. Examples of physical properties are Tg, hardness and Young’s modulus. The main characterisation techniques for these properties are advanced applications of SPM (Scanning Probe Microscopy, see figure 2). In addition, also optical and electron microscopy methods can be included to study changes in topography.
The project may include:
Interested? Contact us!
Paints primarily have a protective and aesthetically value. In this respect, smoothness is an important technological aspect, as recognized by any paint producer or producer of raw materials for paints, in the Netherlands for instance AkzoNobel, Sigma Coatings and DSM.
How does a thin film of applied paints become smooth? The driving force is the surface tension which has to conquer the viscous resistance in the paint. During drying one expects that the viscosity close to the surface increases faster in time than deeper in the film, more close to the substrate. Due to these differences modeling of the drying process is difficult. More importantly, these differences actually never have been experimentally established. However, these data are really necessary if one wants to model for instance how fast the stripes due to the brush disappear during drying. Measuring these local differences in viscosity is the primary goal of this project.
It is the intention to use an Atomic Force Microscope (AFM) to measure these local viscosity differences. Such a microscope is actually developed for much smaller objects, but we have shown that in principle the viscosity in small liquid droplets can be measured. If you choose this project you will investigate how the AFM can be best used for this purpose. The next step is to measure local viscosity differences in a number of paints, first a model type of paint and there after a real paint.
Here, we expect practical as well as interpretation complications, however with enthusiasm and creative initiative it should be possible to overcome these complications
Results will be compared with the smoothness of fully dried films. Dependent on your own interest this comparison can be pragmatic, qualitative or more basic, quantitative.
dr. Jos Lavèn (STO 2.42, Tel: 3682, Email: j.laven@ ). tue.nl
The trend in research in the area of polymers is shifting from designing, synthesis and processing of ordinary (“commodity”) polymers towards specialties, often based on polymer mixtures or polymers products made by special processing. One of the important and wide-spread application of polymers is in packaging materials. In many packaging applications the barrier properties of polymers for diffusion of gases is essential, like in food packaging and with coatings for corrosive materials and solar cells. This project is meant for us as an introduction to this field by studying the permeability of a number of coatings that are interesting to our research group.
Polyester films like many other polymers degrade to some extent by exposure to sun light (UV light). We have indications that specific polyesters degrade but as an unexpected result improve their barrier properties for oxygen. This effect may well go together with improved barrier properties for water (still not known). The goal in this project is
We will start with designing and testing a set-up for measuring oxygen permeation through films. For making the best choice, a survey of existing measurement techniques will be carried out. Then, barrier properties of a couple of polyesters will be investigated, both virgin and sun light exposed ones. This work will be done also in cooperation with PhD students. In order to understand functional differences between different samples, the films will also bee analysed for changes of their micro-structural properties on a local scale, both chemical and physical changes. For this purpose, we have sophisticated equipment available like AFM, Raman microscopy, SEM, TEM and microhardness facilities. An interesting aspect is to what extent filler particles affect the permeability. We envisage that either an increase or decrease can be obtained, depending on the conditions.
dr. Jos Lavèn (STO 2.42, Tel. 3682, Email: firstname.lastname@example.org) ,
prof.dr. Rolf van Benthem (STO 2.48. Tel. 2029, Email: email@example.com ).
The work is concentrated on preparation of large area self-assembled graphene films and their controllable doping with potential application as a chemical sensor. A student will master Hall effect measurement system, large area graphene self-assembly and other skills.
Interested? Contact us and we’ll talk about what you would like to do and what we had in mind.
Magnetite (Fe3O4) is a widespread magnetic iron oxide encountered in geology and biomineralization (www.biomineralization.nl) with many technological applications, such as in ferrofluids, magnetic inks, data storage materials, catalysts and contrast agents in magnetic resonance imaging. As its magnetic properties depend mostly on the size and shape of the nanoparticles, achieving control over the crystal morphology is an important and challenging goal for materials scientists. Synthetic routes to magnetite with controlled size and shape exist, however these involve high temperatures and rather harsh organic solvents, while synthesis in water and at room temperature generally yields poor control over these aspects and therefore over the magnetic properties of the obtained particles. In contrast, in nature organisms such as magnetotactic bacteria – who use chains of magnetite crystals as nano-sized compass needles! – are able to precisely control their morphology, resulting in uniform and monodisperse nanoparticles (Fig. 1a). The magnetite formation in these bacteria is believed to occur through simple co-precipitation of Fe(II) and Fe(III) ions, but is not yet fully understood.
