MGK: Integrated Research Training Group

Wall slip and bulk yielding in soft particle suspensions
Gerhard Jung, Suzanne M. Fielding
Journal of Rheology 65 (2), 199-212 (2021);
Publication resulting from a PhD secondment of Gerhard Jung (TRR student) in Durham in 2018
doi:10.1122/8.0000171

↓ Show Abstract↑ Hide Abstract We simulate a dense athermal suspension of soft particles sheared between hard walls of a prescribed roughness profile, fully accounting for the fluid mechanics of the solvent between the particles and for the solid mechanics of changes in the particle shapes. We, thus, capture the widely observed rheological phenomenon of wall slip. For imposed stresses below the material’s bulk yield stress, we show the slip to be dominated by a thin solvent layer of high shear at the wall. At higher stresses, it is augmented by an additional contribution from the fluidization of the first few layers of particles near the wall. By systematically varying the wall roughness, we quantify a suppression of slip with increasing roughness. We also elucidate the effects of slip on the dynamics of yielding following the imposition of constant shear stress, characterizing the timescales at which bulk yielding arises and at which slip first sets in

Spontaneous spatiotemporal ordering of shape oscillations enhances cell migration
Matteo Campo, Simon K. Schnyder, John J. Molina, Thomas Speck, Ryoichi Yamamoto
Soft Matter 15 (24), 4939-4946 (2019);
doi:10.1039/c9sm00526a

Order–Order Phase Transitions Induced by Supercritical Carbon Dioxide in Triblock Copolymer Thin Films
Anabella A. Abate, Giang Thi Vu, Cristian M. Piqueras, María Cecilia del Barrio, Leopoldo R. Gómez, Gabriel Catalini, Friederike Schmid, Daniel A. Vega
Macromolecules 52 (20), 7786-7797 (2019);
doi:10.1021/acs.macromol.9b01278

↓ Show Abstract↑ Hide Abstract We study the influence of supercritical carbon dioxide(scCO2) on the phase behavior of a cylinder-forming polystyrene-block-polybutadiene-b-polystyrene triblock copolymer thinfilm. Solventannealing with scCO2can produce patterns with long-range order butthese structures become unstable for thinfilms with small thicknesses.These results are in good agreement with self-consistent meanfieldcalculations, which indicate that a drying transition occurs forthicknesses below the radius of gyration of the molecule. Afterdecompression and solvent extraction, the initially swollen polymernanostructure suffers a strong reduction in the average domain spacing, which has a deleterious effect on the degree of order inthe resulting pattern. Both, experiments and Cahn−Hilliard simulations suggest that during decompression the pattern suffersan order−order instability where the collapse of the lattice constant leads to uncommon patterns with long-range orientationalorder but structural distortions at small-length scales.