Volume 48, Issue 3

Surfactants form a unique class of compounds that are used in a variety of applications including laundry detergents, dish washing liquids, agrochemicals, pharmaceuticals, petroleum processing, mineral ores, personal care, floor cleaners, paints, coatings, fuel additives, and photographic films. In the present work a variety of surfactants containing different functional groups (i.e., anionic, non-ionic, amphoteric, cationic) has been used to study their influence on the performance of polymeric iron oxide dispersants. Effects of dispersant dosage, time, and polymer architecture have been investigated. The polymers tested include homopolymers of acrylic acid, maleic acid, methacrylic acid, 2-acrylamido-2-methylpropane sulfonic, 2-ethyloxazoline, and acrylic acid, maleic acid based copolymers containing different functional groups. It has been found that polymer performance as dispersant depends on dosage and polymer architecture. Results on the evaluation of surfactants suggest that compared to polymers, surfactants are ineffective iron oxide dispersants. Results on the impact of cationic surfactant (e.g., cetyltrimethyl ammonium chloride, CTAC) suggest that CTAC exhibits an antagonistic effect on the performance of polymers. It has also been found that cationic polymer (e.g., polydiallyldimethyl ammonium chloride) shows much stronger antagonistic effect than CTAC on the efficacy of polymers used as iron oxide dispersants in industrial water systems. The antagonistic behavior shown by cationic surfactant and cationic polymer on the performance of polymers has been explained in terms of cationic – anionic interactions.

CdS nanorods have been successfully synthesized by using different surfactants such as cetyltrimethyl ammonium bromide (CTAB), sodium dodecyl sulphate (SDS), and poly ethylene glycol (PEG) via hydrothermal method. The products were characterized by means of powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM). The influences of surfactants on the morphologies of CdS nanorods are discussed.

The degradation in aqueous solution of nonionic surfactant, nonylphenyl poly(oxyethylene)ethers (NPE-10), which was photocatalyzed by Au/TiO 2 nanoparticles has been studied. The particles were obtained using modified deposition-precipitation with Urea (DP Urea). The Taguchi method was implemented successfully to optimize the photoactivity for Au/TiO 2 photocatalyst. The optimized catalyst was characterized by XRD, BET, TEM, XPS and UV-visible absorption spectra techniques. It was found that Au 3+ /Ti 4+ molar ratio was the main parameter having significant effect on photocatalytic activity. Under optimal conditions, the observed Au nano-particle size and distributions indicate, that smaller gold nanoparticles (∼1.8 nm diameter) were obtained, and the existing of Au particles promote the photoadsorption of oxygen on the surface of photocatalysts. Both are responsible for the significantly enhanced catalytic activity of commercial TiO 2 (pure P-25) toward the photodegradation of NPE-10-probably by increasing the rate of production of separated electrons and holes.

Disk-like and flower-like ZnO nanostructures were prepared in alcoholic solutions with SDS-free and various sodium dodecyl sulfate (SDS) concentrations by a non-basic solution method. In all cases, the obtained crystals exhibited the crystal structure of wurtzite ZnO and photoluminescence at UV and green regions. The ZnO grown in the SDS solution have a morphology of aggregated disk-like and flower-like structures. The origin of morphology different of the ZnO crystals is explained by a chemical interaction between surface of ZnO seed crystal and SDS micelles.

During the annually arranged Action Day Sustainable Washing on May 10 th , 5284 questionnaires about laundry treatment were collected from private people in Germany with the aim of obtaining information about consumer behaviour and attitudes towards sustainability. This is a non-representative census as only 15% of all respondents were male. Nevertheless, relative distribution and correlation provide a relevant insight into consumers’ behaviour towards washing, drying and ironing. The most important results of the analysis can be summed up as follows: – Nearly 50% of the respondents own a laundry-dryer. – Nearly one third of all respondents never use fabric softeners. The prevention of ecological damage was the reason for not using fabric softeners for 30% of the respondents. – About one fourth of all respondents always use fabric softeners, with younger people having a significantly higher attitude towards using them. – Under good weather conditions, about 90% of the respondents choose energy-saving alternatives to dry their laundry. – The average weekly time spent on ironing is about two hours on average of all respondents who gave information. The analysis shows that laundry treatment beyond the pure washing process is a multi-faceted process with several starting points of improvement in favour of sustainable handling.

