Abstract
Highly enhanced solid-state thermochromism is observed in regioregular poly(3-hexylthiophene), P3HT, when deposited on a superhydrophobic polymer-SiO2 nanocomposite coating. The conformal P3HT coating on the nanocomposite surface does not alter or reduce superhydrophicity while maintaining its reversible enhanced thermochromism. The polymeric matrix of the superhydrophobic surface is comprised of a blend of poly(vinylidene fluoride-co-hexafluoropropylene) copolymer and an acrylic adhesive. Based on detailed X-ray diffraction measurements, this long-lasting, repeatable and hysteresis-free thermochromic effect is attributed to the enhancement of the Bragg peak associated with the d-spacing of interchain directional packing (100) which remains unaltered during several heating-cooling cycles. We propose that the superhydrophobic surface confines π–π interchain stacking in P3HT with uniform d-spacing into its nanostructured texture resulting in better packing and reduction in face-on orientation. The rapid response of the system to sudden temperature changes is also demonstrated by water droplet impact and bounce back on heated surfaces. This effect can be exploited for embedded thin film temperature sensors for metal coatings.
Highlights
Most non-substituted conjugated polymers were not processed by solvents and thermoforming due to strong interchain interactions and chain stiffness
Further surface topography analysis of the superhydrophobic surfaces coated with P3HT was made by Atomic force microscopy (AFM)
Regioregular P3HT displays enhanced, long-lasting, and repeatable thermochromic effect when deposited on a superhydrophobic polymer nanocomposite comprising PVDF-HFP and hydrophobic SiO2 NPs
Summary
Superhydrophobic Surface received: 10 February 2016 accepted: 27 May 2016 Published: 15 June 2016. Enhanced solid-state thermochromism is observed in regioregular poly(3-hexylthiophene), P3HT, when deposited on a superhydrophobic polymer-SiO2 nanocomposite coating. Earlier studies showed that thin films of P3HT deposited on smooth glass or Si-wafer surfaces by spin coating from good solvents, are red-violet at room temperature, but when heated to temperature above 150 °C. change color to light red-orange[18]. We show that solvent-cast regioregular P3HT films demonstrate thermochromism on a soft, smooth, and hydrophobic polymer surface, surprisingly, on a superhydrophobic polymer-silica nanocomposite surface, the thermochromism is remarkably enhanced with fast reversibility, excellent reproducibility and stability exceeding six months under ambient conditions. Superhydrophobic nanocomposites were made by spraying acetone solutions containing PVDF-HFP, acrylic adhesive and Aerosil R812S SiO2 nanoparticles (NPs) onto aluminum substrates. A flat resistive heater was attached on the back side of the coated aluminum substrates in order to collect reflection spectra as a function of temperature (in steps of 10–15 ° C)
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