PREPRINTS OF THE 1997 ANNUAL SCIENTIFIC SEMINAR 71 USER-FRIENDLY COMPUTER PROGRAMS TO PREDICT SURFACTANT SOLUTION BEHAVIOR Daniel Blankschtein, Anat Shiloach, Nancy Zoeller Department of Chemical Engineering, Massachusetts Institute of Technology Cambridge, Massachusetts 02139 Introduction The rich and complex behavior of micelie-containing surfactant solutions is exploited in many practical applications. Fundamental miceliar solution characteristics such as the critical miceliar concentration (CMC) or miceliar shape and size can be correlated with practical and industrially important surfactant performance characteristics such as foam stability, detergency, emulsification, and dispersion ability. In many cases, miceliar shape and size are directly correlated to solution viscosity, which, in turn, can greatly affect processing of suffactant containing products. The CMC can also be correlated with skin irritation, a problem of great importance to the cosmetic industry. Micelie formation is also related to solubilizafion and emulsification, both of which affect the formulation of many cosmetic products in which polar and nonpolar materials are combined to create stable dispersions. In order to facilitate the design of new surfactant products while minimizing costs associated with trial-and-error research, it is desirable to develop a fundamental molecular-level understanding of the broad spectrum of solution properties exhibited by these complex fluids. With this goal in mind, we have recently developed •'2 two user-friendly computer programs, PREDICT and MIX, based on molecular- thermodynamic theories of surfactant solution behavior developed by our group. These programs are capable of quantitatively predicting many solution properties of single and mixed surfactant systems. The fundamental miceliar properties predicted by programs PREDICT and MIX can also be correlated with practical and industrially important surfactant performance characteristics such as viscosity, foam stability, detergency, emulsification, and dispersion ability. Here, we briefly describe programs PREDICT and MIX and present some illustrative examples of their predictive capabilities. Predictive Capabilities of Programs PREDICT and MIX Program PREDICT can be utilized to predict miceliar solution properties of nonionic, ionic, and zwitterionic hydrocarbon-based surfactants under a variety of solution conditions. Program MIX can be utilized to predict solution properties of binary mixtures of these surfactants. Given the surfactant molecular structure and solution conditions (temperature, total surfactant concentration, salt type and concentration, etc.), the following properties can be predicted using programs PREDICT and MIX: •'2 Program PREDICT CMC Optimal Miceliar Shape and Size Polydispersity of the Miceliar Size Distribution Average Aggregation Numbers Phase Behavior and Phase Separation Characteristics Surface Tension Program MIX Mixture CMC [!• Interaction Parameter Optimal Miceliar Shape and Size Optimal Miceliar Composition Miceliar Size and Composition Distribution Monomer Composition and Concentration Programs PREDICT and MIX are designed to be user-friendly both to those interested solely in predicting solution properties of surfactant types already incorporated into the programs, as well as to those interested in incorporating new suffactant structures which are relevant to their specific needs. For both types of users, minimal knowledge of the underlying theoretical details is required. Instead, only the suffactant molecular structure and the solution conditions serve as inputs to the programs. This greatly reduces the level of expertise and computational effort required to make predictions of suffactant solution properties. Due to space limitations, we are unable to present quantitative results for all the predictive capabilities of program PREDICT and MIX. Instead, we present two representative examples. Figure 1 below shows the predicted mixture CMC as a funaim of mixture composition for a mixture of sodium dodeeyl sulfate (SDS) and n-octyl dodeca(ethylene oxide) (C8E•2) at 25øC. The experimentally observed dramatic reduction in the CMC values, due to synergism between the anionie and nonionic surfaetants, is captured very well by program MIX. The fundamental miceliar solution properties predicted by programs PREDICT and MIX are closely related to the performance behavior of surfactant systems in many practical applications. For example, miceliar size is directly correlated to solution viscosity, which, in turn, can greatly affect processing of the miceliar solution in many cosmetic formulations. In Figure 2 below, the predicted number-average aggregation number is shown together with experimental viscosity values for a series of

72 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS n-tetradecyl poly(ethylene oxide) surfactants (C•4Ej, where j denotes the number of ethylene oxide groups in the surfactant polar group) as a function ofj. As j increases, the predicted aggregation numbers and the experimental solution viscosity both decrease. Although program PREDICT does not calculate the solution viscosity directly, the correlation between predicted aggregation numbers and experimental viscosity values represents a useful indicator of the rheological behavior of the miceliar solution. 10 Mixture Composition 2,000 200 ,. 1,000 õ 2oo •' 50 206 7 8 9 I I 12 No. of EO Groups (}) 100 50 • 20 • Figure l. Mixture CMC as a function of mixture composition, ct, for a binary mixture of CaEn (ct=0) and SDS (ct=l). The solid line is the predicted CMC using program MIX, and the circles denote experimental CMC values. Figure 2. Predicted number average aggregation number predicted by program PREDICT (solid line), and experimental viscosity values (circles) as a function ofj for C•nEj surfactants. Conclusions As the need for a detailed understanding of surfactant solution behavior increases, the surfactant technologist is faced with the challenge of modeling the complex behavior of these systems. With this need in mind, we have developed programs PREDICT and MIX to make our comprehensive molecular- thermodynamic theories of miceliar solution behavior accessible to the surfactant teclmologist. We hope that the availability of programs PREDICT and MIX will facilitate the design and optimization of new surfactants and surfactant mixtures possessing desirable properties by alleviating the need for a priori synthesis and characterization of the new chemicals, as well as by reducing the level of experimentation required to evaluate the performance of the new surfactants and surfactant mixtures. • N.J. Zoeller, D. Blankschtein, Ind Eng. Chem. Res., 34, 4150 (1995), and references cited therein. 2 N.J. Zoeller, A. Shiloach, D. Blankschtein, CHEMTECH, 26 (3), 24 (1996), and references cited FORTIFICATION AND WEAKENING OF HUMAN HAIR BY CATIONIC SUBSTITUTED BY CATIONIC SUBSTITUTED POLYSACCHARIDES D. E. Firstenberg •, R. Rigoletto • and L. MoraP •Amerchol Corporation, Edison, NJ 08818 Introduction Cationic substituted polysaccharides have been used as conditioning chemicals in hair care formulations for quite some time. The principal representatives of this group are Polyquaternium-10 and Guar Hydroxypropyltrimonium Chloride. These cationic conditioning chemicals are substantive