Relaxation Behavior Of Poly Research Articles

Relaxation behavior of poly(diisopropyl fumarate) including no methylene spacer in the main chain

Poly(diisopropyl fumarate) (PDiPF) has dynamic mechanical properties different from the relaxation processes of conventional vinyl polymers, due to the absence of a methylene spacer in the main chain. In this study, we investigated the relaxation behavior of PDiPF using dielectric spectroscopy (DS), differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS), and dynamic mechanical analysis (DMA). We have demonstrated that the β relaxation of PDiPF has unusual characteristics originating from the absence of a methylene spacer; for example, the β relaxation of PDiPF follows the Vogel–Fulcher–Tammann (VFT) equation, causes a clear step in the DSC curve, and enhances the microscopic packing of the polymer chains in the solid state. These β relaxation behaviors of PDiPF reflect the enlarged cooperative rearranging region (CRR).

Relaxations and Relaxor-Ferroelectric-Like Response of Nanotubularly Confined Poly(vinylidene fluoride)

Herein, we elucidate the impact of tubular confinement on the structure and relaxation behavior of poly(vinylidene difluoride) (PVDF) and how these affect the para-/ferroelectric behavior of this polymer. We use PVDF nanotubes that were solidified in anodic aluminum oxide (AAO) templates. Dielectric spectroscopy measurements evidence a bimodal relaxation process for PVDF nanotubes: besides the bulk-like α-relaxation, we detect a notably slower relaxation that is associated with the PVDF regions of restricted dynamics at the interface with the AAO pore. Strikingly, both the bulk-like and the interfacial relaxation tend to become temperature independent as the temperature increases, a behavior that has been observed before in inorganic relaxor ferroelectrics. In line with this, we observe that the real part of the dielectric permittivity of the PVDF nanotubes exhibits a broad maximum when plotted against the temperature, which is, again, a typical feature of relaxor ferroelectrics. As such, we propose that,...

Relaxation behavior of poly(trimethylene 2,6-naphthalate) in nanoclay confinement

The relaxation behavior of poly(trimethylene 2,6-naphthalate)/nanoclay composites is investigated using differential scanning calorimetry (DSC) and dynamic mechanical analyzer (DMA). The incorporation of two different types of nanoclays in the PTN matrix intercalated the PTN chains in the narrow space of clay intergalleries and constrained the polymer chains in the vicinity of nanoclay layers. Despite the presence of constrained region, the glass transition temperature of the PTN/nanoclay composite is decreased as compared to neat PTN. Moreover, the activation energy of the PTN is reduced and the relaxation rate of PTN becomes faster in the presence of nanoclays. The enhanced relaxation dynamics of PTN chains at Tg depends on the evolution of local free volume owing to the confining effect of chain intercalation.

Relaxation behavior of poly(lactic acid)/poly(butylene succinate) blend and a new method for calculating its interfacial tension

AbstractThe biomass‐based blend of 80/20 (w/w) poly(lactic acid)/poly(butylene succinate) (PLA/PBS) is prepared using an extruder. The prepared blend shows a typical droplet‐matrix morphology. The relaxation behavior of the blend is investigated in terms of storage modulus, loss tangent, and Cole–Cole plots. In the low frequency region, the blend exhibits higher elastic indices than the pure components on the storage modulus and loss tangent curves, and remarkable deviation from a semicircular shape on the Cole–Cole plot. These features are thought to arise from the relaxation of the deformed droplets. The loss tangent curve is more sensitive to the relaxation behavior of the deformed droplets than the storage modulus curve. Moreover, the complex viscosity of the blend is separated into real and imaginary parts to further analyze its relaxation behavior. Three relaxation times for the blend are defined on the curve of the imaginary part of the viscosity. It is demonstrated that the reciprocal of the frequency corresponding to the peak in the low frequency region on the imaginary part curve is equal to the longest relaxation time of the blend obtained from the storage modulus curve. Based on this result, a new method is proposed to calculate the interfacial tension between the PLA and PBS in the blend, which is 3.7 mN/m. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effect of Alkyl Side Chain Length on Relaxation Behaviors in Poly(n-alkyl Acrylates) and Poly(n-alkyl Methacrylates)

