Complex polarizability as used to analyze dielectric relaxation measurements

The effect of representing dielectric properties in terms of the complex polarizability ^c = – i is examined. Loss curves ( and tan ) are shifted towards higher frequencies, revealing the existence of new relaxations and allowing the clarifications of ones already known. We have calculated the shift ratios (at maximum or tan )/ (at maximum or tan ) from the more conventional empirical equations representing the dielectric behavior. Some examples are given.     

Scattering from concentration fluctuations in polymer blends: A monte carlo investigation

The collective scattering function S_coll( ), which describes light (neutron-, x-ray) scattering under wavevector , is obtained from Monte Carlo simulations for a symmetrical polymer mixture. The polymers are modelled by self-avoiding walks ofN _A=N_B=N steps on a simple cubic lattice, where a fraction _V of sites is left vacant, and an attractive energy occurs if two neighboring sites are taken by the same kind of monomer. Spinodal curves are estimated from linear extrapolation of S _coll ^–1 (0) vs./k _B T, whereT is the temperature. Also the single chain structure factor is obtained and the de Gennes random phase approximation (RPA) can thus be tested. Unexpectedly, strong deviations are found if one species is very dilute. The estimation of an effective Flory-Huggins-parameter from scattering data is also discussed.Contributed paper delivered at the Tagung der Deutschen Physikalischen Gesellschaft, Fachausschuß Polymerphysik, Hamburg, March 14–16, 1987.     

Adsorption behavior of polymers having phosphoric acid group on γ-Fe2O3 and magnetic characteristics in magnetic coatings

Polymers having phosphoric acid groups were prepared as a model binder for magnetic coatings, and the correlation among the adsorption behavior of the polymers onto-Fe₂O₃ particles and the dispersibility, the orientation, and the packing density of-Fe₂O₃ particles in the magnetic coatings was investigated.PMMA homopolymer molecules hardly adsorbed on-Fe₂O₃, and the interfacial tension at a water/polymer solution (toluene) interface ( _W/T) was scarcely changed compared with a water/toluene interface. Increasing with the content of polymeric phosphoric acid group, the adsorbance of polymer increased and the interfacial tension ( _W/T) decreased. When the content of polymeric phosphoric acid groups was over 0.4 mol%, the adsorbance of polymer and interfacial tension ( _W/T ) remained constant. When these polymers were used as a binder for magnetic tapes, the dispersibility of-Fe₂O₃ in the magnetic coatings was improved, increasing with the content of polymeric phosphoric acid group; however, when the content of phosphoric acid group was over 0.2 mol%, its dispersibility decreased abruptly.Studies on Recording Magnetic Materials and Magnetic Composite. XVIII.     

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.     

Effects of pressure and solvent on the diffusion of aromatic compounds through polymers

The diffusion of six azo and five anthraquinone derivatives through nylon 6, poly(ethylene terephthalate) and secondary cellulose acetate films were studied under high hydrostatic pressures of up to 3000 bar and at temperatures 80–130 °C, by analyzing the diffusion profiles yielded in a stacked multiple film, placed in the solution of the diffusant. It was found that the diffusion coefficient,D, of the diffusant decreased with increasing pressure, giving a linear relationship between InD and the pressure, the slope of which gave the activation volume for the diffusion,V . It was revealedV increased linearly with increasing intrinsic molecular volume of the diffusant,V _w , the slopes being different between the azo and the anthraquinone derivatives. The ratio ofV toV _w (V /V _w ) ranged from 0.13 to 0.93, depending in a sensitive manner on the degree of swelling of the polymer matrix which in turn was varied by the solvent. The overall results could be explained in accordance with the formulation,V _{f, local} +V =V _w , whereV _{f, local} represents the free volume contribution. It was proposed thatV _w is increased by solvation when the solvent is good for the diffusant.     

