This paper presents a simultaneous microscopic structure characteristic of shape-memory (SM) poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) inverse opals together with a bulk PVDF-HFP by scanning electron microscopy (SEM). The materials show a thermo-sensitive micro-SM property, accompanied with a reversible and modulated optical property. The introduction of the inverse opal structure into the shape-memory polymer material renders a recognition ability of the microstructure change aroused from complex environmental signals by an optical signal, which can be simultaneously detected by SEM. Furthermore, this feature was applied as a reversible write/erase of fingerprint pattern through the press-stimulus and solvent-induced effect, together with the changes of morphology/optical signal. This micro-SM property can be attributed to the shrink/swell effect of the polymer chain from external stimuli combined with the microscopic structure of inverse opals. It will trigger a promising way toward designing reversible micro-deformed actuators.
Photothermal effect of azopyridine compounds was systematically studied. They showed higher efficiency than their azobenzene analogs, leading to possible applications as light controllable intelligent stickup and photomechanical materials.
A particle-in-hemispherical honeycomb nanoarray (PIHHN) SERS substrate with ultrahigh sensitivity and polydirectional signal stability was introduced by a multi-step bottom-up method.
We have demonstrated a facile and low-cost approach for the fabrication of binary "island" shaped arrays (BISA) with high-density hot spots as reproducible surface-enhanced Raman scattering (SERS) substrates by depositing a self-assembled monolayer Au nanoparticle (AuNP) film with small gaps onto a two-dimensional (2D) silica microsphere opal structure. By varying the size of silica spheres, the SERS performance of the BISA substrate with an enhancement factor (EF) of 3.74 × 10 magnitude and the corresponding signal intensity deviation of below 8% using 770 nm silica sphere arrays were achieved. Compared with the assembled monolayer AuNP film on a planar substrate, the BISA enabled the installation of more AuNPs as a source of hot spots due to the undulation of morphology on the nanoscale within the designated laser-illumination area. In addition, a finite-difference time-domain (FDTD) simulation suggested that the BISA structure provided geometric conditions for increasing the intensity of the formed hot spots, and the strong periodic electric fields on the BISA are located not only in the gap between adjacent AuNPs, but also along the boundary of the neighboring island of silica spheres. Surface plasmon-decayed hot carriers (hot electrons and hot holes) from AuNPs can be applied in the field of energy conversion (i.e., photocatalysis), integrated with the SERS as a sensitive optical indicator to accurately monitor the catalytic reaction process. Furthermore, we examined the catalytic reaction process of the dimerization of 4-ATP into DMAB and found that photocatalytic activity could be tuned by changing the size of silica spheres. This study provides a new design route for the fabrication of the SERS platform with high sensitivity and reproducibility to detect molecules or improve catalyst efficiency.
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