Journal of Surface Science and Technology

T. Mukhim ¹, K. Ismail ¹

Affiliations
1 Department of Chemistry, North Eastern Hill University, NEHU Campus, Shillong, 793022, IN

Abstract

Surface tension and electrical conductance of cetylpyridinium chloride (CPC) in water were measured in the presence of lithium chloride, sodium chloride and potassium chloride at 295, 298 and 303 K. From these experimental data, critical micelle concentration, surface density, counter-ion binding constant and standard free energy of micellization of CPC were determined and no effect of co-ion on these parameters is found. Critical micelle concentration has a minimum around 298 K. Surface density of CPC at the air - water interface increased by the addition of electrolyte. The surface area per molecule of CPC at the air - water interface is about 63 % more compared to that of sodium dodecyl sulfate molecule and hence the pyridine ring of the adsorbed CPC molecule appears to reside at the interface. Aggregation numbers of CPC were estimated from the electrical conductance data by applying the mixed electrolyte model. In the presence of more than 5.2 × 10^-4 mol kg^-1 NaCl, aggregation number of CPC is found to be higher than that in the presence of LiCl and KCl thereby indicating the possibility of co-ion effect on the aggregation number.

Keywords

Cetylpyridinium Chloride, Lithium Chloride, Sodium Chloride, Potassium Chloride, Surface Tension, Electrical Conductance, Critical Micelle Concentration, Surface Density, Counter-Ion Binding Constant, Free Energy of Micellization, Aggregation Number, Co-Ion.

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I. M. Umlong ¹, K. Ismail ¹

Affiliations
1 Department of Chemistry, North Eastern Hill University, NEHU Campus, Shillong 793022, IN

Abstract

Critical micelle concentrations of sodium dodecylsulfate (SDS) and dioctyl sulfosuccinate (AOT) were determined at 25 °C in aqueous medium as a function of sodium salicylate (NaSa) concentration by surface tension and EMF methods. In the case of SDS, conductance method was also used. Salicylate ion is found to affect the critical micelle concentrations of SDS and AOT when the concentration of NaSa becomes > 0.03 and 0.02 mol kg^-1, respectively. In the presence of NaSa, the counter ion binding constant for AOT has a single value equal to 0.47 and that for SDS is equal to 0.56. The higher value of the counter ion binding constant equal to about 0.8 observed earlier for AOT in sodium chloride, sodium acetate, sodium propionate and sodium butyrate solutions above 0.015 mol kg^-1 of salt concentration has not been observed in NaSa solution. The effect of salicylate ion on the critical micelle concentration of SDS and AOT and on the counter ion binding constant of AOT is attributed to mixed micelle formation of salicylate with the anionic surfactants. It is considered that the salicylate ions reside just outside the Stern layer of the anionic micelles and form ion - pairs with the sodium ions bound to the micelles. Salicylate ion does not seem to have significant influence on the surface activity of SDS and AOT. Standard free energies of micellization and adsorption of SDS and AOT in the presence of NaSa were also evaluated.

Keywords

Sodium Dodecylsulfate, Dioctyl Sulfosuccinate, Sodium Salicylate, Surface Tension, EMF, Electrical Conductance, Critical Micelle Concentration, Counter Ion Binding Constant, Surface Excess, Free Energy of Micellization, Free Energy of Adsorption.

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B. C. Paul ¹, S. Dev ¹, K. Gunaseelan ¹, K. Ismail ¹

Affiliations
1 Department of Chemistry, North-Eastern Hill University, Bijni Complex, Laitumkhrah, Shillong 793 003, IN

Abstract

pK values of the first protonation of methyl red (MR) in benzene-water microemulsions (MEs) stabilized by sodium dodecyl sulfate (SDS) + butanol, SDS + propanol, and cetylpyridinium chloride (CPC) + propanol have been determined at 25°C as a function of R (molar ratio of water to surfactant) by studying the electronic spectra of MR in these MEs at various pH values. In two of the MEs, viz., benzene/SDS/butanol/water and benzene/SDS/propanol/water of R = 66, pK values of second protonation of MR have also been measured. The partitioning of the doubly protonated (H₂MR+), singly protonated (HMR), and deprotonated (MR-) species of MR in the different regions of the ME has been ascertained on the basis of the spectral data. The plot of pK of first protonation versus R exhibitis a minimum at low R (R ≈ 10) and a maximum at higher R (R ≈ 40) indicating different types of dependence of pK on R in the w/o, bicontinuous and o/w regions of the ME. pK is shown to be controlled by the effective dielectric constant at the site of protonation, interfacial electrical potential and the partition coefficients of the acidic and basic forms of MR with respect to the different domains of ME. A method for estimating the limiting pH at which first protonation of MR is complete has been suggested.

Keywords

Microemulsion, Sodium Dodecyl Sulfate, Butanol, Benzene, Methyl Red, Pk.

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K. Gunaseelan ¹, B. C. Paul ², J. Das ³, K. Ismail ³

Affiliations
1 Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, US
2 Department of Chemistry, Sankardev College, Shillong, IN
3 Department of Chemistry, North Eastern Hill University, NEHU Campus, Shillong-793 002, IN

Abstract

Electrical conductivity of water/sodium dodecyl sulfate/l-butanol/oil microemulsions having molar ratios of water to surfactant and surfactant to cosurfactant equal to 44 and 0.1144 respectively, was measured at 25°C using eight different oils (octane, benzene, toluene, carbon tetrachloride, chloroform, cyclohexane, m-xylene and nitrobenzene). These microemulsions have been found to fall in the w/o and bicontinuous regions over the range of volume fractions of oils covered in this study. The specific conductivity data were least-squares fitted to a virial expression. In the w/o region the dimensional characteristics of the microemulsions were estimated.

Keywords

Microemulsion, Sodium Dodecyl Sulfate, Butanol, Oil, Electrical Conductivity.

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