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Weak strain overshoot (WSO) of loss modulus accompanying with strain softening under large amplitude oscillatory shear deformation is a common phenomenon that occurs in many systems but is still far from being clarified. Study about WSO has a strong practical significance, for it is directly related to sharp increase of energy dissipation of elastomer nanocomposites experiencing dynamic deformation of large strain amplitudes. Herein a systematical investigation was performed on WSO of uncured natural rubber (NR) and its low-loading carbon black compounds and a frequency-temperature-volume fraction diagram for the onset of WSO is firstly proposed to shed light on the mechanisms. A comparison of rheology behaviors of uncured polyisoprene rubber and NR and cured polyisoprene rubber suggests that WSO in NR originates from the non-isoprene fraction. Fourier-transform infrared spectroscopy measurement suggests the dissociation of hydrogen bonding at high temperatures, which accelerates the stress relaxation.

Nanoparticles significantly reinforce rubber and enhance nonlinear mechanical behavior while the underlining mechanisms are not clear. Herein the effects of crosslinking, filler content and filler surface chemistry on the linear and nonlinear rheological responses of silica filled nitrile butadiene rubber are investigated. A time-concentration superposition principle is employed for constructing rheological master curves. While the strain amplification and dynamics retardation contribute to the high-frequency linear rheology of the compounds, the former is crucial for the vulcanizates with matrix of similar crosslinking degree. In both the compounds and vulcanizates, the Payne effect is initiated at a similar microscopic strain of the rubber phase. A weak overshoot of loss modulus appears in compounds containing hydrophilic silica and vulcanizates containing hydrophobic silica. It is suggested that the viscoelastic matrix is highly important for the rheological responses of the filled compounds and vulcanizates.

Dynamic mechanical properties due to incorporation of carboxylated multiwalled carbon nanotubes into three-layer polymer structure, with high damping property, via in situ emulsion polymerization and also blending are studied in detail. Using of storage modulus, loss modulus and damping behavior obtained from the DMA was investigated the manner of carboxylated MWCNTs into and onto the three-layer polymer structure. It was observed that different morphology and topology were formed using these two manufacturing methods. Also, it was observed that dynamic mechanical and damping properties are due to complex and multifunctional parameters such as adhesion, constrained chains, molecular optimum mobility between polymer and nanotubes.

Design and fabrication of organic and polymeric soft materials exhibiting solvent-free isothermal changes in mechanical properties triggered by photostimulation are challenging. Here, we report dramatic changes in viscoelasticity of coumarin end-functionalized poly(dimethyl siloxane) with a branched macromolecular architecture under a solvent-free isothermal condition upon alternating irradiation of UV at the wavelength of 365 and 254 nm (UV365 and UV254). Significantly, it is disclosed that storage modulus (G′) was increased by a factor of more than 30000. Moreover, the subsequent UV254 irradiation caused sharp decrease in G′ and it became comparable to loss modulus. Furthermore, alternating irradiation of UV365 and UV254 caused repetitive increase and decrease in G′ of the material.

Rheological melt behavior of carbosilane dendrimers from the 3rd up to the 8th generation has been studied experimentally under steady shear, creep and dynamic oscillatory shear. Six orders of magnitude jump in viscosity was found between the 5th and the 6th generations. While the low-generation dendrimer melts demonstrate Newtonian behavior in a wide temperature range of 20÷80 °C, starting from the 6 t h generation, the dendrimer melts lose their ability to freely flow and acquire properties of a material with a well-pronounced yield stress. The storage modulus of high-generation dendrimer melts by far exceeds the loss modulus, furthermore, its value increases with temperature. It is demonstrated that the high-generation carbosilane dendrimers in bulk can be considered a polymer material with unique properties and as that, could find new applications in high-tech areas, in particular, as matrices for sensors.

Cheetah skin carbon nanotube, a novel periodically patterned nanocarbon on CNT synthesized as a highly effective filler for fabrication of high performance composites. The advantage of newly developed morphology lies in the fact that the size of nanocarbon on CNT and their distance can be fully controlled based on the application requirements. Cheetah skin CNT shows an excellent thermal stability and dispersibility in a high density polyethylene (HDPE) compared to pristine CNT/HDPE composite, making cheetah skin CNT a suitable candidate for fabrication of high performance HDPE based composite. The addition of cheetah skin CNT into HDPE resulted in a composite with improved thermomechanical properties. Compared with the pure HDPE and HDPE/pristine CNT, storage modulus and loss modulus of HDPE/cheetah skin CNT improved significantly at low temperatures even with very low content of cheetah skin CNT. Also, the thermal stability of the cheetah skin CNT/HDPE was found to be significantly higher than that of pristine CNT/HDPE composite in both isothermal and non-isothermal degradation performed for composites.

Coarse-grained molecular dynamics (CGMD) simulations are employed to study the viscoelastic properties of cis-1,4-polyisoprene with silica/carbon black (CB) hybrid nanoparticles (NPs). Our simulation work for the first time investigates the rubber with both silica and CB NPs with the potential functions from the iterative Boltzmann inversion (IBI) method. We calculate the dynamic shear modulus of different models, and analyze the effect of silica/CB ratio and grafted NPs. In order to explain the differences in modulus from the microscopic view, we make the quantitative comparisons of the NP-NP, polymer-polymer and NP-polymer structures, such as using the radius of gyration, the coordination number, and the potential energy. The characteristics of dual phase filler are mainly in two aspects of potential functions. One is that the silica-CB interaction is weaker than that of their single components, and the other is that the NP-polymer potential functions are different in shape for Silica and CB. The former causes NPs to be more likely to aggregate in the form of "bridging". The latter causes that the silica-polymer interaction is weaker at small amplitudes, while the CB-polymer interaction is weaker at large amplitudes for the range of the strong CB-polymer interaction is narrow. The simulation result also shows that the break-up of the NP network is the main factor for the Payne effect, and the interfacial separation is the second factor. The reason why the storage modulus curves of the models with grafted NPs decrease slowly at small amplitudes is the hindering effect of the graft chains on the growth of the interfacial voids.

