Three Gel States of Colloidal Composites Consisting of Polymer-Brush-Afforded Silica Particles and a Nematic Liquid Crystal with Distinct Viscoelastic and Optical Properties

Abstract

Colloidal composites consisting of polymer-brush-afforded silica particles (P-SiPs) and a nematic liquid crystal (LC) exhibited three gel states with distinct viscoelastic and/or optical properties depending on temperature: (1) opaque hard gel, (2) translucent hard gel, and (3) translucent soft gel. We demonstrated that the transitions of the optical property and the hardness of the gels were due to the phase transition of the LC matrix and the glass transition of the grafted polymers of P-SiPs, respectively. We then revealed that the gelation (the formation of the translucent soft gel) was caused by the phase separation of P-SiPs and LC matrix in an isotropic phase based on spinodal decomposition. In addition, the particle concentration and molecular weight of the grafted polymer of P-SiPs were observed to significantly affect the elastic moduli and thermal stability of the composite gels. By the addition of an azobenzene derivative into an LC matrix, we achieved photochemical switching of the transparency of the composites based on the photoinduced phase transition of LCs, while keeping self-supporting ability of the composite gel.

Unusual photoresponses in the upper critical solution temperature of polymer solutions mediated by changes in intermolecular interactions in an azo-doped liquid crystalline solvent

“…Using this photochemical behavior, we have previously achieved dynamic control of the viscoelastic and optical properties of liquid-crystalline composite gels. [25][26][27] In this study, we report unusual photoresponses in the UCST of polymer solutions employing an azobenzene-doped liquid crystalline mixture as solvent. We employed 4-heptyl-4 0 -cyanobiphenyl (7CB) containing 5 mol% of an azobenzene derivative (azo-doped 7CB) as the solvent.…”

“…This azo content was confirmed to be enough to induce a definite photoresponse in liquidcrystalline mixtures. 24,26,27 Solutions of poly(methyl methacrylate) (PMMA) and polystyrene (PS) using 7CB were previously reported to exhibit UCST-type phase behavior. 28 We investigated the photoinduced changes of UCST in the PMMA and PS solutions using the azo-doped 7CB in detail.…”

Highly elastic and self-healing nanostructured gelatin/clay colloidal gels with osteogenic capacity for minimally invasive and customized bone regeneration

“…For composites containing high content of nanoclay (High-C/G group), the gels showed the highest elastic modulus G ′ , but also rather higher FDI values than that of Low-C/G and Gelatin gels particularly at high solid contents. This suggested that the excessive amount of nanoclay phase in the composites can increase the viscoelastic feature of the colloidal gels [47,48].…”

Anisotropy Enhanced Phase Separation in Polymer Dispersed Liquid Crystals

“…Polymer dispersed liquid crystals (PDLCs) form a special class of composite materials made of a polymer matrix containing pores filled with a low molecular weight liquid crystal (LC), and as such, they are said to have a Swiss cheese morphology [1,2]. PDLCs have drawn a particular attention in the literature from both fundamental and applied points of view, for their importance in a realm of modern technologies, and interesting properties encompassing morphology, structure, thermodynamic, thermo mechanical and viscoelastic aspects [3][4][5][6][7][8][9][10]. They offer major advantages over materials with similar functionalities because of their high availability, and competitive costs.…”