Volume 51, Issue 5

Newly series of Gemini surfactants have emerged which are composed of two hydrophobic tails and two cationic head groups linked by spacer group. Today, these cationic Gemini surfactants are attracting attention of the researchers as these surfactants are more efficient in lowering surface tension as the conventional ones. Cationic Gemini surfactants have lower critical micelle concentrations (CMC) and higher surface tension reduction as compared to those of corresponding monoalkyl ammonium salts. They have wide industrial and household applications. They can be used as emulsifiers, dispersing and anti-foaming agents etc. Cationic Gemini surfactants show good antimicrobial activity against gram-positive and gram-negative bacteria. Antimicrobial activity has also been studied against fungi and yeast species. These cationic Gemini surfactants can be used as antibacterial, antifungal, antiviral agents. This review paper deals with synthesis, antimicrobial activity, methods for determining antimicrobial activity (MIC means minimum inhibitory concentration) and applications of cationic Gemini surfactants.

The importances of bio-surfactants in industrial applications are huge due to their biodegradable and eco-friendly nature. Bio-surfactants mostly find application in cosmetics and health care products. Moreover, bio-surfactants like sophorolipids (SL) also exhibit antimicrobial and skin healing properties. The current studies involve production of SL using low cost substrates like glycerol (15%) instead of glucose (10%) with non-traditional oils (10%) such as jatropha oil, karanja oil and neem oil by using Starmerella bombicola (ATCC 22214). Neem oil gave lower yield i.e. (1.42 g/L) of SL as compared to jatropha oil (4.74 g/L) and karanja oil (5.91 g/L) with glycerol as substrate. Some pretreatment given to crude neem oil like oil refining and ethanol washing with glycerol helps in improved cell growth and SL yield i.e. 2.73 g/L and 3.82 g/L respectively. The comparison thin layer chromatography (TLC), Fourier Transform infrared spectra (FTIR), high performance liquid chromatography (HPLC), liquid chromatography mass spectra (LC-MS) and proton nuclear magnetic resonance spectroscopy ( 1 H NMR) of SL produced on non-traditional oils with glycerol were carried out with that of SL produced on non-traditional oils with glucose. The surfactant properties of sodium lauryl sulphate (SLS) such as surface tension, interfacial tension, stabilization of foam, emulsification, and wetting were improved when SLS was replaced at different concentration of SL.

This paper evaluates the effect of additives (NaCl and ethanol) on the solution properties of rhamnolipids. The properties are the surface activity, aggregate formations and emulsifying activity as well as the synergistic effects of additives and pH variations on the physical properties of rhamnolipids. Additionally, analysis of fatty acids and rhamnolipid homologues produced using different carbon sources was performed by mass spectrometry. The results indicate that this biosurfactant maintain its properties in the presence of additives. NaCl decreases the size and number of aggregates formed in solutions without pH control, while ethanol to rhamnolipid solutions reduces critical micelle concentration and favors aggregation of monomers. The profiles of fatty acids produced by P. aeruginosa LBI 2A1 varied according to the carbon source used, however for rhamnolipids there was no difference.

The potential of using the biosurfactant surfactin to remove adsorbed metal ions from sand surfaces with continuous flushing approaches was evaluated. With the surfactin solution flushing approach, low removal efficiency of 2–15% for copper ions was detected due to the contact of surfactin with copper ions occurring mainly in the inter-particle pore region. The channeling effect also contributed to the low removal efficiency. By incorporating foam in the flushing operation, the contact of surfactin with copper ions was enhanced due to reduced channeling effect. More copper ions with outer-sphere interaction type were thus available and the removal efficiency was increased. Increasing the surfactin concentration could increase the dynamic foaming capacity and lead to improved removal efficiency of 40%. The results demonstrated that the foam-enhanced solution flushing approach was efficient with a low usage of surfactin.

Novel switchable gemini imidazolium surfactants with different carbon atoms in hydrophobic group were successfully synthesized by condensation of fatty acid with triethylene tetramine, then the intermediates were reacted with CO 2 to give the imidazolinium bicarbonates. The structures of intermediates and products were identified by IR and 1 H-NMR spectra. As the results show, the structures of the products obtained correspond to the target compounds designed. By surface tension measurements, these Gemini surfactants have excellent surface activity with low cmc and surface tension. The conductivity and surface tension cycles show that these surfactants could be switched from imidazoline (neutral form) to imidazolium bicarbonate (charged form) reversibly and repeatedly.

The phase behavior and solubilization of two microemulsion systems 1-alkyl-3-methylimidazolium bromide (C n mimBr, n = 12,14,16)/butyric acid/hexane/brine (5% NaCl) and C n mimBr/1-butanol/hexane/brine (5% NaCl) were studied and compared. The physico-chemical parameters, such as the solubility (∊ B ) of the cosurfactant, the mass fraction of the cosurfactant in the interfacial layer ( A S ), and the solubilization ability ( SP *) of the two microemulsion systems were calculated and discussed. As the carbon chain length of C n mimBr molecules increases, SP * increases, and the difference of SP * values between the two microemulsion systems is reduced. The effects of aqueous and oleic phases and temperatures on the phase behavior and solubilization of C 14 mimBr/butyric acid/alkane/aqueous phase microemulsion systems were also discussed.