Dynamic viscoelastic measurements were performed for a series of poly(4-n-alkylstyrene)s with six different n-alkyl side chains, that is, methyl, ethyl, propyl, butyl, hexyl and octyl groups. Based on the time-temperature superposition principle, storage modulus G′, loss modulus G″ and loss tangent tan δ were shifted with horizontal shift factor aT and vertical shift factor bT, giving well superposed master curves for all the polymers. With increase of the number of carbon atoms, plateau modulus GN0, which corresponds to G′ value at minimum tan δ, decreases, while entanglement molecular weight Me(=ρRT/GN0) increases, where ρ is the polymer density, R is the gas constant and T is the absolute temperature. Degree of polymerization at onset of entanglement, Ne, which defined as Me/M0, where M0 denotes the molecular weight of each monomer, also increases with increase of n-alkyl side chain length. Packing length estimated from the empirical equation by Fetters also increases with increase of n-alkyl lengths. These results are presumably due to large polymer chain thickness caused directly by substituents on phenyl rings of styrene units.

A nanodiamond nanomatrix structure is formed into natural rubber, generating not only entropic elasticity but also energetic elasticity. The radical reaction with tert-butylhydroperoxide (TBHP)/tetraethylenepentamine (TEPA) in the latex stage forms a chemical linkage between the nanodiamond and natural rubber particles after removing proteins from the rubber. To investigate the relationship between morphology and mechanical properties, the as-cast films prepared from nanodiamond-grafting deproteinized natural rubber (DPNR-ND) latex are subjected to transmission electron microscopy (TEM), tensile tests, and dynamic mechanical analyses. The nanodiamond nanomatrix structure markedly increases the tensile strength of natural rubber. The values of the storage modulus and loss modulus are about ten times higher than those of natural rubber in the rubbery plateau region when DPNR-ND contains 40 w/w% ND. Thus, an energetic elasticity is realized in conjunction with the entropic elasticity.

The high values of recycled acrylonitrile-butadiene-styrene plastics (rABS) have drawn wide attentions and research interests. Herein, the renovation of molecular chains and phase interface of rABS was successfully achieved through simple melt-blending modification, in which the in-situ chain extension reaction was conducted between rABS and pyromellitic dianhydride (PMDA). PMDA acted as a chain extender with hydroxyl units. The modified rABS were characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), mechanical properties testing, scanning electron microscopy (SEM), and dynamic mechanical analysis (DMA). The results indicated that compared with rABS, the molecular weight, impact strength, tensile strength, storage modulus and loss modulus of modified rABS were apparently improved. Especially, when PMDA content was 0.9 wt%, the notch impact strength reached 15.9 kJ/m 2 , which was 140% higher than that of rABS. Besides, the interface between polybutadiene (PB) phase and styrene-acrylonitril copolymer (SAN) phase was blurred and the compatibility between two phases became better. The aforementioned results revealed that rABS has been achieved with high-value recycling usage.

Polymeric surfactant is an attractive alternative to conventional surfactant-polymer system for application in enhanced oil recovery, as it plays dual role of reduction of interfacial tension (IFT) and improvement of mobility ratio. The present paper deals with the synthesis and rheological characterization of a novel polymeric surfactant derived from Jatropha oil. Molecular aggregation of polymer in aqueous solution has been confirmed by DLS studies, which increases with increase in concentration. The viscosity results indicate the good shear stability of system at higher shear rate as well as higher temperature for application in conventional oil reservoir. The polymeric solutions show peculiar behaviour with shear thinning nature at low shear rate and shear thickening nature at higher shear rate because of its unique molecular properties. The viscoelastic properties of the solutions were investigated and it has been found that storage modulus (G′) and loss modulus (G″) follow the Maxwellian fluid behavior. Specific frequency (SF) indicated by the crossing point between G′ and G″ on the viscoelastic curve represents the point of transition between elastic and viscous phases of the polymeric surfactant system. The effect of silica nanoparticle on polymer viscosity was also studied and it has been found that introduction of silica nanoparticle dramatically increases the polymer viscosity and stability of the solution with respect to temperature.

Filling significantly reinforces rubbers and introduces rheological nonlinearity, which is usually ascribed to filler networking and destructuring effects while conceptual conflicts still exist. Herein nonlinear rheology of compounds of fumed silica filled emulsion-polymerized styrene butadiene rubber is investigated with respect to silica type (hydrophilic and hydrophobic) and loading. The results revealed that, at low silica loadings, the reinforcement is involved in strain amplification effect and the rheological nonlinearity is initiated by a critical microscopic strain of bulk rubber matrix or a critical stress of the compounds. At high silica loadings when silica tends to develop an agglomerated structure, the reinforcement efficiency and the critical stress for onset of nonlinearity are reduced notably. Instead, an overshoot of loss modulus occurs accompanying with onset of nonlinearity involved in additional dissipation of mechanical energy possibly arising from friction among silica particles in their agglomerates.