Dynamic mechanical analysis (DMA) is used to investigate the effect of alkyl side chain length on the relaxation behavior of poly(n-alkyl acrylates) (PnAA) and poly(n-alkyl methacrylates) (PnAMA) above the glass transition temperature (Tg). Master curves and shift factors (log aT) were obtained using the time–temperature superposition (TTS) principle. The log aT curves of PnAA and PnAMA exhibit a dynamic crossover from one Vogel–Fulcher–Tammann–Hesse (VFTH) equation to another above Tg. The corresponding temperature was designated as the dynamic crossover temperature (Tc). It is found that Tc/Tg and the apparent activation energy (Eg) increases, e whereas the fragility index (m) decreases with increasing alkyl side chain length. Further analysis shows that m ∝ Tg, Eg∝ , and Eg∝ m2 for both PnAA and PnAMA.

Relaxation Behavior of Poly(methyl methacrylate) at a Water Interface

The relaxation behavior of poly(methyl methacrylate) (PMMA), spin-coated on a silicon wafer, at the water interface was examined by lateral force microscopy as a function of temperature and scanning rate. Even in water, the lateral force peak which was assigned to the segmental motion of PMMA plasticized by water molecules was clearly observed in the temperature domain. The apparent activation energy for the plasticized alpha(a)-relaxation process was much smaller than those for the original alpha(a)-relaxation processes at the intact surface and in the bulk. The depth profile of the glass transition temperature (T(g)) of the PMMA film in water was obtained, showing that T(g) decreases with proximity to the water phase. The T(g) depression observed here was best explained in terms of the water content of the film, rather than a confinement effect.

Effect of confinement on the relaxation behavior of poly(ethylene oxide)

It is widely thought that confinement of an amorphous polymer alters the chain mobility, which affects the temperature and intensity of the glass transition. The present study sought to determine whether the same effects extend to semicrystalline polymers. Confinement was achieved by forced assembly of hundreds of alternating layers of poly(ethylene oxide) (PEO) with either poly(ethylene- co-acrylic acid) or polystyrene. The confinement gradually reduced the intensity of the PEO β-relaxation as the layer thickness decreased from the microscale to the nanoscale. By considering the changes in crystalline morphology that accompanied layer confinement, it was possible to completely account for the reduction in relaxation intensity using standard mechanical models. The viscoelastic behavior of the amorphous phase was satisfactorily represented by a modified standard linear solid (SLS). The amorphous and crystalline contributions were combined using a combination of parallel and series coupling in accordance with the Takayanagi model. No adjustment in the viscoelastic parameters of the modified SLS was required, indicating that there was no significant change in amorphous chain dynamics even in layers as thin as 45 nm.

Effect of nanoclay on relaxation of poly(vinylidene fluoride) nanocomposites

AbstractThe effect of Lucentite™ STN nanoclay on the relaxation behavior of poly(vinylidene fluoride) (PVDF) nanocomposites was investigated using dielectric relaxation spectroscopy (DRS) and wide‐ and small‐angle X‐ray scattering. Lucentite™ STN is a synthetic nanoclay based on hectorite structure containing an organic modifier between the hectorite layers. The addition of this nanoclay to PVDF results in preferential formation of the beta‐crystallographic phase. When the STN content increased to 5% and 10%, only the beta‐phase was observed. Bragg long period and lamellar thickness both decrease with STN addition. The relaxation rates for processes termedαa(glass transition, related to polymer chain motions in the amorphous regions) andαc(related to polymer chain motions in the crystalline regions and fold surfaces) can be described either with the Vogel‐Fulcher‐Tamman equation or with Arrhenius behavior, respectively. DRS shows that theαarelaxation rate increases with the concentration of STN because of the reduction of intermolecular correlations between the polymer chains, caused by the presence of layered silicate nanoclay particles, which serve to segregate polymer chains in the amorphous regions. Comparing samples with beta‐crystal phase dominant, the relaxation rate for theαcrelaxation also increases with concentration of STN in all nanocomposite samples. Dielectric properties at low frequencies are dominated by the dc conductivity, and as more STN is added, the conductivity increases rapidly. The addition of 10% STN makes the dc conductivity increase by almost four decades when compared with neat PVDF. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2520–2532, 2009

