Differential scanning calorimetric study of phase changes in poly(ethylene glycol) dodecyl ether-water systems

Phase changes in binary systems of poly(ethylene glycol) dodecyl ethers, C₁₂H₂₅(OC₂H₄)_xOH (x=5, 6 and 8) with water have been studied between –40 to 100 C by differential scanning calorimetry. A number of transitions, including the liquidliquid phase separation, were seen and the transition temperatures and enthalpy changes were determined. The observed temperatures were generally in good agreement with reported phase diagrams. In the C₁₂E₅ system, three of the four three-phase lines were seen and a more complete phase diagram is suggested for the water-rich part of the system. Most of the phase changes seen above 0 C are accompanied by small endothermic enthalpy changes of 0.7 to 0.9 kJ (mol C₁₂E_x)^–1, independent of system studied, type of transition and transition temperature. Water-rich solutions and liquid crystalline phases separate upon freezing into ice and crystals of hydrated amphiphile. Eutectics are developed at the following temperatures and compositions: C₁₂E₅ –3.0 C and 54 wt % C₁₂E₅; Q₂E₆ –4.5 C and 54 wt % C₁₂E₆, C₁₂E₈ –3.8 C and 49 wt % C₁₂E₈.     

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.     

An investigation of micro-brownian motions in polydimethylsiloxane by complementary incoherent-neutron-scattering and nuclear-magnetic-resonance experiments below room temperature

Two different experimental methods, neutron scattering and nuclear magnetic resonance are used to investigate the random methyl group and segmental rotational jump motions in polydimethylsiloxane. It is shown that nuclear magnetic relaxation and line width experiments are complementary to incoherent neutron scattering fixed-window experiments, the principle of the fixed-window experiments being discussed in somewhat detail. Satisfactory agreement of these experimental techniques is achieved as to the determination of the two model parameters of the motional processes in question, i. e. the activation energy and the preexponential factor of the Arrhenius ansatz made for the correlation time or jump time, respectively.Contribution partly presented during the meeting of the Macromolecular Club, June 8–10, 1983 in Uppsala, the spring conference of the Deutsche Physikalische Gesellschaft, March 12–17, 1984 in Münster and the Fourth International Seminar on Polymer Physics, October 22–26, 1984 in Eyba (GDR).     

Kinetics of oxidation of sulphite by hexachloroplatinate(IV) in acidic solution

Summary The kinetics of the oxidation of sulphite by hexachloroplatinate(IV) has been studied over wide range of experimental conditions. The reaction is first-order in substrate and in platinum(IV). The rate decreases with the increase in acidity. The effect of salt and of changing dielectric constants on the reaction rate have been studied. Values of H and S have been calculated and are 26.3 kJ mol^–1 and –35.9 JK^–1 mol^–1, respectively. On the basis of experimental evidence, a two-electron reduction mechanism is proposed.     

Thermal degradation of UHMWPE

The thermal behaviour of ultra-high molecular weight polyethylene (UHMWPE) of different molecular weights was examined by thermal analysis methods. The melting temperatureT _m and the heat of melting H were measured by the DSC method. The thermooxidative degradation process was investigated by using a MOM Q-1500 D derivatograph at various heating rates in air atmosphere. The initial decomposition temperatureT _i was determined from the TG curves, and other characteristic temperatures of decomposition were calculated. It was found thatT _m and H are higher for UHMWPE than those for HDPE, i.e. 146C and 195 J g^–1 for UHMWPE as compared with 133C and 166 J g^–1 for HDPE. The thermal behaviour of the investigated UHMWPE samples is not significantly influenced by molecular weight.     

Determination of the surface free energy of modified carbon fibers and its relation to the work of adhesion

Surface free energy of various carbon fibers was determined by tensiometric method in three different procedures. The dispersive _s ^d and the nondispersive _s ^p components were separately determined by contact angle measurements in two-phase system, formamide-n-alkanes. The _s ^p increased by oxidation and decreased by hydrogen reduction, while the _s ^d remained almost constant.The _s ^p value determined from contact angle of water/ethyleneglycol solution tended to become higher. The critical surface free energy was in harmony with the total free energy determined from formamide-n-alkanes system as long as liquids were properly selected. The formation of oxygen-containing functional groups was evidenced by ESCA, and the surface [O]/[C] ratio was related linearly to the surface polarity defined by _s ^p [ _s ^d + _s ^p ] Oxidation in liquid phase resulted in the formation of both hydroxyls and carboxyls, while only hydroxyls were formed in gas phase. The interfacial shear strength of the fiber-epoxy resin could be closely correlated with thermodynamical work of adhesion calculated on the basis of surface free energy and its component.     

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.     

