(692i) Chromogenic Photonic Crystal Sensors for Detecting Molecular Diffusion in Polymers
A new technique that utilizes principles from two typically disparate fields, the photonic crystal and shape memory polymer (SMP) technologies, allows for chromogenic detection of nanoscopic diffusion in a variety of polymers. In previous reports, we have demonstrated the detection of swelling vapors and liquids; however, here we include the detection of leeching molecules in polymers. Macroporous SMP photonic crystals membranes comprised of a homogenous copolymer blend of polyethylene glycol diacrylate and ethoxylated trimethylolpropane triacrylate with three-dimensional ordered macropores and microscopic thickness (~ 3 mm) are templated using self-assembled colloidal crystals as sacrificial templates. Deformation of periodic macropores can be induced by capillary pressure created during water evaporation, resulting in the membrane becoming transparent. Recovery of the ordered macroporous structure can be achieved through diffusion of swelling molecules in vapor, liquid, or solid phases. This allows for gradual and stepwise recovery of the photonic crystal structure resulting in easily perceived color due to Bragg diffraction. Proof-of-concept tests for detecting leeching uncured polydimethylsiloxane (PDMS) oligomers and dangerous plastic additives (e.g., di(2-ethylhexyl) phthalate) from solid systems (like plastic toys and food containers) have been demonstrated. These sensors allow for cheap and easy detection of leeching molecules in solids that pose a danger to humans through skin contact, especially for infants who commonly display hand-to-mouth contact.