Du Nouy Ring Method Research Articles

Antimicrobial and aggregation properties of asymmetric gemini surfactants based on 1-(2-hydroxypropyl)-4-ethyl piperazine and alkyl bromides

Asymmetric gemini surfactants were synthesized by the quaternization reaction of 1-(2-hydroxypropyl)-4-ethyl piperazine with (C9, C10, C12, and C14) alkyl bromides. The surface tension of their aqueous solutions was determined by the Du Nouy ring method and the conductometric method of specific electrical conductivity. According to the concentration dependence graphs of surface tension and specific electrical conductivity, critical micelle concentration – CMC, degree of association of the counterion – β, surface area occupied by the head group of the surfactant – Amin, maximum surface excess concentration – Γmax, effectiveness or surface pressure –πCMC, adsorption efficiency – pC20 were calculated, and the change of these parameters depending on the length of the alkyl chain was determined. Simultaneously, variations in Gibbs free energies of micellization and adsorption processes were computed. The diameters of aggregates formed by asymmetric gemini surfactants in water were determined by the DLS method. Antimicrobial abilities of asymmetric gemini surfactants against gram positive and gram negative bacteria and fungi were defined by the disk diffusion method.

New surfactants based on soybean oil triglycerides, hexamethylenediamine and alkyl dihalides

The interaction of soybean oil triglycerides with hexamethylenediamine resulted in a nonionic surfactant – hexamethyleneamide of a mixture of soybean oil acids, which was then modified using alkyl dihalides (1,2-dibromoethane, 1,3-dibromopropane, and 1,5-dibromopentane). These reactions synthesized ionic surfactants. The composition and structure of the resulting amidoamine and its modifications with alkyl dihalides were identified using infrared spectroscopy. The obtained products were characterized by key physicochemical parameters. Conductometric measurements of aqueous solutions of the obtained salts with varying concentrations were also performed. It was found that with increasing concentration, the specific conductivity value increases, and these values are significantly higher than the specific conductivity of distilled water, indicating the ionic structure of the obtained substances. Surface activity was measured with a tensiometer using the Du Nouy ring method at the air-water interface. According to the determined surface tension values, surface tension isotherms were constructed. The stabilization of surface tension values for the nonionic surfactant occurs at 35.2 mN/m, while for the ionic surfactants, it occurs at values of 34.2, 34.0, and 33.2 mN/m, respectively. The colloid-chemical properties of the synthesized surfactants were studied, their adsorption characteristics were experimentally determined, and the most important colloid-chemical parameters were calculated, such as the critical micelle concentration, surface tension, maximum adsorption, minimum cross-sectional area of the molecule, surface pressure, adsorption efficiency, and the change in Gibbs free energy of the micellization and adsorption processes. Under laboratory conditions, the relative oil-collecting and oil-dispersing abilities of the obtained products were investigated using thin films (thickness <1 mm) of Balakhani oil on the water surface with different levels of salinity (seawater, freshwater, and distilled water). The synthesized surfactants were used in undiluted form and as 5% aqueous solutions. It was found that in seawater, the maximum oil dispersion coefficient, which indicates the degree of cleaning the water surface, is 91.1%. It is worth noting that transitioning from nonionic to ionic surfactants increases the duration of the reagents’ action.

Polymer-Coated Nanoparticles and Pickering Emulsions as Agents for Enhanced Oil Recovery: Basic Studies Using a Porous Medium Model

