Local Segmental Motion Research Articles

Effects of orientation on the dielectric glass–rubber relaxation of amorphous networks

AbstractThe effects of the orientation on the dielectric glass–rubber relaxation of elongated poly(diethylene glycol isophthalate) networks, are studied. Orientation of the chains shifts the maximum of the α peak, at any frequency, to slightly lower temperature, as occurs in the case of mechanical relaxations. The dielectric behavior is interpreted in terms of the free volume theory. It is found that the ratio of the relative free volume to the parameter B at the glass transition temperature, where B is related to the minimum hole size required for local segmental motions, is almost independent of the elongation ratio λ. Cole–Cole diagrams are circular in the low‐frequency region, but at high frequencies the curves approach the abscissa along straight lines, which are nearly parallel for different values of λ. The difference between the dielectric constant at zero and infinite frequencies (ε0 − ε∞) is a linear function of the elongation ratio, and the Frölich theory suggests strong correlations between the relaxing species. The dielectric behavior of oriented networks is interpreted by using both the coupling model and a model which assumes the presence of defects around which the relaxation processes take place.

Ultrasonic Studies of Polymer Solutions

Recent works on the equilibrium and dynamic properties of polymer solutions obtained from ultrasonic measurements were reviewed. The dissolved states of polymer in solutions, the amount of solvated solvent and hydrated water, and the degree of counterion binding of polyelectrolytes were discussed on the basis of the sound velocity measurement at a few MHz. The ultrasonic relaxation processes in the frequency range from several hundred kHz to a few hundred MHz were interpreted by the local segmental motion of polymer in solution. The ultrasonic degradation of polysaccharides in solutions is briefly discussed.

Dielectric relaxation in concentrated solutions of cis-polyisoprene. Part 3.—Relationship between friction coefficient for dielectric normal-mode process and local segmental motions

The data of dielectric normal mode process (αI) and the segmental mode process (αII) reported in parts 1 and 2 of this series were analysed to find a relationship between the friction coefficient ζ for the normal mode process and the relaxation time τs for the segmental mode process. Assuming τs proportional to ζ, we attempted to superpose the τnvs. molecular weight Mw plots for solutions with different concentrations C. From the vertical and horizontal shift factors, we found that the monomeric friction coefficient ζm is approximately proportional to C2τs. To explain this result, we assumed that the effective size for the segmental motions expands with decreasing C. The molecular weight M0 for the unit of the segmental motion was estimated based on the computer simulation reported by Verdier and Stockmayer. The M0 was found to be 77 for bulk cis-PI and increased with decreasing C approximately in proportion to C–1.

Further investigation of the dielectric normal mode process in undiluted c i s-polyisoprene with narrow distribution of molecular weight

Dielectric relaxations in undiluted cis-polyisoprene (cis-PI) with narrow molecular-weight distribution were investigated. The normal mode process due to fluctuation of the end-to-end distance and the segmental mode process due to the local segmental motions were observed. The average relaxation time τn for the normal mode process was insensitive to the polydispersity Mw/Mn, but the width of the loss curve reflecting the distribution of the relaxation times increased with Mw/Mn. The slope of the double logarithmic plot of τn against Mw changed at the characteristic molecular weight Mc from 2.0 in the range Mw<Mc to 4.0±0.2 in the range Mw>Mc. It was found that although the half-width is nearly independent of Mw, the tail of the loss curve in the high frequency side broadens with increasing Mw. This indicates that by entanglement effects the distribution of the relaxation time for the normal mode process changes slightly. The segmental mode is found to be almost independent of the molecular weight and the polydispersity factor.

Intercomparisons of dielectric relaxation, dynamic light scattering, and viscoelastic properties of the local segmental motion in amorphous polymers

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIntercomparisons of dielectric relaxation, dynamic light scattering, and viscoelastic properties of the local segmental motion in amorphous polymersK. L. Ngai, S. Mashimo, and G. FytasCite this: Macromolecules 1988, 21, 10, 3030–3038Publication Date (Print):October 1, 1988Publication History Published online1 May 2002Published inissue 1 October 1988https://doi.org/10.1021/ma00188a023RIGHTS & PERMISSIONSArticle Views308Altmetric-Citations72LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Electron spin resonance studies of starch-water-probe interactions

