Attractive interaction and bridging transition between neutral colloidal particles due to preferential adsorption in a near-critical binary mixture

摘要

We examine the solvent-mediated interaction between two neutral colloidal particles due to preferentialnadsorption in a near-critical binary mixture. We take into account the renormalization effect due to the criticalnfluctuations using the recent local functional theory [J. Chem. Phys. 136, 114704 (2012)]. We calculate the freenenergy and the force between two colloidal particles as functions of the temperature T , the composition far fromnthe colloidal particles c∞, and the colloid separation u0002. The interaction is much enhanced when the componentnfavored by the colloid surfaces is poor in the reservoir. For such off-critical compositions, we find a surface ofna first-order bridging transition u0002 = u0002cx(T,c∞) in the T -c∞-u0002 space in a universal, scaled form, across which andiscontinuous change occurs between separated and bridged states. This surface starts from the bulk coexistencensurface (CX) and ends at a bridging critical line where u0002 is determined by T as u0002 = u0002c(T ). On approaching thencritical line, the discontinuity vanishes and the derivatives of the force with respect to T and u0002 both diverge.nFurthermore, bridged states continuously change into separated states if c∞ (or T ) is varied from a value on CXnto a value far from CX with u0002 kept smaller than u0002c(T ).