Effect of shear flow on multi-component polymer mixtures

The effect of shear flow on the structure of multi-component polymer blends and solutions is reviewed. The techniques of small-angle light and neutron scattering, optical microscopy, and fluorescence microscopy are used to directly assess the influence of an externally applied shear field on the phase stability and morphology of model polymer blends and solutions. The polymeric fluids of interest vary from miscible blends and pseudo-binary solutions near a critical point of unmixing to thermodynamically unstable and completely immiscible blends undergoing spinodal decomposition and coarsening in the presence of simple shear flow. We review the influence that critical concentration fluctuations, viscoelasticity, and rheological asymmetry have on the shear response of polymer blends and solutions individually, and we discuss the practically important interplay of these three separate effects. We conclude our review by discussing the need for more computational and theoretical efforts focused on shear-induced structure in polymer blends.     

Linear viscoelasticity of polymer blends with co-continuous morphology

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.     

Dynamic and capillary rheology of LDPE‐EVA–based thermoplastic elastomer: Effect of silica nanofiller

The effect of pristine silica nanoparticles on the dynamic and capillary rheology of a model LDPE‐EVA thermoplastic elastomeric system is explored in this paper. The pristine silica nanoparticles were melt‐blended with the LDPE‐EVA system at 1.5, 3, and 5 wt% loadings, respectively, by varying the sequence of addition. In one of the compositions, coupling agent bis‐[3‐(triethoxysilyl)propyl] tetrasulphide (Si‐69) was used to improve the interaction of hydrophilic silica particles with polymer matrix. Results obtained reveal that the viscoelastic behavior of such composites is influenced remarkably by loadings of silica, variation of sequence, and addition of Si‐69. Upon addition of coupling agent, G′ value increases especially at higher strain levels due to increased polymer‐filler interactions. All systems with various loading of nanosilica represent an increase in elastic response with increasing frequency. Both the unfilled and filled blends exhibit rheological behavior of non‐Newtonian fluids. But interestingly, the viscoelastic response varies markedly with the temperature. The dynamic and steady shear rheological properties register a good correlation in regard to the viscous vs. elastic response of such systems. Finally, the rheological behavior is correlated with morphology of the present system processed at various shear rates. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Analysis of holding power in the blends of poly(butyl acrylate) with poly(vinylidene fluoride-cohexafluoro acetone)

Shear adhesion of pressure-sensitive adhesive tapes was evaluated for the blends of poly(butyl acrylate) with poly(vinylidene fluoride-co-hexafluoro acetone). The shear adhesion was determined as the function of the shear strain of pressure-sensitive adhesive tape against elapsed time under the shear stress. Shear adhesion of the blends increased with increasing poly(vinylidene fluoride-co-hexafluoro acetone) content. Experimental shear strain data were characterized with dynamic viscosity, stress and shear rate plot, and a generalized viscoelastic model of shear adhesion. However, the experimental data cannot be expressed with these viscoelastic properties. It is believed that shear adhesion is influenced by the viscoelastic properties and other factors (e.g., friction coefficient between adhesive and adherend or cohesive strength of adhesive polymer). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:727–738, 1998     

Morphology and rheological behavior of maltene–polymer blends. I. Effect of partial hydrogenation of poly(styrene‐block‐butadiene‐block‐styrene‐block)‐type copolymers

