Tuning Lubrication Performance of Phase‐Changing Emulsion‐Filled Gels by Sugar Alcohols

Abstract

Lubrication by hydrogels is proving to be an emerging area in colloid science. Although oil‐driven friction reduction is predominant in literature, emulsion gel‐based lubrication has attracted very little attention to date. We hypothesize that an interplay of viscolelasticity and oil volume fraction may modulate lubricity of emulsion‐filled gels. Herein, phase‐change gelatin‐based emulsion‐filled gels with different sugar alcohol and oil droplet concentrations (0‐30 wt%) were tested for their lubrication performance. The rheological and tribological tests were analysed in conjunction with spectroscopic and structural characterizations in order to reveal structure‐function relationship. Structural characterizations demonstrated that hydrogen bonding was enhanced in pure gelatin gels with the increase of sugar alcohol (glycerol)‐replacement time, which enhanced the storage modulus (G') of the gel networks. Emulsified droplets served as active fillers further strengthening the G’ and strikingly the presence of glycerol reduced the thermo‐responsiveness of the emulsion‐filled gels. Emulsion‐filled gels containing sugar alcohols, irrespective of their type, can greatly reduce the friction coefficients (μ) between hydrophobic surfaces in the boundary and mixed regimes versus the systems without sugar alcohols. In the hydrodynamic regime, the friction coefficient of the system was proportional to the second plateau shear viscosity, regulated by the oil content.This article is protected by copyright. All rights reserved.