Errol Desmond Goddard

Interactions of surfactants with polymers and proteins

Interactions of Surfactants with Polymers and Proteins covers work done in this area over the last 30 years and examines in detail the physico-chemical, microstructural, and applications aspects of interactions of surfactants with polymers and proteins in bulk surfaces and at interfaces. The physical chemistry of individual components (surfactants, polymers, and proteins) is discussed, and extensive coverage of interactions of surfactants with uncharged, oppositely charged, and hydrophobe modified polymers is provided. Other topics addressed include water soluble and insoluble keratinous proteins, the principles and applications of fluorescence spectroscopy, the physical properties and microstructural aspects of polymer/protein-surfactant complexes, and implications of surfactant interactions with polymers and proteins in practical systems. Interactions of Surfactants with Polymers and Proteins provides a wealth of information for chemists involved in a number of different research areas, including cosmetics, pharmaceutics, foods, paints, pigments, lubrication, ceramics, minerals/materials processing, and biological systems.

A study of the solution, interfacial and wetting properties of silicone surfactants

This work reports an investigation of the solution, interfacial and special wetting properties of a group of three silicone surfactants using surface tension, wetting, adsorption, fluorescence and fluorescence decay techniques. Aqueous solutions of two of these surfactants exhibit a c.m.c. type break in the surface tension versus concentration plot. Fluorescence and turbidity measurements show that for one (SS1) the break corresponds to the formation of well dispersed droplets rather than micelles. A second surfactant, SS2, forms micelles in solution of aggregation number around 30 which is significantly lower than that for conventional surfactant micelles. SS1, with a compact hydrophobic group and a long polyether tail, reduces the surface tension of water to 20.5 mN m−1 and exhibits a unique ability to wet low energy surfaces such as polyethylene. Interestingly, fluorocarbon surfactants which can lower the surface tension of water even further do not wet polyethylene as efficiently. The special wetting properties of SS1 are attributed to a variety of factors, i.e., its unique structure, ability to lower the liquid-air surface tension to extremely low values, fast kinetics of adsorption at the liquid-air and solid-liquid interfaces, high affinity of the surfactant for low energy surfaces, and favorable orientation and structure of its adsorbed molecules.

Fluorescence and solubilization studies of polymer—surfactant systems

Abstract The interactions of sodium dodecyl sulfate (SDS) with cationic polymers have been investigated in this study using fluorescence-probe, dye-solubilization and solubility measurements. Information on the polarity of the SDS “micellar” microenvironment, in which the probes are solubilized, and the alterations in it in the presence of polymers have been obtained over a range of SDS concentrations. Dye-solubilization as well as fluorescence measurements indicate the existence of hydrophobic environments in the pre- and post-precipitation regions. Interestingly, these environments in the immediate vicinity of the precipitation region in the case of a cellulosic polymer (Polymer JR)—SDS system are much more hydrophobic than those in an acrylamide copolymer (Reten 220)—SDS system. A comparison of the solubilization capacity of polymer—surfactant aggregates in solution indicates the structure of the complexes on either side of the precipitation maximum to be different. The results obtained point to a hemi-micelle/inverse cylindrical micelle-type aggregate in the pre-precipitation zone and a conventional micelle-type structure beyond the point of maximum precipitation.

Studies of gel formation, phase behavior and surface tension in mixtures of a hydrophobically modified cationic cellulose polymer and surfactant

Abstract The interaction of a variety of surfactants—anionic, cationic and non-ionic—with a hydrophobically modified cationic cellulosic polymer has been studied by solubility, rheology and surface tension methods. Compared with unsubstituted analogs this polymer is different inasmuch as it forms gels with anionic surfactants in the resolubilization zone (excess surfactant) as well as in the pre-precipitation zone. The gels were investigated in detail by mechanical oscillatory measurements and the results, have been analyzed by methods similar to those used for complex dielectrics. Evidence is also provided of interaction with cationic surfactants and non-ionic surfactants.

Mechanism of antifoaming action

Abstract Short-range interfacial forces are known to play an important role in the performance of antifoams. To be effective in a given foaming medium, an antifoam agent should have a positive spreading co-efficient and form an unstable interfacial film incapable of foaming; i.e., it should be highly surface active and of limited solubility. Although these conditions are sufficient to describe the essentials of defoaming activity, they are inadequate to explain the variable effectiveness of different antifoams. In the present investigation, using silicone antifoams, we have shown that antifoam effectiveness can be strongly influenced by dispersibility and long-range interfacial electrical forces. The origin of such electrical forces is ionic surfactant adsorption which can impart identical surface charges to a foam bubble and the antifoam droplet, resulting in a repulsive interaction between them. Using the Gouy electrical double-layer model, this repulsive force has been estimated and correlated with antifoam effectiveness. It is also shown that in foaming systems containing anionic or cationic surfactants, electrical repulsive forces change significantly near the critical micelle concentrations of the foaming surfactants.

