- 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.