Life at ultralow interfacial tension: wetting, waves and droplets in demixed colloid-polymer mixtures

Abstract

Abstract.Mixtures of colloids and polymers display a rich phase behavior, involving colloidal gas (rich in polymer, poor in colloid), colloidal liquid (poor in polymer, rich in colloid) and colloidal crystal phases (poor in polymer, highly ordered colloids). Recently, the colloidal gas-colloidal liquid interface received considerable attention as well. Due to the colloidal length scale the interfacial tension is much lower than in the atomic or molecular analog (nN/m instead of mN/m). This ultra-low interfacial tension has pronounced effects on the kinetics of phase separation, the colloidal gas-liquid profile near a single wall and the thermally induced fluctuations of the interface. The amplitudes of these thermally excited capillary waves are restrained by the interfacial tension and are for that reason of the order of the particle diameter. Therefore, in molecular systems, the capillary waves can only be seen indirectly in scattering experiments. In colloidal systems, however, the wave amplitudes are on a (sub) micrometer scale. This fact enables the direct observation of capillary waves in both real space and real time using confocal scanning laser microscopy. Moreover, the real space technique enables us to demonstrate the strong influence of interface fluctuations on droplet coalescence and droplet break up. PACS

Off-equilibrium surface tension in miscible fluids

“…Most of the previous works have focused on the interface between phase-separated colloidal fluids at thermodynamical equilibrium [52][53][54][55] ; however, colloidal suspensions are also excellent candidates for investigating off-equilibrium surface tension, since diffusion is comparatively slow in colloids or polymers, The first experimental investigation of the EIT in complex fluids miscible in all proportion has been performed by Zoltowski et al 13 , who studied drops of dodecyl-acrylate (DA) in mixtures of DA and poly(dodecyl acrylate) (PDA, molecular weight 25 kD), using a spinning drop tensiometer. Most of the previous works have focused on the interface between phase-separated colloidal fluids at thermodynamical equilibrium [52][53][54][55] ; however, colloidal suspensions are also excellent candidates for investigating off-equilibrium surface tension, since diffusion is comparatively slow in colloids or polymers, The first experimental investigation of the EIT in complex fluids miscible in all proportion has been performed by Zoltowski et al 13 , who studied drops of dodecyl-acrylate (DA) in mixtures of DA and poly(dodecyl acrylate) (PDA, molecular weight 25 kD), using a spinning drop tensiometer.…”

First-passage dynamics of linear stochastic interface models: numerical simulations and entropic repulsion effect

“…[1], we focus on linearized models in one dimension and assume absence of any deterministic force beside surface tension. In particular, we neglect the influence of disjoining pressure, which is experimentally justified for colloidal fluids [35,36]. Accordingly, in this case film rupture is solely driven by noise.…”

Fluid–fluid coexistence in an athermal colloid–polymer mixture: thermodynamic perturbation theory and continuum molecular-dynamics simulation

“…Experimental investigations of the phase behaviour of colloid-polymer mixtures have been performed on a variety of systems ranging from comparatively simple latex-polystyrene and silica-polydimethylsiloxane colloidal dispersions to biological systems containing proteins or DNA [2][3][4][5][6][7][8][9][10][11][12][13]. Phase separation has been described by many authors [3,4,8,[14][15][16][17][18][19][20][21][22][23][24][25][26][27]; see the excellent book of Lekkerkerker and Tuinier [1] for a comprehensive historical review. Fluid-solid coexistence is observed when the radius of gyration of the polymer is small compared to that of the colloid; here one can draw an analogy between the behaviour of the colloids and that of a system of pure hard spheres (HSs).…”