Structured surfactant formulations

Structured Surfactant Formulations (SSF) are close-packed three-dimensional matrices of a liquid crystalline phase that suspend insoluble pesticide materials. The active ingredient can be either solid or liquid. Additional actives and/or adjuvants can be dissolved or suspended in the formulation if desired. The main advantage of an SSF over standard suspension concentrates is that no thickening or suspending agents are required. The SSF formulation can be solvent-fiee if desired, or include an oil adjuvant built in for inqiroved efficacy. 

Structured Surfactant Formulations take advantage of basic aqueous surfiictant phase behavior. Figure 1 shows a schematic of general surfiictant aqueous equilibrium phase behavior as a function of sur ctant concentration. 

Figure 2. Schematic Representation of a Structured Surfactant Formulation...

When the Structured Surfactant Formulation is diluted in the quay tank, a stable, low viscosity suq>ension is formed. The herulites dissolve at the reduced spray tank sur ctant concentration. The dilute suspension can then be applied as any stable SC product... 

Combination products are becoming more inportant, and adjuvants can be formulated into the pesticide concentrate as well. The result can be sophisticated products like suspomicroemulsions. The structured surfactant formulation can be evaluated in lieu of the suspension concentrate. The SSF s main advantages are the absence of thickener, and technology that allows an adjuvant to be built into die pesticide formulation. 

Elsik, C. M., Perdreau, L., RoUinson, M. and Diu, M. L., Agricultural AppUcations of Structured Surfactant Formulations, Pesticide Formulations and Application Systems 23 International Symposium, ASTM STP 1449, G. Volgas, R Downer, and H. Lopez, Eds., ASTM International, West Conshohocken, PA, 2003. 

Comparison of the proposed dynamic stability theory for the critical capillary pressure shows acceptable agreement to experimental data on 100-/im permeability sandpacks at reservoir rates and with a commercial a-olefin sulfonate surfactant. The importance of the conjoining/disjoining pressure isotherm and its implications on surfactant formulation (i.e., chemical structure, concentration, and physical properties) is discussed in terms of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of classic colloid science. 

Surfactants act as solubilizers, stabilizers, emulsiLers, and wetting agents. They can also causi toxicity and disrupt normal membrane structure. Surfactant toxicity is directly related to its concentration. This should be considered by the pharmaceutical formulator so levels below the toxic concentration will be used for a particular application. Many of the toxic effects of the surfactants are related to their physicochemical properties and their interaction with biological membranes and other macromolecular assemblies. The observed protein binding and lipid solubilization is directly... 

Lipid. Lipids or surfactants had been used widely in the delivery of pharmacologically active materials in the form of liposomes, emulsions, or micelles. Since the first description of their potential for exogenous gene transfer, much progress has been made in the development of improved cationic lipid structures and formulations with enhanced gene transfection activity. 

Variables identified as important in the achievement of the low IFT in a W/O/S/electrolyte system are the surfactant average MW and MW distribution, surfactant molecular structure, surfactant concentration, electrolyte concentration and type, oil phase average MW and structure, temperature, and the age of the system. Salager et al. (1979b) classified the variables that affect surfactant phase behavior in three groups (1) formulation variables those factors related to the components of the system-surfactant structure, oil carbon number, salinity, and alcohol type and concentration (2) external variables temperature and pressure (3) two-position variables surfactant concentration and water/oil ratio. Some of the factors affecting IFT-related parameters are briefly discussed in this section. Some other factors, such as cosolvent, salinity, and divalent, are discussed in Section 7.4 on phase behavior. Healy et al. (1976) presented experimental results on the effects of a number of parameters. 

EACNs have been determined for several crude oils (13) and fell into a fairly narrow range from 6 to 9. The EACN can be determined in independent ways by using entirely different sets of surfactant formulations. Values checked in this way always agree, confirming that the EACN is an invariant oil property and, in particular, does not vary with surfactant structure (19). 

The effect of phase structure on the coefficient of friction was studied for TRS 10-410 + isobutanol + salt + water system. The coefficient of friction was measured on aluminum-aluminum metal surfaces using the surfactant formulation at several salt concentrations. A significant change in the coefficient of friction was observed as the salt concentration was increased in the system because of the change from isotropic to anisotropic structure of the surfactant system. 

Recent findings combining liposomal structures and surfactant formulations in pharmaceuticals and cosmetics seem to open thrilling new possibilities. 

With all these factors in mind, we have attempted to carry out the emulsions aspect of the investigations at the University of Florida Improved Oil Recovery Research Program (4,5). The emulsion systems contain TRS 10-410, isobutanol, sodium chloride, dodecane and water. Extensive physical property data and micro-structural studies of the aqueous surfactant formulations have been already reported by Vijayan et al. (6). Also, the structural aspects of the emulsions containing the same species with aqueous to oil ratio of 1 1 as well as various physical property data as a function of salt concentration have been reported by Vijayan et al. (7). A detailed study of the middle phases formed by the same surfactant formulation with dodecane oil with respect to microstructural changes and microemulsion (swollen micelle) phase inversion has been reported by Ramachandran et al. (8). 

The study of flow of aqueous solutions through unconsolidated sand bed thus demonstrates the influence of structural aspects of surfactant formulation on pressure drop values at low shear rate flows. 

In general, the surfactant formulations used for enhanced oil recovery contain a short chain alcohol. The addition of alcohol can influence the viscosity, IFT and birefringent structures of micellar solutions as well as coalescence rate of oil ganglia. The present paper reports the effect of addition of isobutanol to a dilute petroleum sulfonate (< 0.1% cone) solution on IFT, surface shear viscosity, surfactant partitioning, the rate of change of IFT (or flattening time) of oil drops in surfactant solutions and oil displacement efficiency. The two surfactant systems chosen for this study indeed exhibited ultralow IFT under appropriate conditions of salinity, surfactant concentration and oil chain length (11,15,19). 

These desired properties are best brought about by the manipulation of the micelle structures formed by the proper choice of mixtures of surfactants as well as the correct processing procedures needed to assemble the more complex structures. Other chemical species present in real surfactant formulations (perfumes, hydrotropes etc.) can also play a major role in manipulating micellar form if present at significant levels. 

The suspension concentrate can also be prone to hard settling with very poor resuspensibility. The process to make a suspension concentrate is very energy intensive and some type of wet milling is usually required. The multiple formulation obstacles and limitations in performance of the suspension concentrate has led to one future research area that completely replaces die suspension concentrate with a structured surfactant fonnulation dtemative(S). 

Formulation strategies for stabilization of proteins commonly include additives such as other proteins (e.g., serum albumin), amino acids, and surfactants to minimize adsorption to surfaces. Modification of protein structure to enhance stability by genetic engineering may also be feasible, as well as chemical modification such as formation of a conjugate with polyethylene glycol. 

---