5. Stimuli-Responsive Nanomaterials

A single particle nanofabrication technique (SPNT) was successfully applied to the fabrication of homogeneous thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) nanowires over a large area, using N,N′-methylene-bis-acrylamide (MBAAm) as a cross-linker. The PNIPAAm nanowires with high aspect ratio over 130 were formed uniformly on the substrate, and the mechanical strength and the length of the nanowires can be easily controlled by adjusting the MBAAm content. The nanowires were transformed from the non-aggregated to aggregated forms over a lower critical solution temperature (LCST) of approximately 32 °C in water. Furthermore, well-defined and uniform nanowires of the photoresponsive polymer, which composed of photochromic azobenzene and π-conjugated fluorene units, were successfully fabricated by the SPNT. Azo units in the nanowires underwent reversible trans-cis-trans isomerization upon exposure to ultraviolet or visible light, leading to changes in the radius (between ca. 6 and 8 nm) and morphology (straight or wavy) of the nanowires. SPNT is expected to provide various stimuli-responsive nanowires, which are otherwise difficult.