Globally the overall oil recovery factors for primary and secondary recovery range from 35% to 45%, and a tertiary recovery method that can enhance the recovery factor by 10–30% could contribute to the energy supply. The use of nanoparticles in enhanced oil recovery (EOR) processes comprises an emerging and well-promising approach. Polymer-coated nanoparticles (PNPs) were synthesized through the free radical polymerization (FRP) of the monomers 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and dodecyl methacrylate (DMA) on the surface of acrylic-modified spherical silica nanoparticles. The obtained PNPs were characterized using Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and thermogravimetric analysis (TGA). Dispersions of PNPs were prepared in salt (NaCl, CaCl2) aqueous solutions, the static oil/water interfacial tension were measured using the Du Nouy ring method, and changes caused based on the oil/water contact angle were recorded optically. The PNP dispersions were used to stabilize and characterize shear-thinning oil-in-water Pickering emulsions. The capacity of the PNP dispersions and Pickering emulsions to mobilize the trapped ganglia of viscous paraffin oil, which remained after successive tests of drainage and primary imbibition, was tested with visualization experiments of the secondary imbibition in a transparent glass-etched pore network. The synthesized SiO2-P(AMPSA-co-DMA) nanoparticles were stable even at high temperatures (~200–250 °C) and displayed excellent stability in aqueous dispersions at high ionic strengths with the presence of divalent cations, and their dispersions generated stable oil-in-water Pickering emulsions with a shear-thinning viscosity. The oil-recovery efficiency is maximized when the most viscous Pickering emulsion is selected, but if energy cost factors are also taken into account, then the less viscous Pickering emulsion is preferable.

Synthesis of Cationic Surfactant N, N-(2-Laurate-Ethyl) Stearamidium Chloride

The cationic surfactant of N, N-(2-Lauric-Ethyl) Stearamidium Chloride had been successfully synthesized. It is long-chain alkyl surfactant derivative from ammonium salt with amide. Cationic surfactants that are synthesized from fatty acid derivatives are stearic acid and lauric acid. Stearic acid is used as stearamide-making material which is the product of methyl stearate amidation with diethanolamine use methoxide sodium catalyst. Lauric acid was used as esterification material with stearamide thus obtaining N, N-(2-Lauric-Ethyl) Stearamide of alcanolamide ester. Alcanolamide ester continued by salting reaction use HCl gas until obtained cationic surfactant of N, N-(2-Lauric-Ethyl) Stearimidium Chloride. Each compound analyzed function groups by FT-IR spectrophotometric with the analyzed change of melting points, and a part compound analyzed surface tension characteristic with measuring Critical Micelle Concentration (CMC) with use Du Nouy ring method. The analysis product obtained shows that methyl stearate by yield in the amount of 91.66% shows that melting point of 40.5°C, stearamide with yield in the amount of 87.6% show that melting point as 185°C by CMC value 0.133 mol/ L in 40.7 dyne/cm surface tension. Alcanolamide ester with a yield in the amount of 84.7% has a melting point of 55°C by a CMC value of 0.067 mol/L in 36.1 dyne/cm surface tension, and cationic surfactant has a melting point of 45°C by CMC value 0.055 mol/L in 31,1 dyne/cm surface tension. stearamide with a yield in the amount of 87.6% show that melting point of 185°C by a CMC value of 0.133 mol/L in 40.7 dyne/cm surface tension. Alcanolamide ester with a yield in the amount of 84.7% has a melting point of 55°C by a CMC value of 0.067 mol/L in 36.1 dyne/cm surface tension, and cationic surfactant has melting point as 45°C by CMC value 0.055 mol/L in 31,1 dyne/cm surface tension. stearamide with a yield in the amount of 87.6% show that melting point of 185°C by a CMC value of 0.133 mol/L in 40.7 dyne/cm surface tension. Alcanolamide ester with a yield in the amount of 84.7% has a melting point of 55°C by a CMC value of 0.067 mol/L in 36.1 dyne/cm surface tension, and cationic surfactant has a melting point of 45°C by CMC value 0.055 mol/L in 31,1 dyne/cm surface tension.

