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1.
The miscibility and mechanical properties of poly vinyl alcohol (PVA) and poly acrylic acid (PAA)-composited membranes were studied with molecular simulation. The Flory–Huggins parameters (δ) were calculated to prove the good miscibility of PVA and PAA. The radial distribution functions of hydroxyl and carboxyl atoms and the average number of H-bonds were observed to indicate the degree of physical cross-linking between PVA and PAA. The influences of intermolecular physical cross-linking on the glass transition temperature and mechanical properties were estimated. The results revealed that the PVA/PAA membrane with a composition of 2:3 has the best plastic properties, which exhibits a good application value. All of the simulated results showed good agreement with the experimental data. It indicates that the method presented in this work has a promising application prospect. 相似文献
2.
Films of methylcellulose (MC), poly(ethylene glycol)400 (PEG400) plasticized MC, and MC gels (MC crosslinked with glutaraldehyde (GA)) were prepared by casting from aqueous solutions. The swelling test has shown that the MC gels were insoluble in water and that their crosslinking density increased with increasing GA and HCl concentrations. The effect of the addition of PEG400 or GA to MC was investigated through dynamic mechanical analysis (DMA). The DMA analysis of PEG400/MC blends has shown that PEG400 was compatible with MC and was an effective plasticizer since the curves of tan δ against temperature exhibited single peaks (corresponding to a single glass transition temperature), which were displaced to lower values with increasing PEG400 content. The thermogravimetric analysis (TGA) indicated that the thermal stability of MC was not affected by the chemical crosslinking. The tensile strength was slightly increased through crosslinking while the elongation was slightly decreased. The presence of moisture in MC hydrogels decreased the tensile strength and enhanced the elongation while the addition of PEG400 decreased the tensile strength but sharply increased the elongation. 相似文献
3.
Patrick Garidel Christof Johann Lutz Mennicke A. Blume 《European biophysics journal : EBJ》1997,26(6):447-459
The miscibility of phosphatidylcholine (PC) and phosphatidylglycerol (PG) with different chain lengths (n = 14, 16) was examined
by differential scanning calorimetry (DSC) at pH 2 and pH 7. The determination of the coexistence curves of the phase diagrams
was performed using a new procedure, namely the direct simulation of the heat capacity curves as described recently (Johann
et al. 1996, Garidel et al. 1997). From the simulations of the heat capacity curves first estimates for the nonideality parameters
for nonideal mixing as a function of composition were obtained and phase diagrams were constructed using temperatures for
the onset and offset of melting which were corrected for the broadening effect caused by a decrease in cooperativity of the
transition. In most cases, the composition dependence of the nonideality parameters indicated nonsymmetric mixing behavior.
The phase diagrams were further refined by simulations of the coexisting curves using a four-parameter model to account for
nonideal and nonsymmetric mixing in the gel as well as in the liquid-crystalline phase. The mixing behavior of the systems
was analyzed as a function of pH and chain length difference to elucidate the effect of these two parameters on the shape
of the phase diagrams. At pH 7 the phase boundaries are much closer together and a narrower coexistence range is obtained
compared to the corresponding phase diagrams at pH 2. For DPPC/DMPG at pH 2, the shape of the phase diagram and the strongly
positive nonideality parameter ρ
1 for the liquid-crystalline phase indicates an upper azeotropic point. This indicates an unusual behavior of the system, namely
more pronounced clustering of like molecules in the liquid-crystalline phase compared to the gel phase.
Received: 17 March 1997 / Accepted: 4 July 1997 相似文献
4.
(1) The polymorphic phase behaviour of aqueous dispersions of various synthetic phosphatidylethanolamines, both singly and in mixtures, has been investigated by 31P-NMR. (2) PE remains in the lamellar phase up to 90°C. PE exhibits a lamellar to hexagonal (HII) transition between 60°C and 63°C. For PE, the lamellar to hexagonal (HII) transition occurs between 7 and 12°C, whereas for PE, the hexagonal (HII) phase is the preferred structure above ?15°C. (3) Mixtures of PE and PE exhibit near-ideal miscibility behaviour. For mixtures of PE and PE there is evidence of fluid-solid immiscibility at temperatures below the gel-liquid crystalline transition temperature of the PE component. Mixtures of PE and PE exhibit complex phase behaviour involving limited fluid-solid immiscibility at low temperatures and formation of a phase allowing isotropic motional averaging at higher temperatures. (4) 31P-NMR provides a graphic method for investigating the miscibility properties of mixed PE systems. 相似文献
5.
6.
Hydroxy propyl methyl cellulose (HPMC)/polyvinyl alcohol (PVA) blends are edible polymer films used for food packing and directly in foodstuffs. However they are water-soluble in ordinary temperature and have good mechanical properties. The miscibility of HPMC/PVA blend in water was studied by viscosity, ultrasonic velocity, density and refractive index techniques at 30 and 50 °C. Using viscosity data, the interaction parameters μ and α were calculated. These values revealed that HPMC/PVA blend is miscible when the HPMC content is more than 60% in the blend at 30 and 50 °C. And also the result revealed that the change in temperature has no significant effect on the miscibility of HPMC/PVA polymer blend. 相似文献
7.
