Computational and Theoretical Polymer Science最新文献

{"title":"Phase separation of liquid crystal–polymer mixtures","authors":"M Motoyama ,&nbsp;H Nakazawa ,&nbsp;T Ohta ,&nbsp;T Fujisawa ,&nbsp;H Nakada ,&nbsp;M Hayashi ,&nbsp;M Aizawa","doi":"10.1016/S1089-3156(99)00044-6","DOIUrl":"10.1016/S1089-3156(99)00044-6","url":null,"abstract":"<div><p>Phase separation in liquid crystal–polymer mixtures is studied by computer simulations in two dimensions. The domain morphology resulting from the phase separation either by temperature quench or by polymerization is investigated by solving the coupled set of equations for the local volume fraction and the nematic order parameter. In a temperature quench, it is found that transient concentric domains are constituted near the nucleation regime of nematic ordering. Phase separation induced by polymerization is modeled by taking into account the time dependence of the molecular weight of polymer chains. Assuming a strong concentration dependence of the mobility, a transient network-like domain of polymer-rich phase is formed. The morphology is compared with the experimental results.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 287-297"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00044-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84614262","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Crystal structures of the α and β forms of isotactic polypropylene: a Monte Carlo simulation","authors":"M Hirose ,&nbsp;T Yamamoto ,&nbsp;M Naiki","doi":"10.1016/S1089-3156(99)00039-2","DOIUrl":"10.1016/S1089-3156(99)00039-2","url":null,"abstract":"<div><p><span>Isotactic polypropylene has various crystalline modifications (α, β, γ, smectic). Molecular conformations in these modifications are common 3/1 helix of (TG)</span>₃ or (TG^∗)₃<span><span>. However crystal structures of the modifications, that is the modes of chain packing, are quite different and are subjects of intensive investigations nowadays. We study here, the detailed modes of chain packing in the α and β forms by Monte Carlo simulation. We assume that the molecular conformation is a rigid 3/1 helix, and that the chain axes are placed either in a monoclinic lattice (α form) or in a hexagonal lattice (β form). Most stable modes of chain packing are investigated, with respect to chain </span>chirality (right or left handedness), chain rotation and translation, and the methyl-group direction (up or down positioning). We find that an initial random state in the monoclinic lattice converges to the α</span>₁ or to the α₂ form, both with alternating rows of right-handed and left-handed helices; we also investigate a molecular process of growth of the α₂ crystal in the matrix α₁<span> crystal. On the other hand, the arrangement of the molecular axes in the hexagonal lattice is found to give rise to the β form structure, in which the chains form chiral domains surrounded by boundaries parallel to the (110) and (100) planes. It is also shown that detailed chain rotations (setting angles) have a unique superstructure, which conforms to the incommensurate packing recently proposed by Lotz and Meille.</span></p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 345-353"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00039-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75183230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Micelle formation in triblock copolymer solutions","authors":"M. Monzen ,&nbsp;T. Kawakatsu ,&nbsp;M. Doi ,&nbsp;R. Hasegawa","doi":"10.1016/S1089-3156(99)00052-5","DOIUrl":"10.1016/S1089-3156(99)00052-5","url":null,"abstract":"<div><p><span>Using the self-consistent field treatment, we investigate the structures and the phase behavior of micelles formed in symmetric and asymmetric </span>triblock copolymer<span> solutions. We find that the asymmetry of the block copolymer lowers the critical micelle concentration due to the gain of the conformational entropy.