Microgels as viscosity modifiers influence lubrication performance of continuum. Issue 47 (11th October 2019)

• Record Type: Journal Article
• Authors: Andablo-Reyes, Efren; Yerani, Demetra; Fu, Ming; Liamas, Evangelos; Connell, Simon; Torres, Ophelie; Sarkar, Anwesha
• Is Part Of: Soft matter. Volume 15:Issue 47(2019)
• Page Start: 9614
• Page End: 9624
• Publication Date: 2019-10-11
• Subjects: Soft condensed matter -- Periodicals; 530.413
• DOI: 10.1039/c9sm01802f
• Languages: English
• ISSNs: 1744-683X

Abstract

Abstract : Biocompatible microgels modify the rheology of continuum acting as thickening or thinning agents. Here, the influence of high shear rheology of microgels on tribological performance of the continuum is demonstrated. Abstract : Biocompatible microgels have been demonstrated to act as excellent lubricants, however, the influence of the continuum on their overall mechanical performance has been neglected so far. In this work, the mechanical performance of colloidal whey protein microgels (hydrodynamic diameter ∼100 nm measured using dynamic light scattering and atomic force microscopy) of different rigidity dispersed in Newtonian (buffer and corn syrup) or complex non-Newtonian fluids (xanthan gum) is investigated for the first time via rheology and soft tribology. Dispersions of both soft microgels ( G ′ ∼ 100.0 Pa) and hard microgels ( G ′ ∼ 10.0 kPa) were observed to act as thickeners in buffer as well as in low viscosity corn syrup and correspondingly reduced the friction, latter decreased as a function of the increased rigidity of the microgels. Differently, in high viscosity continuum, the microgels acted as thinning agents and increased the friction. In the lubrication limit, microgels in buffer or corn syrup behaved as Newtonian fluids with effective viscosity corresponding to their second Newtonian plateau value ( η ∞ ). However, the lubrication performance of the microgels dispersed in the complex fluid (xanthan gum) could not be described quantitatively by η ∞ . For the low viscosity xanthan gum, the microgels had no influence on friction. Nevertheless, for the high viscosity counterparts, the soft microgels acted as thinning agents whilst the hard microgels accelerated the onset of elastohydrodynamic regime. This study demonstrates that microgels act as viscosity modifiers directly influencing the tribological performance, depending upon a subtle interplay of rheological properties of the particles and continuum.