Sponge Phase Research Articles

Dynamical behavior of microemulsion and sponge phases in thermal equilibrium.

The dynamical behavior of microemulsion and sponge phases is studied with a time-dependent Ginzburg-Landau model. The model has been shown previously to capture many of the essential static properties of these systems. Using a field-theoretic perturbation theory, we calculate the frequency-dependent (complex) viscosity \ensuremath{\eta}(\ensuremath{\omega}), sound velocity c(\ensuremath{\omega}) and damping D(\ensuremath{\omega}), and the scattering intensity S(k,t) in bulk and film contrast. The viscosity is almost frequency independent for small \ensuremath{\omega}, then drops sharply at a characteristic frequency ${\mathrm{\ensuremath{\omega}}}^{\mathrm{*}}$, corresponding to a characteristic relaxation time \ensuremath{\tau}\ensuremath{\sim}1/${\mathrm{\ensuremath{\omega}}}^{\mathrm{*}}$. The same relaxation time is also found to dominate the sound velocity and damping. The characteristic frequency has the scaling form ${\mathrm{\ensuremath{\omega}}}^{\mathrm{*}}$\ensuremath{\sim}${\ensuremath{\xi}}^{\mathrm{\ensuremath{-}}6}$\ensuremath{\Omega}(q\ensuremath{\xi}), where \ensuremath{\xi} is the correlation length and q is the inverse domain size of the microemulsion structure. The scattering intensity S(k,t) decays exponentially in time t for large t with an algebraic prefactor ${\mathit{t}}^{\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\alpha}}}$, both in bulk and in film contrast. In the latter case, we find there are several regimes of the wave vector k with different exponents \ensuremath{\alpha}. \textcopyright{} 1996 The American Physical Society.

Phase science of surfactants

Recent major developments that have taken place in surfactant phase science may be summarized in five points. First, the equilibrium vesicle phase formed by catanionic surfactant mixtures in the very dilute region has been investigated for several systems which also form several mesophases in the concentrated region. Coexistence of two reversed hexagonal phases and first order vesicle→micelle phase transition have been demonstrated. Second, by manipulating the hydrophilic-lipophilic balance and molecular geometry of many surfactant systems, the changes in observed phase behaviour serve to increase our knowledge of aggregation processes in general and the structures of the biréfringent intermediate phases, sponge phase and dilute lamellar phase in particular. Third, the lyotropic nematic and defective mesh-type lamellar phases are readily formed by fluorinated surfactants; the structures of the two phases, which are still debatable, have been studied by several techniques. The first observation of a lower consolute loop along the dilute lamellar phase was reported for the fluorinated anionic surfactant systems. Fourth, the valency of counterions has been shown to have dramatic effects on the aggregation and phase behaviour of ionic surfactants. Finally, surfactant-protein systems form novel gel phases and locations of phases provide information concerning the contribution of electrostatic and hydrophobic effects to surfactant-protein interactions.

Economically producing reactive metals by aerosol reduction

As presently produced, the reactive metals hafnium, titanium, and zirconium are relatively expensive and are usually specified only for compelling applications. These and similar metals will always cost more than the common metals because their liquid- phase reactivity requires specialized melting equipment. However, a considerable fraction of their present expense is due to the large number of unit operations in their extraction from ore. In particular, the end product of extractive operations is the elemental sponge form of each metal, which is expensive to produce and convert to homogeneous ingot. The search for a direct reduction process that bypasses the sponge phase has yet to produce a cost-effective alternative to sponge processes. A new concept combines modern process control equipment with cold-wall induction melting techniques and may finally make possible a process for producing first-melt ingots of these metals directly from the reaction between precursor compounds and liquid-metal reductants.

Sponge Phase Transitions from a Lattice Mode

We use Monte Carlo simulations to obtain thermodynamic functions and correlation functions in a lattice model we propose for sponge phases. We demonstrate that the surface-density correlation function dominates the scattering only along the symmetric-sponge (SS) to asymmetric-sponge (AS) phase boundary but not the boundary between the sponge-with-free-edges (SFE) and symmetric-sponge phases. At this second thermodynamic transition the scattering is dominated instead by an edge-density (or seam-density) correlation function. This prediction provides an unambiguous diagnostic for experiments in search of the SS-SFE transition.

Swelling behavior and local topology of an L3 (sponge) phase.

Swelling behavior and local topology of an L3 (sponge) phase.

Evidence of a Phenomenon of Epitaxy at the Interface between a Lamellar L alpha Phase and a L3 Sponge.