</span></p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 275-280"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00052-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74499327","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"High-precision computer simulations of entangled polymer chains: 1. Determination of entanglement parameters of bond-fluctuation model","authors":"M. Tanaka,&nbsp;K. Iwata,&nbsp;N. Kuzuu","doi":"10.1016/S1089-3156(99)00045-8","DOIUrl":"10.1016/S1089-3156(99)00045-8","url":null,"abstract":"<div><p>High-precision computer simulations of bond-fluctuation (BF) model (volume fraction <em>φ</em><span>=0.5) are performed in the transition region between the non-entanglement and the entanglement regime. Defects of the model called X-traps are newly found which result in serious errors in the long-time behavior of the system. For samples free from X-traps, diffusion coefficient </span><em>D</em> of the center of mass, relaxation times <em>τ</em>_<em>α</em> for Rouse coordinate <strong>R</strong>_<em>α</em> (<em>α</em>=1,2) and <em>τ</em>_<em>L</em> for the end-to-end vector <strong>L</strong> are determined for chains of length <em>N</em>=16–180 within few percent of statistical errors. Their <em>N</em>-dependence changes around <em>N</em>=100 at which entanglement coupling is supposed to begin. By comparing <em>D</em><span> obtained by the simulations with experimental data of polystyrene melts and solutions, the average chain length per entanglement </span><em>N</em>_e was estimated to be 89, which is much larger than 30–42 reported by Paul et al. (J Phys II 1991;1:37). To see the origin of the discrepancy, statistical errors and system size effects are studied in detail and it was found that, to determine <em>D</em> within few percent of error, the number of independent chain samples <em>N</em>_sample should be larger than 10 000 and the size of simulation cells ℓ_cell should be larger than 4<em>R</em>_g; these conditions are not satisfied in the previous simulations. Critical chain length <em>N</em>_c^<em>η</em> for entanglement of BF model is estimated to be <em>N</em>_c^<em>η</em>=170 using the empirical relationship <em>N</em>_c^<em>η</em>/<em>N</em>_e=1.92 for polystyrene melts. It is argued that <em>N</em>_c^<em>η</em>=170 is a universal parameter of entanglement but <em>N</em>_e=89 is a specific value for polystyrenes and it may change with the materials with which comparisons are made.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 299-308"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00045-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81026727","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Molecular simulation of an amorphous poly(methyl methacrylate)–poly(tetrafluoroethylene) interface","authors":"O Okada ,&nbsp;K Oka ,&nbsp;S Kuwajima ,&nbsp;S Toyoda ,&nbsp;K Tanabe","doi":"10.1016/S1089-3156(00)00002-7","DOIUrl":"10.1016/S1089-3156(00)00002-7","url":null,"abstract":"<div><p>Molecular dynamics calculations of an amorphous interfacial system of poly(methyl methacrylate) (PMMA) and poly(tetrafluoroethylene) (PTFE) containing about 10,000 interaction sites were performed for 15<!--> <!-->ns under constant pressure and constant temperature conditions. The time evolutions of the thickness, density and number of atomic pairs in the interfaces suggested that the interfaces reached their equilibrium states with an interfacial thickness of about 2<!--> <!-->nm at 500<!--> <span><span>K. The molecular motion in the interface and bulk was compared using mean square displacement and torsional autocorrelation function. The separation at a PMMA/PTFE interface was mimicked using non-equilibrium molecular dynamics calculations by applying the potential energy to the MD cell in a direction perpendicular to the interface. Initially, the PTFE layer close to the interface was deformed, and before complete separation, some segments of the PTFE molecules extended from the bulk to the surface of the PMMA layer, which were attached by the </span>intermolecular interaction. The remaining PTFE molecules were entangled in the bulk, which probably prevented the transfer of the PTFE molecules to the surfaces of the PMMA layers. On the other hand, the PMMA layer was only slightly deformed. This separation behavior can be explained by taking into account the intermolecular interaction, the barrier to the conformational changes of the backbones and the entanglement of the PTFE molecules in the bulk.