Cavitation Rheology

Cavitation rheology is the study of the mechanical behavior of gels and other soft solids upon the introduction of cavities. In this project we applied cavitation rheology to measure the elastic modulus of a triblock copolymer gel. Gels were obtained by dissolving 5% and 10% volumes of a triblock copolymer, poly(methyl methacrylate)–poly(n-butyl acrylate)–poly(methyl methacrylate), in 2 ethyl-1-hexanol. In these experiments a needle connected to a syringe was inserted in the gel. The air within the syringe was compressed at different rates, ranging from 0.1 to 5 mL/min, using an automated syringe pump, causing a buildup of pressure and leading to cavitation in the form of a rapidly growing bubble. The pressure at which the gel cavitates is called the critical pressure, and is related to the Young’s modulus, or elasticity, of the gel plus the surface tension between the gel and the air and the inverse of the size of the needle tip, which was varied by using needles of different diameters. Both the critical pressure and the size and nature of the bubble are being analyzed to investigate the mechanical behavior of these gel at any arbitrary locations within the material.