Interactions between starch, water and stable nitroxide radicals were studied by electron spin resonance. The motional properties of TEMPO, 4-(2-bromoacetamido) TEMPO (BrAcTEMPO), 5-DOXYL-stearic acid and 16-DOXYL-stearic acid probes as well as a label covalently attached to amylopectin were investigated in concentrated (10–50%) starch-water systems as a function of temperature, concentration of polymer and storage period. Compared with the free probes in solution, TEMPO and BrAcTEMPO showed slower tumbling rates in starch-water dispersions or gels, suggesting a higher microviscosity in the probe's environment. The spectra, however, remained motionally narrowed. In contrast, the three line spectra of the fatty acid probes in solution became highly anisotropic in the presence of starch. The results indicated that these probes were highly immobilized at room temperature by the starch granules or by the polysaccharide gel matrix. These interactions are weakened at elevated temperatures where the spectra revealed the presence of both motionally narrowed and motionally slowed spin populations. The nitroxide label on the amylopectin exhibited a much slower mobility than the corresponding free probe as well as being found to be more motionally sensitive to temperature changes; such motional behavior was interpreted as reflecting contributions from rotation of the label around the chain backbone as well as local segmental motion of the polymer chain itself. Starch gels doped with free probes or the spin labelled amylopectin displayed no change in the motion of the nitroxide group upon storage, i.e. the tumbling rates did not follow the time-dependent conformational changes associated with the retrogradation phenomenon.

Head group interaction in membrane - cholesterol association: Studies in Aerosol OT model membrane system by 13C chemical shifts, relaxation and nuclear Overhauser enhancement effects

The 13C NMR chemical shifts, relaxation times and nuclear Overhauser effects of interfacial Aerosol OT molecules in reverse micellar systems in the presence of cholesterol were studied in order to observe the structure and dynamic properties of the amphiphilic assemblies. It was found that a hydrogen bonding takes place between the 3β-OH group of cholesterol and the oxygen atom of the carbonyl ester group of the Aerosol OT molecule which is close to the electronegative sulphonic ion. The negative nuclear Overhauser enhancement factors (NOEF) of this carbonyl carbon atom gradually increase to positive values with the increased addition of cholesterol to the micelles. The result can be explained by the reduced local segmental motion of the carbonyl group as a consequence of its complexation with a bulky molecule, such as cholesterol, so that the internal oscillatory motion contributes mainly to the relaxation mechanism. The NOEF of the other carbonyl carbon atom is reduced with increased cholesterol content, which indicates that the local motion of the carbonyl group is reduced by the condensation effect of the hydrocarbon chains. It is argued that the cholesterol interaction with the amphiphilic Aerosol OT molecule leads both the polar ester groups towards the hydrophobic part of the interface, leaving only the sulphonic group exposed to the hydrophilic aqueous core.

Dielectric relaxations in the liquid and glassy states of 47% polypropylene oxide in toluene as diluent

AbstractMolecular relaxations in 47‐wt % polypropylene oxide of molecular weight 4000 in toluene as diluent have been studied by dielectric permittivity and loss measurements from 77 to 320 K, in the frequency range 1 Hz to 2 × 105 Hz. One relaxation process (β process) is observed in the glassy state below Tg (= 148 K), and two processes are observed in the supercooled liquid at T > Tg. Relative to the amplitude of the fast relaxation process (i.e., the local segmental motions of the polymer chain), the amplitude of the slow process is increased and that of the β process decreased on dilution of the pure polymer. The β process has an Arrhenius energy of 17 kJ mol−1. The rates of the two relaxations at T > Tg follow the Vogel–Fulcher–Tamman equation and seem to merge on cooling the liquid towards Tg. The relative temperatures at which the three relaxation processes occur at the rate of 1 kHz remain largely unaffected on dilution. The increase in static permittivity of the solution on cooling is more than anticipated from the temperature effects alone. It is suggested that the increase is due to the enhanced short‐range orientational correlation of the dipoles, which may involve H bonding.

Solvent self‐diffusion, polymer NMR relaxation, and free volume in polymer solutions

AbstractThe self‐diffusion coefficient of chloroform in poly(isopropyl acrylate)—chloroform solutions has been studied as a function of concentration and temperature by using the pulsed‐field‐gradient spin‐echo NMR method. It is found that the self‐diffusion coefficient of the solvent can be adequately fitted by using a simple free‐volume approach with either a concentration or temperature superposition. It was noted that the free‐volume parameters derived from the self‐diffusion data are the same as those derived from deuterium NMR transverse relaxation‐time measurements of the polymer in the same system. The equality of these two sets of experiments suggests a fundamental relationship between the two different processes. The simplest explanation is that the free volume necessary for the local segmental motion of the polymer and the translation of the solvent are similar.