In this project, we aim at controlling the size and shape of magnetite, but also the dispersibility and organization in solution and the magnetic properties in a “green” way (in water, at room temperature). We mimic the proteins of the magnetotactic bacteria that direct magnetite formation by random amino acid copolymers with varying monomer content and thereby varying hydrophilicity and net charge (Fig. 1b). These polymers are synthesized by solid-phase peptide synthesis and we study their impact as nucleation and growth control agents by, for example, cryogenic transmission electron microscopy (www.cryotem.nl), powder X-ray diffraction, dynamic light scattering and magnetometry. So far we have found that acidic monomers are the most effective in influencing the properties of magnetite. By changing the polymer composition we can tune the morphology (Fig. 2a) as well as the magnetic properties (Fig. 2d) of the crystals, shifting from ferrimagnetic to superparamagnetic behavior. Further, the polymers bind to the surface of the particles and improve their dispersibility in a pH-dependent manner (Fig. 2b), allowing the nanomagnets to organize into long strings in solution (Fig. 2c). Now we are aiming at achieving even better control over the process by carrying out the synthesis at constant pH, temperature and also redox potential using state-of-the-art titration technology, as well as turning our science into a real product: suistainable ferrofluids (in collaboration with Ioniqa Technologies B.V., www.ioniqa.com ), where forming stable dispersions in ionic liquids is a key factor.
Interested? Feel free to contact us!
Jos Lenders (STO 2.32, Tel.: 3331, E-mail: J.J.M.Lenders@) tue.nl
Nico Sommerdijk (STO 2.44, Tel.: 5870, E-mail: N.Sommerdijk@ ) tue.nl
Waterborne paints are an environmentally friendly alternative for the traditional solvent-based alkyd paints with hazardous catalysts. Research in this area is focused on developing paints without solvent and hazardous catalysts. One way to avoid solvent is to use the alkyd not as diluted in solvent but as an emulsion in water. This leads to very good coating properties. Another improvement is the search for non-hazardous catalysts. Our group, one of the most prominent academic coating groups, is active in both fields.
The key issue
One of the questions is how exactly the solidification (“physical and chemical drying”) of such a paint occurs. The chemical reactions involved are rather complex, but some of the main lines are known. We did already substantial research on how chemical reactions “penetrate” in the film (initiated by diffusion of oxygen) and lead to solidification. Is a solid skin formed first or is the drying throughout the film; can you control this balance? Another long-standing issue in in the paint industry is the effect of ripples in a paint layer. It is known that this especially occurs with thick paint layers. One explanation is that the solidified skin cracks locally so that the amount of surface locally increases.. We have arguments why it occurs in another way. We have a special approach in mind to resolve this question. An experimental tool is Confocal Raman Microscopy that allows us to observe how chemical conversions proceed at any position in a paint film. Although we do use this technique already on a routine basis, we have ideas about major improvements of this technique, especially its spatial resolution.
This project has two goals:
dr. Jos Lavèn (STO 2.42, Tel. 3682, Email: j.laven@.), tue.nl
prof.dr. Bert de With (STO 2.35, Tel. 4947, Email: g.dewith@), tue.nl
prof.dr. Rolf van Benthem (STO 2.48, Tel. 2029, Email: r.a.t.m.v.benthem@ ). tue.nl
Calcium carbonate biominerals are formed through a complex process between organic and inorganic compounds by various – mainly marine – organisms. As an interesting example, the sea urchin spine was found to consist of a mesocrystalline array of nanocrystals embedded in macromolecules, which yet diffract as a single crystal of calcite (Figure 1). In order to understand the formation of this so-called mesocrystal and to transfer the know-how to biomimetic mineral synthesis, it is important to elucidate the mechanism of interaction between the organic and inorganic phase that lead to these hybrid materials.