Enhancing the physical properties of polystyrene nanofibers by adding multiwall carbon nanotubes and natural dye

Polymeric nanocomposites of polystyrene nanofibers and multiwall carbon nanotubes and natural pigment were synthesized using electrospinning technique the polystyrene concentration was 12 wt.% and multiwall carbon nanotube was added by (0, 100, 140, 200 ppm), and natural pigment added by two drops (0.063 g) to the prepared solutions and many tests were carried out to the prepared solutions and the final samples. The solution tests included viscosity test by using cone-plate viscometer and surface tension test using du-nouy ring method. The nano textiles tests included the Fourier transform infrared spectroscope (FTIR) test, Field emission scanning electron microscopy (FESEM) test, contact angle test, and ultraviolet test to extract the energy bandgap using (tauc plot) method. The tests results showed that the viscosity increased by increasing the multiwall carbon nanotube and natural pigment and surface tension slightly increased at a high ratio of 200 ppm of multiwall carbon nanotube and natural pigment and physical type of reaction between the components were confirmed through FTIR, and the addition of multiwall carbon nanotube and natural pigment makes the fibers smoother and fewer beads formation and increase the multiwall carbon nanotube addition made the samples more hydrophobic and the charts of tauc plot show that increasing the MWCNT with natural pigment addition will increase the electrical sensitivity of the prepared samples in which the energy band gap dropped from 1.18 ev to 0.2 ev for the sample of Polystyrene/200 ppm MWCNT/natural pigment this is regarded as an indication of using it as a typical electrical sensor.

Biosurfactant Screening of <i>Halomonas meridiana</i> BK-AB4 for Microbial Enhanced Oil Recovery

Biosurfactant is produced by a certain microorganism to reduce surface tension. Microbial enhanced oil recovery (MEOR) is one of the many applications of biosurfactant. However, the biosurfactant for MEOR needs to be able to withstand the extreme environment of oil reservoirs with high temperature and high salinity. Halomonas meridiana BK-AB4 is a halophilic bacterium obtained from the Bledug Kuwu crater in Central Java, Indonesia. The similarity of both environment condition indicates the potential to produce suitable biosurfactant. This study evaluates the potential of Halomonas meridiana BK-AB4 in producing biosurfactant compared to several bacteria isolated from the crater. The blood agar test of Halomonas meridiana BK-AB4 exhibited greenish discoloration around the colony, indicating the ability of type α-hemolysis. The interfacial tension was measured using the Du Nouy ring method to represent the biosurfactant activity, with the results of 0.014 dyne/cm. These results showed that Halomonas meridiana BK-AB4 has a very good potential for producing biosurfactant for MEOR. The optimum time of the culture starter for production is 6 hours, as determined from the bacterial growth curve.

Adsorption properties of rhamnolipid and ethanol at water/ethanol solution-air interface

Abstract The water/ethanol solutions of surfactants and/or their mixtures are very often used in practice. Alcohol changes largely, among others adsorption, aggregation and wetting properties of the surfactants. Therefore, measurements of the surface tension of the water/ethanol solution of rhamnolipid were made. For this purpose the du Nouy ring method was applied. The measured values of the surface tension of rhamnolipid water/ethanol solution were compared to those calculated using the Miller et al., Connors equations as well as independent adsorption method. These results were also analyzed taken into account the contributions of the adsorbed rhamnolipid and ethanol in the mixed film pressure at the water/ethanol solution-air interface. This analysis allowed us to determine the mutual effect of rhamnolipid and ethanol on their adsorption at the solution-air interface. The adsorption of the rhamnolipid and ethanol was discussed on the basis of the Gibbs, Langmuir and Frumkin equations of the adsorption isotherm. The tendency of rhamnolipid and ethanol to adsorb at the solution-air interface was discussed based on the Gibbs free energy of adsorption which was determined using different methods. The obtained results and their analysis show that there is not a synergetic effect in the water surface tension reduction by the ethanol and rhamnolipid mixture adsorption.

Synthesis, colloidal-chemical and petroleum collecting properties of new counterion coupled gemini surfactants based on hexadecylbis(2-hydroxypropyl)amine and dicarboxylic acids

Eight new cocogem surfactants were obtained as a result of the chemical synthesis between hexadecylbis(2-hydroxypropyl)amine and eight different dicarboxylic acids. Solutions of these cocogem surfactants were prepared at the different concentrations and their surface tension values were measured by Du-Nouy ring method to determine the surface active abilities. Electric conductivity measurements were carried out and, by using the obtained values, very important characteristics of the synthesized surfactants were investigated. The parameters which were determined based on these measurements are critical micelle concentration (CMC), counterion binding degree, surface excess, minimum area occupied by one molecule. Moreover, thermodynamic properties such as Gibbs energy of adsorption and micellization were calculated. It became clear that the spacer group in the surfactant chain strongly influences the properties of the surfactants. By changing the type and the length of the spacer chain, the properties also change considerably. The petroleum collecting ability of the synthesized cocogem surfactants were investigated.

