Monte Carlo simulation for the modification of polymer via grafting

Monte Carlo method has been applied to investigate the kinetic of grafting reaction in free radical copolymerization. The simulation is quits in agreement with that of theoretical and experimental results. It proves that the Monte Carlo simulation is an effective method for investigating the grafting reaction of free radical copolymerization. (C) 2000 Elsevier Science Ltd. All rights reserved.

Stimulated emission in the film of polymer/dye blend

Optically pumped stimulated emission behavior in an organic film was demonstrated in this study. The gain material consists of a laser dye perylene doped into polystyrene (PS) matrix in an appropriate weight ratio. The sample was transversely pumped by the three harmonic output of a mode-locked Nd:YAG laser. The change of the emission spectra showed a clear threshold action and gain narrowing phenomenon when increasing the excitation intensity. Three emission peaks were observed below the excitation threshold, which are locate at 446, 475 and 506 nm, respectively. However, only the gain narrowing peak centered at 475 nm could be detected above the threshold. The spectra narrowing observed results from the amplified spontaneous emission (ASE) in the gain material. (C) 2000 Elsevier Science S.A. All rights reserved.

Phase behavior of polymer blends

The present report deals with some results on phase behavior, miscibility and phase separation for several polymer blends casting from solutions. These blends are grouped as the amorphous polymer blends, blends containing a crystalline polymer or two crystalline polymers. The blends of PMMA/PVAc were miscible and underwent phase separation at elevated temperature, exhibited LCST behavior. The benzoylated PPO has both UCST and LCST nature. For the systems composed of crystalline polymer poly(ethylene oxide) and amorphous polyurethane, of two crystalline polymers poly(epsilon-caprolactone) and poly[3,3,-bis-(chloromethyl) oxetane], appear a single T-g, indicating these blends are miscible. The interaction parameter B's were determined to be -14 J cm(-3), -15 J cm(-3) respectively. Phase separation of phenolphthalein poly(ether ether sulfone)/PEO blends were discussed in terms of thermal properties, such as their melting and crystallization behavior.

Theoretical studies of nonlinear optical properties of compounds K(4)Ln(2)(CO3)(3)F-4 (Ln=Pr, Nd, Sm, Eu, Gd)

K(4)Ln(2)(CO3)(3)F-4 (Ln=Pr, Nd, Sm, Eu, Gd) is a special type of frequency doubling compound, whose crystal structure exhibits a scarcity of fluorine ions. This leads to two different coordination polyhedrons in the general position of K(2) atoms: [K(2)O6F(1)(2)F(2)] and [K(21)O6F(1)(2)] in a 2/1 ratio. The chemical bonding structures of all constituent atoms of the compound K4Gd2(CO3)(3)F-4 (KGCOF) are comprehensively studied; moreover, the relationship between the chemical bonding structure and the nonlinear optical (NLO) properties is investigated from the chemical bond viewpoint. The theoretical prediction of the NLO tensor coefficient d(11) of KGCOF is in agreement with experimental observation. Theoretical analyses show that the nonlinearity of this crystal type mainly originates from K-O bonds. In addition, the correlation between the NLO tensor d(11) and the refractive index n(0) of KGCOF is discussed. (C) 2000 American Institute of Physics. [S0021-8979(00)07506-X].

Fabrication of layer-by-layer deposited multilayer films containing DNA and its interaction with methyl green

Multilayer films were fabricated by layer-by-layer electrostatic deposition techniques between poly(diallyIdimethylammonium chloride) (PDDA) and calf thymus DNA (CT DNA) on glassy carbon and quartz substrates. Electrochemical impedance spectroscopy (EIS), Fourier transform infrared (FTIR) spectroscopy and UV-vis spectroscopy demonstrated the uniform assembly of PDDA/DNA multilayer films, and X-ray photoelectron spectroscopy confirmed the elemental composition of the films. Moreover, the interaction of DNA in PDDA/DNA films with methyl green was investigated by UV-vis spectroscopy and circular dichroism (CD). (C) 2001 Elsevier Science B.V. All rights reserved.

