Chixing Zhou

Shanghai Jiao Tong University, Shanghai, Shanghai Shi, China

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Publications (139)360.7 Total impact

  • Peng He · Bin Chen · Wei Yu · Chixing Zhou ·
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    ABSTRACT: The effect of block structure on the liquid-solid transition (LST) of ethylene-octene multiblock copolymers (OBCs) during isothermal crystallization had been investigated by rheology, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). Due to the mesophase separation in OBC melts, the formation of critical network at LST in the OBCs with low crystallinity (7-14wt %) was found to be different from that in homogeneous systems. The viscoelastic properties at LST in the heterogeneous OBCs suggested a slower relaxation behavior of the critical network, and the liquid-solid transition in strongly segregated OBCs were observed to occur in intermediate or even late stage of crystallization, demonstrated by the much higher crystallinity and large spherulites at LST. The delayed liquid-solid transition had been discussed and can be attributed to the initial confinement of the hard-block domains on the nucleation and growth of the crystals.
    RSC Advances 04/2015; 5(51). DOI:10.1039/C5RA05030H · 3.84 Impact Factor
  • Source
    Yafang Xu · Chongwen Huang · Wei Yu · Chixing Zhou ·
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    ABSTRACT: 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.
    Polymer 04/2015; 67. DOI:10.1016/j.polymer.2015.04.052 · 3.56 Impact Factor
  • Shanshan Lin · Wei Yu · Xianhong Wang · Chixing Zhou ·
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    ABSTRACT: The degradation behavior of poly(propylene carbonate) (PPC) was investigated during melt processing to infer the mechanism and kinetics of thermal degradation. First, the degradation experiments were carried out in a miniature conical twin-screw extruder at different temperatures, rotating speeds, and processing times. Gel permeation chromatography (GPC) was applied to analyze the molecular weight and molecular weight distributions (MWDs) of melt processed PPC samples. The degradation process at various processing conditions was described by the population balance equations (PBEs) with random chain scission and chain end scission. By comparing the prediction of PBE model with the experimental evolution of molecular weight, it is proposed that random chain scission and chain end scission occur simultaneously. At temperature higher than 160 °C, random chain scission dominates with the activation energy about 120 kJ/mol. Second, a method combining the PBE model and rheology was suggested to determine the kinetics of degradation directly from the torque of mixer during melt processing without further measurements on molecular weight. Such method was applied to melt mixing of PPC in a batch mixer, from which a higher kinetic parameter of thermal degradation and similar activation energy were successfully determined as compared to those obtained from extrusion experiments.
    Industrial & Engineering Chemistry Research 12/2014; 53(48):18411-18419. DOI:10.1021/ie404049v · 2.59 Impact Factor
  • Jianye Liu · Shijun Zhang · Wei Yu · Chixing Zhou ·
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    ABSTRACT: The degrading behaviors of three kinds of melt polyolefin elastomers (POEs) at presence of dicumyl peroxides (DCPs) in transient shear flow were evaluated at elevated temperature by parallel plate rheometer. The critical shear rates for degradations of all POEs were different from one to another. The rheological and gel permeation chromatograph (GPC) results showed that the degradation was more and more distinct and the duration to achieve one similar level of molecular weight decreased as the shear rate increased. For quantitative information on chain structure, linear viscoelasticity combined with branch-on-branch (BOB) dynamic model was used to predict probable compositions and chain topologies of the modified products, which were reasonably explained by the suggested mechanism of radical reactions and could confirm that there was a kind of selectivity of shear rate on POE chains for degradation. Higher shear rate can enlarge the differences in mobility of the two scission parts and can further increase the possibility of effective degradation on the original chains.