Examination of the parameters governing oily soil removal from synthetic substrates

The rate of removal of mineral oil soils from model polyester sub-strates by the roll-up mechanism shows a marked dependence on nonionic surfactant concentration even above the critical micelle concentration (cmc). Similarly, although the solid/water interfacial tension is observed to be constant, the equilibrium oil/water inter-facial tension in these systems consistently decreases as the nonionic surfactant concentration is increased. The dependence of removal time and oil/water interfacial tension on surfactant concentration above the cmc is most pronounced for nonionic surfactants having relatively high cmc. At a given concentration, surfactants exhibiting the lowest equilibrium oil/water interfacial tension generally provide the most effective soil removal, suggesting that the reported depen-dence of removal time on surfactant concentration is related to the commensurate lowering of the oil/water interfacial tension. Nonyl phenol ethoxylates perform exceptionally well with mineral oil on polyester substrates because of the combination of a low oil/water interfacial tension and high solid/water adhesion tension. Regardless of surfactant structure, mineral oil on Teflon FEP maintains a high contact angle in the water because the solid/oil interfacial tension is less than the solid/water interfacial tension. Oil removal in such systems occurs only by an inefficient necking and drawing process. Oleyl alcohol displays a high contact angle in the water on both Teflon FEP and Mylar substrates for reasons similar to that of mineral oil on Teflon FEP. Partial oil removal occurs from both substrates in selected built systems, presumably because a low oil/ water interfacial tension promotes necking and drawing. Given sufficient time, unremoved oils develop a liquid crystalline phase which results in slow oil removal via dispersion. Triolein soils also possess a relatively low solid/oil interfacial tension and similarly exhibt a high contact angle (in water) on both Teflon FEP and Mylar substrates in unbuilt surfactant systems. Builder addition lowers the oil/water interfacial tension and thereby prompts necking and drawing action.

Adsorption and critical flotation conditions

Abstract It has been commonly recognized that a mineral surface must be sufficiently hydrophobic for flotation to occur. Thermodynamic treatments that deal with the role of the collector have centered largely on the solid/solution interface emphasizing, for example, contact angles and ζ potentials. The forces which are involved in the flotation process are usually considered to be short-ranged. Although it is known that the collector species adsorb also at the liquid/gas interface, the importance of this phenomenon in flotation has received relatively little attention. Since many collectors that are used for oxide mineral flotation bear a charge opposite to that of the oxide, it is expected that the liquid/gas interface would correspondingly bear a net charge opposite to that of the solid/liquid interface. It is possible, therefore, that the interaction of these two oppositely charged electrical double layers would produce a long-range force of attraction which would influence the kinetics of flotation. Using the Gouy treatment, we have estimated the magnitude of the potential energy of attraction for selected systems.

The sequestering of surfactants from insoluble monolayers by α-, β- and γ-cyclodextrins

Abstract A study of the sequestering of insoluble surfactants by α-, β- and γ-cyclodextrins from monomolecular films at the air/water interface is reported. Sequestering of single-chain surfactants by α- and β-cyclodextrins takes place at a rate consistent with the direct removal of the surfactant molecule from the air/water interface and well in excess of that which would arise from a film/ substrate equilibrium followed by sequestering of the dissolved surfactant. Sequestering involves the formation of surfactant: cyclodextrin complexes, probably 1:1, with the surfactant alkane chain immersed in the hydrophobobic cavity of the cyclodextrin. γ- cyclodextrin, in spite of its larger cavity, failed to sequester a detectable amount of surfactant over a period of one hour under conditions favorable for sequestering by either (α- or β-cyclodextrin. This is explained in terms of the γ-cyclodextrin cavity being effectively less hydrophobic. The rate of insoluble surfactant sequestration was found to decrease with the formation of a liquid condensed as opposed to a liquid expanded film state, with increasing alkane-chain length of the surfactant, and with chain branching. Molecules with two chains, such as lecithins, were not sequestered but cholesterol with a similar cross-sectional area/molecule did show a weak interactive coupling with β-cyclodextrin below 30°C. Based on the observed increased areas/molecule, this latter interaction brought β-cyclodextrin into the air/water interface rather than removing cholesterol, indicating the “complex” still possessed substantial hydrophobicity.

Behavior of surfactant mixtures in model oily-soil detergency studies

A study of roll-up in a model oily-soil detergent system has shown that the addition of a second surfactant in a minor amount to an effective detergent can either enhance or inhibit roll-up. Which effect takes place depends on the relative surface activity of the components, the levels used, and, for ionic surfactants, the electrolyte content. Addition of anionic surfactants can reduce the performance of an effective nonionic under low ionic strength/low hardness conditions. However, in high ionic strength/high hardness solutions, where the anionic is effective, the situation is reversed and addition of the nonionic component can, in some cases, reduce the rate of roll-up. Roll-up behavior appears to be controlled by the oil/ water interfacial tension. When the interfacial tension increases above a critical value, roll-up is inhibited. A theory that has been used to predict surface tensions of mixtures is also useful in estimating oil/water interfacial tensions. The theory provides an understanding of why the interfacial tension can rise when mixed micelles are formed.

Adsorption study of nonionic surfactants on polyester fibers

An adsorption study of a series of nonionic surfactants on polyester fiber was performed to determine the relative importance of sub-strate affinity in the detergency process. The fiber used in this study was a multifilament polyester yarn. Because of the relatively low surface area/g of the yarn, analytical methods for detecting the depletion of surfactant due to adsorption have to be extremely sensitive. One qualitative technique used was streaming potential measurements. The electrokinetic effect, which the streaming poten-tial measures, depends on the nature of the electrical double layer at the fiber/solution interface. The modification of the streaming potential indicates that the extent of surfactant adsorption onto the fiber surface is very similar for the nonionic surfactants studied. A very sensitive, quantitative analytical technique, which can only be used for surfactants with an appropriate chromophore, is ultraviolet (UV) spectroscopy. The UV study showed that the adsorption of the nonylphenol ethoxylate onto the polyester is Langmuirian with the adsorption plateau occurring at the critical micelle concentra-tion. For alcohol ethoxylates without a UV chromophore, con-venient quantification at the ppm level represents a difficult analyt-ical problem. In this work, total carbon analysis was developed as a sensitive analytical tool for surfactant determination. Agreement between the UV and total carbon data for the nonylphenol ethox-ylate was quite good. The relevance of the data to the detergency process is discussed.