Monte Carlo simulation of phase behavior of polymer blends with special interactions

Full Paper: The phase, behavior of A-B-random copolymer/C-homopolymer, blends with special interaction was studied by a. Monte, Carlo simulation in two dimensions. The interaction between I segment A and segment C was repulsive, whereas it was attractive between segment B and segment C. The simulation results showed that the blend became two large co-continuous phase domains at lower segment-B component compositions, indicating that the blend showed spinodal decomposition. With an increase of the segment-B component, the miscibility between the copolymer,and the polymer was gradually improved up to being miscible. In addition, it was found that segment B tended to move to the surface of the copolymer phase in the case of a lower component of segment B. On the other hand, if was observed that the average, end-to-end distances ((h) over bar) for both copolymer and polymer changed slowly with increasing segment-B component of the copolymer up to 40%, thereafter they increased considerably with increasing segment B component. Moreover, it was found that the (h) over bar of the copolymer was obviously shorter than that of the homopolymer for the segment-B composition, region from 0% to 80%. Finally, a, phase diagram showing I phase and - II phase regions under the condition of constant-temperature is presented.

Fabrication of nanometer-sized electrodes and tips for scanning electrochemical microscopy

A novel method for fabrication of nanometer-sized electrodes and tips suitable for scanning electrochemical microscopy (SECM) is reported. A fine etched Pt wire is coated with polyimide, which was produced by polymerization on the Pt surface initiated by heat. This method can prepare electrodes with effective radii varying from a few to hundreds of nanometers. Scanning electron microscopy, cyclic voltammetry, and SECM were used to characterize these electrodes. Well-defined steady-state voltammograms could be obtained in aqueous or in 1,2-dichloroethane solutions. Ibis method produced the nanoelectrodes with exposed Pit on the apex, and they can also be employed as the nanotips for SECM investigations. Different sizes of Pt nanotips made by this method were employed to evaluate the kinetics of the redox reaction of Ru(NH3)6(3+) on the surface of a large Pt electrode by SECM, and the standard rate constant kappa (o) of this system was calculated from the best fit of the SECM approach curve. This result is similar to the values obtained by analysis of the obtained voltammetric data.

The effect of electrostatic field on the micro-crystal morphology of polymer films

The micro-crystal morphology of the films of isotactic polypropylene (iPP), poly(3-dodecylthiophene) (P3DDT) and iPP/P3DDT blend grown in different electrostatic environments has been investigated by using scanning electron microscope. The experimental results show that the micro-crystal morphology of polymer films was strongly dependent on electrostatic field. It was found that the micro-crystal morphology of the films of iPP, P3DDT and iPP/P3DDT blend grown in the electrostatic field was in the form of dendrite crystals, in which main stems were aligned in the field direction, and some branches of P3DDT were ruptured. However, the micro-crystals of the films of iPP, P3DDT and iPP/P3DDT blend have no crystal orientation in the absence of electrostatic field. (C) 2001 Elsevier Science Ltd. All rights reserved.

Study of elastic modulus and yield strength of polymer thin films using atomic force microscopy

Nanometer-scale elastic moduli and yield strengths of polycarbonate (PC) and polystyrene (PS) thin films were measured with atomic force microscopy (AFM) indentation measurements. By analysis of the AFM indentation force curves with the method by Oliver and Pharr, Young's moduli of PC and PS thin films could be obtained as 2.2 +/- 0.1 and 2.6 +/- 0.1 GPa, respectively, which agree well with the literature values. By fitting Johnson's conical spherical cavity model to the measured plastic zone sizes, we obtained yield strengths of 141.2 MPa for PC thin films and 178.7 MPa for PS thin films, which are similar to2 times the values expected from the literature. We propose that it is due to the AFM indentation being asymmetric, which was not accounted for in Johnson's model. A correction factor, epsilon, of similar to0.72 was introduced to rescale the plastic zone size, whereupon good agreement between theory and experiment was achieved.

