The mechanism of nanoparticle actuation by stimuli-responsive polymer brushes triggered by changes in the solution pH was discovered and investigated in detail in this study. The finding explains the high spectral sensitivity of the composite ultrathin film composed of a poly(2-vinylpyridine) (P2VP) brush that tunes the spacing between two kinds of nanoparticles-gold nanoislands immobilized on a transparent support and gold colloidal particles adsorbed on the brush. The optical response of the film relies on the phenomenon of localized surface plasmon resonances in the noble metal nanoparticles, giving rise to an extinction band in visible spectra, and a plasmon coupling between the particles and the islands that has a strong effect on the band position and intensity. Since the coupling is controlled by the interparticle spacing, the pH-triggered swelling-shrinking transition in the P2VP brush leads to pronounced changes in the transmission spectra of the hybrid film. It was not established in the previous publications how the actuation of gold nanoparticles within a 10-15 nm interparticle distance could result in the 50-60 nm shift in the absorbance maximum in contrast to the model experiments and theoretical estimations of several nanometer shifts. In this work, the extinction band was deconvoluted into four spectrally separated and overlapping contributions that were attributed to different modes of interactions between the particles and the islands. These modes came into existence due to variations in the thickness of the grafted polymeric layer on the profiled surface of the islands. In situ atomic force microscopy measurements allowed us to explore the behavior of the Au particles as the P2VP brush switched between the swollen and collapsed states. In particular, we identified an interesting, previously unanticipated regime when a particle position in a polymer brush was switched between two distinct states: the particle exposed to the surface of the collapsed layer and the particle engulfed by the swollen brush. On average, the characteristic distance between the particles and the islands increased upon the brush swelling. The observed behavior was a result of the anchoring of the particles to polymeric chains that limited the particles' vertical motion range. The experimental findings will be used to design highly sensitive optical nanosensors based on a polymer-brush-modulated interparticle plasmon coupling.
Microcapsules
loaded with n-docosane as phase change material (mPCMs)
for thermal energy storage with a phase change transition temperature
in the range of 36–45 °C have been employed to impregnate
cotton fabrics. Fabrics impregnated with 8 wt % of mPCMs provided
11 °C of temperature buffering effect during heating. On the
cooling step, impregnated fabrics demonstrated 6 °C temperature
increase for over 100 cycles of switching on/off of the heating source.
Similar thermoregulating performance was observed for impregnated
fabrics stored for 4 years (1500 days) at room temperature. Temperature
buffering effect increased to 14 °C during heating cycle and
temperature increase effect reached 9 °C during cooling cycle
in the aged fabric composites. Both effects remained stable in aged
fabrics for more than 100 heating/cooling cycles. Our study demonstrates
high potential use of the microencapsulated n-docosane for thermal
management applications, including high-technical textiles, footwear
materials, and building thermoregulating covers and paints with high
potential for commercial applications.
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