We present an approach to quantify different contributions to dissipation in elastomer nanoparticle composites based on strain sweeps. A modified Kraus equation is successfully used to approximate the loss modulus depending on strain amplitude G ″ γ measured at different temperatures. For natural rubber composites containing > 10 vol% carbon black or > 3 vol% carbon nanotubes two different contributions to dissipation due to (i) breaking and (ii) deformation of glassy rubber bridges in the filler network are identified. Filler fraction and temperature-dependent trends support physical pictures considering that glassy rubber bridges are responsible for the visco-elasticity of the filler network. Constant extra contributions to dissipation are associated with the bulk-like fraction of the elastomer matrix or filler network independent effects. The achieved understanding should be very important for the optimization of elastomer nanoparticle composites for special applications like tire treads.

The mechanical properties of a new type of nanocomposite gel, consisting of varying concentrations of the biopolymer alginate and the synthetic clay Laponite®, together with the temperature-sensitive copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO, trade name Pluronic® F127), are reported. These “ALP” gels (alginate-Laponite®-Pluronic®) were prepared and studied using rheology. Gels with multiple networks and gelation mechanisms have been explored as one strategy to strengthen and stiffen conventional hydrogels, which usually consist of a single polymer network. This work shows that the ALP gels exhibit significantly higher storage and loss modulus (G′, G″) values than gels composed of only alginate and Laponite®. Moreover, the interaction between the components appears to be synergistic; that is, the resulting multicomponent hydrogels are much more elastic than the additive effects of individual components. For example, the G′ of one series of the nanocomposite gels containing F127 Pluronic® experiences two orders of magnitude enhancement compared to its respective control containing only alginate and Laponite®. Furthermore, the ALP gels show a 20-40x enhancement in storage modulus, with values as high as 10,000–20,000 Pa, over the 30–55 °C temperature range. The large degree of enhancement in the storage modulus of the ALP gels with addition of Pluronic® is quite remarkable, compared to alginate-Laponite® gels on their own at comparable concentrations and temperatures, which form relatively weak gels. These results provide a simple strategy for significantly increasing the mechanical properties of polymer hydrogels used in biomaterials applications.

The high strain-rate rheological and mechanical properties of bi-modal epoxy polymer networks were characterized using molecular dynamics simulation. The complex Young's modulus was found by applying a cyclic sinusoidal strain over a wide range of temperatures spanning the glass transition. The non-linear stress response was studied in the glass transition region using uni-axial deformation. We discuss special considerations in computing viscoelastic properties at the high strain-rates available to molecular dynamics. As in experimental studies, the complex modulus is shown to be a function of the network composition and strain rate. However, the high strain-rate simulations performed here predict the existence of broad peaks in the temperature-dependent loss modulus and slow relaxation of the storage modulus. In general, it is observed that network compositions with larger amounts of short, stiff 4,4’-methylenebis(cyclohexylamine) (MCA) cross-linkers lead to an increase in the mechanical glass transition temperature as well as the breadth of the glass transition compared to longer, more flexible poly(oxypropylene) diamine (POP) cross-linkers. When the networks of any composition were deformed beyond the linear region, the stress response displayed a plateau that was associated with the extension of network chains.

Polyurea is a block copolymer with excellent shock absorption. It has a unique phase separation structure, yet there are few reports on how the mesoscale structure affects the dynamic mechanical properties. In this paper, the effect of two-phase structure on the dynamic modulus and shock-wave dissipation of polyurea is investigated by coarse-grained molecular dynamics. Shear relaxation modulus is calculated by the Green-Kubo method. Pulse load is applied by non-equilibrium molecular dynamics. The two-phase structure improves the dynamic modulus by restricting the segment movement. Shock-wave energy is dissipated by heat dissipation, viscous retardation, and plastic dissipation. The two-phase structure must obey deformation coordination, which results in more strain energy and internal friction. Hydrogen bond dissociation and structure destruction occur during the impact. Furthermore, the simulations results are verified by AFM, X-ray diffraction, and DMA experiments.

This work describes the effects of tailoring the morphology of the re-agglomeration network and interfacial bonding by embedding poly(methyl methacrylate) decorated single wall nanotubes (SWNTs) into an epoxy resin. We report the time history of the re-agglomerations in the resin, and the rheological properties of the uncured suspensions to assess the effectiveness of the carbon nanotubes crosslinking on the curing process. A dispersion index was used to quantitatively evaluate the level of re-agglomeration. Both the pristine SWNTs and the polymer decorated SWNTs showed the effectiveness of re-agglomeration in improving rheological storage and loss modulus up to 770% and 50% respectively comparing with samples containing uniformly dispersed filler structure, suggested a novel filler arrangement for optimum composites damping performance. Dynamic mechanical analyser tests of the cured composites show that the re-agglomeration provides an increase of the energy dissipation capability when an appropriate interfacial bonding is in place. These results suggest that the morphology of re-agglomerates offers an effective interesting nano-reinforcement architecture for composites targeted at energy absorption and vibration damping.

This study investigated some special effects of high molecular weight poly(p-phenylene terephthamide) (PPTA) on steady-state and transient rheology of lyotropic PPTA/H2SO4 solutions. The solutions with the same concentration were prepared to possess different ratios of the high molecular weight PPTA (Hi-PPTA, η inh = 7.15 dL/g) to ordinary PPTA (Ord-PPTA, η inh = 5.43 dL/g). With increased Hi-PPTA amount in the solutions, viscosity of the solutions was reduced in the “Newtonian” plateau of the flow curve. The first normal stress difference N1 in the high shear rate range was strongly affected by Hi-PPTA. Increasing the Hi-PPTA amount, the PPTA/H2SO4 solutions showed a significant decrease in the negative N1 minimum and increase in the corresponding shear rate γ ˙ min . After cessation of steady-state shearing, the recoverable strain obviously increased for the solutions with the increasing Hi-PPTA amount. Accordingly, the dynamic modulus ( G ″ ) maximum and time corresponding to the G ″ maximum became smaller for the relaxation process.