Insight into reverse selectivity and relaxation behavior of poly[1-(trimethylsilyl)-1-propyne] by flux-lateral force and intrinsic friction microscopy

Novel scanning force microscopy techniques (SFM) were employed to investigate poly[l-(trimethylsilyl)-1-propyne] (PTMSP), a high-free volume, highly permeable reverse-selective membrane material. This study reports, for the first time, reverse selectivity in relation to the interfacial gas adsorption capacity of the PTMSP membrane with the gas permeants CO 2 and helium. With flux-lateral force microscopy (F-LFM), mechanical property changes caused by permeant gas infiltration were recorded within the polymer interfacial downstream region. In conjunction with bulk permeation measurements and varying sequential exposure to the two permeants, CO 2 is found to saturate the membrane faster, i.e. at a lower differential pressure by about 0.3 bar, in comparison to helium. It is also identified as modifying agent for PTSMP causing a significant change in the mechanical properties of the polymer matrix, which consequentially leads to a considerable helium transport reduction, and thus, an increase in reverse selectivity from 1.2 to 4.7. Also in this study, thermally available activation modes of 6–8 kcal/mol were revealed by intrinsic friction analysis (IFA) that were attributed to backbone methyl-group rotations in accordance with conformational calculations. Bulk thermally activated modes were found to be modestly affected by interfacial constraints on the sub-100 nanometer scale, which is an important finding for interpreting interfacial constraints in PTMSP nanocomposites involving silicon-oxides.

Effects of quenching and physical aging on the relaxation behavior of nanophase-separated side chain polymers

The influence of quenching and physical aging on the relaxation behavior of poly(nalkyl methacrylates) with long alkyl groups in the side chain is studied by dielectric spectroscopy. Typical for these side chain polymers is a nanophase separation of incompatible main and side chain parts and the existence of alkyl nanodomains with a typical dimension of 0.5-1.5nm. In larger alkyl nanodomains a polyethylene-like glass transition αPE occurs at temperatures below the conventional a relaxation. For quenched samples additional peaks on the high frequency wing of this aPE process have been detected in a similar frequency-temperature range where the Arrhenius-like βPE process is observed for slowly cooled side chain polymers with short alkyl groups and small alkyl nanodomains. This is interpreted as an amplification of the localized dynamics in the alkyl nanodomains and related to the production of additional free volume in quenched samples which disappears during physical aging slightly below Tg(α). Similarities to the aging behavior of conventional glasses and the importance of non-equilibrium effects for the properties of nano-structured materials in the glassy state are discussed.

Influence of the Fine Structure on the Response of Polymer Chains to Perturbation Fields

The relaxation behavior of poly(3-methylbenzyl methacrylate), poly(3-fluorobenzyl methacrylate), and poly(3-chlorobenzyl methacrylate) was thoroughly studied by broadband dielectric spectroscopy with the aim of investigating the influence of slight differences in chemical structure on the response of polymers to electric perturbation fields. Retardation spectra calculated from dielectric isotherms utilizing linear programming regularization parameter techniques were used to facilitate the deconvolution of strongly overlapped absorptions. Above the glass transition temperature, the spectra of the two halogenated polymers present a secondary γ process well separated from a prominent peak resulting from the overlapping of the α and β relaxations. The spectra of poly(3-methylbenzyl methacrylate) exhibit at long times a well-developed α absorption followed in decreasing order of time by two weak absorptions, named β and γ, whose intensities increase with temperature. The temperature dependence of the distance of the α peak from the β and γ peaks, expressed in terms of log(fmax,β/fmax,α) and log(fmax,γ/fmax,α), respectively, is studied. The Williams ansatz and the extended ansatz give a fairly good account of the relaxation behavior of the polymers. The stretch exponent associated with the α relaxation increases with temperature from ca. 0.2 at low temperatures to the vicinity of 0.5 at high temperatures. At low temperatures, the α relaxation is described by a Vogel-type equation, but at high temperature the β and α processes are roughly described by the same Arrhenius equation. In the whole temperature range, the activation energy o the γ relaxation is significantly lower than that of the β absorption. The mechanisms involved in the development of the secondary relaxations are qualitatively discussed.

