Polymethylmethacrylate and stearic acid compatibility in monolayers

Mixed monolayers of polymethylmethacrylate (PMMA) and stearic acid (SA) on substrates with different pH are examined at 25 °C.The spreading isotherms of the pure components and their mixtures in different molar ratios indicate a critical pH value of the support, above which the components are miscible.This limiting pH value, which is confirmed also by surface potential measurements, allows a sufficient ionization of the carboxilic acid.This study was supported by CNR and MPI.     

Influence of nozzle geometry on polystyrene degradation in convergent flow

Polymer degradation is readily observed in flows where the extensional component surpasses the rotational component of the velocity gradient. This type of flow is conveniently obtained by pushing a liquid into a convergent channel across an orifice. Kinetics of chain scission is sensitive to subtle modification of the coil conformation, which in turn depends on the details of the pervading flow field. By changing the orifice diameter and the conical angle of the inlet, it is possible to modify the spatial distribution of the velocity gradient, and hence, the residence time of a fluid element in the high strain-rate region. Degradation yields, measured under -conditions in decalin by Gel Permeation Chromatography, showed a strong dependence on the fluid velocity at the orifice, but not on the magnitude of the strain-rate. This result is contrary to the common belief that assumes viscous friction, proportional to the strain-rate, is the determining factor for the scission rate of a bond under stress. Rather, experimental findings tend to indicate that the driving force for chain scission was provided by the energy accumulated in the coil during the flow-induced deformation process. The sharp propensity for mid-chain scission was maintained regardless of the nozzle geometry.Dedicated to Prof. W. R. Pechhold on the occasion of his 60th birthday     

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.     

Broadband dielectric spectroscopy on a discotic liquid crystalline polymer

Broadband dielectric spectroscopy is employed for the first time to study the molecular dynamics in discotic liquid crystalline polymers. One dielectric relaxation process is found which is strongly broadened and asymmetric. It is assigned a local hindered rotation of the ester groups attaching the spacer to the discotic mesogen. This assignment is supported by NMR measurements on the identical substance.Dedicated to Prof. E. W. Fischer on the occasion of his 60th birthday.     

Viscosity B coefficients of polyethyleneglycols in water

The viscosity B coefficients of polyethylene glycols (M=62–1000) are determined at 25 °C. The B coefficient increases non-linearly with the number of ethyleneoxide (EO) units. The increase of the B coefficient per EO(0.111 dm³/mole) is less than the B value for two methylene groups (0.160 dm³/mole). This is discussed in terms of changes in the configurations of polyethylene glycols with long EO chains.Molecular size is the major factor that contributes to B at shorter chains, but solvation (hydration) becomes dominant as the number of ethyleneoxide groups increases. The hydration parameter,(gH₂O/g ethyleneglycol), shows a linear dependence on B at low mass followed by a non-linear increase at high molecular mass and the viscosity C coefficient accounts for the solute-solute interactions.Symbols absolute viscosity - _d absolute viscosity of dispersion medium - _r relative viscosity - _sp specific viscosity - ¦ _o ¦ intrinsic viscosity at infinite dilution - ¦ _c ¦ intrinsic viscosity as a function of solute concentration - partial specific volume - volume fraction - hydration (weight of H₂O hydrating 1 g of polyethylene glycol) - _c hydration as a function of solute concentration - K shape function - K _c shape function as a function of solute concentration     

The dispersion of hydrophilic and hydrophobic flame-hydrolysed silicas in short-chained alkanols

The ultrasonic dispersion of Aerosil 200 and some n-alkyl surface-modified derivatives thereof in alkanols have been examined. The sizes of the aggregates formed during this process were investigated from measurements of sol viscosity and quasi-elastic light scattering (QELS). In the former technique, the aggregate volume ratios (AVR) were calculated at very low volume fractions of silica. The AVR values so obtained indicated that the silica monomers were highly aggregated in all systems, as expected. Differences between the various alkanols were found, however. Decreasing continuum polarity from water to hexan-1-ol produced decreasing AVRs. From hexan-1-ol to octan-1-ol, however, the AVRs increased. The n-alkyl surface-modified silicas gave AVRs substantially different to A 200, related most likely to wetting and solvation of the solid surface during dispersion. QELS measurements were subsequently found to be of limited use for these systems, since the aggregate size distributions in these sols were evidently very broad. The results indicated that these size distribution were non-Gaussian. The use of QELS to investigate systems of such high aggregation appears to be limited.     