Vesicles can be found in many applications like drug delivery or as models for cell membranes. It is often necessary to produce vesicles which are easy to adjust in size and which can be filled with different types of ingredients. In this publication we used phase transfer techniques in to form well defined vesicles. The synthesis of these particles occurred in three different steps. First, a water phase was covered by an oil phase containing surfactants. A water-in-oil emulsion was then added to the oil phase. In the third step the phase transfer was stimulated by sedimentation or centrifugation processes. In a series of experiments we measured the vesicle sizes and encapsulation efficiencies. Giant vesicles, formed by sedimentation processes had typical sizes between 1–10 μm. Smaller vesicles between 100–500 nm were observed after centrifugation processes. With both methods we could produce vesicles with encapsulation amounts about 10%.

Surfactants have been widely used as auxiliaries in many areas of textile finishing. The nature of the interactions between dyes and surfactants is one of the basic piece of information for understanding the process of dyeing and finishing of textile material. The role of attractive interactions between the hydrocarbon tails and repulsive interactions between the surfactant head groups on the micellar association process have been studied. The presented work is oriented on the determination of the critical micelle concentration and molar conductance, in aqueous solution of cationic surfactant cetyltrimethyl ammonium bromide by using the electric conductivity method. From conductivity data parameters for dyes – surfactant interaction such as micellar ionization degree α, counter ion binding and free energy of micellization have been calculated. On the basis of results it is clear that critical micelle concentration depends on the nature of ionic group and concentration of counter ion in solution.

The effect of electrolytes on the interaction between the anionic dye C.I. Reactive Orange 16 and the cationic surfactant dodecylpyridinium chloride was investigated using surface tension measurement in a certain concentration range. The influence of the concentration of electrolyte on critical micelle concentration (CMC) values was observed in the following order; 0.1 M NaCl > 0.5 M NaCl > 1.0 M NaCl. Also, the influence of the electrolyte cations was observed as Na + > Mg 2+ > K + . An increase on CMC values of dye-surfactant solution with increasing electrolyte concentration is explained as charge screening and also the decrease in these values for higher concentration of electrolyte is attributed to the change of micelle shape. Furthermore this change is due to ionic polarizability, valency and hydrated radius. Using Rubingh's regular solution theory, the values of micellar interaction parameters (β), were found as negative in all studied mixtures.

A series of bis-diquaternary ammonium salts (cationic Gemini surfactants) with different length in spacer were prepared and characterized. The surface properties such as the critical micelle concentration CMC, minimum surface tension γ CMC , effectiveness of the surface tension reduction π CMC , maximum surface excess Γ max and surface area per molecule A min have been determined by means of surface tension measurements. As expected, these surfactants have good surface activities than those conventional monomeric ones (dodecyl trimethyl ammonium chloride (DTAC)) and the spacer plays an important role in the surface properties. Under experimental conditions, surface parameters decreases with the increase of carbon number of the spacer the except analogue with a benzene ring due to its inflexibility. The aggregation ability of some practically used reactive azodyes (C.I. Reactive Red 198) in aqueous solutions and the prepared surfactants was investigated using UV-visible spectroscopic methods. The spectroscopic studies were extended in order to determine the effect of molecular structure of the surfactants on the aggregative properties of C.I. Reactive Red 198 (RR 198). The aggregation behaviour of the RR 198 in solutions and in the presence of additives is related to their apparent deviations from Beer's law and aggregation number (N). The aggregation constant (K n ) of the monomer/dimer equilibrium was calculated. The aggregate structures and the nature of the interacting pairs in this dye were discussed using Kasha exciton theory.

The research work carried out in our group can be referred to as “Colloid and Interfacial Chemistry”. We subdivide this rather broad research area into four main topics which are covered by the projects presented in this overview. The surfaces we study are surfactant-loaden water-air surfaces, the films are mainly free-standing thin foam films of less than 100 nm thickness, and the foams are 3D aqueous foams whose stability and drainage we investigate. As regards the topic “Complex Fluids” we study lyotropic liquid crystalline phases and microemulsions. In the past, we were able to establish two new tuning parameters for the formation and destruction of lyotropic liquid crystals, while current research focuses on the lyotropic mesomorphism of new surfactants and of surfactant mixtures. Apart from lyotropic liquid crystals microemulsions are a central theme in the group. Due to their unique properties and fascinating structure variety microemulsions offer a great potential as templates for the synthesis of new functional materials, which is a further research topic in our group. These studies involve the gelation of and the polymerisation in microemulsions preserving their nanostructure to create high surface area polymers. Currently, we also use microemulsions as tailor-made nano-compartmented reaction media. The studied reactions are either enzyme-catalysed conversions of substrates or the reduction of metal salts to synthesize mono- or bimetallic nanoparticles. In this context we focus on bicontinuous and water-in-oil droplet microemulsions. Last but not least we also synthesize new surfactant structures such as inositol-based surfactants and explore the properties.