    Colloid and Polymer Science 12/2014; 292(12):3261-3269. DOI:10.1007/s00396-014-3367-9 · 1.87 Impact Factor
  • Zhiyong Wang · Wei Yu · Chixing Zhou ·
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    ABSTRACT: Thermally induced phase separation (TIPS) has been widely used to prepare microporous membrane. The interaction and dynamic asymmetry between polymer and solvent sometime make the transition happen through viscoelastic phase separation (VPS) mechanism. Under such condition, cell like structure is obtained with low water permeability. In this paper, a new method is proposed to obtain high permeability membranes by TIPS. Dibenzylidene sorbitol (DBS) and HDPE-g-MAH are introduced into the polyethylene/di-iso-decyl phthalate (HDPE/DIDP) system, which exhibits an upper critical solution temperature (UCST) behavior and undergoes VPS mechanism during cooling. DBS can self-assemble and form fibril network both in HDPE and DIDP. The addition of HDPE-g-MAH make DBS mainly distributed in HDPE-rich domains, while it mostly locates in the DIDP-rich domain in the ternary system due to their similar polarity. The self-assembly of DBS in the HDPE-rich domains can induce the secondary liquid-liquid phase separation, which significantly change the structure in walls between cells. High permeability of pure water and high retention of permeability in silica suspension can be obtained under proper control of the extent of these phase transitions.
    Polymer 11/2014; 56. DOI:10.1016/j.polymer.2014.11.032 · 3.56 Impact Factor
  • yafang xu · Wei Yu · Chixing Zhou ·
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    ABSTRACT: Miscibility in blends of polylactic acid (PLA) and poly (ethylene glycol) (PEG) was investigated by means of differential scanning calorimetry (DSC), polarized optical microscopy (POM) and rheology with specifically designed thermal procedure. Direct observation of phase separated morphology via phase contrast optical microscopy is difficult because of the quite close refractive index of two components. Liquid-liquid phase separation (LLPS) was confirmed by appearance of two glass transitions after the sample been annealed at low temperatures (95~125 oC). Moreover, the accelerated crystallization rate after the sample been annealed at high temperatures (140~160oC) also indicate the existing of LLPS according to the fluctuation assisted nucleation mechanism. An upper critical solution temperature (UCST) type of phase diagram was constructed via combination of DSC and rheological methods. Furthermore, the effects of LLPS on the kinetics of subsequent crystallization of PLA in blends with 15wt% PEG and 30wt% PEG were investigated. Considering the complex effect of LLPS on crystallization, we proposed a new model that integrates the Lauritzen-Hoffman theory and the self-concentration theory to account for the influence of miscibility on the crystallization in blends with different thermal histories. It is suggest that acceleration or deceleration of LLPS on the subsequent crystallization in highly asymmetric system depends on the interplay between the fluctuation assisted nucleation and the variation of mobility during LLPS.
    RSC Advances 10/2014; 4(98). DOI:10.1039/C4RA08985E · 3.84 Impact Factor
  • Hong Zheng · Shengcai Zhu · Wei Yu · Chixing Zhou ·
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    ABSTRACT: Six different solvents, i.e., diphenyl sulfone (DPS), diphenyl isophthalate (DPIP), benzoin (BZ), epsilon-caprolactam (CPL), hydrogenated terphenyl (HTP), and cyclohexyl pyrrolidinone (CHPN), were selected as diluents for poly(phenylene sulfide) (PPS) microporous membranes development via the thermally induced phase separation (TIPS) method. Phase separation behaviors for the various solvents were first identified through thermal analysis of their PPS solutions. Liquid-liquid separation behavior was identified for a group of solvents including DPS, DPIP, and BZ, whereas systems with the solvents CPL, HTP, and CHPN underwent solid-liquid separation during the cooling process. A newly designed casting device, which well simulated the industrial film casting process, was then used to produce films; it consisted of a side-by-side high-temperature plate and room-temperature plate. The different cooling conditions able to be produced by this casting device were found to greatly affect the TIPS process and the properties of the final membranes. The properties of PPS membranes prepared on this device from 30 wt.% binary solutions with the six solvents were investigated. The morphology of PPS membranes was also observed on the samples prepared under different cooling processes for the six solvents.
