Abstracts

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Invited speakers

Zhigang Suo (Harvard University) (10.30-11.15)
Hydrogels of unusual properties and applications
Several recent findings show that hydrogels can achieve properties and applications well beyond previously imagined. Hydrogels can be as tough as rubber, retain water in low-humidity environment, and be stable above 100 degrees centigrade. We have used hydrogels to develop devices to mimic the functions of muscles, axons, and skins. They are highly stretchable and transparent. This talk will highlight recent progress on toughness, adhesion, fatigue resistance, and water retention.
Mariana Oshima Menegon (Eindhoven University of Technology) (11.15-11.45)
Self-organisation of semi-flexible rod-like colloids and the effect of single-ended functionalisation
Elongated colloidal particles, including rod-shaped viruses, exhibit a host of symmetry-broken, liquid crystal and crystal phases that are affected by the characteristics of, interactions between, and concentration of the particles. We employ computer simulations to study the stability and structure of ordered phases of repulsive rod-like particles, focusing in particular on the impact of aspect ratio and bending flexibility. We find that the phase transitions shift to larger concentrations upon increasing particle flexibility. Increasing the aspect ratio has the opposite effect. If we include attractive end groups, one particular phase, the layered smectic A phase, is stabilised at the expense of the uniaxial nematic phase. This is confirmed by recent experiments on filamentous viruses. We also present phase diagrams and cluster statistics of the semi-flexible rods as a function of the concentration and the strength of the interaction between the end groups.
Alvaro Marin (Twente University) (13.30-14.15)
Particle trajectory entanglement in confined particle solutions
A non-Brownian particle flowing in a confined channel have no particularly special behavior. But actually two particles can show interesting interesting dynamics. In this talk I will present an overlooked phenomenon occurring when dilute particle solutions are forced to travel in a narrow channel which is only a few times their size. At critical interparticle distances, particles tend to interlace their trajectories, only bonded by hydrodynamic interactions. While classical studies on non-Brownian self-diffusivity report average particle displacements of fractions of the particle diameter, the trajectories observed in our system show displacements of several particle diameters. Furthermore, entangled particles seem to synchronize their motion with others located at several particle diameters. The results are then compared with particle dynamics simulations and analysed to elucidate the nature of the hydrodynamic interactions entering into play. The reported phenomenon could be applied to promote advective mixing in micro-channels or particle/droplet self-assembly.
Debu Banerjee (Leiden University) (14.15-14.45)
Odd viscosity in chiral active fluids
Chiral active fluids are materials composed of self-spinning rotors that continuously inject energy and angular momentum at the microscale. Out-of-equilibrium fluids with active-rotor constituents have been experimentally realized using nanoscale biomolecular motors, microscale active colloids, or macroscale driven chiral grains. In this talk we will see how such chiral active fluids break both parity and time-reversal symmetries in their steady states, giving rise to a dissipationless linear-response coefficient called odd viscosity in their constitutive relations. Odd viscosity couples pressure and vorticity leading, for example, to density modulations within a vortex profile. Moreover, chiral active fluids flow in the direction transverse to applied compression as in shock propagation experiments. We envision that this collective transverse response may be exploited to design self-assembled hydraulic cranks that convert between linear and rotational motion in microscopic machines powered by active-rotors fluids.
Marcel Workamp (Wageningen University and Research) (16.00-16.30)
Friction and Flow of a Granular Emulsion
What do mayonnaise and mud have in common? They are both structured fluids: mayonnaise contains droplets, while mud contains solid particles. The droplets or particles are typically closely packed, so they touch each other all the time. The interactions between droplets and rigid particles are obviously different. How do these differences influence the flow behavior of the materials? We show here that frictional interactions play a crucial role. To investigate the role of friction in suspensions, we use a suspension of soft hydrogel spheres. Similar to the droplets in an emulsion, hydrogel particles are soft, so we can make a dense suspension. However, similar to a granular material, their interactions are frictional. We thus have a “granular emulsion” or muddy mayonnaise. We use hydrogels with varying chemical composition to make the particles, and measure the friction coefficient of the materials with a custom tribometer. We link the microscopic friction of the particles to the rheological behavior of the suspension, by combining rheological measurements with optical techniques in a 3D printed Couette geometry. We find that the friction coefficient of the material directly determines the amount of dissipation in the suspensions, provided it exceeds a critical value. This suggests two dissipation mechanisms contribute to the shear resistance of the suspension.
Hans Hendrikse (Amolf) (16.30-17.00)
Bio-Inspired Microstructures converted to Functional Materials
Biological microstructures are a source of diverse and complex shapes that often serve as a source of inspiration for artificially made materials. Recently our group has been able to mimic such complexity on a microscopic level, which offers a wide diversity of programmable shapes of nano-crystal assemblies. Here we present a new method to convert these nano-crystal assemblies into functional materials. By doing so we are able to separate the control of shape from the control of material composition and open up a new path to use self-assembly as an effective method to create complex functional materials.