In the quasiternary lyotropic system CpCl $/$brine $/$hexanol, the interface between the lamellar ${L}_{\ensuremath{\alpha}}$ and the ``sponge'' ${L}_{3}$ phase adopts geometries characteristic of a tilted anchoring of the lamellar layers on the sponge phase. Quantitative measurements of this new phenomenon are performed at equilibrium. Additionally, the evolution of the characteristic distances ${d}_{\ensuremath{\alpha}}$ and ${d}_{3}$ of the two phases in the biphasic region with swelling variation was determined by x-ray scattering. Our results support the hypothesis of an epitaxial matching between the two phases.

Isotropic phases of bilayers

The bending properties of surfactant bilayers are the foundation for the formation and stability of the so-called L 3 sponge phase. During the past two years, improved theoretical interpretations and models of this fascinating multiconnected disordered structure have been worked out. On the experimental side, critical behaviours observed in the very dilute region have been explored, leaving the issue of the topological transition of the L 3 phase towards disconnected micelles unresolved. Comparatively little attention has focused on the dynamics and rheology of the sponge.

Microemulsions — phase equilibria characterization, structures, applications and chemical reactions

The progress in understanding microemulsion structure on a molecular level as well as from extensive experimental studies of phase diagrams is reviewed. In this respect the studies involve both ionic and nonionic surfactants. Structures discussed involve the hard sphere model, the bicontinuous model, sponge phases and the flexible surface model. The progress in spectroscopic techniques (like NMR and TDS) together with scattering techniques, when applied to microemulsion systems, is also briefly discussed. Technical applications of microemulsions involve general applications as cleaning systems, fuels and in the field of crude oil exploitation. The last topic summarizes the use of the systems in EOR, acidizing and transport. The major emphasis of the review is in the utilization of microemulsions as systems in chemical reactions. These reactions involve preparation of inorganic particles, polymerization of organic monomers together with preparation of both organic and inorganic complexes and clusters. Enzyme catalyzed reactions involving the enzymes lipase, trypsin, α-chymotrypsin and alcohol dehydrogenase in different microemulsions are also summarized.

Measurement of the Membrane Flexibility in Lamellar and “Sponge” Phases of the C12E5/Hexanol/Water System

The present work is primarily concerned with the measurement, by several different methods (using X-ray and static light scattering experiments or dynamic light scattering experiments), of the elasticity of bilayers made up of n-dodecyl pentaethylene glycol monoether (C12E5) and hexanol molecules. The membrane bending elasticity modulus, κ, has been measured for both the Lα (lamellar) and the L3 (“sponge”) phase of the C12E5/hexanol/water system. For the lamellar phase, κ was measured using both the excess area and the dynamics of the fluctuations, while for the sponge phase κ was measured using only the excess area. The values of κ measured seem to be of the same order (approximately kBT) for both the lamellar phase and the sponge phase, although the molar ratio of hexanol to C12E5 is 4 times bigger in the sponge phase. The effect of temperature on κ was also studied: the slight increase in κ found for this system with temperature seems to be related to a decreasing polar head area of the C12E5 molecule...

Comment on “Thermodynamics of the L 3 (Sponge) Phase in the Flexible Surface Model" by John Daicic et al.

Comment on “Thermodynamics of the L 3 (Sponge) Phase in the Flexible Surface Model" by John Daicic et al.

Reply to Comment on “Thermodynamics of the L 3 (Sponge) Phase in the Flexible Surface Model"

Reply to Comment on “Thermodynamics of the L 3 (Sponge) Phase in the Flexible Surface Model"

Phase Transition Induced by Shearing of a Sponge Phase

For the first time it has been shown that upon shearing of a sponge phase in a Couette cell a phase transition to a new highly birefringent phase with the same viscosity was induced. This transition is dependent upon the concentration of solvent, the length of time of shearing, and the history of the system.

On swelling and structure of composite materials. Some theory and applications of lyotropic mesophases

Swelling relations linking structural dimensions to composition in two-phase composite materials are derived as a function of domain shape and swelling mode. Planar, cylindrical, globular and hyperbolic (“sponge”) monodisperse shapes are analysed and compared in detail. The effect of small variations in domain shape about some average form is also shown to modify the swelling exponent from that associated with the shape parameter of monodisperse (and “homogeneous”) domain morphologies. Both exponential and polynomial variations of characteristic dimensions of the composite with concentration arise, depending on the swelling mode. Swelling exponents are shown to be simply related to a shape parameter, which is a useful index of the shape of domains within the composite. It is shown that the usual relation used to identify lamellar structures holds equally well for other morphologies, particularly sponges, in certain situations. Applications of the swelling theory are presented to re-investigate the mesostructures of a cubic phase, hexagonal phases and a sponge phase in lyotropic lipid assemblies. The analysis forcefully demonstrates the paradoxical nature of swelling as a probe of domain structure in composite materials. On the one hand, the swelling behaviour of a single composite structure is exquisitely sensitive to the detailed mechanism of composite swelling, such as the occurrence of neutral surfaces within the material during swelling. On the other, many different composite geometries can display identical swelling behaviour, given distinct specific swelling mechanisms for each morphology.

