Local Segmental Motion Research Articles

Normal Functional Local Alignment and Segmental Motion at the Thoracolumbar Junction: A Cross-Sectional Study of Healthy Subjects

Several studies have investigated the mechanical behavior of the thoracolumbar spine. However, finding an accurate reference for the normal functional local alignment and segmental motion (SM) at the thoracolumbar junction (TLJ) is challenging. Therefore, this study aimed to assess age- and sex-related changes and differences in local alignment and SM at the TLJ. The study recruited healthy subjects aged 20 to 79 without complaints of back pain. Healthy subjects (60 males and 60 females) with appropriate imaging results were enrolled in the study. The subjects were divided into age groups (20-29, 30-39, 40-49, 50-59, 60-69, and 70-79years); each group included 10 subjects of each sex. The SM at the TLJ was small but noticeable, and the motion gradually increased toward the lower level of the TLJ, closer to the lumbar region. No significant differences were observed between male and female subjects in any SM measurements at the TLJ. The SM at the TLJ gradually decreased with age, while local kyphosis of TLJ progressed. The results also showed that the thoracolumbar slope value did not change with age and remained at a mean of-12.8±7.2° (P=0.893). This study's results provide valuable guidance for appropriate surgical planning and rehabilitation of patients with spinal diseases or trauma. Furthermore, the results can be the basis for categorizing accurate criteria to evaluate the degree of disability after treatment.

Fast Motions Dominate Dynamics of Intrinsically Disordered Tau Protein at High Temperatures.

Reorientational dynamics of intrinsically disordered proteins (IDPs) contain multiple motions often clustered around three motional modes: ultrafast librational motions of amide groups, fast local backbone conformational fluctuations and slow chain segmental motions. This dynamic picture is mainly based on 15 N NMR relaxation studies of IDPs at relatively low temperatures where the amide-water proton exchange rates are sufficiently small. Less is known, however, about the dynamics of IDPs at more physiological temperatures. Here, we investigate protein dynamics in a 441-residue long IDP, tau protein, in the temperature range from 0-25 °C, using 15 N NMR relaxation rates and spectral density analysis. While at these temperatures relaxation rates are still better described in terms of amide group librational motions, local backbone dynamics and chain segmental motions, the temperature-dependent trend of spectral densities suggests that the timescales of fast backbone conformational fluctuations and slower chain segmental motions might become inseparable at higher temperatures. Our data demonstrate the remarkable dynamic plasticity of this prototypical IDP and highlight the need for dynamic studies of IDPs at multiple temperatures.

Relaxation modes of metaphosphate glasses with entropic shrinkage

We have reconfirmed the anomalistic reversible strain (shrinkage) after tensile creep in the specific metaphosphate glass melts with entropic elasticity in a wide range of applied stresses. We attempted to elucidate the origin of the anomalistic shrinkage by focusing on the relaxation modes. The fast mode was identified for all glasses by two different measurements, i.e., the dynamic viscoelasticity in the linear range and the creep recovery in the non-linear range. In contrast, the slow mode in addition to the fast mode was confirmed only for the glasses showing the anomalistic shrinkage. The slow mode induced the essential shrinkage at whole tensile stresses, whereas the fast mode, especially at higher tensile stresses, contributed to the moderate shrinkage. As the most likely mechanism in the linear range, the local segmental motion with mobile cation motion and the large-scale relaxation of the connected molecules through scission and renewal of the bond between alkali cations and the oxygen anion were assigned to the fast and the slow modes, respectively. In the non-linear range, the dimensionless strain-rate dependence of the reversible strains for both modes had a similar characteristic to that of the viscosity.

Disentangling proton-transfer and segmental motion relaxations in poly-vinyl-alcohol aqueous solutions by means of ultrasonic relaxation spectroscopy

