Polypeptides mixed monolayers: collapse mechanism

The mechanism of the collapse process of monolayers of poly-L-alanine and of its mixtures with poly--methyl-L-glutamate was studied at the water/air interface at temperatures of 15°, 20°, 25°, and 30 °C.From measurements of the collapse surface pressure as a function of molar ratios and from the determination of the collapse kinetics, as well as from ellipsometrical measurements of the thickness of the film, the complete solubility of the components, even in the collapsed phase, was deduced.Furthermore, activation energies and values ofG*,H*, andS* in relationship to the kinetics of this process were deduced; it was shown that this process is constituted of a first phase of nucleation and of a second phase of growth both for the poly-L-alanine alone and for its mixtures with poly--methyl-L-glutamate.     

Electrically conducting,thermally stable,and mechanically strong CuS-poly(parabanic acid) composite films and their shielding effect of electromagnetic wave

Poly(parabanic acid)-CuS composite film (wt-% of CuS=20–50) prepared by using organosol of CuS (=1500 Å) showed electrical conductivity of 0.1–70 S cm^–1, high thermal stability up to 250°C, high mechanical strength (breaking stress=7.0–12 × 10⁷ Pa), and good shielding effect of electromagnetic wave.     

Thermally stimulated currents in poly(bis(p-fluorophenoxy)phosphazene)

Thermally stimulated currents (TSC) were examined for poly(bis(p-fluorophenoxy)phosphazene) (PBFPP) film. TSC showed peaks at the glass transition temperature (Tg=–4 °C) and atT(1) (160 °C – 170 °C), where-form crystal phase transformed to mesophase of-form structure. Another peak was found atT _cc betweenTg andT(1). Linear relationship between polarization field and peak current ofT _cc -peak was found, which shows thatT _cc -peak was caused by motion of dipolar groups in crystalline phase. When heating (up to 200 °C) and cooling (down to 20 °C) thermal process was repeated,T _cc -peak shifted to higher temperature region approachingT(1) and simultaneously, the peak current ofT(1)-peak became smaller. Activation energy, time constant of dipolar relaxation and charge mobility were evaluated forT _cc -peak. From these results, it was concluded that-form and more ordered- form crystalline phases coexisted in PBFPP once heated aboveT(1) and the content of- form phase increased by repeated thermal hysteresis.     

Spreading and compression of n-hexadecyl acrylate at liquid-air interface

Usingn-hexadecyl acrylate, surface pressure-area (F-A) curves and equilibrium spreading pressuresF ^e were measured at various temperatures (5.7°–46°C) by the Langmuir balance (F-A) and the Wilhelmy-plate method (F ^e). At low temperatures (T<13 °C) condensed films and the liquid-condensed/solid condensed transition can be observed. At high temperatures (T>30 °C) liquid-expanded films occur. In the intermediate range the compression curves have two transition points. The transition pressureF ₁ between liquid-expanded and condensed film has a marked temperature dependence. The transition enthalpiesH ₁ decrease with increasing temperature and become zero at 29.2 °C. The second transition is related to a transition between the condensed films (F ₂). The slight temperature dependence of this transition is accompanied by an increasing change of area as well as by increasing transition enthalpiesH ₂.TheF ^e-T curve has two distinct breaks, at the melting pointT _m and atT=30 °C. The break atT _m is due to the melting process and the break atT=30 °C is caused by a phase transition between a liquid-expanded film and a condensed film.The phase diagram was constructed from the transition pressures. It can be demonstrated that the highest pressures of the thermodynamic stable film occurs atT _m. At temperaturesT>T _m equilibrium spreading pressure and equilibrium collapse pressure are identical whereas atT _m supercompression of the monolayer occurs. The film in this state behaves like a supercooled liquid. Obviously, rupture and collapse of such a film lead to a thermodynamically metastable bulk phase.     

New functional microspheres with active succinimide groups

Radiation-induced polymerization of monomers, for example N-methacryl-oxysuccinimide (MASu) and diethylene glycol dimethacrylate (2G), in ethyl propionate, was performed from +25°C to –78°C. The copoly (MASu/2G) microspheres were obtained in MASu monomer compositions of 30 wt % or below. The average particle diameter of copoly(MASu/2G, 20/80 wt %) microspheres obtained at irradiation temperatures of 25°, 0°, and –43 °C were 0.81±0.29, 0.63±0.26, and 0.90±0.43 m, respectively. No microspheres were formed when irradiated at –78 °C. The reactivity of the succinimide groups on the surface of copoly(MASu/2G, 20/80 wt%) microspheres was checked by reacting with ethylene diamine. The maximal amount of reacting succinimide groups was 9.4±0.5 nol/g, which corresponds to about 1 % of the total number of succinimide groups in the microsphere.     

