Phases bicontinuous

Bicontinuous disordered phase (Bicontinuous microemulsion Sponge phase)... 

Figure 2a shows a schematic phase diagram for lyotropic liquid crystals. This figure shows the formation of micelles, cubic phases, bicontinuous cubic phases, and lamellar phases as the concentration of surfactant increases. Also shown in this figure is a schematic diagram of an ordered bicontinuous cubic phase (Fig. 2b). Another interesting example in...

Bicontinuous cubic phase Lamellar phase Bicontinuous cubic phase Reverse hexagonal columnar phase Inverse cubic phase (inverse micellar phase)... 

Cr Cub, Cubv d E G HT Iso Isore l LamN LaniSm/col Lamsm/dis LC LT M N/N Rp Rh Rsi SmA Crystalline solid Spheroidic (micellar) cubic phase Bicontinuous cubic phase Layer periodicity Crystalline E phase Glassy state High temperature phase Isotropic liquid Re-entrant isotropic phase Molecular length Laminated nematic phase Correlated laminated smectic phase Non-correlated laminated smectic phase Liquid crystal/Liquid crystalline Low temperature phase Unknown mesophase Nematic phase/Chiral nematic Phase Perfluoroalkyl chain Alkyl chain Carbosilane chain Smectic A phase (nontilted smectic phase)... 

In addition to single phase microemulsions, several phase equilibria known as Winsor systems [4] are also shown at low surfactant concentrations. A Winsor I (WI) system consists of an 0/W microemulsion that is in equilibrium with an oil phase, while a Winsor II (WII) system is a W/0 microemulsion in equilibrium with an aqueous phase. A Will system has a middle phase (bicontinuous) microemulsion that coexists with both oil and aqueous phases. 

While there have been efforts to polymerize other surfactant mesophases and metastable phases, bicontinuous cubic phases have only very recently been the subject of polymerization work. Through the use of polymerizable surfactants, and aqueous monomers, in particular acrylamide, polymerization reactions have been performed in vesicles (4-8). surfactant foams ), inverted micellar solutions (10). hexagonal phase liquid crystals (111, and bicontinuous microemulsions (121. In the latter two cases rearrangement of the microstructure occured during polymerization, which in the case of bicontinuous microemulsions seems inevitable b ause microemulsions are of low viscosity and continually rearranging on the timescale of microseconds due to thermal disruption (131. In contrast, bicontinuous cubic phases are extremely viscous in genei, and although the components display self-diffusion rates comparable to those... 

Typical surfactant-water-phase diagrams are shown in Fig. 3.4 for single-chained ionic, and non-ionic surfactants respectively. Below a "Krafft" temperature characteristic of each surfactant, the chains are crystalline and the surfactant precipitates as a solid. Increased surfactant concentration (Fig. 3.4) results in sharp phase boundaries between micellar rod-shaped (hexagonal), bilayer (lamellar) and reversed hexagonal and reversed micellar phases. (The "cubic" phases, bicontinuous, will be ignored in this section and dealt with in Chapters 4,5 and 7.)... 

Figure 4.9 Phase diagram of the system water-decane-CioE4 at equal volume fractions of water and decane as a function of the temperature T and the surfactant concentration cf>7. At low (f>7 there is a three-phase coexistence, while at moderate cf>7 the one-phase bicontinuous microemulsion appears. At even higher cf>7 the lamellar phase appears. At high and low temperatures a microemulsion phase coexists with either excess water or oil. The polymer fraction cf>p is raised symmetrically for the water- and oil-soluble polymers, and the one-phase microemulsion window closes continuously. The 2 K temperature shift is due to the use of heavy water. (From Ref. [40], reprinted with permission of the American Chemical Society.)...

The optimum formulation is a surfactant system with which maximum oil recovery can be achieved. For that purpose, the interfacial tension has to be as low as possible and the oil solubilisation in the microemulsion as large as possible [15,115,121,123,127,140,142-144]. In general, formulation is a concept that tunes the properties of a water-oil-surfactant system such that it can be used for the certain application (see Chapter 3). Extensive studies on the optimum formulation for EOR and various other applications have shown that many variables have to be considered to achieve an ultra-low interfacial tension at relatively low surfactant concentration, or the occurrence of a single-phase bicontinuous microemulsion at high surfactant concentration [15, 143, 144]. 