    Journal of Macromolecular Science Part B 09/2014; 53(9). DOI:10.1080/00222348.2014.931189 · 0.74 Impact Factor
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    Sijun Liu · Wei Yu · Chixing Zhou ·
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    ABSTRACT: We have systematically studied phase separation behavior in ultra-high molecular weight polyethylene/ liquid paraffin/dibenzylidene sorbitol (UHMWPE/LP/DBS) ternary blends. The aim of this paper is to investigate the combined effect of DBS and flow field on the structure and water permeability of UHMWPE microporous membrane. The experimental results show that DBS molecules self-assemble into fibrils firstly during cooling and the blends exhibit a gel-like state before liquid liquid phase transition. The relaxation time of DBS fibrils is quite long, which shows a great sensitivity to flow field as compared to UHMWPE chain. UHMWPE microporous membrane was prepared via thermally induced phase separation method. DBS fibrils, as in situ formed nucleating agent, decrease the pore size and water permeability and enhance mechanical properties of membrane remarkably. Shear flow can result in alignment of DBS fibrils, which facilitates the nucleation of UHMWPE and induces the lamellae aligned perpendicular to flow direction. This feature was used to design thermal and mechanical histories and obtained oriented UHMWPE microporous membrane. In comparison to the isotropic UHMWPE microporous membrane, the oriented UHMWPE microporous membrane provides low tortuous paths across the membrane and produces high water permeability. (c) 2014 Elsevier Ltd. All rights reserved.
    Polymer 04/2014; 55(8). DOI:10.1016/j.polymer.2014.02.068 · 3.56 Impact Factor
  • Jinxiu You · Wei Yu · Chixing Zhou ·
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    ABSTRACT: The crystallization of poly(lactic acid) (PLA) is usually slow and related to the content of d-lactide. A new approach is suggested in this work to accelerate the crystallization of PLA via the synergistic effect of nanofibril nucleating agent (dibenzylidene sorbitol, DBS), plasticizer (poly(ethylene glycol), PEG) and long-chain branching in PLA. It is found that premade DBS/PEG gel can act as an active nucleating agent of PLA, which makes the crystallization peak appear during cooling. The preparation of DBS/PEG gel before mixing with PLA is important because self-assembly of DBS directly in PLA melt is difficult even in the presence of PEG. The mixing temperature is also found to be critical, which determines the amount of residual nanofibrils after melt mixing. Tuning the chain structure into long-chain branching via multifunctional monomer pentaerythritol triacrylate (PETA) will further speed up the crystallization of PLA because of the additional interaction between DBS nanofibrils and the grafted monomers. It is proven that the acceleration of crystallization is not ascribed to the change of crystal form but is due to the dominating increase in the nucleation density as well as the faster growth rate of spherulites in the presence of the plasticizer. Therefore, the problems of low melt strength and slow crystallization of PLA can be solved simultaneously via the present approach.
    Industrial & Engineering Chemistry Research 01/2014; 53(3):1097–1107. DOI:10.1021/ie402358h · 2.59 Impact Factor
  • Peng He · Wei Shen · Wei Yu · Chixing Zhou ·
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    ABSTRACT: Chain shuttling polymerization enables an efficient production of ethylene–octene block copolymers (OBCs) that combine different mechanical properties in a polymer chain. However, this method results in molecular weight polydispersity and multiblock chain structure. The melt-phase behavior and mesophase transition of the polydisperse OBCs with low octene content but different molecular weight and block composition were investigated by rheology, differential scanning calorimetry (DSC), atomic force microscopic (AFM), polarized optical microscopy (POM), and small-angle X-ray scattering (SAXS). Three rheological methods, namely the deviation of the scaling dependence of zero shear viscosity on molecular weight, the terminal behavior and the failure of time–temperature superposition (TTS), and two-dimensional rheological correlation spectrum, are used to reveal the mesophase separation with increasing sensitivity. The occurrence of mesophase separation transitions (MST) was observed in such low octene content and low molecular weight OBC systems, with much lower degree of segregation than the theoretical predictions in diblock copolymers. The extent of mesophase separation is further justified by its effect on subsequent crystallization behaviors.
