Surfactants are widely used in numerous applications, including detergents, emulsification, flotation, foaming control, surface-wetting modification and surfactant-based separation processes. The fields of surfactant chemistry and application are now so vast, there have been so many interesting recent development in its. Chemically, surfactant molecules usually are classified according to the nature of the hyrophilic group, in anionic, cationic, amphoteric and nonionic type. While, the nature of the hyrophobic groups are usually less pronounced than in the nature of the hydrophilic group. Generally, they are long-chain hydrocarbon residues. Polysiloxane and perfluoroalkyl group have also been used as the hydrophobic group in the surfactant. Recently, hybrid type surfactants having both hydrocarbon and fluorocarbon group were developed. Furthermore, many other functional surfactants have been newly developed by sophisticated organic synthesis and enzymatic reactions. Here, we report the overview of surfactants, especially recent research and development of novel surfactants.

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A variety of double-chain or triple-chain surfactants with two or three ionic head groups such as sulfonate, sulfate, carboxylate, phosphate, ammonium, and taurine were prepared according to conventional synthetic procedures and their surface properties were compared with those of the corresponding single-chain surfactant with one ionic group. The former showed much better micelle forming ability, ability to lower surface tension and solubility in water than the latter. These findings are reasonably explained by considering the change in the intra- and intermolecular interactions. This method, which simply combines two or three single-chain surfactants using an appropriate skeletal structure, should be useful for the molecular design of surfactants.

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Synthesis and properties of a series of fluoroalkylated oligomers by using fluoroalkanoyl peroxides have been reviewed. The synthetic methods of fluoroalkylated acrylic acid, nonionic, and cationic oligomers were illustrated. These fluoroalkylated oligomers, in particular, fluoroalkylated acrylic acid, nonionic, and cationic oligomers were in general shown to become soluble not only in water but also in common organic solvents such as methanol, ethanol, dimethyl sulfoxide, benzene and toluene. These fluoroalkylated oligomers have quite unique structure that fluoroalkyl groups are substituted only on the both terminals of oligomer chain, and can be regarded as double-chain type surfactant. They exhibit excellent surface active properties attributable to fluoroalkyl groups, such as quite low surface and interfacial tension, and anti-foaming property, and so on.
Fluoroalkylated acrylic acid homo-and co-oligomers were demonstrated to exhibit a potent anti-HIV-1 activity in vitro. Furthermore, fluoroalkylated cationic oligomers were found to have an antibacterial activity. Therefore, these fluoroalkylated acrylic acid and cationic oligomers have been widely applicable to various fields as the novel functional materials which possess both a unique property imparted by fluorine and an anti-HIV-1 or antibacterial activity.

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This review focuses on the self-organization of novel amphiphilic polymers prepared by relatively simple synthetic techniques including free-radically initiated random copolymerization of hydrophilic and hydrophobic monomers and chemical modification of water-soluble polymers with functional hydrophobic molecules. These polymers exhibit various types of self-organization in aqueous solution due to intra- and/or interpolymer hydrophobic associations depending on the chemical structure of the polymers. Structural factors that affect the self-organization behavior include the type and content of hydrophobes contained in the polymers, distribution of the hydrophobic and hydrophilic units within a polymer chain, and spacer bond between the hydrophobe and the polymer chain. Various types of micelles are formed as a result of various modes of the self-organization. The relationship between the polymer structure and the micellar structure is discussed.

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Bile Salts as a biosurfactant have been frequently developed as solubilizers, emulsifiers and dispersion agents for water-insoluble substances in many fields of cosmetics, medical and chemical industries, and then many chemical papers and their reviews concerning the colloidal and interfacial properties of aqueous solutions of bile salts have so far been reported. As these bile salts have bulky and hydrophobic steroidal rings and one carboxyl group at the end of alkyl chain on a position of 17 carbon atom of the rings in a molecule, their colloidal and interfacial properties are different from those of ordinary surfactants with a linear hydrocarbon chain. Furthermore, their properties depend remarkably on the numbers and configuration of hydroxyl groups bound to the rings. In this report, the unique structures of bile salts will be discussed about how to reflect fundamental colloidal and interfacial properties on the basis of the results from various interfacial measurements and applications of bile salts.

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Recent studies of the synthesis and properties of chemically cleavable surfactants are reviewed. Surfactants bearing acetal-linkage are easily hydrolyzed in acidic aqueous solution. These surfactants lose the surface active properties by addition of acid after expected usage such as emulsification, dispersion and cleaning. The treatment of inactivation of surfactants gives the improvement of the yield and purity of product after organic synthesis and polymeriztion in emulsion system. Moreover, most of organic materials can be easily removed from waste water containing these surfactants by oil-water separation technique after expected usages. These surfactants are synthesized by the reaction of carbonyl compounds with polyols or epoxides, followed by saponification, sulfation, sulfonation, ethoxylation and quaternization. Generally, anionic surfactants are hydrolyzed most easily. Other chemically cleavable surfactants are also described.

