Motion Of Polymer Chains Research Articles

Scaling theory of polymer thermodiffusion

The motion of a linear polymer chain in a good solvent under a temperature gradient is examined theoretically by breaking up the flexible chain into Brownian rigid rods, and writing down an equation of motion for each rod. The motion is driven by two forces. The first one is Waldmann’s thermophoretic force (stemming from the departure of the solvent’s molecular-velocity distribution from Maxwell’s equilibrium distribution) which here is extrapolated to a dense medium. The second force is due to the fact that the viscous friction varies with position owing to the temperature gradient, which brings an important correction to the Stokes law of friction. We use scaling considerations relying upon disparate length scales and omitting non-universal numerical prefactors. The present scaling theory is compared with recent experiments on the thermodiffusion of polymers and is shown to account for (i) the existence of both signs of the thermodiffusion coefficient of long chains, (ii) the order of magnitude of the coefficient, (iii) its independence of the chain length in the high-polymer limit and (iv) its dependence on the solvent viscosity.

Electrical conductivity and dielectric behaviour of PPG4–AgCF3SO3:Al2O3 nanocomposite gel polymer electrolyte system

In this report, the synthesis of solvent-free poly(propylene glycol) 4000 (PPG4)–silver triflate (AgCF3SO3):xAl2O3 nanocomposite gel polymer electrolytes containing four different amounts of Al2O3 nanoparticles corresponding to x = 1, 3, 5 and 7 wt.%, respectively, with an ether oxygen-to-metal cation ratio (O–M) of 4:1 together with their vibrational spectroscopic characteristics derived from Fourier transform infrared (FT-IR ) spectroscopic analysis at room temperature (25 °C) is described. Furthermore, a detailed investigation concerning their mechanism of ion transport performed by means of complex impedance analysis in the frequency range 20 Hz to 1 MHz and over the temperature region 25–90 °C and analysed in terms of electrical conductivity spectra, electrical modulus spectra and impedance spectra has indicated that the typical composition PPG4–AgCF3SO3:5 wt.% Al2O3 would exhibit the best room temperature electrical conductivity of 6.2 × 10−4 S cm−1 owing to the mobility of coordinated silver cations through the mechanism of enhanced segmental motion of the PPG4 polymer chains as aided by the various coordinating sites available within the polymer network. It is also demonstrated from the present FT-IR results that significant changes in the intensity, shape and position of the different vibrational bands corresponding to –OH stretching, C–O–C stretching, C–H stretching and C–O–C in C–H stretching modes occur as a result of the incorporation of Al2O3 nanofiller particles into the PPG4–AgCF3SO3 complex. It is evident from the conductivity data that the observed enhancement in electrical conductivity would result from appropriate changes in ionic association occurring in the form of probable ion–ion and ion–polymer interactions involving Al2O3 nanofiller additive in accordance with the Lewis acid–base model of polymer–salt–filler interactions.

An 8-chain Model for Rubber-like Materials Accounting for Non-affine Chain Deformations and Topological Constraints

Several industrial applications involve rubber and rubber-like materials, and it is important to be able to predict the constitutive response of these materials. In the present paper, a new constitutive model for rubber-like solids is proposed. The model is based on the 8-chain concept introduced by Arruda and Boyce (J. Mech. Phys. Solids 41, 389–412, 1993) to which two new components are added. Real polymer networks do not deform affinely, and in the proposed model this is accounted for by the inclusion of an elastic spring, acting in series with the representative polymer chain. Furthermore, real polymer chains are not completely free to move, which is modelled by imposing a topological constraint on the transverse motions of the representative polymer chain. The model contains five model parameters and these need to be determined on the basis of experimental data. Three experimental studies from the literature were used to assess the proposed model. The model was able to reproduce experimental data performed under conditions of uniaxial tension, generalised plane deformation, and biaxial tension with an excellent accuracy. The strong predictive abilities together with the numerically efficient structure of the model make it suitable for implementation in a finite element context.

