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

Abstract

A study is presented of the oscillatory shear-ordering dynamics of viscoelastic photonic crystal media, using an optical shear cell. The hard-sphere/“sticky”-shell design of these polymeric composite particles produces athermal, quasi-solid rubbery media, with a characteristic viscoelastic ensemble response to applied shear. Monotonic crystallization processes, as directly measured by the photonic stopband transmission, are tracked as a function of strain amplitude, oscillation frequency, and temperature. A complementary generic spatio-temporal model is developed of crystallization due to shear-dependent interlayer viscosity, giving propagating crystalline fronts with increasing applied strain, and a gradual transition from interparticle disorder to order. The introduction of a competing shear-induced flow degradation process, dependent on the global shear rate, gives solutions with both amplitude and frequency dependence. The extracted crystallization timescales show parametric trends which are in good qualitative agreement with experimental observations.

Complex 3D‐Printed Mechanochromic Materials with Iridescent Structural Colors Based on Core–Shell Particles

“…We therefore conclude that the thermomechanical properties of the CSP are mainly influenced and controllable by composition and amount of the elastomeric shell material, confirming experimentally the findings of Finlayson and Baumberg. [ 38 ]…”

“…Without external shear forces, mobility of the rigid spheres is highly inhibited by the gum‐like matrix and Brownian motion is suppressed. [ 8a,38,40 ] Given these prerequisites, we assume that the following mechanisms contribute to the observed shear‐thinning: Shear‐induced disentanglements of polymer strands of the grafted shell polymer decrease the flow resistance of individual particles. The generation of non‐equilibrium structures, such as strings, may also decrease flow resistance under shear force.…”

Transparent Polymer Opal Thin Films with Intense UV Structural Color

“…This initially created ordering beginning at the surfaces of the sample, which subsequently permeated inwards with further shear, and a basic representation of this process is shown in Figure 1b. The physical mechanisms of the BIOS process shear ordering are theoretically elucidated in detail elsewhere [24,31].…”

“…Fabrication of the thin films is discussed further in Section 3. Polymer opals displaying visible structural color have been characterized extensively [29][30][31][32][33], with the tunability of the structural color with sphere geometry and size being particularly well documented. However, we believe our work to be among the first reports of these systems being engineered toward the ultraviolet band of the electromagnetic spectrum, thus forming the primary focus of this paper.…”

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

“…After processing, the opals have a characteristically brilliant blue-green iridescence (Figure 1c), and can then be readily peeled away from the PET tapes to produce free-standing films as required. Experimental and micrographic determinations of the physical mechanisms of BIOS shear-ordering, and the resultant structural ordering metrics, have been extensively reported on [17,28,29] and theoretically elucidated elsewhere [30], and these issues are thus not a focus of the present paper.…”