In this project we use a polyelectrolyte (polystyrene sulfonate; PSS) to investigate the formation of calcium carbonate (meso)crystal formation in the lab. We can grow complex morphologies of calcite - which appear to consist of smaller individual nanoparticles - on a substrate by using an ammonia diffusion method in a desiccator together with the PSS (Figure 2A). However, by overgrowth on calcite single seed crystals we can create similar morphology bulk structures (Figure 2B). These results show that under the conditions used, the mesocrystal formation of these larger structures is in fact an overgrowth mechanism on a single crystal of calcite. In situ AFM confirmed the modification of the obtuse and acute steps of the calcite crystal on a growth hillock “live” in solution, where similar facets can be observed as in the bulk morphology (Figure 2C).
We are now interested in the chemistry of this overgrowth mechanism, and want to probe interactions between calcium, carbonate and PSS. In this project you will use fluid cell TEM as a great tool to visualize dynamic transformations in initial mineralization formation, as well as Zeta-potential measurements, calcium-titrations and other interesting techniques to investigate this. Furthermore, you get to cooperate (in)direct with collaborators in Berkeley, USA. Do not hesitate to talk to us about the possibilities.
(Scanning) Transmission Electron Microscopy (STEM) is one of the most successful and most employed techniques to study nanostructured multiphase materials such as e.g. polymer composites or heterogeneous catalysts. Nevertheless, images are conventionally acquired only from small portions or areas of the sample thus leaving a significant knowledge gap at the meso scale. To address problems within this meso gap such as e.g. variability in particle distribution or particle networks, large areas of the sample need to be imaged at once. In particular, bringing local high magnification detail in context using low magnification overviews is a significant advantage over conventional approaches. While these tasks could in principle be performed manually, automation of image acquisition and image stitching would increase analysis speed by orders of magnitude and thus allow for statistically significant sample portions to be analyzed. Finally, image analysis of obtained datasets provides the means to study local properties and their variability over large areas quantitatively. An example of a inhomogeneous carbon nanotube network in a polymer nanocomposite is given below with (a) overview and (b,c) higher magnification details.
The MSc project focuses on the distribution and network formation of conductive carbon structures in polymer nanocomposites and will cover the entire workflow of nanocomposite preparation, bulk conductivity measurements, TEM sample preparation including ultramicrotomy, TEM imaging, TEM automation, and quantification of filler distribution and networks by image analysis. TEM automation will be addressed in collaboration with a MSc student of Dr. A. Tejada Ruiz (Mechatronics Systems Design TU Delft). The principal goal of the project is to describe how structural variability affects overall performance. Interested? Contact us and we’ll talk about what you would like to do and what we had in mind.
Can solar cells and flat panel displays be made flexible?
Electronic devices like solar cells, e-readers and flat panel displays are typically rigid and produced as a stack of functional layers of between 10 nm and 100 μm. To give an example, the right figure shows how a light emitting diode (LED) is built up: in this particular case the light is generated between the cathode and the ITO anode, and then runs through the transparent barrier and carrier layers. Normally, the transparent carrier is made of glass, making the device rigid. However, by replacing it with a polymer foil, the whole assembly becomes flexible, which can be bent or rolled to a radius of centimeters curvature without losing its functionality
Here are some examples of flexible electronic devices in application, such as the flexible LED lighting, foldable sensor devices, rollable e-readers, bendable solar cell panels and flexible flat panel displays. Also the production process to make the flexible devices, called Roll-to-Roll, is much easier and allows a cheap, large scale production. Therefore, it is not only possible but also preferable to make the new generation electronic devices flexible
What are the interesting topics for you?
As you may know the functional layers, in which the LED or solar cell function is residing, are vulnerable to moisture that slowly diffuses through the polymer towards these layers. Therefore a transparent inorganic barrier layer is inserted in between to prevent the ingress of moisture from the environment. Here questions are coming. Since the flexible electronic devices will experience many mechanical deformations during production and usage, how much bending can such a “brittle” inorganic layer withstand? When it cracks the barrier function will be lost. Can we predict the reliability and lifetime of the flexible device based on the durability of barrier layer? These are the key questions in this project.
This project is in close cooperation with several industrial partners, such as Philips research, Fujifilm and Holst Center. It is open for both Master and Bachelor students who are interested in any of the following topics.
