Amphiphilic film

Exerowa and co-workers [201] suggest that surfactant association initiates black film formation the growth of a black film is discussed theoretically by de Gennes [202]. A characteristic of thin films important for foam stability, their permeability to gas, has been studied in some depth by Platikanov and co-workers [203, 204]. A review of the stability and permeability of amphiphile films is available [205]. [Pg.522]

The most simple type of amphiphile film or a polymer film would be a gaseous state. This film would consist of molecules that are at a sufficient distance apart from each other such that lateral adhesion (van der Waals forces) are negligible. However, there is sufficient interaction between the polar group and the subphase that the filmforming molecules cannot be easily lost into the gas phase, and the amphiphiles are almost insoluble in water (subphase). [Pg.74]

The analogy between three- and two-dimensional phase diagrams can be carried much further. Monomolecular amphiphilic films show ordered phases similar to three-dimensional systems [579], The phases of an amphiphilic monolayer can be detected most conveniently in pressure-area (7r-versus-OA) isotherms. These may look different for different substances. The behavior of simple amphiphilic molecules, like long-chain alcohols, amines, or acids, was extensively investigated (reviews Refs. [580,581]). In monolayers so-called mesophases can occur. In a mesophase the tail groups are ordered over relatively large areas, while the order in the hydrophilic head groups is only over a much smaller distances. [Pg.283]

Reverse miceUes have been applied in the separation of amino acids and proteins. The separation is based on the balance between electrostatic forces and hydrophobic interactions [120]. The pH value is a crucial parameter determining this balance. If reversed miceUes are applied in LMs, then the underlying interactions are determined by interfacial partition coefficients of the amino acids/proteins separated, that is, hydrophobicity of the compounds separated, ionic strength of the feed and stripping solutions, the chemical nature of the electrolytes present, and the intertacial curvature of the amphiphilic film [121]. Changing the above-mentioned conditions, the overaU charge of the reverse miceUe can be altered, and so the separation conditions can be manipulated [122]. [Pg.380]

However, using double-chain ionic surfactants, e.g. sodium-bis-ethylhexylsulfo-succinate (AOT) [9, 67] and didodecyl dimethyl ammonium bromide (DDAB) [68], no co-surfactant is necessary to time the mean curvature of the amphiphilic film from positive to negative. In the following the quaternary (pseudo-ternary) system H20/NaCl (A)-n-decane (B)-AOT (D) will be discussed to show the main features of ionic microemulsions. Subsequently, the knowledge gained for alkylpolyglucoside micro emulsions (see Section 1.2.3) will be applied to understand the complex behaviour of five component ionic mixtures. [Pg.18]

Ionic surfactants with only one alkyl chain are generally extremely hydrophilic so that strongly curved and thus almost empty micelles are formed in ternary water-oil-ionic surfactant mixtures. The addition of an electrolyte to these mixtures results in a decrease of the mean curvature of the amphiphilic film. However, this electrolyte addition does not suffice to drive the system through the phase inversion. Thus, a rather hydrophobic cosurfactant has to be added to invert the structure from oil-in-water to water-in-oil [7, 66]. In order to study these complex quinary mixtures of water/electrolyte (brine)-oil-ionic surfactant-non-ionic co-surfactant, brine is considered as one component. As was the case for the quaternary sugar surfactant microemulsions (see Fig. 1.9(a)) the phase behaviour of the pseudo-quaternary ionic system can now be represented in a phase tetrahedron if one keeps temperature and pressure constant. [Pg.21]