    Macromolecules 12/2013; 47(2). DOI:10.1021/ma402330a · 5.80 Impact Factor
  • Jinxiu You · Lijuan Lou · Wei Yu · Chixing Zhou ·
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    ABSTRACT: Long chain branching (LCB) of polylactic acid (PLA) was successfully prepared by melt radicals reaction with pentaerythritol triacrylate (PETA) and bis (1-methyl-1-phenylethyl) peroxide (DCP). The topological structure of the LCB was investigated by rheology and branch-on-branch (BOB) model was used to estimate the exact chain structures of the products, where comb-like LCB structures were generated due to the complex coupling between different macro-radicals. LCB structure was found to affect the crystallization of PLA products. In the temperature range of 110–130°C, the crystallization rate parameter (k) was improved sharply and the half crystallization time was decreased significantly after the grafting of PETA, which was ascribed to the enhanced hydrogen bonding in PETA-grafted long chain branching PLA. By comparing with the LCB PLA made from chain extension using multifunctional monomer, it shows that the crystallization becomes slower in a highly branched material with extremely long relaxation time if the effect of hydrogen bonding is similar. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
    Journal of Applied Polymer Science 08/2013; 129(4). DOI:10.1002/app.38912 · 1.77 Impact Factor
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    Sijun Liu · Wei Yu · Chixing Zhou ·
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    ABSTRACT: Dibenzylidene sorbitol (DBS) was chosen as an in situ forming nucleating agent to study ultrahigh molecular weight polyethylene (UHMWPE)/liquid paraffin (LP) physical gel and complex phase separation. The experimental results indicated that DBS self-assembled into fibrils first and the solution became a physical gel before liquid–liquid phase separation (LLPS) and crystallization during thermally induced phase separation (TIPS) of UHMWPE/LP/DBS solution. The temperature of DBS self-assembly and viscoelasticity of UHMWPE/LP/DBS gel show a strong dependence on DBS concentration, temperature, and time. By controlling the relative quenching depth and annealing time, the grow rate of the characteristic length showed a crossover from LLPS to crystallization, which was further justified by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). With decreasing temperature further, crystallization occurred with the aid of DBS fibrils. Those interactions were affected mutually, showed complex phase separation behavior. We proposed a new mechanism of “self-assembly assisted liquid–liquid phase separation”, which explained excellently the relationship of DBS self-assembly and LLPS. On the basis of rheometer and optical microscopy (OM and POM), we obtained the phase diagram of UHMWPE/LP/DBS ternary blends. Meanwhile, DSC indicated the overwhelming changes of crystallization kinetics after the varying LLPS in the double quenching procedure, which was consistent with the “fluctuation assisted nucleation” mechanism.
    Macromolecules 08/2013; 46(15):6309-6318. DOI:10.1021/ma400915g · 5.80 Impact Factor
  • Wei Yu · Yu Du · Chixing Zhou ·
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    ABSTRACT: Nonlinear oscillation shear has become an important method to study the complex fluids. However, choosing the suitable material functions is not as simple as that in linear viscoelasticity. A framework is suggested in this work to account for the stress-strain and stress-strain rate relationship based on the concept of mean stress and mean strain (rate) in the Lissajous curves. The applications of such framework in an imposed oscillatory shear strain and an imposed oscillatory shear stress are clearly demonstrated. The intracycle nonlinear modulus and viscosity are defined from the slope of the stress-strain curve and the stress-strain rate curve, respectively. The intercycle nonlinear behaviors are obtained from the strain (rate) amplitude dependence of the zero mean strain (rate) modulus or viscosity. We justify the strain-hardening/ softening and shear-thickening/thinning behaviors of nonlinear moduli and viscosities by using typical constitutive models like Bingham model and the Maxwell model. It is found that the modulus (viscosity) defined from the stress-mean strain (rate) curves is the most physical reasonable quantity. In addition, we apply the new analysis method to two yield stress fluids, which reveals critical balance between aging and shear rejuvenation. (C) 2013 The Society of Rheology.