In desert coastal areas, like the Namib Desert, early-morning fogs are regular phenomena, due to the cold and humid air currents of the ocean which are pushed inwards into the desert. Since rainfall is scarce, many animals and plants in the Namib region rely on this fog as the main source of water. The Namib Desert beetles for instance, can collect and drink water from humid air due to hydrophilic and hydrophobic domains at its carapace surface, which direct the collected water into its mouth. Similarly, some spiders are capable of capturing humidity on their silk networks due to spindle-knots and joints present on their surface (Fig. 1 a). Collecting water from the dew or early-morning fogs and releasing it in a controlled way to the atmosphere or soil, would be an ideal solution to reduce the water depletion problem in these areas.
Inspired by these examples in Nature, we are designing thermo-responsive “sponge-like” cotton fabrics which collect and release water, as a response to temperature changes within the day-and-night temperature range of dry areas (+10°C to +40 °C). These smart cotton fabrics have a remarkably superior ability to absorb water from a humid environment at low temperature, which is then released as the temperature rises. Furthemore, this behaviour is reversible and repeatable for several cycles.
These materials may provide intelligent solutions for fresh water collection, uni-directional conduction and purification which can find application in clothes, tents, building covers, water condensers or similar water engines.
Are you looking forward to an “out-of-the-box” challenging project?
dr Catarina Esteves (STO 2.26, Tel: 3034, Email: a.c.c.esteves@ ) tue.nl
Superhydrophobic and self-cleaning surfaces are already widely present in nature, but this property is still a challenge for synthetic coatings. The most famous example in Nature is the lotus leaf that remains clean despite growing in muddy water. Research has revealed that this property originates from the combination of a dual-size surface topology and a low surface-energy species (Fig. 1).
For synthetic coatings, a dual-size roughness combined with low surface energy species appears to be essential to reach superhydrophobicity. A nature-inspired approach – christened the ’raspberry’ approach – has been scientifically developed, leading to man-made superhydrophobic surfaces. In this method, the key to introduce well-controlled dual-size roughness involves the synthesis of raspberry-like inorganic silica particles (Fig. 2). However, due to the large particle size, this superhydrophobic coating is not optically transparent. Hence, the first aim of this project is to develop a structure with sufficient hydrophobicity, as well as transparency.
Up to know, we already achieved the synthesis of raspberry-like silica particles, with a total diameter of ~ 100 nm (Fig. 2). The purification of these particles and a suitable coating procedure, to provide the desired surface roughness, are currently under investigation. In a later stage, the scratch-resistance of these coatings will also be studied. In this graduation project, your main focus will be on the formation of transparent and superhydrophobic coatings originated from these raspberry-like silica particles. The work includes synthesizing the particles and characterizing the coatings obtained. Interested? Contact us and we will talk about what you would like to do and what we had in mind.
dr. Catarina Esteves (STO 2.26, Tel: 3034, Email: a.c.c.esteves@ ). tue.nl
Organic photovoltaic (OPV) are expected to become a significant player in the solar energy market, as they have the potential to be produced on a large scale at minimal cost. The Holst Centre focuses on up-scalable methods for the roll-2-roll (R2R) production of light weight and semi-transparent OPVs on flexible and transparent foils. Inkjet printing is a R2R compatible technique for the deposition and patterning of functional layers, like the photo-active layer containing a polymer-fullerene blend.
The main challenge for inkjet printing is the ink formulation. The ink needs to fulfill several requirements in terms of viscosity, surface tension and boiling point. In addition, it should dissolve the active material and the functionality of the deposited layer needs to be maintained. Finally, to be applicable in an industrial environment, all solvents are required to be halogen free. There is a strong correlation between the performance of OPV and the deposition process of the photo-active layer. The photo-active polymer and electron accepting fullerene derivative should from a bicontinuous network with domain sizes in the nanometer range. This project focusses on the processing of photo-active layers by inkjet printing and the relation to the device performance. The student will, after a literature survey, assess factors influencing the photo-active layer morphology to determine a range of suitable ink formulations. Devices with inkjet printed photo-active layers will be prepared in order to evaluate the effects of formulations as well as processing parameters on the morphology of the photo-active layer and, finally, the device performance. We are looking for an ambitious student from materials science, chemistry, chemical technology or nanotechnology with both theoretical and practical skills. You have good communication skills in English and you are independent but also a team player. You are looking for a thesis project or internship of at least 6, preferably 9 months.
