Bu-Yao Zhu

THE SURFACE PHYSICO-CHEMICAL PROPERTIES OF SURFACTANTS IN ETHANOL-WATER MIXTURES

Abstract The surface physico-chemical properties of various kinds of surfactants (including cationic, anionic, nonionic and catanionic surfactants) in mixed ethanol–water solvents were investigated. In different surfactant systems, ethanol content influences the cmc and γcmc differently. It is found that the varying tendency of γcmc induced by ethanol addition can be predicted according to their saturation adsorption and γcmc values in water. For the systems with bigger saturation adsorption and smaller γcmc values in aqueous solutions without ethanol, their γcmc values rise with ethanol addition. For the systems with smaller saturation adsorption and bigger γcmc values in aqueous solutions, the ethanol effect on γcmc is opposite. On the other hand, for the influence of ethanol addition on the cmc of surfactant systems, the type of surfactant is important. In ionic surfactant systems, ethanol addition makes the cmc decrease followed by an increase. However, in the systems of nonionic or catanionic surfactants, ethanol addition just makes the cmc go up.

Surface properties of cationic bolaamphiphiles and their mixed systems with oppositely charged conventional surfactant

Surface properties of three cationic bolaamphiphile eicosanediyl 1,20-bis(pyridinium bromide) [Py � (CH2)20Py � ]2Br � , phenyl 1,4-bis(oxyhexyl trimethyl ammonium bromide) (C6PhC6), phenyl 1,4-bis(oxydecyl trimethyl ammonium bromide) (C10PhC10), and their mixed systems with oppositely charged conventional surfactant sodium dodecyl sulfite (SDS) were studied. The results showed that bolaamphiphiles with rigid group also adopted reverse U-shape conformation at the air/water interface as those with flexible skeleton. Micellization in these bolaamphiphile systems is easier than those of the comparable conventional surfactants. Micellization thermodynamic parameters were calculated according to the phase separation model and entropy was found to be the main driving force in the process of micellization. Diagrams for the C6PhC6/SDS and C20Py2/SDS mixed systems were constructed based on the regular solution theory. It was found that the structural difference between the two bolaamphileles affects the interaction between the two components in each mixed systems greatly. # 2002 Elsevier Science B.V. All rights reserved.

Reverse time effect of surface tension in cationic bolaform surfactant/anionic surfactant mixed systems

The time effect in a series of flexible and rigid bolaform amphiphiles and their mixed systems with oppositely charged conventional surfactants was investigated. An increase of surface tension with time was found in these systems at surfactant concentrations below the cmc. This result can be attributed to large numbers of surfactant molecules being gradually adsorbed on the wall of the vessel, which causes great changes of concentration and composition in mixed surfactant solutions. Contact angle data and UV research supported our proposal. It was also found that this reverse time effect in single bolaform cationic surfactant systems is decided by the structure of the hydrocarbon chains and only happens in flexible cationic bolaform surfactant solutions.

Phase separation and crystallization in mixed monolayers of FC and HC surfactants

Abstract Mixed insoluble monolayers of anionic fluorocarbon amphiphile (C8F17COOH) and anionic hydrocarbon amphiphile (C18H37SO3NA) were investigated by means of a Langmuir balance, atomic force microscopy (AFM) and friction force microscopy (FFM). π–A curves and topographic images of monolayers were provided. These pictures and data provide strong experimental evidence for two-dimensional phase separation and crystallization. Further studies from the viewpoints of thermodynamics and molecular dynamics were conducted. An explanation and a mechanism for the observations is suggested.

Surface-chemical study of an aqueous mixture of α-sulfolauric acid salts with cationics

The physicochemical properties of an aqueous mixture of α-sulfolauric acid (H2LS) and its various salts, including sodium α-sulfolaurate (NaHLS), triethanolammonium α-sulfolaurate (TeAHLS) with a cationic surfactant, decyltrimethylammonium bromide (DeTAB), have been investigated. The surface activities of H2LS and its salts were enhanced greatly in the mixed systems; e.g. for a 1:1 mixed solution, the cmc and γcmc can be reduced from 1.4 × 10−2 mol dm−3 and 45 mN m−1 to 5 × 10−4 mol dm−3 and 24 mN m−1 respectively. The effect of inorganic electrolytes (NaBr and HBr) on the surface activity and the molecular interactions between the two surfactants in the mixed adsorption layer and micelles have been studied systematically. It was found that the phase separation concentrations (PSCs) of the mixed surfactant solutions are greater than the cmcs. For 1:1 NaHLS-DeTAB solution, PCS/cmc=3.2. It is also revealed that, unlike the common anionic-cationic mixture, e.g. C10H21SO4Na-DeTAB, the mixed micellar solution is thermodynamically stable up to 3 × cmc.

Vesicle formation of 1:1 cationic and anionic surfactant mixtures in N,N-dimethylformamide and tetrahydrofuran solutions

In the last two decades, many works on vesicle formation from natural amphiphiles (mainly phospholipids) and synthetic surfactants were reported [1,2]. However, up to 10 years ago amphiphiles used to form vesicles are mainly the double chained compounds including natural and synthesized amphiphiles. In 1989, Kaler et al. [3] revealed the vesicle formation from mixed cationic and anionic surfactants using cetyltrimethyl-ammonium tosylate and sodium dodecylbezene sulfonate. Similar work was done in our laboratory, using mixed surfactants of carboxylate and alkyltrimethylammonium compounds [4,5]. However, most works on vesicle formation have been involved in aqueous systems and those in non aqueous systems are less. Some works about vesicle formation in aprotic solvent systems were reported [6,7], which were concentrated on the systems of double-chained fluorocarbon surfactants [8–11]. On the other hand, the studies about vesicle formation in non aqueous polar solvent and mixed polar solvents’ systems are mainly on the liposome of phospholipids [12– 14]. Comparing with phospholipids and other double-chained amphiphiles, the cationic and anionic surfactants used as precursors for vesicle formation have the predominances of simple structure, excellent stability, and convenience in production. Therefore, investigation on vesicle formation by cationic and anionic surfactants is of great significance in both theoretics and applications. It is well known that many drugs are insoluble in water but soluble in organic solvents, and many useful reactions can be carried out in nonaqueous systems. However, the investigations about vesicle formation of mixed cationic and anionic surfactants in non-aqueous polar solvents are scanty. Obviously, it is important to study the vesicle formation in non aqueous or mixed solvents. In a previous paper [15], we reported the * Corresponding author.

Preparation of CdS nanoparticles at the monolayer of N-methyl-p-(p-tetradecyloxystyryl)pyridinium iodine

Abstract CdS nanoparticles were prepared at the monolayer of a cationic functional amphiphile, N -methyl- p -( p -tetradecyloxystyryl)pyridinium iodine, by prior converting of Cd 2+ to CdEDTA 2− . The particles can be transferred onto substrates along with the monolayer. The density and size of the nanoparticles can be controlled.