arXiv subjects

Rudi Podgornik

Publications and source records attributed to Rudi Podgornik.

21 records · Page 2Linked to original sources

arXiv2000

Osmotic Properties of Charged Cylinders: Critical Evaluation of Counterion Condensation Theory

The osmotic coefficient of B-DNA in water may, in moderately dilute solutions, deviate as much as 100 % from predictions based on a simple 'counterion condensation' theory. We determine the results for osmotic properties via a cell model description of the ionic atmosphere near a cylindrical polyelectrolyte. The cell model predictions for the osmotic properties disagree with predictions based on simple condensation theory, but are in surprisingly good harmony with experimental findings. We argue that the neglect of finite-radius effects makes simple condensation theory inapplicable at all but impractically low polyelectrolyte concentrations and, unable to reproduce osmotic properties of polyelectrolytes such as DNA.

cond-mat.soft↗

arXiv2000

Elastic moduli renormalization in self interacting stretchable polyelectrolytes

We study the effect of intersegment interactions on the effective bending and stretching moduli of a semiflexible polymer chain with a finite stretching modulus. For an interaction potential of a screened Debye-H\" uckel type renormalization of the stretching modulus is derived on the same level of approximation as the celebrated Odijk-Skolnick-Fixman result for the bending modulus. The presence of mesoscopic intersegment interaction potentials couples the bending and stretching moduli in a manner different from that predicted by the macroscopic elasticity theory. We advocate a fundamental change in the perspective regarding the dependence of elastic moduli of a flexible polyelectrolyte on the ionic conditions: stretchability. Not only are the persistence length as well as the stretching modulus dependent on the salt conditions in the solution, they are fundamentally coupled via the mesoscopic intersegment interaction potential. The theory presented here compares favorably with recent experiments on DNA bending and stretching.

cond-mat.soft↗

arXiv1999

Buckling, Fluctuations and Collapse in Semiflexible Polyelectrolytes

We present a systematic statistical mechanical analysis of the conformational properties of a stiff polyelectrolyte chain with intrachain attractions that are due to counterion correlations. We show that the mean-field solution corresponds to an Euler-like buckling instability. The effect of the conformational fluctuations on the buckling instability is investigated, first, qualitatively, within the harmonic (``semiclassical'') theory, then, systematically, within a 1/d-expansion, where d denotes the dimension of embedding space. Within the ``semiclassical'' approximation, we predict that the effect of fluctuations is to renormalize the effective persistence length to smaller values, but not to change the nature of the mean-field (i.e., buckling) behavior. Based on the 1/d-expansion we are, however, led to conclude that thermal fluctuations are responsible for a change of the buckling behavior which is turned into a polymer collapse. A phase diagram is constructed in which a sequence of collapse transitions terminates at a buckling instability that occurs at a place that varies with the magnitude of the bare persistence length of the polymer chain, as well as with the strength and range of the attractive potential.

cond-mat.soft↗