Fig. 5: Stribeck curves in hard-soft contact surfaces in presence of plant protein microgels.

Tribological performance of steel ball on PDMS surfaces in the presence of plant protein microgels, native plant protein (matched protein content for Φ = 70 vol% with numbers displayed relating to total protein content) or oil-in-water emulsion. Friction coefficient (µ) as a function of entrainment speed (U) scaled with high rate viscosity (η ∞ = 1000 s − 1) in the presence of plant protein microgels prepared using (a1–a3) pea protein concentrate to form a 15.0 wt% total protein microgel, (PPM15), (b1–b3) potato protein isolate to form a 5.0 wt% total protein microgel (PoPM5), (c1–c3)), potato protein isolate to form a 10.0 wt% total protein microgel, (PoPM10), and (d1–d3) using a mixture of pea protein concentrate at 7.5 wt% total protein and potato protein isolate at 5.0 wt% total protein microgel (PPM7.5:PoPM5) with 1, 2 and 3 showing increased volume fractions from 10 to 70 vol%, respectively. Frictional responses of the plant proteins at the highest concentration and 20 wt% oil-in-water emulsion (O/W emulsion) and buffer are included in each graph (a-d) as controls. Results are plotted as average of six repeat measurements on triplicate samples (n = 6 × 3) with error bars representing standard deviations. Statistical comparison of mean at 0.1 Pa m is shown in Supplementary Table 3. Original friction coefficient versus entrainment speed curves for the microgel dispersions at each volume fractions are shown in Supplementary Fig. 7.