Basics on emulsification technologies including the preparation method, selection of emulsifiers, analysis of emulsification process and the formation of fine droplets with molecular assemblies were reviewed. The states of emulsions are greatly affected by the process because of their thermodynamic instability. The optimum emulsification process can be analyzed with three-component phase diagrams composed of oil, water and surfactant. The emulsification which passes through the region of infinite association of surfactants like liquid crystal or surfactant phase, D-phase, during the emulsification, produces fine emulsion due to the remarkable decrease in interfacial tension. Therefore emulsification methods using liquid crystals and D-phase as the media of continuous phase at the initial stage of the emulsification are developed and applied for the practical systems. Based on the current situation, the future trend of emulsification is predicted.

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When surfactants are adsorbed at interfaces (e.g., gas/liquid, liquid/liquid, or solid/liquid interfaces), a remarkable change in their interfacial properties occurs. In general, however, surfactants are distributed to the interface layer as a surface excess toward bulk concentration, and hence, the effective amount of surfactants to stabilize the interface is significantly decreased from an added amount in the system. In order to control interfacial properties more effectively, surfactants are required to be only present between two phases. From this point of view, we propose a new category of amphiphilic materials to be called “Active Interfacial Modifier (AIM)”. AIM is intrinsically molecularly soluble neither in water nor in organic solvents, but has attractive moieties to each immiscible liquid phase. Hence, AIM practically stays just at the interface to make emulsion stable. In this review, we present physicochemical properties of an emulsion system stabilized by a silicone-type amphiphilic polymer material and future directions of our AIM studies.

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Transdermal drug delivery systems attract much attention due to several unique advantages over other administration routes. The transdermal delivery, however, has been known to be limited to the delivery of low molecular weight drugs. Delivery of hydrophilic drugs through the skin is generally difficult due to the hydrophobic property of the skin surface. Based on the Solid-in-Oil (S/O) technique, hydrophilic drugs including proteins were coated with hydrophobic surfactant molecules to form surfactant-protein complexes. These complexes could be easily dispersed in an oil-base solution which has a permeation-enhancing effect. The main function of the new system is to promote hydrophilic drug penetration through the hydrophobic skin barrier, mainly due to stratum corneum. This approach is unique in that it is based on a non-aqueous vehicle for transdermal hydrophilic drug delivery.

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Recently, amphiphilic polymers have come to actual use as an emulsifying agent in oil industries. They can provide stability and reduce an amount of low-molecular-weight surfactants. They stabilize emulsions by “adsorption at an oil and water interface” and/or “associating thickening”. This overview summarizes several types of polymeric emulsifier and emulsification mechanism mainly in cosmetic field and describes recent studies of a new water-soluble amphiphilic polysaccharide HHM-HEC. HHM-HEC formed a gel through aggregation of hydrophobic moieties in water and stabilized O/W emulsions by the associative thickening mechanism.

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Drug-loaded PLGA (poly lactic-co-glycolic acid)-nanoparticles prepared using the emulsion solvent diffusion (ESD) method applying the “Marangoni Phenomenon” developed by Kawashima’s group. This technology could be applied further to not only pharmaceutical have the function of DDS (drug-delivery-system) but also medical devices and cosmetics. In this paper, we would like to introduce a part of our research and development results.

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