Title of Invention

A PROCESS FOR PREPARING SURFACTANT ION SELECTIVE MEMBRANES AND MEMBRANE ELECTRODES MADE THEREFROM

Abstract

The present invention relates to A process for preparing ion - selective membranes and membrane electrodes, which comprises: i. reacting together a predetermined set of anionic and cationic surfactants in around equimolar ratio; ii. extracting the product with a non - polar solvent and drying the extract; iii. mixing the dried product with water insoluble organo polymer and an organo aster iv. cleaning and drying the clear liquid obtained in step (iii); v. attaching a section / piece of the dried product to a tubular body and vi. making an electrochemical set - up with standard electrodes. The membrane electrodes are also easily made and can be stored under ambient conditions for considerable length of time. Preparation of membranes and electrodes from indigenous material will result in considerable saving of foreign exchange.

Full Text

The present invention relates to a process for preparing surfactantion. - selective membranes and membrane electrodes made therefrom. More particularly, this invention pertains to the preparation of surfactant ion selective membrane which in turn may be conveniently be utilised in constructing a membrane electrode for accurately determining the concentrations of ionic surfactants in solutions, such determination being extremely difficult. Methods practised heretofore often necessitated use of freshly prepared membranes having virtually very little shelf life. Some of the membranes imported from abroad could be used only for a limited number of times and posed problems for storage and preservation, not to speak of the cost involved. Variable weather conditions also affected reproducibility and accuracy of results. In recent times use of surface active agents, both anionic and cationic, has gone up in leaps and bounds, particularly for cleaning and washing purposes. The surfactant ions are leached out in effluent water and often results in creating problems by dint of their capacity ? of binding with other polymers and bipolymers. It often becomes necessary to determine surfactant concentration in liquid media for various practical purposes, e.g., for recycling effluent waste water from industrial units or municipal bodies. Discharge of surfactant laden effluent water / waste water into water courses or water bodies causes pollution and adversely affects both plant and marine life. Presence of surfactants beyond certain specified limits has been found to cause problems for higher life forms, including human beings. Removal of surfactant from effluent / wastewater should be preceded by determination of surfactant concentration to estimate the quantum of chemicals needed for removal of this contaminant from effluent / waste water. The principal object of the present invention is to provide a novel process for preparing ion - selective membrane.„ A further object of this invention is constructing an ion - selective membrane electrode for determining concentration of surfactant in experimental solution. 2 A still further object of this invention is to evolve a simple yet effective procedure for determining surfactant concentration in an unknown sample ofwater. Yet another object of this invention is to provide a set - up for obtaining reproducible and accurate test results. According to this invention there is provided a process for preparing surfactantion - selective membranes and membrane electrodes, which comprises: i. reacting together a predetermined set of anionic and cationic surfactants such as herein described in around equimdar ratio ; ii. extracting the product with a aqueous non - aqueous -solvent and drying the extract; iii. mixing the dried product with water insoluble organo polymer and an organo diester such as herein described; iv. cleaning and drying the clear liquid obtained in step (iii); v. attaching a section / piece of the dried product to a tubular body and vi. making an electrochemical set - up with standard electrodes as herein described. As discussed above, for preparing ion - selective membrane judicious selection of surfactants has to be made. Such selection may be made from the surface active components which, inter alia, are as follows: Cetyltrimethyl ammonium bromide ( CTAB ), tetradecyltrimethyl ammonium bromide (TTAB), dodecyftrimethyl ammonium bromide ( DTAB ), sodium dodecyl sulphate( SDS ), sodium dodecyl benzene surfonate ( SDBS ), sodium deoxycholate (NaDC), sodium taurochenodeoxycholate ( NaTCDC), sodium - bis ( 2 ethylhexyl) - sutfosuccinate ( AOT) [ marketed under the brand name" Aerosol OT" ], etc. Certain dibasic or polybasic organo esters having surface active properties such as, for example, dioctyl phthalate (DOP), dibutyl phthalate ( DBP), dipropyl phthalate (DPP ) etc. have also been found to be effective as one of the starting materials, for the subject 3 process effective as plasticier. Some medium range organopolymers like polyvinyl chloride, polyvinyl acetate, polyolefins like polypropylene, etc. also find application as a starting compound. It has been observed that reaction between a cationic and an anionic surfactant results in the formation of an adduct , called " coacervate ". This reaction is usually carried out in a polar solvent medium, usually water. The formed coacervate may be