Xiangbing Zeng

Poly(vinylidene fluoride) (PVDF) was crystallized under a combination of shear rate (0–31 s–1), pressure (50–600 MPa), and temperature (150–200 °C), producing flexible pressure sensor films with a high piezoelectric stress coefficient g33 of up to 1.2 V·m·N–1. This matches the highest value reported in the literature, but is achieved more quickly, at lower temperatures, and at significantly lower pressures. The key was to overcome the entropically favored gauche-rich centrosymmetric alpha form and obtain almost exclusively the trans-rich piezoelectric β and γ forms. This was achieved by steering the system through the highly supercooled hexagonal mesophase, normally achievable only at high pressures, but here, aided by shear, was transiently reached at only 1 kbar (100 MPa). A further advantage of the highly oriented shish-kebab structure that results from this process is that the favorable molecular dipole orientation is intrinsically higher compared with that in the normal spherulitic structure. A qualitative, thermodynamics-based mechanism is proposed, explaining the synergism of flow and pressure. The films were obviously poled, although no special poling procedure was applied. The “self-poling” was attributed to the temperature gradient in the pressure-shear cell. Global symmetry breaking is assumed to have occurred at the transition from the hexagonal mesophase to the crystalline beta form.

The Grotthuss mechanism is a proton conduction mechanism where proton transports through the hydrogen-bonding network of water molecules. This mechanism enables high ionic conductivity, which is well utilized in nature and some proton-active artificial devices. Since this mechanism requires cleavage and reformation of hydrogen-bonding networks, its activation energy (E_a) is generally in the range of 10–15 kJ mol^–1. Aiming to create a new mechanism beyond the Grotthuss mechanism, we focused on the surface proton hopping conduction (SPHC) mechanism, where a proton hops between neighboring sulfonate groups via bound water molecules. Generally, the SPHC mechanism requires a large E_a. Our idea is that constructing densely aligned sulfonate groups should lead to small E_a (≤10 kJ mol^–1) and high proton transport efficiency. To realize high-density alignment of sulfonate groups with an average distance of ca. 5 Å, we employed the self-assembly of a liquid-crystalline (LC) discotic molecule TPES. TPES self-assembled into a hexagonal columnar LC structure in the presence of an appropriate amount of water. The TPES/H₂O mixtures showed a maximum proton conductivity of 3.5 × 10^–1 S cm^–1 at 30 °C and a small E_a of 6.0 kJ mol^–1 when the water content X = 53 wt %. We confirmed that extremely fast proton conduction and a small E_a were achieved through only bound water. The dynamics of this bound water were quantitatively evaluated by QENS measurement. These results led us to conclude that the high proton conductivity in the columnar LC materials is primarily based on an extremely activated SPHC mechanism.

A liquid crystal (LC) polymethylsiloxane (PMS) with rod‐like aromatic side‐groups attached via an alkylene spacer and bearing three n‐dodecyl end‐tails is found to form an unusual cubic structure. In a normal LC double gyroid (DG), the two chiral subspaces, one each side of the G‐surface, are occupied by one network each. Here each such network is split into two aromatic strands that wind around the central polysiloxane bundle, forming a double helix, resulting in a four‐network gyroid (4NG). While in previous normal LC DGs the network twist was assumed to follow that of the subspace, in 4NG the twist sense of the double‐helix is opposite to that of the subspace., i.e., while a right‐handed subspace twists by +70.5° between junctions, the double‐helix “supertwists” by −109.5°, and the opposite is true for the left‐handed subspace. Detailed analysis by X‐ray diffraction, DSC, and depolarized fluorescence (DF) shows a gradual but significant reversible change in the degree of mixing between the aromatic side groups and the polysiloxane backbones at 120 °C–130 °C in 4NG. Also, a significant increase in the system mobility starts only at ∼40 °C above the melting point, indicating persistence of local double‐helical segments even in the melt.