Because of the importance of the maltene–polymer interaction for the better performance of polymer‐modified asphalts, this article reports the effects of the molecular characteristics of two commercial poly(styrene‐block‐butadiene‐block‐styrene‐block) (SBS) polymers and their partially hydrogenated derivatives [poly{styrene‐block[(butadiene)_1?x–(ethylene‐co‐butylene)_x]‐block‐styrene‐block} (SBEBS)] on the morphology and rheological behavior of maltene–polymer blends (MPBs) with polymer concentrations of 3 and 10% (w/w). Each SBEBS and its parent SBS had the same molecular weight and polystyrene block size, but they differed from each other in the composition of the elastomeric block, which exhibited the semicrystalline characteristics of SBEBS. Maltenes were obtained from Ac‐20 asphalt (Pemex, Salamanca, Mexico), and the blends were prepared by a hot‐mixing procedure. Fluorescence microscopy images indicated that all the blends were heterogeneous, with polymer‐rich and maltene‐rich phases. The rheological behavior of the blends was determined from oscillatory shear flow data. An analysis of the storage modulus, loss modulus, complex modulus, and phase angle as a function of the oscillatory frequency at various temperatures allowed us to conclude that the maltenes behaved as pseudohomogeneous viscoelastic materials that could dissipate stress without presenting structural changes; moreover, all the MPBs were more viscoelastic than the neat maltenes, and this depended on both the characteristics and amount of the polymer. The MPBs prepared with SBEBS were more viscoelastic and possessed higher elasticity than those prepared with SBS. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Isochrone based mastercurves of viscoelastic functions

Summary Composite curves of the viscoelastic functions may be obtained not only by the usual shift of isotherme data along the frequency axis, but also by a shift of the respective isochrones along the reciprocal temperature axis. This shift along the 1 / T axis is equivalent to that of the isochrones of dynamic viscosity, along the slope of zero shear apparent activation energy of flow. It is demonstrated that both types of shift are related to this zero shear activation energy of flow, so that an unique shift mechanism is effective in both cases.Isochrone based mastercurves are favourable for studies on polymer blends particularly, because the problematical choice of the reference temperatures of the components is circumvented.     

Phase separation of poly (methyl methacrylate) / poly (styrene-co-acrylonitrile) blends in the presence of silica nanoparticles

The effects of silica nanoparticles on the phase separation of poly (methyl methacrylate)/poly (styrene-co-acrylonitrile) (PMMA/SAN) blends are studied by the rheological method. The binodal temperatures of near-critical compositions were obtained by the gel-like behavior during spinodal decomposition, which is a character of polymer blends with co-continuous morphology. The shifted Cole–Cole plot method was introduced to determine the binodal temperatures of off-critical compositions based on the appearance of shoulder-like transition in the terminal regime of blends with droplet morphology. Such method is found also applicable in nanoparticle filled polymer blends. Moreover, a new method to determine the spinodal temperature from Fredrickson-Larson mean field theory was suggested, where the concentration fluctuation's contribution to the storage modulus is used instead of the whole dynamic moduli. This method was also successfully extended to nanoparticle filled polymer blend. The influences of the concentration and the average diameter of silica particles on the phase separation temperature were studied. It was found that the small amount of the silica nanoparticles in PMMA/SAN blends will significantly change the phase diagram, which is related to the selective location of silica in PMMA. The comparisons with thermodynamic theory of particle-filled polymer blends are also discussed.     

Studies on equilibrium swelling,dye adsorption,and dynamic shear rheology of polymer systems based on chitosan-poly(vinyl alcohol) and montmorillonite

Chitosan-poly(vinyl alcohol)/clay membranes were prepared by physical blending. These hybrid systems were characterized through infrared spectroscopy, microscopy, swelling, and oscillatory rheology. Adsorption of a commercial reactive dye by these membranes was further studied. Results showed that more stable blend membranes were formed due to the strong interaction in the polymers. These membranes showed substantial percent swelling in water and shrinking in saline solution. Adsorption analysis showed the ability of the blends to fix organic dyes, and to be used in liquid waste processing. In dynamic rheology, it was observed that all measured viscoelastic properties were influenced by polymer composition and clay content. For all samples, results show a typical behavior of an entangled system in the case of low concentrated macromolecular viscoelastic fluids. The dynamic moduli exhibited higher values for blends, compared with values of the pure polymers, which is an indication of good stability and tendency of gel formation.     

