title: Hard and soft colloids at fluid interfaces: Adsorption, interactions, assembly & rheology.
abstract: Soft microgel particles inherently possess qualities of both polymers as well as particles. We review the similarities and differences between soft microgel particles and stiff colloids at fluid-fluid interfaces. We compare two fundamental aspects of particle-laden interfaces namely the adsorption kinetics and the interactions between adsorbed particles. Although it is well established that the transport of both hard particles and microgels to the interface is driven by diffusion, the analysis of the adsorption kinetics needs reconsideration and a proper equation of state relating the surface pressure to the adsorbed mass should be used. We review the theoretical and experimental investigations into the interactions of particles at the interface. The rheology of the interfacial layers is intimately related to the interactions, and the differences between hard particles and microgels become pronounced. The assembly of particles into the layer is another distinguishing factor that separates hard particles from soft microgel particles. Microgels deform substantially upon adsorption and the stability of a microgel-stabilized emulsion depends on the conformational changes triggered by external stimuli.
authors.affiliation: Physics of Complex Fluids Group, Dept. Science and Technology, University of Twente, Enschede, The Netherlands.
authors.forename: Omkar S
authors.initials: OS
authors.lastname: Deshmukh
authors.affiliation: Physics of Complex Fluids Group, Dept. Science and Technology, University of Twente, Enschede, The Netherlands.
authors.forename: Dirk
authors.initials: D
authors.lastname: van den Ende
authors.affiliation: Physics of Complex Fluids Group, Dept. Science and Technology, University of Twente, Enschede, The Netherlands; Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Wageningen, The Netherlands.
authors.forename: Martien Cohen
authors.initials: MC
authors.lastname: Stuart
authors.affiliation: Physics of Complex Fluids Group, Dept. Science and Technology, University of Twente, Enschede, The Netherlands.
authors.forename: Frieder
authors.initials: F
authors.lastname: Mugele
authors.affiliation: Physics of Complex Fluids Group, Dept. Science and Technology, University of Twente, Enschede, The Netherlands. Electronic address: m.h.g.duits@utwente.nl.
authors.forename: Michel H G
authors.initials: MH
authors.lastname: Duits
keywords: Interfacial rheology; PNIPAM microgel particles; Particle laden interfaces; Pickering emulsions