223,757 research outputs found

    Polymer Release out of a Spherical Vesicle through a Pore

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    Translocation of a polymer out of curved surface or membrane is studied via mean first passage time approach. Membrane curvature gives rise to a constraint on polymer conformation, which effectively drives the polymer to the outside of membrane where the available volume of polymer conformational fluctuation is larger. Considering a polymer release out of spherical vesicle, polymer translocation time Ļ„\tau is changed to the scaling behavior Ļ„āˆ¼L2\tau\sim L^2 for R<RGR<R_G, from Ļ„āˆ¼L3\tau\sim L^3 for Rā‰«RGR\gg R_G, where LL is the polymer contour length and RR, RGR_G are vesicle radius and polymer radius of gyration respectively. Also the polymer capture into a spherical budd is studied and possible apparatus for easy capture is suggested.Comment: 14 pages RevTeX, 6 postscript figures, published in Phys. Rev. E 57, 730 (1998

    Dynamics of a polymer chain confined in a membrane

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    We present a Brownian dynamics theory with full hydrodynamics (Stokesian dynamics) for a Gaussian polymer chain embedded in a liquid membrane which is surrounded by bulk solvent and walls. The mobility tensors are derived in Fourier space for the two geometries, namely, a free membrane embedded in a bulk fluid, and a membrane sandwiched by the two walls. Within the preaveraging approximation, a new expression for the diffusion coefficient of the polymer is obtained for the free membrane geometry. We also carry out a Rouse normal mode analysis to obtain the relaxation time and the dynamical structure factor. For large polymer size, both quantities show Zimm-like behavior in the free membrane case, whereas they are Rouse-like for the sandwiched membrane geometry. We use the scaling argument to discuss the effect of excluded volume interactions on the polymer relaxation time.Comment: 13 pages, 6 figures, Accepted for publication in Eur. Phys. J.

    Polymer Electrolyte Membrane Fuelcell Dan Pembahasan Umpan Hidrogen

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    Teknologi masa depan yang berpotensi sebagai sistem penyedia daya adalah fuelcell. Teknologi fuelcell yang mengkonversikan energi kimia menjadi energi listrik secara elektrokimia menghasilkan emisi yang rendah serta efisiensi yang relatif tinggi. Namun penggunaan fuelcell secara massal dan komersial masih membutuhkan waktu. Terdapat beberapa jenis fuelcell. Fuelcell jenis Polymer Electrolyte Membrane yang beroperasi pada suhu rendah merupakan suatu pilihan sistem penyediaan tenaga untuk kendaraan dan pembangkit listrik skala kecil. Tulisan ini menguraikan sistem Polymer Electrolyte Membrane FuelCell yang terkait dengan analisa umpan hidrogen dan keekonomiannya

    Surface Polymer Network Model and Effective Membrane Curvature Elasticity

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    A microscopic model of a surface polymer network - membrane system is introduced, with contact polymer surface interactions that can be either repulsive or attractive and sliplinks of functionality four randomly distributed over the supporting membrane surface anchoring the polymers to it. For the supporting surface perturbed from a planar configuration and a small relative number of surface sliplinks, we investigate an expansion of the free energy in terms of the local curvatures of the surface and the surface density of sliplinks, obtained through the application of the Balian - Bloch - Duplantier multiple surface scattering method. As a result, the dependence of the curvature elastic modulus, the Gaussian modulus as well as of the spontaneous curvature of the "dressed" membrane, ~{\sl i.e.} polymer network plus membrane matrix, is obtained on the mean polymer bulk end to end separation and the surface density of sliplinks.Comment: 15 pages with one included compressed uuencoded figure

    Local entropic effects of polymers grafted to soft interfaces

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    In this paper, we study the equilibrium properties of polymer chains end-tethered to a fluid membrane. The loss of conformational entropy of the polymer results in an inhomogeneous pressure field that we calculate for gaussian chains. We estimate the effects of excluded volume through a relation between pressure and concentration. Under the polymer pressure, a soft surface will deform. We calculate the deformation profile for a fluid membrane and show that close to the grafting point, this profile assumes a cone-like shape, independently of the boundary conditions. Interactions between different polymers are also mediated by the membrane deformation. This pair-additive potential is attractive for chains grafted on the same side of the membrane and repulsive otherwise.Comment: 10 pages, 9 figure