Increased flow property of polycarbonate by adding hollow glass beads

The steady shear viscosity and dynamic viscoelastic properties of glass beads (GB) filled polycarbonate (PC) melts were studied at varying filler diameters and concentrations. The PC/GB composites containing small amounts of GB bore lower melt viscosity and dynamic modulus than those of pure PC at studied frequencies and shear rates, showing a “ball‐bearings” effect. For highly filled systems, the viscosity and dynamic modulus were decreased further at higher frequencies and shear rates. This ball‐bearings effect was enhanced by changing the GB from larger to smaller one. The oscillatory experiments with modified shear stress showed a stress‐dependent decrease of the viscoelastic properties, and revealed an interfacial slip mechanism, combined with the polymer chains disentanglement at melt/solid interfaces. The scaling relationship between the relative viscosity and the mean interparticle gap confirmed that the interfacial slip and polymer chains disentanglement were induced by the extremely high local shear developed in the narrow gaps between the nearby rotating spheres. POLYM. ENG. SCI., 45:1119–1131, 2005. © 2005 Society of Plastics Engineers     

基于流固耦合的密炼机动力学特性分析

采用单向与双向流固耦合计算方法,对密炼机在3种不同工况下的内流场及结构场进行分析,得到流场瞬态剪切率和结构场最大应力位置与最大位移位置的等效应力,以及最大位移的波动情况。计算结果表明,流场剪切率变化由转子几何外形决定,剪切率波动主频为1倍转子棱倍频,且双向耦合计算结果高于单向耦合计算结果;2种耦合计算得到的转子棱部应力、变形分布具有一致性,波动主频以转子棱顶啮合产生的低频为主;转子外轮廓结构是最大应力波动的主要因素,最大应力位置的自转频率对应力波动影响很小,但最大位移位置的自转频率对应力波动影响较大。     

Evaluation on the degrading behavior of melt polyolefin elastomer with dicumyl peroxide in oscillatory shear flow by Fourier transform rheology

The degradation of melt polyolefin elastomer (POE) at the presence of dicumyl peroxides (DCP) was estimated at elevated temperature in oscillatory shear flow. Large amplitude oscillatory shear (LAOS) experiments followed by Fourier transform rheology (FTR) were carried out to detect and evaluate the branching architecture of the products. The third complex harmonic (I₃^∗) and other two parameters, small strain elastic shear modulus (M) and large strain elastic shear modulus (L), which describe the nonlinearity and elasticity of a material obtained from FTR, are mainly used to characterize the topological structure of polymer chains. The results indicate the degradation appeared just after a large amount of the long chain branches (LCB) created rather than as soon as the reaction started when the strain was applied within the linear viscoelastic regime of the original POE at high frequencies. This is different from our previous result that the dominant reaction was coupling in linear shear flow. The threshold strain for degradation decreased with the oscillatory frequency, and the frequency owned a different acting mechanism from the strain amplitude to cause the degradation reaction. Moreover, there is a kind of selectivity of shear rate on the polymer chains for degradation. Low frequency results in short linear scission segments and a long branched chain suffers from degradation more than once. At high frequency, the possibility of degradation at the sites near the branching points of LCB increases.     

Rheology of a miscible blend of SAN and SMA

We present results of oscillatory shear rheology experiments on miscible blends of commercial styrene‐acrylonitrile (SAN) and styrene‐maleic anhydride (SMA) copolymers. We find that this blend system upholds the empirical time‐temperature superposition principle. We compare the thermorheological behavior in this system with other blends, on which oscillatory shear data have been published in the literature. We show that thermorheological behavior in these blends is indeed comparable to other known thermorheologically simple blends. Thermorheological simplicity in this blend is nicely anticipated by a thermorheological phase diagram in the parameter space of dynamic asymmetry and free volume, which we have recently proposed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1245–1249, 2000     

