Volume 49, Issue 3

A considerable number of biosurfactants have been investigated for their antibacterial, antifungal or antiviral activity that is mostly based on the ability to destroy microbial cell membranes. In addition, some of them are also able to inhibit the adhesion of microorganisms to surfaces and tissues. Although these antimicrobial properties can be generally explained by a strong detergency effect, there are further mechanisms, such as the interaction with membrane phospholipids or the alteration of the electrical conductance of membranes, resulting in the damage of microbial cells. Typically, antimicrobially active biosurfactants are glycolipids (e.g. rhamnolipids) or cyclic lipopeptides (e.g. Polymyxin). Since most of these substances were not available in larger quantities in the past, their potential applications in cleaners and cosmetics was not studied intensely, however, their versatility and the possibility of combining different properties, such as cleaning and antimicrobial effects, suggest a further consideration of biosurfactants even for mass-market products.

This review article will give a broad overview of the synthesized and characterised surfactants within the competence centre SNAP (Centre for Surfactants Based on Natural Products). The surfactants differ within their hydrophilic groups, hydrophobic groups as well as the linkage between these groups. The main focus was put on sugar-based surfactants and surfactants containing polyhydroxyl groups so this part will be the most extensive in the review. Interactions between surfactants and polymers have also been investigated and will be described in the final part of the review. SNAP resulted in the publication of 239 scientific articles and 22 PhD degrees.

A series of catanionic surfactants based on the general formula CH 3 CH 2 (CH 2 ) 11 CH 2 N + (CH 3 ) 3 · − OOCCH 2 (CH 2 ) n CH 2 CH 3 (n = 2, 4, 6, 8, 10) were synthesized, and measured their critical micelle concentrations (CMC) and the corresponding surface tension at CMC (γCMC). The results revealed that the surface tensions of water were decreased to 21–34 mN · m −1 when applying these surfactants at a concentration range from 10 −3 to 10 −4 mol · L −1 . Moreover, the performance of foaming, emulsification, anti-static and rewetting of the surfactants were investigated and the results showed that both the rewetting and emulsifying ability of the prepared surfactants were much better than that of conventional surfactants. In addition, the anti-static and foaming properties were also improved at the same condition compared to that of conventional surfactants.

A novel environmentally friendly type of calcium carbonate and iron(III) scale inhibitor (ALn) was synthesized. The anti-scale property of the Acrylic acid-allylpolyethoxy carboxylate copolymer (AA-APELn or ALn) towards CaCO 3 and iron(III) in the artificial cooling water was studied through static scale inhibition tests. The observation shows that both calcium carbonate and iron(III) inhibition increase with increasing the degree of polymerization of ALn from 5 to 15, and the dosage of ALn plays an important role on calcium carbonate and iron(III)-inhibition. The effect on formation of CaCO 3 was investigated with a combination of scanning electronic microscopy (SEM), Transmission electron microscopy (TEM), X-ray powder diffraction (XRD) analysis and Fourier transform infrared spectrometer, respectively. The results showed that the ALn copolymer not only influences calcium carbonate crystal morphology and crystal size but also the crystallinity. The crystallization of CaCO 3 in the absence of inhibitor was rhombohedral calcite crystal, whereas a mixture of calcite with vaterite crystals was found in the presence of the ALn copolymer. Inhibition mechanism is proposed that the interactions between calcium or iron ions and polyethylene glycol (PEG) are the fundamental impetus to restrain the formation of the scale in cooling water systems.

Phase diagram of poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) copolymer (AL-64) and nonionic surfactant dodecyl polyoxyethylene (23) ether (Brij 35) aqueous solutions has been determined at 25°C using the titration method. Hexagonal, cubic and two lamellar liquid crystalline phases were found and characterized by use of polar optical microscopy and small-angle X-ray scattering (SAXS) techniques. Dynamic rheological measurements were further performed on the found liquid crystals. It has been shown that the cubic and lamellar phases exhibit elastic properties, while the hexagonal phase presents viscoelastic properties. At the constant water content, with increase in the concentration of the copolymer AL-64, the rheological G′ and G″ moduli, the critical shear stress and the network strength of the hexagonal liquid crystals get decreased. The two lamellar phases exhibit clearly different rheological properties, and the lamellar phase lies in Brij35 rich side possess stronger network strength than the hexagonal phase, through the rheological data analyses.

