Formation and Transfer of Aqua Structure at Glass–Water Interfaces: Rheological Change in Rolling Droplets

Abstract

A water droplet moving over a solid substrate undergoes repeated renewal of its contact region while exchanging matter, charge, and interfacial forces with the surface. Co-author Ivan Stefanov reported observing a pronounced, rapid change in the apparent mechanical consistency of an initially pure water droplet rolling over freshly ground and cleaned microscope glass, described as honey-like thickening. The physical character of this response is examined using published measurements of silica–water hydration, glass dissolution and colloidal transfer, internal circulation of moving drops, and rheological changes in confined or particle-bearing aqueous systems. We analyze glass and water as interacting compartments whose states can evolve during contact. Material gain and loss, rolling-dependent exposure, and the distinction between bulk viscosity and interfacial resistance provide a quantitative basis for interpreting the observed response. Two sequential-transfer pathways are considered: subsequent water contacting the previously exposed glass and water contacting a second vessel previously exposed to the treated droplet. Matched chemical, rheological, surface and flow measurements are specified to distinguish these pathways and identify the physical carriers. Together, these observations and relationships define an experimentally accessible problem of formation, persistence and transfer of aqua structure at water–solid interfaces.