Rheological characterization of the gel point in polymer‐modified asphalts

In this work, the rheological characterization of the gel point in polymer‐modified asphalts is carried out. The viscoelastic properties of polymer‐modified asphalts, in which the polymer is styrene–ethylene butylene–styrene (SEBS) with grafted maleic anhydride (MAH), were measured as a function of MAH concentration. The crosslinking reaction that leads to gelation is characterized by power‐law frequency‐dependent loss and storage modulus (G″ and G′). The relaxation exponent n (a viscoelastic parameter related to the cluster size of the gel) and gel strength S (related to the mobility on the crosslinked chain segments) were determined. The value of the power‐law exponents depends on the composition of polymer, ranging from 0.30 to 0.56, while the value of the rigidity modulus at the gelation point (S) increases with the amount of reactive groups of the modifier polymer. Both n and S are temperature‐dependent in the blends. The blends containing gels present a coarse morphology, which is related to the rheological properties of the matrix and dispersed phase. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Viscoelastic properties of polyamic acid solutions—precursors of polyimides

The rheology of polyamic acid (PAA) solutions, precursors of polyimides used in microelectronic device applications, has been investigated by dynamic (oscillatory) shear flow measurements. Frequency dependent storage and loss moduli and dynamic viscosity were measured in the frequency range 10^?1 to 10³ rad/s at 23°C. The storage modulus G′ (ω) and loss modulus G″ (ω) exhibited quadratic and linear dependence in frequency at low frequencies respectively, the viscoelastic fluid behavior commonly predicted for polymer solutions from many molecular theories. At high frequencies both dynamic moduli become proportional to ω^2/3. The results show that PAA solutions are very high loss viscoelastic fluids, judging from the loss tangent values which far exceed unity. It is suggested that dynamic viscoelastic properties could be used to monitor the degree of imidization since there is a gradual change from viscoelastic fluids to soft viscoelastic solids to hard viscoelastic solids as PAA is converted to polyimides. Onset of non-Newtonian flow as shown on the frequency dependent dynamic viscosity was in the range 30 to 200 rad/s. The viscoelastic constants, zero-shear rate viscosity η_o and steady-state compliance J_e⁰, where also determined from the dynamic data and compared to previous steady shear flow results.     

Phase morphology and melt viscoelastic properties in blends of ethylene/vinyl acetate copolymer and metallocene-catalysed linear polyethylene

The aim of this study was to determine the linear viscoelastic properties of a series of ethylene/vinyl acetate copolymer/metallocene-catalysed polyethylene (mPEs) blends. Newtonian viscosity showed a pronounced positive deviation from the double reptation model, which assumes miscibility or, at least, cooperative relaxation between the mixed species. Enhanced values of steady-state compliance and elastic indices with respect to those of the pure components were also noted. These features are typical of emulsion-like polymer blends and are thought to arise from additional relaxation processes associated with dispersed phase deformability. Application of the Palierne model for emulsions of two viscoelastic liquids showed good agreement with our experimental dynamic results at both ends of the phase diagram. However, the model failed at intermediate compositions. Through the application of several rheological criteria we were able to locate the phase inversion concentration at a weight fraction of w=0.60 in the mPEs. It is suspected that, in this composition range, a fully co-continuous phase develops due to the phase inversion mechanism, which has considerable effects on the viscoelastic properties of the blends.     

Rheological properties of polybutadiene/polyisoprene blend in the unstable and metastable regions under oscillatory shear

The rheological properties of polybutadiene (PB)/polyisoprene (PI) in the unstable and metastable regions under oscillatory shear flow has been studied. Based on the shear quench experiment, it showed that the time dependent storage modulus G^′$G^{\prime }$ initially increased and then decreased with time in the unstable region. The concentration fluctuation led to the increasing part and the coarsening of the bicontinuous structure led to the decreasing of the storage modulus. The rheological response of the nucleation/growth in the metastable region was similar to that of spinodal decomposition. The fluctuation-assisted nucleation theory proposed by Balsara et al. was similar to the spinodal decomposition mechanism, which led to the similar rheological response. However, the continuous nucleation led to the slow growth and the almost linear decayed rheological curve, which was different from that in the unstable region. According to this theory, the relative nucleation rate on the early stage of nucleation could be calculated, which increased exponentially with the reciprocal of quench temperature in the metastable region. The spinodal point under oscillatory shear was also determined by the difference of maximum value of the storage modulus and the bulk modulus.     

