Studies of polymer solvation by dielectric relaxation spectroscopy I: polyvinyl pyrrolidone in propylene carbonate,dimethyl sulfoxide and tetramethyl urea

The dielectric relaxation behavior of the title solutions of PVP 40000 is measured in the frequency domain (50 MHz to 36 GHz) at 20 °C. The polymer content of the solutions (up to 0.25 mole fraction of monomer units) is such that it does not yet contribute significantly to dielectric loss. The solvent relaxation shows in all cases a bulk and a slowed down contribution, both characterized by concentration-independent relaxation times. The slow contribution is ascribed to the solvate. Solvation numbers for dilute solutions roughly range between 2 and 4 per PVP repeat unit.     

Dielectric relaxation of specially prepared polystyrene terminated with rigid polar groups

Two polystyrenes terminated withp-cyanobenzyl andp-cyanobiphenyl groups (=labels) were prepared and their complex dielectric constants were measured in the glass transition region in the frequency range 10^–2–10⁶ Hz. The glass temperaturesT _g (DSC) were considerably different, 92 and 97.5°C, resp., although their molecular weights were very similar (11 000 and 10 000 g/mol, resp.). Their relaxation behavior showed that the cyano groups relax cooperatively with the polymer segments. The cyanophenyl groups were found to relax with shorter relaxation times than the cyanobiphenyl groups. The measured relaxation strengths showed that there was no association between the dipoles. The relaxation mechanisms of the cyano groups in both labels seemed to be different although the only difference between them was an additional phenyl group in the case of the second label.     

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.     

Dielectric relaxation in polymeric solids Part 1. A new model for the interpretation of the shape of the dielectric relaxation function

A model is proposed which explains the shape of the dielectric relaxation function at the glass transition of polymers. The model is based on the idea that the molecular mobility at the glass transition is controlled by intra- and intermolecular interaction. In addition, a specific model for the local chain dynamics in amorphous polymer systems is used. According to the scaling hypothesis of molecular dynamics the model relates the high frequency dependence of the dielectric loss curve to the local chain dynamics and the low frequency dependence to the intermolecular correlation.     

CPS K 221 Model of proton longitudinal magnetic relaxation in hydrated crosslinked poly(methacrylic acid)

Proton longitudinal magnetic relaxation time (T₁) measurements have been made at 30 MHz over a wide range of temperature for crosslinked poly(methacrylic acid), PMA, hydrated with H₂O as well as with D₂O. From the point of view of nuclear magnetic relaxation, PMA hydrogel is a multiregion system in which three proton regions (a, b, c) can be distinguished. Region a is regarded as to be formed by the nonexchangeable polymer protons, region b by the protons of -COOH · H₂O combinations, and region c by the protons of remaining water molecules. Cross relaxation between polymer and water protons and a log normal distribution of correlation times have been assumed to take place. Temperature dependences of the T₁ time for the particular regions have been determined, from which the distribution width parameter, the second moment and the intramolecular proton-proton distance for sorbed water have been calculated.     

Effects of uniaxial stretching and shrinkage on proton spin-lattice and spin-spin relaxation times of isotactic polypropylene

An isotactic polypropylene film was stretched at 120 °C in poly(ethylene glycol) and thermally shrunk at various temperatures. Proton spin-lattice,T ₁, and spin-spin,T ₂, relaxation times were measured using a broad line pulse spectrometer operating at 19.8 MHz in the temperature range 40 °C–100 °C. The temperature ofT ₁ minimum shifts to higher temperatures and the value ofT ₁ minimum increases in magnitude as the stretching ratio is increased. In contrast the temperature ofT ₁ minimum shifts to lower temperatures as shrinkage is increased, whereas the value ofT ₁ minimum increases in magnitude because of the increase in crystallimty during shrinkage. T_2a, the longestT ₁ associated with the mobile amorphous regions, increases during shrinkage, indicating that chain mobility in the amorphous regions increases substantially during shrinkage. It was found that an orientation function of the amorphous regions,f _a, correlates well withT _2a .Presented in part at the 52nd Annual Meeting of the Japan Chemical Society, Kyoto, April 1986.     

Thermotropic gelation of ovalbumin 1. Viscoelastic properties of gels as a function of heating conditions and protein concentration at various pH values