Theory of swelling of a crosslinked substance in equilibrium with a solvent in various phases

In this paper the thermodynamic theory of a body in a liquid, crystalline or vaporized solvent is treated. The equilibrium swelling curves are discussed for the different states of the solvent. The slopes of the swelling curves are dependent on the differential enthalpy of dilution of the solvent and, additionally, on the enthalpies of vaporization, crystallization and sublimation of the solvent related to the state of the swelling agent. The slopes of the swelling curves are determined by the differential heat of vaporization, the differential heat of solution of the solvent or the differential heat of fusion according to the state of the swelling agent. Directly below the melting pointT _m,1, or directly above the boiling pointT _b,1 of the solvent the swelling curves change their slopes with a sharp bend. This phenomenon can be used to determine (₁/w ₁) at constant temperature and pressure, which means the change of the chemical potential ₁, with the change of the weight fractionw ₁ of the solvent. Using a simplified statistical thermodynamic relation it is possible to describe the principal courses of the swelling curves in all states of the solvent.     

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.     

A fluorescence detection system for the analytical ultracentrifuge and its application to proteins,nucleic acids,and viruses

A fluorescence detection system was developed for the analytical ultracentrifuge Spinco model E. Fluorescence is excited by a laser beam which is focussed into the cell and illuminates an area with a dimension of 60 m in radial direction. For scanning the laser beam is moved in radial direction. After passing the cell, the laser beam is quenched by a carbon light trap and a set of optical filters. Fluorescence emission intensity is monitored by a photomultiplier located behind the light trap and the set of filters. The sensitivity of the detection system was tested by applying it to the sedimentation analysis of proteins and nucleic acids. Bovine serum albumin (BSA) was covalently labelled with the fluorescence-dye fluorescein-isothiocyanate (FITC), and its sedimentation coefficient could be determined even if BSA was analyzed in a concentration as low as 10^–10 M. Nucleic acids were labelled non-covalently by the intercalating dye ethidium bromide. Only 8 ng RNA were needed for the determination of the sedimentation coefficient. The particular advantages of the fluorescence detection system were exploited for the establishment of a new method for quantitative virus detection. To tobacco mosaic virus (TMV) a monoclonal anti-TMV antibody from mouse was bound, and to this a second, anti-mouse antibody that carried the fluorescence-label FITC was attached. Either by UV-irradiation or by incubation with glutaraldehyde, the first antibody was covalently crosslinked to TMV, and the second antibody to the first. In CsCl density centrifugation with fluorescence detection as little as 3.2 ng virus/80 l or 6×10⁸ virus particles/ml were recorded in a well expressed band at the corresponding buoyant density. Tenfold lower concentration would result still in a significant band. The sensitivity compares well with those of the most advanced techniques from immunology. Due to the specific labelling of viruses by antibodies it will be possible to carry out quantitative physical characterization of virus containing samples without purifying the virus. Future applications of the fluorescence detection system and of the virus detection technique are discussed.This paper was presented at the VI. Symposium on Analytical Ultracentrifugation, Marburg, FRG, February 16–17, 1989.     