部分相容聚合物共混体系相分离的流变学表征方法

针对具有不同动态非对称性的部分相容聚合物共混体系,阐述了用于表征和探测其相分离特征的流变学方法,包括小振幅振荡剪切考察时温叠加原理的有效性和温度扫描,以及稳态剪切温度扫描;并且分析了共混体系的复杂结构对温度依赖性形成差异的深层原因,总结比较了各方法应用时的优缺点及其针对不同强弱动态非对称体系的适用性。     

Measurement of dynamic viscoelastic properties of polymer melts and liquids by the modified rheovibron

A new technique is presented which permits the quantitative characterization of the dynamic viscoelastic properties of polymer melts and liquids. A new sample holding system with oscillatory shear platen and modification of the amplifier and oscillating unit made it possible to measure rheological properties of the viscous liquids using the Rheovibron. The dynamic shear modulus, viscosity, and internal friction of acrylic dope, and silicone fluids are obtained by using the new procedure and developed mathematical expressions. This technique will be useful in studies on the rheological properties characterization of polymer melts and liquids in conjunction with process parameters.     

Rheological examination of temperature dependence of conventional and polymer‐modified road bitumens

Rheological characterization of two types of road bitumens, conventional and polymer‐modified, has been examined in the temperature range between 20°C and 140°C. Tests were carried out before and after ageing following a thin‐film oven test. Polymer‐modified bitumens exhibit non‐Newtonian behaviour up to the 120°C due to a complex secondary structure formed by added polymers. For conventional bitumens, Newtonian behaviour was observed above 60°C. Special attention was paid to measurements and to analysis of the dynamic data of oscillatory shear. The mechanical spectra in a wide frequency range have been obtained using the WLF time‐temperature superposition principle. The analysis of viscoelastic data clearly showed the differences between the two types of bitumen. Conventional bitumens were more sensitive to temperature and to the ageing effects. For polymer modified bitumens, the elastic contribution to viscoelastic response was more pronounced, and independent of temperature and ageing.     

Rheological behavior of CPE/NR blends filled with precipitated silica

Blends of elastomeric chlorinated polyethylene (CPE) and natural rubber (NR) at the blend composition ratio of 80/20 CPE/NR with various precipitated silica loadings from 0 to 30 phr were prepared. Their rheological behaviors were determined using two rheometers with different shear modes, i.e., the oscillatory rheometer (Rubber Process Analyzer, RPA2000) and the rate‐controlled capillary rheometer (Goettfert Rheotester 2000). Results obtained reveal that the viscoelastic behavior of blends is influenced remarkably by loadings of silica. Within the oscillatory shear strains of 0.3–30%, the unfilled blend appears to be almost insensitive to shear strain that means the unfilled blend possesses a broad linear viscoelastic (LVE) region. As silica is incorporated, the elastic modulus (G′) of blends increases, particularly at silica loadings of 20 and 30 phr. The increase in G′ as a function of silica loading could be explained by a reinforcing effect via a hydrodynamic effect as well as a strong interaction between chlorine atoms on CPE molecules and silanol functional groups on silica surfaces associated with a formation of silica tridimensional transient network, usually known as a secondary filler network. Also, all blends with various loadings of precipitated silica reveal an increase in elasticity with increasing frequency, and those with high silica loadings (i.e., 20 and 30 phr) give a more time‐independent elastic response, which supports the presence of filler transient network in these blends. By applying the Cox and Merz concept to the rheological results, the superimposition of flow curves determined from of the oscillatory shear flow and steady shear flow in the highly silica filled blends is possible if the silica transient network effect is eliminated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2565–2571, 2006