Correlation of volumes and entropies of activation for oxidation of coordinated sulfur in bis-ethylenediaminecobalt(III) complexes by peroxodisulphate,hydrogen peroxide and periodate and for peroxodisulphate oxidation of diimine-cyanide–iron(II) complexes

Activation parameters H , S and V and correlations between S and V are reported for peroxodisulphate oxidation of [Fe(CN)₆]^4–, [Fe(bipy)₃]²⁺ (bipy = (2, 2-bipyridyl), [Fe(phen)₃]²⁺ (phen = 1,10-phenanthroline), cis-[Fe(bipy)₂(CN)₂], [Fe(bipy)(CN)₄]^2–, [Fe(phen)(CN)₄]^2–, [Co(en)₂(glyS)]⁺ (glyS = mercaptoacetate, SCH₂COO^2–), [Co(en)₂(cyS)]⁺ (cyS = cysteinate, SOCH₂CH(COO)NH₂ ^2–) and [Co(en)₂(amS)]²⁺ (amS = ethanesulphenaminate, SCH₂CH₂NH₂ ^–) and for periodate and hydrogen peroxide oxidation of the three last-named complexes. Activation parameters are discussed in terms of electrostriction, solvation and ligand size contributions. Opposite trends for S /V correlations were found for oxidations of Fe^II complexes in comparison with oxidations of coordinated sulphur in the Co^III complexes.     

Use of porous biodegradable polymer implants in meniscus reconstruction. 2) Biological evaluation of porous biodegradable polymer implants in menisci

Several series of porous, biodegradable PU/PLLA foams were used for meniscus reconstruction in dogs. PLLA-fiber reinforced PU/PLLA composites, PU/PLLA, and PU foams were implanted in severe meniscus lesions. The healing process was initiated as a result of blood vessels and other cells ingrowth into these porous materials. To accomplish good ingrowth of fibrocartilaginous tissue, the materials should have interconnected macropores of 200–300n with a high total pore volume. PLLA fibers were used to reinforce the materials, but seem to retard the degradation process and the ingrowth of fibrocartilaginous tissue.     

Small-angle neutron scattering on shear-induced micellar structures

Small-angle neutron scattering (SANS) experiments on sheared aqueous surfactant solutions of tetradecyltrimethylammoniumsalicylate (TTMA-Sal) are reported. A5-mM-solution without shear shows a weak correlation peak at a momentum transfer of 0.09 nm^–1 which has its origin in the micellar interaction. For shear rates above a threshold value of =40 s^–1 the scattering pattern shows an irregular increase in anisotropy. The analysis of the anisotropic pattern reveals the existence of two types of micelles: Small rodlike micelles which are weakly aligned and very large rodlike aggregates which are strongly aligned and which are present above the threshold value of. The two micelles are in equilibrium with each other and the equilibrium shifts with increasing shear rate to the side of the large oriented micelles.     

Effect of the chemical structure of nitroxyl radicals on their reactivity in the reaction with hydrazobenzene and tetranitromethane

The reaction rate constants of reduction of stable radicals of different classes by hydrazobenzene in hexane at 20C, in the range of 0.4–5·10³ M^–1sec^–1, were determined; a single scale of the oxidative properties of stable nitroxyl radicals was constructed. The rate constants of oxidation of a series of nitroxyl radicals by tetranitromethane in aqueous medium at 20C, in the range of 0.06–10 M^–1·sec^–1, were determined. It was shown that the oxidative properties of the nitroxyl group decrease slightly with an increase in its reducing properties for nitroxyl radicals of the piperidine and imidazoline series in reactions with ascorbic acid and tetra-nitromethane in aqueous medium, respectively.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2575–2582, November, 1990.     

Molecular motions in poly(diethyl siloxane) studied by solid-state29Si NMR

Molecular motions in poly(diethyl siloxane) were studied by solid-state²⁹Si-NMR in the temperature range 180–350 K. In this temperature range two solid phases ₁ and ₂, a mesophase _m, and an amorphous isotropic phase exist. The nature of the chain mobility in the different phases was deduced from the resulting changes in the NMR line-shape governed by anisotropic chemical shift. In the intermediate solid phase ₂ its anisotropy is reduced by 25% compared with the low temperature phase ₁ due to the onset of oscillations around the chain axis and conformational transitions. In the mesophase _m the polymer chain rotates about its long axis yielding an axially symmetric chemical shift tensor opposite in sign to that in the ₁, ₂ phases. The broad transition of the mesophase into the isotropic phase is accompanied by an increase in a narrow Lorentzian line arising from the amorphous phase. The results are compared with previous¹H NMR, Raman-spectroscopy and x-ray measurements.After completion of this work we learnt that PDES has recently also been studied through¹³C-MAS and²⁹Si-NMR by Möller et al. [13].     