Soundbites

Ruud van der Sman

Wageningen university & Research
Hyperelastic model for brocolli drying
We investigate anomalies in moisture migration during brocolli drying with hyperelastic model, coupling moisture transport and stress development.

Ling Liu

University of Groningen
Light-guided surface morphing of liquid crystal films
Liquid crystal (LC) polymers, co-polymerized with light-sensitive azobenzene molecules, can respond to ultra-violet (UV) light by undergoing mechanical deformations. This responsive film features photo-guided surface morphing and roughness changes, when the alignment of LC molecules can be well designed. Possible applications include manipulation of frictions and wetting properties, as well as microfluidic functions.

Agustin Iniguez-Rabago

Amolf
Finding the mechanically stable states of prismatic architected materials
We investigate anomalies in moisture migration during brocolli drying with hyperelastic model, coupling moisture transport and stress development.Advances in fabrication technologies are enabling the production of architected materials with unprecedented properties. While most of these materials are characterized by a fixed geometry, an intriguing avenue is to add internal mechanisms capable of reconfiguring their spatial architecture enabling tunable functionality. Previously we proposed a design strategy based on space-filling extruded polyhedra to create 3D reconfigurable materials comprising a periodic assembly of rigid plates and elastic hinges. Interestingly, when the rigidity constraint of the faces is softened, new folding pathways open up that lead to multiple mechanically stable states. By performing numerical analysis and harnessing symmetries that exits in these geometries, we systematically explore the energy landscape to find the possible stable states. The final goal is to understand and design a wealth of multistable materials that can switch between different mesostructures through applying global stimuli.

Shari Patricia Finner

TU Eindhoven
Conducting Plastics!
The design of polymer composites with conducting fillers like carbon nanotubes has a wide range of potential applications in the electronics and photovoltaics industry. Above a critical particle concentration called the percolation threshold, the nanorods start forming a system-spanning network which strongly affects the macroscopic mechanical and transport properties of the material. The percolation threshold of a polydisperse system has long been known to scale with the inverse weight-average of the particle length distribution. Invoking connectedness percolation theory, we find that this relation does not generally hold anymore in the presence of external alignment fields, such as electric fields, elongational flow fields and molecular fields provided by nematic liquid-crystalline hosts.

Abheeti Goyal

TU Eindhoven
Towards High-Efficiency Organic Solar Cells: A Computational Approach
Organic solar cells may well be responsible for the next energy and technology revolutions owing to their low cost, efficient fabrication techniques and compatibility with flexible substrates. However, their present-day performances are still low. A thin photovoltaic layer with bulk heterojunction forms the core of organic solar cells. The processing step involves deposition of polymeric electron donors and acceptors by phase separation and solidification driven by forced evaporation of the organic solvent. The morphology of the final solid phase is directly affects the overall photo-conversion efficiency of the device. In this interaction, I will discuss the methodology we employ to study the basic fluid dynamics physics of multi-component phase separation and solidification of suspensions under steady evaporation in order to improve the photo conversion efficiency of organic solar cells.

