An Experimental and Theoretical Determination of Oscillatory Shear-Induced Crystallization Processes in Viscoelastic Photonic Crystal Media

Dial-In Synthesis of 'Polymer Opal' Core-Interlayer-Shell Composite Nanoparticles

The emulsion polymerization process via which core-interlayer-shell polymer nanoparticles are synthesized is engineered to offer a crucial control of the eventual size and monodispersity of the polystyrene (PS) cores. We examine the role of key experimental parameters, optimizing the temperature, reactant purity, and agitation (stirring) rate. The subsequent addition of a poly(methyl-methacrylate) (PMMA) grafting layer and a poly(ethyl-acrylate) (PEA) shell layer produces composite particles, which are shear-orderable into opaline films, known as 'polymer opals'. We thus demonstrate pathways toward a 'dial-in' process, where the time taken to obtain the target core size is mapped to the expected resultant structural color. At reaction temperatures of 60 and 70 °C, viable conditions are found where all syntheses give an excellent level of monodispersity (polydispersity index < 0.02), suitable for interlayer and shell growth. These reports may be readily applied to a wider industrial scale fabrication pipeline for these polymeric photonic materials.

Transparent Polymer Opal Thin Films with Intense UV Structural Color

We report on shear-ordered polymer photonic crystals demonstrating intense structural color with a photonic bandgap at 270 nm. Our work examines this UV structural color, originating from a low refractive index contrast polymer composite system as a function of the viewing angle. We report extensive characterization of the angle-dependent nature of this color in the form of 'scattering cones', which showed strong reflectivity in the 275-315 nm range. The viewing range of the scattering was fully quantified for a number of planes and angles, and we additionally discuss the unique spectral anisotropy observed in these structures. Such films could serve as low-cost UV reflection coatings with applications in photovoltaics due to the fact of their non-photobleaching and robust mechanical behavior in addition to their favorable optical properties.

Spectroscopic Ellipsometry and Optical Modelling of Structurally Colored Opaline Thin-Films

The method of spectroscopic ellipsometry is applied to complex periodic nanomaterials, consisting of shear-ordered polymeric nanosphere composites, with intense resonant structural color. A corresponding multilayer optical quasi-model of the system, parametrizing the inherent degree of sample disorder and encompassing key properties of effective refractive-index and index-contrast, is developed to elucidate the correlation between the ∆ and Ψ ellipsometric parameters and the shear-induced opaline crystallinity. These approaches offer reliable means of in-line tracking of the sample quality of such “polymer opals” in large scale processing and applications.