A detailed temperature- and concentration-dependent ultrasonic relaxation study has been conducted in aqueous polyvinyl alcohol (PVA) solutions as a function of frequency under isobaric conditions. Concentration and temperature have similar effect on acoustic spectra. Two well-resolved relaxation processes were observed in the experimental acoustic spectra that seem to follow a Cole-Cole distribution function. The systematic analysis of the variation of the acoustic parameters with frequency, temperature and concentration revealed that both processes have collective and not local nature. The low-frequency relaxation mechanism is assigned to segmental motions of the polymer chains and the high-frequency relaxation to proton-transfer reaction, respectively. The characteristic relaxation frequencies were found independent of molecular weight, as expected for relative flexible vinyl-polymer chains with molecular weight above ~104. Based on Eyring's theory, the activation enthalpy of the low- and high-frequency relaxation were estimated equal to ΔΗ1* = 4.5 ± 0.2 kcal/mol and ΔΗ2* = 19.7 ± 0.8 kcal/mol, respectively. The contribution of the low-frequency lying normal mode relaxation has been quantitatively estimated in the context of relevant theories of the field and found almost four order of magnitude lower in amplitude compared to segmental motion process indicating that the experimentally detected relaxation is dominated by the latter. The experimental results were complemented with molecular mechanics calculations performed in parallel. The comparison between the experimental data and the outcome of the theoretical calculations evidenced that the length of the relaxing element in a PVA polymer chain is between 5 and 8 monomers in agreement with what is expected for vinyl-polymers and established the local segmental motions of the PVA polymer chains in the solution.

Characterization of Dielectric Relaxation Process by Impedance Spectroscopy for Polymers: Nitrile Butadiene Rubber and Ethylene Propylene Diene Monomer

We invented a dispersion analysis program that analyzes the relaxation processes from dielectric permittivity based on a combination of the Havriliak–Negami and conductivity contribution functions. By applying the created program to polymers such as nitrile butadiene rubber (NBR) and ethylene propylene diene monomer (EPDM), several relaxation processes were characterized: an α process due to segmental motions of the C-C bond, an α′ process attributed to fluctuations in the end-to-end dipole vector of the polymer chain, the conduction contribution by the filler observed above room temperature, and secondary relaxation processes β and γ of motion for the side group in NBR. In the EPDM specimen, the β process associated with the rotational motion of the side groups, the α process associated with the relaxation of local segmental motion, and the αβ process associated with the origin of the β process at high temperatures above 305 K were observed. The Maxwell–Wagner–Sillars effect and conduction contribution were also presented. The molecular chains responsible for the relaxation processes were assigned by building molecular models of the two polymers. The temperature dependence of the relaxation strength and the shape parameters that characterize the process were investigated. From the temperature-dependent relaxation analysis, the merged αβ process, activation energy, and glass transition temperature were determined and compared.

Homogenously dispersed ultrasmall niobium(V) oxide nanoparticles enabling improved ionic conductivity and interfacial compatibility of composite polymer electrolyte

Composite polymer electrolytes (CPEs) decorated with ceramic fillers have emerged as appealing structures that exhibit coalesced merits of both inorganic and polymer solid electrolytes, but are currently challenged by the particle agglomeration that weakens ionic conductivity and electrochemical performances. Herein, a facile solvothermal method is proposed to fabricate the ultrasmall niobium(V) oxide (Nb2O5) nanoparticle of average size being less than 3 nm, enabling the composite polymer electrolyte with homogenous dispersity (nano-CPE). Owning to the superior dispersity of ultrasmall Nb2O5 nanoparticles, the polymer chains can be effectively disordered to enhance the local segmental motion through the physical interruption. Moreover, strong Lewis acid-based interactions between Nb2O5 nanoparticles and lithium salts are formed, resulting in accelerating the dissociation of lithium salt and releasing more free charge carriers. Therefore, the 3D connected Li+ fast pathways along the amorphous region between the Nb2O5 nanoparticles and polymer chains are constructed, ensuring the improved ionic conductivity. In addition, the homogenous Li deposition can also be simultaneously achieved through the intimate interfacial contact, which can efficiently suppress the growth of lithium dendrite in the metal anode. The fabricated nano-CPE presents a high ionic conductivity of 6.6 × 10−5 S/cm at room temperature and wide anti-oxidative potential of 5.1 V. The lithium symmetric battery using nano-CPE delivers a decent lithium plating/stripping performance for 200 h at 0.5 mA/cm2. The solid-sate LiFePO4 battery achieves long stable cycling performances (151mAh/g and 140 mAh/g after 230 cycles at 0.5C and 1.0C, respectively). This work may offer a facile and efficient synthesized method of highly dispersed ultrasmall nanoparticles for advancing the CPE with improved ionic conductivity, interfacial contact and cell performances.

