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Molecular dynamics simulations of electrophoresis of polyelectrolytes in nano confining cylindrical geometries
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10.1063/1.4794195
/content/aip/journal/jcp/138/10/10.1063/1.4794195
http://aip.metastore.ingenta.com/content/aip/journal/jcp/138/10/10.1063/1.4794195
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

(Top) Schematic cross-section of (dashed) constant, and (black) periodically modulated diameter cylinders. (Middle) The corresponding surface gradient R (z) as a function of z-coordinate. (Bottom) The driving pulse electric field of maximum amplitude as a function of time. The off-time window takes 70% of a time period T = 578τ. δ notes the diameter of the constriction.

Image of FIG. 2.
FIG. 2.

Illustration of a sample configuration from molecular dynamics simulations of (black) charged polymer chain of length N = 150, (green) coions and (red) counterions in confining cylinder of variable diameter. The chain extends on two neighboring cavities and passes through constrictions by forming loops. (The direction of motion is from right to left.) For clarity, the solvent molecules are not represented here.

Image of FIG. 3.
FIG. 3.

Electrophoretic velocities v z of charged chains of length N as a function of the applied field in uniform (noted cyl.) and modulated (noted mod.) diameter cylinders, and in modulated cylinders under pulse field of amplitude (noted ). The error bars are smaller than the symbol size. (The off-time window of the pulse field is 70% of a time period.)

Image of FIG. 4.
FIG. 4.

Bar diagram of average positions z after a set time interval of electrophoresis of charged chains of length N in constant (noted cyl.) and variable diameter (noted mod.) cylinders under constant applied fields , and similar positions in modulated cylinders (noted ) in applied pulse fields of relative strength

Image of FIG. 5.
FIG. 5.

Schematic illustration on the center of mass motion z = z(t), at constant low fields , of the trapping time t b of charged chains in the cavities of modulated diameter cylinders and the transit velocity v t through constrictions.

Image of FIG. 6.
FIG. 6.

Illustrative trajectories at small time scale of the center of mass motion of charged chains in modulated diameter cylinders under pulse electric fields. The relaxation (or free diffusion) of the chains in the off-time window of the pulse field appears as a backtrack motion and makes the trajectories appear zigzagged.

Image of FIG. 7.
FIG. 7.

The long time average of the transverse radius of the chain normalized by the bond length b as a function of constant applied field in constant (noted cyl.), variable diameter cylinders (noted mod.), and in pulsed fields (noted ). The error bars are smaller than the symbol size. (In the case of pulse fields, is rescaled by a factor of 1/3 to account for the off-time window of a time period.)

Image of FIG. 8.
FIG. 8.

Projected length |z max z min | in the field direction normalized by the contour length Nb of the chains. The legend notation is the same as in Fig. 7 . The error bars are smaller than the symbol size.

Image of FIG. 9.
FIG. 9.

Transit velocities v t and average electrophoretic velocities v z of the charged chains driven in modulated diameter cylinders as a function of the applied field (not pulse field). At high fields, both v t and v z coincide. The largest chain of N = 150 passes through constrictions almost unhindered, at fields .

Image of FIG. 10.
FIG. 10.

(Left) Schematic representation of a compression blob model of a chain squeezed in a cylindrical confining cavity of diameter R 0. At equilibrium between forces of entropic and electric origin, the chain occupies the confined volume . (Right) At higher applied electric fields, n monomers of the chain are pushed into the connecting channel of diameter δ for a distance x.

Image of FIG. 11.
FIG. 11.

(Points) Log-linear plot of the trapping time t b of the chains in the cavities of the variable diameter cylinder as a function of the applied electric field (not pulse) and (continuous line) scaling prediction from Eq. (16) . Only at the lowest field value t b could be measured for the chain with N = 150.

Image of FIG. 12.
FIG. 12.

Electrophoretic mobilities μ z of the chains in straight and variable diameter cylinders as a function of the applied electric field.

Image of FIG. 13.
FIG. 13.

Electrophoretic mobilities μ z of the chains under applied pulse electric fields in variable diameter cylinders. ( is rescaled by a factor of 1/3 to account for the off-time window of the time period.) As a reference, the electrophoretic mobilities μ z of the chains under applied constant electric fields from Fig. 12 are also reproduced here.

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/content/aip/journal/jcp/138/10/10.1063/1.4794195
2013-03-13
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Molecular dynamics simulations of electrophoresis of polyelectrolytes in nano confining cylindrical geometries
http://aip.metastore.ingenta.com/content/aip/journal/jcp/138/10/10.1063/1.4794195
10.1063/1.4794195
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