Theory of spin-lattice relaxation in lipid bilayers and biological membranes. Dipolar relaxation

In this work we have calculated spin-lattice (T1) relaxation time expressions for the homo- and heteronuclear dipolar relaxation of lipid bilayers, in addition to the heteronuclear Overhauser enhancement (NOE), using correlation functions derived previously. The results can be applied to the analysis of the 1H and 13C T1 times of lipid bilayers and the 13C–1H NOE. Three different models for the segmental fluctuations of the membraneous lipid molecules have been considered: (i) a simple diffusion-type model for the local segmental motions; (ii) a noncollective model in which relatively slow bilayer fluctuations are described by a single correlation time; and (iii) a collective model for the slow motions characterized by a continuous distribution of correlation times. For the diffusion model, the dependence on the bilayer orientation, order parameters 〈 P2〉 and 〈 P4〉, and the diffusion tensor anisotropy have been included in a general manner. Depending on the degree of segmental ordering and the anisotropy of the diffusion tensor, the maximum 13C–1H NOE can be either greater or less than the value of 2.988 obtained in the absence of an ordering potential. The various relaxation models were fit to 13C T1 data recently obtained for vesicles of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at seven different magnetic field strengths, i.e., resonance frequencies, in the liquid crystalline state. A simple diffusion-type model (i) based on analogies to paraffinic liquids provides a very poor fit to the above 13C T1 data as a function of temperature and frequency, even for extreme values of the ordering and diffusion tensor anisotropy, and thus can be rejected at the present time. The 13C results can be fit satisfactorily over the range 15.0–126 MHz by models which include contributions from relatively slow bilayer fluctuations. A noncollective model (ii) with three or four adjustable parameters or a collective model (iii) with two parameters both describe the data to within experimental error. At present, the 13C T1 results suggest that the relaxation of the bilayer hydrocarbon region, in the liquid crystalline state, can best be accounted for by a collective model with a relaxation expression of the type T−11≂Aτ(2)f+BS2CH ω−1/2I, as concluded from a similar analysis of the 2H T1 data for DPPC multilamellar dispersions. In the above expression, τ(2)f is the correlation time for the local motions, SCH(=SCD) is the observed bond segmental order parameter, ωI is the resonance frequency, and A and B are constants which depend on the nucleus considered. Thus, the observed relaxation rate includes contributions from fast or local-type motions, in addition to cooperative fluctuations of a more long-range character. For the collective model, extrapolation of the 13C T−11 values obtained for the DPPC vesicles to infinite frequency yields estimates of τ(2)f which agree with those calculated from the frequency-independent T−11 rates of n-hexadecane at the same absolute temperature, suggesting that the segmental microviscosities of the two systems are similar, in agreement with 2H NMR studies.

New view of lipid bilayer dynamics from 2H and 13C NMR relaxation time measurements.

Natural abundance 13C spin-lattice (T1) relaxation time measurements are reported for unilamellar vesicles of 1,2-dipalmitoylphosphatidylcholine (1,2-dipalmitoyl-sn-glycero-3-phosphocholine), in the liquid crystalline phase, at magnetic field strengths of 1.40, 1.87, 2.35, 4.23, 7.05, 8.45, and 11.7 tesla (resonance frequencies of 15.0, 20.0, 25.1, 45.3, 75.5, 90.5, and 126 MHz, respectively), and the results are compared to previous 2H T1 studies of multilamellar dispersions. For both the 13C and 2H T1 studies, a dramatic frequency dependence of the relaxation was observed. At superconducting magnetic field strengths (4.23-11.7 tesla), plots of the 13C T1(-1) relaxation rates as a function of acyl chain segment position clearly reveal the characteristic "plateau" signature of the liquid crystalline phase, as found previously from 2H NMR studies. The dependence of T1(1) on ordering, determined previously from 2H NMR, and the T1(-1) dependence on frequency, determined from both 13C and 2H NMR studies, suggest that a unified picture of the bilayer molecular dynamics can be provided by a simple relaxation law of the form T1(-1) approximately equal to A tau f + BS2C-H omega -1/2(0). In the above expression, A and B are constants, SC-H (= SC-D) is the bond segmental order parameter, and omega 0 is the nuclear Larmor frequency. The first (A) term includes contributions from fast, local segmental motions characterized by the effective correlation time tau f, whereas the second (B) term describes slower, collective fluctuations in the local ordering. The value of tau f approximately equal to 10(-11) sec, obtained by extrapolating T1(-1) to infinite frequency, suggests that the segmental microviscosity of the bilayer hydrocarbon region does not differ appreciably from that of the equivalent n-paraffinic liquids of similar chain length.

