Institute for Applied Surfactant Research - Fundamental Surfactant Research

Research sponsored by IASR encompasses a wide spectrum of technological applications as outlined in previous sections. However, members of the Institute strongly believe that the underlying forces responsible for the phenomena of surfactant behavior must be understood in order to provide a firm basis for applying knowledge to practical problems, Fundamental research is a basic part of the program at IASR, both in relation to specific technological problems and as a part of the larger goal of improving our understanding of surfactant behavior in general.

A characteristic property of surfactant molecules is their tendency to aggregate at interfaces. Examples are adsorption on solids and monolayer formation at an air-water interface. Surfactants will sometimes create their own interface by forming very small aggregates like micelles or vesicles to remove a portion of their structure from contact with a solvent. On the other hand, surfactant aggregates can form separate thermodynamic phases such as microemulsions and coacervates.

An important facet of research at IASR is the investigation of the similarities and differences between the many aggregates that surfactants can form, both in single surfactant systems and in mixtures of surfactants. Because some of the same effects are responsible for the formation of many of the aggregates, comparison of aggregation thermodynamics can shed light on surfactant interactions in the process of clustering under different conditions. This type of approach, which should lead to comprehensive theories of several aggregation processes, is a unique aspect of IASR research.

The study of thermodynamic properties of micellar solutions is an important area of both practical and fundamental interest. The ability of surfactant micelles to bind or solubilize components in aqueous solutions gives these systems the unique properties responsible for many of the processes described in this brochure. Unfortunately, our understanding of the molecular equilibria and dynamic behavior of micellar systems is still fairly primitive.

Active areas of research at IASR include thermodynamic studies of the formation of micelles from individual surfactant molecules, the binding or solubilization of individual compounds or ions by micelles, and the prediction of solubilization phenomena with molecular theories or models. All of these studies are fundamental in character, but advances in our knowledge of micellar properties will relate directly to many types of technological improvement. IASR's experimental and theoretical expertise in the field of surfactant thermodynamics should enable the group to make substantial contributions in this important area of research.

As we have pointed out in previous sections of these pages, surfactant mixtures have numerous synergisms in practical applications. However, the surfactant interactions in these systems are also inherently of great theoretical interest. Interaction between dissimilar surfactants in various aggregation processes is being investigated.

Fundamental models are being developed to describe surfactant mixture effects in specific processes. Experimental data provide a test of these models. It is this type of approach, balancing theory and experimental verification, that IASR is using to advance knowledge in this field.


*Coacervate*	*Air-Liquid or Liquid-Liquid*

Our efforts in surfactant synthesis involve preparation of new fluorinated surfactants in connection with our research on perfluorochemical blood substitutes. The goal is to synthesize fluorinated surfactants that will form stable, non-viscous microemulsions containing high contents of fluorocarbons, with very small emulsified particles that are not adsorbed on the surface of red blood cells. The synthetic procedure is straightforward, and the yield is high. Our methods lead to the production of fluorinated surfactants which are free from the toxic impurities that frequently result from conventional syntheses.

The micellar-enhanced ultrafiltration (MEUF) technique has important applications in industrial separation processes. However, there are two aspects in the MEUF technique which need to be improved, namely surfactant loss and membrane obstruction. To overcome these problems, we consider the use of polymeric surfactants instead of normal monomeric surfactants in MEUF.

The research on polymeric surfactants includes synthesis, characterization and binding studies. Three types of compounds are being investigated. The first type is w-alkenyl sulfates, which can form micelles easily and can be polymerized. The second type is polymeric alkyl ammonium bromide, which is prepared from partial alkylation of polyethyleneimine. The third type is partially sulfonated polystyrene, which is prepared by reacting sulfuric acid and acetic anhydride with low-molecular weight polystyrene. Preliminary studies show that these new polymeric surfactants can bind organic molecules and counterions similar to micelles of ordinary surfactants, sometimes with larger binding constants. When compounds with proper molecular weights are used, there is no loss of surfactants through membrane permeation. Therefore, the polymeric surfactants are promising new compounds for MEUF and other applications.

IASR researchers have recently synthesized a new type of surfactants which have unusual and interesting structures and properties. These surfactants contain a hydrocarbon chain and a fluorocarbon chain attached to the same hydrophilic head group, and are called hybrid surfactants. It is well known that hydrocarbon and fluorocarbon surfactants with the same type of head groups do not form ideal mixtures because the two types of chains repel each other. However, in a hybrid surfactant, a hydrocarbon chain and a fluorocarbon chain are forced to tie to the same head group in the same surfactant molecule by covalent bonding, leading to some interesting properties. When the hybrid surfactants form micelles, the dependence of the CMC on the chain lengths follows Kieven's equation: the logarithm of the CMC is linear with respect to the number of carbon atoms in each chain. However, the slopes of such plots are different with respect to each type of chain, showing that the fluorocarbon chain dominates the tendency of micelle formation. The micellar aggregation numbers are 10-35 and become smaller as the chain lengths increase. When the hydrocarbon chain bears three carbons or more, both kinds of chains are incorporated inside the micelle.

The structures and dynamics of these double-tail hybrid surfactants have been studied in detail by F-19 NMR. It was found that the rotation of the fluorocarbon chain along the C-C bonds is restricted upon micelle formation, making the two fluorine atoms in each CF_2, group inequivalent. For all the members in different homologous series of the hybrid surfactants, the exchange rate between the monomer and micellar states is 2-3 orders of magnitude slower than that for normal hydrocarbon or fluorocarbon surfactants.

Research on other aspects of the hybrid surfactants, such as the formation of thin films, is in progress.