Phase separation in colloidal dispersions with nonadsorbing polymer

The influence of the volume restriction effect on phase separation in colloidal dispersions consisting of a nonadsorbing polymer has been studied using statistical mechanical cell models and perturbation theories in combination with Monte Carlo experiments. The attractive interparticle potential proposed by Asakura and Oosawa is used to represent the effect of polymer depletion between the particles. The equilibrium properties are determined using the cell model for the solid-like phase (with Monte Carlo simulations for the structure of the solid phase) and a perturbation theory for the liquid-like phase. Both aqueous and nonaqueous dispersions are considered, and the phase separation behavior predicted is compared with available experimental and theoretical results.     

The effect of segment length and concentration on dielectric properties of polypropyleneoxide-based polyurethanes

Three series of segmented polyurethanes based on MDI, variable chain extender, and polypropylene oxide of MW=1000, 2000, and 3000 were synthesized and their dielectric behavior examined.Dielectric relaxations in the segmented polyurethanes were investigated between –150°C and +150°C in the 100 Hz to 10 kHz range. In general, three transitions, designated as, , and were observed, and ascribed in accordance with calorimetric relaxations to glass transitions of the hard and soft segments, and Shatzki-type motions, respectively. The effect of structure variables such as soft segment size, type of chain extender (ethylene glycol, butane diol, and hexane diol) and soft segment concentration, as well as the effect of interaction of the phases on dielectric properties was discussed. It was found that a certain degree of phase mixing exists in all series, detected by the variation of theT _g of the soft segment with soft segment concentration, contrary to DSC results, which was ascribed to thermal treatment prior to the dielectric measurements. It appears that interfacial polarization becomes important only above the transition temperature.     

Localization of carboxyl groups at surface layer of carboxylated polymer emulsion particles by alkali treatment

For the purpose of localizing carboxyl groups from inside to particle surface, styrene — butyl acrylate — methacrylic acid (74.3/17.0/8.7, mol ratio) terpolymer emulsion was kept under pH 9 at different temperatures. The amount of carboxyl groups at the particle surface, As, was remarkably increased by the alkali-treatment above 35 °C. On the other hand, As value of the alkalitreated emulsion was decreased by keeping under ph 3 above 45 °C, although in the case of the original emulsion without the alkalitreatment, it was not changed by the acid-treatment. These results suggest that a part of polymer segments which have ionized carboxyl groups is dragged out at the surface by an increase in the affinity of the groups against water, and the dragged segments turn back into the inside again when the carboxyl groups are deionized.Part 97 of the series Studies on Suspension and Emulsion.     

Macromolecular conformations at the water-air interface: Interactions between alpha and beta conformations of polypeptides

Bidimensional miscibility between alpha and beta conformations of polypeptides was investigated at the water-air interface in the 15°–30°C temperature range. The polypeptides were poly--methyl-L-glutamate (PGMG), poly--benzyl-L-glutamate (PGBG) and poly--benzyl-L-aspartate (PBBA). The polypeptide conformations, alpha or beta, were checked by IR spectroscopy using the MIR technique.The spreading isotherms for mixed monolayers alpha-PGMG/alpha-PGBG and beta-PGMG/beta-PBBA showed bidimensional miscibility both for alpha-alpha and beta-beta mixtures.For the alpha-alpha system, attractive interactions among the polypeptide alphahelices were found (G_mix<0) and the driving factor appeared to be the entropic one (packing). Compressibility moduli and surface potential measurements showed a fluidification effect of alpha-PGBG on mixed monolayers. In the case of beta-beta mixed monolayers, ideal behaviour was observed and no fluidification effect detected.Scanning electron micrographs made on collapsed monolayers showed hexagonal structures for alpha-alpha mixtures and no well-defined or characterized features for the beta-beta system.     

Kinetics of nonisothermal crystallization and melting of normal high density and ultra-high molecular weight polyethylene blends

The kinetics of nonisothermal crystallization and melting of blends of ultra-high molecular weight polyethylene (UHMWPE) and polyethylene high density with normal molecular weight (NMWPE) are investigated by means of differential scanning calorimetry (DSC). Mixing the components at a temperature below the flow temperature of UHMWPE (215 °C) results in increased crystallization/melting rates of the individual components in the blends above the corresponding additive values. The morphological observations of the blends, carried out by means of polarization microscopy, show that a strong boundary of both types of structures (UHMWPE non-flowing aggregates and NMWPE spherulite structures) does not exist. The NMWPE spherulites' dimensions decrease on increasing the UHMWPE concentration in the blends, but their number increases. The facilitation of the crystallization/melting of the components in the blends is explained in terms of mutual influence exhibited by the components with respect to each other. It is due to the inner stresses in nonflowing UHMWPE characterized with a lot of entangled tie molecules and to the partial co-crystallization of NMWPE molecules with the flowing part of UHMWPE. At mixing temperatures above 215 °C the melting/crystallization integral kinetic curves have only one linear part in contrast to these of the same blend (11 ratio of components), prepared at 190 °C. The rates of melting/crystallization remain almost constant with the increase of the mixing temperatures.     