Non-Debye segmental relaxation of poly-N-vinyl-carbazole in dilute solution

Ultrasonic absorption measurements were carried out for poly-N-vinyl-carbazole in dilute 1,2-dichloro-ethane solution at frequencies from 1 to 50 MHz over a temperature range of 10–45°C with increments of 5°C under constant pressure. For the specific solution a single relaxation process was observed experimentally in the frequency range studied. The relaxation frequency of poly-N-vinyl-carbazole in 1,2-dichloro-ethane solution is comparable to the relaxation frequency observed in vinyl-type polymers despite the structural differences and the corresponding relaxation process is thermal in nature and assigned to the local segmental motions of some monomeric units. From the temperature dependence of the acoustic parameters we were able to estimate the thermodynamic parameters related to the segmental motion of the PVK polymer chains in solution. Furthermore, we performed molecular mechanics calculations on polymeric chains with a relatively low number of monomers to elucidate the mechanism behind the relaxation process and to establish the suggested local segmental motions of the polymer in 1,2-dichloro-ethane solution. The experimental and theoretical results have been compared and discussed in the context of relevant theories of the field.

Recent advances in the physics of polymer systems

Recent advances in the physics of polymer systems

Change in dielectric relaxation with the presence of water in highly filled composites

It is important to determine the dielectric characteristics of semiconductor encapsulation materials based on epoxy resins. We employed the dielectric spectroscopy technique to investigate the dielectric relaxation in the presence of water and how it changes the relaxation. It was observed that the dielectric relaxation of the material was significantly influenced by absorbed water, the local segmental motion (also known as Johari–Goldstein ([Formula: see text]) relaxation) was influenced most by the presence of the water, it was modified by the wet sample compared to dry one, and required high activation energy. The relaxation related to the glass transition was contributed by the cooperative motion (the [Formula: see text]-relaxation) of the epoxy resin system. The [Formula: see text]-relaxation was shifted to a low temperature in the wet sample compared to dry one. The relaxation was modeled with a clear Vogel–Fulcher–Tammann–Hesse (VFTH) behavior; the Vogel temperature of the wet sample was 8[Formula: see text]K lower than the dry sample. The presence of water acts as a plasticizer for the molecular relaxation, and speed-up the cooperative process. The measured data were also used to estimate the electrical properties of the resin system by employing an effective-medium model together with a porous media continuum model by taking into account the physical properties of the system. It is already known that the influence of water in semiconductor packaging is important in sensitive applications. The presented measurements and the analysis method would be appreciated within the semiconductor packaging community to improve material selection and performance evaluation efforts.

Macromolecule and Particle Dynamics in Confined Media

Dynamic properties play an important role in designing functional polymer nanocomposites, impacting molecular transport and phase separation kinetics. When nanoparticle (NP) size is comparable to polymer chain size, segmental relaxations may be influenced by changes in chain conformations and packing at the polymer/NP interface. Following the reptation model, these changes can perturb the longest relaxation time, in particular, the center-of-mass (COM) dynamics of polymer chains in entangled melts. This Perspective focuses on unsolved issues in polymer COM diffusion and local dynamics and segmental motions in the presence of NPs. The article introduces the effect of NP size, shape, surface modification, and enthalpic interactions on polymer diffusion and further relates dynamic studies in PNCs to macromolecular transport in bio-related systems and nanopores. Studies of local dynamics also provide insights into how entanglement density, monomeric friction, and chain conformation are influenced by NPs and h...

Modeling and fundamental aspects of structural relaxation in high-solid hydrocolloid systems

The structural relaxation properties of high-solid gelling polysaccharides, gelatin and whey protein with small-molecule co-solute have been reviewed focusing on the glass transition region and glassy state of the mechanical master curve. Compliance with the principle of thermorheological simplicity is established allowing horizontal superposition of viscoelastic functions in the form of small-deformation stress relaxation or dynamic oscillation modulus. Numerical calculations via the Tikhonov regularization yield smooth stress relaxation spectra over a broad timescale that encompasses the isothermal process of vitrification in these systems. Next, the molecular coupling theory addressed the polymer chain dynamics of the local segmental motions that determine the glass transition temperature (Tg) of condensed matrices. Thus a more complete picture of the physics of intermolecular interactions in the short-time region of the glass dispersion has emerged. It allows estimation of the relaxation time for local segmental motions at Tg, and the extent of cooperativity between adjacent chemical moieties governing kinetics of viscoelastic relaxation in hydrocolloid based systems at the glass transition region.