Microemulsions can also coexist in equilibrium with various phases, the most widely studied being the so-called Winsor phase equilibria Winsor I is a globular O/W microemulsion in equilibrium with excess oil, Winsor II a globular W/O microemulsion in equilibrium with excess water, and Winsor III a middle-phase bicontinuous microemulsion in equilibrium with both oil and water phases [10]. 

Figure 24.7 Comparison of effects of phase bicontinuity on nanocomposites. Nanocomposite particulate nanocomposite. Hybrid Bicontinuous nanocomposite (without molybdate dopant).

Mascia, L., Prezzi, L., and Haworth, B. (2006) Substantiating the role of phase bicontinuity and interfadal bonding in epoxy-silica nanocomposites. J. Mater. Sci., 41, 1145. 

The purpose of a phase scan is to determine the temperature (in case of nonionic surfactants) or salinity (in case of ionic surfactants) that can produce a microemulsion of desired type (O/W, W/O, or bicontinuous) and properties (such as solubilization). Figure 10.5 shows a typical phase scan (Rosen 2004). Phase scan is normally run from type 1 (Winsor 1) system to type 11 (Winsor 11) system by increasing the temperature (in case of nonionic surfactant) or salinity (in case of ionic surfactant). As shown in Figiue 10.5, oil solubilization increases from sample 1 to 2 with the increase in temperature or salinity. With the increase in temperature/salinity, the surfactant becomes more lipophilic due to the increased dehydration. Consequently, the interaction between oil and water phase (Yai,) increases and the interfacial tension (yow) decreases. As surfactant becomes continuously more lipophilic with the increase in temperature/salinity, a phase (bicontinuous or middle phase) begins to separate from phase (water continuous O/W microemulsion phase). At the start of the separation (sample 3), the interfacial tension between oil and phase (Yob) is still high and the interfacial tension between B and water phase (ybw ) is zero (fi and water are miscible). 

Intermicellar forces are generally of a repulsive nature (i.e., charged amphiphiles) and a reduction of such repulsion accompanies the transformation from spherical to cylindrical micelles. Further increase of concentration results in the formation of linear assemblies and liquid crystalline lyotropic mesophases (cf. Section ni.B). Not only nematic (Nc and Nd from rodlike or disklike shapes, respectively), hexagonal, and smectic phases, but also biaxial (mixtures of Nc and Nd) and complex cubic phases (bicontinuous networks or plastic crystals)... 

The porosity of solid polystyrene produced by polymerization in a middle-phase (bicontinuous) microemulsion is greater than that obtained by polymerization in either water-continuous or oil-continuous microemulsion. The first account of a middle-phase microemulsion-based porous polymer was reported by Haque and Qutubuddin in 1988 [71]. The microemulsions were formulated with styrene, water, sodium dodecyl sulfate (SDS), and 2-pentanol or butyl cellosolve as the cosolvent. (Since butyl cellosolve has greater solubility than 2-pentanol in polystyrene, it increases the stability of SDS microemulsion.) Figure 3.14 shows the structure of polystyrene when obtained from middle-phase microemulsion polymerization at 60 °C for 36 h, the composition (wt%) before polymerization being SDS 10 %, 2-pentanol 25 %, styrene 40 %, and water 25 %. The polymerized stmcture shows pores in both micron and submicron ranges. The observed greater porosity of this solid compared to the solids obtained from polymerization of oil-continuous microemulsion (SDS 10 %, 2-pentanol 25 %, styrene 55 %, water 10 %) and water-continuous microemulsion (SDS 10 %, 2-pentanol 25 %, styrene 5 %, water 60 %) is apparently related to the fact that middle-phase microemulsions contain interconnected domains of both water-continuous and oil-continuous regions. 

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