A systematic rheological method is suggested to study the kinetics of concentration fluctuation during phase separation. It is based on the idea that the storage modulus of a phase separating polymer blend is composed of modulus due to the growing domains (interfacial contribution) and due to the thermally induced local composition fluctuations inside the domains (components' contribution). The two part contributions to the blend modulus varied with frequency. A crossover frequency was determined, below and above which the elastic modulus is dominated by the interfacial contribution and by the components' contribution, respectively. At frequency much above the crossover frequency, the variation of storage modulus is due to the change of local compositions, which can be calculated according to the relationship between the blend composition and the dynamic modulus in miscible state. In addition, the steady state values of local compositions can be considered as the thermodynamic equilibrium compositions at the annealed temperature, which help us to construct phase diagram. Moreover, the interfacial contribution at frequency lower than the crossover frequency could be isolated by subtracting the components' contribution from the blend's modulus. The characteristic length of domains were got through YZZ model with the equilibrium interfacial tension, which is comparable to the results from transmission electron microscopy (TEM). Furthermore, from the evolution of local compositions and the growth way of the characteristic length of domains, the crossover time from the intermediate stage to the late stage of spinodal decomposition can be specified. This method is tested on poly (methyl methacrylate)/poly (styrene-co-acrylonitrile) (PMMA/SAN) blend, and would be applicable in other polymer blends with viscoelastic asymmetry.

Epoxy-silica hybrids were produced from a diglycidyl ether of bisphenol-A resin using Jeffamine 230 hardener with a two-step in situ generation of siloxane domains. The siloxane component was obtained by hydrolysis and condensation of a mixture of gamma-glycidoxypropyl-trimethoxysilane and tetraethoxysilane, which was added to the epoxy resin after removal of the formed alcohols and water. The morphological structure of the hybrids was examined by TEM, SAXS and WAXS analysis, and confirmation of the identified co-continuity of the constitutive phases for nominal silica contents greater than 18%wt was obtained by TGA and DMA analysis. While the loss modulus was found to increase monotonically over the entire range of siloxane content, the glass transition temperature exhibited a stepwise increase upon reaching the conditions for phase co-continuity. Molecular dynamics simulations were used to produce model structures for silsequioxanes cage-like structures, as main constituents of the siloxane phase. The predicted interdomain distance between the silsequioxane structures was in agreement with the SAXS experimental data.

A novel triblock copolymer, having a center block of high molecular weight polyisobutylene (PIB) and alloocimene (allo) end-blocks, was synthesized and the mechanical properties characterized. The phase-separated morphology consists of tethered PIB, with the glassy allo domains functioning as reinforcing filler. Thus, at ambient temperature the dynamic modulus is larger than that of PIB homopolymer by about 40%, and there is pronounced reinforcement from the glassy domains. The triblock polymer exhibits thermoplastic elastomer behavior, consistent with the structure. For temperatures above the allo glass transition (71 °C), the material undergoes an order–disorder transition, which causes substantial softening; however, this lability of the mechanical response is largely reversible. Since the repeat units of polyisobutylene cannot be crosslinked, this new material offers a route to processible, PIB based networks.

In a recent work published by Haugan et al. (ACS Macro Lett., 2018, 7, 525–530.), the linear viscoelastic behaviors of a series of random graft polymers as a function of grafting density ( Z ) and backbone degree of polymerization ( n b b ) for a constant side chain degree of polymerization was investigated. The results were interpreted to imply that as Z increases the backbone concentration decreases and the distance between entanglements increases (the number of backbone degree of polymerization between entanglements ( n e , b b ) increases from 55 for Z = 0 to 550 for Z = 1 .). One evidence of entanglement formation was that the zero-shear rate viscosity ( η 0 ) showed a departure from Rouse scaling to reptation scaling as molecular weight increased. However, the values of η 0 from the dynamic modulus measurements used in that work were, for multiple cases, underestimated because the Newtonian plateau at low frequencies was not reached. In the present work, the rheological data for these graft polymers are reanalyzed, some samples are measured again, and the resulting new estimates of the zero shear-rate viscosity ( η 0 ) lead to changes in the interpretation of the results. Furthermore, we calculated the retardation spectra (L(τ)) for the samples, showing that the entanglement behavior of these systems is similar to but not identical to the behavior of the linear chain polymer. The results show that in the transition from Rouse-like to entangled behavior η 0 exhibits a M w 3.4 dependence on molecular weight rather than the M w 3 previously reported for these graft polymers. By plotting η 0 as a function of n b b at different Z , the data collapse into two families of behavior and the critical grafting density Z is approximately 0.2–0.25. The onset of entanglements as n b b or M w increases at fixed Z is confirmed from the retardation spectrum, However, the progressive development of the retardation spectrum for these side chain diluted systems differs from that of entangled polymer solutions in that the spectrum first broadens at short times before splitting into two distinct peaks, while for solutions the appearance and shifting to longer times of a second peak occur more abruptly.