E.s.r. study of annealing and melting effects on the molecular motion of spin trapped chain-end radicals located on the polyethylene surface

E.s.r. spectra of chain-end spin labels on the surface of polyethylene powder were obtained for high and low density polyethylene samples at various stages of heat treatment process. The subsequent crystalline structures of the samples were examined with wide angle and small angle X-ray diffraction spectra. The effects of annealing on the motion of the labels were dependent on annealing temperature and the type of the samples. Higher temperature annealing decreased the rotational correlation times ( τ c ) and their activation energy in high density polyethylene but did not affect those of low density polyethylene. Melting decreases the values of τ c and ΔE for both high an low density polyethylene samples. The cause of these decreases were attributed to the changing of the sites of the chain-end labels. The motion of the labels appeared to be influenced by the local segmental motion of the polymer main chains.

Structure of native and regenerated cellulose as revealed by proton NMR analysis

AbstractDifferences in fiber structure between cotton and cuprammonium rayon are studied by a refined broad‐line proton NMR analysis of samples swollen with deuterated dimethyl sulfoxide, which has no effect on the spectra but enhances differences in molecular mobility between crystalline and noncrystalline regions. The spectra obtained are decomposed into four components: broad, medium, narrow, and extremely narrow. These components are identified as contributions, respectively, from crystalline and rigid noncrystalline (frozen glassy) material, a noncrystalline glassy component exhibiting local segmental motion, a noncrystalline rubbery component exhibiting liquidlike molecular motion, and protons included in DMSO‐d6 as an impurity. The mass fraction of the narrow component in cotton was about 0.01, whereas it was as high as 0.18 in cuprammonium rayon. It is concluded that even in the swollen state, native cellulose is devoid of a liquidlike mobile component, but regenerated cellulose contains a considerable amount of a noncrystalline component involving liquidlike segmental motion of molecules.

13C Nuclear Magnetic Relaxation of Poly(D-glutamic acid) in Aqueous Solution

The molecular conformation and dynamics of poly(D-glutamic acid) in aqueous solution were studied by 13C nuclear magnetic resonance spectroscopy. Chemical shift, spin—lattice relaxation time (T1), spin—spin relaxation time (T2), and the nuclear Overhauser enhancement (NOE) were measured as functions of pH at 300 K. Increasing pH resulted in upfield shifts of Cα and peptide C′ carbons, reflecting the helix-to-coil transition and downfield shifts of Cβ, Cγ, and Cδ carbons, reflecting the ionization of the side-chain carboxyl group. T1 T2, and NOE increased with increasing pH. The effective reorientational correlation time (τeff) of Cα obtained from the combination of T1 and NOE was 2.8 nsec in the helix region. This indicates that τeff of Cα is determined by not only the overall motion of the molecule but also by appreciable local segmental motions of the backbone. When going to the coil, τeff of Cα decreases by a factor of 4.3 as a result of the onset of rapid segmental motion. There is a progressive increase in T1 values of the side-chain carbons as going away from the backbone, suggesting that the end of the side-chain undergoes more a rapid internal reorientation than the others even in the helix state. The peptide carbonyl carbons relaxes more slowly in D2O than in H2O, suggesting that the relaxation is contributed appreciably from the amide proton which is exchanged with deuterium in D2O solution.

Depolarized Rayleigh scattering of dilute polymer solutions

We have studied the time-correlation function associated with depolarized Rayleigh scattering in dilute polymer solution starting from a general expression, we have reduced the time-correlation function of polarizability to two parts: one involving the overall rotation of the whole molecule and the other the local segmental motion modulated by overall rotation. The time-correlation function for segmental motion is expressed in terms of reorientation of chain segments through angles of arbitrary size.