    Journal of Rheology 07/2013; 57(4):1147. DOI:10.1122/1.4805093 · 3.36 Impact Factor
  • Hongliang Chen · Chongwen Huang · Wei Yu · Chixing Zhou ·
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    ABSTRACT: Thermally reduced graphite oxide (TrGO) was prepared by thermal exfoliation and reduction of highly oxidized graphite. The pCBT/TrGO nanocomposites were prepared by in situ ring-opening polymerization (ROP) of cyclic butylene terephthalate (CBT). The polymerization kinetics of pCBT/TrGO was monitored by dynamic time sweep in a parallel-plate rheometer. It was found that the increasing TrGO content depressed the rate and degree of CBT polymerization, which is ascribed to the reaction between the growing pCBT chains terminated with carboxyl groups and TrGO surface groups such as hydroxyl and epoxy groups at the initial polymerization stage. The grafted pCBT chains were confirmed by X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA) measurements, and the grafting content was up to 53 wt%. Small amplitude oscillation shear (SAOS) was applied to investigate the rheological properties of pCBT/TrGO and the critical loading to form percolation network was determined as 0.47 vol%, which confirmed the good dispersion of TrGO in matrix. The grafting reaction was also justified from nonlinear rheology and the fractal dimension analysis.
    Polymer 03/2013; 54(6):1603–1611. DOI:10.1016/j.polymer.2013.01.036 · 3.56 Impact Factor
  • Chunyan Liu · Shanshan Lin · Chixing Zhou · Wei Yu ·
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    ABSTRACT: This paper investigated the effect of catalyst on transesterification and transesterification mechanism between poly(lactic acid) (PLA) and polycarbonate (PC) under flow field. Three catalysts (zinc borate, titanium pigment and tetrabutyl titanate) were evaluated. It is found that transesterification reaction can take place without any catalyst, while three catalysts can all promote the transesterification reaction between poly(lactic acid) and polycarbonate to a greater extent. 1H nuclear magnetic resonance spectroscopy, gel permeation chromatography and dynamic mechanical analysis revealed that structures of copolymers are not identical in the blends with and without catalyst. For pure blend, most of copolymers have relatively high molecular weight with low PC content, which implies that transesterification reaction most likely happens only once between a PLA chain and a PC chain during mixing process, and only a small amount of multiple reactions happen. However, for the catalyst systems, catalysts induce much more multiple reactions accompanying with the reducing molecular weight in copolymers and increasing PC content. Moreover, it is found that the catalysts not only affect the chain compositions of the product copolymers, but also influence the amount of polymers involved in the reaction. Tetrabutyl titanate is found to be the most effective catalyst in this study where the amount of reacted polycarbonate is more than 4 times of that in pure blend. It is found that PLA segments in copolymer are easily aligned on the interface due to its relatively high Deborah number, which increases the probability of its contact with more PC chains. Although the flow effect on the alignment of chain segment is similar in blends with and without catalysts, the acceleration of reaction due to catalyst makes it possible for multiple reactions. The match of the reaction time and contact time of chain segment of PC and PLA at interfaces is then of key importance in the interfacial transesterification reaction. The effect of flow field on the interfacial reaction is then not only from the interfacial update, but also from the change of chain conformation near the interface.
    Polymer 01/2013; 54(1):310-319. DOI:10.1016/j.polymer.2012.11.047 · 3.56 Impact Factor
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    Sijun Liu · Wei Yu · Chixing Zhou ·
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    ABSTRACT: The gel behavior of dibenzylidene sorbitol (DBS) in different solvents was studied by rheology, optical microscopy and transmission electron microscopy. It was found that DBS molecules would self-assemble into fibrils with a helical structure, and the fibrillar diameter decreased with increasing solvent polarity. The gel dissolution temperature was extremely sensitive to the DBS concentration and solvent polarity, which could be explained by the Gibbs–Thomson equation through interfacial stress. The phase diagram, which classified the sol, the gel and the cluster regime in different solvents was determined by rheology and optical microscopy. The critical gel concentration was found to increase as the difference in the polar and hydrogen-bonding components of the solubility parameter (Δδph) between the gelator and solvents decreased. Meanwhile, the difference in the critical gel concentration in different solvents could explain the difference in the relaxation exponent and the gel strength at the gel point well. In the stable gel state, the plateau modulus depended on the gelator concentration according to a power-law scaling, GoN ∝ c2, which was consistent with entanglement theory and independent of the type of solvent. However, the gelator–solvent interaction and its temperature dependence were found to affect the stability of the gel substantially under large amplitude oscillatory shear. The critical strain would increase as Δδph decreased, and showed more evident temperature dependence on solvents with a smaller Δδph.