Properties of PVDF-MCM41 Nanocomposites Studied by Dielectric, Raman and NMR Spectroscopy

To obtain information on the polymer-inorganic filler interactions and on the confinement effect of polymer chains we studied the properties of solution-cast poly(vinylidene fluoride)-MCM41 molecular sieve nanocomposites. The dielectric response of the nanocomposites was found to be determined generally by the response of the polymer matrix, whereas the polymer-filler interactions resulted in an increase of the relaxation rates of the local mode and segmental motions in the amorphous phase of the poly(vinylidene fluoride) matrix. The effect has been related to a reduction of intermolecular correlations between the segments and was confirmed by the dispersion of 1H spin-lattice relaxation times in PVDF-MCM41 composites. Moreover, the relaxometry experiments have shown that the dynamics of poly(vinylidene fluoride) chains confined to MCM41 molecular sieve channels can be described by tube/reptation model proposed by De Gennes, Doi and Edwards.

Multilayered damping composites with damping layer/constraining layer prepared by a novel method

The alternating multilayered damping composites, chlorinated butyl rubber (CIIR) as damping layer and polymethyl methacrylate (PMMA) as constraining layer, were first prepared through novel multilayered co-extrusion. The damping properties of the CIIR/PMMA multilayered damping composites were investigated by dynamic mechanical analysis (DMA). The results showed that the damping peak moved to high temperature and the efficient damping temperature range was broaden with the layer number increasing. The shift of the loss peak was ascribed to the move of Rouse mode of CIIR, which was attributed to the motion of longer chain segment, but the local segmental motion was not changed. Finite element analysis (FEA) was used to simulate the distribution of shear strain in the multilayered damping composites. The FEA results exhibited that, in the temperature range between Tg-CIIR and Tg-PMMA, the shear strain occurred in the CIIR layer under vibration field, since the storage modulus ( E ′) of PMMA was much higher than that of CIIR. Furthermore, the average shear strain was increased with the layer number increasing.

The molecular dynamics of different relaxation modes in asymmetric chlorinated butyl rubber/petroleum resin blends

The PR plays a role like an anti-plasticizer in decreasing the free volume fraction of the CIIR/PR blend. The mobility of Rouse modes is confined significantly more than that of local segmental motion.

The proper glass transition temperature of amorphous polymers on dynamic mechanical spectra

Glass transition is crucial to the thermal and dynamical properties of polymers. Thus, it is important to detect glass transition temperature (T g) with a sensitive and proper method. Dynamic mechanical analysis (DMA) is one of the most frequently used methods to determine T g due to its advantage of high sensibility. However, there is controversy in the past literatures to determine the proper glass transition temperature among three transition temperatures, i.e., T g1, T g2 and T g3 in the dynamic mechanical spectra, which correspond to the temperature abscissa of intersect value of two tangent lines on storage modulus (E′), the peak of the loss modulus (E″) and the peak of the loss tangent (tan δ). In this work, these three transition temperatures were compared with the glass transition temperature determined by DSC (T gDSC). Based on the discussion of different modes of molecular motion around the glass transition region, it is demonstrated that T g1 and T g2 have the same molecular mechanism as T gDSC, i.e., local segmental motion which is enthalpic in nature and determines the proper glass transition temperature, while T g3 is assigned to the transition temperature of entropic Rouse modes, thus cannot be used as the proper glass transition temperature.

Li+Transport in Poly(Ethylene Oxide) Based Electrolytes: Neutron Scattering, Dielectric Spectroscopy, and Molecular Dynamics Simulations

The dynamics of Li(+) transport in polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imde mixtures are investigated by combining neutron spin-echo (NSE) and dielectric spectroscopy with molecular dynamics (MD) simulations. The results are summarized in a relaxation time map covering wide ranges of temperature and time. The temperature dependence of the dc conductivity and the dielectric α relaxation time is found to be identical, indicating a strong coupling between both. The relaxation times obtained from the NSE measurements at 0.05 Å(-1)<q<0.2 Å(-1) are of similar magnitude as the relaxation time of Li(+) predicted by MD simulation. Our results suggest that the characteristic live times of the ions within the oxygen cages are mainly determined by the α relaxation that corresponds to local segmental motions of polymers, to a much lesser extent by the main chain relaxation, and not at all by the β relaxation or other faster processes. It is the first time decisive experimental evidence for a microscopic picture of the Li ion transportation process is shown in which the PEO chain forms EO cages over several monomer units and the Li ion "jump" from cage to cage. The role of the backbone of the polymer is discussed and contributes signifcantly to the Li ion transportation process. Moreover, detailed characteristic length and time scales of the Li(+) transport process in this polymer electrolyte are identified and interpreted.