Pervaporation separation of isopropanol/benzene mixtures using inorganic–organic hybrid membranes

AbstractA series of pervaporation hybrid membranes were prepared from polyethylene glycol (PEG) and phenylaminomethyl trimethoxysilane (PAMTMS) based on the sol‐gel process, in which PEG was used as an organic moiety to improve the affinity for organic alcohols and silicone of PAMTMS was used as inorganic moiety to increase the permeation flux of organic species. Their application to separate isopropanol/benzene mixtures was investigated. FTIR spectra confirmed the reaction products. DSC measurement revealed that the influence of PEG content on the Tg and thermal behavior of membranes A, B, and C. FE‐SEM images exhibited that phase‐separated structure has occurred when the PEG content elevated to some extent. Pervaporation experiments showed that the permeation flux increased and the separation factor decreased with an increase in isopropanol (IPA) content in feed at 30°C. Meanwhile, the separation factor increased with an increase in feed temperature at 60 vol % IPA content. Moreover, it was found that the permeation flux was independent of the feed temperature, suggesting that feed temperature has little impact on the thermal motion of polymer chains. The increasing cross‐linking degree in hybrid matrix might be responsible for such trend. Based on these findings, it can be concluded that these pervaporation hybrid membranes have potential applications in the separation of isopropanol/benzene binary mixtures. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Dispersion and reinforcing mechanism of carbon nanotubes in epoxy nanocomposites

Carbon nanotube based epoxy composites have been fabricated at room temperature and refrigeration process using sonication principle. Flexural moduli, electrical conductivity, glass transition temperature of epoxy resin as well as nanocomposite samples have been determined. Distribution behaviour of carbon nanotubes in the epoxy matrix was examined through scanning electron microscopy. Composite samples showed better properties than resin samples due to strengthening effect of the filled nanotubes. Refrigerated nanocomposites obtained increasing mechanical property because of better dispersion due to low temperature settlement of polymers. Improvement of electrical conductivity was due to the fact that aggregated phases form a conductive three-dimensional network throughout the whole sample. The increasing glass transition temperature was indicative of restricting movement of polymer chains that ascribe strong interaction presented between carbon nanotubes and epoxy chains that was again supplemented by Raman study and SEM.

Molecular dynamics in grafted polydimethylsiloxanes

Rheological and dielectric behavior of linear PDMS and alkyl-modified PDMS melts has been studied. Molecular dynamics of linear PDMS, being a model of grafted polydimethylsiloxanes studied, has been examined carefully with particular attention paid to its ability to form the semicrystalline phase. Random incorporation of alkyl groups into PDMS chain has been shown to prevent the polymer crystallization. The glass transition temperature of the grafted PDMS changes proportionally to the modifier content. Both techniques allow characterization of the main α-relaxation, which is related to the glass transition and exhibits similar behavior in all systems. This relaxation is discussed in terms of the Vogel–Fulcher–Tammann–Hesse (VFTH) approach. The fragility of grafted PDMS materials was found to be higher as compared to the linear polymer. The analysis of the rheological data shows the existence of additional slow relaxation, which has been interpreted as the polymer chain motion.

Percolation network of organo-modified layered double hydroxide platelets into polystyrene showing enhanced rheological and dielectric behavior

A hybrid organic inorganic layered double hydroxide incorporating 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) is characterized by means of XRD, FTIR, and XPS. The in situ polymerization is scrutinized by 13C CPMAS as well as by a set of XRD experiments with varying temperature. It is found that the in situ polymerization is complete at 200 °C, and the hybrid framework sustains temperatures as high as 350 °C. Direct incorporation of poly(AMPS) is reported and the resulting hybrid LDH phases studied. Subsequently, all generated hybrid platelets are used as organo-modified 2D-type filler dispersed into polystyrene (PS). An immiscible PS composite structure with salient gel-like viscoelastic properties is obtained after bulk polymerization. In the low-frequency region, the typical Newtonian flow behaviour of PS is found to change progressively against filler loading into a shear-thinning behaviour evidenced by a pseudo-plateau in the elastic and loss modulus curves and associated with a shift of the glass transition temperature of PS to higher temperature. It is interpreted by hybrid LDH platelet domains presenting a large interface with the polymer, thus having the effect of restricting the plastic deformation by obstructing polymer chain motion. Such dispersed hybrid LDH tactoids forming a three-dimensional percolated network are indirectly evidenced by the enhancement of the dielectric properties illustrated by an increase in bulk dc conductivity of about one order at room temperature and in the dissipation factor. The study shows that hybrid LDH assembly is of relevance in topical applications regarding mechanical reinforcement as well as electrostatic energy dissipation.