Role of ionic species and valency on the steady shear behavior of partially hydrolyzed polyacrylamide solutions

Polyacrylamides are anionic polymers with a large number of charges along the polymer chains. The rheological properties of aqueous polyacrylamide solutions can be significantly modified by varying the solvent environment with the addition of salt. The presence of cations substantially reduces the inter- and intra-molecular interactions of the macroions. It was found that the valency of the cation has a strong effect on the rheological behavior of polyacrylamide solutions, but the size and type of salt have a negligible effect.The reduction in the solution viscosity with di-valent salts (e.g., CaCl₂, MgCl₂, BaCl₂, and MgSO₄) can be as high as an order of magnitude compared with mono-valent salt (KI, KC1, NaCl, and NaBr), depending on the salt concentration and shear rate. An identical viscosity function can be obtained for different types of polyacrylamide solutions by varying the salt content in solution. This interesting feature provides a useful means in the development and preparation of certain ideal fluids for simulation studies of complex flow problems.     

Longitudinal volume viscosity of 1,4 cis polybutadiene

Volume flow of 1,4 cis polybutadiene (1,4 cis PB) of ¯M _n =311.900,T _g =156 K, andT _m =266 K, has been measured.Elastic modulus of the elastic wave, longitudinal volume viscosity, initial longitudinal volume viscosity, and retardation times are described at compression rates of ca. 1.0 to 200.0×10^–5 s^–1, and at temperatures of 293 K to 373 K, and pressures up to 150 MPa.Longitudinal volume viscosity decreases with increasing compression rate, and with decreasing volume deformation, the behavior being in all cases a typical non-equilibrium one. Longitudinal volume viscosity decreases with increasing temperature (except at 293 K), the volume flow activation energy being of about 18.2 KJ/mol.     

Morphology and viscoelasticity of bilayer aqueous colloids of low-molecular and macromolecular amphiphiles

Aqueous colloids of didodecyldimethylammonium bromide (DMA), allylbis[2-(dodecanoyloxycarbonyl)ethyl]methylammonium bromide (ADM) and polymer of ADM (PADM) were employed for morphological and rheological studies.The polymerization was carried out by irradiation of UV-light for the monomeric colloid. Weight average molecular weight of the polymer is about 16.3×10⁴.Diameters of vesicles at critical micelle (aggregate) concentration were 8 10 nm in the aqueous colloids of DMA, ADM and PADM. Various bilayer textures which were dependent upon the concentration and the temperature could be found in these amphiphiles. In particular, the bilayer textures were full in variety in the PADM system.Rheological properties of the aqueous colloids of these amphiphiles depended strongly upon the bilayer textures.     

An investigation of aging aqueous poly(vinyl alcohol) solutions by the light scattering method

Aqueous poly(vinyl alcohol) solutions of various concentrations were investigated. The aged solutions were diluted and then analyzed by the light scattering method, size exclusion chromatography, and viscometry. It was found that a relatively small quantity of supermolecular formations arise during aging; they are dispersed in the molecular solution of the predominant part of the polymeric material present. The amount of these aggregated structures and their formation rate increase with concentration of the aging solution.     

Adhesive effect of low-density polyethylene gels on polyethylene moldings

Adhesive effect of low density polyethylene (LDPE) gels in organic solvents such as decalin, tetralin, ando-dichlorobenzene on high density polyethylene (HDPE) moldings has been investigated by shearing tests, electron microscopy, and DSC measurements. When heated at 110°C for 2 h, all of the gels showed strong adhesive strengths around 30 kg/cm², which is sufficiently strong for practical uses. It has been found that the adhesive strength increases with the heating temperature and that the temperature at which the heated gel begins to exhibit the adhesive effect depends upon solvents and is about 30° lower than that of the HDPE gels.     

Automated determination of particle-size distributions of dispersions by analytical ultracentrifugation

The ultracentrifugation method for determining the particle-size distribution of dispersions has been automated and its precision and capacity improved.A mixture of seven monodisperse calibration latices can be analysed and two lattices with a difference in diameter of 10% can be resolved by a base-line separation.This paper was presented at the VI. Symposium on Analytical Ultracentrifugation, Marburg, FRG, February 16–17, 1989.     

