Effect of Smectic Layers on Thermal Diffusivity of Side-Chain Polymer Liquid Crystals

Abstract

The thermal conductivity (TC) of polymers is known to be effectively enhanced by liquid crystallinity. Liquid crystals (LCs) exhibit anisotropic TC with a greater magnitude in the orientation direction. However, the effects of other LC structures than the orientational order, such as smectic layer structures, on TC have not been well studied. This study investigated the correlation between LC structures and thermal diffusivity using a series of LC PMnMA polymethacrylates having azobenzene mesogens in the side chains. PMnMA formed nematic (N), smectic A (SmA), and smectic C (SmC) phases. These LCs were aligned by a magnetic field or large-amplitude oscillatory shear, yielding glassy LC films with mesogen long axes in the in-plane or out-of-plane direction. These glassy LCs increased thermal diffusivities in the LC orientation direction with the degree of LC orientation, whereas N and SmC LCs had smaller values than SmA LCs. These results demonstrated that smectic layers can enhance thermal diffusivity in their normal direction.

Thermal Conductivity Enhancement of Liquid Crystal Polymer–Solid Particle Composites by Grafting a Main-Chain-Type Liquid Crystal Polymer onto Particle Surfaces

“…The LC orientation is anchored to the particle surfaces, and the LC between the surfaces will decrease the orientational order as the distance between the particle surfaces increases. LCs decrease the λ // (or α // ) values as the degree of orientational order decreases. ,,, Thus, the PThE5b3- g -MgO/PThE5b3 composites decreased the λ m as the v MgO decreases (Figure b). A similar variation of λ m upon v MgO found for the control MgO/PTh5b3 composites suggests that the allyl-modified MgO surface can induce a similar homeotropic LC alignment on the particle surface.…”

“…Measuring the thermal diffusivity (α) for homeotropic- and planar-aligned LC films along the film thickness direction enabled the anisotropic α values of LCs, α // and α ⊥ , respectively, to be determined. , Equation enabled the α value to be determined using the known film thickness ( t ) and the slope of the plots of Δθ vs the square root of ω (Figure S2). The slope of this type of plot is affected by t ; however, the plots of Δθ/ t vs ω 0.5 increase the slope in the same order as the magnitude of the α value increases . Thus, the plots shown in Figure indicate the anisotropic α values that increase in the order of α ⊥ < α non < α // , where α non was measured for the nonoriented sample film.…”

“…The slope of this type of plot is affected by t; however, the plots of Δθ/t vs ω 0.5 increase the slope in the same order as the magnitude of the α value increases. 11 Thus, the plots shown in Figure 5 indicate the anisotropic α values that increase in the order of α ⊥ < α non < α // , where α non was measured for the nonoriented sample film. These α values allow us to estimate the corresponding λ values, namely, λ // , λ ⊥ , and λ non , according to eq (3).…”

“…Liquid crystal polymers (LCPs) have attracted attention due to their high TCs. − These LCPs possess a long-range orientational order and spontaneously extend polymer chains along the LC director orientation. Such extended chains are included in ultra-high-drawn polyethylene , and nanofibers, which are high-TC polymer materials, thus indicating the possibility of developing high-TC LCPs.…”

Synthesis and Phase Behavior of (Semifluorinated Alkane)‐Based Side‐Chain Liquid Crystalline Copolymers

“…Compared with main-chain liquid crystalline polymers DOI: 10.1002/marc.202200266 (MCLCPs), side-chain liquid crystalline polymers (SCLCPs) have significant advantages in terms of chemical structural designability and aggregational structural complexity, which is of great importance in not only fundamental understanding of molecular assembly [7][8][9] but also nanotechnology applications. [10][11][12] Normally, the self-assembly structures of SCLCPs can be adjusted from molecular level by changing LC mesogen, [13,14] flexible spacer, [15,16] or intermolecular interactions. [17,18] While few studies have focused on the design and effect of SCLCP backbones.…”