Insoluble monolayers of irisresorcinol at the air/water interface

Monolayer properties of irisresorcinol [5-(cis-10-heptadecenyl) resorcinol] were measured at the air/water interface. TheA-T isobars of the monolayers at 10 and 15 mN/m gave two-dimensional thermal expansivities of 1.4 × 10^–4/K and 1.3 × 10^–4/K at a temperature span from 7–40 C, respectively. The- A isotherms of the material showed only a little dependence on temperature from 5–35 C and onpH except at highpH, where monolayers expanded by ionization of resorcinol headgroups. Some types of saccharose in the subphase exhibited a characteristic interaction with irisresorcinol in monolayers, and there is a possibility that this material will be used for molecular recognition of some saccharoses.     

A monolayer model of the interfacial region of microemulsions

Mixed monolayers of tetradecanol and oleic acid at the water-air interface were studied to provide a static related structure featuring the interface between water and oil of water-dodecane microemulsions.The films of pure components as a function of temperature show a strong area contraction between 25 ° and 30 °C, caused by a change in the head groups hydration. This agrees with similar discontinuities found for some properties of the microemulsion in the same temperature range. At the water-air interface, the composition range of tetradecanol/oleic acid mixtures with the highest thermodynamic stability corresponds to the same stability range of the water-in -dodecane-potassium oleate microemulsions.Adsorption isotherms of tetradecanol and hexanol at the dodecane-water interface were studied to compare the surface behaviour of the two alcohols; the results indicate that the two alcohols have very similar two-dimensional surface phases and adsorption energies.     

Lamellar phases in mixtures of low molecular weight alkanols and cetyltrimethylammonium bromide (CTAB)

Partial phase diagrams showing the domains of existence of a transparent, viscous, lamellar-structured (D)-phase that transforms reversibly into fluid single phase solutions at high temperature are presented for the system: cetyltrimethylammonium bromide (CTAB), two low molecular weight alcohols, and water with and without additives. At constant temperature and with a fixed amount of surfactant, the size and location of this phase in the phase diagram depends upon three composition variables: i) the ratio of concentrations of medium chain alcohol to long chain alcohol (R), ii) the ratio of concentrations of medium chain alcohol to surfactant (R), and iii) the concentrations of small amounts (up to 10 % by weight) of additives such as ethylene glycol, propylene glycol, and dimethylformamide, as well as NaBr. Small-angle x-ray scattering measurements of these mixtures reveal a lamellar structure. The observed lamellar repeat distances range from 60 A to 290 Å and depend upon the ratiosR andR and the concentration of the additives. The mechanical and structural properties of theseD-phases can be tuned by adjustingR andR. TheD-phase-to-isotropic transition temperature can be varied from near room temperature to above 80 °C by adjustingR andR.     

Mechanical properties and molecular mobility in oriented polyolefines

The static modulus of elasticity (E) and the correlation time of rotation ( _c ) of 2,-2,6,6-tetramethylpiperidine-1-oxyl are studied as a function of the temperature (210<T <350°K) for oriented films of isotactic polypropylene and polyethylene of high and low density.E and _c change both upon heating and polymer orientation; this result indicates that sample properties are influenced by the microstructure of the amorphous phase where probes are localized.     

Production of anomalous polymer microspheres having uneven surfaces by “stepwise” heterocoagulation technique

Anomalous polymer microspheres having uneven surfaces were produced by stepwise heterocoagulation technique of small polymer particles (SPs) onto large polymer particles (LPs).SPs andLPs have surface charges opposite to each other in the emulsion states.SPs were produced by emulsion copolymerization of styrene and methacryloyloxyethyltrimethylammonium chloride, andLPs by emulsion terpolymerization of styrene, butyl acrylate and methacrylic acid, with nonionic emulsifier being used in both cases. Maximum covering ofLP bySPs was obtained under the conditions that both emulsions were blended without the coagulation at pH 3 at room temperature and then left stand to coagulate with each other at 70 °C for 4 h at pH 9.Part CXI of the series Studies on Suspension and Emulsion.     