The Holst Centre is an independent open innovation research centre founded by TNO and IMEC that is developing roll-to-roll production techniques for foil-based organic electronics and wireless autonomous transducer solutions, in corporation with industry and universities. Solliance is an alliance of TNO, TU/e, imec, ECN and the Holst Centre for research and development in the field of thin film photovoltaic solar energy.
Block copolymers possessing both hydrophilic and hydrophobic moieties (amphiphiles) self-assemble in aqueous solution. The aggregates that form have a variety of morphologies, most commonly spherical micelles, cylinders and vesicles. More complex morphologies such as toroids, multi-compartment micelles and internally-structured nanospheres are being observed more frequently through alterations in preparation conditions and block copolymer structure.
The fundamental factor dictating the aggregate morphology resides within the polymer’s actual design; namely the architecture, monomer composition, relative block volume and molecular weight. Highly controlled polymerization techniques are needed to enable manipulation of these parameters, of which atom transfer radical polymerization (ATRP) is widely used for the polymerization of vinyl monomers with low polydispersity.
Recently, our group has experimentally observed micelles with complex internal bicontinuous structure from diblock copolymers of poly(ethylene oxide) and poly(octadecyl methacrylate) synthesized by ATRP. The origin of this complexity is as yet not fully understood but is thought to reside in the comb-like structure of the octadecyl side-chains. It is of great interest to be able to direct the internal morphology of these nanospheres for their use as templates for biomimetic mineralization.
The principal objective of this research is to understand how the length of the alkyl side chain affects the observed internal morphology of these aggregates. This involves synthesizing and characterizing block copolymers of poly(ethylene oxide) and methacrylic monomers with varied side-chain lengths and comparable relative block volumes using the control afforded by ATRP. The morphologies formed in solution will then be identified and characterized using CryoTEM, tomographic studies and dynamic light scattering (DLS).
The observation of Nature has been an inspiring source for surfaces with specific functions, such as protection from aggressive environments, control of diffusion processes, mechanical resistance or self-cleaning ability (Fig 1.a). Following this concept many synthetic surfaces have nowadays a coating which intends to provide similar functions to the synthetic materials (Fig 1.b).
Biological surfaces are carefully built up for each purpose through controlled structures and surface morphologies (Fig 1.c). A striking thought is that such surfaces are constantly regenerated through self-healing processes to grant living organism’s survival and health (Fig 1.d). Although some functional synthetic coatings are available, for instance with self-cleaning ability, anti-corrosion, anti-fouling or water repellent properties, the self-healing of those materials is still on its infant steps and far from being fully understood.
Self-healing of low-surface energy coatings will prolong their lifetime and reduce the maintenance effort and costs. Therefore, understanding and controlling the self-replenishing processes through which low-surface energy groups migrate to the surface in polymeric systems is a challenge (Fig 1.e). It will have great impact not only on coatings but also on general materials surfaces.
Aim of the project: Understand and control the self-replenishing behaviour of low-surface energy polymeric systems (coatings). Several polymer coatings will be prepared and characterized. A number of experimental variables (e.g. polymer type and Mn, cross-linking density, length and amount of the low surface-energy groups on dangling chains) will be varied. The response of the systems in terms of surface characteristics recovery (self-replenishing) will be evaluated. The main target is to understand and relate experimentally the influence of the parameters varied (such as polymer network mobility (Tg), miscibility of network constituents and dangling ends, temperature effect, etc.) on the self-replenishing behaviour of the coating. The polymeric precursors and the cross-linked coatings will be characterized mainly by FTIR and NMR spectroscopy, Mass Spectrometry, GPC, DSC and DMA.
dr. Catarina Esteves (STO 2.26, Tel: 3034, Email: a.c.c.esteves@ . tue.nl
Since early times, scientists were curious on how plants leafs remain clean even in dirty environments. In most of the cases, this is achieved by the combination of a hydrophobic waxy layer and a micro/nano structured surface. The erosion/damage of this waxy surface occurs naturally and the plant constantly regenerates it through self-healing processes providing its survival and good health.
