Multi-energy dissipation mechanisms in supramolecular hydrogels with fast and slow relaxation modes.

Reversible cross-links by non-covalent bonds have been widely used to produce supramolecular hydrogels that are both tough and functional. While various supramolecular hydrogels with several kinds of reversible cross-links have been designed for many years, a universal design that would allow control of mechanical and functional properties remains unavailable. The physical properties of reversible cross-links are usually quantified by thermodynamics, dynamics, and bond energies.

Phase equilibrium and dielectric relaxation in mixture of 5CB with dilute dimethyl phthalate: effect of coupling between orientation and composition fluctuations on molecular dynamics in isotropic one-phase state.

Phase equilibrium and dielectric relaxation were examined for mixtures of liquid-crystalline (LC)-forming 4-cyano-4'-pentylbiphenyl (5CB) with dilute dimethyl phthalate (DMP). The mixtures were in an isotropic one-phase state at high temperatures T but were separated into nematic and isotropic phases at low T < TIN (isotropic-to-nematic transition temperature), and the isotropic phase disappeared and a nematic one-phase state was realized on a further decrease of T below another transition temperature . These TIN and data (phase diagram) were described considerably well by a simple model of free energy contributed from a Flory-Huggins type mixing entropy (no enthalpic contribution) and a Landau-de Gennes type nematic interaction.

Viscoelastic Relaxation of Polymerized Ionic Liquid and Lithium Salt Mixtures: Effect of Salt Concentration.

Polymerized ionic liquids (PILs) doped with lithium salts have recently attracted research interests as the polymer component in lithium-ion batteries because of their high ionic mobilities and lithium-ion transference numbers. To date, although the ion transport mechanism in lithium-doped PILs has been considerably studied, the role of lithium salts on the dynamics of PIL chains remains poorly understood. Herein, we examine the thermal and rheological behaviors of the mixture of poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide (PC-TFSI)/lithium TFSI (LiTFSI) in order to clarify the effect of the addition of LiTFSI.

Glass Transition Behaviors of Poly (Vinyl Pyridine)/Poly (Vinyl Phenol) Revisited.

We examined the composition and molecular weight dependence of the glass transition temperature in detail for two types of hydrogen bonding miscible blends: poly (2-vinyl pyridine)/poly (vinyl phenol) (2VPy/VPh) and poly (4-vinyl pyridine)/poly (vinyl phenol) (4VPy/VPh). Regarding the functional form of the glass transition temperature, , as a function of the weight fraction, we found a weak deviation from the Kwei equation for 2VPy/VPh blends. In contrast, such a deviation was not observed for the 4VPy/VPh blend.

Relationship between global and segmental dynamics of poly(butylene oxide) studied by broadband dielectric spectroscopy.

Relationship between segmental relaxation and normal-mode relaxation has been studied for molten poly(butylene oxide)s having various molecular weights by broadband dielectric spectroscopy over a wide temperature (T) range. We found that T dependence of the segmental relaxation time, τ, was weaker than the normal mode time, τ, at high T(>250 K ∼ T + 50 K), and the τ/τ ratio systematically decreased with increasing temperature. This high temperature complexity, whose mechanism has not been discussed in detail so far, was quantitatively explained by assuming the two step processes: local conformation change of polymers (elementary process) occurs first, and then the motion of a segment unit (second process) occurs.

Polymerized Ionic Liquids: Correlation of Ionic Conductivity with Nanoscale Morphology and Counterion Volume.

The impact of the chemical structure on ion transport, nanoscale morphology, and dynamics in polymerized imidazolium-based ionic liquids is investigated by broadband dielectric spectroscopy and X-ray scattering, complemented with atomistic molecular dynamics simulations. Anion volume is found to correlate strongly with -independent ionic conductivities spanning more than 3 orders of magnitude. In addition, a systematic increase in alkyl side chain length results in about one decade decrease in -independent ionic conductivity correlating with an increase in the characteristic backbone-to-backbone distances found from scattering and simulations.

Rapid Stretching Vibration at the Polymer Chain End.

Stretching vibrations of aliphatic C-D bonds at the chain end and midchain site of partially deuterated polystyrene (PS) were determined by Fourier transform infrared (FT-IR) spectroscopy. It was first found that the stretching vibration at the chain end is more rapid compared to that at the midchain site in the glassy bulk state. The difference in the frequencies of the stretching vibrations at the chain end and midchain site changed little even when the PS was dissolved in toluene.

Dielectric relaxation of guest molecules in a clathrate structure of syndiotactic polystyrene.

Structure and dynamics of semicrystalline polymer films composed of syndiotactic polystyrene (sPS) and 2-butanone were examined through X-ray diffraction, polarized FTIR, and dielectric relaxation measurements. The X-ray and FTIR measurements revealed its crystal structure to be δ-clathrate containing 2-butanone molecules inside. The carbonyl group of 2-butanone in the crystal was found to orient preferentially parallel to the ac plane of the crystal through the polarized ATR FTIR measurements.

Glass transition temperature and β relaxation temperature around chain end of polystyrene determined by site specific spin labeling.

A glass transition temperature, T(g), and a β relaxation temperature, T(β), of spin-labeled polystyrene (PS) having a number average molecular weight (M(n)) of ca. 25 kDa were determined by the microwave power saturation (MPS) method of electron spin resonance (ESR). Spin labeling was selectively carried out at chain ends or midchain segments.

Synthesis of dibenz[b,f]oxepins via manganese(III)-based oxidative 1,2-radical rearrangement.

The oxidation of monoalkyl 2-(9H-xanthenyl)malonates 1 with Mn(OAc)(3) gave the 9- or 10-dibenz[b,f]oxepincarboxylates 2 in good yields. The reaction proceeds with high regioselectivity except for the case of (1-methoxyxanthenyl)malonate 1 (R(1) = Me, R(2) = 1-MeO), which gave two regioisomers. It was proposed that the process for the formation of 2 must include the 1,2-aryl radical rearrangement followed by oxidative decarboxylation.