The correlation between rheological behavior and time evolution of the phase separation patterns was investigated in the epoxy/thermoplastic blends. Before and during the induction period of phase separation, the storage and loss modulus initially increased with epoxy curing reaction and the concentration fluctuation. At the late stage of phase separation, the modulus values also increased and showed a sharp enhancement around the epoxy gel point. However, the time evolution during the reaction induced phase separation process differed a lot at various thermoplastic (TP) concentrations. At the low TP concentrations, the rheological parameters decreased with the coarsening of sea-island structure. At the high TP concentrations, the TP-rich continuous structures initially formed and maintained until the end, resulting in a continuous increase for the rheological characters. At middle TP concentrations, formation and evolution of the three-layered structure displayed a complicated rheological behavior. It was found that the storage modulus quickly increased, reached a vertex, then rapidly decreased, reached a minimum, and increased again afterwards. Although the rheological behaviors were almost phenomenologically similar as that in the normal dynamically symmetric system, driving force for the variation was fundamentally different. Especially for the case of middle TP concentrations, the behavior of the holistic volume shrinking of the slow dynamic TP-rich network and the flowing out of the fast dynamic epoxy-rich phase from the network during this period, as radically transformed the nature of the matrix from an elastic network to a macro-phase separated layer structure and caused the dramatic change of the rheological behaviors.

Blends of two elastomeric ethylene–octene copolymers with similar octene contents having a random (ORC) and a blocky architecture (OBC) are prepared by melt mixing. The thermal and mechanical properties of ORC, OBC and their blends are investigated by DSC, dynamic mechanical analysis and tensile tests. The morphology of the semi-crystalline samples is studied by AFM and WAXS. Two types of crystals have been observed: (i) Orthorhombic crystals forming lamellae with an estimated thickness of about 13 nm composed mainly of long polyethylene-like sequences of OBC that melt a temperature of about 120 °C and (ii) fringed micellar crystals with a thickness of 2–4 nm formed basically by short polyethylene-like sequences of ORC that have melting temperatures between 30 and 80 °C. The amorphous phase contains a relatively homogeneous mixture of segments of both components indicated by the relatively uniform shape of the loss modulus peaks from dymamic-mechanical measurements for all investigated copolymers and blends. ORC crystallization is hindered in blends as indicated by lower melting enthalpies. This might be related to the high octene content of the amorphous phase at the relevant crystallization temperature as well as geometrical constraints since ORC crystallization occurs in an already semi-crystalline polymer. The results of tensile tests show that the mechanical behavior can be tailored via blend composition and morphology of the semi-crystalline material. The findings clearly indicate that blending is a powerful strategy to optimize the properties of polyolefin-based copolymers.

We compare the nonlinear mechanical properties of silks under load with the quasi-static and isothermal dynamic mechanical properties of nylon as well as human hair. For silk and nylon, the dynamic storage modulus increases with increasing static load, while the quasi-static modulus decreases considerably through yield. However, the modulus of hair decreases irreversibly for both loading conditions. For silk, the increase in storage modulus is only partially reversible after high-loading and is accompanied by a non-recoverable strain. For nylon, the dynamic modulus increase is largely reversible after increased static loading up to a second high stress yield point, where modulus then decreases. Taken together, our data suggest that the dynamic modulus increases with increasing order in the silk and nylon structures under static load, whereas the morphology of hair is gradually degraded under load.

How the viscoelastic asymmetry affects the concentration fluctuation and its manifestation in rheology of miscible polymer blends are examined in this work. The linear viscoelastic stress of polymer blends is divided into the components stress and the stress due to concentration fluctuation. The dynamic coupling between the fluctuation in concentration and the stress is represented by the two-fluid model, which is linearized and solved under small amplitude oscillatory shear to give the concentration fluctuation induced stress. A strong influence of components’ viscoelasticity on the concentration fluctuation is clearly demonstrated in the viscoelastic asymmetric system through the enhancement in the elastic modulus at low frequency. The decisive parameter is the viscoelastic length which depends mainly on the dynamic asymmetric parameter and the zero shear viscosity of blends. It is also found that the dynamic coupling effect gradually fades as it gets close to the spinodal point, where pure concentration fluctuation dominates. The dynamic moduli due to the concentration fluctuation at spinodal point exhibits the same power law dependence on oscillatory frequency, which is a characteristic of critical gel and could be used as an alternative criteria to determine the spinodal temperature.

In the present paper, dynamic mechanical properties of poly(n-alkyl acrylates) (PnAA) and poly(n-alkyl methacrylates) (PnAMA) with different alkyl side chain length were studied. The results show that with the increase of alkyl side chain length, the storage modulus changes more steadily, and the loss modulus peak and the tanδ peak become broader for PnAA and PnAMA. At the same time, the tanδ peak is more and more apart from the loss modulus peak and the point where the storage modulus begins to drop. For quantitative discussion, three variables, the steepness index (S), the transition wideness (W) of storage modulus and the integration area (A) of tanδ were defined to investigate the potential correlation between the dynamic mechanical properties and alkyl side chain length. It can be observed that S decreases while W and A increase with increasing alkyl side chain length. Moreover, the relaxation spectra of the two series of polymers are calculated from the corresponding mechanical spectra. The shapes of the relaxation spectra are broader and broader with the increase of the alkyl side chain length. These phenomena are interpreted by the perspective of fragility, molecular packing efficiency and intermolecular coupling.

The mechanical properties of artists’ acrylic (latex) paint films containing different volume fractions of TiO2, CaCO3 and kaolin were measured in uni-axial tension over a broad range of temperatures and crosshead speeds. Young’s modulus results in the glassy region were first compared with several micromechanics theories for particle-filled composites containing elastic phases. It was found that the Mori–Tanaka theory slightly under-predicted the modulus enhancement, while the Lielens approach provided the most accurate results. A nonlinear viscoelastic material model involving a Prony series and the neo–Hookean hyperelastic function was used to represent the tensile data up to relatively small strains of a few percent. From the experimental data, the material model was calibrated and the required parameters were determined. The derived parameters were then used to re-construct relaxation modulus plots, which were compared with the approximations given by Clements and Mas for the viscoelastic Mori–Tanaka theory in the time-domain. It was found that the experimentally observed modulus enhancement was much stronger than the predicted values in the rubbery region. Mechanisms such as constrained polymer at the inorganic particle interface, and the possible formation of a percolation network are discussed.

