Solvation forces versus the nano-colloidal structural forces under the film confinement: Layer to in-layer structural transition in wetting solids

This work reviews the origins, similarities, measurement techniques, and differences of the solvation and nano-colloidal oscillatory structural forces in confined domains. With an increasing confinement, the particles' structural transition changes from 2D random layering to 2D crystalline packing, as observed experimentally and revealed by the radial distribution function. The 2D in-layer structural energy transition was estimated to be 1.8 kT using the Boltzmann normal distribution law. The transition from a 2D random structure away from the vertex to 2D cubic/hexagonal domains near the vortex was discontinuous and was confirmed by the particle density profile computed by an integral equation. The critical roles of the solvation and nano-colloidal oscillatory structural forces on the wetting and spreading of the simple liquids and complex liquids on solid surfaces are elucidated.