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Syntheses and solution properties of novel fluorinated surfactants with branched tail, especially on anionic surfactants having two polyfluoroalkyl chains and on anionic surfactants having different hydrophobic chains (hybrid surfactants), are reviewed.
For example, when the fluorocarbon chain length in the surfactants possessing two polyfluoroalkyl chains increased, the Krafft points and the area of surfactant molecule at the air-water interface increased, the critical micelle concentration decreased, but the degrees of ionic dissociation of micelle were almost the same. Moreover, the flocculation and redispersion abilities of these surfactants for dispersed magnetic particles in water were enhanced by an increase in the chain length.
The hybrid surfactants were found to have the ability to considerably lower surface tension, and they can emulsify a ternary-component system of hydrocarbon/water/perfluoropolyether oil. Furthermore, some of the hybrid surfactants shows anomalous solution properties and viscoelasticity due to the micellar structure changes with increasing its concentration.

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Effects of the stereochemistry of oligosaccharide headgroups on the physical properties of aqueous synthetic glycolipid, 1, 3-di-O-dodecyl-2-O-(β-glycosyl) glycerols bearing cellooligosaccharides (β-1, 4-O-glycosidic bonds) and maltooligosaccharides (α-1, 4-O-glycosidic bonds) as hydrophilic groups have been studied. The increase in the number of glucose residues, N, in the two different headgoups exhibited opposite effects on the physical properties of the aqueous glycolipids. For the maltooligosaccharide-containing lipids, Mal_N(C₁₂)₂, increasing N in the headgroups decreases the hydrated-solid/liquid-crystalline phase trasition temperature T_m, and increases the “hydrophilicity” of the lipids. However, the T_m of the cellooligosaccharide-containing lipids Cel_N(C₁₂)₂ increases with increasing N of the cellooligosaccharide headgroups. It is noteworthy that T_m jumps from 59°C (for N=4) to above 160°C (for N=5), so that the Cel₅(C₁₂)₂ cannot form a liquid crystalline phase, and is totally insoluble in water. The results can be explained in terms of different conformations of the headgroups, i.e., a “helical” conformation of the maltooligosaccharides and an “extended” conformation of the cellooligosaccharides.

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The microbial biosurfactants produced by microorganisms have been attracting the interest as the new functional and ecological material since they have the special properties such as a wide variety of possible structures, highly biodegradable, low toxicity and biological activity. Microbial bissurfactants surveyed here and the properties of polycarboxylic biosurfactant as detergent such as surface activity, calcium binding capacity, and detergency is summarized in comparison with those of commercially available synthetic detergents and soaps.

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The thermodynamic equations were summarized for the adsorption of surfactants and surfactant mixtures from monomeric and micellar solution to the air/water and oil/water interfaces. The phase diagrams of adsorption and micelle formation were introduced and discussed for some examples such as ideal mixing, and nonideal mixing showing negative azeotrope and heteroazeotrope. Also the thermodynamic quantity changes associated with adsorption were shown and the effect of a coexistent oil phase was examined briefly. Furthermore the results of the adsorption of oil-soluble substances from an oil phase and the finding of the phase transition of adsorbed films were introduced.

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Recent studies on self-assemblies in solutions are reviewed. Especially, formation mechanism of an L₃ phase, phase transition between different liquid crystal phases, and results of computer simulation of micelles are described.

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This paper was roughly reviewed for the topically interesting adsorption phenomena of surfactants at various liquid interfaces. The interfacial phenomena were of adsorption at the interfaces of air water, monolayer-water (penetration), oil water, air with monolayer-oil-water. Complicated interfacial phenomena caused with mixed surfactants have been introduced to be capable of being analyzed by the combination of adsorption theory with the experimental data; i.e., negative adsorption of co-ions at the charged adsorbed surface, adsorption of complex ions present in mixed surfactants, penetrated adsorption into the insoluble monolayers. It was also emphasized that the synergetic phenomena taken place in mixed surfactant solution could be analyzed quantitatively in terms of the surface compositions determined as a function of bulk compositions.

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Phase behavior of polyoxyethylene-Type nonionic surfactant is highly influenced by temperature. At the particular temperature called HLB temperature, nonionic surfactant forms a three-phase region containing middle-phase microemulsion or surfactant phase. Maximum solubilization, ultralow interfacial tension, and phase inversion in emulsions take place at the HLB temperature. The HLB temperature in a multi-surfactant system is explained by analyzing the three-phase behavior. HLB number of commercial surfactant can be calculated from the HLB temperature. The effect of mixing nonionic surfactant on the maximum solubilization power is discussed. Finally, the unique phase behavior of biocompatible sucrose alkanoate is also described.