The co-continuous morphology of polymer blends has received much attention not only because of its potential promotion of mechanical or electrical properties of polymer blends, but also due to its importance in phase separation by spinodal decomposition. Compared to the recent advances in the characterization of co-continuous structure, the rheology of co-continuous blends has not been understood clearly. In this work, a rheological model is suggested to correlate the linear viscoelasticity and the structural information of co-continuous blends. The dynamic modulus of co-continuous blends is composed of the contribution from components and the interface. The interfacial contribution, which is most important in the rheology of blends, is calculated from a simplified co-continuous structure. This model has been compared satisfactorily with available experimental results, which proves a reasonable connection between the co-continuous structure and linear viscoelasticity of blends.

The selective distribution of aluminum borate whisker in isotactic polypropylene (iPP)/syndiotactic polypropylene (sPP) blends was studied. For iPP/sPP/whisker composites, whiskers are distributed in iPP phase, which follow the theory of interfacial tension. When Irganox 1010 is introduced into the composites, the distribution of whiskers is changed from iPP phase to sPP phase. The results of contact angle tests indicate that the characteristics of the whisker surface are modified by Irganox 1010 and the interactions between the whisker and the matrix are dominated by van der Waals type power law. An entropy-penalty process dominates the change of distribution of whiskers in the composites. The DMA tests show that the loss modulus of composites is improved when whiskers distribute in sPP phase.

In this paper we present the results of comparative dynamic stress relaxation studies performed with poly(styrene-b-isobutylene-b-styrene) (SIBS), polyurethane (PU) and polyester (PED) biomaterials in air and simulated body fluid (SBF) at 24 °C and 37 °C. SIBS showed the highest value of relieved stress under constant strain (24.1% after 100,000 cycles in air) with PED and PU having similar relative change (12.2% and 10.5%). In spite of its softness (Shore A 56 vs. 80), the dynamic modulus (Edyn) and stiffness of SIBS were in between PED and PU. The behavior of the materials was correlated to their structure: SIBS is an amorphous block copolymer with a long elastomer midblock, while PU and PED are semicrystalline segmented copolymers with much shorter soft blocks, and hydrogen bonding. SIBS and PED were relatively insensitive to SBF and temperature changes, while PU experienced the largest changes in physical properties in vitro (simulated body fluid, 37 °C).

Electro-rheological (ER) effect of a blend composed of two liquid crystalline materials with different molecular weights is described in this article. The results indicated that ER effect of the blend was observed at the temperature range where each neat sample did not show ER effect. Furthermore, both storage modulus ( G ′) and loss modulus ( G ″) decreased drastically at the temperature range for the blend in dynamic viscoelastic measurements. We show that steady ER effect could be obtained by using a blend made up of two liquid crystalline components, whereas remarkable increment in shear stress was not observed for each component under applied electric field.

The dynamic mechanical properties of nanocomposites of functionalized single-walled carbon nanotubes dispersed in polystyrene are reported as a function of temperature. For nanocomposites containing less than 0.1 wt% nanotubes, the enhancement of the magnitude of the complex modulus | E ∗ | = E ′ 2 + E ″ 2 , where E′ and E″ are the elastic and loss moduli, respectively, exceeded the predictions of the Halpin–Tsai model (this model is often used to predict the properties of macroscopic composites). In this concentration range, however, the loss tangent, tan δ = E″/E′, of the nanocomposite remained comparable to that of pure PS, i.e., comparable elasticity. At larger concentrations the mechanical response became more elastic than PS, but the magnitude of the complex modulus fell appreciably below predictions based on the Halpin–Tsai model. An alternate hypothesis that relies on the role of attractive interactions between the nanotubes and polystyrene chains, and consistent with previous Raman scattering and glass transition temperature data, is proposed to describe the observed dynamic response.

Viscoelastic behavior of highly elastic magnetic elastomers has been studied by three different experimental techniques: elongation, static and dynamic shears. It has been shown that the elastic modulus of the materials increases considerably in an external homogeneous magnetic field of up to 0.3 T (100-fold increase of the tangential modulus has been observed at small 1–4% deformations). The appearance of the new effect of pseudo-plasticity induced by the magnetic field has been observed leading to a considerable (up to 100-fold) increase in the shear loss modulus of the composites.

The addition of silicalite-1 nanoparticles (0.2–20 wt%) increased slightly the crystallization temperature of HDPE with silicalite-1 content, at 20 wt% loading by ca. 2.5 °C, but it had little effect on the melting temperature. The nanocomposites displayed a little higher onset degradation temperature than pure polymer by 7–11 °C. The WAXD profiles showed that the intensity of diffraction peaks for HDPE was decreased with increasing silicalite-1 content from 5 wt% but that the peak position of every crystal plane did not shift in the presence of silicalite-1 nanoparticles. The incorporation of the nanoparticles increased the melt viscosity of HDPE with silicalite-1 content. It also increased both storage ( G ′) and loss modulus ( G ″). In the so-called Cole–Cole plot, pure HDPE showed a single master curve whose slope was 1.37, while the nanocomposites with 10 and 20 wt% silicalite-1 exhibited the inflection in the low frequency range before which the slopes were 1.22 and 1.02, respectively. Much more accelerated crystallization behavior under shear was observed with silicalite-1 content at the isothermal crystallization temperature of 125 °C than at 120 °C.

