Abstract
Fluoropolymers represent a unique class of functional polymers due to their various interesting and important properties such as thermal stability, resistance toward chemicals, repellent behaviors, and their low refractive indices in comparison to other polymeric materials. Based on the latter optical property, fluoropolymers are particularly of interest for the preparation of photonic crystals for optical sensing application. Within the present study, photonic crystals were prepared based on core-interlayer-shell particles focusing on fluoropolymers. For particle assembly, the melt-shear organization technique was applied. The high order and refractive index contrast of the individual components of the colloidal crystal structure lead to remarkable reflection colors according to Bragg’s law of diffraction. Due to the special architecture of the particles, consisting of a soft core, a comparably hard interlayer, and again a soft shell, the resulting opal films were capable of changing their shape and domain sizes upon applied pressure, which was accompanied with a (reversible) change of the observed reflection colors as well. By the incorporation of adjustable amounts of UV cross-linking agents into the opal film and subsequent treatment with different UV irradiation times, stable and pressure-sensitive opal films were obtained. It is shown that the present strategy led to (i) pressure-sensitive opal films featuring reversibly switchable reflection colors and (ii) that opal films can be prepared, for which the written pattern—resulting from the compressed particles—could be fixed upon subsequent irradiation with UV light. The herein described novel fluoropolymer-containing photonic crystals, with their pressure-tunable reflection color, are promising candidates in the field of sensing devices and as potential candidates for anti-counterfeiting materials.
Highlights
In the recent past, the self-assembly of monodisperse colloidal particles attracted enormous attention due to their unique ability to crystallize into well-ordered structures [1,2,3,4]
The following chapter is divided into five sections, starting with the preparation and characterization of the investigated core-interlayer-shell particles, followed by the preparation of the opal film via the melt-shear organization, the investigation of the optical properties, and the investigation of the compression-responsive behavior of the opal films
Poly seed particles were synthesized in a batch process, which was initiated by using a redox initiator, followed by the continuous addition of benzyl acrylate (BzA) and allyl methacrylate (ALMA) in order to prepare the core particles in the second step
Summary
The self-assembly of monodisperse colloidal particles attracted enormous attention due to their unique ability to crystallize into well-ordered structures [1,2,3,4]. The fabrication of monodisperse polystyrene (PS) and poly (methyl methacrylate) (PMMA), as well as silica nanoparticles are reported for particle sizes ranging from 100 nm to 1 μm by using a variety of different polymerization techniques and the Stöber method for silica particles, respectively [8,29,30] The majority of these techniques allows for the relatively convenient production of particles followed by self-assembling methods for the preparation of photonic crystals. Based on the core-interlayer-shell architecture and the presence of well-defined spherical particles, opal films can be produced by the application of the melt-shear organization technique, which involves processing with moderate pressure and temperature. It is expected that the resulting novel opal films are interesting candidates for compression-responsive (reversible) sensing materials and potential candidates for anti-counterfeiting materials, based on their convenient UV-mediated cross-linking chemistry, reversibly switchable reflecting colors, and the fixation of the written patterns
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