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Aggregation structures of bilayer assemblies formed from single-chain azobenzene amphiphiles are discussed on the bases of “two-dimensional crystal engineering”. Besides the hydrophobic effect, many weak interactions (electrostatic interaction, π-π stacking, cation-π electron interaction, etc.) are shown to be structural factors of bilayer formation. Based on the “two-dimensional crystal engineering”, molecular design of some functional bilayer assemblies are described. Recent investigations on the molecular-recognition directed assembling of hydrogen bonding amphiphiles are summarized briefly, too.

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Prior to fabrication of functional molecular organized thin film, control of molecular orientation and packing as well as domain structures and sizes in monolayers were studied in situ. Molecular recognition, inclusion and adsorption of functional molecules by lipid or CDs monolayers at the air/water interface have been also valid to control the molecular arrangements. The monolayer assemblies were constructed by the Langmuir-Blodgett method and the horizontal lifting technique to give a well-defined organization of amphiphilic functionalized molecules in layered structures. Some characteristics of optical properties and electrical behaviours for these monolayer assemblies have been discussed.

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The principle of small-angle neutron scattering (SANS) technique and its applications to surfactant systems were reviewed. SANS is a very powerful tool to study the structure of the order of about 30 to 300Å. By SANS, many information about micellar systems such as size and shape of the micelle particle, solution structure, intermicellar interaction, phase behavior, etc. can be obtained depending on the measuring condition. The contrast variation method using isotopes, which is a characteristic of SANS, gives us a detailed information of inner and partial structures of scattering particles which SAXS can not give. Recent applications of SANS to various surfactant micelles and polymer micelles were briefly reviewed.

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This review describes recent developments in the characterization of the adsorbed layer and the adsorption feature of ionic surfactant molecules on solid surfaces. Attention was especially paid to the nano-scale and in situ measurements. The ionic surfactants adsorbed on polar solid surfaces, e.g., silica and mica, interact with both the solid surface and adsorbed molecules each other. Therefore, various structures of aggregate form on the solid surface based on the contribution of these interactions. The information about the structure and the feature of the aggregated ionic surfactants on the solid surface is reviewed together with the newly developing experimental techniques, especially focused on scanning force microscope.

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This review illustrates applications of the surface forces measurement for characterizing interactions of surfactant assemblies. The measurement provided new insights into dispersion properties of surfactants at the molecular level. Phenomena discussed include: (1) spontaneous vesicle formation upon changing counterions of an ammonium surfactant from bromide to acetate; (2) the cloud point of nonionic (polyoxyethylene) surfactant micelles; (3) salt (NaCl) induced fusion and aggregation of vesicles containing the ammonium or the phosphate group as a hydrophilic part; (4) an unusually long-range attraction (>200 nm) between hydrophobic surfaces. The forces measurement was employed also to study the adsorption of polyions. The obtained force profiles revealed that polystyrene sulfonate adsorbed onto the ammonium monolayers at 1:1 stoichiometry in a flat configuration. Another new study used polyelectrolyte-functionalized surfactants to prepare brush layers of polyelectrolytes. The brush layer structures of polyelectrolytes such as poly (glutamic acid) were inferred from the analysis of the steric components of the force profiles. The analysis permitted the determination of the elastic compressibility modulus of an oriented, single polymer brush layer in a solvent.

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The characterization of supramolecular assemblies is carried out on the thermotropic, hydrodynamic, spectroscopic, electromagnetic, scattering, and microscopic methods. Among them, the microscopic observation informs directly the size and shape of assemblies, different from other methods. In this article, the techniques of the optical, electron, scanning probe microscopes are briefly explained, and the researchs of surfactant assemblies by the microscope are reported. The formation of micelles and reverse micelles were verified by the electron microscope (TEM). Liquid crystals displayed the characteristic polarized optical microscopic textures and TEM images. The existence of bilayers in vesicles and reverse vesicles were confirmed by the freeze-fracture TEM observation. The flocculation, fusion, and destroy of vesicles and emulsions were chased by the differential interference contrast microscope. The structures of molecular assemblies in the multicomponent systems of surfactant/water/oil (organic solvent) were determined. The various types of supramolecular fibers were observed by the cryo TEM. Dimentional ordered structures such as Langmuir-Blodgett films were compared between the homogeneous and heterogeneous systems by the atomic force microscope.