A Confined Complex Liquid. Oscillatory Forces and Lamellae Formation from an L3 Phase

In this paper, we present the results from measurements of forces between macroscopic mica surfaces immersed in an L 3 (sponge) phase. Two different surfactant systems are investigated. As previously reported (Petrov, P. ; et al. Langmuir 1994, 10, 988) for the AOT/brine/water L 3 phase, two distinct regions in the force profile are observed : At large separations (40-120 nm), the force is oscillatory due to the structure in the bulk solution. In a confined space, at separations smaller than ∼30 nm, there is a topological transition to a layered, lamellar-like structure with a force having huge repulsive barriers with a period of 3-3.5 nm, weakly dependent on concentration. The same characteristic forces are observed for an L 3 phase made of C 12 E 5 /hexanol/water. The period of long-range oscillations, scaled by the thickness of the bilayer, is inversely proportional to the surfactant volume fraction and shows a uniform functional dependence for both L 3 -phase systems, in accordance with the general scaling law. Model calculations of the force profile within the flexible surface model reproduce and rationalize all qualitative observations and give a reasonable quantitative estimate of the force. We derive generally applicable conditions for the appearance of stable lens of lamellar phase between curved surfaces in a bulk L 3 solution and calculate the force explicitly, without invoking the Derjaguin approximation.

Sponge-lamellar instability of fluctuating membranes.

We consider the instability of amphiphilic sponge phases with respect to a fluctuating lamellar phase in a consistent random interface model based on the curvature-elastic Hamiltonian of the membranes. The phase behavior is investigated in terms of bending moduli and surfactant concentration. First-order transitions are found upon changes in surfactant concentration, bending modulus, or saddle-splay modulus in agreement with experimental observation.

Effects of weak shear on hyperswollen lyotropic smectic liquid crystals

We have developed a Zimm-type viscometer specially designed for the simultaneous measurements of the structure factor and the viscosity of hyperswollen lyotropic liquid crystals under a very weak shear. We have investigated the shear effects on the layer undulation fluctuation in the lamellar structure and the transition from the anisotropic lamellar to the isotropic sponge phase. We have found a significant difference in the rheological properties between the lamellar and the sponge phase: The former exhibits non-Newtonian flow behavior, while the latter exhibits Newtonian behavior.

Light scattering from the L3 (sponge) phase: Evidence against logarithmic corrections to ideal scaling.

We present compressibility data over a broad range of surfactant concentrations from static light scattering experiments on the ${\mathit{L}}_{3}$ phase appearing in the system AOT [sodium bis(2-ethylhexyl) sulfosuccinate]\char21{}NaCl\char21{}water. The results are seen to support a model for the thermodynamics of this phase recently proposed by the present authors. They also provide strong evidence against logarithmic corrections to the free energy of the sponge phase, previously suggested to arise from renormalization effects.

Dynamics of microemulsions as seen by neutron spin echo

Neutron spin echo (NSE) was employed to study the dynamics of a variety of microemulsion phases. Starting from the droplet phase, we present very recent results on the lamellar and sponge (L3) phases. Combining the well-known contrast-variation method of small-angle neutron scattering (SANS) with the unique energy resolution of NSE we can separate motions which are otherwise undetectable. Combining the static and dynamical experiments, microscopic parameters like the bending rigidity ( K) could be deduced. We find, for example, that the local dissipation is 4–6 times higher than would be predicted from the solvent viscosities.

Comment on "Fluctuating interfaces in microemulsion and sponge phases"

In a recent paper Gompper and Goos [Phys. Rev. E 50, 1325 (1994)] use the random-interface approach to discuss film scattering from sponge and microemulsion phases. We show that their calculations of the film scattering lack the integration measure so that subsequent conclusions about the random-level-surface model have to be revised. Furthermore we find in contrast to that paper that a sponge-lamellar transition in the random-interface approach is possible.

Reply to "Comment on 'Fluctuating interfaces in microemulsion and sponge phases' "

In reply to the preceding Comment of Pieruschka, Safran, and Marc\ifmmode \breve{}\else \u{}\fi{}elja, we show that the scattering intensity of level surfaces of Gaussian random fields has the same asymptotic behavior for small wave vectors, both for interfaces of constant and of fluctuating thickness. In the former case, Monte Carlo simulation results for the film correlation function in a Ginzburg-Landau model are found to be in very good agreement with variational results; in particular, the oscillatory component of the correlation function is found to be much more pronounced than for interfaces of fluctuating thickness.