Emulsions lipophilic component

Crystallization from the emulsified state may lead to different nucleation processes than observed for the same fat in bulk liquid form. It has been suggested that nucleation often occurs at the interface of the droplet where surface-active agents are located. The general similarity of the lipophilic components of surfactants oriented at the surface may provide some ordering and structure for the lipid molecules within the droplet and enhance nucleation, as found for example by Kaneko et al. (40) for a hydrocarbon emulsion. Walstra (11) also suggests that formation of compound crystals from emulsions of natural fats may be different than the same fat crystallized from bulk liquid. The initial polymorph formed may also be different, with more stable polymorphs more likely to form in the emulsion (38). 

The lipophilic component should be an amphiphile that promotes the formation of w/o emulsions and is capable of complex-ing with the hydrophilic surfactant at the o/w interface. Its concentration should be at least sufficient to form a close-packed... 

For a seborrheic skin hydrophilic bases have to be chosen hydrophilic gels, emulsions or creams. Especially for acne treatment bases without or with only a small percentage of lipophilic components are indicated. 

The optimum stability of the emulsion is relatively insensitive to changes in the HLB or the PIT of the emulsifier, but instability is very sensitive to the PIT of the system. It is essential, therefore, to measure the PIT of the emulsion as a whole (with all other ingredients). At a given HLB, the stability of the emulsions against coalescence increases markedly as the molar mass of both the hydrophilic and lipophilic components increases. 

When an 0/W emulsion is prepared using a nonlonlc surfactant of the ethoxylate type and is heated, then at a critical temperature (the PIT), the emulsion inverts to a W/0 emulsion. At the PIT the hydrophilic and lipophilic components of the surfactant are exactly balanced and the PIT is sometimes referred to as the HLB temperature. At the PIT the droplet size reaches a minimum emd the interfacial tension also reaches a minimum. However, the small droplets are unstable and they coalesce very rapidly. 

This should be a surface-active agent which by itself promotes oil-in-water emulsions and is capable of complexing with the lipophilic component at the oil-water interface. 

Its concentration should at least be sufficient to form a close-packed mixed monolayer with the lipophilic component. To promote semi-solid emulsions it should be in excess of its critical micelle concentration in the aqueous phase. 

McClements, D. J. (2010). Emulsion-design to improve the delivery of functional lipophilic components. Annual Review of Food Science and Technology, 1, 241-269. 

Microemulsions can be obtained in different ways. For ethoxylated nonionic emulsifiers the temperature is the decisive parameter therefore, the micro-emulsion phase is stable only in a certain limited temperature range. If other specific types of surfactants are used, e.g., alkyl polyglycosides, the temperature dependence is less pronoimced or even negligible. In this case, the formation of microemulsions is enabled by adjusting a specific mixing ratio of different emulsifiers, i.e., balancing the hydrophilic to lipophilic components in the surfactant system. 

Water Water is the primary raw material in pharmaceutical formulations. It is the most used vehicle since it is the major component of the human body. For many products, it is the main component, and, even in those containing non-water-soluble substances, water must be present. Depending on the product and the form of administration, lipophilic drugs are prepared as water-oil emulsions. 

At low temperature, nonionic surfactants are water-soluble but at high temperatures the surfactant s solubility in water is extremely small. At some intermediate temperature, the hydrophile—lipophile balance (HLB) temperature (24) or the phase inversion temperature (PIT) (22), a third isotropic liquid phase (25), appears between the oil and the water (Fig. 11). The emulsification is done at this temperature and the emulsifier is selected in the following manner. Equal amounts of the oil and the aqueous phases with all the components of the formulation pre-added are mixed with 4% of the emulsifiers to be tested in a series of samples. For the case of an o/w emulsion, the samples are left thermostated at 55°C to separate. The emulsifiers giving separation into three layers are then used for emulsification in order to find which one gives the most stable emulsion. 

Recovery of lipophilic compounds binding to components of the dialysis equipment, could be increased by including albumin or a lipid emulsion to the dialysate (Cameheim). 

During sulfite pulping the fatty acid esters are saponified to an extent determined by the conditions. Some of the resin components can also become sulfonated, resulting in increased hydrophilicity and better solubility. However, the partial removal of resin that always occurs during sulfite cooking and subsequent mechanical treatment is mainly associated with the formation of finely dispersed resin particles in stable emulsions. The dissolved lignosulfonic acids act as detergents with respect to the lipophilic resin components. 

Emulsifying properties. One of the major functions of commercial lecithins is to emulsify fats. In an oihwater system, the phosphohpid components concentrate at the oUrwater interface. The polar, hydrophilic parts of the molecules are directed toward the aqueous phase, and the nonpolar, hydrophobic (or lipophilic) parts are directed toward the oil phase. The concentration of phospholipids at the oihwater interface lowers the surface tension and makes it possible for emulsions to form. Once the emulsion is formed, the phosphohpid molecules at the surface of the oil or water droplets act as barriers that prevent the droplets from coalescing, thus stabilizing the emulsion (159). 

---