Volume 59, Issue 2

A series of novel dimeric pyridinium surfactants has been synthesised and the effects of a semi-flexible p -xylyl spacer and flexible, polyethylene glycol spacers have been studied. The nature of the spacer determines solubility and aggregation behaviour in two- and three-dimensional systems. Some of these insoluble compounds form two-dimensional, rigid-condensed structures at the air–water interface, while others form liquid-analogue monolayers. Whereas the latter compounds become soluble after exchange of the counterions, the former remain insoluble. The aggregation behaviour of Langmuir layers was, inter alia, investigated by Brewster angle microscopy. The micellisation behaviour of diluted aqueous solutions of soluble surfactants was primarily investigated by conductometric measurements and thermodynamic parameters of aggregation have been deduced with respect to the spacer length.

Among glycolipids, mannosylerythritol lipids (MEL), are mild and environmentally friendly surfactants used in various industrial applications. MELs are produced by biofermentation using non-traditional oils with various water-soluble carbon sources as cell growth booster. This substrate affects the production yield and cost of MEL. In this research work, the non-traditional oils jatropha oil, karanja oil and neem oil were used as new substrates along with glucose, glycerol and honey as new water-soluble substrates. All these oils are new feedstocks for the production of MEL using Pseudozyma antarctica (ATCC 32657). Jatropha oil, karanja oil and neem oil with honey as substrates resulted in higher MEL yields of (8.07, 7.75, and 1.86) g/L and better cell growth of (8.07, 7.75, and 1.86) g/L, respectively, than non-traditional oils with glucose and glycerol as substrates. Neem oil gave a lower yield of MEL (1.54 g/L) as well as cell growth (6.06 g/L) compared to jatropha oil and karanja oil (7.03 and 6.17) g/L, respectively. Crude MEL from the fermentation broth was detected by thin-layer chromatography (TLC), Fourier transform infrared spectrommetry (FT-IR), high performance liquid chromatography (HPLC) and proton nuclear magnetic resonance spectroscopy ( 1 H NMR). Purified MEL has been used as an antimicrobial agent in cosmetic products associated with gram-positive and gram-negative bacteria and fungi.

The micellation behaviour of mixtures of sodium lauryl sulphate (SLS) and octylphenol ethoxylate-10 (OPE-10) was investigated using tensiometry and dye solubilisation. The interaction parameters for the system were determined using Rubingh’s model for non-ideality and the adsorption parameters were calculated. The surfactant mixture was found to behave synergistically in terms of CMC reduction and dye solubilisation. Furthermore, the mixture appears to mimic the adsorption and micellation properties of OPE-10 more closely than SLS, regardless of composition. With this knowledge, and considering that OPE-10 is typically more expensive than SLS, the formulator can now use only a fraction of the required amount of OPE-10 for a given application (instead of using 100% OPE-10), resulting in high performance yet economical products. It was also found that the said mixture exhibits azeotropic behaviour at a certain fixed composition.

Solutions of sodium dodecyl benzene sulfonate (SDBS) and N , N -dimethyldodecan-1-amine oxide (DDAO) with mole fractions of 0.00, 0.25, 0.50, 0.75 and 1.00 were prepared and their surface tension was measured as a function of total surfactant concentration. The critical micelle concentration (CMC) values of these mixed solutions were also determined. The minimum area occupied by a surfactant molecule at air/water interface was calculated for single and binary surfactant mixtures. A pronounced synergistic interaction between SDBS and DDAO was detected. The surface tension and CMC-values of SDBS/DDAO mixtures are significantly lower than those of the single surfactant. The mixed system of SDBS/DDAO exhibits a highly negative interaction parameter ( β  = −10.6) according to regular solution model, and is found to fulfill the condition of Hua and Rosen, indicting a strong synergistic interaction between the two surfactants. The contact angle measurements show the wettability of the surfactant mixture onto polyethylene substrate is higher than of the respective single surfactant. In addition, the adsorption of SDBS and DDAO or their mixtures on 1.0% activated carbon and 5.0% Jordanian natural clay (JNC), respectively, was investigated using the depletion method. The individual surfactants were found to adsorb to a considerable extent on activated carbon, and a slightly higher adsorption tendency was even measured for mixed SDBS/DDAO surfactant systems. Although no SDBS molecules adsorbed on JNC, adsorption was observed for solutions containing DDAO and SDBS/DDAO surfactants. The improvement in wettability and adsorption of SDBS/DDAO surfactants at the air/water and solid/water interfaces is directly related to the synergistic interaction between the two surfactants.