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

Crystalline transformation of isotactic polybutene-1 in supercritical CO2 studied by in-situ fourier transform infrared spectroscopy

The solid-solid crystalline transformation of isotactic polybutene-1 (iPB-1) from tetragonal form II to hexagonal form I could be accelerated by supercritical carbon dioxide (scCO2). In this study, in-situ Fourier transform infrared spectroscopy (FTIR) and two dimensional correlation spectroscopy (2DIR) is used to observe and investigate the crystallization behaviour of iPB in scCO2 and compressed CO2. Based on the transform sequence given by 2DIR analysis, this transformation of helical chain structures is found to be initiated with the motion of side chains and followed by the movement of main chains. It is speculated that the motion of polymer chains was enhanced with the diffusion of CO2. Also this crystalline transition is observed even in compressed CO2, suggesting that CO2 could also diffused into polymer under high pressure near the critical pressure. This diffusion of CO2 is indicated by the growth of IR bands being assigned to the stretching vibration of C–O. A further investigation on the mechanically heating and freely cooling of iPB provides more evidences on the process of structure transition. The result implies that the nucleus of tetragonal form II formed in the melt is not affected by the existence of scCO2, but the crystallization temperature become obviously lower.

Hydrogen bond interaction in poly(acrylonitrile‐co‐methylacrylate)/attapulgite nanocomposites

AbstractIn this article, poly(acrylonitrile‐co‐methylacrylate)/attapulgite (AT) nanocomposites have been prepared by mechanical blending. The hydrogen bonding (H‐bonding) behavior between the copolymer and unmodified AT were investigated by Fourier Transform Infrared. The results indicated that the H‐bond index (HBI) decreased with increasing AT content. According to the dynamic mechanical analysis, the storage modulus and heat distortion temperature of the nanocomposites gradually increased with increasing AT content while the glass transition temperature reached the maximum when AT content was 1 wt%. X‐ray diffraction results demonstrated that the sample with the highest HBI value had the lowest crystallinity, suggesting the H‐bond interaction restricted the motion of polymer chains, thus decreased crystallinity of the nanocomposites. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Hydrogel membrane electrolyte for electrochemical capacitors

Polymer electrolytes are known to possess excellent physicochemical properties that are very useful for electrochemical energy systems. The mobility in polymer electrolytes is understood to be mainly due to the segmental motion of polymer chains and the ion transport is generally restricted to the amorphous phase of the polymer. Gel polymer electrolytes (GPE) that are formed using plastizicers and polymers along with ionic salts are known to exhibit liquid-like ionic conductivity while maintaining the dimensional stability of a solid matrix. In the present study, the preparation and characterization of poly(vinyl alcohol)-based hydrogel membranes (PHMEs) as electrolytes for electrochemical capacitors have been reported. Varying HClO4 dopant concentration leads to different characteristics of the capacitors. The EC comprising PHME doped with 2 M HClO4 and black pearl carbon (BPC) electrodes has been found to exhibit a maximum specific capacitance value of 97 F g−1, a phase angle value of 78°, and a maximum charge-discharge coulombic efficiency of 88%.

Ultrasonic characterization of the crystallization behavior of poly(ethylene terephthalate)

AbstractOn the basis of the previous observations that the ultrasonic signals are sensitive to the crystallization of polymers (Tatibouet and Piché, Polymer 1991, 32, 3147), we have expanded our efforts to study the detail relationship between the ultrasonic signals and crystallization process in this work. The nonisothermal and isothermal crystallization of virgin poly(ethylene terephthalate) (PET) and PET samples after degradation were studied by using a specially designed pressure‐volume‐temperature (PVT) device, with which an ultrasonic detector was combined. The results showed that the evolution of the ultrasonic signals not only can be used to probe the crystallization process but also can qualitatively characterize the crystallization rate, crystallinity, crystallite size, and amorphous. DSC measurement was used to verify such results. Ultrasonic signals could be as a complementary tool to polymer chain movement and well be applied to characterize the crystallization behavior. Furthermore, the ultrasonic measurement has the potential use to characterize crystallization of products in‐line during processing (i.e., injection molding, micromoulding). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Electromechanical response of semiconducting carbon–polyimide nanocomposite thin films

Electromechanically responsive polymer nanocomposite thin films can provide embedded microscale sensing elements for unobtrusive monitoring of strain, torque and pressure particularly for composite structures. Thin nanocomposite carbon–polyimide films with thicknesses up to 90 μm were produced with carbon contents that yield semiconducting behaviour attributable to distance dependent electron hopping between isolated nanoparticles. The tensile modulus and the strain at break indicated minimum interaction between polymer and nanoparticle surfaces. A decreasing storage modulus with increasing temperature indicated increasing free volume inducing polymer chain motions. Well below the percolation threshold the electromechanical sensitivity was linear, while approaching this threshold nonlinearity arose through a contribution to conductivity from limited nanoparticle aggregates. These semiconducting thin films exhibited sensitivities (gauge factors) that ranged to 8.0 depending upon their geometric profile compared to about two for traditional metal foil gauges. This dependency on Poisson’s ratio occurs from competing interparticle spacing effects where longitudinal applied strain increases particle spacings reducing conductivity and transverse contraction decreases spacings enhancing conduction.