Surface tension and interfacial compositions of binary glycerol/alcohol mixtures

The main aim of this research was to study the surface tension and interfacial composition of different binary mixtures of glycerol and alcohols. To achieve this aim, mixtures of glycerol and ethanol, 1-propanol, 2-propanol, and 1-butanol were prepared. By using the Du-Nouy ring method, surface tensions were experimentally measured as a function of composition in the temperature range of (293–333) K. The equality of chemical potentials of components at the surface layer and bulk liquid was considered for simultaneous prediction of surface tension and composition. The model was employed by using different approaches, including an activity based and a fugacity-based method. The UNIFAC activity model and PSRK EOS were used to calculate the activity and fugacity coefficients, respectively. The results of this study showed that the ability of the activity-based approach is limited (overall AADσ = 26.78%) while the fugacity-based method successfully predicted the surface tensions of the studied mixtures (overall AADσ = 1.84%). Our hypothesis is that the fugacity-based method was more accurate because it accounted for the partial molar area of the components.

Physico-chemical evaluation of hydrophobically modified pectin derivatives: Step toward application

Present study reports synthesis and physico-chemical evaluation of hydrophobically modified pectin derivatives, obtained by reacting of pectin with di-acyl chlorides (glutaryl and sebacoyl chloride). Depending on length of the inserted carbon chains, the acylation resulted in possible formation of mono-grafted (isolated chains) and bi-grafted (chemical gels) structures. The structural features of obtained derivatives were investigated using FTIR spectroscopy, confirming the successful synthesis. The concentrated aqueous solutions of modified pectin showed interesting rheological properties, having lower values of apparent viscosity compared to neat pectin. Since the GPC analysis indicated that no degradation occurred, the viscosity decrease was explained by more heterogeneous organization within modified pectin solutions (microparticles together with sticky polymer entanglement). A shift in particle size distribution proved that proposed modifications also affected pectin solution properties in diluted regime. The modified samples turned to be more sensible to thermal degradation than neat pectin, whereby the increasing size of flexible acyl chains attached to a polymer backbone reduced the glass transition temperature. The hydrophobicity of obtained derivatives was evaluated by sessile drop and du Nouy ring methods. It was found that acylation enhanced hydrophobicity of the pectin molecule, while hydrophobically associative character turned to be inconsistent in aqueous and non-aqueous environment.

Experimental densities and surface tension and models generating the best-current-knowledge values of them for members of 1-Cn-3-methylimidazolium bromide homologous series

Abstract Although 1- C n -3-methylimidazolium bromides are used in a variety of applications, their properties are still poorly studied and it is desirable to complete the experimental knowledge of them. This study presents 121 and 208 new experimental data on the density and surface tension, respectively, for [ C 1 IM][Br] and [ C n MIM][Br] with n = 2–10 at temperatures from (288 to 365) K and at the pressure of 0.1 MPa. The reported resultant data are means of sets of individual measurements performed at a given temperature. The density was measured by the buoyancy method and the surface tension concurrently by the Wilhelmy plate and du Nouy ring method. Their respective expanded combined uncertainties at the 0.95 confidence level do not exceed 0.86 kg · m−3 (0.007 ϱ ), 0.08 mN · m−1 and 0.8 mN · m−1. Models are presented generating density and surface tension values that represent the best current knowledge of these properties for the members of the studied homologous series. The estimated maximum deviations of the obtained recommended values from the true density and surface tension values are 0.1 kg · m−3 and 0.4 mN · m−1, respectively.

