Thermoplastic elastomers (TPEs) constitute an important class of commercial polymers due to their widespread use in various technologies. A distinguishing feature of TPE triblock copolymers is their inherent ability to form rubbery networks stabilized by endblock-rich microdomains that are glassy or semicrystalline at application temperature. Upon incorporation of a midblock-selective solvent, the midblocks become highly swollen, yielding a thermoplastic elastomer gel (TPEG). Depending on composition, these systems can exhibit a full range of morphologies, and the structural features and mechanical properties of TPEGs generated from commercial and model styrenic TPEs will be surveyed. Midblock-selective cosolvents are employed to yield TPEGs that, according to dynamic rheology, exhibit time-composition equivalence under isothermal conditions, and master curves and composition-based shift factors are presented for several systems. These materials, subjected to electrical stimulation as dielectric elastomers, can achieve actuation strains greater than 300% and electro-mechanical coupling efficiencies in excess of 90% at relatively low fields. The electrostatic mechanism by which electroactuation proceeds, as well as comparisons with other materials, will be discussed. Judicious use of co-solvents yields electroactive polymers with controllable molecular relaxation and high energy densities. In the case of acrylic TPEs, electroactuation occurs without the need for mechanical prestrain (often required to thin specimens so that lower voltages can be used to achieve high fields). Mechanical tests are likewise used in conjunction with small-angle scattering to probe the morphology of these TPE systems. This design paradigm is used to generate ionic polymer-metal composites (IPMCs) from multiblock ionomers. Development of stimuli-responsive, hyperelastic and shape-recovering polymeric materials, such as electro-elastomers and IPMCs, is critical for technologies such as (micro)robotics to grow into a commodity industry. These materials are suitable candidates for stretchable hybrid flextronics and can also be utilized for energy harvesting, as well as shape control in haptic, biomedical, electronic, and microfluidic devices.

Renaissance of thermoplastic elastomer gels as next-generation soft and stretchable materials

247th National Meeting (2014)

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