Fluorescent bracelet-like Cu@cross-linked poly(vinyl alcohol) (PVA) microrings by a hydrothermal process

Abstract

Novel bracelet-like Cu@cross-linked poly(vinyl alcohol) (PVA) microrings have been prepared through a PVA-assisted hydrothermal process. Bracelet-like microrings are composed of inner copper nanorings and outer cross-linked PVA beads. The formation of bracelet-like microrings consists of two steps, i.e. the growth and self-coiling of PVA-wrapped copper nanowires and corresponding adhering of cross-linked PVA to form bracelet-like structures. Copper nanowires are formed by reduction from a mixed copper source consisting of CuCl₂ and CuBr in the presence of NaBr by PVA. When an appropriate amount of NaBr was added, a product with a high yield of microrings can be obtained. A further investigation on ultra-thin section TEM images indicates that addition of the appropriate amount of NaBr leads to thinner copper nanowires within the crosss-linked PVA coatings. We proposed that thinner copper nanowires have less elastic resistance during bending processes, so PVA wrapped copper nanowires are more easily bent arbitrarily during vigorous Brownian motion at 210 °C. When two ends of one single nanowire join, the formation of van der Waals bonds and diminishing of the interfacial area through overlapping compensate the elastic resistance to get stable ring-like structures.