Composites of surface treated and untreated non-colloidal CaCO3 particles and high-density polyethylene (HDPE) with different filler loading (0–30 vol%) were prepared. Their viscoelastic properties were studied by dynamic strain sweep and small amplitude oscillatory shear and correlated to the particle–particle and particle–matrix interactions. The results gave insight into the mechanism of polymer reinforcement by solid inclusions and the factors that lead to the often observed solid-like response in the terminal zone. With increasing filler volume fraction, the particles tend to agglomerate and build clusters (local structures) that can be disintegrated by shearing. Up to 30 vol% no evidence for a space-filling particle network could be found. The presence of clusters increases the viscosity, the moduli and the viscoelastic non-linearity of the composites. Coating the filler surface by a stearic acid monolayer reduces its tendency to agglomerate as well as the adhesion between the particles and the polymer, leading to lower viscosity and interfacial slippage with increasing strain amplitude. Solid inclusions increase the storage modulus more than the loss modulus, hence decrease the material damping. The hydrodynamic reinforcement is frequency independent and dominates at high frequency. Polymer adsorption on the particles surface results in a transient filler–polymer network, which together with the topological restraints exerted by the inclusions on the polymer chain reptation leads to slow relaxation. These slow relaxation processes are sensitive to the oscillation frequency and strongly contribute to the polymer reinforcement at low frequencies. Agglomerates differ in shape and packing from the nearly spherical primary particles, and exert strong restraints on the polymer chain relaxation, hence offer an additional contribution to the composite's moduli. The sum of these effects results in higher moduli and a shift of the crossover (liquid-like to solid-like) frequency to lower values with increasing filler volume fraction. They also lead to the often-observed tendency towards a solid-like response in the terminal zone before a space-filling filler network is formed. Hydrodynamic and micromechanical models can only predict the hydrodynamic reinforcement, provided that the polymer strongly adheres to the inclusions.

In many applications, polymer materials undergo a large variety of mechanical loading conditions, wherein the influences of temperature and strain rate are of prime importance. Mahieux and Reifsnider [Mahieux CA, Reifsnider KL. Polymer 2001;42:3281. [19]] have proposed a statistical model to describe the stiffness variation of polymers over a wide range of temperatures. However, this model does not consider any frequency/strain rate dependence of the stiffness modulus. Starting from this consideration, we propose here to transform this latter model into a robust physically based model for the prediction of the stiffness modulus for a wide range of temperatures and frequencies/strain rates. This new formulation has been successfully validated for two amorphous polymers, polymethylmethacrylate (PMMA) and polycarbonate (PC), using dynamic mechanical analysis and uniaxial compression testing. Good agreement has been found between theory and experiment for the non-linear behavior of the initial Young's modulus, at the very high strain rates.

Exfoliated polystyrene (PS)/organo-modified montmorillonite (MMT) nanocomposites were synthesized through in situ free radical bulk polymerization by dispersing a modified reactive organophilic MMT layered silicate in styrene monomer. The original MMT was modified by a mixture of two commercial cationic surfactants, [2-(acryloyloxy)ethyl](4-benzoylbenzyl)dimethylammonium bromide (ADAB) and cetyltrimethylammonium bromide (CTAB), with the former containing a polymerizable vinyl group. The exfoliating and intercalating structures were probed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Comparing with pure PS, the nanocomposites show much higher decomposition temperature, higher dynamic modulus, stronger shear thinning behavior and a smaller die swell ratio. The leveling-off of the storage modulus at low frequencies in the oscillatory shear measurements, as well as the observed yield like behavior, implies that the formation of a percolating nanoclay network is the origin of the enhanced viscoelasticity in these composites.

Dynamic mechanical analysis was performed to characterize the viscoelastic properties of binary and ternary blends of fluorocarbon elastomer (FKM), acrylic elastomer (ACM) and liquid crystalline polymer (LCP). The results showed that the storage and loss modulus of all the blends increased significantly with the weight percentage of the LCP. The glass transition temperature evaluated at the loss modulus peak, were in the range of −10–+5 °C for all the blends. The time temperature superposition principle was applied for the FKM/ACM and 20% LCP filled FKM/ACM blend in order to evaluate the changes in the viscoelastic properties of FKM/ACM blend by the addition of LCP. The Arrhenius and William–Landel–Ferry (WLF) equations were used to quantify the viscoelastic behaviour at the glass transition region. Both the blends exhibited a single relaxation, which is glass transition, observed as a peek in the loss modulus at 1 Hz. The glassy moduli of these two systems were found to be comparable, but the rubbery moduli of the LCP filled FKM/ACM was much higher than the LCP unfilled system. However, the viscoelastic behaviour of these two systems and their sensitivity to time temperature may be considered to be quite similar.

Additional developments in the comprehension of the rheological behaviour of polymer latices, especially near the high critical concentration ϕ c , are presented for two polystyrene latices of average particle diameters close to 200 nm with different electrostatic properties. Not surprisingly, there is a rapid transition in the rheological characteristics over a narrow range of polymer volume fractions as the concentration of the disperse phase increases. By examining twelve different polymer volume fractions a unique value of the critical volume concentration, ϕ c , was found for each latex. At this point, the steady shear viscosity, dynamic modulus, and dynamic shear viscosity change dramatically. Furthermore, these critical concentrations are well confirmed by the percolation theory for the dynamic zero shear viscosity as a function of volume fraction. The Cox–Merz rule is not obeyed by these dispersions at the concentrations greater than ϕ c . By using a controlled strain Couette rheometer with a gap of 1.2 mm, shear thickening limits were also observed for both latices. The concentration dependence of the onset shear rate for shear thickening changes near ϕ c for each of the two latices.

