Alcohol-swollen polymer gels are used as model physically associating systems for rheometer-based gel fracture and healing experiments. The model gel is thermoreversible, composed of acrylic triblock copolymer dissolved in a midblock-selective solvent. At elevated temperatures, the copolymer is fully dissolved and the system behaves as a viscoelastic liquid with near Maxwellian relaxation. As the system is cooled, the copolymer self-assembles into a three-dimensional transient network composed of spherical endblock aggregates interconnected by flexible midblock bridges. The relaxation time increases dramatically as temperature is reduced, such that at room temperature the system behaves as a viscoelastic gel.During shear inception experiments at relatively high shear rates, the physical crosslinks within the gel's network structure are disrupted, and the gel displays a corresponding overshoot in the measured stress response due to cohesive fracture, which has been confirmed by particle tracking flow visualization techniques (Langmuir, 28, 4472-4478 (2012)). When the fractured gel is heated above a critical temperature (33-36oC) and then cooled to room temperature, the physically crosslinked network is re-formed and the gel recovers its original elasticity. Interestingly, partial to full recovery of the fractured gel can also be achieved by room temperature aging at zero shear rate. This healing behavior at different aging times and temperatures can be quantified using rheometry by re-fracturing an aged gel after the desired aging time and comparing the original value of the stress overshoot peak with the post-aging overshoot value. By studying the fracture-healing response of this model gel system at different aging times and temperatures, the observed healing kinetics can be related with simple mathematical models to the gel's characteristic relaxation behavior and temperature sensitivity.

Rheological characterization of fracture-healing behavior displayed by a physically associating polymer gel subjected to shear deformation

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.