Effects of octa(3-chloroammoniumpropyl)octasilsesquioxane on the epoxy self-polymerisation and epoxy–amine curing

The effect of quaternary ammonium functionalised polyhedral oligomeric silsesquioxane (POSS) on the self-polymerisation of the diglycidyl ether of bisphenol A (DGEBA) and on the DGEBA–Jeffamine-T403 curing was investigated by differential scanning calorimetry. The acidic ammonium groups of POSS were found to catalyze the self-polymerisation of DGEBA but termination reactions severely compete with the propagation and only low conversions in epoxy groups are attained (<20%). A reaction between POSS and DGEBA was revealed at the POSS–matrix boundary suggesting the release of amino functionality of POSS during thermal cure. The catalytic effect of POSS over the epoxy–amine reaction was also demonstrated. The efficiency of this catalytic effect was found to be significantly dependent on the processing conditions. Finally, two competitive effects were found to affect the glass transition temperature of POSS modified epoxy networks cured under dynamic conditions. It is proposed that the inclusion of POSS at the nanometer scale is responsible for the increase in free volume of the system which results in the depression of T g's while a restriction effect of POSS cages on polymer chain motions (enhanced T g's) is associated to the development of POSS aggregates in the networks with high POSS loadings.

Polymer motion as detected via dielectric spectra of 1,4- cis-polyisoprene under large amplitude oscillatory shear (LAOS)

In order to investigate the global polymer chain motion under large amplitude oscillatory shear (LAOS), the dielectric properties under LAOS are measured by a new rheo-dielectric combination. The design of the rheo-dielectric setup including a new fixture and modified oven is explained in detail. For 1,4- cis-polyisoprene, having type-A dipoles parallel to the backbone, the dielectric dipoles can detect the global polymer chain motion via the end-to-end vector. Thus rheological and dielectric (rheo-dielectric) properties reflect the dynamics of the polymer chain motion under LAOS. In this study, we investigate the rheo-dielectric properties under LAOS with 1,4- cis-polyisoprene as model component. As the strain amplitude was increased under LAOS, the relaxation strength from dielectric properties decreased for the whole spectra without changing the shape of the dielectric spectra. These results are analyzed on the basis of the molecular model of dynamic tube dilation (DTD) induced by the convective constraint release (CCR). It is found that the global chain motion under LAOS flow is affected by both rheological frequency and strain amplitude. It is also observed that segmental motion is affected via the oscillatory frequency under LAOS. This result differs from experiments under steady shear.

Proton-conducting electrolyte membranes based on hyperbranched polymer with a sulfonic acid group for high-temperature fuel cells

The hyperbranched polymers ( HBP-SA-Acs) with both a sulfonic acid group as a functional group and an acryloyl group as a cross-linker at terminals in different ratios of sulfonic acid group/acryloyl group (SO 3H/Ac) were successfully synthesized as a new thermally stable proton-conducting electrolyte. The cross-linked hyperbranched polymer electrolyte membranes ( CL-HBP-SAs) were prepared by thermal polymerizations of the HBP-SA-Acs using benzoyl peroxide, and their ionic conductivities under dry condition and thermal properties were investigated. The ionic conductivities of the CL-HBP-SAs were found to be in the range of 2.2 × 10 −4 to 3.3 × 10 −6 S/cm, depending upon the SO 3H unit contents, at 150 °C under dry condition, and showed the Vogel–Tamman–Fulcher (VTF) type temperature dependence, indicating that proton transfer is cooperated by local polymer chain motion. All CL-HBP-SAs were thermally stable up to 260 °C, and they had suitable thermal stability as electrolyte membranes for the high-temperature fuel cells under dry condition. Fuel cell measurement using a single membrane electrode assembly cell with a cross-linked electrolyte membrane was successfully performed under non-humidified condition. It was demonstrated that applying the concept of dry polymer system to proton conduction is one possible approach toward high-temperature fuel cells.