Edson Minatti

UFSC Florianópolis Brazil
GLYCOCUBOSOMES
Amazing nanoestructures made from the self-assembly of a sugar based copolymer: we observed extraordinary cubosomes when dissolving this copolymer in water. By electron tomography experiments we were able to see the inner organization of these structures.

Lukas Helmbrecht

Amolf
Metaminerals
Inspired by the complexity found in biomineralized structures researchers are creating a variety of self-assembled carbonate microstructures. Albeit the material is of little technological use, we found nano-crystalline carbonates to be an excellent starting point for the subsequent conversion into state of the art semiconducting materials.

Thijs van der Heijden

Eindhoven University of Technology
Destructive droplets: impact of droplet evaporation on thin polymer films
Addressing the impact of evaporating droplets is of importance to the semiconductor industry. Photolithography is used to write circuitry on chips, where water immersion techniques are used to increase the resolution of the imprinted nanostructures. Any droplets left behind on the polymer-based photoactive film turn out to have a detrimental effect on the desired imprint. We propose a simple model to examine the impact of such droplets, and our predictions for pattern deformation resemble experimentally observed ones.

Steven Cornet

Wageningen UR
Understanding water holding for juicier meat replacers
Water holding by bio-polymer gels can be described using Flory-Rehner theory, which takes into account polymer-water interactions, ion-water interactions, and network elasticity. Recent studies have successfully used Flory-Rehner theory to describe the water holding of food gels. The current research will use Flory-Rehner theory to describe the water holding by mixed bio-polymer gels with separated domains that contain an additional capillary phase. This research is being conducted in the context of meat replacers.

Beybin Ilhan

University of Twente
Rheological Behavior of Frictional Colloids
TBD

Karsten Baumgarten

TU Delft
Dilatancy in elastic networks
Some materials expand when sheared, while others contract – this is dilatancy. Despite the fact that effects of dilatancy can be significant even for small shear strains, our intuition about its origins, and even its sign, is poor. We study dilatancy in random networks of springs, which are a minimal model for a wide range of amorphous solids.

Willem Boon

Utrecht University
Concentration profiles in magnetized ferrofluids
Magnetized ferrofluids are used in a wide variety of engineering applications and the stability of the ferrofluid is a primary requirement. Sedimentation of the magnetic particles out of suspension occurs but is difficult to characterize. We are studying the analytical centrifugation of fluids in the presence of a magnet as a way to measure concentration profiles of magnetized ferrofluids. To account for the effect of strong (nonlinear) magnetic fields, theoretical interpretation requires an extension of classical sedimentation equilibrium theory to include magnetic interactions and excluded volume.

Sandra Veen

Electric Ant Lab
Virtual Prototyping of Complex Fluids and Flowing Materials
High-fidelity simulations are extremely powerful tools to understand, predict, and improve the rheology and transport of complex fluids and their processing. They provide quantitative insight into the micro-structural origins of rheological effects shown by many complex fluids. Existing material formulations can be better understood and new ones can be prototyped without elaborate synthesis and wet-lab experiments. EAL works at the forefront of this technology, pushing its boundaries, and translates it to solutions in scientific and industrial contexts.

Thijs de Goede

Universiteit van Amsterdam
Droplet Fragmentation by impact on Polyester Fabric
Although droplet spreading on smooth surfaces is well known, spreading on textile materials is still not fully understood. Compared to a solid surface, on textile the liquid can penetrate the holes in the fabric but also spontaneously ow through the porous networks inside the fabric (wicking), making droplet spreading more complex compared to smooth surfaces. Understanding droplet spreading on textile materials is important for applications in forensic research and the textile industry. We study droplet impact on polyester fabric as a function of the fabric pore size and wettability. At high vimpact, the droplets penetrate the fabric and break up into microdroplets of a well-dened size given by the mesh size of the fabric.

