CHAPTER - 2 EXPERIMENTAL. Sodium dodecyl benzene sulphonate (SDBS) and Sodium dodecyl sulfate

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1 2.1 Materials CHAPTER - 2 EXPERIMENTAL Surfactants Sodium dodecyl benzene sulphonate (SDBS) and Sodium dodecyl sulfate (SDS) were procured from Sigma and used as received without any further purification. The concentration of the anionic surfactant in a solution was determined employing the technique of phase titration. The Phase titration of the anionic surfactants was performed against standard cationic surfactant, benzethonium chloride (hyamine) using methylene blue as indicator to check the purity of the anionic surfactants. The purity of the cationic surfactants, Cetyl trimethyl ammonium bromide (CTAB) and Tetra decyl trimethyl ammonium bromide (TTAB) (all from Sigma) were determined by phase titration method using standard SDS solution. The sample of the nonionic surfactant, Triton X-100 (TX-100) also obtained from Sigma were used as received without any further purification Solvents Glycols: Analytical reagent grade samples of ethylene glycol, 2-methoxy ethanol (ME), 2-ethoxy ethanol (EE) were supplied by S.D. Fine Chemicals, (Mumbai). The samples were purified by drying over anhydrous calcium sulfate followed by fractionation after the removal of the dessicant. 1,2 The samples were then reflux over anhydrous Sn(II) chloride for nearly six hours 33

2 using fractionating column. The sample was then decanted and fractionally distilled. Cyclic Ethers: Tetrahydrofuran (THF) were procured from Merck (India) while AR grade sample of dioxane (DIO) were obtained from Glaxo India Ltd. The solvents were dried initially over calcium sulphate before being kept under reflux over calcium hydride. 2-4 The solvent is finally fractionally distilled. Alkyl Amines: High purity samples of ethyl amine (EAM) and triethyl amine (TAM) were procured from Glaxo India Ltd while AR grade sample of diethyl amine (DAM) was obtained from SRL, India. The samples were fractionally distilled three times and finally the middle fraction was collected and stored for the study. 1 Alcohol Amines: AR grade samples of mono ethanol amine (MEA) and triethanol amine (TEA) were obtained from S.D. Fine Chemicals (Mumbai) and diethanol amine (DEA) from Merck (India). The samples were purified by fractional distillation prior to their use. 1,5 Poly Ethylene Glycols: High purity samples of poly ethylene glycols namely PEG-200, PEG-300, PEG-400 and PEG-600 were procured from CDH, Mumbai. All the samples were used as received without any further purification. 34

3 2.1.3 Pinacyanol Chloride Dye Pinacyanol chloride (PC) was obtained from Sigma-Aldrich (USA) and used as such without further purification Iodine Extra pure reagent grade sample of iodine (I 2 ) was obtained from Merck (India) and potassium iodide (KI) having purity of over 99.5 % was procured from Loba Chemie (India). The sample of iodine was purified by allowing it to sublime and condense on a clean glass surface, which was then collected for the study. The sublimation-condensation cycle was repeated for at least three times Polymers Polymers employed in the study namely poly vinyl pyrollidone (PVP, M w - 40,000), polyethylene oxide (PEO, M w -50,000), hydroxyl propyl cellulose (HPC, M w -100,000) and gelatin A were procured from Sigma-Aldrich (USA) and used as such without further purification treatment. 2.2 Preparation of the Solutions All the solutions were prepared by dissolving a known weight of the solute in a known volume of the solvent. All the solid samples were weighed using an electronic digital balance (OHAUS). Double distilled water was used all through the study. Stock solutions of the surfactants were prepared by dissolving a weighted amount of the surfactants in a known volume of 35

4 doubled distilled water having a conductivity value of less than 2 µs. For systems containing mixed aqueous organic media, surfactant solutions were prepared by dissolving a weighted amount of the surfactants in a known volume containing appropriate percentage of the organic solvent. For example, a standard stock solution of CTAB in 5% EG was prepared by dissolving the required amount of the surfactant in a 100ml volumetric flask and dissolving it in 5% aqueous EG solution. Stock solution of PC (0.5 mm) in aqueous media was prepared in 100 ml volumetric flask and kept in dark so as to minimize the photodecomposition of the dye solution during storage. 6 In mixed aqueous organic media, dye solutions of a desired concentration were prepared by diluting the stock solution with appropriate amount of organic solvent in a 10 ml volumetric flask and finally making up the volume by distilled water. Freshly prepared stock solutions of Iodine were used in the study. Saturated Iodine solutions were prepared by dissolving an excess amount of iodine in water in a volumetric flask. The resultant supersaturated solution was continuously shaken for nearly 1 hr and the liquid was drained out. The process was repeated for at least 3 times. The last fraction collected after a few cycles was employed as saturated iodine solution and the actual iodine concentration in the solution was determined by titrating against standard hypo solution. 7 The iodine solution thus prepared showed band at 460 nm 36