Perhaps the most striking property of a microemulsion in equilibrium with an excess phase is the very low interfacial tension between the macroscopic phases. In the case where the microemulsion coexists simultaneously with a water-rich and an oil-rich excess phase, the interfacial tension between the latter two phases becomes ultra-low [70,71 ]. This striking phenomenon is related to the formation and properties of the amphiphilic film within the microemulsion. Within this internal amphiphilic film the surfactant molecules optimise the area occupied until lateral interaction and screening of the direct water-oil contact is minimised [2, 42, 72]. Needless to say that low interfacial tensions play a major role in the use of micro emulsions in technical applications [73] as, e.g. in enhanced oil recovery (see Section 10.2 in Chapter 10) and washing processes (see Section 10.3 in Chapter 10). Suitable methods to measure interfacial tensions as low as 10 3 mN m 1 are the sessile or pendent drop technique [74]. Ultra-low interfacial tensions (as low as 10 r> mN m-1) can be determined with the surface light scattering [75] and the spinning drop technique [76]. [Pg.23]

As was mentioned earlier, it is above all the water/oil interfacial crab that plays an important role in technical applications. Thus, much work has been carried out to obtain the variation of surfactant ratio 8[16, 90]. In the following the variation of the water/oil interfacial as a function of temperature and composition of the amphiphilic film (see Section 1.2.3) is discussed by way of example. [Pg.27]

Figure 1.15(a) shows the variation of the interfacial tension aab with the temperature for the system water-n-octane-Ci0E4 [17] and aab as a function of the composition of the amphiphilic film 8Vji (8v,i is the volume fraction and can be calculated by replacing m in Eq. (1.9) with V) in the quaternary system FbO-w-octane-P-QGj-QEo at T = 25°C (Fig. 1.15(b)) [90]. In both cases a log-scale is used for the interfacial tension because of the strong variation over several orders of magnitudes. [Pg.27]

Figure 1.15 Water/oil interfacial tension crab (plotted on log-scale) as function of the relevant tuning parameter, (a) Variation of crab with temperature T, exemplarily shown for the water-n-octane-C- oE4 system [17]. (b) Variation of crab with the composition of the amphiphilic film 8yi in the quaternary system hbO-n-octane-fS-CsG-i-CsEo at T = 25°C [90]. Both systems show that the water/oil interfacial tension runs through a distinct minimum in the middle of the three-phase region. The full line is calculated considering the bending energy difference between a curved amphiphilic film in the microemulsion and the flat film of the macroscopic interface [96].

In Sections 1.2.3 and 1.3.3, it was shown that in temperature-insensitive quaternary CnGm systems the composition of the amphiphilic film instead of the temperature has to... [Pg.32]

In order to use electron microscopy to visualise the microemulsion structure, the problem of the fixation of the liquid mixtures has to be solved. The method of choice is to solidify the microemulsion structure via cryofixation. However, given that the phase behaviour as well as the curvature of the amphiphilic film (see Fig. 1.18) and with it the microstructure of most micro emulsions show a strong temperature-dependence it has to be ensured that the cooling rate should be as high (>104 K/s) and the reorganisation kinetics of the microstructure as slow as possible. [Pg.34]

Gradzielski, M., Langevin, D. and Farago, B. (1996) Experimental investigation ofthe structure of nonionic microemulsions and their relation to the bending elasticity of the amphiphilic film. Phys. Rev. E, 53, 3900-3919. [Pg.81]

Gradzielski, M., Langevin, D., Sottmann, T. and Strey, R. (1997) Droplet microemulsions at the emulsification boundary The influence of the surfactant structure on the elastic constants of the amphiphilic film. /. Chem. Phys., 106, 8232-8238. [Pg.81]

Appell, J., Ligoure, C. and Porte, G. (2004) Bending elasticity of a curved amphiphilic film decorated with anchored copolymers A small angle neutron scattering study. /. Stat. Mech. Theor. Exp., P08002, 1-4. [Pg.144]

The interpretation of small SANS data from systems of type D20/NaCl- -decane/triolein-CioE4 showed that the order of the microstructure systematically decreases with increasing triolein content (Fig. 11.8(c) and Table 11.3). However, the value of the amphiphilicity factor [49, 50] /a = —0.65 indicates that the pure triolein microemulsion is still a microemulsion in the narrower sense. The bending constants k and i< obtained from phase diagrams and scattering curves furthermore verify that the rigidity of the amphiphilic film decreases with increasing triolein content (Fig. 11.9). [Pg.360]

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