Surfactants system surfactant molecular volume

Table I shows various surface and microscopic properties such as surface tension, surface viscosity, foaminess (i.e. foam volume generated in a given time) and bubble size in foams of the surfactant solutions as a function of chain length compatibility. The results indicate that a minimum in surface tension, a maximum in surface viscosity, a maximum in foaminess and a minimum in bubble size were observed when both the components of the mixed surfactant system have the same chain length. These results clearly show that the molecular packing at air-water interface influences surface properties of the surfactant solutions, which can influence microscopic characteristics of foams. The effect of chain length compatibility on microscopic and surface properties of surfactant solutions can be explained as reported in the previous section.

Here Pn is the fraction of surfactant molecules surfactant/(surfactant + water)) that are incorporated into micelles of aggregation number N. The volume fraction of aggregates of size N is thus proportional to Pn/N. For simplicity we consider the case where the molecular volumes of the surfactant and the solvent are equal, so that Pn which is the fraction of surfactant molecules in the system, can also be written as... 

The quantity of a substance that can be solubilized in surfactant micelles will depend on many factors, some of which have already been discussed. From the standpoint of the additive itself, such factors as molecular size and shape, polarity, branching, and the electronegativity of constituent atoms have all been found to be of some significance, depending on the exact system. One extensively explored factor relating the chemical structure of the additive to its solubilization is the relationship between the molar volume of the additive and the maximum amount of material that can be incorporated in a given surfactant solution. In general, one finds an inverse relationship between the molecular volume of the additive and the amount of material solubilized. 

Interfacial area is thus inversely proportional to the radii of the dispersed objects. Since interfacial tension 7 is a factor limiting dispersion, the interfacial energy is increased correspondingly. The idea then is to introduce a surfactant system that will considerably lower 7, and if possible cancel it altogether. We have already seen that 7 depends on the area occupied by each molecule (cf. Fig. 4.7). Consequently, there is a simple geometrical relation between the dispersed volume 4> per unit volume of solution, the droplet radius i , the required number Ug of surfactant molecules (of molecular area ao) per unit volume and the number of droplets no ... 

The salinity at which the middle phase microemulsion contains equal volumes of oil and brine is defined as the optimal salinity. The oil recovery is found to be maximum at or near the optimal salinity (8,10). At optimal salinity, the phase separation time or coalescence time of emulsions and the apparent viscosity of these emulsions in porous media are found to be minimum (11,12). Therefore, it appears that upon increasing the salinity, the surfactant migrates from the lower phase to middle phase to upper phase in an oil/brine/surfactant/alcohol system. The -> m u transition can be achieved by also changing any of the following variables Temperature, Alcohol Chain Length, Oil/Brine Ratio, Surfactant Solution/Oil Ratio, Surfactant Concentration and Molecular Weight of Surfactant. The present paper summarizes our extensive studies on the low and high surfactant concentration systems and related phenomena necessary to achieve ultralow interfacial tension in oil/brine/surfactant/alcohol systems. 

To model the polymer-surfactant system, we consider a mixture of polymers and low-molecular weight surfactant molecules in a solvent. Each polymer is assumed to carry the number / (> 2) of associative groups of the volume ro along its chain, which is composed of r/ statistical units. Each surfactant molecule is modeled as a molecule of a volume r carrying a single hydrophobe connected to the hydrophilic head (see Figure 10.1) [1]. 

As we have seen in the previous section, there are several factors that determine the bulk phase of a surfactant system. One of these is the overall shape of the molecule (e.g., head group area, tail volume, and tail length). The geometric effects that overall molecular shape can have on phase behavior are summarized neatly in a quantity known as the packing parameter. This quantity can be used to predict the likely phase of a particular surfactant system. 

One of the most attractive roles of liquid liquid interfaces that we found in solvent extraction kinetics of metal ions is a catalytic effect. Shaking or stirring of the solvent extraction system generates a wide interfacial area or a large specific interfacial area defined as the interfacial area divided by a bulk phase volume. Metal extractants have a molecular structure which has both hydrophilic and hydrophobic groups. Therefore, they have a property of interfacial adsorptivity much like surfactant molecules. Adsorption of extractant at the liquid liquid interface can dramatically facilitate the interfacial com-plexation which has been exploited from our research. 

The most widely studied deformable systems are emulsions. These can come in many forms, with oil in water (O/W) and water in oil (W/O) the most commonly encountered. However, there are multiple emulsions where oil or water droplets become trapped inside another drop such that they are W/O/W or O/W/O. Silicone oils can become incompatible at certain molecular weights and with different chemical substitutions and this can lead to oil in oil emulsions O/O. At high concentrations, typical of some pharmaceutical creams, cosmetics and foodstuffs the droplets are in contact and deform. Volume fractions in excess of 0.90 can be achieved. The drops are separated by thin surfactant films. Selfbodied systems are multicomponent systems in which the dispersion is a mixture of droplets and precipitated organic species such as a long chain alcohol. The solids can form part of the stabilising layer - these are called Pickering emulsions. 

The chiral ligand was in all cases (2S,4S)-N-tert-butoxycarbonyl-4-diphenylphos-phino-2-diphenylphosphinomethylpyrrolidine (BPPM) and the catalyst was formed in an in situ system of [Rh(COD)2] BFT The asymmetric hydrogenation is well investigated in organic solvents like methanol, but the presence of water usually causes loss of activity and enantioselectivity because of the low solubility of both the catalyst and the substrate in water [27, 29]. The addition of low-molecular surfactants or commercially available polymeric amphiphiles increases the activity (here given as time of consumption of half the stoichiometric volume of hydrogen, t/2) as well as the enantioselectivity [4]. Tab. 6.1 summarizes selected experiments with different polymeric amphiphiles. 

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