The flow behavior and mechanics of two distinct stimuli-responsive acrylic gels were studied using shear rheology. The first gel system was a thermoreversible copolymer physical gel composed of poly(methyl methacrylate) (PMMA) end block aggregates connected by poly(n-butyl acrylate) (PnBA) midblock bridges in a midblock selective alcohol. The PMMA-PnBA-PMMA gels were used as a model system to investigate fracture-healing behavior at various temperatures and gel concentrations. The shear stress values of the gels were measured under constant shear conditions and fracture was indicated by a decrease in the stress response, which were confirmed from in situ flow visualization experiments. The fractured gels were then allowed to rest in the rheometer for set periods of time and were tested again using the same constant shear rate to measure the recovery of the shear stress response. The time for fully healed networks, which ranged from minutes to several hours, was found to be dependent on the applied strain deformation and needed to be 100-1000 times greater than the characteristic relaxation times of the gel. The second gel system investigated was poly(acrylic acid) (PAA) composite hydrogels to study viscosity and swelling at low and high pH conditions in aqueous solutions. Linear polymer chains of PAA at various molecular weights were synthesized using controlled radical polymerization methods and then end-crosslinked or grafted onto silica nanoparticles. Gel solutions were tested to probe possible shear thinning and jamming behavior.

Synthesis and shear rheology of thermoreversible and pH-sensitive polymer gels

254th National Meeting (2017)

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