Characterization of air entraining admixtures in concrete using surface tension measurements

Air entraining admixtures (AEA) are generally used for increasing the workability and resistance to freezing and thawing in concrete. These admixtures generate air bubbles with diameters ranging from 10 μm to 1 mm, providing spaces for the expansion of ice, and therefore facilitate frost protection. In this study, performances of AEAs were investigated based on surface tension measurements, accounting for the effect of AEAs on surface tension. For this purpose, a new test method was developed which depends on surface tension measurements according to the Du Nouy ring method. All types of AEAs used in the scope of this research presented a substantial influence on the surface tension. It was observed that a significant relationship between the air void system and surface tension exists. The surface tension method was found as a useful tool to determine the AEA type and content to obtain the desired air void system in concrete.

Experimental study on surface activity of surfactants on their ability to cleaning oil contaminations

In order to obtain a recipe for an effective degreasing agent, a selection of suitable surfactants is required. The present investigation addresses essentially the determination and comparison of the static and dynamic adsorption as well as wetting properties of selected surfactants and their binary mixtures which are potential components of the degreasing compositions. Equilibrium surface/interfacial tension in the air/water system for individual compounds and their binary mixtures were measured by du Nouy ring method. Moreover, the interfacial properties of binary surfactant mixtures with different polarity were investigated. The experimentally obtained isotherms: surface tension of the air/water systems and interfacial tension of oil/water systems for all investigated surfactants allowed to compare the surface activity of compounds considered. Surface and micellar properties of surfactants and their mixtures were discussed on the basis of equilibrium surface tension measurements and the study of kinetics of adsorption. The Rosen theory was used to characterize the synergism effects observed in the case of systems with binary surfactant mixture. The results indicated that the studied compounds reveal both different efficiency as well as different effectiveness of adsorption in the air/water system. Some of analysed binary surfactant mixtures show strong synergistic effects in lowering the surface tension and in the wettability of solid surfaces. The wetting properties of considered compounds strongly depend on the character of wetting surface. The dynamics of adsorption in considered systems is significantly affected by the concentration of surfactant solution. Generally, the efficiency of lowering surface tension is significantly higher in the micellar solutions. The results obtained allow to select mixture of nonionic surfactant and amphoteric one as potential components of the degreasing compositions.

Tensiometric, IR- and 19f-NMR Analysis of Nafion Solutions for PEMFCs and PEMELs

In the construction of polymer electrolyte membrane fuel cells (PEMFCs) and polymer electrolyte membrane electrolyzers (PEMELs), Nafion® (sulfonated tetrafluorethylene) is used as a membrane material and as proton conductor in the porous catalysts layers of membrane electrode assemblies (MEAs). Efficiency can be increased and costs reduced by optimizing and controlling the porous catalyst layer in MEAs. It is important to understand the polymer properties, which can be achieved by using different solutions and varying concentrations of one mixture for manufacturing the dispersion. Furthermore, the findings are of particular importance for the coating process. The efficiency of the PEMFCs and PEMELs depends on the number of active centers in the porous catalyst layer. The formation of the triple phase boundary is of great importance. This can be ensured by controlling the structural properties of the dispersion. Thereby, the static and dynamic surface tensions are analyzed. Surface tension and interfacial tension are necessary for understanding the coating process and adhesion to a transfer layer. The complex system was simplified and research on the surface properties performed with an aqueous Nafion® solution in an alcohol concentration series. Hence, the only aspect that changed was the alcohol, while the dynamic surface tension was measured with a bubble pressuretensiometer (BP100, KRÜSS GmbH). The static surface tension and interfacial surface tension were carried out with a force tensiometer (K100, KRÜSS GmbH) after Wilhelmy plate respectively the duNouy Ring method. In addition the solution was analyzed by means of IR- and 19F-NMR- spectroscopy. It will be demonstrated in this contribution that the static and dynamic surface tensions differ significantly at lower alcohol concentrations in solution series with and without Nafion®. While at higher alcohol concentrations the static surface tension between both series is similar, the dynamic surface tension shows a different trend with varied bubble age. This can be explained by the interaction between alcohol and Nafion®. In accordance with the previous interface outcomes, the 19F-NMR- and IR- spectra are analyzed. According to the first results, it is also apparent that there are interactions between Nafion® and alcohol. The application of these methods provides an understanding of the interaction between the molecules in the catalyst dispersions. This information is essential for understanding the interactions between the components of catalyst dispersion during electrode manufacturing.