Characterization of polymer networks by measurements of the freezing point depression

Based on the phenomenon of freezing point depression of a solvent byT, experimental evidence is presented to show that the distance between the junction points can be calculated fromT. Direct measurements of the temperature-time-curve of the cooling network and the Differential Scanning Calorimetry offer the determination ofT. Except the mean distances ¯d _c in dependence on cross-linking density, swelling degree, and other network parameters, the distribution of the distance between the junction pointsH(d_c) can be determined, which allows conclusions on the course of cross-linking reaction. This paper attempts to give experimental evidence of influences of the breadth ofH(d_c) on application-relevant properties.     

Formation of ultra-thin films consisting of proteins or polysaccharides and syndiotactic-rich poly-vinyl alcohol mixtures adsorbed at air-solution interface

Ultra-thin films of syndiotactic-rich poly-vinyl alcohol (s-PVA) with several proteins and polysaccharides were prepared by the bubble and frame methods using a mixed dilute aqueous solution (1.5g/dL).The mixed amount of-cyclodextrin (-CD) was the largest among these proteins and polysaccharides giving a weight ratio (-CD/s-PVA) of 1. The ratios of silk fibroin(SF), lysozyme, pepsin, and pectin tos- PVA were 0.58, 0.40, 0.35, and 0.35, respectively. For the-CD/s-PVA and SF/s-PVA blend thin films, the phase separation was observed.     

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.     

Orientation of the diphenylene propane unit in stretched polycarbonate from two-dimensional magic-angle-spinning NMR

Two-dimensional magic-angle-spinning (2D-MAS) NMR has been used to measure the orientation parameter, P₂, of the diphenylene propane unit in bisphenol-A polycarbonate oriented by stretching to various extension ratios,, atT=295K andT= 403 K.P ₂ is proportional to the birefringencen, with a maximum birefringencen ₀= 0.189. There is some evidence that the order parameterP ₂ of the DPP units with respect to the chain axis deviates from unity.n ₀ is therefore expected to be different from the birefringence,n ₀ , of perfectly aligned chains of polycarbonate. The experimental results obtained forP ₂() are compared to those predicted by the aggregate model.     

Determination of dispersive and nondispersive components of the surface free energy of glass fibers

The dispersive component _s ^d of the surface free energy of glass fibers and its interaction energy with alkanes, benzene, 1-nitropropane, ethyleneglycol, glycerol, formamide, and water were quantitatively determined by the tensiometric method within two liquids. The values of nondispersive interaction energy I _SL ^p were found to be a linear function of the square root of the nondispersive component of the surface free energy of liquids. This suggests that the nondispersive interaction energy may be represented by the geometric mean of the nondispersive component of the surface free energy of a solid and a liquid. The slope gave the nondispersive component _s ^p of the surface free energy. The _s ^p values are 33 and 14 mJ/m² for the untreated and aminosilane-treated fibers, respectively, suggesting that organophilic character has developed on the surface after aminosilane treatment. The _s ^p value was almost similar after the treatment, probably because of the polar characteristics of amino groups.     

Studies of Nanocrystalline Phase and Residual Amorphous Phase of FeCuNbSib Alloy Using TG(M) Technique

The —T and d/dT—T curves of the FeCuNbSiB amorphous alloy, which are the relationship between the total saturated magnetic moment per unit mass and temperature, are investigated by magnetic thermogravimetry analysis (TG(M)) technique. It is found that the crystallization process of the samples can be divided into five stages. The studies of samples annealed in temperature range of 480–610°C for 1h show that when the annealing temperature (T_a) is less than 540°C, the quantity of nanocrystalline -Fe(Si) phase increases evidently with T_a, and the Curie temperature (T_C) of residual amorphous phase also increases linearly with T_a, i.e. T_C=0.52T_a+91.7°C, with correlation coefficient =0.98. The variation of volume fraction of -Fe(Si) nanocrystalline phase or residual amorphous phase with T_a is measured by TG(M) technique.This revised version was published online in November 2005 with corrections to the Cover Date.     

