Thermodynamics of the L3 (Sponge) Phase in the Flexible Surface Model

Kroll

1998

Phys. Rev. Lett.

Much of the phase behavior observed in self-assembling amphiphilic systems can be understood in the context of ensembles of random surfaces. In this article, it is shown that Monte Carlo simulations of dynamically triangulated surfaces of fluctuating topology can be used to determine the structure and thermal behavior of sponge phases, as well as the sponge-to-lamellar transition in these systems. The effect of the saddle-splay modulus,k, on the phase behavior is studied systematically for the first time. Our data provide strong evidence for a positive logarithmic renormalization ofk; this result is consistent with the lamellar-to-sponge transition observed in experiments for decreasing amphiphile concentration.[S0031-9007(98)

mentioning

confidence: 43%

“…Two other forms for the free energy f͑f͒ have been suggested recently [24,25]. In both cases, the renormalization of k andk is not considered.…”

mentioning

confidence: 99%

Membranes with Fluctuating Topology: Monte Carlo Simulations

Kroll

1998

Phys. Rev. Lett.

“…However, this result has been questioned by Daicic et al [14,13]. This has lead to a intensive debate, with arguments against [15,16] and in favor [91,86] of the existence of a logarithmic renormalization of elastic moduli in the sponge phase.…”

Section: Comparison With Experimentsmentioning

confidence: 99%

Bicontinuous Surfaces in Self-assembling Amphiphilic Systems

Schwarz

Morphology of Condensed Matter

2002

Amphiphiles are molecules which have both hydrophilic and hydrophobic parts. In water-and/or oil-like solvent, they self-assemble into extended sheet-like structures due to the hydrophobic effect. The free energy of an amphiphilic system can be written as a functional of its interfacial geometry, and phase diagrams can be calculated by comparing the free energies following from different geometries. Here we focus on bicontinuous structures, where one highly convoluted interface spans the whole sample and thereby divides it into two separate labyrinths. The main models for surfaces of this class are triply periodic minimal surfaces, their constant mean curvature and parallel surface companions, and random surfaces. We discuss the geometrical properties of each of these types of surfaces and how they translate into the experimentally observed phase behavior of amphiphilic systems.

“…(32) assumes small volume fractions, the form p = aφ 3 + bφ 5 incorporating a next-to-leading order correction as φ 5 has been suggested. 59,60 On the other hand, the bending rigidity κ and the saddle-splay modulusκ are logarithmically renormalized by thermal fluctuations as discussed in Sec. II C. In contrast to the high-density correction, the renormalization becomes important at low densities, i.e., at high dilution, since the role of the length scale in the renormalization is played by the inverse area density (S/V) −1 of the surfactant monolayer.…”

Section: A Equation Of Statementioning

confidence: 99%

Scattering intensity of bicontinuous microemulsions and sponge phases

Peltomäki

The Journal of Chemical Physics

Kroll

2012

Monte Carlo simulations of dynamically triangulated surfaces of variable topology are used to investigate the scattering intensities of bicontinuous microemulsions. The bulk scattering intensity is shown to follow the Teubner-Strey expression. The domain size and the correlation length are extracted from the scattering peaks as a function of the bending rigidity, saddle-splay modulus, and surfactant density. The results are compared to earlier theories based on Ginzburg-Landau and Gaussian random field models. The ratio of the two length scales is shown to be well described by a linear combination of logarithmically renormalized bending rigidity and saddle-splay modulus with universal prefactors. This is in contrast to earlier theoretical predictions in which the scattering intensity is independent of the saddle-splay modulus. The equation of state, and the asymptotics of the bulk and film scattering intensities for high and low wave vectors are determined from simulations and compared with theoretical results.