The molecular weight dependence of intrinsic viscosity of rod-like micelles of dodecyldimethylammonium chloride

It is shown that the non-linear logarithmic dependence of the intrinsic viscosity on the molecular weight for rod-like micelles of dodecyldimethylammonium chloride (as reported by Ozeki and Ikeda [1]) can be interpreted in terms of the Yamakawa-Fujii theory of worm-like chains. Characteristic parameters of the micelles are estimated: persistence length (a=14 nm), linear mass density (M _L=4800 nm^–1), diameter (d=3 nm), molecular pitch (b=0.052), and the number of surfactant chains in a layer of rod-like micellen=12. The results are compared with those derived from light-scattering measurements.     

Viscoelastic properties of polyacrylonitrile particles stabilised by a poly-2-vinylpyridine/polytert butylstyrene block copolymer

The viscoelastic properties of a dispersion of polyacrylonitrile particles stabilised by a block copolymer poly-2-vinylpyridine/polytert butylstyrene dispersed in solvesso have been measured as a function of particle concentration and frequency at ambient temperatures. At low volume fraction of particles it was found that the loss modulus of the dispersions was larger than the storage modulus, whilst at volume fractions > 0.40 the storage modulus dominates the rheology. This is attributable to there being a steric repulsion between the particles as a result of an increasing concentration of particles and the resultant reduction in interparticle separation in the dispersion. In addition the observed exponential increase of the storage modulus with increasing particle volume fraction mirrors the exponential increase in force with decreasing surface separation of the same type of polymers adsorbed to mica.     

Chain dynamic parameters for some acrylic polymers

The dielectric relaxation data of Ishida et al. on a number of acrylic polymers are represented in terms of the relaxation function proposed by Havriliak and Negami using the multi-response techniques developed by Havriliak and Watts. Two of the parameters of this function are interpreted in terms of a temperature dependent distribution of relaxation times. In this method of interpretation the breadth of the distribution function is temperature-dependent while the skewness is not. The temperature dependence of the breadth of the distribution function is similar for most of these acrylic polymers.The parameters of the relaxation function are also interpreted in terms of Mansfield's model which represents intra- and inter-molecular interactions in terms of springs and dash pots. Briefly, increasing the side chain length for the methacrylate series increases the inter-molecular relaxation time which may be due to an increase in the entropy of activation for the orientation process. The difference between the one acrylate in this study and the four methacrylates of the series is a reduction in the intra-molecular relaxation time, apparently due to the lack of the alpha methyl group.     

Force-length relation for a short freely jointed chain: mass and volume dependence

We evaluate the force-length relation for short model chains. It is shown that this relation is markedly different when evaluated for static and dynamic model chains with rigid segments. The relation also differs for chains with rigid segments when they are isolated and coupled to a canonical heatbath, respectively. Furthermore, it is derived that the variation of the masses along the chain only has a small influence on the force-length relation. On the other hand, restricting the motion of the chain by walls perpendicular to the chain extension has a pronounced effect. We especially find that in this situation the chain has a finite equilibrium length.Dedicated to Professor W. Pechhold on the occasion of his 60th birthday     

Flocculation studies of non-aqueous poly(methyl methacrylate) dispersions. II. Stabilization with the diblock copolymer poly (styrene-b-[ethylene-co-propylene])

Well defined non-aqueous dispersions of poly(methyl methacrylate) stabilized by the diblock copolymer poly(styrene-b-[ethylene-co-propylene]) have been studied with a dispersion medium consisting of a binary liquid mixture of n-heptane and n-propanol. Flocculation was induced by adding n-propanol at constant temperature, to find the critical flocculation volume, and by cooling, to find the critical flocculation temperature. Theta conditions for ethylene-propylene copolymer in the same binary liquid mixture were determined using samples obtained by hydrogenating polyisoprene standards. These dispersions just retained stability at theta conditions, with flocculation occurring when the dispersion medium was slightly worse than a theta system for the stabilizing ethylene-propylene chains.