The viscoelastic properties of different silica filled polymers were investigated. A variety of rheological observations was studied in the molten state, such as Payne effect and modulus recovery kinetics, in ethylene vinyl acetate, polystyrene and polypropylene filled with non-porous silica. The concept of the filler network breakdown seems to be adequate in describing the strain-dependence of dynamic mechanical properties of composites. Recovery tests of the complex shear modulus performed by subsequent strain sweep or time sweep experiments show evidence that the initial equilibrium network structure cannot completely restore within several hours. Furthermore, new strain sweep experiment after in situ crystallisation (or glass transition in polystyrene composites) of the sample leads to a total recovery of the linear modulus suggesting that the silica network structure in molten state have the memory of the silica structure in solid state. On the other hand, the complex shear modulus measured at lower strain for cross-linked EVA composites are perfectly recoverable in few seconds as proven by subsequent strain sweeps.

The structure and rheological behavior of atactic poly(vinyl alcohol) (a-PVA) hydrogels prepared by freeze/thaw cycles were investigated as a function of polymer concentration and number of freeze/thaw cycles. The presence of phases with different mobilities was observed using 13 C CP/MAS and DP/MAS NMR experiments. The degree of crystallinity of the a-PVA-rich phase was determined by 1 H NMR free decay experiments. Measurements of the shear storage and loss modulus were performed at a fixed frequency of 1 Hz and a strain value of 0.1%, i.e. under conditions where the deformation imposed on the gel structure is entirely reversible. Results thus obtained showed that an increase in the number of freeze/thaw cycles induces an increase in the degree of crystallinity in the polymer-rich phase together with an increase in the storage modulus. The a-PVA hydrogels became more fragile as the number of freeze/thaw cycles was increased. Moreover, both the percentage of protons in a rigid environment measured by 1 H NMR and the storage modulus values tended to a limiting value after six freeze/thaw cycles. These results show that the first five or six freeze/thaw cycles play a very important role in determining the hydrogel structure and rheological properties. A more detailed comparison of NMR and rheological data led to the conclusion that the storage modulus is mainly controlled by the a-PVA crystallinity while the hydrogen bond interactions have a much smaller contribution.

This study was designed to determine the linear viscoelastic properties of a family of metallocene-catalysed propylene homopolymers in the ‘plateau’ and terminal regions. A low value of the plateau modulus, around 4.8×105 Pa, was obtained. Our results differ from those reported for conventional amorphous polypropylene in several recent studies. As previously undertaken for metallocene-catalysed polyethylenes, the rheological behaviour observed was discussed in terms of a possible decrease in the entanglement density and/or an increase in chain flexibility with respect to other polymers of similar chemical composition. We subsequently applied an existing model, based on simplified molecular dynamics, that provided a correct description of the dynamic modulus from knowledge of the form of the molecular weight distribution and the materials' rheological constants GN0 and η0. This method has been successfully applied to several types of polymer.

The rheological properties of poly(trimethylene naphthalene-2,6-dicarboxylate) (PTN) were studied using a dynamic stress rheometer with oscillatory parallel plates. The influence of temperature and molecular weight on the storage modulus, loss modulus, and complex viscosity was investigated. It was possible to express the temperature dependence of the shift factors a T with the Arrhenius equation; the activation energy was found to be 85 kJ/mol. A comparison of molecular weight determined: (a) by rheological measurements and (b) by Mark–Houwink–Sakurada equation showed excellent agreement.

A novel EMAA ionomers with the incorporation of low molecular weight carboxylic acid have been developed to reduce melt rheology without changing the complete transparency of ionomers. Here, a blend of EMAA-59Zn (93 wt%) and montanic acid (MA, C 27 H 55 COOH, 7 wt%) was investigated in terms of TGA, DSC, FT-IR, and dynamic shear viscosity. A good heat stability of MA during melt blending preparation and melt viscosity measurement was confirmed by TGA. DSC showed only one peak (86.9°C) for the blend sample, and FT-IR exhibited additional peaks (1545, 1625 cm −1 ) by the blending. These facts suggested that the blend is a homogeneous mixture and the blend induced an additional new coordination structure between Zn and carboxylic acid. Dynamic melt rheological measurement exhibited a significant decrease of storage modulus and loss modulus by the blending. The reduction of melt rheology was more than the addition of plasticizing effect and the decrease of neutralization. The newly induced coordination structure implies a relationship with the unexpected additional reductions.

The influence of β crystals on the mechanical properties of isotactic polypropylene is studied on compression-moulded sheets without filler or filled with stearate-coated calcium carbonate particles. A crystallisation procedure is setup for producing sheets with various amounts of β crystals, trying to keep constant crystallinity, spherulite size and crystal thickness. An optimum of β crystals among α crystals is first produced by isothermal crystallisation at 110°C. Then gradual transformation of β into α crystals is carried out through thermal annealing at 152°C after an intermediate cooling down to room temperature. Due to the thermal inertia of the large sheet thickness, the amount of β crystals does exceed 10% for unfilled sheets and 50% for filled sheets. Dynamic mechanical behaviour shows that molecular mobility is higher in the β crystals than in the α crystals, as judged from the temperature of the crystalline relaxation. Loss modulus in the temperature range of the crystalline relaxation also indicates greater damping capacity for the β crystals. This is discussed in terms of activation of conformational defects moving along the chain stems in the crystal. Plane strain compressive testing reveals better ductility for β rich samples. Interpretation is provided using an approach of semi-crystalline polymer plasticity based on dislocation-governed crystallographic slip. Correlation is made with the viscoelastic behaviour through the concept of conformational defects.