APPLICATIONS AND NONLINEAR MECHANICAL PROPERTIES OF THERMOREVERSIBLE TRIBLOCK COPOLYMER GELS

Kendra A. Erk1 and Kenneth R. Shull2

1 Polymers Division, Material Measurement Laboratory, NIST, Gaithersburg MD 20899 USA
2 Department of Materials Science and Engineering, Northwestern University, Evanston IL 60208 USA

Thermoreversible triblock copolymer gels display a wide variation in mechanical behavior over a temperature range that is experimentally accessible. At elevated temperatures these gels behave as freely flowing solutions, exhibiting fast relaxation behavior. The relaxation time increases dramatically as temperature is reduced, such that at room temperature the gels become strong elastic materials.

The nonlinear mechanical properties of triblock copolymer gels are ultimately dependent on the structure of the underlying physically associating network of triblock copolymer molecules and how this structure evolves during deformation and aging. The aim of this research is to characterize the structure-property relationships of triblock copolymer gels utilizing shear rheometry over a wide range of temperature and deformation rates. Behavior of the gels in the nonlinear regime i.e., the stress response during deformation to large strain or strain rate is of particular interest.

Triblock copolymer gels were successfully applied as model systems for a variety of engineering and biophysical applications. The thermoreversible nature and mechanical strength of the gels was found to be advantageous in a low-temperature casting process for titanium foams of complex shape. The gels were also demonstrated to be excellent synthetic model systems for strain-stiffening biological materials. Additionally, evidence of shear-induced strain localization in the triblock copolymer gels coupled with the well-defined structure of the gels and the wide range of accessible relaxation times makes these gels ideal model systems for future studies of deformation-induced failure in physically associating materials and complex fluids.