Evaluation of high temperature polymers in nanolayered films and gradient refractive index (GRIN) lenses

A new polymer nanolayer gradient refractive index (GRIN) system with more robust thermal stability because of incorporation of a high glass transition temperature polyester, OKP4HT, was demonstrated. A combination of extruded nanolayered GRIN film systems, comprised of five unique polymer materials, were combined to produce laminate optics comprised of a large internal refractive index gradient distribution, n = 1.445 – 1.630, without degradation of optical transmissive properties. The optical performance of a series of varied magnitude GRIN lenses, ranging from Δn = 0 to 0.185, was evaluated. Increasing the lens refractive index range resulted in decreased optic sphericalaberrations that followed analytical predictions. An analytical approach was reported to correlate the polymer material upper service temperature (UST) to the onset of polymer material loss modulus as measured by DMTA. Thermo‐optical interferometry measurements of irreversible lens deformation confirmed the lenses UST at 125°C for the OKP4HT/PC system as compared to 75°C for a PMM/SAN17 system. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42741.     

Gas sensing properties of a composite composed of electrospun poly(methyl methacrylate) nanofibers and in situ polymerized polyaniline

Poly(methyl methacrylate) (PMMA) nanofibers with different diameters were fabricated by electrospinning and their composites with polyaniline (PANI) were formed by virtue of in situ solution polymerization. The coaxial composite nanofibers so prepared were then transferred to the surface of a gold interdigitated electrode to construct a gas sensor. The structure and morphology of the PANI/PMMA composite fibers were characterized by UV–vis spectroscopy and scanning electron microscopy, which indicated that the coaxial nanofibres of PANI emeraldine salt and PMMA were successfully prepared. The electrical responses of the gas sensor based on the composite nanofibres towards triethylamine (TEA) vapors were investigated at room temperature. It was revealed that the sensor showed a sensing magnitude as high as 77 towards TEA vapor of 500 ppm. In addition, the responses were linear, reversible and reproducible towards TEA vapors ranging from 20 to 500 ppm. The diameters of the electrospun PMMA fibers had an effect on the sensing magnitude of the gas sensor, which is proposed to relate to the difference in the surface-to-volume ratio of the fibers. Furthermore, it was found that the concentration of doping acids only led to changes in resistance of the sensor, but could not affect its sensing characteristics. In contrast, the nature of the doping acids was determinative for the sensing magnitude of the sensor. The gas sensor with toluene sulfonic acid as the doping acid exhibited the highest sensing magnitude, which is explained by taking into account of the sensing mechanism and the interactions of doping acids with TEA vapor.     

Triple‐shape‐memory polymer films created by forced‐assembly multilayer coextrusion

Triple‐shape‐memory polymers are capable of memorizing two temporary shapes and sequentially recovering from the first temporary shape to the second temporary shape and eventually to the permanent shape upon exposure to a stimulus. In this study, unique three‐component, multilayered films with an ATBTA configuration [where A is polyurethane (PU), B is ethylene vinyl acetate (EVA), and T is poly(vinyl acetate) (PVAc)] were produced as a triple‐shape‐memory material via a forced‐assembly multilayer film coextrusion process from PU, EVA, and PVAc. The two well‐separated thermal transitions of the PU–EVA–PVAc film, the melting temperature of EVA and the glass‐transition temperature of PVAc, allow for the fixing of the two temporary shapes. The cyclic thermomechanical testing results confirm that the 257‐layered PU–EVA–PVAc films possessed outstanding triple‐shape‐memory performance in terms of the shape fixity and shape‐recovery ratios. This approach allowed greater design flexibility and simultaneous adjustment of the mechanical and shape‐memory properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44405.