Based on the premise that the addition of glass beads （GB） could hardly influence the linear viscoelasticity in low frequency （ω） region for homogeneous polymer systems, the dynamic rheological behaviors of unfil...Based on the premise that the addition of glass beads （GB） could hardly influence the linear viscoelasticity in low frequency （ω） region for homogeneous polymer systems, the dynamic rheological behaviors of unfilled and filled poly（methyl methyacrylate） （PMMA）/poly（styrene-co-acrylonitrile） （SAN） blends were studied in order to explore the effect of GB on the phase-separation of binary polymer matrix. Results show that GB has an induced effect on the phase-separation, which embodies that the phase-separation temperature （Ts） of PMMA/SAN blend filled with GB is lower than that of the unfilled system. The higher content of GB, the higher is the ＂secondary plateau＂ of ω in the terminal region of storage modulus （G＇） versus ω plot. The ＂secondary plateau＂ appearing in the terminal region is attributed to the phase-separation of PMMA/SAN blends and it becomes more fiat for filled polymer blends under the same conditions. However, it is suggested that this kind of ＂induced effect＂ is related to the GB content; the higher content of GB particles might enhance the interaction between the particles and polymer matrix. Moreover, it is found that the addition of GB also has an influence more or less on the morphology and domain size of polymer matrix. It is believed that the plot of dynamic viscosity （η＇） versus the loss viscosity （η＂） is sensitive to examine the effect induced by GB on the phase-separation of binary polymer matrix.展开更多
The experimental observations about remarkable influence of the substrates on the isothermal crystallization rate of a high density polyethylene(HDPE) were presented.Two methods were used to characterize the crystalli...The experimental observations about remarkable influence of the substrates on the isothermal crystallization rate of a high density polyethylene(HDPE) were presented.Two methods were used to characterize the crystallization rate:the change of turbidity of the HDPE specimen and the changes of the complex viscosity and storage modulus measured by a rotational rheometer,which gave consistent results showing that the isothermal crystallization rate decreased in sequence as the specimen contacted with aluminum,brass and stainless steel plates,respectively.As to the dominant influence factor,the chemical composition of the substrates can be excluded via insulating the plate by an aluminum foil.Instead,we propose the plate's ability of removing the latent heat of crystallization from the specimen.Rheological measurement is sensitive to the crystallization process.The colloid like model proposed by BOUTAHAR et al for the crystallization of HDPE gives reasonable predictions of the crystallized fraction from the measured storage modulus.展开更多
The flow past a cylinder in a channel with the aspect ratio of 2 ： 1 for the upper convected Maxwell （UCM） fluid and the Oldroyd-B fluid with the viscosity ratio of 0.59 is studied by using the Galerkin/Least-squar...The flow past a cylinder in a channel with the aspect ratio of 2 ： 1 for the upper convected Maxwell （UCM） fluid and the Oldroyd-B fluid with the viscosity ratio of 0.59 is studied by using the Galerkin/Least-square finite element method and a p-adaptive refinement algorithm. A posteriori error estimation indicates that the stress-gradient error dominates the total error. As the Deborah number, De, approaches 0.8 for the UCM fluid and 0.9 for the Oldroyd-B fluid, strong stress boundary layers near the rear stagnation point are forming, which are characterized by jumps of the stress-profiles on the cylinder wall and plane of symmetry, huge stress gradients and rapid decay of the gradients across narrow thicknesses. The origin of the huge stress-gradients can be traced to the purely elongational flow behind the rear stagnation point, where the position at which the elongation rate is of 1/2De approaches the rear stagnation point as the Deborah number approaches the critical values. These observations imply that the cylinder problem for the UCM and Oldroyd-B fluids may have physical limiting Deborah numbers of 0.8 and 0.9, respectively.展开更多
Studies on the viscoelastic behavior of styrene- [ethylene-(ethylene-propylene)]-styrene block copolymer (SEEPS) were carried out, and some characteristic viscoelas-tic parameters were calculated. The longest relaxati...Studies on the viscoelastic behavior of styrene- [ethylene-(ethylene-propylene)]-styrene block copolymer (SEEPS) were carried out, and some characteristic viscoelas-tic parameters were calculated. The longest relaxation time τmax was obtained through simulating the relaxation spec-trum on the basis of a modified Baumgaertel-Schausberger- Winter (mBSW) model. The results revealed that there exists a “second plateau” in the low frequency region of the master curves. The reason for this phenomenon is attributed to the entanglement of macromolecular chains. It is suggested that the hard blocks, polystyrene, act as entanglement points, resulting in a topology restraint to the movement of macro-molecular chains. Meanwhile, it is found that the horizontal shift factors (aT) vs temperature in the master curve could be fitted to the Williams-Landel-Ferry (WLF) equation and Ar-rhenius equation respectively and the flow activation energy (Ea) is 127.88 kJ/mol. In addition, the plateau modulus (GN0) and entanglement molecule weight (Me) were calculated.展开更多
基金This project was supported by the National Natural Science Foundation of China(No.20304014)the Special Funds for National Science Funds for Distinguished Young Scholars(No.50125312).