An investigation into the electrical behavior of oil/water/reservoir rock interfaces: The implication for improvement in wettability prediction

Abstract Wettability and contact angle are crucial factors in oil and gas industries. They have essential influences on oil recoveries and fine migration. Therefore, their reliable predictions are of great importance. We have designed a set of experiments to measure different properties of oil/water and sand/water interfaces at different pHs and salinities. Zeta potentials of the both interfaces as well as interfacial tensions of oil/water interface have been measured using electrophoresis and Du Nouy ring methods, respectively, at different aqueous solutions. Disjoining pressure (sum of double layer, van der Waals, and structural forces) between the interfaces was calculated for each aqueous solution. Contact angle and wettability of each aqueous solution were calculated using augmented Laplace–Young equation. Adhesion tests and contact angle measurements were used to check the validity of the results. Comparing experimental and predicted values indicated the poor capability of simple DLVO model in prediction of contact angle. We thoroughly investigated different factors and assessed their importance in improving the predicted data. Considering effective factors, a new model was proposed. The results show noticeable enhancements in wettability, contact angle, and adhesion predictions.

Effect of surface tension on SiO2 -methanol nanofluids

Surface tension, the cohesive energy of an interface dominated the transportation behaviour of the liquids play an important role in the heat transfer performance. A new class of heat transfer fluid denoting “Nanofluids” with impressive thermo-physical properties, proved its promising potentiality in the heat transfer performance. However, very few numbers of studies observed for the effect of nanoparticles on the surface tension of liquids, also noted controversial results. In the present study, SiO2 nanoparticles dispersed in methanol solution to investigate the effect of surface tension with the change of concentration and their sizes. The most common Du-Nouy ring method was used to measure the surface tension of methanol based nanofluids by an automatic surface tensiometer.The results denote that the surface tension of the nanofluids increases with increase in concentration. On the other hand, the results indicate that the surface tension decreases with the increase in temperatures. Besides, the surface tension of SiO2-methanol nanofluids enhances compared to pure methanol. All in all, the enhancement observed 1.7% to 8.9% of the variation of volume fractions (0.05 Vol % to 0.25 Vol %) and the temperature change of 25 °C to 50 °C.

Physiological studies on a locally isolated rhamnolipid producer, Pseudomonas strain

Aim Bacterial strains were isolated from different soil samples and evaluated for their ability to produce biosurfactants. Preliminary identification was made of the selected strain Kh4, as well as of the type of produced biosurfactant. Finally, the most optimum conditions for improving growth and the percentage of reduction in the culture surface tension (ST) were investigated. Materials and methods The genus of the selected strain was preliminarily identified on the basis of some biological tests and characterized pigmentation on a specific medium. Rhamnolipid production was confirmed using both Siegmund Wagner and Dubois methods as well as thin-layer chromatography. Quantitative measurements of the ST of cell-free supernatants were determined using the Du Nouy ring method in order to estimate the amount of biosurfactant produced. Cultivation conditions were studied on the basis of both flask and 7 l stirred tank bioreactor levels. Results A total of 66 bacterial strains were isolated from Egyptian soil and assessed for biosurfactant productivity. The selected isolate, preliminarily identified as a Pseudomonas spp., has the ability to produce rhamnolipid and hence to decrease the ST of the fermentation medium from 60 to about 35 mN/m. The optimum fermentation medium, used for the growth and maximum decrease in ST, was determined. Some physiological parameters such as the initial pH, incubation temperature, and time were also studied. Furthermore, the effect of pH control during the fermentation production of rhamnolipid in a 7 l stirred bioreactor was also studied. Accordingly, a maximum decrease in the ST of the cell-free culture medium of 32 mN/m was reached, confirming the production of a satisfactory level of rhamnolipid biosurfactant. Conclusion These results qualified the locally isolated Pseudomonas spp. Kh4 for use in the bioremediation of hydrocarbon-contaminated sites as well as in petroleum industries.