Potassium N-lauroyl glycinate (PLG) is an amino acid surfactant widely used in detergents and has excellent chemical properties. In the present work, PLG was mixed in different molar ratios (α 1 ) with the commonly used amphoteric surfactant lauryl amidopropyl betaine (LAB) or the non-ionic surfactant alkyl glycoside (APG). Subsequently, the surface tension, average hydrodynamic radius and number of micellar aggregates of the individual surfactants and the compound systems were measured using the hanging plate method, dynamic light scattering and fluorescence probe method, respectively, and the corresponding surface activity parameters were calculated. The results show that the binary PLG/LAB and PLG/APG systems exhibit non-ideal behaviour and that there was mutual attraction in the systems. The broad distribution of the micelle radius of the PLG/LAB compound system indicates that there are two types of micelles, namely spherical and rod-shaped in the systems. The distribution of the micelle radius of the PLG/APG compound system decreases to the minimum value at α 1  = 0.5. At α 1  = 0.7 and 0.9, double peaks and a broad distribution were also observed. The number of micelle aggregates in the PLG/LAB and PLG/APG compound systems is less than that of the individual surfactants at the respective mole fractions.

The effect of three handheld ultrasonic devices for the pretreatment of stains on textiles was evaluated under household conditions. Twenty soiled textiles were treated and the mean increase of lightness Δ L * of the soiled textiles was used as a measure for the cleaning effect. It was shown that the combination of a pretreatment and a washing cycle at 20 °C yields a higher mean increase of lightness, Δ L * = 19.5, compared to a 40 °C washing cycle without pretreatment, Δ L * = 15.3. The effect is most pronounced for mixtures consisting of oily soils with pigments, Δ L * = 25.1. During the pretreatment, the soil was soaked in a detergent solution and the effect of soaking was measured separately.

Froth stability is an important factor in determining flotation yield, and one of the factors affecting froth stability is dependent on the concentration and type of surfactant. Since detergents contain different types of surfactants, it is possible that they affect the froth stability (together with the frothing agent and the collector) and consequently the flotation yield. Therefore, the effect of detergents containing lauryldimethylamine oxide and sodium laureth sulphate was investigated in this study. The results showed that the addition of detergents increased the froth stability by more than 30% and 45% in terms of froth formation and froth decay, respectively. The flotation tests also showed that the addition of detergents increased the sulphur content of the concentrate by about 0.7%.

Etofenprox emulsions in water were prepared by mixing polyoxyethylene (20) castor oil ether (EL-20) with the surfactants polyoxyethylene (10) octylphenyl ether (OP10), polyoxyethylene styrenated phenol ether (602), polyoxyethylene (40) castor oil ether (EL-40) and octylphenyl polyoxyethylene phosphonate (OPP), respectively. Emulsion stability was investigated and analysed based on the hydrophilic-lipophilic equilibrium, surfactant structure and surface tension of the diluted emulsion. The results showed that the emulsions (EL-40 + EL-20) and (OPP + EL-20) had relatively high stability. Subsequently, the surfactants polyoxyethylene-polyoxypropylene-styrenated phenol ether (1601), polyalkoxylated butyl ether (LQ) and OPP were added separately to the emulsions (EL-40 + EL-20), (602 + EL-20) or (OPP + EL-20) to obtain the ternary surfactant systems. Emulsion stability was further investigated and discussed based on droplet size, zeta potential and surface tension. The results revealed that the addition of OPP and LQ could further improve the stability of (EL-40 + EL-20) emulsions, and that LQ was also beneficial for the stability of (OPP + EL-20) emulsions. The stability mechanism of the emulsion was also discussed.

Corn cob and tea leaves waste are used as raw materials for condensed phenolic structures. In this study phenolics were extracted from these waste materials, characterized, and modified to obtain surface active materials. The phenolic structures of corn cob were HGS-type lignin with 10% by mass of initial dry weight, while of tea waste were condensed tannin with catechin-like fragments with 15% by mass. Hydroxymethylation reactions were carried out to increase the reactive sites and also the water solubility. The phenolics of the corn cob were hydroxymethylated to a higher rate than the phenolics of the tea leaves waste (85 vs. 48%). Subsequent modification with maleic anhydride was carried out at a rate of about 40% for both types. Visual determinations indicated that all the materials obtained behaved like non-ionic surfactants. However, sulfonation of tannin structure (at a rate of 40%) resulted in an anionic surfactant structure, as expected.