Electro‐optical behavior of ferroelectric liquid crystalline polyphenylene derivatives

Liquid crystalline (LC) polyphenylene derivatives, such as poly(para‐phenylene) (PPP), poly(meta‐phenylene) (PMP), poly(meta‐biphenylene) (PBP), and poly (meta‐terphenylene) (PTP) derivatives, were synthesized through substitution of fluorine‐containing chiral LC groups into side chains, with an aim to develop ferroelectric LC (FLC) conjugated polymers. All the polymers, except PTP, showed enantiotropic liquid crystallinities, where several types of mesophases were observed in both heating and cooling processes. Among them, PPP and PMP derivatives showed chiral smectic C (S_C*) phases responsible for ferroelectricity. In fact, they exhibited quick response to electric field, in spite of high viscosities inherent to polymers, giving rise to switching times of less than 1 s between two S_C states with reversely directed alignment. Hysteresis loops between the polarization and electric field were also observed for PPP and PMP. The spontaneous polarization (P_S) of PMP remained unchanged even after the electric field became zero, affording the residual polarization (P_R) whose value was the same as that of P_S. This indicates that PMP has a prospective memory function based on FLC nature. The present study is the first report for realizing a quick switching in macroscopic alignment using electric field and also for generating a potential memory function in π‐conjugated polymers. It is elucidated that unusual polymer main chains such as polyphenylenes can be used to prepare new ferroelectric polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3591–3610, 2008     

Theoretical CDNR analysis on radio-to-optic direct conversion SCM coherent radio-over-fibre system

This paper newly proposes a sub-carrier multiplexing (SCM) coherent radio-over-fibre system using radio-to-optic direct conversion (ROC) scheme, which directly converts multi-carrier radio signals into an optical frequency division multiplexing signal without changing frequency intervals and a signal format. Theoretical analysis of the received carrier-to-distortion-plus-noise-power ratio shows that the proposed radio-to-optic conversion system can provide a larger transmission capacity than the conventional SCM AM or IM system.     

Cross section of supercooled238UF6 in multiphoton absorption induced by 16 micrometer Raman-laser radiation

Measurements of multiphoton absorption of 16 µm Raman-laser radiation in supercooled²³⁸UF₆ at 90 K were performed by using a pulsed Laval nozzle with an optical path length of 50 cm. The laser fluence was varied between 50 and 500 mJ/cm² for four frequencies in the range from 625 to 629 cm^–1. The energy absorbed by²³⁸UF₆ molecules was investigated as a function of laser frequency or fluence, and highly accurate results were obtained with the use of the nozzle whose optical path length is much greater than that of nozzles used before. The results indicated that the absorption cross section at the peak absorption frequency (627.8cm^–1) was proportional to the –1/3 power of the fluence.     

Gel strength and swelling of acrylamide‐protic acid superabsorbent copolymers

The viscoelastic and swelling properties of polyacrylamide‐based superabsorbent copolymers were investigated as a function of the ionic comonomer structure. Superabsorbent copolymers were synthesized by free‐radical crosslinking copolymerization of acrylamide and one of the monoprotic acids (acrylic acid and crotonic acid) or the diprotic acids (maleic acid and itaconic acid) as the investigated ionic comonomer. The reaction composition of all components, i.e. monomer, comonomer, initiator, co‐initiator, and crosslinker, was fixed to be the same for the synthesis of all four superabsorbent copolymer systems. Viscoelastic measurements were performed in all systems where the particles were closely packed. The network structures of all systems were evaluated via viscoelastic and swelling measurements. The results indicated that superabsorbent polymers (SAPs) with high water absorbency were accompanied by low gel strength and the calculated high value of molecular weight between crosslinks ($\bar {M}{}_c$ ) and low value of effective crosslinking density (ν_e). Diprotic acid‐containing SAPs showed higher water absorbency over monoprotic acid‐containing and non‐ionic ones. The differences in $\bar {M}{}_c$ and ν_e values of each system were explained with respect to the differences in the monomer reactivity ratio and hydrophilicity of the comonomers. Copyright © 2010 John Wiley & Sons, Ltd.     

Development of a novel antifouling platform for biosensing probe immobilization from methacryloyloxyethyl phosphorylcholine-containing copolymer brushes

The immobilization of thiol-terminated poly[(methacrylic acid)-ran-(2-methacryloyloxyethyl phosphorylcholine)] (PMAMPC-SH) brushes on gold-coated surface plasmon resonance (SPR) chips was performed using the "grafting to" approach via self-assembly formation. The copolymer brushes provide both functionalizability and antifouling characteristics, desirable features mandatorily required for the development of an effective platform for probe immobilization in biosensing applications. The carboxyl groups from the methacrylic acid (MA) units were employed for attaching active biomolecules that can act as sensing probes for biospecific detection of target molecules, whereas the 2-methacryloyloxyethyl phosphorylcholine (MPC) units were introduced to suppress unwanted nonspecific adsorption. The detection efficiency of the biotin-immobilized PMAMPC brushes with the target molecule, avidin (AVD), was evaluated in blood plasma in comparison with the conventional 2D monolayer of 11-mercaptoundecanoic acid (MUA) and homopolymer brushes of poly(methacrylic acid) (PMA) also immobilized with biotin using the SPR technique. Copolymer brushes with 79 mol % MPC composition and a molecular weight of 49.3 kDa yielded the platform for probe immobilization with the best performance considering its high S/N ratio as compared with platforms based on MUA and PMA brushes. In addition, the detection limit for detecting AVD in blood plasma solution was found to be 1.5 nM (equivalent to 100 ng/mL). The results have demonstrated the potential for using these newly developed surface-attached PMAMPC brushes for probe immobilization and subsequent detection of designated target molecules in complex matrices such as blood plasma and clinical samples.     

Temporal Fluctuation and Its Power Law in the Crystalline-To-Glass Transition During Electron Irradiation

Temporal nanostructural fluctuations brought about by transient metastable atom-cluster formation during radiation-induced amorphizing transformation in the intermetallic compound NiTi, observed using a combination of high-resolution high-voltage electron microscopy and molecular dynamics simulation, were characterized in terms of power-law responses of non-equilibrium energy-dissipative systems. Within the framework of the multi-Lorentzian picture, the resultant power law also describes the multirelaxation time (i.e. cluster lifetime) distribution. In addition, a unified relation for the autocorrelation functions for such fluctuation phenomena is discussed.     

Gas Permeation Properties of Carbon Molecular Sieve Membranes Prepared in Alkali Metal-Organic Solvent Systems

Abstract

Intercalation of alkali metals into carbon molecular sieve (CMS) membranes was studied to get new materials for gas separation. The preparation was carried out in ether solutions, containing phenanthrene and alkali metal. The mechanical stability was satisfied for potassium doped CMS, prepared in MeTHF. XRD analysis suggested a random stage structure for the modified membrane due to the low crystallinity of the original host carbon. Characterized by time-lag method some increase in the He and N₂ permeability was observed by intercalation, because the graphite-like hexagonal layers were expanded and/or larger pathways were formed, so that the gas molecules could easily diffuse through. One membrane doped with potassium, followed by partial de-intercalation, exhibited an interesting perm-switch behavior at around 323 K.