The present thesis is concerned with the production of optical sensors to detect deformation or temperature changes via the incorporation of excimer-forming dyes into a polymer host. These sensors are very simple and inexpensive to create, and can readily be produced in a variety of forms (films, fibers, etc.). In addition, the sensing scheme can be exploited in virtually all types of polymers.
Binary blends between polyethylene (PE), poly(ethylene terephthalate), or poly(ethylene terephthalate glycol) and highly photoluminescent (PL) cyano-substituted oligo(phenylene vinylene) (cyano-OPV) dyes were prepared using conventional meltprocessing techniques. Mechanical deformation of nano-phase-separated blends, which initially exhibit predominantly excimer emission, leads to a pronounced change in the PL characteristics of the blend from excimer to monomer dominated emission due to breakup of dye aggregates and the formation of a molecularly mixed system. In a study with PE it was found that the ability of the polymer host to break up dye aggregates upon deformation is related to the plastic deformation process of polymer crystallites (specifically those arranged in a lamellar morphology) and increases with increasing polymer crystallinity, decreasing dye aggregate size, and decreasing rates of deformation.
In addition to polymer / dye blends, mechanochromic polyurethane elastomers (TPU) were created by covalently integrating cyano-OPVs into the TPU’s backbone. The polymers thus produced exhibit a pronounced and reversible fluorescence color change upon deformation which mirrors the stress response of the material.
The ability to control the emission color of a material by tuning the extent of dye aggregation can also be used to create threshold temperature sensors. In these materials molecular mixtures of cyano-OPVs and host polymers are kinetically trapped in a thermodynamically unstable glassy state by rapidly quenching a homogeneous melt blend to below its T g. Subjecting blends of sufficiently high concentration to temperatures above their T gallows for dye aggregation and excimer formation, and is concomitant with a permanent and pronounced change in the material’s PL emission spectra. The threshold temperature at which aggregation begins to occur can be easily tailored by selecting a polymer host with the desired T g. The rate of color change increases with higher dye concentration and with increased temperature above T g.