Chixing Zhou

Shanghai Jiao Tong University, Shanghai, Shanghai Shi, China

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Publications (129)178.91 Total impact

  • 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.
  • Sijun Liu, Wei Yu, Chixing Zhou
    Polymer. 01/2014;
  • 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). · 1.40 Impact Factor
  • 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. · 5.93 Impact Factor
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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.
  • 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. · 4.15 Impact Factor
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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. · 5.93 Impact Factor
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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.
  • 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. · 4.15 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.
  • Hongliang Chen, Wei Yu, Chixing Zhou
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    ABSTRACT: Cyclic butylene terephthalate oligomers (CBT) with ultra-low melt viscosity can be polymerized into poly (butylene terephthalate) (pCBT) via entropically-driven ring-opening polymerization (ED-ROP) in a short time (ranging from several seconds to 10 min) with no chemical emission and no heat generation during the polymerization process. Due to no heat generation, dynamic rheological measurements were used to monitor the polymerization of CBT from 220 to 250°C. The polymerization was accompanied by a steep increase of the melt viscosity and modulus in isothermal rheological tests, and much faster at higher temperature. With rheological results, reptation theory and Double reptation model were adopted to determine the variation of the molecular weight and concentration with time for pCBT. According to the ED-ROP mechanism of CBT, kinetics equations were also established to simulate the polymerization process. Furthermore, using the results of variation of molecular weight with time for pCBT and kinetics equations, the polymerization rate constants for initiation and propagation steps were evaluated, and the activation energy was also obtained. It was proved that rheological method is a convenient and reliable way to investigate the kinetics of ED-ROP of CBT. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers
    Polymer Engineering and Science 01/2012; 52(1). · 1.24 Impact Factor
  • Peng Wang, Jianye Liu, Wei Yu, Chixing Zhou
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    ABSTRACT: The isothermal crystallization behavior and crystal structure of the polypropylene (PP) component in wood plastic composites (WPC) with respect to wood particle content and maleic anhydride-grafted polypropylene (MAHPP) compatibilizer were studied by means of polarized optical microscopy, scanning electron microscopy, x-ray diffraction, and differential scanning calorimetry. It was found that under the experimental conditions of this research, the speed of crystallization of PP was faster in WPC with MAHPP than in composites without MAHPP. This is ascribed to the difference in undercooling due to the change in the equilibrium melting temperatures (T 0 m ) of the PP component in WPC due to the addition of wood flour and MAHPP compatibilizer. T 0 m decreased with the increase of wood particle content, and it decreased more severely with the addition of wood flour than the addition of compatibilizer. The half-crystallization time was the smallest in PP/wood composites, intermediate in PP/wood/compatibilizer system, and the largest in pure PP under the same undercooling. The fast crystallization in PP/wood composites is ascribed to the heterogeneous nucleation effects of wood particles, which could be hindered by the MAHPP compatibilizers; this was verified by the higher fold surface free energy in WPC with compatibilizer than in WPC without compatibilizer.
    Journal of Macromolecular Science Part B 12/2011; Part B(Vol. 50):2271-2289. · 0.63 Impact Factor
  • Wei Yu, Chixing Zhou
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    ABSTRACT: A theoretical model for droplet dynamics and rheology of blends with viscoelastic interface and interfacial slip is suggested in this work. The interfacial constitutive equation, so called as the Boussinesq–Scriven equation, is integrated in the pertubation analysis on the flow field inside and outside the droplet, while the interfacial slip is introduced via Navier slip boundary conditions. The results of small deformation analysis is extended to larger deformation using the ellipsoidal shape tensor. The effect of Boussinesq number, the interfacial viscosity ratio and the interfacial thickness on the characteristic relaxation time of droplet, the steady deformation of droplet and the shear viscosity of blends are discussed in detail. The model is validated by certain experimental data using interfacial viscosities that are reasonably measured in experiments.
    Soft Matter 06/2011; 7(13):6337-6346. · 4.15 Impact Factor
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    Ying Guo, Wei Yu, Yuanze Xu, Chixing Zhou
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    ABSTRACT: An optical visualization apparatus has been designed to measure the particle velocity of concentrated particle suspensions in a stress controlled rheometer equipped with a quartz parallel-plate. Suspensions with high and low matrix viscosity were used to investigate the nonlinear rheology and the local flow mechanism, as well as the correlations between particle velocity profiles and transition behaviors. Herein, it is shown that the sedimentation has great effects on the flow behavior of suspensions and on the particle velocity profiles. Local flow behaviors e.g. shear banding, drift in the center position of oscillatory shear and dynamic wall slip, have been studied comprehensively. By Fourier-transform rheology (FTR) analysis, the shear banding phenomenon is proved to be strongly linked with the nonlinear rheology of suspensions.
    Soft Matter 03/2011; 7(6):2433-2443. · 4.15 Impact Factor
  • Wei Yu, Runming Li, Chixing Zhou
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    ABSTRACT: Rheological methods have been frequently used to study the phase separation behavior of partially miscible polymer blends. Usually the binodal temperature can be determined from the failure of time–temperature superposition (TTS) principle in isothermal experiments, or the deviation of the storage modulus from the apparent extrapolation of modulus in miscible regime in non-isothermal experiments. However, these methods are shown in this work to be not widely applicable even in blends with weak dynamic asymmetry due to the thermo-rheological complexity. A rheological model which is an integration of the double reptation model and the self-concentration model is found to describe the linear viscoelasticity of miscible blends quite satisfactorily, from which it is possible to follow the contribution from the miscible blends even in the two phase regime. Then, the binodal temperature is readily defined as the deviation of experimental data from such model prediction for miscible blends. Such method is successfully applied in a model polymer blend (poly(methyl methacrylate)/poly(styrene-co-maleic anhydride), PMMA/SMA) with weak dynamic asymmetry.