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Liposomes are recognized as the most potential drug carrier to a specific cell or tissue.
One of the major problems still remaining unsolved is the question, “is it possible to accumulate liposomes to some target in the body avoiding reticuloendothelial system (RES)?”. Intentional surface chemical approaches were required for solving this problem. Fixed aqueous layers outside the surface of liposomes were formed by, e.g., incorporating polyethyleneglycol (PEG)-lipid into the liposomal membrane. The fixed aqueous layer thickness (FALT) was determined. FALT increased by PEG-modification and RES avoiding was dependent on FALT.
In this review, some recent papers on sterically stabilized liposomes, their FALT determination, their biodistributions, their pharmacological effects and their safety will be presented.

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The use of surfactants in personal care products falls into two categories: hair care (cleansing) and skincare. In hair-care, two different developments are apparent: the search for mild surfactants and for conditioning agents. Also, the combination of surfactants with other ingredients can result in special characteristics of shampoos. Since the development of rinses, which employ cationic surfactants that adhere to hair, researchers try to improve the surface treatment of hair.
In skincare, highly functional ingredients require new surfactants. In addition, surfactants that allow the formation of highly structured complexes such as liposomes or liquid crystals, which resemble natural structures, are being developed.

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Detergency is accomplished by a combination of effects involving several interfacial properties and a number of different mechanisms are involved in the process. Restricting attention to oily soils, three basic mechanisms have generally been accepted; rolling-up, emulsification and solubilization. Although all three have been recognized for many years, recent investigation has greatly increased knowledge of these mechanisms. This article reviews the role of surfactants in these mechanisms and also topics relating to the oleochemical-based-surfactants with novel properties utilized in heavy duty detergents.

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Control of interface in food systems is a major consideration in the development, production, and marketing of food products such as bakery goods, confections, dairy products, cake mixes, margarines and cooking oils. Emulsifiers are commonly used in food applications for this purpose. The emulsifiers as food additives are controlled by a health organization in each country, and must meet the specifications. In Japan thirteen emulsifiers are approved by the Ministry of Health and Welfare. They are esters of edible fatty acids and polyols, such as glycerol, propylene glycol, sorbitol and sucrose. These esters can be modified by further esterification with organic acids such as lactic, diacetyl tartaric, succinic and acetic acids. In this paper we would like to describe interactions of emulsifiers with the components of foods including water, carbohydrates, fats and oils and protein from the viewpoint of surface chemistry.

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Surface-active agents as chemical admixtures are widely used in concrete industry to improve the properties of fresh concrete. By the introduction of admixtures, the use of high strength concrete with low water content became popular, and the durability of concrete structures was largely improved. The most frequently used admixtures are (1) water-reducing and setretarding admixtures to reduce the water requirement of concrete or retard the set, or both [these include ligninsulfonic acid, hydroxylcarboxylic acids, carbohydrates, polyols, and the salts], (2)air-entraining admixtures to introduce a system of small air bubbles into the fresh concrete dung mixing [these are anionic surface-active agnets]. A new group of water-reducing admixtures, termed superplasticizers, has been introduced in the last few years [these are naphthalenesulfonic acid, specific ligninsulfonic acid, and polycarboxylic acid]. They are about twice as effective as the conventional admixtures.

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Recently, the development of alternatives to animal testing has become one of the most important issues in the field of safety assessment of cosmetic ingredients, especially surfactants. In this review, both general concept and current status of alternatives are described. Also, the hemoglobin denaturation (HDR) test, one of the in vitro methods we developed, is explained in detail as an example. HDR test has been systemically studied from various aspects and has developed as an alternative to Draize eye irritation test. The advantages of HDR test are high reproducibility as well as an easy handling without aseptic operation. Factorial analysis on the data obtained from the in vivo test and several in vitro tests suggested a battery system, the useful combination of in vitro methods based on different mechanisms, for the purpose of predicting eye irritancy. Furthermore, quantitative structure-activity relationship for surfactants was investigated to discuss eye irritancy predicted by HDR test. In the near future, the necessity of development of in vitro methods will be increased as seen in eye irritation test.

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Surfactants are one of the major components of detergent or household cleaning products. Several are commonly found in river waters and consequently, their impact on the aquatic environment has been discussed in the U.S.A, Western Europe and Japan. This paper reviewed the studies on the environmental monitoring, environmental fate, acute, chronic and sublethal toxicity, and environmental risk assessment of anionic surfactants. The reported acute and chronic toxicity data overlapped with some worse case of LAS environmental concentrations in rivers in Japan for a lack of adequate treatment of household gray water. Aquatic safety of other surfactants was considered preliminary and limited until validated with corresponding exposure measurements and chronic toxicity data for test species. Life-Cycle Assessment on surfactants was also reviewed.

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