A liquid crystal (LC) polymethylsiloxane (PMS) with rod‐like aromatic side‐groups attached via an alkylene spacer and bearing three n‐dodecyl end‐tails is found to form an unusual cubic structure. In a normal LC double gyroid (DG), the two chiral subspaces, one each side of the G‐surface, are occupied by one network each. Here each such network is split into two aromatic strands that wind around the central polysiloxane bundle, forming a double helix, resulting in a four‐network gyroid (4NG). While in previous normal LC DGs the network twist was assumed to follow that of the subspace, in 4NG the twist sense of the double‐helix is opposite to that of the subspace., i.e., while a right‐handed subspace twists by +70.5° between junctions, the double‐helix “supertwists” by −109.5°, and the opposite is true for the left‐handed subspace. Detailed analysis by X‐ray diffraction, DSC, and depolarized fluorescence (DF) shows a gradual but significant reversible change in the degree of mixing between the aromatic side groups and the polysiloxane backbones at 120 °C–130 °C in 4NG. Also, a significant increase in the system mobility starts only at ∼40 °C above the melting point, indicating persistence of local double‐helical segments even in the melt.

FePt nanoparticles (NPs) with thermally responsive array structures were prepared by surface modification with a liquid-crystalline phenylethyl ether-type dendron. Dendron modification was carried out in two steps. In the first step, COOH moieties were introduced on the surface of oleyl-modified FePt NPs by ligand exchange using terminal COOH-substituted n-alkyl phosphonic acid. This was followed by the amidation reaction between COOH moieties and the amino-substituted dendron. Infrared spectroscopic measurement and thermogravimetric analysis confirmed that the dendrons were successfully grafted onto the surface of FePt NPs. Transmission electron microscopy also showed an increase in interparticle distance due to dendron modification. Small-angle X-ray scattering (SAXS) revealed that the dendronized NPs pack on an FCC lattice, which melts above 100 °C in thermal response, consistent with the endothermic peak observed in differential scanning calorimetry (DSC). Electron density maps offer detailed insights into the structural organization of the dendronized FePt NP array. These results indicate that the formation of an FCC phase through self-assembly and its thermal transition into a disordered phase enabled dynamic control over magnetic NP arrays. Finally, changes in magnetic properties during thermal phase transition were investigated by a superconducting quantum interference device. The results show certain changes in magnetization behavior introduced by the thermal phase transition. These results demonstrate that dendron modification of FePt NPs enables the introduction of thermal responsiveness in their supramolecular structure and magnetic behavior. The flexible control of magnetic properties is expected to expand the application potential of the magnetic NPs used as building blocks for tunable smart magnetic devices.

A polysiloxane with tris-alkoxy-ended rod-like mesogenic side groups forms an unusually low-symmetry antiferrochiral liquid crystal, space group P1̅, consisting of distorted left- and right-handed double-helices containing alternating splay and twist sections. The unit cell contains two double-helical columns. On faster cooling, a closely related metastable orthorhombic structure is formed, symmetry Fddd, with 8 double helices per cell.

We investigate two unusual phenomena in self‐assembly of anisotropic molecules from isotropic (Iso) melt: a heat‐capacity ( C _p ) maximum and spontaneous formation of the recently discovered chiral liquid (Iso*). Based on experiments on new nonchiral monomers, dimers, and polymers, we construct a statistical theory that shows why many complex meso‐structures form in two stages: continuous equilibrium growth of nano‐clusters in melt through strong interactions, causing the C _p ‐maximum, followed by establishment of positional long‐range order (LRO) through a weak first‐order transition. We also show why many achiral compounds additionally form an intermediate chiral Iso* liquid through what we find is a second‐order transition. We propose that the first process is equivalent to “supramolecular polymerization” in solutions, where the lack of intercluster interaction rules out LRO. Furthermore, we argue that separation into a broad and a sharp transition is universal in condensed matter where strong interactions by themselves cannot lead to LRO, either because the clusters are 1D or due to strong frustration. Clusters must first grow to critical size when, at T _c , the combined weak interactions reach ∼k _B T _c , prompting LRO formation. A situation similar to that in soft self‐assembly is seen in spin ordering in magnetic crystals, but only near 0 K.