Morphology, Dielectric and Thermal Properties of Poly(sulfobutylbetaine)/Montmorillonite (PMBS‐4/MMT) Nanocomposites as Solid Polymer Electrolytes

AbstractPolymeric electrolyte composites based on polymer poly(sulfobutylbetaines) (PMBS‐4) and 1%, 3% and 5% montmorillonite (MMT) modified with organic ions, dodecyldimethyl(3‐sulfo‐propyl) ammonium hydroxide (C12SB) were synthesized. The structural modification and electrochemical properties of samples were investigated to understand the effects of organic MMT in a polymer matrix on ionic conductivity. The modification of the clay with organic ions resulted in a larger d‐spacing which makes easier the penetration of PMBS‐4 into the interlayer galleries. The values of Tg obtained from differential scanning calorimetry are 18 °C, 20 °C, 20 °C and 27 °C for PMBS‐4, PMBS‐4/C12SB‐MMT 1%, PMBS‐4/C12SB‐MMT 3% and PMBS‐4/C12SB‐MMT 5% respectively. Since PMBS‐4 and PMBS/C12SB‐MMT were examined in the absence of Li salt, the conductivity of samples was attributed to the motion of dipoles in chains of zwitterionic PMBS‐4. The increase in conductivity with increasing temperature was explained as a local structural relaxation and segmental motion of polymer. The values of σ, at 25 °C, for: PMBS‐4, PMBS‐4/C12SB‐MMT 1%, PMBS‐4/C12SB‐MMT 3% and PMBS‐4/C12SB‐MMT 5% were 6.2 × 10−6 S/cm, 1.2 × 10−6 S/cm, 1.7 × 10−6 S/cm and 9.1 × 10−6 S/cm respectively.

A Model for Aging

Materials Science When cooled below the glass transition temperature, amorphous polymers show a sudden and rapid increase in viscosity, which macroscopically manifests as a hardening or solidifying of the material. Nonetheless, even at these temperatures, local segmental motion is possible, and the

Mechanical Relaxation Studies of Sub-Rouse Modes in Amorphous Polymers

Mechanical spectroscopy is a powerful tool for the investigation of molecular dynamics of amorphous polymers over a large temperature range and frequency scale. In this work, by using high precision shear mechanical spectroscopy tool, we have investigated the segmental dynamics from local segmental relaxation to sub-Rouse modes in a series of amorphous polymers. We have demonstrated the existence of sub-Rouse modes slower than the local segmental motion in amorphous polymers. The sub-Rouse modes exhibit a similar change of dynamics at the same temperature TB ~1.2 Tg, as the local segmental relaxation through the temperature dependence of relaxation time and relaxation strength. Furthermore, the crossover relaxation time of the sub-Rouse modes at TB is almost the same for all the polymers investigated, i.e. τα'(TB) = 10-1±0.5 s, which is independent of molecular weight and molecular structure. This remarkable finding indicates that solely the time scale of the relaxation determines the change in dynamics of the sub-Rouse modes. According to the coupling model, the crossover is suggested to be caused by the onset of strong intermolecular cooperativity below TB. Hence the results suggest that the sub-Rouse modes and their properties are generally found in amorphous polymers by mechanical spectroscopy, and reveal the cooperative nature of the sub-Rouse modes.

Atomistic molecular dynamics study of cross-linked phenolic resins

In this study, we analyzed cross-linked phenolic resins by using atomistic molecular dynamics simulations. Cross-linked structures consisting of a network of three functional phenols and two functional methylenes with degrees of cross-linking of 0.70, 0.82, and 0.92 were prepared by cross-linking reactions of linear novolac-type phenolic resins in a unit cell under three-dimensional periodic boundary conditions. Uniaxial elongations of the cross-linked structures to a strain of 0.03 were performed at 300 K. At this temperature, all structures were apparently in a glassy state, which was confirmed by the analysis of specific volume as a function of the temperature. The uniaxial elongation did not cause a significant change in the distribution of bonding potential energies (i.e., bond stretching, angle bending, and torsion angle potentials). On the other hand, the change in the potential energies owing to the uniaxial elongation indicated that cross-links suppressed local segmental motions in the cross-linked structure, probably at the region around the linear and terminal phenols, which resulted in an increase in the degree of cross-linking accompanied by a decrease in Poisson's ratio and an increase in Young's modulus.