Dichroic nanocomposites based on polymers and metallic particles: from biology to materials science

Abstract

Dichroic nanocomposites change their colors when they are viewed through a turning polarizer. In the case of polymer matrices containing inorganic nanoparticles, this color effect originates in anisotropic structures of inorganic moieties, such as uniaxially oriented linear assemblies of spherical nanoparticles or parallel oriented nanorods. The orientation of the particles or particle assemblies, respectively, is induced by the polymer matrix, either through oriented elongated hollow spaces or drawing. Matrices based on biopolymers (e.g. cellulose, polypeptides, chitin) as well as synthetic polymers (e.g. polyethylene, poly(vinyl alcohol)) have been employed. The dichroic colors have been generated so far mainly by silver or gold particles (including nanorods), but also other metals and occasionally also semiconductors (metalloids). Notably, dichroism is also disclosed in optical absorption spectra recorded with polarized light. Dichroism in biopolymer‐based objects with incorporated nanoparticles has been exploited for the cognition of biological fine structures, while dichroic films with technical polymers as matrices have been considered as optical switches in bicolored liquid crystal displays and authenticity cachets for documents, banknotes and packaging films. In this context, micropatterning of dichroic nanocomposites, which has been achieved by local heating procedures of materials composed of metal nanorods, is also of interest. © 2017 Society of Chemical Industry

Synthesis and Analysis of Polymorphic Silver Nanoparticles and Their Incorporation into the Polymer Matrix

“…We hypothesized that this phenomenon is caused by a unique combination of sizes and shapes of nanoparticles. Similar optical properties of colloidal AgNPs solutions have been observed and studied by other authors [5,6,30]; based on their conclusions, the formation of the dichroic solution is due to the polydispersity of the nanoparticles (large and non-symmetrical particles).…”

“…There are several works dealing with the explanation of the dichroic effect. In his work, Caseri analyzed several works from which, it is clear, that there are discrepancies in the explanation of the dichroic effect, and there are several hypotheses about what this effect (in the case of colloidal solutions) causes [30]. Most authors agree that anisotropic metal particles are responsible for the dichroic effect.…”

Plasmon-Coupled Gold Nanoparticles in Stretched Shape-Memory Polymers for Mechanical/Thermal Sensing

“…Polymer nanocomposite thin films containing functional nanoparticles (NPs) are a rich and complex system, where the organization of the NPs can determine their properties based on their orientation or coupling. − When plasmonic NPs, such as Au NPs, are dispersed within or assembled on the surfaces of polymer films, their organization determines the interparticle distances and extent of coupling of their surface plasmon resonances (SPRs). − Therefore, nanocomposites based on elastomers and shape-memory polymers (SMPs) are of special interest, where there is a capability to alter the spacing between NPs and thereby control the optical properties of the thin film. Plasmonic elastomer and SMP nanocomposites have a wide range of potential applications, including sensors, optoelectronics, and optical filters. − …”

Experimental and Theoretical Studies on Sustainable Synthesis of Gold Sol Displaying Dichroic Effect

“…This transmitted color changes to other colors when the particle morphology changes—for example, wine red for spherical, (5–20 nm) [ 16 , 17 ], blue for nanoflowers (50–100 nm) [ 18 ], reddish-brown [ 19 ], green [ 20 ] and orange for gold nanorods of different aspect ratios or gold nanoflowers [ 20 , 21 ] and finally to black when particles are in the form of nanowire networks or twisted gold nanorods [ 22 , 23 ]. All of these morphologies have attracted great scientific attention due to their wide range of applications in various engineering and technological fields such as laser applications [ 24 ], solar cells [ 25 ], photothermal therapy [ 26 ], drug delivery [ 27 ], X-ray computed tomography [ 28 ], sensors [ 29 , 30 ], dichroic polarizer [ 31 , 32 ], display (LCD) devices [ 31 , 33 ] and paint technology [ 34 , 35 ]. In general, establishing control over the sizes and shapes of the nanoparticles has prompted nanocrystal research to explore new methods to finely control the architecture of the nanocrystals for various scientific and technological applications [ 36 ].…”