Resins with “Nano-Raisins”

Thermosensitive hydrogels are materials which globally shrink/swell in water when the surrounding temperature crosses the lower critical solution temperature (LCST). We demonstrate here a novel class of cross-linked polymeric materials, which do not shrink/swell in water globally, but nevertheless reveal a hydrogel-like, stimuli-responsive behavior. In particular, they demonstate a positive thermosensitive release of the embedded fluorescent dye significantly modulated when temperature crosses the LCST. Using staining with copper, transmission electron microscopy and energy dispersive X-ray analysis, we show that this effect is associated with nanogel “raisins” dispersed in such materials (e.g., polymer nanofibers). Shrinkage of individual nanogel “raisins” at elevated temperatures increases nanoporosity via increased exposure of the existing nanopores to water, or formation of new nanopores/nanocracks in the overstretched polymer matrix in the vicinity of shrinking nanogel “raisins”. As a result, the release rate of the embedded dye from the nanofibers increases at elevated temperatures. We suggest that similar functional materials with embedded nanogel “raisins” will find applications in nanofluidics and as drug carriers for controlled drug release.