Gas permeability of block copolymers of styrene and butadiene

The permeability of styrene-butadiene block copolymer foils with different composition prepared by casting and pressing has been investigated for the gases Ar, CO₂, and CH₄ at pressure difference of 400 mbar and at the temperature range 298 T [K] 333.The permeation process can be described by the solution diffusion mechanism. The diffusion coefficients decrease in the sequence of the gases Ar, CO₂, and CH₄ and the solubility coefficients increase in the sequence Ar, CH₄, CO₂.The dependence of the permeability on the composition of the block copolymer can be interpreted by the help of percolation theory and the effective medium theory. It follows the critical volume fraction of the percolation of the transport phase _PB ^c (= 0,23) and the coordination numberz (= 4) giving an information concerning the multiphase structure of the block copolymer.Presented in part at the 33^rd Annual Meeting of the Colloid-Gesellschaft, Graz, Austria, September 14–16, 1987.     

Transient photocapacitance study in 4-nitro-4′-aminodiphenyl layers

In 4-nitro-4-aminodiphenyl (NAD) layers the photocapacitance (PhC) transients were investigated. PhC spectral distribution as well as the temperature dependences of time constants (under/_on/or after/_off/illumination) have been measured. The photocapacitance spectral distribution possesses maxima at 350, 500, and 750 nm. It was shown that _on (T) is of exponential form while _off (T) is more complicated. The values of thermal activation energies (0.65±0.05) eV of both time constants coincide. The mechanism of photocapacitance process has been disclosed in NAD layers.     

The thermal transition behavior of poly(bis(p-flourophenoxy)phosphazene)

The thermal transition behavior of poly(bis(p-fluorophenoxy)phosphazene) was studied as a representative aryloxy-substituted poly(organophosphazene) using X-ray diffraction, differential thermal analysis and density measurements. The crystal structure of-form contained in as-cast film had marked paracrystalline disorder. The crystal phase transformed into the mesophase atT(1) (110 140 °C). The structure of the-form observed in the mesophase was a representative hexagonal-packing of macromolecular chains which rotate around the chain axes. When the mesophase was cooled to room temperature, a more ordered crystal phase of the-form could appear. The most ordered crystal structure of the-form has a monoclinic unit cell with the following lattice parameters: a=18.9, b=13.2, c=4.90 Å, and=77°. The chain conformation is nearly planar cis-trans, which has been observed commonly in poly(organophosphazenes). The macroscopic deformation of the film sample was also examined, taking into account the microscopic deformation of the lamellar crystal due to the crystal-mesophase transition.     

Studies on cross-linkable copolyimides

Some new flexible and cross-linkable copolyimides containing rubbery unsaturated aliphatic chain moiety (CPLA) were prepared by low temperature polycondensation betweenm-phenylene diamine,bis- 3(4 carboxy phthalimido) benzene, and liquid, bis [2-(4 piperazinyl) ethyl aminocarbonyl] poly-(butadiene-co-acrylonitrile) (ATBN) in (DMAC) solution. The effect of rubbery aliphatic moiety in these copolyimides on the polymer properties has been reported. A comparative study on the properties of these copolyimides (CPLA) with the mixture of ATBN and a low molecular-weight cross-linkable copolyimide possessing the same molecular structure as the aromatic moiety of CPLA polymers has been made.     