Following Nature’s example, many researchers are currently aiming to develop coatings with a specific surface functionality, i.e. self-cleaning or water repellence. For this reason, superhydrophobic surfaces have been intensively investigated and several models and synthetic approaches are currently available. However, these surface structures are in most of the cases fragile and can be easily damaged, by the routine handling of the materials. This irreversible loss of the surface characteristics reduces the life-time of the materials coating, exposing the under-layers to external factors and leading to severely degraded materials.
Although some steps have being given on self-healing process for polymeric materials, they are far from being controlled or fully understood. In this sense, a self-replenishing mechanism has been reported previously at SMG for low-surface-energy polymeric surfaces that recover chemical groups segregated at the surface. However, self-healing of superhydrophobic surfaces has not been addressed so far.
Are you looking for a project which will give you a broad view on the materials science field and the opportunity to work in a highly relevant industrial topic? So this project is for you! You will make polymer coatings with a specific surface morphology targeting a superhydrophobic, “Lotus type” surface. For this purpose you will apply chemical procedures developed at SMG, and make use of several experimental techniques, e.g. DLS, FT-IR Spectroscopy, SEM and AFM. The main goal of this project is however, to investigate the self-replenishing effect on these superhydrophobic surfaces. A specific CryoMicrotome set-up/procedure will be used to intentionally damage the coatings surfaces. After damage, the response in terms of surface characteristics recovery will be evaluated. The coatings morphology and self-replenishing behaviour will be accessed by AFM, SEM, XPS and contact angle measurements.
dr. Catarina Esteves: (STO 2.26, Tel: 3034; Email: firstname.lastname@example.org ).
Coatings with a protective, hydrophobic, or other, function are useful. However, when the surface is scratched and the coating is damaged this function disappears. We would like to design coatings with self-healing ability when damaged. One of the mechanisms we investigate is self-replenishing. The functional coating repairs itself by replenishing with material that is stored in the bulk of the material.
Computer simulations give unique possibility to optimize the design of these materials. In simulations we can vary parameters such as crosslink density, chain-lengths of polymers, their functional groups etc. Broad variation of parameters allows simulations to serve the guide for experiments and gives the possibility of developing a deep understanding of the underlying mechanisms. Besides, simulations give clues for improving the design.
We will also study polymer coatings with big colloidal particles incorporated into it. Such coatings allow for the formation of superhydrophobic surfaces. In close collaboration with experimentalists in our group the knowledge obtained from the simulations is tested in reality. (See elsewhere in this document for an experimental project on this topic.)
If you want to learn more on molecular simulations of self-replenishing coatings? Please, contact us.
Motivated by numerous recent reports indicating attractive properties of composite materials of carbon nanotubes (CNTs) and liquid crystals (LCs) and a lack of research aimed at optimizing such composites we propose to perform the systematic simulation research on dispersing CNTs in thermotropic LCs. It was experimentally shown that the quality of dispersion depends strongly on which LC molecules (mesogens) are used. Mesogens with a core comprising one cyclohexane and one phenyl ring are markedly better, yielding the smallest aggregate size and best stability. Moreover, the length of the terminal alkyl chain(s) has a strong impact on the result.
It is extremely important for the improved material design to understand how the different enthalpic, entropic and kinetic factors that influence the stability of a liquid crystalline CNT dispersion interplay in a complex manner. Simulations can provide a first provisional guideline on how to best prepare dispersions of carbon nanotubes in liquid crystals, both in terms of processing and in identifying optimum LC materials. Following these guidelines future synthesis efforts towards tailoring mesogen design may take the study and application of CNT-LC composites to a new level.
Are you keen to learn more on molecular simulations of materials? Please, contact us.
dr. Katya Lyakhova (STO 2.45, Tel. 3051, Email k.lyakhova@), tue.nl
prof.dr. Bert de With (STO 2.35, Tel. 4947, Email email@example.com).
In this project you study the adhesion of epoxy on metal-oxide substrates by means of molecular simulation. A fundamental understanding of adhesion between different materials is important in many areas. A typical application is packaging of electronic devices.