5 while the band at 350nm (due to tri-iodide) was found to be negligibly small. Stock solution of the polymers (2%w/v) was prepared by dissolving weighted amount of polymer in 100ml volumetric flask. The solutions were kept in a low temperature water bath for nearly 6 hours under constant stirring and finally the dissolution of the polymer sample were carried out by standing the solution for about 48 hours at room temperature. All the other solutions of lower concentrations of either the surfactant or dye in aqueous or mixed aqueous organic media were prepared by dilution method using water or the appropriate organic solvent. 2.3 Experimental Techniques Tensiometric measurements Surface tension measurements of the surfactants in aqueous and mixed aqueous organic media were performed using a Du-Nouy type tensiometer, STT-78 (SC Dey & Co., Kolkata, India) equipped with a platinum ring. Tension was measured by the principle of detachment of the platinium ring. In a typical experiment, a known volume (20 ml) of the solvent was taken in the inner portion of a double walled glass container around which thermostated water from a Haake Thermostat was circulated and the ring was dipped in the center of the solution. The surface tension was recorded directly from the dial by turning the knob behind the dial when the ring just 37

6 dispatched from the surface of the solution. Small aliquots of standard surfactant solution prepared in the relevant solvent were added at regular intervals with the help of a Glaxo Qualipatte, Finland and the surface tensions were measured. The measurements were reproducible to within ±0.5 dyne cm -1. The surface tension of water was periodically measured to check the accuracy of the tensiometer Conductivity Measurements Conductance measurements of surfactants in aqueous and mixed aqueous organic media were carried out using a Conductivity Meter (Eutech Con-510, Oakton, USA). The conductivity cell was calibrated with standard KCl solution. The precision of the measurements was within ±0.003 ms cm 1. All the measurements were performed at constant temperature controlled by circulating water from Haake Thermostat. Periodical measurements of the conductance of the water (less than 2µs) were performed to check the accuracy of the measurement Spectophotometric Measurements The UV-Visible absorption spectra of the dye solutions and iodine-iodide solutions in absence or in presence of surfactant at different media were recorded using either a Shimadzu UV or Perkin Elmer Lamda 35 UVvisible spectrophotometer using a pair of quartz cuvete of 1cm optical length kept in a cell holder to which a pelteir temperature programmer PTP-1 is 38

7 connected. The spectra were recorded in the wave length range nm. Temperature of all the solutions were maintained constant to within ± 0.1K Cyclic Voltametric Measurements Cyclic voltagram of the iodine-iodide in aqueous and aqueous surfactant media were measured using electrochemical analyzer (Model 600CH Instrument). The measurement were carried out using a classic cell equipped with three electrodes - platinium as working, platinium as auxillary and an Ag/AgCl electrode as reference electrode Laser Light scattering Measurements Laser Light Scattering measurements were carried out using NaBiTec, Laser- Spectroscatter 201 equipped with a laser diode with a wavelength of 660nm and an optical power of 100mW. The samples were taken in a round cuvette kept in the cell holder temperature of which is maintained constant through a built-in peltier heating system. 39

8 Reference 1. J. A. Riddick, W. B. Bunger, Organic Solvents: Physical Properties and Methods of Purifications, Vol. II, 4 th Ed., John Wiley and Sons, Inc., B. S. Furniss, A. J. Hannaford, P. W. G. Smith, A. R. Tatchell, Vogel s text book of Practical Organic Chemistry, Longman Publication, 5 th Ed, H. N. Solimo, A. C. G. Marigliano, J. Solution Chem., 22, 951, K. B. Singh, Thermodynamic Investigation on Ternary Systems of Some Selected Liquids in Tetrahydrofuran and Dioxane Mixed Solvents, Ph.D. Thesis, Submitted to Manipur University, Canchipur, H. Naorem, S. D. Devi, J. Surface Sc.and Technol., 22, 89, R. Sabate, J. Estelrich, J. Phys. Chem. B, 107, 4137, J. Mendham, R. C. Denney, J. D. Barnes, M. J. K. Thomas, Vogel s text book of Quantitative Chemical Analysis, Pearson Education Ltd., 6 th Ed,