Structure of casein micelles II. α s1-casein

Following the earlier study of the- and-casein micelle structure, we will now report results from the _s1-casein. Static and dynamic light scattering measurements were performed in a concentration range from 0.5 to 6.0 mg/ml atT=35 °C. A constant apparent molecular weight of 3.4×10⁶ daltons was found over the whole range. The apparent radii of gyration and the diffusion coefficients also show no detectable concentration dependence. The ratio of the two radiiR _g /R _H =2.78+0.21 is characteristic of extended rigid structures.R _g is the radius of gyration andR _H the hydrodynamic radius defined via the Stokes-Einstein relationship from the translational diffusion coefficient. This is in agreement with the analysis of the pronounced angular dependence of the scattered light, which leads to the conclusion that _s1-casein forms very long worm-like micelles. The contour length of one cylinder was found to beL1600 nm and the chains appear to be composed of about 12 Kuhn segments. At higher concentrations, lateral aggregation proportional to the concentration is observed. Beyond the overlap concentrationc ^* the asymptotic scattering curve changes its shape, which is interpreted as the beginning of a reversible gelation.     

Solutions of alkali soaps and water in fatty acids XIII. Circumstances that regulate the extension of theL 2-phase and the role of the acid-soaps rich in fatty acid for the occurrence of the phase

A basic requirement for that type ofL ₂-phase which exists in the system sodium octanoate-octanoic acid-water is the formation of acid-soaps. In order for the phase to be formed at all, the temperature must lie above the melting point of the fatty acid so that a reaction in non-aqueous milieu between neutral soap and fatty acid is possible. In order to obtain the characteristic shape and complete extension of the phase in direction of high water content the temperature must be so high that also the hydrated acid-soaps occur in fluid state. On the other hand the temperature cannot be so high that the acid-soaps become unstable.At temperatures at which the phase has obtained its full extension those circumstances differs which in different regions regulate the location of the phase borders; they depend on the composition of the acid soaps and on their amounts. In that part of the phase where the molar ratio between octanoic acid and sodium octanoate lies between 2 and 3 and where one has a continuous transition from reversed to normal structure only the two acid octanoates 1 NaC₈ 2 HC₈ x H₂O and 1 NaC₈ 3 HC₈ x H₂O occur and both are at 20 °C in fluid state.At water contents from about 22 % to 40 % the hydrate-water molecules belonging to the first mentioned soap are capable of contributing actively to the formation of large aggregates of acid-soap, a process which however is counteracted by the inmixing of the latter acid-soap. This mixture of the two acid-soaps decides in this region where the border of the phase will lie in direction towards an increased content of sodium octanoate; the result is that in spite of the fact that the hydration is increased, the border is only slowly displaced towards a higher content of fatty acid. As soon as the hydration of the acid octanoates has been completed and the additional water occurs as unbound bulkwater, the location of the phase boundary will no longer be influenced by the water content — now it will be the amphiphilic composition of the acid-soaps that determines the location of the border and it remains at the molar ratio 2.5 between octanoic acid and sodium octanoate at water contents from about 40% and up to 82%.In the direction of decreasing content of neutral sodium octanoate and increased content of water theL ₂-phase both at the highest content of fatty acid and the highest contents of water will be in equilibrium with the water-richL ₁-phase; in the first mentioned region with theL ₁-phase below the lac where at the border it is saturated with octanoic acid and in the latter region with theL ₁-phase just above the lac, where the dilute sodium octanoate solution contains dissolved 1 NaC₈ 1HC₈ x H₂O. In the large central part of theL ₂-phase, from about 20 % to about 86 % of water, the location of the border is dominated by the acid octanoate 1 NaC₈ 3 HC₈ x H₂O and that makes an equilibrium with theL ₁-phase impossible; instead one has an equilibrium via a two-phase zone between the amphiphile-rich region of theL ₂-phase and its water-rich region. In the first region the location of the border is regulated by the decreasing capability of the hydrated acid octanoate 1 NaC₈ 3 HC₈ x H₂O to dissolve octanoic acid; in the latter it is regulated by the fact that 1 NaC₈ 3 HC₈ x H₂O is the most fatty acid-rich acid-soap that is formed and that the octanoic acid is very little soluble in water and in the aqueous solution of this acidsoap.The middle part of theL ₂-phase, especially the region between about 55 % and 82 % of water, constitutes a direct continuation of the liquid crystalline lamellarD-phase. The liquid crystalline character of theD-phase is lost at the transition, but the lamellar organization is retained. That the molecules at least up to a water content of about 40 % are of the original reversed type and have an elongated shape with a central part of hydrated polar groups, from which core the hydrocarbon chains extend in two opposite directions, is the reason to that they, at crowding, form transient layer-like agglomerates of tightly packed more or less parallel molecules; this facilitates the transformation to coherent double amphiphilic layers, in which all molecules lie with the hydrated polar groups outwards toward coherent domains of bulk-water, without another liquid phase occurs.     