A study has been undertaken of stress relaxation in ovalbumin thermotropic gels with a concentration of 8–20%, depending on time and temperature of heating (respectively, 20–60 min, 70°–110°C), at pH 2.5–10.0. In all instances, the dependence of the initial gel elasticity modulus on heating has a single maximum. Gelation conditions corresponding to this maximum are considered optimal. Optimal gelation time is 30 min, regardless of pH. On the other hand, the optimal heating temperature depends on pH. To the right and left of the isoelectric point of protein (2.5pH<4.0 and 5.5G) of gels on heating conditions, pH and protein concentration (X ₁,X ₂,X ₃,X ₄), as well as on time of relaxation (t) may be generally described asG(X ₁,X ₁,X ₁,X ₁,t)=G _e(X ₁,X ₂,X ₃,X ₄)f(t), whereG _e is the equilibrium value of the elasticity modulus, and f(t) the relaxation function. Thus, a change in the parameters only affects the value of the equilibrium elasticity modulus, and exerts no effect on the relaxation time spectrum. For this reason, all the relaxation curves obtained may be transformed into two normalized relaxation functions:f(t)=f(t)/f(1)=G(X ₁,X ₂,X ₃,X ₄,t)/G(X ₁,X ₂,X ₃,X ₄, 1)Each of these normalized functions corresponds to one of the homologous groups. Rheological similarity of gels in each homologous group evidently points to their structural similarity. Invariance of the gel relaxationproperties with regard to protein concentration, leads to a concentration dependence of the equilibrium modulus at various pH values. These dependences are curvilinear on a double logarithmic scale. The slope of the curve exceeds 2 in the entire concentration interval studied. In other words, the dependences obtained cannot be described by the usual law of squares. On the other hand, they adequately match Hermans theoretical relation for a network formed by random association of identical polyfunctional particles without cyclization. This simple model evidently gives a true picture of the major regularities of thermotropic gelation for ovalbumin. An agreement between this theory and experiment was achieved for a protein concentration ofC ^*=6.0±1.0% at the gel point regardless of pH. Invariance of gelpoint position with regards to pH demands further confirmation.List of symbols T _h,t _h heating temperature and time - T _h ^* ,t _h ^* optimal heating temperature and time - C protein concentration - C ^* protein concentration in gel-point - G relaxation modulus - G _e equilibrium modulus - f(t) relaxation function - t time of relaxation - f(t) normalized relaxation function - fT _A (t), f _B (t) normalized relaxation functions of groups A and B - G ₁ T _h,t _h-reduced modulus - G ₂ T _h,t _h, pH-reduced modulus - G ₃ C-reduced modulus - b ₁ T _h, t_h reduction parameter of modulus - b ₂ pH reduction parameter of modulus - b ₃ C reduction parameter of modulus - W_g gel-fraction     

Dielectric relaxation of rod-like labels in polyisoprene

Rod-like molecules with a strong dipole in the long axis were mixed with synthetic polyisoprene (IR305) in low concentrations (0.1–5 wt%) and measured dielectrically in the frequency range 10^–2–10⁶ Hz and the temperature range –60°–0°C (glass relaxation range). The measurements showed an additional symmetrical relaxation process slower than the glass process by a factor ranging from 10 to 100 times, depending on the length and structure of the label. The label relaxation process was characterized by a narrow distribution of relaxation times and its strong coupling with the segmental motion. For the labels with only a longitudinal dipole moment, no relevant part of the label relaxation was observed in the relaxation frequencies of the glass process; this may be attributed to the parallelism and compactness of the polyisoprene chains. In contrast, the labels with an additional vertical dipole component showed an additional relaxation process superimposed on the glass relaxation with also almost the same distribution of relaxation times. The slow label relaxation could be attributed to a diffusion or rotational diffusion relaxation process through a multistep relaxation mechanism determined by the segmental motion of the matrix.     

Theoretical study of dielectric behavior of microcapsule suspensions with distributed drug release rate

Theoretical consideration is made concerning the dielectric behavior of aqueous suspensions of W/O-type microcapsules containing aqueous electrolyte solutions, especially concerning distribution effects of the electrolyte release rate on the dielectric behavior.It is shown at first that the distribution of the release rate causes electrical conductivity of the capsule interior. Next, it is deduced, in the light of a theory of the interfacial polarization, that the distribution characteristics of the capsule interior's electrical conductivity are closely related to those of the relaxation time for a dielectric relaxation exhibited by the suspensions. Several formulas are derived to describe the relation between the distribution characteristics of the release rate and those of the relaxation time.     

Analysis of dielectric observations of KCl-charged poly(methyl methacrylate) microcapsules using a two-component model consisting of KCl-permeable and KCl-impermeable capsules

Dielectric measurements were carried out on aqueous suspensions of poly(methyl methacrylate) microcapsules charged with KCl solutions to examine the KCl permeability of the microcapsules. The specimens exhibited three kinds of dielectric relaxation. Two kinds of dielectric relaxation were observed immediately after washing the specimens with distilled water. These overlapped each other when the specimen was left standing in the measuring cell for a long time. Their relaxation frequencies were affected by the KCl concentration of the suspending medium in which the specimen was kept before washing. Another relaxation was observed distinctly when the spepcimens were washed thoroughly with distilled water. Its relaxation frequency was affected by the KCl concentration of the charged solution. These results were explained by assuming that the specimens were mixtures of KCl-permeable and KCl-impermeable capsules. The theoretical analysis procedure was devised in the light of dielectric theory of interfacial polarization to estimate the parameters which characterize the structure of the specimens.     