文摘Based on the premise that the addition of glass beads （GB） could hardly influence the linear viscoelasticity in low frequency （ω） region for homogeneous polymer systems, the dynamic rheological behaviors of unfilled and filled poly（methyl methyacrylate） （PMMA）/poly（styrene-co-acrylonitrile） （SAN） blends were studied in order to explore the effect of GB on the phase-separation of binary polymer matrix. Results show that GB has an induced effect on the phase-separation, which embodies that the phase-separation temperature （Ts） of PMMA/SAN blend filled with GB is lower than that of the unfilled system. The higher content of GB, the higher is the ＂secondary plateau＂ of ω in the terminal region of storage modulus （G＇） versus ω plot. The ＂secondary plateau＂ appearing in the terminal region is attributed to the phase-separation of PMMA/SAN blends and it becomes more fiat for filled polymer blends under the same conditions. However, it is suggested that this kind of ＂induced effect＂ is related to the GB content; the higher content of GB particles might enhance the interaction between the particles and polymer matrix. Moreover, it is found that the addition of GB also has an influence more or less on the morphology and domain size of polymer matrix. It is believed that the plot of dynamic viscosity （η＇） versus the loss viscosity （η＂） is sensitive to examine the effect induced by GB on the phase-separation of binary polymer matrix.
基金Project(20050335050) supported by the Special Foundation of Education Ministry of ChinaProject(10472105) supported by the National Natural Science Foundation of China
文摘The experimental observations about remarkable influence of the substrates on the isothermal crystallization rate of a high density polyethylene(HDPE) were presented.Two methods were used to characterize the crystallization rate:the change of turbidity of the HDPE specimen and the changes of the complex viscosity and storage modulus measured by a rotational rheometer,which gave consistent results showing that the isothermal crystallization rate decreased in sequence as the specimen contacted with aluminum,brass and stainless steel plates,respectively.As to the dominant influence factor,the chemical composition of the substrates can be excluded via insulating the plate by an aluminum foil.Instead,we propose the plate's ability of removing the latent heat of crystallization from the specimen.Rheological measurement is sensitive to the crystallization process.The colloid like model proposed by BOUTAHAR et al for the crystallization of HDPE gives reasonable predictions of the crystallized fraction from the measured storage modulus.
基金The project supported by the National Natural Science Foundation of China(50335010 and 20274041)the MOLDFLOW Comp.Australia.
文摘The flow past a cylinder in a channel with the aspect ratio of 2 ： 1 for the upper convected Maxwell （UCM） fluid and the Oldroyd-B fluid with the viscosity ratio of 0.59 is studied by using the Galerkin/Least-square finite element method and a p-adaptive refinement algorithm. A posteriori error estimation indicates that the stress-gradient error dominates the total error. As the Deborah number, De, approaches 0.8 for the UCM fluid and 0.9 for the Oldroyd-B fluid, strong stress boundary layers near the rear stagnation point are forming, which are characterized by jumps of the stress-profiles on the cylinder wall and plane of symmetry, huge stress gradients and rapid decay of the gradients across narrow thicknesses. The origin of the huge stress-gradients can be traced to the purely elongational flow behind the rear stagnation point, where the position at which the elongation rate is of 1/2De approaches the rear stagnation point as the Deborah number approaches the critical values. These observations imply that the cylinder problem for the UCM and Oldroyd-B fluids may have physical limiting Deborah numbers of 0.8 and 0.9, respectively.
基金This work was supported by the National Science Foundation for Distinguished Young Scholars (Grant No.50125312) the National Natural Science Foundation of China (Grant No.50133020).
文摘Studies on the viscoelastic behavior of styrene- [ethylene-(ethylene-propylene)]-styrene block copolymer (SEEPS) were carried out, and some characteristic viscoelas-tic parameters were calculated. The longest relaxation time τmax was obtained through simulating the relaxation spec-trum on the basis of a modified Baumgaertel-Schausberger- Winter (mBSW) model. The results revealed that there exists a “second plateau” in the low frequency region of the master curves. The reason for this phenomenon is attributed to the entanglement of macromolecular chains. It is suggested that the hard blocks, polystyrene, act as entanglement points, resulting in a topology restraint to the movement of macro-molecular chains. Meanwhile, it is found that the horizontal shift factors (aT) vs temperature in the master curve could be fitted to the Williams-Landel-Ferry (WLF) equation and Ar-rhenius equation respectively and the flow activation energy (Ea) is 127.88 kJ/mol. In addition, the plateau modulus (GN0) and entanglement molecule weight (Me) were calculated.