Characterization of water-soluble,cationic polyelectrolytes as exemplified by poly(acrylamide-co-trimethylammoniumethylethacryate chloride) and the establishment of structure-property relationships

The cationic copolymerization products of poly (acrylamide-co-trimethylammoniumethylmethacrylate chloride (PTMAC) having cationic monomer percentages of 8%, 25%, and 50% as well as the cationic homopolymer, were characterized with respect to their molecular dimensions. The light-scattering and viscometric measurements were carried out for molecular weights ranging from 200 000 to 12 800 000 g/mol in 1 M NaCl solution at 25°C. It was possible to establish a relationship between the molecular weight and the two parameters: intrinsic viscosity and radius of gyration, for all four polymers.Rheological investigations of the flow properties in 1 M NaCl solution were also carried out using the polymer with a cationic monomer of 50% (PTMAC 50). Structure-property relationships were formulated which made it possible to describe and predict the shear viscosity, both in the zero-shear region (Newtonian region) and in the shear-dependent region (non-Newtonian region) as a function of the polymer concentration, the molecular weight, and shear rate.Abbreviations a exponent of the []-M relationship - A ₂ 2^nd virial coefficient/mol·cm³·g^–2 - AAm acrylamide - b slope of the flow-curve in the shear-rate dependent region - c concentration/g·cm^–3 - dn/dc refractive index increment/cm³·g^–1 - f function - K constant of the []-M relationship/cm³·g^t-1 - m _c proportion of cationic monomers/mol % - M molecular weight/g·mol^–1 - M _w weight-average molecular weight/g·mol^–1 - M _n number-average molecular weight/g·mol^–1 - NaCL sodium chloride - PAAm polyacrylamide - PS polystyrene - PTMAC poly(acrylamide-co-trimethylammoniumethylme thacrylate chloride) - R_G ^20.5 radius of gyration/nm - TMAC trimethylammoniumethylmethacrylate chloride - shear rate/s^–1 - critical shear rate/s^–1 - viscosity/Pa·s - 0 zero-shear viscosity/Pa·s - _s solvent viscosity/Pa·s - _sp specific viscosity - [] intrinsic viscosity/cm³·g^–1 - relaxation time/s     

Crystal structure of ionic and non-ionic surfactants based on polyoxyethylenated dodecanol: A13C-CP-MAS-NMR and x-ray investigation

Crystal structure of monodisperse non-ionic surfactants having the general formula C₁₂H₂₅O–(CH₂–CH₂–O)_nH (C₁₂E_n),n=7,9, 10, 15, 16 and ionic derivatives, C₁₂H₂₅–O–(CH₂–CH₂–O)_n–CH₂COONa (C₁₂E_nC),n=3,4,5,6,7,9, 12 has been investigated by¹³C-CP-MAS-NMR and x-ray diffraction. A structural model, in which aliphatic and polyether segments are segregated in bilayers stacking parallel to the elongation direction of the molecules, fits the experimental data for both series. The experimental values of the repeat distance along the stacking directiond(001) are linearly dependent onn and the slope is nearly equal to twice the repeat distance of7/2 helix conformation, which is typical for crystalline polyethyleneoxide. The values ofd(001) agree very well with the values expected for the C₁₂ segment in a planar zig-zag conformation, which is tilted with respect to the polyerther segment (7/2 helix conformation) in such a way that both the aliphatic and the polyether regions adopt the mass density of the corresponding crystalline compound. Two additional phases have been detected for C₁₂E_nC. One of them is probably characterized by the planar zig-zag conformation of the polyether chain. The meader model, previously proposed in the literature for surfactants containing polyethylene oxide segments is inconsistent with the obtained experimental data.     

Effect of random copolymerization on growth transition and morphology change in polypropylene

The growth rate of an ethylene-propylene random copolymer with a 2.8% w/w ethylene content was studied in a similar manner to polypropylene. A growth regime transition associated with a birefringence change was observed at 130C, while the same phenomena appeared at 138C in isotactic polypropylene. In both polymers positive birefringence corresponds to Regime III, whereas negative birefringence of spherulites is associated with Regime II. The birefringence change is attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae at low temperature (Regime III) and preferentially radiating lamellae at higher temperature (Regime II). We confirm that such a morphological change can be interpreted using the concept of non-adjacent re-entry introduced in Hoffman's kinetic theory. Thus, quadritic morphology seems to have a partly kinetic origin. The shift of the transition temperature in the copolymer is due to the rejection of ethylene segments at the surface of crystalline lamellae of polypropylene.     

