- Joost de Graaf (University of Utrecht) (10.30-11.15)
The Impact of Hydrodynamics on Colloidal Gel Collapse
- Many industrial systems require micron-sized particles, so-called colloids, to remain suspended in a liquid medium at low volume fractions, e.g., pesticides, beauty products, and paints. To achieve the desired shelf life, one must postpone phase separation and reduce the tendency of density-mismatched colloids to sediment to the bottom of a container. This is often done by introducing strong, short-ranged attractions between the colloids using polymer-based depletion, which lead to kinetic arrest of the phase-separating suspension. That is, the particles become stuck to each other and form a space-spanning network structure, a colloidal gel. This network can provide protection against applied stress, whilst allowing for flow, and it can even exhibit self-healing properties. In this presentation, we introduce an experimental model system, by which colloidal gelation and gel collapse - the eventual break-down of stability under the influence of gravity - can be studied. From the experimental studies , it becomes clear that fluid flow plays an important role in determining the stability of colloidal gels. This inspired us to perform detailed molecular dynamics simulations accounting for hydrodynamic interactions via the lattice-Boltzmann algorithm to gain a better understanding of these systems. We reveal how hydrodynamic interactions can lead speed up and slow down colloidal gel collapse, depending on the colloid volume fraction. We will also comment on the relation between our numerical results and the experiment, as well as those of other groups working in this field. Finally, we present an outlook for future research into gelation that goes beyond the limitations of our current work.
- Huanshu Tan (University of Twente) (11.15-11.45)
Evaporating/dissolving multicomponent drops with the ouzo effect
- Ouzo is an anise-flavored aperitif, primarily consisting of water, ethanol and anethole oil. Diluting the solution with water causes oil phase to separate out generating long-lived small oil droplets spontaneously, and this process is known as the ouzo effect. We introduced the ouzo effect into multi-component drop systems by letting sessile ouzo drops evaporate in the air or dissolve in liquid. The outcome is amazingly rich thanks to the complexity of the system, and we discovered many interesting phenomena. For instance, the ouzo effect could be triggered by evaporation/diffusion, and the preferential location of oil droplets nucleation is tunable; The nucleated oil droplets could merge up, forming an oil ring sitting at contact line or suspending inside the drop; In different cases, the flow in the system had different patterns. In this talk, I will present and discuss these phenomena.
- Corentin Coulais (University of Amsterdam) (13.30-14.15)
From Mechanical Metamaterials to Machine Materials
- Manipulating physical signals such as light, sound, heat or motion is a vital challenge in multiple areas of science, with far-reaching ramifications for technology and society. Due to recent advances in digital fabrication techniques, the last years have seen a revolution in artificial periodic composites with on-demand electromagnetic, acoustic, thermal and mechanical properties that surpass that of their constituents and that have important applications in e.g. telecommunications, energy management and medicine. These so-called metamaterials become particularly interesting in mechanics, where geometrical effects, nonlinear responses and coupling to the environment are much more accessible and stronger than in any other physical field. In this talk, I will show that mechanical metamaterials using geometrical nonlinearities and activity lead to entirely new properties and functionalities such as programmable and self-oscillatory responses. Using 3D printing of flexible materials, precision desktop experiments, numerical modelling and theory, we demonstrate that flexible metamaterials can be designed, fabricated and programmed for specific mechanical tasks. Such approach opens up promising pathways to bridge the gap between Matter and Machine.
- Abheeti Goyal (TU Eindhoven) (14.15-14.45)
Impact of Substrate Wetting on Domain Morphology and Demixing Dynamics of Binary Fluid Mixtures
- Understanding of the evolution kinetics of the demixing of fluids on a substrate is important in the context of the fabrication of membranes, photonics and photovoltaics. By means of lattice Boltzmann simulations we study the structural evolution of binary fluid mixtures undergoing demixing by spinodal decomposition on a substrate that preferentially wets one of the components. We find that this preferential wetting significantly affects the demixing dynamics and morphology both normal and parallel to the substrate. A concentration wave emerges at the substrate, leading to a continuous domain growth normal to the substrate that is much faster than what happens in bulk. We find non-monotonic domain growth in the direction along the substrate, resulting from the eventual breakdown of a bi-continuous morphology into droplets. The time evolution of the length scales normal and along the substrate are found to be linked. The early stages of demixing are significantly affected by the imposed initial noise level, while the late stage coarsening we find to be dominated by hydrodynamics.
- Michele Zanini (University of Utrecht) (16:00-16:30)
From liquid interfaces to soft matter: when the single particle surface roughness matters
- Surface roughness significantly affects many properties of colloids, from depletion and capillary interactions to their dispersibility and use as emulsion stabilizers. Here, we synthesize a library of all-silica microparticles with uniform surface chemistry, but tuneable surface roughness and we study both their adsorption at oil-water interfaces and the effect of nanoscale surface roughness in linking the rheology of dense suspensions to the particle-particle tribology. In the former case, we demonstrate that surface roughness strongly pins the particle contact lines. As a consequence, the adsorption is arrested in long-lived metastable positions and tremendous contact angle hysteresis are observed. As a unique consequence, the same rough particles can be used as universal stabilizers for both water-in-oil and oil-in-water emulsions by just changing the phase in which they are initially dispersed. When used in dense suspensions, rougher surfaces lead to a significant anticipation of discontinuous shear thickening (DST) onset, in terms of both shear rate and solid loading. Direct measurements of particle–particle friction therefore highlight the value of an engineering-tribology approach to tuning the thickening of suspensions These results both shed light on fundamental phenomena concerning rough particles, indicating new design rules for particle-based emulsifiers and validate surface roughness as an engineering parameter to tune the rheological properties of dense suspensions.
- Christian Sproncken (TU Eindhoven) (16.30-17.00)