Chain Dynamics of Polymers with Highly Flexible Side Groups

AbstractSummary: The relaxation behaviour of poly(5‐acryloxy‐5‐methyl‐2,3‐dioxacyclohexne), poly(2,3‐dichlorobenzyl methacrylate) and poly(3‐chlorobenzyl methacrylate) was thoroughly studied by broadband dielectric spectroscopy with the aim of investigating how the chemical structure affects the response of polymers to electric perturbation fields over a wide temperature window. Retardation spectra calculated from dielectric isotherms utilizing linear programming regularization parameter techniques were used to deconvolute strongly overlapped absorptions. Special attention is paid to both the splitting region and the fitting of the Williams ansatz to the experimental results. Attempts are made to explain the molecular origin of the relaxations observed in the retardation spectra of the polymers.

Alpha Relaxation Study of Poly(Vinyl Chloride Co-Vinylacetate-Co-2-Hydroxypropyl Acrylate)

By using thermally stimulated depolarization current (TSDC) technique, and coupling it with the thermal sampling (TS) method, the relaxation behavior of Poly(vinyl chloride-co-vinylacetate-co-2-hydroxypropyl acrylate) (PVVH) has been investigated in the vicinity of its glass transition temperature, Tg. The global TSDC spectra of amorphous PVVH with varying the poling field and poling temperature revealed the presence of two TSDC peaks. The first peak at about 347 K and is ascribed to the glass transition temperature and can be referred as α-relaxation. The second one is obtained in the temperature range 353–383 K and is attributed to the space charge relaxation and can be referred as ρ-relaxation. Fine structure of α-relaxation peak was obtained using the thermal sampling method. All the molecular parameters, such as activation energy (Ea) and preexponential factor (τ0), have been estimated. In addition, the compensation law was found to be valid; and the compensation parameters such as compensation temperature (Tc) and compensation time (τc) have been determined.

Deconvolution of the relaxations associated with local and segmental motions in poly(methacrylate)s containing dichlorinated benzyl moieties in the ester residue

The relaxation behavior of poly(2,3-dichlorobenzyl methacrylate) is studied by broadband dielectric spectroscopy in the frequency range of 10(-1)-10(9) Hz and temperature interval of 303-423 K. The isotherms representing the dielectric loss of the glassy polymer in the frequency domain present a single absorption, called beta process. At temperatures close to Tg, the dynamical alpha relaxation already overlaps with the beta process, the degree of overlapping increasing with temperature. The deconvolution of the alpha and beta relaxations is facilitated using the retardation spectra calculated from the isotherms utilizing linear programming regularization parameter techniques. The temperature dependence of the beta relaxation presents a crossover associated with a change in activation energy of the local processes. The distance between the alpha and beta peaks, expressed as log(fmax;beta/fmax;alpha) where fmax is the frequency at the peak maximum, follows Arrhenius behavior in the temperature range of 310-384 K. Above 384 K, the distance between the peaks remains nearly constant and, as a result, the a onset temperature exhibited for many polymers is not reached in this system. The fraction of relaxation carried out through the alpha process, without beta assistance, is larger than 60% in the temperature range of 310-384 K where the so-called Williams ansatz holds.