Simone Ciarella

Technische Universiteit Eindhoven
A dynamical model for bond-exchange materials
We developed a numerical model which is able to simulate the swapping of bonds conserving the total number of them. We use it to study how those swaps affect the static (elasticity) and the dynamic (relaxation) properties of a polymer network, mimicking the behavior of the so called vitrimers. We show that turning on the swapping mechanism can turn a solid gel into a liquid.

Adeline Pons

University of Twente
Effect of fluid chemistry on cornstarch suspensions: linking particle interactions to macroscopic rheology
Suspensions of cornstarch in water exhibit strong dynamic shear-thickening. We show that partly replacing water by ethanol strongly alters the suspension rheology. We perform steady and non-steady rheology measurements combined with atomic force microscopy to investigate the role of fluid chemistry on the macroscopic rheology of the suspensions and its link with the interactions between cornstarch grains. Upon increasing the ethanol content, the suspension goes through a yield-stress fluid state and ultimately becomes a shear-thinning fluid. On the cornstarch grain scale, atomic force microscopy measurements reveal the presence of polymers on the cornstarch surface, which exhibit a co-solvency effect. At intermediate ethanol content, a maximum of polymer solubility induces high microscopic adhesion which we relate to the macroscopic yield stress.

Roland Gouzy

Unilever/UvA
Suspension of cellulose nanofibrils in surfactant systems: homogenization level matters
Cellulose nanofibrils are popular class of nature-based nanomaterials. Their specific properties, cellulose in the form of nanofibrils provide plenty of applications in diverse areas ranging from food products to high-strength composites. Properties like rheology and structure of complex systems containing cellulose nanofibrils dispersed in surfactant systems present unique opportunities. In this work. Qualitative and quantitative structural analysis of these dispersions using confocal microscopy show that the structures obtained are heterogeneous before homogenization. The degree of dispersion of the CNFs in the solvent increases with the number of homogenization steps. The homogeneity of the CNF network increases as a function of the degree of deagglomeration and particle rearrangement. We observe a strong increase of the elastic modulus with the number of homogenization steps reflecting the presence of a more connected and more homogeneous network.

Gianmarco Venditti

TU/e
Spreading and imbibition of water-based printing inks in porous media
tbd

Piermarco Fonda

Leiden University
Modelling phase separation on artificial closed lipid membranes
Artificial lipid membranes are a valuable physical systems which might provide great insight in exploiting the mechanisms which happen in living cells. Nonetheless, such systems are valuable per se and exhibit a challenging complexity, whose understanding involves non-trivial notions of geometry, mechanics and thermodynamics. With the support of new experimental results on multicomponent lipid-coated freely suspended colloids, in this work we discuss how to build proper models of such systems, focusing in particular on the interplay between membrane curvature, domain formation and interface dynamics.

Utkarsh Jain

Physics of Fluids, University of Twente
Complex buckling of 'simple' structures : the case of holey column
Elastic metamaterials with periodically repeated microstructures can undergo internal buckling and show unexpected pattern switching behaviour. A good understanding of the pattern switching phenomenon can lead to several potential applications such as DNA manipulation to aircraft engineering, which span over a large range of length scales. We show the results from one such simplified system: an elastic column with holes. We briefly showcase the richness of its behaviour, its scalability, the means to control the onset of specific buckling modes and more intricate results such as inter-mode transitions via secondary bifurcations and inter-mode jumping via snap-through transitions.

Maxime Costalonga

Physics of Fluids, University of Twente
Droplet interactions on viscous films
Every morning at their breakfast, cereal eaters can see that floating objects on a liquid bath attracts to form clusters : this is the so-called Cheerios effect. It has been shown recently that droplets on elastic substrates also interact, either attracting or repelling each other depending on the local slope of the substrate where they lie. Here we present an experiment extending these results to the interaction of droplets deposited on a thin viscous film. By measuring independently the velocity of the droplets and the surface topography of the film, we identify non-monotonic interactions that are due to waves appearing on the film. The drag force exerted onto the droplets is also investigated. We show that the thickness of the film below the drop is intrinsically selected by the velocity of the drop, by a mechanism similar to Bretherton’s bubble rising in a confining tube.