Effect of plasticizer concentration on the hysteresis,tear strength and stress-relaxation characteristics of black-loaded rubber vulcanizate

The effect of plasticizer concentration on the stress softening, tear strength and stress relaxation of black loaded bromobutyl rubber vulcanizate has been investigated. The stress softening in the rubber vulcanizate, an energy dissipative process at higher strain, may be explained primarily by changes that take place in the rubber phase of the filled vulcanizate. Increased plasticizer concentration leads to decrease in the equilibrium hysteresis. A quantitative relationship between energy density and hysteresis has been derived, which is applicable at and below the elongation at break. Increase in plasticizer concentration results in decrease in the effective diameter of the tip of the tear, which in turn decreases the tear strength. Rate of relaxation decreases with increase in the plasticizer concentration in the carbon-black-filled vulcanizate.     

Recent development in dielectric relaxation spectroscopy of polymers

An evaluation strategy for dielectric measurements in the frequency and/or time domain is presented which provides complete information about a relaxation mechanism (intensity, position, and shape of the relaxation function) independent of overlapping with neighboring mechanisms. As an example results on poly-(ethyleneterephthalate) are given.     

Dielectric analysis of PMMA microcapsules containing an aqueous KCl solution to derive a distribution function of the release rate of KCl

Release of KCl from a batch of PMMA microcapsules containing an aqueous 3 mM KCl solution was studied with the following two methods: 1) dielectric measurements of suspensions of the microcapsules in distilled water. The electrical conductivity of capsule interior was estimated with this method. 2) Measurements of the conductivity of suspending medium of the microcapsule suspensions. These two kinds of experiments provided us with information about the amount of KCl remaining in the capsules and that diffused outside. Results of these experiments showed that the microcapsules varied in their release rate of KCl. A distribution function of the release rates was derived from the results of the dielectric measurements. That distribution function was successful in explaining the results of the measurements of the conductivity of suspending medium. Furrther examination revealed that the release rate increased with the increase in the thickness of capsule wall.     

Time domain dielectric spectroscopy. A new effective tool for physical chemistry investigation

The general principles of time domain dielectric spectroscopy (TDS) are summarized. The methods of data treatment and presentation, and different TDS methods which enable one to obtain the permanent spectrum of ^* () in the frequency range of 10⁵–10¹⁰ are given. The examples of TDS application for the investigation of dielectric properties in samples of different nature and structure are considered in this review.     

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.     

Dynamics of hydrogen bond complexes in polymer melts

The dynamics of hydrogen bond complex formation between functional groups which are attached to a polymer chain, is studied in the molten state. The concentration of complexes in the thermodynamic equilibrium is distorted by the application of a large oscillatory strain in the nonlinear viscoelastic regime. The relaxation back to the thermodynamic equilibrium is studied as a function of the temperature in the linear viscoelastic regime. From the mechanical response the kinetic analysis can be performed using a modified Doi-Edwards theory. Using the equilibrium constants obtained from IR-spectroscopy, the rate constants for complex formation and decomplexation are obtained. The temperature dependence is equivalent to the temperature dependence of the zero shear viscosity which implies that complex formation is a diffusion-controlled process.     

DC dielectric study of polyethylene/CaCO3 composites

The dielectric properties of composite samples prepared by polymerizing ethylene on the surface of filler are compared to those of mechanical mixtures consisting of CaCO₃ and ultra high molecular weight polyethylene. After presenting the normalized master curves of AC dispersion and loss measured at different relative humidities, the field strength dependence of the 50 Hz AC and DC responses were studied. With one exception, the effect is small. Thermally stimulated polarization (TSP) and depolarization (TSD) curves are presented; the peak appearing on the TSP curves of the samples stored under ambient conditions is interpreted as a result of water desorption. The high temperature DC conductivity and the depolarization current density are higher in the composites and mechanical mixtures than in the matrix. The dielectric properties of the wet filler particles were calculated from the measured composite and matrix data using various mixture formulae. The results can be understood and interpreted if the dielectric properties of adsorbed water are described by the cluster theory of dielectric relaxation.     

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).     

FTIR spectroscopic and NMR studies of hard elastic polypropylene

The variation of amorphous orientation and crystalline regularity of hard elastic polypropylene (HEPP) films during cyclic deformation and stress relaxation processes were studied using a FTIR spectrometer. The result proves entropic elasticity and shows the orientational hysteresis in the amorphous region or within the microfibrils, and also shows that the amorphous orientation increases, but that the crystalline regularity decreases with the increase of extension rate.Three spin-spin relaxation timesT _2f,T _2m, andT _2s and associated mass fractionsF _f,F _m, andF _s of HEPP fibers were measured with a solid echo of NMR method at different elongations and after relaxation or recovery for a long time A new possible interpretation was proposed that, while the microfibrils are formed in HEPP, the medium decay component should be ascribed to inner molecules of the microfibrils, and the slow decay component to the surface molecules of the microfibrils. According to this interpretation, the results implied that subfibrillation is the main process when HEPP is stretched up to 15% strain, and that at above 15% strain thinning and lengthening of the microfibrils become the main process. Thickening of the microfibrils was found in the recovery and relaxation processes.