An experimental approach to the determination of two-dimensional gel-point: A film balance study

Abstract

Two-dimensional gelation has been modelled by the lateral compression of microparticles at water(aqueous solution)-air interfaces in a film balance. The compression induced network formation manifested itself in increased surface pressure (II) at significantly higher surface areas (A) than those observed in hexagonally close-packed particle ordering. The gel-point of a system in these experiments is definec as a surface area (or rather suface coverage) at which the particle-aggregates reach their “solid state”. It can be determined by fitting a tangent to the “solid-state-part” of II-A isotherm and extrapolating it to II=0.

The threshold of gelation was studied from the point of view of particle-particle interactions. The colloid and capillary interactions were influenced by the hydrophobicity of the particles and the composition of liquid phase. Computer simulations of the two-dimensional gelation were also investigated. Both the experimental and numerical results indicate decreasing gel-point (given in surface coverage) with increasing adhesion between the particles. This is in full accord with the well-known particle-particle achesion to the specific volume of sediments (in three dimensions) relationship.