A comprehensive study of an unusual jammed nanocomposite structure using hybrid layered double hydroxide filler

Polystyrene nanocomposites using hybrid organic inorganic (O/I) layered double hydroxide (LDH) and 4[12-(methacryloylamino)dodecanoylamino]benzenesulfonate (MADABS) interleaved molecules were studied as a function of the filler miscibility, dispersion, and the rheological behavior. Incorporation of the I/O filler gave rise to an expanded intercalated PS nanocomposite structure, while an immiscible structure was obtained after a thermal pre-treatment. However the utmost non-linear viscoelasticity in the low- ω region was obtained from the immiscible PS nanocomposite structure. Indeed, the presence of a sub-micrometer percolated structure was here depicted resulting in a jammed structure that progressively changed the typical low-frequency Newtonian flow behavior of PS to a shear-thinning behavior against the filler percentage, having as a consequence to restrict the plastic deformation in the low- ω region by obstructing polymer chain motion. From several characterizations XRD, TEM, and rheology, we demonstrated the presence of LDH agglomerates in spite of PS chain crawling in between the layers, whereas the apparent immiscible structure was composed of well dispersed LDH tactoids forming a three-dimensional percolated network. The gel-like behavior illustrated by the frequency power law dependence of the complex viscosity | η ∗ | ∝ ω n , n ≈ − 0.75 at 10 wt% of MADABS/LDH hybrid filler was then explained by the interconnected and concatenated hybrid LDH platelets domains developing an interfacial attrition with PS chains.

Anhydrous solid proton conductors based on perfluorosulfonic ionomer with polymeric solvent for polymer electrolyte fuel cell

Novel anhydrous polymeric proton conductors have been prepared from perfluorosulfonic acid ionomer with polymer solvent as supplying proton pathway through the segmental motion of polymer chains for polymer electrolyte fuel cell (PEFC) application. Since the membranes do not contain liquid-state acid or solvent, the membranes may promise more stable performances during the operation of PEFC. The Nafion-based anhydrous proton conductors showed maximum proton conductivity of about 4.0 × 10 −3 S cm −1 at 130 °C under anhydrous condition. The mechanical properties of the membranes were enhanced by introducing H +-doped TiO 2 nanoparticles without the conductivity degradation. In addition, the electrochemical properties of the membrane electrode assembly (MEA) employing the anhydrous membrane as ionomer have been investigated, showing stable open circuit voltages (OCVs) over 0.9 V under non-humidified condition.

Fluctuation-assisted crystallization of an iPP/PEOc polymer alloy prepared on a single multicatalyst reactor granule

The new fluctuation-assisted mechanism for nucleation and crystallization in the isotactic polypropylene/poly(ethylene-co-octene) alloy has been studied. We found that the liquid–liquid phase separation (LLPS) had a dominant influence on the crystallization kinetics through the nucleation process. After LLPS, the nucleation of crystallization mainly occurred at the interface of the phase-separated domains. It is because that the concentration fluctuations of the LLPS induced the motion of polymer chains and possibly some segmental alignment and/or orientation in the concentration gradient regions through interdiffusion, which could assist the formation of nuclei for crystallization. In other words, the usual nucleation energy barrier could be overcome (or at least partially) by the concentration fluctuation growth of LLPS in the unstable regions. This could be viewed as a new kind of heterogeneous nucleation and could be an addition to the regular nucleation and growth mechanism for crystallization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 166–172, 2009

Aggregation behavior of new cyclic saturated copolymers synthesized via ring-opening metathesis polymerization

Cyclic saturated copolymers were prepared from 8-methyl-8-methoxycarbonyltetracyclo[4.4.0.12,5.17,10]dodec-3-ene (MMT) with polar ester group and dicyclopentadiene (DCP) without polar group. This procedure consisted of ring-opening metathesis polymerization (ROMP) followed by hydrogenation. Monomer reactivity of DCP was higher than that of MMT; the monomer reactivity ratio rDCP/rMMT varied from 2.135 to 1.159 in a temperature range from 80 to 130°C. These kinetic results indicated that the copolymer had distribution of DCP composition in a macromolecule chain, which could provide the interesting aggregation behavior. The aggregation behaviors of the hydrogenated copolymer and the homopolymer in various solvents were also examined using dynamic light scattering (DLS) and static light scattering (SLS). DLS analysis indicated that the fast mode in each polymer is attributed to the diffusive motion of each single polymer chain, while the slow mode in the copolymer is caused by aggregated polymer. The aggregation degree of the copolymer decreased with increasing hydrophobicity of solvent, decreasing polymer concentration, decreasing molecular size of solvent and increasing temperature. Based on these findings, the mechanism of aggregation behavior was clarified that the DCP-rich unit in a macromolecule might be acting as core to give the aggregation in poor solvent.