Relaxation response of polymers containing highly flexible side groups monitored by broadband dielectric spectroscopy

The relaxation behavior of poly(5-acryloxymethyl-5-methyl-1,3-dioxacyclohexane), a polymer containing highly flexible side groups, is studied by broadband dielectric spectroscopy in the frequency and temperature ranges 10(-1)-10(9) Hz and 123-473 K, respectively. Above the glass transition temperature T(g) the dielectric loss in the frequency domain exhibits a prominent alpha absorption, followed in increasing order of frequencies by two secondary absorptions called beta and gamma. At temperatures slightly higher than T(g), the a relaxation is well separated from the beta, but as temperature increases overlapping between both relaxations augments forming an alphabeta absorption in the vicinity of 420 K. This latter absorption displays a shoulder on its high-frequency side corresponding to the y relaxation. The strength of the a relaxation decreases with increasing temperature, eventually vanishing at the temperature at which the alphabeta absorption is formed. The time retardation spectra of the isotherms are calculated and further used to facilitate the deconvolution of the overlapping relaxations. The fact that the temperature dependence of the beta relaxation also describes that of the alphabeta absorption suggests that both relaxations have the same nature. It seems that as temperature increases, the a relaxation feeds on the beta absorption until its complete disappearance. The gamma relaxation, in turn, seems to increase at the expense of the alphabeta process at high temperature.

Relaxation behavior of poly(ethylene terephthalate)/poly(ethylene naphthalene 2,6‐dicarboxylate) blends prepared by cryogenic blending

AbstractA method including cryogenic grinding, melt pressing from the molten state, and quenching was used to prepare blends of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene 2,6‐dicarboxylate) (PEN) in which the two phases were highly dispersed. The effect of melt‐pressing times on the thermal properties and relaxation behavior of PET/PEN films were characterized with differential scanning calorimetry and dielectric spectroscopy. For short melt‐pressing times, two glass‐transition, two crystallization, and two melting peaks were observed, indicating the presence of PET‐rich and PEN‐rich phases in these blends. Longer melt‐pressing times revealed a single glass transition and a single α‐relaxation process, showing that PET–PEN block copolymers were likely to be formed during the melt pressing. The experimental findings were examined in terms of the transesterification reactions between the blend components, as revealed by 1H NMR measurements. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2570–2578, 2002

Relaxation Behavior of Poly(ester carbonate) Block Copolymer Across the Melting Region

The dielectric behavior of a family of block copolymers based on poly(butylene terephthalate) (PBT) and aliphatic polycarbonate (PC), with the composition of PBT varying from 100 wt.-% to 40 wt.-%, has been investigated by broad-band dielectric spectroscopy in the frequency range from 10–1 to 109 Hz. At temperatures above the glass transition, the merging of local γ process and the cooperative β process was studied for PBT and 40/60 and 60/40 PBT-PC copolymers. The experimental data can be satisfactorily analyzed considering a sum of two Havriliak-Negami functions indicating that both β and γ relaxations can be treated as independent processes. Dielectric measurements for the 40/60 copolymer were extended over and above the melting region to characterize the influence of crystal melting on the dynamic behavior. It is shown that the progressive loss of the crystalline lamellar stack microstructure, as characterized by differential scanning calorimetry and small- and wide-angle X-ray scattering, provokes a dramatic change in the dynamic behavior of both the β and γ process.

