Density jumps across phase transitions in soft-matter systems

Graf, Hartmut; Löwen, Hartmut

doi:10.1103/physreve.57.5744

Cited by 73 publications

(78 citation statements)

References 28 publications

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“…Both are mean-field theories in the sense that they ignore fluctuations in microion distributions. An advantage of linear response theory, however, is that it encompasses the volume energy, which can be important for describing phase behavior [18,21,23,24,25,26]. Moreover, response theory can be straightforwardly generalized to incorporate nonlinear response, which entails both many-body effective interactions and corrections to the pair potential and volume energy [27].…”

Section: Theorymentioning

confidence: 99%

“…(31), long recognized as important for phase behavior [1], represents the entropy of free counterions; the second term accounts for the cohesive electrostatic energy of microion-macroion interactions. The volume energy, analogous to its counterpart for charged colloids [18,24,25,25], depends on the average macroion concentration and thus has the potential to influence phase behavior and other thermodynamic properties. Equations (20), (21), (25), (29), and (31) are the main analytical results for star macroions.…”

Section: A Star Macroionsmentioning

confidence: 99%

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Counterion penetration and effective electrostatic interactions in solutions of polyelectrolyte stars and microgels

Denton

2003

Phys. Rev. E

129

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Counterion distributions and effective electrostatic interactions between spherical macroions in polyelectrolyte solutions are calculated via second-order perturbation (linear response) theory. By modelling the macroions as continuous charge distributions that are permeable to counterions, analytical expressions are obtained for counterion profiles and effective pair interactions in solutions of star-branched and microgel macroions. The counterions are found to penetrate stars more easily than microgels, with important implications for screening of bare macroion interactions. The effective pair interactions are Yukawa in form for separated macroions, but are softly repulsive and bounded for overlapping macroions. A one-body volume energy, which depends on the average macroion concentration, emerges naturally in the theory and contributes to the total free energy.

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Section: Theorymentioning

confidence: 99%

Section: A Star Macroionsmentioning

confidence: 99%

Counterion penetration and effective electrostatic interactions in solutions of polyelectrolyte stars and microgels

Denton

2003

Phys. Rev. E

129

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“…If one characterizes this difference by the ratio x (>1) of the two coexisting densities, one finds x 3 [5] and x = 1.5 [6] for fluid-solid coexistence and x 1.26 [7] and x = 1.78 [8] for bcc-fcc coexistence. To appreciate the large magnitude of these density jumps, one recalls that x = 1.1 for the fluid-fcc density jump in the hard-sphere system, that any repulsive softness tends to decrease x towards unity (a smaller jump) [10], that the density jump across the fcc-bcc transition in soft-sphere systems is so small that one usually does not bother to determine it, and that 'volume' terms (which can be seen as coarsegrained many-body potentials) tend to decrease density jumps in low-salt suspensions [11]. In this article we explain the observed large density differences between the coexisting phases in low-salt colloidal suspensions, for the first time, as a direct consequence of non-pairwise interactions.…”

Section: Introductionmentioning

confidence: 99%

Effect of triplet attractions on the phase diagram of suspensions of charged colloids

Hynninen

Dijkstra

Roij

2003

J. Phys.: Condens. Matter

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We study, by simulation, the effect of attractive triplet interactions on the phase behaviour of suspensions of charged colloidal particles at low ionic strength, i.e. in the regime where the pair interactions are purely repulsive. We use the pair and triplet interactions that were obtained recently from a numerical, nonlinear Poisson-Boltzman study (Russ et al 2002 Phys. Rev. E 66 011402). Our simulations tentatively explain, for the first time, experimental observations of a rather large density difference between coexisting body centred cubic and face centred cubic crystal phases.

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“…The effect of these degrees of freedom is to add an extensive term to the free energy of the system [15],…”

Section: Afh Afp Afi Fmmentioning

confidence: 99%

Phase Behavior of Columnar DNA Assemblies

et al. 2002

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The pair interaction between two stiff parallel linear DNA molecules depends not only on the distance between their axes but on their azimuthal orientation. The positional and orientational order in columnar B-DNA assemblies in solution is investigated, based on the DNA-DNA electrostatic pair potential that takes into account DNA helical symmetry and the amount and distribution of adsorbed counterions. A phase diagram obtained by lattice sum calculations predicts a variety of positionally and azimuthally ordered phases and bundling transitions strongly depending on the counterion adsorption patterns.PACS numbers: 82.35. Rs, 87.14.Gg, 82.70.Dd DNA is a polyelectrolyte molecule. In aqueous electrolyte solutions, cations along its helices dissociate from it and dissolve into the mixture, leaving behind negative charges that reside on the phosphates of the DNA backbone. According to the Manning condensation theory, a fraction of the cations condenses into the Bjerrum layer near the molecular surface [1]. If some of the ions specifically adsorb onto DNA, its surface could be almost fully neutralized [2] or even overcharged [3]. Far from its axis, DNA can be apprehended as a charged cylinder. If the charge were continuously smeared, there would be only an electrostatic repulsion between two molecules, exponentially screened by the electrolyte. However, the net distribution of charge on the molecules is not homogeneous and this can dramatically alter the interaction potential at intermediate distances. Indeed, in order to condense DNA in an aggregate, one has either to apply osmotic stress [4] or use condensing agents, such as salts with Mn 2+ , Cd 2+ , spermidin, protamine or cobalt hexammine [5] cations. These cations are known to specifically adsorb on DNA, predominantly in the DNA grooves [6]. Other counterions, such as, e.g., Ca 2+ or Mg 2+ , that have strong affinity to phosphates and adsorb preferentially on the strands do not induce DNA aggregation. Obviously, one effect of these specifically adsorbing counterions is the reduction of the net charge on the DNA. However, were this to be the only effect, it would have been hard to explain the observed sensitivity to the sort of counterions of DNA condensation [5] and of the mesomorphism of resulting aggregates [7].Recently a new explanation of the features of DNA aggregation was suggested [8] resting on a Debye-Bjerrum theory of electrostatic interaction between helical macromolecules [9]. The theory offered first a formalism for a description of interaction between cylindrical molecules (with parallel axes) for arbitrary surface charge distributions on the molecules [9]. Then it explored its consequences for helical charge distributions, including those typical for double stranded B-and A-forms of DNA [9,10]. Various patterns of adsorbed counterions, including those spiraling through DNA major and minor groves, were considered. Thus, the effect of helically structured separation between negative and positive charges on each molecule was rationalized, explainin...

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Density jumps across phase transitions in soft-matter systems

Cited by 73 publications

References 28 publications

Counterion penetration and effective electrostatic interactions in solutions of polyelectrolyte stars and microgels

Counterion penetration and effective electrostatic interactions in solutions of polyelectrolyte stars and microgels

Effect of triplet attractions on the phase diagram of suspensions of charged colloids

Phase Behavior of Columnar DNA Assemblies

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