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Invited speakers

Martin Haase (University of Utrecht) (10.30-11.15)
Tailoring bicontinuous materials by phase separation and interfacial assembly
Porous materials are composed of solid scaffolds that are interpenetrated by 3-dimensional pore networks. By pumping fluids through the pores, they can be used as adsorbents, catalysts, and filters. Can we create a macroporous material that allows two separate fluids to flow in and out of the pores without directly touching each other? Ideally, this material is made of two intertwined pore networks that are separated by a thin solid wall with controllable permeability and surface chemistry. If we succeed, advances for energy efficient separations including seawater desalination, organic solvent nanofiltration or phase transfer catalysis will be possible. Here, I will describe our recent work on bicontinuous interfacially jammed emulsions (bijels) formed by solvent transfer induced phase separation (STrIPS). STrIPS-bijels are generated by phase separation and interfacial nanoparticle assembly. Their bicontinuous pore networks open new possibilities for transport processes in porous materials based on their semipermeability, surface chemistry and high-surface-area.
Lukas Helmbrecht (AMOLF) (11.15-11.45)
Directed Emission and Circular Retardance from Self-Assembled Microhelices
Hierarchical structural ordering provides a powerful strategy to integrate multiple functionalities within a single material. We demonstrate that simple, linearly birefringent nanocrystals can self-assemble into microscopic helices that display both directional emission and rotation of the polarization direction of light. Surprisingly, the optical performance of these self-assembled hierarchical materials far exceeds the intrinsic properties of the building blocks. By employing a combination of state-of-the-art microscopy setups, we find that the hierarchical organization of the building blocks is essential for achieving these distinctly different optical effects: The microscale morphology of the helix determines the direction and dispersion of light emission, while the nanoscale helical ordering of the building blocks controls the polarization direction of the light (i.e. circular retardance) with a sign that is fully controlled by the twist direction of the helix.
Camilla Terenzi (University of Wageningen) (13.30-14.15)
NMR and MRI of confined fluids and heterogeneous materials
Nuclear Magnetic Resonance (NMR) and Imaging (MRI) methods provide us with a powerful toolkit for non-invasively characterizing both chemical and physical properties of optically-opaque heterogeneous materials, that cannot be investigated in situ by other spectroscopic techniques. In this talk, I will show how NMR and MRI techniques can enable assessing the molecular-scale origin of macroscopic properties of multiphase materials widely encountered e.g. in polymer or food industry, oil & gas engineering, or bio-medical applications. Two examples of case studies from my recent research will include (i) the characterization of water states, hydrogen bonding and biopolymer mobility by 1D NMR and molecular dynamics simulations, and (ii) the spatially- and chemically-resolved quantification of liquids inside porous media by 2D NMR techniques. Finally, I will give an overview of the ongoing and future research in soft matter, food science, and medicine in my new NMR group at the Laboratory of Biophysics in Wageningen University, where an array of NMR/MRI techniques is, or will be, combined with flow/shear/tensile measurements, in vitro case studies, and fast data processing methods.
Vincent Peters (University of Eindhoven) (14.15-14.45)
Phase Behaviour of Rod-Polymer Mixtures
Dispersions of colloidal rod-like particles, like tobacco mosaic or feline distemper viruses, cellulose nanocrystals, or boehmite rods, can demix into two or more coexisting phases upon addition of non-adsorbing polymers. This polymer-mediated phase separation is the result of excluded volume interactions between the polymers and the rods and can be described by Free Volume Theory (FVT). We extend FVT to predict the liquid crystalline phase behaviour of dispersions containing hard rods mixed with non-adsorbing polymers up to dense phases, including the smectic and crystal phase states. By only taking into account excluded volume interactions a remarkably rich phase behaviour is found. Among the results we find four- and five-phase coexistences. It will be discussed whether this finding contradicts the Gibbs’ phase rule in our system, from which a maximum of three coexisting phases is naively expected.
Tom Kodger (University of Wageningen) (16.00-16.45)
Bringing soft matter design strategies to materials
Soft matter physics and chemistry rely on thermal energy to do work. Unlike classical materials science where high temperature or pressure is a necessity for fabrication, soft materials are formed through room temperature self-assembly and polymerization exploiting design strategies such as phase separation and interfacial templating. I will tell you about two such designer soft materials from my lab. First, I will explain how to make a photonic paint by combining commercial water-based binders and photonic pigments designed and realized using a scalable emulsion templating fabrication process. The photonic pigments are silica spheres containing air pores where the periodicity and long-range order define their colour and iridescence. Secondly, I will discuss solving a societal problem where soft matter seemingly cannot play a role: reducing our dependence on harmful pesticides in agriculture. Trichomes are small adhesives spheres produced by some plants that provide a physical defence mechanism against harmful herbivores by immobilization. We are currently working on a bioinspired mimic of these trichomes using bio-sourced materials and soft matter design.
Robin van Damme (University of Utrecht) (16.45-17.15)
Interparticle torques suppress motility-induced phase separation for rod-like particles
Far-from-equilibrium physics has been a hot topic in recent years, finding success in describing the dynamics of seemingly unrelated systems such as bird flocks, skin cells and mosh pits at metal concerts. One particular phenomenon that only occurs far from thermodynamic equilibrium is motility-induced phase separation (MIPS). With MIPS, self-propelled particles separate into dense and dilute regions even without any attractive interactions between them. This effect appears to be extremely robust: it occurs in both 2D and 3D, for both bacterial-like and phoretically-driven motion, and for repulsive and attractive interactions alike. Given this fact, it is tempting to think that MIPS will emerge in any system with a strong enough self-propulsion. However, that is not the case. In this work, we demonstrate that for self-propelled rod-like particles with torques acting between them, the MIPS phase vanishes entirely once the rods become longer than as little as twice their width, and that no amount of self-propulsion is enough to recover the MIPS phase once this happens. To explain why this happens, we propose an intuitive (though somewhat handwavy) argument based on the duration of particle collisions, and argue that this can explain both the suppression of MIPS found here for rod-like particles as well as the enhancement of MIPS found for particles with Vicsek interactions.