Shearing-induced contact pattern formation in hydrogels sliding in polymer solution

TL;DR

This study observes and analyzes the formation of dynamic, in-phase contact patterns on hydrogels sliding in concentrated polymer solutions, revealing their dependence on shear conditions and gel properties.

Contribution

It is the first to report in situ observation of rotating contact patterns on hydrogels in polymer solutions and links pattern formation to non-linear rheology.

Findings

Patterns form more quickly at higher velocity, concentration, and pressure.

Pattern periodicity develops into fine characters over time.

Softness of gel significantly affects pattern characteristics.

Abstract

The contact of a hydrogel during the rotational shearing on glass surface in concentrated polymer solution was observed in situ. Dynamic contact patterns that rotate in-phase with the rotational shearing of the gel were observed for the first time. The contact patterns with a periodicity in the circumferential direction appeared and developed into fine characters with the shearing time. The patterns appeared more quickly at elevated sliding velocity, polymer concentration, and normal pressure. Furthermore, the softness of the gel also substantially influenced the character of the patterns. The pattern formation was discussed in terms of the non-linear rheology of the polymer solution at the rotational soft interface.