Gel network amplifies Nano-Scale adsorption at Solid/Liquid interface to Sub-Millimeter-Scale

We have proposed a spreading-flow model of the solvent movement in a gel, which states that the solvent flows along the gel network segment much easier than in any other direction. An excess amount of the solvent component adsorbed on a flat solid surface in a gel will be transferred over the macroscopic gel network by the spreading-flow. Then, by measuring the concentration distribution of each solvent near the solid surface at the sub-millimeter scale, it should be possible to evaluate adsorption occurring on the nanometer scale.

Confocal Raman microscopy was employed to map the concentration distributions of mixed solvents of p-xylene, mesitylene, and octanenitrile gelled by 12-hydroxystearic acid near the atomically flat mica surface. The measured concentration profiles were analyzed by the spreading-flow theory to construct adsorption isotherms.

Nearly all isotherms follow power laws with similar exponents, which is consistent with the van der Waals multilayer adsorption with weak adsorbate-adsorbent interactions. The present study demonstrates the concept of gel network amplification and its usefulness for probing nano-phenomena using macro-technology.