Aim of the project:
The goal is to perform simulations that can predict the adhesion properties of these materials. Molecular simulations are complimentary to experimental investigations. With computer simulations it is easy to study individual molecules, which is very hard to do experimentally. Therefore computer simulation is a useful tool to get a deeper understanding of all kinds of material properties. Within the laboratory of materials and interface chemistry we perform simulations on systems that are also studied experimentally. In this way we hope to achieve a cross-fertilization effect. Combining both angles of attack we obtain a deeper understanding than is possible with each of these two scientific approaches separately.
We would like to predict adhesion in multi-materials and the dependencies of the adhesion on environmental circumstances such as humidity. From the theoretical point of view there is surprisingly little fundamental knowledge on the interaction between metals and polymer. A multi-scale approach is used to both model atomistic interactions (chemisorption, curing) correctly and incorporate mesoscopic parameters (grain size distributions). The aim of the project is to improve predictions of adhesive properties and, in this way, have a tool to design better materials. This project is challenging from both an application and fundamental point of view.
Are you keen to perform molecular simulations of materials? Then, please contact us!
MSc Gökhan Kacar (STO 2.24, Tel 4945, Email firstname.lastname@example.org )
prof. dr. Bert de With (STO 2.35, Tel. 4947, Email email@example.com).
Coatings for outdoor applications must be able to withstand harmful environmental influences such as UV radiation, (acid) rain, particle abrasion etc. After long times though, even the most resilient coatings suffer some damage. The coating properties change during this process, which is called “weathering”. The approach to understand these changes by modelling and simulation is becoming increasingly popular.
The first stage in modelling the weathering process, is to describe the chemical transformations that occur. The coating system that we try to describe is a polyester-urethane thermoset coating. Because fully detailed simulations of such a big system and such a complex process are unfeasible, we first simplify the chemical structure of the model coating by grouping atoms together in beads (coarse graining), as schematically displayed in figure 1. The next step is to simplify the reactions that occur during weathering by identifying the most important mechanisms and translating the atomistic reactions to reactions between beads (e.g. see figure 2).
After defining all the possible reactions, reactants and products, we have to define rate equations that describe how fast all reactions occur. Such a reaction rate depends on the concentration of the reactants involved, internal properties of the beads and some external parameters (e.g. for the scission reaction, the flux of incident photons). After calculating all these reaction rates, we will use a Monte Carlo method to simulate the weathering process step-by-step. The algorithm is as follows:
Ultimately, we aim to extend this method to include the position inside the coating (3D description) and to relate the (time-)evolution of chemical composition to the changes in physical properties.
The project may include:
Implementation of improvements and/or additions to the existing code; Gathering data for rate equations, based on literature or possibly based on measurements as well; Running simulations with systematic variation of selected input parameters, analysis of the outcome, determination of which parameters are (un)important for the weathering process; Your own preferences and wishes, so we can tune the detailed assignment to what suits you best!
Koen Adema (STO 2.40, Tel: 3053, Email: k.n.s.adema@), tue.nl
Prof.dr. Bert de With (STO 2.35, Tel: 4947, Email: firstname.lastname@example.org).
The scarcity of oil resources and the environmental and political issues are encouraging the development of environmental friendly materials with the intent of replacing existing plastics. In coatings technology, following this growing interest, new formulations based on renewable materials are developed. However, in order to be suitable for long-life applications, a lot of effort is done to develop bio-based materials that show similar mechanical properties as their petrol-based analogues.
In terms of life time and long-term performance of coatings, resins and composites, moisture can play a certain role. If water is absorbed from a humid environment, it can act as a plasticizer and weaken the mechanical performance of the material. In addition, water can accelerate degradation processes resulting in lower performance and shorter life time, as often observed for bio-based materials. Consequently, a way to better understand and eventually improve the long-term performance of various materials is to investigate the influence of the humidity on their mechanical properties.
In our work, we used a DMA-RH accessory to achieve controlled humidity conditions in order to investigate the mechanical properties of these new bio-based resins and correlate eventual differences in properties with a detailed investigation of the microstructure using several characterization techniques.
Interested? Please, contact us!!!
dr. Maurizio Villani (STO 2.41, Tel. 3132, Email: m.v.villani@), tue.nl
prof.dr. Rolf van Benthem (STO 2.48, Tel. 2029, Email: r.a.t.m.v.benthem@), tue.nl
prof.dr. Bert de With (STO 2.35, Tel. 4947, Email: g.dewith@). tue.nl