Yanshen Li

University of Twente
Monostable Superrepellency
Superrepellency is an extreme situation where liquids stay at the tops of rough surfaces, in the so-called Cassie state. Owing to the dramatic reduction of solid-liquid contact, such states lead to many applications, such as antifouling, droplet manipulation, hydrody- namic slip, and self-cleaning. However, superrepellency is often destroyed by impalement transitions triggered by environmental disturbances whereas inverse transitions are not observed without energy input. Here we show through controlled experiments the existence of a monostable region in the phase space of surface chemistry and roughness, where transitions from Cassie to (impaled) Wenzel states become spontaneously reversible. We establish the condition for observing monostability, which might guide further design and engineering of robust superrepellent materials.

Anwesha Bose

TU/e
Mechanics of barely over-constrained frames
We present a two-dimensional disordered bead-spring network model to study the effects of states of self-stress (SSS) on the linear mechanics of frames. We examine how SSS can be used to control the mechanical response in materials and discuss the basic physical mechanism behind this.

Liz Mensink

University of Twente
Wetting of brushes in humid air
Polymer brushes consist of densely end-anchored macromolecules. They can be used to mimic the soft hairy structures appearing in biological systems such as lungs, joints and intestines. The wetting behavior of these brushes is complex, because the polymers stretch away from the surface making the system highly anisotropic. A proper understanding of the behavior of brushes in a humid environment is key to understanding the workings of these diverse biological systems. Here we present Molecular Dynamics (MD) simulations by which we look into the wetting behavior of brushes under humid circumstances. We will discuss the surface tension for polymer brushes, and the wetting behavior of liquid droplets on brush substrates.

Sven Boots

Wageningen University
A Softbreak project: Understanding fracture nucleation of mechanical heterogeneous polymer networks
Polymeric materials under a high mechanical stress will fracture. Griffith’s theory describes fracture as a competition between the energy required to break bonds versus the energy released due to elastic deformation. However, this simple description becomes more complicated for real networks that have mechanical heterogeneity where the number of bonds varies spatially. Computational work has shown that networks with low heterogeneity are probable to break in a single crack whereas networks with high heterogeneity will break percolated. Experimental work is lacking. In this project, we synthesize reproducible heterogeneous polymer networks that incorporate innovative mechanochemical tools that enable a direct measure of the spatial and temporal distribution of strains and bond rupture events. A first example is dioxetane, a probe that emits a photon upon scission. A second example is azobenzene, a molecule that can cycle between moduli by controlling the illumination condition.

Melle Punter

Amolf
Perturbation Theory for Hydrogels
We investigate the response of hydrogels upon compression. Hydrogels obey Darcy's law and the force balance equation which form a coupled set of partial differential equations. By applying perturbation theory the response of a hydrogel to an osmotic shock is found. Moreover, we investigate hydrogels clamped to parallel plates under uniaxial compression.

Melle Punter

Amolf
Perturbation Theory for Hydrogels
We investigate the response of hydrogels upon compression. Hydrogels obey Darcy's law and the force balance equation which form a coupled set of partial differential equations. By applying perturbation theory the response of a hydrogel to an osmotic shock is found. Moreover, we investigate hydrogels clamped to parallel plates under uniaxial compression.

Chiara Raffaelli

tuE
Network Structure of Biocompatible Hydrogels
We present a coarse-grained simulation model for hydrogels with both reversible and irreversible crosslinks, motivated by recent experimental results for tetra-PEG hydrogels. We determine how the concentration of tetra-PEG monomers influences the gelation process and the statistical properties of the resulting network.

Myrthe Bruning

Twente University
Evaporation-driven creasing of droplets in elastic gels
The collapse of spherical cavities is a phenomenon known from cavitating bubbles and it is typically related with fast and violent processes. However, a quite violent but very slow effect occurs with spherical cavities collapsing in an elastic medium. To study this process, we generate a cavity inside a silicone-based gel by placing a water droplet inside. As the droplet slowly evaporates, strain develops in the gel. At a critical strain, creases start to form. Depending on the properties of the gel, the creasing occurs at different stages and different instabilities can be observed.

