Wim Noorduin (Harvard)
Rationally designed complex, hierarchical micro-structures - The emergence of complex nano/microstructures is of fundamental interest, and the ability to program their form has practical ramifications in fields such as optics, catalysis and electronics. We developed carbonate/silica microstructures in a dynamic reaction-diffusion system that allows us to rationally devise schemes for precisely sculpting a great variety of elementary shapes. Detailed understanding of the underlying mechanisms allows us not only to program these elementary shapes, but steer the precipitating reactants into complex flowers, corals, vases, and messages, with precise control over placement of stems, leaves, etc. via sequential combinatorial assembly of the developing shapes. These findings may hold profound implications for understanding and ultimately expanding upon nature’s morphogenesis strategies, and outline a novel approach to use sequences of dynamic modulations of the environment to steer self-assembly processes as a route to advanced, highly complex microscale materials and devices.
Henri Lhuissier (Twente)
Explosive boiling? A drop immersed in a non-volatile liquid bath, with which it is immiscible, and resting on a solid surface, that it wets, can be superheated by typically 100 C above its saturation temperature before it nucleates the rst vapor bubble and explosively evaporates within 1 ms. However, when the liquid of the drop does not wet either the liquid of the bath or the solid, the vapor bubble nucleates at the drop's interface and the boiling dynamics is strongly modied, proceeding, for instance, by the successive formation of small vapor bubbles for as long as tens of seconds. The locus of nucleation and its key role in those dierent boiling behaviors will be discussed on the basis of experimental observations on water and pentane drops.
Nico Sommerdijk (Eindhoven)
Nucleation and growth in bio-inspired mineralization - The often astonishing materials properties of crystalline biominerals are generally related to the hierarchical assembly of specifically interacting organic and inorganic components. A yet unfulfilled dream of many scientists is to synthesize new materials with similar advanced properties applying Nature’s biomimeralization strategies. For the design of such materials with predetermined structure and properties it is essential to understand the factors that dictate their formation.
The in situ study of the development of mineral formation can make an important contribution to the understanding of the crystallization processes. It is however not a trivial matter to obtain morphological and structural information of such systems in their native hydrated state. In recent years we have presented the possibility to use cryoTEM as a method to investigate the early stages of mineral formation without removing the developing particles from their aqueous environment.
Using dedicated tools including a vitrification robot with attached glovebox also makes it possible to investigate mineral formation at interfaces, while cryo-electron tomography allows us to investigate template-mineral interactions in 3D. Moreover, we combine cryo-TEM imaging with more materials science oriented techniques such as cryo-STEM/EDX and low dose selected area electron diffraction to combine morphology with structural and chemical information. We will discuss our recent results in the investigation of calcium phosphate and magnetite (Fe3O4), two materials with high societal and technological relevance. For both systems we find that crystal formation occurs through so-called non-classical multistep nucleation mechanisms. Nevertheless we demonstrate that these mechanisms can be explained by classical nucleation theory.
Céline Charbonneau (Wageningen)
pH and salt tuning of the dynamics of physical hydrogels: from solids to viscoelastic fluids - We have investigated the rheological properties of hydrogels based on the self-assembly of amphiphilic triblock copolymers containing n-butyl acrylate (nBA) hydrophobic units and acrylic acid (AA) hydrophilic units. PnBA-b-PAA-b-PnBA triblock copolymers consisting of pure PnBA outer blocks bridged by a PAA middle block lead to frozen microgels when dispersed in water. On the contrary, the controlled incorporation of AA units within the outer hydrophobic blocks renders the system dynamic.
The exchange dynamics of the outer blocks between hydrophobic microdomains have been probed by viscoelastic measurements which display the existence of a terminal relaxation time (t). The latter can be finely tuned over 11 orders of magnitude by modifying the ionisation degree (a) of the AA units, the exchange dynamics being faster when a increases and almost prohibited for the lowest a investigated. Adding salt increases also t on several decades. Moreover, when a is modified in situ, the system ages before reaching the stationary state: t increases over time until a constant value. The aging was explained by a progressive local restructuring of the hydrophobic domains inducing a dehydration of the cores.
In conclusion, we demonstrated that the incorporation of hydrophilic units within the hydrophobic blocks of amphiphilic triblock copolymers is a promising way for tuning the rheological properties of hydrogels through the pH and salt thanks to a modification of the exchange dynamics of the “moderately” hydrophobic blocks.
Anjan Prasad (Utrecht)
Phase Diagram and Structural Diversity of a Family of Truncated Cubes: Degenerate Close-Packed Structures and Vacancy-Rich States - We studied the thermodynamic phase behavior of a family of truncated hard cubes, where the shape evolves smoothly from a cube via a cuboctahedron to an octahedron. We used Monte Carlo simulations and free-energy calculations to establish the phase diagram. Surprisingly, this phase diagram exhibits a remarkable diversity in crystal structures and distinct close-packed structures, including a fully degenerate crystal structure and vacancy-stabilized crystal phases, all depending sensitively on the precise particle shape. Our results are not only crucial for better understanding the relation between phase behavior and building-block shape, but they are also of interest for guiding future experimental studies on polyhedral-shaped nanoparticles.
Saber Naderi (Eindhoven)
Cooperativity and allosteric effects in the self assembly process of a silk-like protein - We study conformational changes in the structure of a silk-like protein in aggregates containing one, two, three and four of this protein in aqueous solution by performing replica exchange molecular dynamics simulations with explicit and implicit water models. We find that in monomeric and dimeric states the protein has a disordered, globular structure. We surmise that this must be due to unfavorable interaction of hydrophobic residues of the protein with water. We furthermore find that in aggregates of three and four proteins, their conformation changes and form inter- and intra-molecular beta-sheet structures. This indicates that the self-assembly process of these proteins must be cooperative and involve allosteric effects. Our findings are in agreement with recent experiments on fiber formation of the silk-like protein in aqueous solution.