223,757 research outputs found
Polymer Release out of a Spherical Vesicle through a Pore
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 is changed to the scaling behavior for
, from for , where is the polymer contour
length and , 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
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
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
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
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
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
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
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
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
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
is higher than , 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
where is the polymer contour length. When ,
however, the translocation time undergoes a sharp crossover to
for sufficiently long polymers, following the second order conformational
(adsorption) transition. The translocation time is found to exhibit the
crossover around , which is lower than for polymers shorter than
a critical length().Comment: 19 pages RevTeX, 5 postscript figures, to be published in J. Chem.
Phys. 108(7), 3013 (1998
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