2D Cosmetic Emulsion & Skin Barrier Lab

A cosmetic emulsion only stays mixed because emulsifier molecules park themselves at the oil/water interface, their polar head facing the continuous phase and their nonpolar tail dipping into the dispersed droplets — the balance between those two ends, expressed as HLB (Hydrophile–Lipophile Balance), decides whether oil ends up dispersed in water (O/W, light and spreadable) or water ends up dispersed in oil (W/O, richer and occlusive). This 2D companion draws that cross-section directly on canvas: a vial view shows droplets ringed by emulsifier heads and tails that reorient when you switch emulsion type, while a brick-and-mortar diagram of the stratum corneum on the right lets you fire a test molecule through the skin barrier and time its crossing using the Potts–Guy regression (log K_p = −2.7 + 0.71·logK_ow − 0.0061·MW), the same real skin-permeability equation used in the 3D version.