Qimeng Wu

Wageningen University
Syneresis in Food Emulsions
Adding nonadsorbing polymer to an emulsion renders an attractive interaction between the latter. Stability of such systems against syneresis and creaming is crucial to many food products, such as low fat mayonnaise. Due to the complexity of real food system, we use a model system comprised of monodispersed copolymer droplets and PNIPAm polymer as microgels or linear coils. The scaling behaviour of the elasticity as a function of dispersed phase volume fraction is measured by rheology and the effects of osmotic pressure and elasticity of the added polymer on the macroscopic elasticity are studied. Particle coordination number, fractal dimension, percolation and local mobility in the hybrid networks are analyzed from 3D structure using confocal microscopy as the system is transparent. We discuss the relationship between the complex 3D microscopic structure and the elasticity of the hybrid network.

Bart Weber

ARCNL
Molecular Probes Reveal Deviations from Amontons Law in Multi-asperity Frictional contacts
Amontons law defines a material-dependent constant, the friction coefficient, as the ratio between friction force and normal force. Amontons law is commonly explained with the two non-trivial assumptions that both the frictional and normal force depend linearly on the real contact area between the two sliding surfaces. Most surfaces are rough and experimental testing of frictional contact models has proven difficult, because few in-situ experiments are able to resolve this real contact area. Here, we present a new contact detection method with molecular-level sensitivity, and independently probe the two relations that form the microscopic origin of Amontons’ law. While the friction force is proportional to the real contact area, we find that this real contact area does not increase linearly with normal force. Contact simulations performed on the identical surface show that the breaking of Amontons law is due to both elastic interactions between asperities on the surface and contact plasticity of the asperities. We exactly reproduce contact area and fine details of the measured contact geometry by including plastic hardening into the simulations. These new insights into contact mechanics pave the way for a quantitative microscopic understanding of contact mechanics and tribology. Adding nonadsorbing polymer to an emulsion renders an attractive interaction between the latter. Stability of such systems against syneresis and creaming is crucial to many food products, such as low fat mayonnaise. Due to the complexity of real food system, we use a model system comprised of monodispersed copolymer droplets and PNIPAm polymer as microgels or linear coils. The scaling behaviour of the elasticity as a function of dispersed phase volume fraction is measured by rheology and the effects of osmotic pressure and elasticity of the added polymer on the macroscopic elasticity are studied. Particle coordination number, fractal dimension, percolation and local mobility in the hybrid networks are analyzed from 3D structure using confocal microscopy as the system is transparent. We discuss the relationship between the complex 3D microscopic structure and the elasticity of the hybrid network.

Rianne van der Pol

University of Twente
End-group positioning in polymer brushes: Effects of size and solvent-mediated polymer-end group interactions
Polymer brushes consist of long macromolecules attached with one end to a surface. Their anchoring density is close enough that the polymers start to stretch and form a brush. The other end of the polymer can be used to attach different end groups and provide different properties to the end groups of the polymer. These end groups can be bio-receptors, dyes and polymers with different properties such that the brushes can be employed as sensors. It is, however, unknown how these end groups are distributed throughout the polymer brush. We study the positioning of the end-groups in polymer brushes using molecular dynamics simulations. In particular, we study the effect of different interactions between the polymer, solvent and end group, the size of the end groups, the density of the end groups and the grafting density of the polymer brush. To verify the results, PMMA brushes have been functionalized with a fluorescent dye. With fluorescent life time imaging the distribution is reconstructed as a distance from the surface.