Relaxation behavior of acrylate and methacrylate polymers containing dioxacyclopentane rings in the side chains

The synthesis of poly[(2,2-dimethyl-1,3-dioxolan-4-yl) methyl acrylate)] (PACGA) and poly[(2,2-dimethyl-1,3-dioxolan-4-yl) methyl methacrylate] (PMCGA) is reported. Both polymers present dielectric and mechanical β subglass absorptions at −128 and −115 °C, respectively, at 1 Hz, followed by ostensible glass–rubber or α relaxations centered in the vicinity of 0 and 67 °C, respectively, at the same frequency. The values of the activation energy of both the mechanical and dielectric β absorptions lie in the vicinity of 10 kcal mol−1. The critical interpretation of the relaxation behavior of PMCGA suggests that dipolar intramolecular correlations play a dominant role in the response of the polymer to an electric field. The subglass relaxations of PACGA and PMCGA are further compared with the relaxation behavior of poly(1,3-dioxane acrylate), poly(1,3-dioxane methacrylate), and other polymers in the glassy state. The strong conductive processes observed in PMCGA at low frequencies and high temperatures were studied under the assumption that that these processes arise from Maxwell–Wagner–Sillars effects occurring in the bulk combined with Nernst–Planckian electrodynamic effects caused by interfacial polarization in the films. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 286–299, 2001

Influence of oxycycloaliphatic groups in the relaxation behavior of acrylic polymers

A comparative study on the mechanical and dielectric relaxation behavior of poly(5-acryloxymethyl-5-methyl-1,3-dioxacyclohexane) (PAMMD), poly(5-acryloxymethyl-5-ethyl-1,3-dioxacyclohexane) (PAMED), and poly(5-methacryloxymethyl-5-ethyl-1,3-dioxacyclohexane) (PMAMED) is reported. The isochrones representing the mechanical and dielectric losses present prominent mechanical and dielectric β relaxations located at nearly the same temperature, approximately −80°C at 1 Hz, followed by ostensible glass–rubber or α relaxations centered in the neighborhood of 27, 30, and 125°C for PAMMD, PAMED, and PMAMED, respectively, at the same frequency. The values of the activation energy of the β dielectric relaxations of these polymers lie in the vicinity of 10 kcal mol−1, ∼ 2 kcal mol−1 lower than those corresponding to the mechanical relaxations. As usual, the temperature dependence of the mean-relaxation times associated with both the dielectric and mechanical α relaxations is described by the Vogel–Fulcher–Tammann–Hesse (VFTH) equation. The dielectric relaxation spectra of PAMED and PAMMD present in the frequency domain, at temperatures slightly higher than Tg, the α and β relaxations at low and high frequencies, respectively. The high conductive contributions to the α relaxation of PMAMED preclude the possibility of isolating the dipolar component of this relaxation in this polymer. Attempts are made to estimate the temperature at which the α and β absorptions merge together to form the αβ relaxation in PAMMD and PAMED. Molecular Dynamics (MD) results, together with a comparative analysis of the spectra of several polymers, lead to the conclusion that flipping motions of the 1,3-dioxacyclohexane ring may not be exclusively responsible for the β-prominent relaxations that polymers containing dioxane and cyclohexane pendant groups in their structure present, as it is often assumed. The diffusion coefficient of ionic species, responsible for the high conductivity exhibited by these polymers in the α relaxation, is semiquantitatively calculated using a theory that assumes that this process arises from MWS effects, taking place in the bulk, combined with Nernst–Planckian electrodynamic effects, due to interfacial polarization in the films. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2486–2498, 1999

Comparative study of mechanical and electrical relaxations in poly(etherimide). Part 2

The curves describing the relaxation behaviour of poly(etherimide) at several frequencies shows in the dielectric loss–temperature plot γ and β relaxations centred at -95°C and 100°C, respectively, at 10Hz. The glass–rubber relaxation or α process appears at 225°C at 10Hz; at this temperature free charge conductivity and blocking electrode phenomena become dominant at frequencies below 10Hz. The same three relaxations are observed by dynamic mechanical thermal analysis (DMS). The strength of the γ and α relaxations can be estimated from the fitting of empirical relaxation functions, such as the Fuoss–Kirkwood and Havriliak–Negami equations, to the dielectric data measured in the frequency domain. An electric model was used to separate the dipolar response from conductivity contributions in the glass–rubber relaxation. Finally, the effect of water on the low-temperature relaxation has been demonstrated by dielectric and mechanical measurements. © 1998 SCI.