Effect of the reduction temperature on the formation and activity of bimetallic Ni-Tc catalysts

The effect of the temperature on the formation, surface state, and catalytic activity in the reactions of dehydrogenation of cyclohexane and dehydrocyclization of n-hexane by Ni-Tc/-Al₂O₃ mono- and bimetallic catalysts was investigated. TcO₂, NiCl₂, and metal phases, and at a high temperature (500–700C), NiAl₂O₄ spinel and Ni-Tc clusters, were found on the surface of all of the catalysts. It was shown that the maximum activity is observed in reduction of monometallic catalysts at 500C and bimetallic catalysts at 700–800C. Synergism appeared in the bimetallic catalysts due to the formation of Ni-Tc clusters.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2486–2490, November, 1990.     

Effect of thick fixed-charge layers on electrostatic interaction — a theoretical approach

The electrostatic interaction pressure of charged surface layers is considered qualitatively and quantitatively. In the case of mutual penetration of the surface layers in addition to Maxwell stress and osmotic resp. hydrostatic pressure an isotropic stress on the fixed charges carrying molecules of the surface layers has to be taken into account. The derivation of the pressure-distance equations is given starting from both thermodynamic/electrostatic and hydrostatic/electrostatic principles. A possible biological significance of the additional stress is discussed emphasizing its role in modifying the structure of surface layer molecules.List of symbols e ₀ elementary charge - k Boltzmann constant - n _i concentration of theith ionic species in the bulk solution - P hydrostatic pressure - P hydrostatic pressure in the bulk volume (× ) - P ^h integration constant, independent on ×:P ^h =P(h) - T absolute temperature - Z _i electrovalence of theith ionic species - thickness of the surface layer - , ₀ relative and absolute permittivities - II(×) osmotic pressure at position × - II osmotic pressure in the bulk solution (× ) - osmotic pressure in the symmetry plane of interacting identical surface layers (electric field strength equals zero) - integration constant, independent on ×: - _e ^h electrostatic component of the disjoining pressure _e ^h = _e (h) - (×) mobile charge density profile (cations and anions of the electrolyte) - (×) fixed charge density profile - ^t(x) total charge density profile ( ^t = +) - ¹(x) fixed charge density profile of one of the two surface layers ( ¹(×) 0 for 0×) - (×) electric potential profile     

Kinetics and mechanism of the interaction of thiourea with cis-diaquaethylene-diamineplatinum(II) perchlorate in aqueous medium

The kinetics of the interaction of thiourea with [Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺, [thiourea] and temperature at a particular pH(4.0), where the substrate complex exists predominantly as the diaqua species and the thiourea ligand as a neutral molecule. The reaction proceeds via a rapid outer sphere association followed by two slow consecutive steps, the second step exhibiting first order dependence on the aqua ion and thiourea concentrations. The activation parameters for both the steps have been evaluated: (H ₁ = 54.8 ± 1.2 kJ mol^–1, S ₁ = –96 ± 4 J K^–1 mol^–1, H ₂ = 27.9 ± 0.8 kJ mol^–1 and, S ₂ = –183 ± 2.6 J K^–1 mol^–1). The low enthalpy of activation and large negative values of entropy of activation indicate an associative mode of activation for both consecutive steps.     

Interaction of Na+, K+, Li+ and Ca2+ ions in Tris-HCl buffer substrate with monolayers of phosphatidic acid and homologous phosphatidic acid alkyl esters

The interaction of ions (Na⁺, K⁺, Li⁺, Ca²⁺) with monolayers of phosphatidic acid alkyl esters (alkyl = methyl, ethyl,n-propyl,n-pentyl) were investigated at the air/water interface on Tris-HCl buffer, as well as on the electrolytes containing subphases.Qualitatively it can be stated that there are no considerable interactions between Na⁺ ions in the substrate and the head groups of phosphatidic acid esters in the monolayers. On the whole, the modification of the shape in the /a and v/a isotherms ( ^s = film pressure, v ^s = film potential) of the homologous phosphatidic acid esters as a function of the length of the ester group on the subphase containing NaCl, KCl, and LiCl corresponds to that on Tris-HCl buffer without admixture of electrolytes.On the other hand the strength of interaction between Ca²⁺ ions and the homologous phosphatidic acid esters depends on the length of the ester group. The film-condensing effect of Ca²⁺ ions becomes smaller with increasing length of the ester group.     

Thermal heterocyclization of methyl aryl ketazines. 2. Reactions of the tautomeric enehydrazine form

Over the temperature range 220–280C the thermal reactions of methyl aryl ketazines (Ar=C₆H₅-, 4-CH₃C₆H-, 4-CH₃OC₆H₄-, and -naphthyl-) proceed with their cyclization to give pyrazoline and benzodiazepine derivatives. With an increase in temperature to 320–350C the subsequent transformations of these compounds lead to the formation of substituted pyrazoles, 1-methyl-1,2-diarylcyclopropanes isomeric olefins, low-molecular-weight aromatic hydrocarbons, and isoquinolines.See [1] for Communication 1.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 908–917, July, 1986.