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).

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.

Project Aims
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).

Contact persons:
dr. Beulah McKenzie (STO 2.29, Tel: 2405, Email: b.e.mckenzie@remove-this.tue.nl)
dr. Nico Sommerdijk (STO 2.44, Tel: 5870, Email: n.sommerdijk@remove-this.tue.nl)

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.

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 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.

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.

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 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@remove-this.tue.nl)

Nico Sommerdijk (STO 2.44, Tel.: 5870, E-mail: N.Sommerdijk@remove-this.tue.nl )

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The setting
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.

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).

(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 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.

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.

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.    

Contact persons:
dr. Katya Lyakhova (STO 2.45, Tel. 3051, Email k.lyakhova@remove-this.tue.nl),
prof.dr. Bert de With (STO 2.35, Tel. 4947, Email g.dewith@tue.nl).

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!    

Contact persons:
MSc Gökhan Kacar (STO 2.24, Tel 4945, Email g.kacar@tue.nl )
prof. dr. Bert de With (STO 2.35, Tel. 4947, Email g.dewith@tue.nl).

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!!!  

Contact persons:
dr. Maurizio Villani (STO 2.41, Tel. 3132, Email: m.v.villani@remove-this.tue.nl),
prof.dr. Rolf van Benthem (STO 2.48, Tel. 2029, Email: r.a.t.m.v.benthem@remove-this.tue.nl),
prof.dr. Bert de With (STO 2.35, Tel. 4947, Email: g.dewith@remove-this.tue.nl).