Etienne Jambon-Puillet

University of Amsterdam
Evaporation of pointy ice drops: smoothing out the singularity
Although not as commonly observed as the evaporation of liquid water, ice does evaporate below its melting temperature provided the surrounding air is sufficiently dry. Using a combination of experiments, simulations and theory we study the evaporation of ice droplets crowned with a conical tip: pointy ice drops. We show that, like liquid droplets, their evaporation is diffusion limited and strongly enhanced at sharp points: their edges and tip. However, unlike liquid droplets whose sharp edges are maintained by surface tension, the tip and edges of our pointy ice drop, originally sharp are quickly smoothed out. We propose a simple analytic model to explains the dynamic of the tip smoothing and the evaporation of the latter smoothen ice drop. This model, in good agreement with experiments and simulations, is expected to be also relevant for diffusion limited dissolution of solids.

Anne Meeussen

AMOLF/Leiden University
Shape-switching mechanical materials
Compared to bulk materials, thin structures show extreme mechanical behaviour: they bend, snap and twist. The energy landscape of thin materials is dominated by stretching and bending, which compete via geometry. This energetic competition leads to strong nonlinearities, resulting in complex, functionalizable behaviour. We present a thin, undulating material that exhibits fast, reversible snap-through instabilities into many passively stable shapes. We explore the design rules that relate this material's microstructure to its large-scale behaviour.

Charlie Maslen

Utrecht University
Light Controlled Hydrogel Microcrawlers
Stop-flow lithography can be used to synthesise PNIPAM crosslinked with PEGDA hydrogels, loaded with gold nanoparticles (GNPs) and of well defined shape in the microscale. The microgels shrink when irradiated by green laser light as a result of the GNPs photothermally heating the PNIPAM above it's critical solubility temperature. With periodic irradiation, the shrinking-expansion cycles result in crawling motion of the microgels. This is attributed to the already established adhesion hysteresis in the heating and coolling cycle of PNIPAM chains on a surface. These soft microcrawlers may have applications in active matter research, 'lab on chip' technologies and micro-manipulation.

Ireth Garcia Aguilar

Leiden University
Mechanics of shape-shifting droplets
Surfactant-stabilized oil emulsion droplets in water have been observed to undergo spontaneous shape-transitions when the system is cooled down. The spherical droplets deform into faceted polyhedral shapes for temperatures where there is a crystalline monolayer of surfactant molecules in the interface while the bulk oil and water remain liquid. We sought to understand the mechanism driving the volume-conserving deformations by modelling fixed geometries and studying the interplay of the different energy contributions on the droplet's interface.

Dion Koeze

TU Delft
Attractive emulsions: a sticky problem?
How do sticky particles jam? Unlike the purely repulsive particles used in most numerical and theoretical studies materials like foam bubbles, powders and emulsion droplets typically have a weak attractive interaction. In this soundbite I will show you that the jamming transition has a different character for these packings, which results in large protocol dependence and more work required to obtain well defined quantities such as the critical packing fraction and the coordination number.

Mazi Jalaal

Physics of Fluids Group - University of Twente
Viscoplasticity (with P)
At low stresses, viscoplastic fluids (a.k.a yield stress materials) behave like elastic solids. Nevertheless, if the stress is large enough, they act like a viscous fluid. I will show the importance of this feature in some fluid mechanics problems.

Frank Aangenendt

TU/e
Swelling and compression of hydrogels in the presence of macromolecules
We have performed swelling and compression experiments with hydrogels in solvents containing macromolecules that, depending on their molecular weight, can penetrate the hydrogel network. Our experiments show that when such macromolecules penetrate a hydrogel network, significant changes in solvent quality can occur, which directly affects the equilibrium swelling volume.

Peter Cats

Utrecht University
The Solvent of the Future
Room Temperature Ionic Liquids (RTIL’s) are dense fluids composed of mixtures of cations and anions with or without a solvent. RTIL’s have many applications and are sometimes called solvents of the future. They are also a hot research topic as many aspects and properties of these “magical” electrolytes are yet unknown or ill understood, in particular their dynamics poses many challenges for theory, simulation, and experiment, mainly because their strong (and long-ranged) Coulomb interactions are coupled to steric packing effects, polarisation, and double-layer formation near electrodes. Unfortunately, none of these issues will be resolved in this sound-bite since I just started my PhD on theory of RTIL’s earlier this month.