Phase inversion 320 INDEX

Thus, an estimation can be made of the hydrophilicity of the crown ring. The acetal-type crown ring obtained from hexaethyl-ene glycol and a higher aliphatic aldehyde is estimated to be e-quivalent to about four OE units in an alkyl POE monoether, from our study of the cloud point (11). Moroi et al. concluded, from a comparison of the cmc, that a diaza-18-crown-6 is equivalent to 20 OE units in the usual type of nonionic (12). Okahara s group evaluated the effective HLB based on the cloud point, phenol index and phase-inversion-temperature in emulsion of oil/water system and they concluded that 18-crown-6 and monoaza-18-crown-6 rings with dodecyl group are approximately equivalent to 4.0 and 4.5 units, respectively, of OE chains with the same alkyl chain (17). 

It should be noted that phase inversion prediction models focus on only a single composition, whereas in reality, co-continuous structures are observed over a composition range. Considering the definition of co-cmitinuous structure and equations based on the percolation theory, a model was proposed to correlate a continuity index (/) with the volume fraction at onset of co-continuity (0,- ) (see Table 7.3) (Lyngaae-Jorgensen et al. 1999). Numerical simulation predicted cr to be about 0.2 for classical percolation in three-dimensional systems (Dietrich and Airmon 1994 Potschke and Paul 2003). 

Fig. 5. Composition range of co-continuous structure. Full line continuity index of phase 2, broken line continuity index of phase 1. Ocri, 2, vn a o are voliune fractions of phase 1 or 2 at which partial or full co-continuity of the related phase start, opi designate phase inversion composition. Reproduced with permission from Reference 69.

The selection of different surfactants in the preparation of EWs emulsion is still made on an empirical basis. This is discussed in detail in Chapter 6, and only a summary is given here. One of the earliest semi-empirical scales for selecting an appropriate surfactant or blend of surfactants was proposed by Griffin [49, 50] and is usually referred to as the hydrophilic-lipophilic balance or HLB number. Another closely related concept, introduced by Shinoda and co-workers [51-53, 58], is the phase inversion temperature (PIT) volume. Both the HLB and PIT concepts are fairly empirical and one should be careful in applying them in emulsifier selection. A more quantitative index that has received little attention is that of the cohesive energy ratio (CER) concept introduced by Beerbower and Hill [54] (see Chapter 6). The HLB system that is commonly used in selecting surfactants in agrochemical emulsions is described briefly below. 

The refractive index of the cured ERL-4221-HHPA system is 1.5070, which is significantly different from the refractive index of CTBN (1.5142). This difference can possibly account for the considerable haze of the systems containing the low concentration (10 to 70 phr) of rubber. As the concentration of CTBN is increased, instead of two distinctly separated phases, two continuous phases are formed, along with an inversion of the phases plus considerable intermixing of the rubber and epoxy components, the differences in the refractive indices are gradually diminished. More specifically, the refractive index of the ERL-4221-HHPA modified with 100 parts CTBN is 1.5110 which is obviously between those of the two pure phases. 

In the systems (I) and (III) 2-simplex consists of a sole cell, all the trajectories inside which approach SP corresponding to homopolymer Ms where rs < 1. The systems (I) and (III) topologically are equivalent, since they differ from each other only by the inversion of the monomer indexes therefore their phase portraits are of the same type, too. In the systems (II) and (IV) the azeotropic point separates the simplex into the two cells. However, the system (IV), in which both parameters r, and r2 exceed unity practically is non-realizable [20-24]. That is why the stable binary azeotropes are excluded from the consideration, and the dynamics of the copolymerization of two monomers is exhaustively characterized by only two types (I) and (II) of phase portraits. 

Although many (perhaps most) applications do not require the existence of a complete band gap, significant efforts to develop such structures have been undertaken. For a given symmetry, the characteristics of an induced band gap depend upon the refractive index contrast and filling factor of the two phases (e.g., silica spheres and air interstices). Inverse opals are negative replicates of the sterically packed structures that have been described above. In this case, one generally has... 

Moreover, the isolation of self-assembled LiNbOj powders using this route has added credibility to the methodology they were otherwise prepared by templating colloidal crystals of polyelectrolyte-coated spheres. The interest in LiNb03 inverse opals stems from the fact that they have a constant refractive index, but a spatially periodic second-order nonlinear susceptibility. Such nonlinear periodic structures allow for efficient qnasi-phase-matched second-order harmonic generation, which conld find applications where simultaneous conversion of multiple wavelengths is reqnired. Thns, in this chapter we will focus our... 

Figure 20. (a) Orientational correlation time t in the logarithmic scale as function of the inverse of the scaled temperature, with the scaling being done by the isotropic to nematic transition temperature with Ti-N. For the insets, the horizontal and the vertical axis labels read the same as that of the main frame and are thus omitted for clarity. Along each isochor, the solid line is the Arrhenius fit to the subset of the high-temperature data and the dotted line corresponds to the fit to the data near the isotropic-nematic phase boundary with the VFT form, (b) Fragility index m as a function of density for different aspect ratios of model calamitic systems. The systems considered are GB(3, 5, 2, 1), GB(3.4, 5, 2, 1), and GB(3.8, 5, 2, 1). In each case, N = 500. (Reproduced from Ref. 136.)... 

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