Semiflexible Chains

Equilibrated conformations of isolated semiflexible polyelectrolyte chains are presented vs. Ct and kang for comparison with flexible conformations. Electrolyte concentration ranges from Ct = 0 (k-1 = ^ ) to Ct = 1 M (k-1 = 3 A), and kang values are adjusted from 0 to 0.02 kBT/deg2, the chain length being equal to 200 monomers (f = 1). Table 2 demonstrates that the semiflexible polyelectrolytes exist as extended and SAW configurations controlled by both the intensity of the electrostatic repulsions between the monomers and intrinsic stiffness kang. When kang = 0 kBT/deg2, i.e., when fully flexible chains are considered, a decrease in the ionic concentration causes a gradual spreading of the polyelectro-lyte dimensions, so that rodlike structures are achieved to minimize the electrostatic energy of the chain. When Ct = 1 M, chain stiffness has full effect.

TABLE 2 Monte Carlo Equilibrated Conformations of Isolated Polyelectrolytes (N = 200) as a function of the Intrinsic Polyelectrolyte Stiffness kang and Ionic Concentration Ca

[KeT/deg ]

0

0.0005

0,001

0.02

Q[M]

0

x >

\

\

J

V

J <

f

Cn v) %f j

\ \j

\ \ \

"When electrostatic interactions between monomers are screened (Q = 1 M ), the increase in chain stiffness induces the formation of rigid domains that are connected to each other by more flexible regions.

"When electrostatic interactions between monomers are screened (Q = 1 M ), the increase in chain stiffness induces the formation of rigid domains that are connected to each other by more flexible regions.

However, a different picture of chain stretching has to be considered. The increase of intrinsic stiffness locally destroys a large amount of chain entropy and results in the formation of rigid domains connected to each other by flexible bonds (see, for example, Table 2, C = 1 M and kang = 0.001 kBT/deg2). As shown in Fig. 3 where <R2ee> variations are presented as a function of kang for different C values, electrostatic interactions and intrinsic stiffness influence each other but at different scales. Although long-range electrostatic repulsions have full effects when Ci = 0 M, it is still possible to increase the chain dimension through local geometrical constraints. It is worth noting that (1) both electrostatic and intrinsic rigidity are required to achieve straight poles and (2) chain dimensions

2.0x106

2.0x106

0.000 0.005 0.010 0.015 0.020 0.025

kang [kBT/deg2]

FIG. 3 Mean square end-to-end distance <R2ee> as a function of the chain intrinsic rigidity klmg at different ionic concentrations C. The <Ree> variation for a neutral chain is represented by the dotted line. Rigid rods are achieved by both increasing the electrostatic repulsions between the monomers (large-scale effects) and intrinsic stiffness (local effects).

of screened rigid polyelectrolytes (C = 1 M and kimg = 0.02 kBT/deg2) and unscreened flexible polyelectrolyte (C = 0 M and ktms = 0 kBT/deg2) are similar.

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