Ultrasonic Absorption of Polycarbonate in Dioxane and in Chloroform

Measurements of ultrasonic absorption were carried out for polycarbonate in dioxane and in chloroform at frequencies from 1 to 130 MHz over a temperature range of 10 to 55°C. The molecular weight of the sample was about 4.0×104. In both systems double relaxation processes were observed. For the first relaxation process (at a lower frequency) the relaxation frequencies of polycarbonate in solutions do not differ very much from those of vinyl-type polymers in spite of structural differences in the backbone chains. The first relaxation process is attributed to the local segmental motions concerned with several monomer units or more. The second relaxation process (at a higher frequency) in solutions of polycarbonate and of vinyl-type polymers are strongly affected by solvents.

A theoretical study of the depolarized Rayleigh scattering time-correlation function of a dilute polymer solution

The depolarized Rayleigh spectra of macromolecules in solution have been studied theoretically. From a general expression of the time-correlation function, two correlation functions respectively related to molecular rotation and local segmental motion are obtained in a natural way. Previous work has not demonstrated this connection. The result of the present analysis is valuable in the interpretation of the experimentally observed spectra of polymers in solution.

Mechanical properties of biaxially oriented poly(vinyl chloride)

AbstractThis report describes the influence, of (a) degree of biaxial orientation, (b) stretching rate, and (c) stretching temperature on the tensile, dynamic mechanical and dielectric properties of non‐impact modified PVC. A new parameter designated “planar strain” is used to correlate anisotropic property values with both equal and unequal biaxial stretching in a single two‐dimensional plot, thereby providing a direct comparison of the effects of two or more biaxial stretching ratios. It is shown that optimum stretching conditions depend to some extent upon end use and that a 2 × 2 stretch ratio is optimum for impact resistance. The actual property/processing condition relationships exhibit very complicated interactions and are correlated empirically in this study. The dynamic measurements suggest that overall local segmental beta motion is increased after orientation but that the relative chain alignment makes it more difficult to activate this motion.

Origin of impact strength in polycarbonate. III. Effect of liquids and orientation

Abstract The effects of Arochlor 5442 (a chlorinated terphenyl) dibutyl phthalate, butyl stearate, a high molecular weight polyester plasticizer, acetone, methyl ethyl ketone, isopropyl alcohol, carbon tetrachloride, and water on the dynamic mechanical properties of polycarbonate have been studied. Results show that all liquids except water and carbon tetrachloride suppress the low-temperature β-transition loss peak and shift the temperature of maximum loss to lower temperatures. Water causes the β loss peak to broaden and be more asymmetrical. Nonpolar carbon tetrachloride causes a splitting of the β loss peak which may indicate a selective suppression of local segmental motions in nonpolar regions of the polymer. Polycarbonate liquid blends may also exhibit additional loss peaks at temperatures above or below the β loss peak. Volume losses are observed for all blends whose specific volume has been measured. Electron microscopy of etched polycarbonate blends indicates 600 to 1100 Å structures exist in brittle polycarbonate blends with Arochlor 5442 whereas a 300-Å structure exists in ductile blends with dibutyl phthalate or unmodified polycarbonate. Tensile property measurements demonstrate that absorbed liquids do not embrittle glassy polycarbonate though largely reducing yield strain. Orientation decreases specific volume and produces only slight changes in shape and intensity of the low temperature β-transition loss peak. The major effect of orientation is to enhance “intermediate” loss processes at 80 and 120°C in glassy polycarbonate. The β-transition appears isotropic; however, the intermediate loss process at 80°C is anisotropic. These results tend to question previously suggested correlations between high-impact strength and the low-temperatureβ-transition or free volume. It is suggested that the impact strength of polycarbonate at 23°C may be associated with loss processes at higher temperatures. This association is supported by a comparison of activation energies for yielding with activation energies for transitions due to molecular motion.

Mechanism of yielding and cold flow in glassy polymers

Abstract Tensile and compressive yield stress as well as tensile and compressive flow stress are determined as functions of strain rate, temperature, and thermal history for atactic polystyrene, isotactic polystyrene, polycarbonate, and poly-(methyl methacrylate). An Eyring-type activated flow analysis is employed to calculate both activation energy and shear activation volume over the range of experimental conditions studied, and the results are interpreted in terms of a two-phase amorphous microstructure consisting of both ordered and disordered regions. Similar values for yielding activation energies and activation energies obtained from dynamic mechanical analysis suggest that at temperatures well below Tg, yielding is controlled by cooperative local segmental motion. With increasing temperature, increasing degrees of local segmental motion are involved. Only when the test temperature approaches Tg does a transition to cooperative long-chain motion occur. Equivalent values for shear activation volume ...