Water self-diffusion in micellar solutions and in lyotropic mesophases of the system water/Triton TX-100

Studies by Pulsed Field Gradient NMR (PFG-NMR) methods and other physico-chemical experiments have been used to clarify the processes connected with water self-diffusion in mixtures formed by water and Triton TX-100. In micellar solutions the solvent diffusive trend is related to micelle hydration and, to a much less extent, to micelle size and shape. Hydration numbers from PFG-NMR are close to those obtained by viscosity experiments. In solution phases of the reversed kind, water in oil, water self-diffusion data suggest that aqueous domains are large and bicontinuous. Water self-diffusion in the hexagonal lyotropic mesophase has been interpreted by introducing a geometrydependent contraint, , termed structural factor, which is related to the parameters of the phase.     

Melt drawing as a route to high performance polyethylene

Well established routes for obtaining stiff and strong polyethylene (PE) involve solid state drawing either of solution crystallized gel films or melt crystallized spherulitic PE. The aim of this work is to show the potential of melt deformation as an alternative route for obtaining highly oriented products. Our previous work on the melt deformation route showed that oriented PE fibers could be directly extruded under appropriately controlled conditions [8,9]. Here, we show that PE films (or filaments) can also be melt drawn in the temperature window 130–160 °C, thus yielding oriented products. The advantage of melt drawing over direct melt extrusion is that it allows a wider operational latitude and thus does not require such carefully controlled conditions.The morphology produced by melt deformation is different from solid state deformation and consists of extended chain fibrils with platelet overgrowths. The relative amount of fibrils and platelets depends on operating parameters. The temperature window of PE melt drawing is identified with the regime where some flow induced crystallization takes place. The conditions for melt drawability are of wider generality for crystallizable flexible chain polymers. They are: (i) adequate strain rate to overcome entropie resistance to chain extension, (ii) but not high enough to activate the elastic response of the transient networks in the entangled system, (iii) sufficient strain to fully extend the chain, (iv) appropriate temperature for flow-induced crystallization and strain hardening, and (v) cooling to freeze the oriented structure.Ultra high molecular weight PEs were not the most suitable for melt drawing due to their high recoverable elongation in the melt (melt elasticity) in addition to added limitations imposed by their nascent grain systeme. Our work suggests that an optimum molecular weight for melt drawing is¯M _w(400–900)×10³ with further possibilities for improvement through multimodal distributions.     

Electrical properties of poly(bis(β-phenoxyethoxy)phosphazene) and its complexes

Electrical and dielectrical properties of poly(bis(-phenoxyethoxy)phosphazene) (I) and its complexes with various content ratios of AgSO₃CF₃ to monomeric unit (0.25/1 (II) and 0.5/1 (III) in molar ratio) were investigated.Dc conductivity of respective samples at 18 °C were 6.1×10^–12, 4.4×10^–9, and 7.1×10^–8 S/m.Dc conduction was considered to be due to ion hopping. Charge mobility ranged from 3×10^–12 to 6× 10^–11 m²/Vs depending on the applied field in sample II. In sample I, a tan peak was found which can be ascribed to molecular relaxation of main chains. The peak vanished upon introducing AgSO₃ CF₃. Temperature dependence of total conductivity ( _T ) measured byac method in the temperature range between –150 °C and 50 °C showed several peaks at the temperatures corresponding to the peak temperatures of tan. Total conductivities of respective samples at 100 kHz were 4.9×10^–7 (69 °C), 1.7×10^–4 (45 °C), and 1.5×10^–4(40°C)S/m.     

Wide angle X-ray diffraction studies of polytetrafluoroethylene and ethylen-tetrafluoroethylen-bipolymers in the range 9.5 K–270 K

PTFE shows in the whole temperature range investigated a triclinic crystal structure with cell parametersa=0.952 nm,b=0.559 nm,c=1.706 nm,=87.9°, = 90.0° and=91.8°. The temperature dependence ofa andb-axis is linear, thec-axis shows a change in thermal expansion at 150 K. The inherent strain is small. The crystallite sizes are measured, paracrystalline distortions are absent.The bipolymers show only an ordered arrangement in lateral direction under maintenance of the helical structure. The lateral arrangement is very distorted and the range of order is aboutD _L 10 nm.     

New organosols of ZnS and HgS in N,N-dimethylformamide and dimethyl sulfoxide. Use in the preparation of semiconductive polymer-metal sulfide composite films

Organosols of ZnS and HgS in N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were prepared by reaction of Zn and Hg salts with H₂S. ZnS in the DMF organosol has a particle size of about 300 Å, determined by an argon laser scattering technique. The form of HgS in the organosols varies with temperature, concentration of HgS, and type of solvent;-HgS in a DMF organosol is converted into-HgS at –30 °C or above. Poly(acrylonitrile)-ZnS or -HgS composite films prepared from organosols are semiconductive, and the electrical conductivity of the film increases by a factor of 10²–10³ on exposure to moisture or alcohol vapour. Poly(acrylonitrile)--HgS composite films, prepared from heated-HgS, show electrical conductivity of a range of 10^–1–10^–2 S cm^–1 and a large electron mobility.