    Polymer. 01/2011; 52(12):2693-2700.
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    Peng Wang, Jianye Liu, Wei Yu, Chixing Zhou
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    ABSTRACT: The microstructure of wood plastic composite (WPC) with respect to wood particle content and maleic anhydride-grafted polypropylene (MAHPP) compatibilizer is studied by both linear and nonlinear rheological methods in this article. The complete long characteristic relaxation behavior in linear region, which is closely related to the structure of wood particle aggregates and MAHPP compatibilizing effect at the interface, is limited by observing time. Fortunately, the Fourier transform rheology (FTR) by the stress control mode is found to be an effective method for further investigating the structure with long relaxation time in WPC system. The plateau value of I 31 at high stress and the range of ϕ 31 are proved to be corresponding to the content of wood particle agglomerates in the WPC melts and the type of interfacial hydrodynamic interaction. The interesting outcomes suggest that MAHPP do has the effect on changing the properties of the heterogeneous interface and confirm the difference of the structure with long relaxation time in WPC can be easily captured by the high sensitive FTR indeed. KeywordsWood plastic composite–Dynamic viscoelasticity–Fourier transform rheology–Compatibilization
    Polymer Bulletin 01/2011; 66(5):683-701. · 1.33 Impact Factor
  • Sijun Liu, Chixing Zhou, Wei Yu
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    ABSTRACT: Phase separation behavior of binary polyolefin blends, ultra-high molecular weight polyethylene (UHMWPE) and liquid paraffin (LP), was investigated through combination of differential scanning calorimetry, rheology and optical microscopy. It was found that the liquid–liquid phase separation (LLPS) could not be differentiated from crystallization in the process of non-isothermal measurements since the LLPS was relatively slow and binodal temperature was quite close to the crystallization temperature. However, by controlling the quench depth rheological dynamic time sweeps and cyclic frequency sweeps showed a clear evidence of liquid–liquid phase separation, which was further justified by optical microscopy. The liquid–liquid phase separation temperature was obtained more accurately by the “inverse quenching” method in rheological time sweeps. Based on the phase diagram, UHMWPE membranes with different porous structures were prepared through thermal induced phase separation with the control of the liquid–liquid phase separation and crystallization. It was found that the LLPS dominated process would produce membranes with the larger porosity and cell size, but relatively smaller tensile strength.Highlights► We differentiate L–L phase separation from crystallization for UHMWPE and LP blend. ► L–L phase separation temperature is obtained by the “inverse quenching” method. ► Rheological measurements are more sensitive to the microstructure change. ► The properties of UHMWPE membrane depend on quenching depth and annealing time.
    Journal of Membrane Science 01/2011; 379:268-278. · 4.09 Impact Factor
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    Jianye Liu, Wei Yu, Chixing Zhou
    Journal of Rheology 01/2011; 55. · 2.80 Impact Factor
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    Ji Zhou, Jian Li, Wei Yu, Xin Li, Chixing Zhou
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    ABSTRACT: The spinning process of noncircular fiber was investigated in this work. A combination of numerical simulations and experiments made it possible to find out the optimum processing condition for shaped fiber. First, an inverse method which combined two-dimensional/three-dimensional simulation with experiments was utilized to find out the temperature and draw ratio dependent surface tension in melt spinning of shaped fiber. The surface tension as a function of temperature and draw ratio was found to be decisive to the change of cross-section. Second, an orthogonal numerical experiment and statistics analysis were carried out to determine the optimum spinning condition for the desired noncircular fiber. The optimum spinning condition was well validated by experiments. It was then proved that the integrated method in this work, including the numerical method, the inverse method to determining the surface tension, and the orthogonal analysis, can be a good solution for the design and processing of profiled fibers. POLYM. ENG. SCI., 50:1935–1944, 2010. © 2010 Society of Plastics Engineers
    Polymer Engineering and Science 09/2010; 50(10):1935 - 1944. · 1.24 Impact Factor
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    ABSTRACT: Long chain branching (LCB) of polylactide (PLA) was successfully prepared by the successive reactions of the end hydroxyl groups of PLA with pyromellitic dianhydride (PMDA) and triglycidyl isocyanurate (TGIC) together. The topological structures of the LCB generated from functional group reactions as well as free radical reactions were investigated thoroughly by gel permeation chromatography (GPC) and rheology. Qualitative information about the branching structures could be readily obtained from linear viscoelasticity, non-linear oscillatory shear experiments and strain hardening in elongational experiments. For quantitative information on chain structure, linear viscoelasticity combined with branch-on-branch (BOB) dynamic model was used to predict exact compositions and chain topologies of the products, which were reasonably explained by the suggested mechanism of functional group reactions. It was found out that the tree-like LCB structure generated in these reactions contributed remarkably to the enhancement of strain hardening under elongational flow, which improves the foaming ability substantially.
    Polymer. 01/2010; 51(22):5186-5197.

Publication Stats

923 Citations
178.91 Total Impact Points

Institutions

  • 2000–2014
    • Shanghai Jiao Tong University
      • Department of Polymer Science and Engineering
      Shanghai, Shanghai Shi, China
  • 2002–2008
    • Shanghai University
      Shanghai, Shanghai Shi, China
    • Jilin University
      • Department of Chemistry
      Jilin, Jilin Sheng, China
  • 2006–2007
    • University of British Columbia - Vancouver
      • Department of Mathematics
      Vancouver, British Columbia, Canada
    • Henan University
      • Department of Chemical Engineering
      Kaifeng, Henan Sheng, China
  • 2004
    • City University of New York - York College
      New York City, New York, United States