Liquid‐Crystalline Elastomers with Gold Nanoparticle Cross‐Linkers

Abstract

Embedding nanoparticles in a responsive polymer matrix is a formidable way to fabricate hybrid materials with predesigned properties and prospective applications in actuators, mechanically tunable optical elements, and electroclinic films. However, achieving chemical compatibility between nanoparticles and organic matter is not trivial and often results in disordered structures. Herein, it is shown that using nanoparticles as exclusive cross-linkers in the preparation of liquid-crystalline polymers can yield long-range-ordered liquid-crystalline elastomers with high loadings of well-dispersed nanoparticles, as confirmed by small-angle XRD measurements. Moreover, the strategy of incorporating NPs as cross-linking units does not result in disruption of mechanical properties of the polymer, and this phenomenon was explained by the means of all-atom molecular dynamics simulations. Such materials can exhibit switchable behavior under thermal stimulus with stability spanning over multiple heating/cooling cycles. The presented strategy has proven to be a promising approach for the preparation of new types of hybrid liquid-crystalline elastomers that can be of value for future photonic applications.

Nanostructured Composites Based on Liquid-Crystalline Elastomers

“…The X-ray patterns can give information not only about the average order, but also about the homogeneity of distributions, and about the nature of the mesophases. Both Figure 12a,b evidence the occurrence of lamellar (smectic) structures for two gold-nanoparticle LCE composites, namely LCE-GNP1 and LCE-GNP2 [68], with layer spacings in the range of 39–44 Å (Figure 12c), thus indicating the presence of a partially interdigitated structure. The diffuse XRD signal observed at high angles, corresponding to 4.5 Å, reflects the liquid-like order of mesogens within the smectic layers.…”

“…In addition to the large use of carbon-based nanostructured materials as fillers and dopants of LCE systems, several researches report LCE-based composites prepared using a wide variety of nanomaterials, such as ferroelectric ceramic nanoparticles [59,60], conductive molybdenum-oxide nanowires [61], magnetic iron-oxide nanoparticles [62,63,64,65], and gold nanomaterials [66,67,68]. In the following sections, the synthesis, properties, and applications of these composites are reviewed.…”

“…A new synthetic strategy was recently proposed by Wjjcik et al [68] to prepare LCE-based composites including gold nanoparticles (GNPs) in the LCE matrix. The approach, shown in Figure 8, consists of the synthesis of gold nanoparticles functionalized with an olefin mesogenic ligand (L2) to obtain metal nanoparticles acting as cross-linking agents (GNP@L2) for the polymer backbones (PMHS).…”

“…Following a synthetic procedure similar to the “two-step” cross-linking reaction, the final LCE-based composites contain metal nanoparticles covalently attached to the polymer chain (LCE-GNP), without any problems of uncontrolled aggregation, ensuring a homogeneous distribution of nanoparticles within the polymer matrix [68].…”

“…The addition of gold nanoparticles to LCEs was investigated by several groups [66,67,68,80], with the aim of producing photo-thermal effects related to the localized surface plasmon resonance of gold nanoparticles. Several works [66,67,80] proposed the doping of LCE micro-particles or LCE micro-pillars with gold nanoparticles to induce shape deformations, rotations, and/or translations using optical manipulation.…”