Thermal properties of thio-and selenocyanatocopper(II) complexes with bipyridine and phenanthroline

The paper deals with the thermal properties of complex compounds of the general formula CuL₂(NCX)₂ (whereL=bipy or phen,X=S or Se). The phenanthroline complexes exhibit a higher thermal stability than those with bipyridine. For the latter complexes thermal decomposition begins with the release of bipyridine molecules, while for the phenanthroline complexes redox reactions of pseudohalogenide ligands with Cu(II) take place. The redox reactions start at a lower temperature for the selenocyanate complexes than for the thiocyanate complexes.

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Zusammenfassung Vorliegende Arbeit behandelt die thermischen Eigenschaften von Komplexverbindungen der allgemeinen Formel CuL₂(NCX)₂ (mitL=Bipyridin oder Phenanthrolin undX=S oder Se). Die Phenanthrolinkomplexe zeigen eine grössere thermische Stabilität als die Bipyridinkomplexe. Die thermiscne Zersetzung letzterer beginnt mit der Abgabe von Bipyridinmolekülen, während bei den Phenanthrolinkomplexen Redoxreaktionen von Pseudohalogenidliganden·mit Cu(II) stattfinden. Diese Redoxreaktionen beginnen bei den Selenozyanatkomplexen bei niedrigeren Temperaturen als bei den Thiozyanatkomplexen.

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CuL₂(NCX)₂, L= , X= . . , — . - , .

     

Chain entanglement,mechanical properties and drawability of poly(lactide)

The observed brittle fracture behavior of amorphous polylactides seems to be contradicted by the low value ofC =2 determined for poly(L-lactide) by Flory and coworkers. Such very flexible polymer chains deform by shear yielding, and fracture in a ductile manner. In this study,C was estimated in a number of ways, resulting in much higher values ofC =11.7 andC =9.1 for poly(L-lactide) and L- and D-lactide copolymers, respectively. These high values ofC and the low entanglement density account for the brittle fracture behavior of amorphous poly(lactide), as well as for the maximum attainable draw ratios of poly(L-lactide) networks and melt spun fibers. Bulk polymerized poly(L-lactide) networks, where crystallization during polymerization impedes severe entangling, could be hot-drawn most effectively to draw ratios of 8–16, resulting in very strong materials with tensile strengths of 550–805 MPa. By comparison, amorphous, non-crystallizable L/D lactide networks, which do not crystallize during polymerization, could be drawn less, to =7. These materials with strengths up to 460 MPa could, nevertheless, be oriented much more effectively than linear, amorphous L/D lactide copolymers.     

Halogenated poly-(N-vinylcarbazoles): flexibility and viscometric constants

N-vinylcarbazole, 3-Cl-N-vinylcarbazole, and 3-Br-N-vinylcarbazole were homopolymerized via radical polymerization. Several monodispersed samples of respective polymers were obtained by fractionation and their intrinsic viscosities were measured in tetrahydrofurane at 25°C. The viscometric constantsK anda, the monomeric unit projection length , and the flexibility parameter were determined using the gel permeation chromatography technique to determine the elution volumeVe and apply a newly derived relationship between the flexibility parameter and molecular weight. The presence of halogen atoms in the carbazole group of PNVC varies the value of and, consequently, the rigidity of the polymer.