    Soft Matter 12/2012; 9(3):864-874. DOI:10.1039/C2SM27030G · 4.03 Impact Factor
  • Chongwen Huang · Jianping Gao · Wei Yu · Chixing Zhou ·
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    ABSTRACT: Effects of selective location of silica nanoparticles on the phase separation of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) (PMMA/SAN) blends were investigated via combination of rheological method and optical microscopy. Through grafting polystyrene chain to the surface of silica nanoparticles, the silica nanoparticles were controlled to selectively locate at interfaces or in the PMMA-rich domains. Power-law analysis of the moduli and shifted Cole–Cole plots were applied to determine rheological transition temperature (apparent binodal temperature) of blend with near-critical and off-critical compositions for both neat blends and particle-filled blends. The particle location had significant influence on the rheological transition temperature but little impact on optically determined binodal temperature. This discrepancy was discussed through morphology observation via transmission electron microscopy (TEM) for blends under different phase separation conditions. It was found that nanoparticles retard coarsening of morphology during phase separation. The most striking slowdown was found in off-critical blends with nanoparticles located on the interface. On the other hand, nanoparticles preferentially locating in the minor phase could act as nucleation sites but decreased the total number of nuclei. The difference in the rheological transition temperatures is ascribed to the effect of nanoparticles on the components’ viscoelasticity and the morphology during phase separation.
    Macromolecules 10/2012; 45(20):8420-8429. DOI:10.1021/ma301186b · 5.80 Impact Factor
  • Jianping Gao · Chongwen Huang · Nan Wang · Wei Yu · Chixing Zhou ·
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    ABSTRACT: 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.
    Polymer 04/2012; 53(8):1772–1782. DOI:10.1016/j.polymer.2012.02.027 · 3.56 Impact Factor
  • Qi He · Wei Yu · Youjun Wu · Chixing Zhou ·
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    ABSTRACT: The rheology and morphology of 8CB (4-octyl-4-biphenylcarbonitrile) and PDMS (polydimethylsiloxane) blends with different concentrations of 8CB were investigated. The blends showed gel-like behaviour when 8CB is in the smectic state during mixing, whose morphologies resemble the foam-like structure of a highly concentrated emulsion with 8CB as the continuous phase. Once formed, such a structure is stable when 8CB is in a smectic and nematic state but unstable when 8CB is in an isotropic state. The stability of the foam-like structure is ascribed to the elasticity of 8CB films, which is justified by the concentration dependence of the interfacial contribution to the plateau modulus, i.e., the yield stress of 8CB instead of the Laplace pressure controls the deformation of the PDMS droplet. A new mechanism of phase inversion is suggested based on the direct observation of the breakup mode of an 8CB droplet. The formation of the foam-like structure was the result of the erosion breakup of the 8CB droplets and the subsequent local phase inversion, where the erosion breakup is ascribed to the shear banding inside the droplet due to the yield stress of 8CB in the smectic state.
    Soft Matter 02/2012; 8(10):2992-3001. DOI:10.1039/C2SM06963F · 4.03 Impact Factor
  • Wei Yu · Chixing Zhou ·
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    ABSTRACT: 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.
    Polymer 02/2012; 53(3):881–890. DOI:10.1016/j.polymer.2011.12.025 · 3.56 Impact Factor

Publication Stats

2k Citations
360.70 Total Impact Points


  • 2000-2015
    • Shanghai Jiao Tong University
      • Department of Polymer Science and Engineering
      Shanghai, Shanghai Shi, China
  • 2002-2006
    • Shanghai University
      • Department of Chemical Engineering and Technology
      Shanghai, Shanghai Shi, China
    • Jilin University
      • Department of Chemistry
      Yung-chi, Jilin Sheng, China