Structure and dynamics of particle monolayers at a liquid–liquid interface subjected to shear flow

Abstract

The effect of shear flow on the structure and dynamics of monodisperse spherical polystyrene particles suspended at the interface between decane and water was observed. While undisturbed, the particles arrange themselves on a hexagonal lattice due to strong dipole-dipole repulsion resulting from ionizable sulfate groups on their surfaces. As the interface is subjected to shear flow, however, the lattice adopts a new semi-ordered, anisotropic state for which two distinct regimes are observed. At low particle concentrations or high shear rates, nearest neighbors in the lattice align in the flow direction and create strings of particles that slip past each other fairly readily. This results in a stretching of the overall structure and achievement of a steady state orientation in the system. In contrast, at high concentrations or low shear rates, the interparticle forces gain importance and tend to keep the particles more strongly in their lattice positions. As a result, domains within the lattice are forced to rotate, thus giving rise to movement of particles perpendicular to the flow direction. Thus a rotation, in addition to stretching, of the structure is apparent in this case.

Direct Measurements of the Effects of Salt and Surfactant on Interaction Forces between Colloidal Particles at Water−Oil Interfaces

“…For example, the most efficient stabilization of Pickering emulsions will probably be achieved by a relatively low surface coverage and weakly aggregated structure at the droplet interfaces [8,9]. Planar monolayers of particles with controlled interactions also enable fundamental studies of colloid physics, such as crystal melting [10], aggregation [11,12,13,14], packing and self-assembly of non-spherical particles [15,16] and even elucidate the effects of shear or extensional flow on the microstructure of suspensions [17,18]. In all cases, predictive control over the generated structures is needed, necessitating a detailed understanding of the colloidal interactions.…”

Confocal microscopy of colloidal dispersions in shear flow using a counter-rotating cone–plate shear cell

“…Similarly, Varadan et al [16] studied colloidal gels under shear by imaging immediately after stopping the flow. Quantitative data on individual particles during flow were obtained by Hoekstra et al for attractive particle systems as well as by Stancik et al for repulsive systems, because they limited their shear set-up to 2D [17,18].…”

Adsorption of Ellipsoidal Particles at Liquid–Liquid Interfaces

“…The rules which control interaction forces for colloidal systems in bulk are no longer as simple or as subtle for particles at interfaces. For example, electrostatic and Van der Waals interactions are strongly enhanced 2,3 where the former can be used to direct the formation of non-close packed twodimensional crystals useful as model materials [4][5][6] . For rough or non-spherical particles strong lateral capillary interactions arise, due to the deformation of the interface caused by an undulating contact line or by particle shape effects [7][8][9] .…”