Fabrication of agar-gel microelectrodes and their application in the study of ion transfer across the agar-water 1,2-dichloroethane interface

In this paper, we describe a simple procedure to make agar-gel microelectrodes by filling micropipettes. These microelectrodes were used to study K+ transfer across the agar-water \ 1,2-dichloroethane interface facilitated by dibenzo-18-crown-6 (DB18C6), and the transfer of tetraethylammonium (TEA(+)). The results observed were similar to those obtained at micro-liquid \ liquid interfaces. The effect of various amounts of agar in the aqueous phase was optimized and 3% agar was chosen based on the potential window and solidification time. The different shapes of micro-agar-gel electrodes were prepared in a similar way. The fabricated agar-gel microelectrodes obey the classical micro-disk steady-state current equation, which is different from the behavior of a normal micropipette filled with aqueous solution without silanization. (C) 2001 Elsevier Science B.V. All rights reserved.

A new type of polymer-supported metallocene catalyst for ethylene polymerization

A new polymer-supported metallocene catalyst has been prepared, The polymer-supported metallocene displayed considerably high activity in ethylene polymerization, the highest being 3.62x10(7) gPE/molZr.h, the molecular weight of the polyethylene produced was Mn = 1.29x10(5). about 3-4 times those of corresponding homogeneous zirconocenes. The polymer-supported metallocene keeps the characteristics of homogeneous metallocene catalysts, and offers some features, such as adaptable to gas phase and slurry processes: easy to prepare in low cost: relatively high activity and lower MAO/Zr ratio; lower inorganic residues in the polyolefins as compared to cases of SiO2, Al2O3 or MgCl2; unitary active structure, no complex surface as with SiO2; good control of morphology of the resulting polymer.

Preparation of polymer-supported zirconocene catalysts and olefin polymerization

A novel polymer-supported metallocene catalyst with crosslinked poly(styrene-co-acrylamide) (PSAm) as the support has been prepared and characterized. The probability of long sequences of acrylamide (Am) in PSAm is still low even at an Am amount of 32.8 mol %, implying the relatively homogeneous distribution of Am. The infrared spectra of PSAm and the supported catalyst substantiate that an amide group in PSAm coordinates with methylaluminoxane through both oxygen and nitrogen atoms. Ethylene/alpha-octene copolymerization showed that the catalytic activity is not markedly affected by adding alpha-octene. C-13 NMR analysis of the ethylene/alpha-octene copolymer indicated that the composition distribution of the copolymer is uniform. (C) 1999 John Wiley & Sons, Inc.

Calculation of nonlinear optical coefficients of orthorhombic Re-2(MoO4)(3) crystals

From the chemical bond viewpoint, the second-order nonlinear optical (NLO) tensor coefficients of some Re-2(MoO4)(3) (ReMO)-type tare earth molybdates, with Re = Pr, Nd, Sm, Eu, Gd, Tb and Dy, have been calculated by using the chemical bond theory of complex crystals and the modified bond charge model. All kinds of constituent chemical bonds are considered in the calculation. The major part of the NLO properties of these ReMO crystals is found from the ReO7 groups. The NLO coefficients of these ReMO crystals decrease with Re from Pr to Dy. (C) 1998 Elsevier Science Ltd. All rights reserved.

Effect of polymer chain structure and chain distance on luminescent efficiency

Three kinds of PPV-based copolymers were synthesized and characterized. Their luminescent properties were investigated and discussed by PL spectrum, and time-dependence luminescent spectrum in film and solution stare. The results show that in the range of our study, the PL intensity and lifetime of luminescent decay increase with the increasing length of flexible segments and the solution diluting, indicating the tendency of the increase of luminescent efficiency.

The role of Li-O bonds in calculations of nonlinear optical coefficients of LiXO3-type complex crystals

The second-order nonlinear optical (NLO) tenser coefficients of LiXO3 (X = I; Nb or Ta) type complex crystals have been calculated using the chemical bond theory of complex crystals. Contributions of each type of bond to the total second-order NLO coefficient d(ij) and the linear susceptibility X are quantitatively determined. All tensor values thus calculated are in good agreement with experimental data. The Li-O bonds are found to be an important group in the contributions to the total NLO tenser coefficient, especially for those in LiNbO3 and LiTaO3. The importance of Li-O bonds depends on the environment of Li atom in these crystals.