Three polysiloxane bola surfactants containing carbohydrate (ATPS-LA) were synthesized using a two-step method. Structure characterization was performed by infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy ( 1 H NMR). Their surface activities and aggregation properties in aqueous solution were investigated by surface tension measurements and transmission electron microscopy (TEM). The results indicated that these three surfactants have much higher surface activity than those of conventional hydrocarbon bola surfactants, such as sodium eicosanedioate, in aqueous solution, and they can self-assemble into spherical micelles with average diameters in the range from 100 to 600 nm.

To improve the hydrolysis resistant ability (HRA) of ionic trisiloxane surfactants, three novel ionic twin-tail trisiloxane surfactants have been synthesized. Their formulas are of (R) 2 N + (CH 3 ) 2 I − ( A ), (R) 2 N(CH 2 ) 3 SO 3 − Na + ( B ) and (R) 2 N + (I) − (CH 3 )(CH 2 ) 3 SO 3 − Na + ( C ) [R = Me 3 SiOSiMe(CH 2 ) 3 OSiMe 3 ], respectively. Their structures were characterized by ESI-MS, 1 H-NMR and 13 C-NMR spectroscopy. The surface activity and hydrolysis resistance of the synthesized ionic twin-tail trisiloxane surfactants are significantly better than that of the ionic single-tail analogue surfactants. The critical aggregation concentration (CAC) values of these ionic twin-tail trisiloxane surfactants are at levels of 10 −6 ∼10 −5 mol L −1 and the surface tension (γ) values of their aqueous solutions at CAC are below 21.0 mN m −1 . The γ values of the aqueous solutions of anionic trisiloxane surfactant B and zwitterionic trisiloxane surfactant C are still less than 21 mN m −1 after having been placed in alkaline environment (pH 10.0) for 29 days. However, the spreading ability (SA) of their aqueous solutions on low-energy solid surfaces is not as good as that of the nonionic twin-tail trisiloxane surfactants previously prepared by us. By weight loss methods the cationic trisiloxane surfactant A was confirmed to be able to use as a corrosion inhibitor. The structure and surface area per molecule (a s m ) of zwitterionic surfactant C were also discussed.

Novel glucose-based non-ionic gemini surfactants consisting of two sugar head groups, two hydrophobic tails having chain length of C 8 , C 10 , C 12 , C 14 , C 16 , C 18 and –CH 2 -C 6 H 4 -CH 2 – as a rigid spacer were synthesized and investigated for their micellar encapsulation properties. The head groups of the geminis consist of glucose entities (with reducing function blocked in cyclic acetal group) connected through C-6 to tertiary amines. These surfactants were explored for micellar encapsulation of some polynuclear aromatic hydrocarbons (PAHs) viz. fluorene, anthracene, triptycene and pyrene in 20% ethanol–water mixture. Micellar studies revealed that PAHs were encapsulated in the sequence fluorene > anthracene > triptycene > pyrene and the better efficiency of gemini surfactant was dependent on longer alkyl tail but lesser HLB value.

Non-ionic surfactants (NS) are a major source of synthetic organic carbon discharged into surface water. The aim of this work was the investigation of the influence of different factors on NS removal in an activated sludge sewage treatment plant (STP). Tensammetric analytical tools were used for fast and inexpensive NS determination. The STP in Blonie (Poland) was the subject of research. The STP's reconstruction caused a spectacular lowering of NS concentration in the treated sewage; however, in subsequent years, NS concentration significantly rose, due to a dramatic increase in the NS load. The NS load reduction in the reconstructed STP was relatively high (93.4–97.9%). The presence of exclusively alcohol ethoxylates was confirmed in the raw sewage. The residual NS concentration in treated sewage is dependent on the hydraulic retention time, the NS load and on the sludge volume index.

Bleached cotton and polyester/cotton blend fabrics were laundered at 60°C and 90°C with standard ECE detergent with addition of selected fluorescent compounds through 10 cycles. As fluorescent whitening agents for cellulosic materials are most often used in detergents, two types of these were selected – stilbene and biphenyl. UV absorber, a stilbene derivative, as a separate type of fluorescent compounds, was added on its own and in a combination with both types of fluorescent whitening agents. After each laundering cycle cotton and PES/cotton blend fabrics were exposed to artificial light for 60 and 180 minutes. Obtained optical and protective effects were monitored through whiteness degree, remission and Ultraviolet Protection Factor (UPF). Optical effects of cotton fabrics laundered in a detergent containing fluorescent whitening agents of stilbene and biphenyl type exhibit considerable sensitivity to light. It was not found that irradiation reduces the UPF meaning that even decomposition products of fluorescent compounds, created by irradiation, absorb UV radiation as well.

The current EN 50242/EN 60436:2008 tests the performance of electric household dishwashers by using soiled dishes persistently dried in a thermal cabinet. Assuming the conditions of soiling load and persistence of the soiling as representative for consumer behaviour may be challenged. The difficulty in laboratory testing is to simulate usage behaviour under restrictions of limited time and personnel conditions. The task was to verify if the thermal drying of dishes in a thermal cabinet is able to mimic the typical air drying of dishes in consumer households. Experiments were conducted comparing the cleaning performance of a dishwasher load after air drying the soiled dishes in controlled ambient conditions to the cleaning performance of a dishwasher load after a thermal drying process in a thermal cabinet. Results show that thermal drying is able to display dishwashing frequencies for 91.6% of German households.