</span></p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 371-381"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(00)00002-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76500126","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Molecular dynamics simulation of entangled polymers in shear flow","authors":"T. Aoyagi ,&nbsp;M. Doi","doi":"10.1016/S1089-3156(99)00041-0","DOIUrl":"10.1016/S1089-3156(99)00041-0","url":null,"abstract":"<div><p>Large scale molecular dynamics simulation is conducted for a system of entangled polymers in shear flow. The polymer consists of 100, 200 and 400 beads, which is 3–10 times larger than the number of beads between the entanglement points. The simulation reproduces many characteristic features of the rheological properties of real polymeric liquids. The steady state viscosity <span><math><mtext>η(</mtext><mtext>γ</mtext><mtext>̇</mtext><mtext>)</mtext></math></span> plotted against the shear rate <span><math><mtext>γ</mtext><mtext>̇</mtext></math></span>, approaches a power law curve <span><math><mtext>η(</mtext><mtext>γ</mtext><mtext>̇</mtext><mtext>)∼</mtext><mtext>γ</mtext><mtext>̇</mtext><msup><mi></mi><mn>−n</mn></msup></math></span> which is independent of the molecular weight with the exponent <em>n</em>≃1. The second normal stress coefficient <span><math><mtext>Ψ</mtext><msub><mi></mi><mn>2</mn></msub><mtext>(</mtext><mtext>γ</mtext><mtext>̇</mtext><mtext>)</mtext></math></span> is negative and its ratio to the first normal stress coefficient <span><math><mtext>Ψ</mtext><msub><mi></mi><mn>1</mn></msub><mtext>(</mtext><mtext>γ</mtext><mtext>̇</mtext><mtext>), −Ψ</mtext><msub><mi></mi><mn>2</mn></msub><mtext>/Ψ</mtext><msub><mi></mi><mn>1</mn></msub></math></span> approaches to zero with the increase of the shear rate. The bond orientation is measured as a function of the position of the bond along the chain, and the profile is consistent with the recent theory of Mead et al. for the convective constraint release.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 317-321"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00041-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89858244","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Monte Carlo simulation of polarization reversal of ferroelectric polymer polyvinylidene fluoride","authors":"T. Koda,&nbsp;K. Shibasaki,&nbsp;S. Ikeda","doi":"10.1016/S1089-3156(99)00043-4","DOIUrl":"10.1016/S1089-3156(99)00043-4","url":null,"abstract":"<div><p><span>We consider a system composed of planar zigzag chain molecules of ferroelectric polymer PVDF. Taking the Lennard–Jones potential and the dipole–dipole interaction into consideration and assuming restrictions on molecular degrees of freedom, we have performed a </span>Monte Carlo simulation which enables us to discuss the polarization reversal of PVDF under constant external electric field. Our simulation shows that the phenomenon is accompanied by nucleation and expansion of reversed domains. It also indicates that the dipole–dipole interaction between molecules causes growth anisotropy of the reversed domains.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 335-343"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00043-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87007669","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Molecular dynamics simulation of local motion of polystyrene chain end—comparison with the fluorescence depolarization study","authors":"J. Horinaka ,&nbsp;S. Ito ,&nbsp;M. Yamamoto ,&nbsp;T. Matsuda","doi":"10.1016/S1089-3156(99)00040-9","DOIUrl":"10.1016/S1089-3156(99)00040-9","url":null,"abstract":"<div><p><span>Molecular dynamics (MD) simulation of the local motion of a polystyrene (PS) chain with anthryl group at the chain end surrounded by benzene molecules was performed and the results were compared with those obtained experimentally by the fluorescence depolarization method. The molecular weight dependence of the relaxation time of the probe obtained by the MD simulation was qualitatively in agreement with the results obtained by the fluorescence depolarization method. We also estimated the molecular weight dependence of the relaxation time for the end-to-end vector. Below the degree of polymerization (DP)≤3, the mean relaxation time </span><em>T</em>_m for the end-to-end vector was similar to that for the vector corresponding to the transition moment of the probe. With the increase of DP, the <em>T</em>_m<span> for the probe tended to reach an asymptotic value unlike that for the end-to-end vector, which monotonically increased with DP. This indicates that the entire motion of a polymer coil contributes to the local motion to a lesser extent as the molecular weight increases. The MD simulations using artificial restraints showed that the rotational relaxation of the probe at the chain end for a dynamically stiff PS chain is realized by the cooperative rotation of the main chain bonds. The internal modes which takes place below 5 monomer units mainly led to the rotational relaxation of the probe at the PS chain end. Finally, the change of </span><em>T</em>_m with the position along the PS main chain was examined.