Shear ordering in polymer photonic crystals

Abstract

Optical scattering spectra are recorded in situ on flowing colloidal polymeric nanocomposites which are sheared into photonic crystals at 150 degrees C using a high-pressure quartz-cell multipass rheometer. Broadband spectroscopy of the resonant Bragg scattering peak allows the direct observation of crystal formation and melting of monodisperse core-shell particles. A range of flow conditions of this solventless, highly viscous melt reveals four distinct regimes of crystal growth and decay which match a simple rheological model. Extraction of crystal thickness, order and lattice spacing are validated by one-dimensional electromagnetic simulations.

Interplay of index contrast with periodicity in polymer photonic crystals

“…As discussed previously, such a model results in Lorentzian spectral profiles. 5 The linear dependence of the predicted peak intensities on Dn is shown in Figure 2(c), with excellent agreement to the experimentally observed trend. The predicted quadratic dependency from Fresnel theory is modified by disorder in such opals, to produce a linear dependence on jDnj.…”

“…Such polymeric opals have intrinsic advantages over other self-assembling colloidal systems, 3,4 in which the structures formed are solvent-free and permanently formed into a visco-elastic solid. 5 The refractive index contrast between the core beads and the matrix polymer is essential for the appearance of such structural color, through spectrally resonant multiple Bragg scattering. 6 However, it is not clear how the strength of such resonances changes as the index contrast increases.…”

Inducing Symmetry Breaking in Nanostructures: Anisotropic Stretch-Tuning Photonic Crystals

“…Compression, extrusion, and rolling can yield films of high order, and these techniques have been optimized to produce the current films. The mechanism of such highly ordered shear-induced assembly is still under study [15], but the consistent anisotropies observed here match theory for a perfect fcc film and support the full 3D order suggested by spectroscopy and microscopy [16]. Such films, which have now been produced on the 100-m length scale, result in intense structural color coming from the Bragg scattering peak [Figs.…”

Utilizing Stretch‐Tunable Thermochromic Elastomeric Opal Films as Novel Reversible Switchable Photonic Materials

“…However, large‐scaled opaline structures are normally prepared by drying or spin coating of particle dispersions, but they can also be prepared by using the melt‐shear organization. This process involves the compression of hard core–soft shell particles between the plates of a press and it permits the preparation of large‐area freestanding opal films …”