共查询到20条相似文献,搜索用时 0 毫秒
1.
《Molecular physics》2012,110(11-12):1359-1373
Hyperbranched polymers have attracted increased interest because of their tunable properties, which are affected by their architecture and a wide range of different functional groups. Many applications of hyperbranched polymers have been proposed based on their liquid–liquid phase behaviour. In recent years, the Lattice Cluster Theory (LCT) has been used to consider the impact of the architecture on the phase behaviour of hyperbranched polymers. In the theoretical framework of the LCT, the chain architecture is included in the Helmholtz energy, so all derived properties are influenced by polymer architecture. Until now, the application of the LCT in the field of hyperbranched polymers has been limited to ternary systems composed of one polymer with an arbitrary chain structure, one trimer and one solvent. This paper aims to extend the LCT to a ternary system that includes two polymers with an arbitrary chain structure and one solvent occupying one lattice site. In contrast to previous studies, the ternary system consists of Boltorn H20?+?butan-1-ol?+?water, where all of the binary subsystems show demixing behaviour. Whereas experimental data are reported in the literature for the binary subsystems Boltorn H20?+?water and butan-1-ol?+?water, no experimental information is available for the binary subsystem Boltorn H20?+?butan-1-ol. Therefore, the phase behaviour of this subsystem was measured using the visual method. The paper discusses the possibility of predicting the ternary phase behaviour with the LCT in combination with the modified Wertheim theory based on knowledge of the phase behaviour of the corresponding binary subsystems. To verify the theoretical results, the ternary phase equilibria at constant temperature were also measured. In addition, the dependence of the thermodynamic properties on the special production lot of the commercially available Boltorn H20 is discussed. 相似文献
2.
If two good solvents become poor for a polymer when mixed, the solvent pair is called a cononsolvent pair. The sharp reentrant coil-to-globule-to-coil transition of a poly(N-isopropylacrylamide) chain observed in the mixed solvent of water and methanol is shown to be caused by the competitive hydrogen bonding by water and methanol molecules onto the polymer chain. On the basis of a new statistical-mechanical model for competitive hydrogen bonds, the mean square end-to-end distance is theoretically calculated and compared with experiment. The chain sharply collapses at the molar fraction xm approximately 0.2 of methanol, stays collapsed up to xm approximately 0.4, and finally recovers the swollen state at xm approximately 0.6. Such a reentrant coil-globule transition takes place because the total number of hydrogen bonds along the chain exhibits a similar square-well-type depression as a result of the competition. 相似文献
3.
Holzer W. Penzkofer A. Gong S.-H. Davey A. P. Blau W. J. 《Optical and Quantum Electronics》1997,29(7):713-724
The lasing performance of the polymers poly(2,5-dioctadecyloxy-paraphenylene-ethynylene-co-2,5-thienyl) (OPT) and poly(2,5-dioctadecyloxy-paraphenylene-ethynylene-co-2,5-pyridinyl)
(OPP) in organic solvents was studied. A two-mirror resonator was transversally pumped using single pulses of the second harmonic
of a mode-locked ruby laser. OPT in tetrahydrofuran lased in the region from 480 nm to 525nm and OPP in tetrahydrofuran showed
laser action in the region from 460 nm to 490nm. The polymer solutions are characterized by absorption and fluorescence spectroscopic
analysis. Effective stimulated emission cross-sections are reported. High excited-state absorption cross-sections and residual
ground-state absorption reduce the lasing efficiency.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
4.
Wetting phenomena in porous silicon layers are experimentally investigated by Raman scattering. The experimental results show a reversible blue-shift of Raman spectra of wetted porous silicon layers with respect to the unperturbed layers. We ascribe the shift to a compressive stress due to the increased lattice mismatch between the porous silicon layer and the bulk silicon substrate in wetting conditions. 相似文献
5.
Andre Cardoso Barato 《Journal of statistical physics》2010,138(4-5):728-766
When a nonequilibrium growing interface in the presence of a wall is considered a nonequilibrium wetting transition may take place. This transition can be studied through Langevin equations or discrete growth models. In the first case, the Kardar-Parisi-Zhang equation, which defines a very robust universality class for nonequilibrium moving interfaces, with a soft-wall potential is considered. While in the second, microscopic models, in the corresponding universality class, with evaporation and deposition of particles in the presence of hard-wall are studied. Equilibrium wetting is related to a particular case of the problem, it corresponds to the Edwards-Wilkinson equation with a potential in the continuum approach or to the fulfillment of detailed balance in the microscopic models. In this review we present the analytical and numerical methods used to investigate the problem and the very rich behavior that is observed with them. 相似文献
6.
P. Terech 《Il Nuovo Cimento D》1994,16(7):757-764
Summary Viscoelastic solutions of a binuclear copper(II) tetracarboxylate (Cu2S8) in tert-butylcyclohexane (TBC) have been investigated by rheology and small-angle neutron scattering techniques. The data
are analysed in the theoretical framework of the so-called ?living polymers?. The Cu2S8 aggregates are semi-rigid thin heterogeneous molecular threads undergoing scission/recombination reactions. Structural and
dynamical correlations have been made with the thermotropic columnar phase and some lyotropic swollen mesophases of the system.
The simplicity of the composition and structural constitution enables to avoid the usual salt and composition problems of
the aqueous analogues and also to deduce some most probable behaviours related to the scission mechanisms, chain flexibility
and dynamics of stress relaxation.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.
Member of CNRS. 相似文献
7.