Using enthalphy data from differential scanning calorimetry experiments and 13C-NMR linewidths of specifically ( lipids, the miscibility properties of phosphatidylcholines and lysophosphatidylcholines in liposomal dispersions have been investigated. It was found that 16 : 0 lysophosphatidylcholine mixes homogeneously in 16 : 0/16 : 0 phosphatidylcholine bilayers. Mixtures of 16 : 0 lysophosphatidylcholine with 18 : 1c/18 : 1c phosphatidylcholine, of 18 : 1c lysophosphatidylcholine with 16 : 0/16 : 0 phosphatidylcholine and of 18 : 1c lysophosphatidylcholine with 18 : 1c/18 : 1c phosphatidylcholine exhibited immiscibility in the phosphatidylcholine gel state. 相似文献
8.
The behaviour of dipalmitoylphosphatidylcholine (DPPC), mixed with stearonitrile (SN), was investigated at the air-water interface by surface pressure-area (pi-A) measurements and by direct visualisation of monolayers by Brewster angle microscopy (BAM). The pi-A-X diagram of system DPPC/SN was compared with the corresponding diagrams of systems DPPC/stearic acid (SA) and DPPC/octadecanol (OD) at 20 degrees C. Monolayers of the three systems reach the closest packing of alkyl chains in the 0.4-0.6 range of XDPPC. Thermodynamic analysis indicates miscibility in the three binary systems with negative deviations from the ideal behaviour. Morphological features of system DPPC/SN change significantly with XDPPC and temperature in the range 10-30 degrees C. At 10 and 20 degrees C mixed monolayers form condensed states from low pi all over the composition range. At 30 degrees C, the liquid-expanded (LE)--liquid-condensed (LC) phase transition occurs at increasing pi with XDPPC. The shape and size of condensed domains change with XDPPC and pi. Contrarily to the behaviour of pure components, mixed monolayers of DPPC/SN exhibit orientational order in the 0.2-0.6 mol fraction range of DPPC. BAM observation confirmed the partial miscibility indicated by GE data in a limited range of compositions at 30 degrees C. 相似文献
9.
Bodil Ramstedt 《生物化学与生物物理学报:生物膜》2006,1758(12):1945-1956
This review is focused on the formation of lateral domains in model bilayer membranes, with an emphasis on sphingolipids and their interaction with cholesterol. Sphingolipids in general show a preference for partitioning into ordered domains. One of the roles of cholesterol is apparently to modulate the fluidity of the sphingolipid domains and also to help segregate the domains for functional purposes. Cholesterol shows a preference for sphingomyelin over phosphatidylcholine with corresponding acyl chains. The interaction of cholesterol with different sphingolipids is largely dependent on the molecular properties of the particular sphingolipid in question. Small head group size clearly has a destabilizing effect on sphingolipid/cholesterol interaction, as exemplified by studies with ceramide and ceramide phosphoethanolamine. Ceramides actually displace sterol from ordered domains formed with saturated phosphatidylcholine or sphingomyelin. The N-linked acyl chain is known to be an important stabilizer of the sphingolipid/cholesterol interaction. However, N-acyl phosphatidylethanolamines failed to interact favorably with cholesterol and to form cholesterol-enriched lateral domains in bilayer membranes. Glycosphingolipids also form ordered domains in membranes but do not show a strong preference for interacting with cholesterol. It is clear from the studies reviewed here that small changes in the structure of sphingolipids alter their partitioning between lateral domains substantially. 相似文献
10.
Condensed state structure and biocompatibility of the konjac glucomannan/chitosan blend films 总被引:6,自引:0,他引:6
Specialised blend films have been prepared by blending 1% w/v konjac glucomannan aqueous with 1% w/v chitosan solution in acetate solution and drying at room temperature for 24 h. The condensed state structure and miscibility of the blend films were studied by Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, and wide-angle X-ray diffraction. The results indicated that the blend film obtained from an 80/20 mixing ratio of konjac glucomannan and chitosan derivate showed the highest miscibility and blend homogeneity, and that strong intermolecular hydrogen bonds took place between the amino groups of chitosan and the hydroxyl groups of konjac glucomannan; thus the tensile strength also achieved its maximum in this ratio. The cell morphologies on the pure and blend films were examined by light microscopy and cell viability was studied by using MTT assay. The results showed that the particular blend film was more suitable for the cell culture than the pure konjac glucomannan film, and that the cells cultured on this blend film had greater spreading coefficients than that of the pure konjac glucomannan film. As a result of the good mechanical properties, miscibility and biocompatibility, the blend film is a promising biomaterial matrix. 相似文献