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 365-370"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00040-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78760834","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Micellization and relaxation kinetics of diblock copolymers in dilute solution based on A–W theory: I. Description of a model for core–corona type micelles","authors":"T. Nose,&nbsp;K. Iyama","doi":"10.1016/S1089-3156(99)00047-1","DOIUrl":"10.1016/S1089-3156(99)00047-1","url":null,"abstract":"<div><p>On the basis of the Aniansson–Wall (A–W) theory, a calculation method for the time evolution of association-number distribution during micelle<span> formation of diblock copolymer in solution is presented. The rate constant for the elemental process of a chain expulsion from a micelle is evaluated as a function of the association number by application of Halperin's treatment based on the Kramers rate theory. Numerical calculations are carried out for both cases of micellization from unimer state and micellar relaxation under a temperature jump from one micellar state to another. In the micelle relaxation, the micelle size changes stepwise with two steps, clearly showing the characteristic feature of the A–W mechanism, where there exist two processes, the fast process undergoing by consuming/releasing free unimers and the slow process accompanied with almost no change of unimer concentration. On the contrary, in the micellization from unimer state, the very fast process is observed, where the free chains get together quickly to form temporal micelles, and is followed by an ordinary micellar relaxation.</span></p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 249-257"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00047-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89096083","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Correspondence relation with respect to entanglement among different simulation models: comparison between bead-spring and bond fluctuation model","authors":"M. Tanaka,&nbsp;N. Kuzuu,&nbsp;S. Imai,&nbsp;K. Iwata","doi":"10.1016/S1089-3156(99)00046-X","DOIUrl":"10.1016/S1089-3156(99)00046-X","url":null,"abstract":"<div><p>A novel index for comparing different simulation model polymers with respect to entanglement is proposed. It is the number of elements <span><math><mtext>N</mtext><msub><mi></mi><mn><mtext>e</mtext></mn></msub><msup><mi></mi><mn>∗</mn></msup></math></span> of ring polymers whose average number of entanglement per molecule is unity; <span><math><mtext>N</mtext><msub><mi></mi><mn><mtext>e</mtext></mn></msub><msup><mi></mi><mn>∗</mn></msup></math></span> can be calculated with a small-scale computer simulation. We also proposed a method to equilibrate the entangled ring polymers. As an example we calculated <span><math><mtext>N</mtext><msub><mi></mi><mn><mtext>e</mtext></mn></msub><msup><mi></mi><mn>∗</mn></msup></math></span><span> with a molecular dynamics simulation using a bead-spring (BS) model which is equivalent to the model proposed by Kremer and Grest [J Chem Phys 92 (1990) 5057], and with a Monte Carlo simulation using bond fluctuation (BF) model. We obtained </span><span><math><mtext>N</mtext><msub><mi></mi><mn><mtext>e</mtext></mn></msub><msup><mi></mi><mn>∗</mn></msup><mtext>=82±1</mtext></math></span> for BS model with volume fraction <em>φ</em>=0.43 and <span><math><mtext>N</mtext><msub><mi></mi><mn><mtext>e</mtext></mn></msub><msup><mi></mi><mn>∗</mn></msup><mtext>=59±1</mtext></math></span> for BF model with <em>φ</em>=0.5. By comparing with the recent result of our group, <em>N</em>_e=89 for BF model with <em>φ</em>=0.5, we can assume that <span><math><mtext>N</mtext><msub><mi></mi><mn><mtext>e</mtext></mn></msub><mtext>≃1.5</mtext><mtext>N</mtext><msub><mi></mi><mn><mtext>e</mtext></mn></msub><msup><mi></mi><mn>∗</mn></msup><mtext>.</mtext></math></span> If this assumption holds for BS model, its <em>N</em>_e is estimated to be 120, which is 3.4 times greater than the estimated value by Kremer and Grest. The origin of this difference is discussed.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 309-315"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00046-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83181694","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}