Ultra-high-molecular-weight-polyethylene (UHMWPE) surfaces are characterized in terms of roughness and wetting. Changes in the surface morphology of the polymer were induced macroscopically by mechanical friction and microscopically by ion implantation. The ion irradiation was obtained by using 300?keV Xe+ beams with doses ranging between 1014 and 1015?ions/cm2. Roughness and wetting measurements were performed in order to investigate the UHMWPE surface properties before and after the surface treatments. The wetting angle of the polymeric surface increases with the decrease of the roughness and with the increase of the absorbed dose. Results are discussed from the point of view of the biological reactions that could degrade the UHMWPE biocompatible surfaces employed in different mobile prostheses. 相似文献
8.
9.
《Comptes Rendus Physique》2013,14(7):531-541
This is a review of the wetting properties of solid helium on various solid substrates. Due to its extreme purity and to its very fast growth dynamics, solid helium 4 is often considered as a model system in materials science. Several wetting phenomena have been studied with helium 4 crystals, namely contact angles on solid substrates with variable roughness, wetting on graphite where epitaxial growth takes place, the roughening transition as a function of film thickness, the wetting of grain boundaries by the liquid phase. 相似文献
10.
The role of the solvent in the passive Q-switching of lasers by solutions of organic dyes has been examined in detail. It was found that several pure organic solvents could themselves partially Q-switch the laser, in the absence of the dye. This behaviour was observed for both ruby and neodymium: glass lasers. Pulse-widths as short as 20 nsec were occasionally recorded. Peak powers up to 2 MW have been observed using 1-chloronaphthalene to switch a ruby laser. It is proposed that Q-switching arises from an enhancement of reflectivity of the liquid, during the evolution of the laser pulse, through the formation of a periodic refractive index modulation in the liquid by the action of standing waves.Research Fellow, attached from Royal Holloway College. 相似文献
11.
A. T. DiBenedetto 《Journal of Macromolecular Science: Physics》2013,52(4):657-678
The fracture energy of a polymer depends strongly on the viscoelastic responses of the material, and therefore is a function of temperature and crack velocity. The toughness of a composite is determined by the way in which the reinforcing filler modifies the energy dissipating mechanisms of the polymeric matrix. The fracture toughness of a variety of polymeric glasses and their composites with glass beads, glass fibers, and rubber particles was measured. The velocity of rapidly moving cracks and the crack propagation rates under controlled loading conditions were also measured. It was found that the crack propagation velocities in unfilled and glass bead filled materials were controlled by the longitudinal stress waves in the matrix and that the only effects of the glass beads were to blunt the crack tip and limit the viscous deformation. The effect on fracture toughness was relatively small and either positive or negative, depending on which of the above two factors dominated. The presence of rubber particles as a second phase lowered terminal crack propagation velocities and greatly increased the fracture toughness, indicating a crack retarding effect of the rubber particles. This is related to the induction of crazes in the matrix by the rubber phase. Glass fibers had a tendency to bridge the tip of a propagating crack, thereby greatly increasing the fracture toughness. In this case the work of fracture comes from a combination of the elastic strain energy stored in the fibers, the energy dissipated in debonding the fibers from the matrix, and the fracture energy of the matrix itself. 相似文献
12.
13.
14.
We present in this Letter a free-energy approach to the dynamics of a fluid near a nanostructured surface. The model accounts both for the static phase equilibrium in the vicinity of the surface (wetting angles, Cassie-Wenzel transition) and the dynamical properties like liquid slippage at the boundary. This method bridges the gap between phenomenological phase-field approaches and more macroscopic lattice-Boltzmann models. 相似文献
15.
16.
The phase transition properties of blends of polyethylene glycol (PEG) with cellulose (CELL) prepared from solution in N,N-dimethylacetamide/lithium chloride (DMAC/LiCI) and those from solution in dimethylsulfoxide/paraform- aldehyde (DMSO/PF) were found to be completely different. The differences of the phase transition properties were probably related to the different miscibilities of these two polymers in the two solvent systems. In DMAC/LiCl, the miscibility of CELL and PEG was limited; the composite obtained exhibited a solid- liquid phase transition and had a small phase transition enthalpy. However, in DMSO/PF, these two polymers had a high level of miscibility; the composite obtained exhibited a solid-solid phase transition and had a large phase enthalpy. It is suggested that the differences of miscibility and the phase transition properties were caused by the different dissolving mechanisms of CELL and the different interactions in these two solutions. 相似文献
17.
18.
19.
20.
M. Büyükyıldız M. A. Taşdelen Y. Karabul M. Çağlar O. İçelli E. Boydaş 《辐射效应与固体损伤》2018,173(5-6):474-488
In the present study, commercially important high-performance polymers and their composites have been investigated with respect to photon interactions as means of mass attenuation coefficient (μ/ρ), mean free path (MFP), half-value layer (HVL), effective atomic number (Zeff), effective electron density (Neff), and energy absorption and exposure buildup factors (EABF and EBF) at different photon energies. For this purpose, sample plates were prepared by extrusion and injection techniques using polyethersulfone, polyetherimide, acrylonitrile butadiene styrene copolymer, polyamide 66, polyphthalamide, and polypropylene copolymers as high-performance polymers and glass and carbon fibers as reinforcement. The (μ/ρ)s of the materials were measured at 81 and 356?keV photon energies to determine MFP, HVL, Zeff, and Neff. The theoretical values of these parameters were calculated via ZXCOM, WinXCom and Monte Carlo N-Particle simulation code (MCNP), and a good agreement was obtained between WinXCom–MCNP and MCNP–Exp. Finally, EABFs and EBFs of the samples were calculated up to around 40 MFP in the energy region 0.015–15?MeV and significant variations were observed in the continuous energy and MFP regions. 相似文献