Additives, phase behaviour

The results obtained from the characterisation of the phase behaviour and in the beam house imply that Eusapon OD is a suitable alternative allowing for an eco-friendly degreasing of animal skins. However, the understanding of the so far unidentified degreasing mechanism is the key goal for a continuous development of the degreasing process itself. In order to clarify the role of microemulsions in degreasing additional phase behaviour and interfacial tension measurements were conducted. 

As shown in section C2.6.6.2, hard-sphere suspensions already show a rich phase behaviour. This is even more the case when binary mixtures of hard spheres are considered. First, we will mention tire case of moderate size ratios, around 0.6. At low concentrations tliese fonn a mixed fluid phase. On increasing tire overall concentration of mixtures, however, binary crystals of type AB2 and AB were observed (where A represents tire larger spheres), in addition to pure A or B crystals [105, 106]. An example of an AB2 stmcture is shown in figure C2.6.11. Computer simulations confinned tire tliennodynamic stability of tire stmctures tliat were observed [107, 1081. 

It is clear that systems of hard ellipsoids exhibit an intriguingly simple phase behaviour with some resemblance to that of real nematogens. However, such systems cannot form smectic or columnar phases and in addition the phase transitions are not thermally driven as they are for real mesogens. As we shall see in the following sections the Gay-Berne potential with its anisotropic repulsive and attractive forces is able to overcome both of these limitations. 

In addition to Rh-catalysed hydroformylation, this special phase behaviour has been successfully applied to other continuous catalytic reactions - such as Ni-catalysed, enantioselective hydrovinylation [66] and the lipase-catalysed kinetic resolution and enantiomer separation of chiral alcohols [67]. 

The application of thermomorphic solvent systems as a new recycUng concept was investigated in various C - C bond-forming reactions. Therefore methods for a systematic choice of solvent combinations were developed. In addition to common organic solvents more unusual solvents Hke cycHc carbonates, pyrroUdones, polyethylene glycols and lactones were used in the investigations. The phase behaviour of the new solvent systems was determined by cloud titrations. From these experiments information about the temperature dependency and an appropriate composition for the reactions could be obtained. The results were used in the development of an expert system for the solvent selection. 

In comparison with System A, we thus find that different surfactants would give divergent phase behaviour, due to the dependence of Yow surfactant characteristics. Further, the addition of n-butanol gives rise to a lowering of yow by about 2 mN/m (Fi-... 

Older compilations about the state of the art can be found in several review articles [41 -47]. It is surprising that most work is carried out with the surfactant bis-ethylhexyl-sulfosuccinate (tradename AOT or Aerosol OT). The reasons seem to be the variability of the obtained reverse micelles (from very low up to high water concentrations) and the well-known phase behaviour of AOT with water and several oils [48,49]. AOT is approved for medical application, e.g. as an additive in suppositories, but not for food engineering. 

In order to obtain a thermodynamically stable micro emulsion, the analysis of the phase behaviour is indispensable. With bovine serum albumin instead of an enzyme (because of the cost of the bio-catalyst) phase behaviour studies are shown in Fig. 2. A strong shift of the phase boundary is observed, yielding a system that solubilises much less water in the presence of the protein. In case of hydrophobic enzymes, the addition of dry lyophilised protein to an already prepared reverse micellar solution can also work well [53]. 

The majority of the published investigations are concentrated onto the reaction conditions of enzymes in reverse micelles at low substrate concentrations, because high substrate concentrations in microemulsions influence their phase behaviour. Additionally, high substrate and enzyme concentrations often lower the enzyme stability to uneconomical values. At high enzyme concentrations the activity can be lowered due to the formation of protein aggregates. 

Equilibrium Phase Behaviour. Phase studies were performed using approximately 10 g samples of oil-surfactant mixture diluted sequentially by the weighed addition of water. The initial binary mixture contained 5-70 w/w surfactant at 5 intervals. Phase boundaries were determined to + 0.5 water. The ternary mixtures in Pyrex glass tubes fitted with PTFE lined caps were equilibrated to the required temperature (20-65 0.1°C) for 2 hours and then thoroughly mixed for 5 minutes using a Fisons orbitsil whirlimixer. The tubes were then returned to the waterbath and left undisturbed for 48 hours before identification of the phase type using a crossed polarised viewer and an optical microscope. 

EOS models were derived for polymer blends that gave the first evidence of the severe pressure - dependence of the phase behaviour of such blends [41,42], First, experimental data under pressure were presented for the mixture of poly(ethyl acetate) and polyfvinylidene fluoride) [9], and later for in several other systems [27,43,44,45], However, the direction of the shift in cloud-point temperature with pressure proved to be system-dependent. In addition, the phase behaviour of mixtures containing random copolymers strongly depends on the exact chemical composition of both copolymers. In the production of reactor blends or copolymers a small variation of the reactor feed or process variables, such as temperature and pressure, may lead to demixing of the copolymer solution (or the blend) in the reactor. Fig. 9.7-1 shows some data collected in a laser-light-scattering autoclave on the blend PMMA/SAN [46],... 

Given the morphological complexity of AB diblock and ABA triblock copolymers, it might be expected that the phase behaviour of ABC triblocks would be even more rich, and indeed this has been confirmed by recent experiments from a number of groups. From a practical viewpoint, ABC triblocks can also act as compatibilizers in blends of A and C homopolymers (Auschra and Stadler 1993). In addition to the composition of the copolymer, an important driving force for structure formation in these polymers is the relative strength of incompatibilities between the components, and this has been explored by synthesis of chemically distinct materials. 

The phase behaviour of PEO PBO has recently been determined in detail, including the effect of addition of the salt K2S04 (Deng et al. 1995). Increasing the concentration of aqueous K2S04 reduces the upper sol-gel transition as shown in Fig. 4.15 however, it has a much weaker effect on the lower gel boundary. This is because the effect of salt in reducing the micellar expansion factor (<5t) is compensated at the lower boundary by more favourable conditions for formation of micelles in the poorer solvent (i.e, a lower cmc) whereas no such compensation is possible at the upper boundary. Regions of clear and cloudy,... 

Figure 3.22 (right) represents the three-phase temperature intervals for Q2E4 and Q2E5 vs the number n of carbon atoms of n-alkanes (for the phase behaviour of ternary systems see Section 3.4.2, Figure 3.26). The left part of Figure 3.22 shows the detergency of these surfactants for hexadecane. Both parts of Figure 3.22 indicate that the maximum oil removal is in the three-phase interval of the oil used (n-hexadecane) [22]. This means that not only the solubilisation capacity of the concentrated surfactant phase, but probably also the minimum interfacial tension existing in the range of the three-phase body is responsible for the maximum oil removal. Further details about the influence of the polarity of the oil, the type of surfactant and the addition of salt are summarised in the review of Miller and Raney [23].

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