Insights into the Multiscale Lubrication Mechanism of Edible Phase Change Materials

Abstract

Investigation of a lubrication behavior of phase change materials (PCM) can be challenging in applications involving relative motion, e.g., sport (ice skating), food (chocolates), energy (thermal storage), apparel (textiles with PCM), etc. In oral tribology, a phase change often occurs in a sequence of dynamic interactions between the ingested PCM and oral surfaces from a licking stage to a saliva-mixed stage at contact scales spanning micro-(cellular), meso-(papillae), and macroscales. Often the lubrication performance and correlations across length scales and different stages remain poorly understood due to the lack of testing setups mimicking real human tissues. Herein, we bring new insights into lubrication mechanisms of PCM using dark chocolate as an exemplar at a single-papilla (meso)-scale and a full-tongue (macro) scale covering the solid, molten, and saliva-mixed states, uniting highly sophisticated biomimetic oral surfaces with in situ tribomicroscopy for the first time. Unprecedented results from this study supported by transcending lubrication theories reveal how the tribological mechanism in licking shifted from solid fat-dominated lubrication (saliva-poor regime) to aqueous lubrication (saliva-dominant regime), the latter resulted in increasing the coefficient of friction by at least threefold. At the mesoscale, the governing mechanisms were bridging of cocoa butter in between confined cocoa particles and fat coalescence of emulsion droplets for the molten and saliva-mixed states, respectively. At the macroscale, a distinctive hydrodynamic viscous film formed at the interface governing the speed-dependent lubrication behavior indicates the striking importance of multiscale analyses. New tribological insights across different stages and scales of phase transition from this study will inspire rational design of the next generation of PCM and solid particle-containing materials.

A Teaching-Learning Framework for Materials Characterization

“…Cocoa butter reveals a series of peaks attributed to the complex polymorphic behavior and melting process . It is worth noting that the thermal analysis data could be used to assess the behavior of paraffin, waxes, and cocoa butter as phase change materials and lubricants ,− and would allow one to identify connections between structure, microstructure, and thermal and tribological properties.…”

Bimetallic PdPt alloy nanoparticle-decorated track-etched polyethylene terephthalate membranes for efficient H2 separation

“…Two binding energy peaks of the Pt 4f 7/2 components can be attributed to the Pt 0 (71.26 eV) and Pt II (72.31 eV) species, respectively, in the deconvoluted spectrum, and the peaks with binding energies of 74.55 and 75.82 eV, which are assigned to Pt 0 and Pt II species of the Pt 4f 5/2 components, can be attributed to the formation of the Pd-Pt alloy. 49,50 The energies of palladium and platinum in bimetallic systems tend to migrate to lower levels, which can be attributed to the charge transfer and electronic disturbances between them. As previously stated, this change in binding energy is due to the alloy formation and influenced by the chemical environment.…”

Understanding mechanisms behind the oily mouthcoating perception of pure vegetable oils using tribology

“…In aqueous systems, friction in the mixed regime is modulated by the amount and size of fat droplets (Wang et al, 2021), and solid fat content (SFC) in the oil phase increases lubrication via coalescence of oil droplets (Liu et al, 2015; Zhou et al, 2022). A few studies applied soft tribology to oil continuous foods, such as water in oil emulsions (Douaire et al, 2014) or chocolate (Soltanahmadi et al, 2023). However, such studies focused on the variation of particle sizes and structuring rather than oil composition.…”