(396d) A Novel Chromogenic Technique for Measuring Nanoscopic Diffusion Phenomena in Polymers

Here we report a novel chromogenic technique for measuring nanoscopic diffusion phenomena in a large variety of polymers. This innovative technique is enabled by integrating scientific principles drawn from two disparate fields – the fast-growing photonic crystal and shape memory polymer (SMP) technologies, which do not typically intersect with diffusion measurements. In this approach, macroporous polymer photonic crystal membranes with 3-D ordered macropores are first fabricated by a templating approach using self-assembled colloidal crystals as structural templates. The periodic macropores can then be deformed by various “cold” programming approaches, leading to transparent appearance of the deformed membranes. Diffusion of swelling solvent molecules in vapor, liquid, and solid phases leads to gradual and stepwise recovery of the deformed macropores, resulting in easily perceived diffractive color changes that can be easily correlated with the diffusion dynamics of the solvent molecules in the polymer. A large variety of polymers and solvents have been systematically investigated in this work and the experimental results match well with the theoretical modeling using Fick’s laws of diffusion. In addition to providing a simple and sensitive optical technique for in-situly investigating nanoscopic diffusion phenomena in polymers, this innovative approach also enables new chromogenic sensors for a wide spectrum of applications ranging from environmental monitoring to threat detection.