    Polymer Translocation Through a Long Nanopore

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    Polymer translocation through a nanopore in a membrane investigated theoretically. Recent experiments on voltage-driven DNA and RNA translocations through a nanopore indicate that the size and geometry of the pore are important factors in polymer dynamics. A theoretical approach is presented which explicitly takes into account the effect of the nanopore length and diameter for polymer motion across the membrane. It is shown that the length of the pore is crucial for polymer translocation dynamics. The present model predicts that for realistic conditions (long nanopores and large external fields) there are two regimes of translocation depending on polymer size: for polymer chains larger than the pore length, the velocity of translocation is nearly constant, while for polymer chains smaller than the pore length the velocity increases with decreasing polymer size. These results agree with experimental data.Comment: 14 pages, 5 figure

    Thermodynamics of polymer adsorption to a flexible membrane

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    We analyze the structural behavior of a single polymer chain grafted to an attractive, flexible surface. Our model is composed of a coarse-grained bead-and-spring polymer and a tethered membrane. By means of extensive parallel tempering Monte Carlo simulations it is shown that the system exhibits a rich phase behavior ranging from highly ordered, compact to extended random coil structures and from desorbed to completely adsorbed or even partially embedded conformations. These findings are summarized in a pseudophase diagram indicating the predominant class of conformations as a function of the external parameters temperature and polymer-membrane interaction strength. By comparison with adsorption to a stiff membrane surface it is shown that the flexibility of the membrane gives rise to qualitatively new behavior such as stretching of adsorbed conformations

    Membrane consisting of polyquaternary amine ion exchange polymer network interpenetrating the chains of thermoplastic matrix polymer

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    An ion exchange membrane was formed from a solution containing dissolved matrix polymer and a set of monomers which are capable of reacting to form a polyquaternary ion exchange material; for example vinyl pyride and a dihalo hydrocarbon. After casting solution and evaporation of the volatile component's, a relatively strong ion exchange membrane was obtained which is capable of removing anions, such as nitrate or chromate from water. The ion exchange polymer forms an interpenetrating network with the chains of the matrix polymer

    Fluctuations in Polymer Translocation

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    We investigate a model of chaperone-assisted polymer translocation through a nanopore in a membrane. Translocation is driven by irreversible random sequential absorption of chaperone proteins that bind to the polymer on one side of the membrane. The proteins are larger than the pore and hence the backward motion of the polymer is inhibited. This mechanism rectifies Brownian fluctuations and results in an effective force that drags the polymer in a preferred direction. The translocated polymer undergoes an effective biased random walk and we compute the corresponding diffusion constant. Our methods allow us to determine the large deviation function which, in addition to velocity and diffusion constant, contains the entire statistics of the translocated length.Comment: 20 pages, 6 figure

    Polymer translocation induced by adsorption

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    We study the translocation of a flexible polymer through a pore in a membrane induced by its adsorption on \trans side of the membrane. When temperature TT is higher than TcT_c, the adsorption-desorption transition temperature, attractive interaction between polymer and membrane plays little role in affecting polymer conformation, leading to translocation time that scales as Ļ„āˆ¼L3\tau\sim L^3 where LL is the polymer contour length. When T<TcT < T_c, however, the translocation time undergoes a sharp crossover to Ļ„āˆ¼L2\tau\sim L^2 for sufficiently long polymers, following the second order conformational (adsorption) transition. The translocation time is found to exhibit the crossover around T=Tcā€²T=T_c', which is lower than TcT_c for polymers shorter than a critical length(N<NcN<N_c).Comment: 19 pages RevTeX, 5 postscript figures, to be published in J. Chem. Phys. 108(7), 3013 (1998
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