Conductivities of alkyl trimethyl ammonium bromides (alkyl = hexyl-, octyl-, decyl-, dodecyl-, tetradecyl-, hexadecyl-, and octadecyl-) in aqueous solutions were measured as afunction of molarity of surfactants, length of chain and temperature. Critical micelle concentrations (CMC) were estimated from the dependence of the specific conductivity on molarity of the surfactants. It was determined that the temperature dependence of CMC is U-shaped with aminimum shifting toward higher temperatures with decreasing chain length of the alkyl group. Quantities characterizing behaviors of surfactants below and above CMC were calculated and compared from conductivity measurements. Measured and calculated values of studied compounds were also compared with results of many other authors. The paper has the form of a minireview. It is a comparison of the presented experimental data of alkyltrimethylammonium bromides (C6–C18) with earlier works reported.

Ionic liquids like 1-butyl-3-methylimidazolium chloride ([BMIM] Cl, 1-butyl-3-methyl-imidazolium hexafluorophosphate [BMIM] PF 6 , 1-butyl-3-methyl-imidazolium tetrafluorobrate [BMIM] BF 4 , 1-butyl-3-methyl-imidazolium bis (trifluoromethylsulfonyl) imide [BMIM] NTf 2 ) were used as doping elements in polyaniline. Pure polyaniline (EB) and polyaniline doped with different anions of ionic liquids (ESs) were chemically synthesized using ammonium peroxydisulphate (APS) and ionic liquids as oxidants. Junctions have been prepared by evaporating chalcogenide materials (ZnSe, CdSe) on conducting polyaniline (EB & ESs) pellets using a vacuum evaporation technique. I-V characteristics of junctions have been studied at room temperature using the Keithley electrometer 6517A. I-V measurements show the rectification effect. A junction of ES [BF 4 − ] anion may be preferred over the other junctions due to its low ideality factor and maximum rectification ratio.

Bitumen emulsions are preferred over conventional pavement systems due to their biologically and environmentally acceptable formulation, safety, low viscosity, storage stability, and cost effectiveness. The present investigation deals with the systematic study to synthesize ortho-cocodi-amido toluene and four quaternary derivatives by amidation of coconut oil and ortho toluene diamine (OTD), followed by quaternization with formaldehyde, formic acid mixture, and acrylonitrile, resulted in a new quaternary compound useful as cationic emulsifier in bitumen emulsions. The roles of temperature and reaction time in determining optimum conditions were investigated as well. Emulsifying behavior of these quaternary compounds was studied by sieve residue test, settlement and storage stability test of emulsified asphalt, and water solubility. The results show that the acrylonitrile imidazolinium derivative of o-cocodi-amido toluene (VI) can be used as a rapid-medium setting emulsifier.

Three series of Guerbet betaine surfactants with ethylene oxide groups were synthesized by Guerbet alkyl polyoxyethylene ether surfactants, epichlorohydrin, dimethylamine and sodium chloro-acetate. Their structures were confirmed by MS. The critical micelle concentrations (CMC) and surface tension at CMC (γ CMC ) of all prepared Guerbet betaine surfactants were determined by K100C processor tensiometer with the Wilhelmy-plate method at 25°C. It is found that synthesized surfactants exhibit great efficiency of reducing surface tension. As the number of ethylene oxide groups increases, the γ CMC gradually increases. As the length of the hydrophobic chain of Guerbet betaine surfactants increases, the γ CMC increases firstly and then decreases.

The research topics of our group are in general from the field of physical chemistry of colloidal systems. Within this rather wide layout a large variety of quite different questions and systems are tackled, where the common bridging factor is the aim of understanding the properties of colloidal systems based on their mesoscopic structure and dynamics, which in turn are controlled by their molecular composition. With such an enhanced understanding of the correlation between mesoscopic structure and the macroscopic properties the goal then is to employ this knowledge in order to formulate increasingly complex colloidal system with correspondingly more variable and interesting functionalities. From this general context of investigations, some representative systems and questions that have been studied in recent time by us are covered in this text. They comprise the phase behaviour and the structures formed in solutions of surfactants and amphiphilic copolymers. Once these static properties are known, we also have a high interest in the dynamic properties and the kinetics of morphological transitions as they are observed under non-equilibrium conditions, since they are frequently encountered in applications. A key property of amphiphilic molecules is their ability to solubilise sparingly soluble compounds thereby forming microemulsions or nanoemulsions, where the ability to form such systems depends strongly on the molecular architecture of the amphiphiles. By turning to polymeric amphiphiles the concept of surfactants and their architecture can be extended largely towards more versatile structures, more complex self-assembly and much larger length and time scales. Another direction is the surfactant assisted formation of nanoparticles or mesoporous inorganic materials. By combining copolymers with other polymers, copolymers, colloids, or surfactants – for instance via electrostatically driven co-assembly – one may then form increasingly complex colloidal aggregates. By doing so one is able to control rheological properties or develop complex delivery systems, whose properties can be tailor-made by appropriate choice of the molecular build-up. This striving towards well controlled complexity achieved by means of self- and co-assembly then leads to increasingly more functional systems and is the key direction for future research activities in our group.