Shear Rheology Using De Noüy Ring To Evaluate Formation and Inhibition of Calcium Naphthenate at the Water/Oil Interface

The extraction of crude oils rich in tetraprotic naphthenic acids along with formation water under pH conditions above 6.5 favors the formation of naphthenic acid salts that can generate deposits with high consistency and very low solubility in the oil and water phases. There is still much uncertainty regarding the behavior of naphthenates, and only a small number of tests exist to evaluate it. The aim of this study was to obtain the parameters necessary to assess the formation of calcium naphthenate film through shear rheology (Du Nouy ring method) and to assess the rheological behavior of this film at the water/oil interface as a function of the ARN acid concentration, calcium concentration, presence of magnesium ions, and addition of commercial chemical inhibitors. We observed an increase in the elastic modulus (G′) and a reduction of the viscous modulus (G″) with the formation of the calcium naphthenate film and that the viscous deformation is restricted, which is coincident with the formation of a cr...

Production and characterization of rhamnolipid biosurfactant from waste frying coconut oil using a novel Pseudomonas aeruginosa D

To improve biosurfactant production economics by the utilization of potential low-cost materials. In an attempt to utilize cost-effective carbon sources in the fermentative production of biosurfactants, various pure and waste frying oils were screened by a standard biosurfactant producing strain. Considering the regional significance, easy availability and the economical advantages, waste frying coconut oil was selected as the substrate for further studies. On isolation of more competent strains that could use waste frying coconut oil efficiently as a carbon source, six bacterial strains were isolated on cetyltrimethyl ammonium bromide-methylene blue agar plate, from a soil sample collected from the premises of a coconut oil mill. Among these, Pseudomonas aeruginosa D was selected as the potential producer of rhamnolipid. Spectrophotometric method, TLC, methylene blue active substance assay, drop collapse technique, surface tension measurement by Du Nouy ring method and emulsifying test confirmed the rhamnolipid producing ability of the selected strain and various process parameters were optimized for the production of maximum amount of biosurfactant. Rhamnolipid components purified and separated by ethyl acetate extraction, preparative silica gel column chromatography, HPLC and TLC were characterized by fast atom bombardment mass spectrometry as a mixture of dirhamnolipids and monorhamnolipids. The rhamnolipid homologues detected were Rha-Rha-C(10) -C(10) , Rha-C(12) -C(10) and Rha-C(10) -C(8) /Rha-C(8) -C(10) . These results indicated the possibility of waste frying coconut oil to be used as a very effective alternate substrate for the economic production of rhamnolipid by a newly isolated Ps.aeruginosa D. Results of this study throws light on the alternate use of already used cooking oil as high-energy source for producing a high value product like rhamnolipid. This would provide options for the food industry other than the recycling and reuse of waste frying oils in cooking and also furthering the value of oil nuts.

Surface tension of viscous biopolymer solutions measured using the du Nouy ring method and the drop weight methods

The discrepancy of the existing literature data on the surface tension values of biopolymer solutions could be affected by the measurement technique. The aim of the study was to compare the surface tension values of biopolymer solutions, measured using the du Nouy ring method and the drop weight methods (Harkins–Brown correction factors method and the LCP coefficient method). Four biopolymers were chosen (sodium alginate, carboxymethyl cellulose, xanthan gum and pectin) and the surface tensions of the solutions were measured as a function of biopolymer concentration. The surface tension was found to increase with biopolymer concentration when measured using the du Nouy ring method. On the other hand, the drop weight methods gave an opposite trend. The results verified the discrepancy of the existing literature data. The error may be caused by the correction factors calculation and the solution viscosity when the du Nouy ring method was used. The LCP coefficient method which is independent of correction factors and liquid properties is proposed for measurement of the surface tension of viscous biopolymer solutions.