Stepwise Unwinding of Polyelectrolytes under Stretching

Tamashiro, M. N.; Schiessel, Helmut

doi:10.1021/ma992025s

Cited by 39 publications

(61 citation statements)

References 41 publications

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“…(70) and (G15). We should mention, however, that explicit analytical comparison in the exactly solvable planar case 27 does not show any improvement of the agreement between the nonlinear and linearized equations with the inclusion of the quadratic contribution to the average densities. Any numerical indications in this direction, which were indeed observed in the planar case, 27 are purely fortuitous.…”

Section: G Legendre Transformation At the Linearized Levelmentioning

confidence: 81%

“…This can be seen most clearly in the analytically tractable case of two infinite charged planes in electrochemical equilibrium with an infinite salt reservoir, which we present in a companion paper. 27 To avoid confusion we should stress at this point the exactness of the PB nonlinear solution at the mean-field level, its range of validity and limitations. In this work we discussed the linearization procedure in the framework of the nonlinear PB and the WS-cell model.…”

Section: Discussionmentioning

confidence: 99%

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Where the linearized Poisson–Boltzmann cell model fails: Spurious phase separation in charged colloidal suspensions

Tamashiro

Schiessel

2003

The Journal of Chemical Physics

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We perform a linearization of the Poisson-Boltzmann (PB) density functional for spherical WignerSeitz cells that yields Debye-Hückel-like equations agreeing asymptotically with the PB results in the weak-coupling (high-temperature) limit. Both the canonical (fixed number of microions) as well as the semi-grand-canonical (in contact with an infinite salt reservoir) cases are considered and discussed in a unified linearized framework. In the canonical case, for sufficiently large colloidal charges the linearized theory predicts the occurrence of a thermodynamical instability with an associated phase separation of the homogeneous suspension into dilute (gas) and dense (liquid) phases. In the semi-grand-canonical case it is predicted that the isothermal compressibility and the osmotic-pressure difference between the colloidal suspension and the salt reservoir become negative in the low-temperature, high-surface charge or infinite-dilution (of polyions) limits. As already pointed out in the literature for the latter case, these features are in disagreement with the exact nonlinear PB solution inside a Wigner-Seitz cell and are thus artifacts of the linearization. By using explicitly gauge-invariant forms of the electrostatic potential we show that these artifacts, although thermodynamically consistent with quadratic expansions of the nonlinear functional and osmotic pressure, may be traced back to the non-fulfillment of the underlying assumptions of the linearization.

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Section: G Legendre Transformation At the Linearized Levelmentioning

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Where the linearized Poisson–Boltzmann cell model fails: Spurious phase separation in charged colloidal suspensions

Tamashiro

Schiessel

2003

The Journal of Chemical Physics

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“…The PB equation [48] can be derived from a mean-field free energy functional [49,50,51,52,53,54] which itself is obtained from the underlying Hamiltonian either (i) as the saddle point of the field theoretic action [55,56,57,58], (ii) as a density functional reformulation of the partition function combined with a first order cumulant expansion of the correlation term [59], or (iii) from the Gibbs-Bogoljubov inequality applied to a trial product state [53]. The PB approximation gives a good description in the limit of high temperature and/or small charge densities (weak-coupling limit) when the microionic correlations that are neglected at the mean-field level are unimportant.…”

Section: Simulation Techniquementioning

confidence: 99%

Many-body interactions and the melting of colloidal crystals

Dobnikar

Chen

Rzehak

et al. 2003

The Journal of Chemical Physics

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We study the melting behavior of charged colloidal crystals, using a simulation technique that combines a continuous mean-field Poisson-Boltzmann description for the microscopic electrolyte ions with a Brownian-dynamics simulation for the mesoscopic colloids. This technique ensures that many-body interactions between the colloids are fully taken into account, and thus allows us to investigate how many-body interactions affect the solid-liquid phase behavior of charged colloids.Using the Lindemann criterion, we determine the melting line in a phase-diagram spanned by the colloidal charge and the salt concentration. We compare our results to predictions based on the established description of colloidal suspensions in terms of pairwise additive Yukawa potentials, and find good agreement at high-salt, but not at low-salt concentration. Analyzing the effective pairinteraction between two colloids in a crystalline environment, we demonstrate that the difference in the melting behavior observed at low salt is due to many-body interactions. If the salt concentration is high, we find configuration-independent pair-forces of perfect Yukawa form with effective charges and screening constants that are in good agreement with well-established theories. At low added salt, however, the pair-forces are Yukawa-like only at short distances with effective parameters that depend on the analyzed colloidal configuration. At larger distances, in contrast, the pair-forces decay to zero much faster than they would following a Yukawa force law. This is explained with a screening effect of the macroions. Based on these findings, we suggest a simple model potential for colloids in suspension which has the form of a Yukawa potential, truncated after the first coordination shell of a colloid in a crystal. Using this potential in a one-component simulation, we find a melting line that shows good agreement with the one derived from the full PoissonBoltzmann-Brownian-dynamics simulation.2

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“…The interesting thing is that the force is already zero even before the two strands are completely unzipped. This corresponds to the unraveling transition in the case of polymer in the condensed globule state being pulled by an external force [49][50][51][52]. There it was shown that for a polymer chain with N monomers, the number of monomers remaining in the globule state at the transition is still large and goes as N-n max ∼ N 3/4 [49].…”

Section: Unzipping Dna From a Condensed Globule State At Constanmentioning

confidence: 99%

Unzipping DNA from the condensed globule state—Effects of unraveling

Lam

Lévy

2005

Biopolymers

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We study theoretically the unzipping of a double stranded DNA from a condensed globule state by an external force. At constant force, we find that the double stranded , where the exponent χ is either 1 or 2 depending on whether the double stranded DNA sequence is homogeneous or heterogeneous respectively. In the case of unzipping at constant extension, we find that for a double stranded DNA with a very large number N of base pairs, the force remains almost constant as a function of the extension, before the unraveling transition, at which the force drops abruptly to zero. Right at the unraveling transition, the number of base pairs remaining in the condensed globule state is still very large and goes as N 3/4 , in agreement with theoretical predictions of the unraveling transition of polymers stretched by an external force.

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Stepwise Unwinding of Polyelectrolytes under Stretching

Cited by 39 publications

References 41 publications

Where the linearized Poisson–Boltzmann cell model fails: Spurious phase separation in charged colloidal suspensions

Where the linearized Poisson–Boltzmann cell model fails: Spurious phase separation in charged colloidal suspensions

Many-body interactions and the melting of colloidal crystals

Unzipping DNA from the condensed globule state—Effects of unraveling

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