(708h) Understanding Failure Behavior of a Physically Assembled Thermoreversible Triblock Copolymer Gel

The polymeric gels have applications in many fields such as in drug delivery, tissue engineering, and bio-adhesives. Here, we present the structural evolution and mechanical properties of a physically assembled polymeric gel consists of poly (styrene)-poly (isoprene)-poly (styrene) [PS-PI-PS] dissolved in mineral oil, a PI block selective solvent. At high temperature, both PS and PI blocks are soluble in mineral oil, as a result, the system behaves like a viscous liquid. As the temperature is decreased, the solubility of PS in mineral oil decreased significantly. As a result, multiple endblocks collapse and associate to form aggregates which act as physical crosslinks. The solvated midblocks bridge those aggregates leading to the formation of a 3D network. We have studied the effect of polymer volume fraction, entanglement of the midblocks, midblock and endblock molecular weight, and the addition of homopolymers on the gel mechanical and failure behavior through experiments and simulations. The gelation temperature was captured by shear-rheometry. The small angle x-ray (SAXS) study indicated micellar microstructure at room temperature. The tensile test results performed on a custom-built setup captured the strain rate dependence of these gel. The creep failure tests represent the delayed fracture in these gels as a result of the thermally activated process. Pure shear mode failure experiments reveal the dependence of energy release rate on the crack velocity. Cavitation rheology experiments were also performed on these gels. A finite element framework was developed to model the cavitation rheology experiment. The individual and coupled effect of surface tension and boundary confinement on the cavitation phenomenon was investigated. In summary, we attempted to relate the macroscopically observed failure behavior to the gel microstructure.