extracted with organic solvents like chloroform, acetonitrile, etc., and dried thereafter. The dry coacervate is to be mixed with a low molecular weight organic polymer, like PVC and an organic diester and the mixture is to be dissolved in solvent like cydohexanonetetrahydrofuran, etc., at an elevated temperature, say around 40° - 60°C. This should result in a clear solution which may be poured into an inert receptacle to allow solute to form into a membrane, and the solvent to evaporate on standing. Normally a porcelain or glass receptacle may be employed. For better results the clear solution may be spread over clean mercury surface in a petri -dish of suitable diameter, and subjecting the solution to air drying for about 40 hours. The dried product assumes the shape of a membrane or thin sheet. Preparation and setting up of membrane electrode: The formed membrane was carefully lifted off the mercury surface and then cut into pieces of a suitable dimension say 2 cm2, and attached to one end of a hollow, tubular body open at both ends. Such tubular bodies should be made of an inert material like glass, fibreglass or Teflon,the last one being preferred. The membrane may be attached by means of a rubber band. Thereafter the membrane was conditioned by being immersed overnight in CTAB solution of around 0.75 - 1.5 mM strength, followed by careful washing with distilled water and then equilibrated with experimental surfactant solution of unknown strength to take the measurements. 4 A surfactant solution of predetermined or known strength of around 0.5 to 5.0 mM was poured carefully into the Teflon tube plugged / covered at one end. An electrochemical set - up was made as under: " calomel electrode / reference solution // experimental solution / calomel electrode" and the cell e. m. f was measured with a digital multimeter. Varying concentrations of surfactants of the experimental solution, e. m. f. values may be determined under conditions of equilibrium. A calibration curve plotted with e. m. f. vs [surfactant] may be drawn to be used as the standard curve. For a surfactant solution of unknown strength, the concentration may be determined by measuring the cell e. m. f as above using the calibration curve. Different membranes may be prepared by using varying sets of coacervates, such as, for example - ( CTAB/+SDBS + AOT + NaDC + NaTCDC ): (CTAB + TTAB + DTAB + SDBS ) In each case the overall cationic and antonic molar ratios were found to be around 1:1. Interestingly, it was found that the membranes prepared by using coacervate of a mixture of surfactants responded well for all the surfactants from which the coacervate was prepared. The membrane retained its ion - selective activity even after eight months. Preparation of the membrane; 0.01 - 0.04 g of the complex (coacervate) was taken with 0.2 - 0.5 g low molecular PVC in a beaker and to it 1.0 - 1.2 g dioctylphthalate ( plasticiser) was added. The mixture was dissolved in 10ml cyclohexanone solvent under heating condition. The clear solution obtained was then spread on cleared Hg (mercury) surface in a 10 cm diameter petri - dish and the solvent was allowed to evaporate for two days. A thin and elastic membrane was obtained which was stored in a container under water. Preparation of complex (Coacervate): A cationic and an anionic surfactant when mixed in 1:1 molar ratio in aqueous medium usually forms an insoluble complex (called" coacervate") which can be extracted by a solvent like chloroform and dried by removing the solvent and keeping in a dessicator. 5 In the present invention, such complexes of CTAB + SDS; CTAB +.NaDC; CTAB +SDBS; CTAB + AOT; CTAB + NaTCDC^SDBS + DTAB; CTAB + ( SDS + SDBS + AOT + NaDC + NaTCDC ); ( CTAB + TTAB + DTAB ) + SDBS were prepared. In the preparation of coacervate, the overall concentrations of cationic and anionic surfactants were kept in 1:1 molar proportion. The ion selective membranes prepared according to the process of the present invention have been found to be extremely useful in determining surfactant concentration with accuracy, which was difficult to estimate by other conventional techniques / methods. The membranes of this invention have found particular use in the field of surface chemistry when determination of low concentration of surfactant solution is required. The membranes have found a unique application in determining CMC ( critical micellar concentration ), a significant physico - chemical parameter for determining behaviour of surfactants in solution. It has also been found to be useful in the study of binding of surfactants to/the plot of e. m. f vs. log [ surfactants] were found to be in agreement with the observations made by earlier scientific workers. The data collected are graphically represented by Figures 1 and 2 of the drawings accompanying the Provisional Specification. Although the slopes did not always show the value of 0.569 v ( a value that should be obtained when the electrode behaviour is of Nemstian type ), yet the variation of the e. m. f. with log [ surfactant ] was found to follow a linear path almost invariably. A couple of suitable working examples are given below to illustrate the invention: Example 1 A particular pair of cationic and anionic surfactants were mixed together in 1:1 molar ratio in aqueous medium. Cetyttrimethyl ammonium bromide ( CTAB ) and sodium dodecyl sulphate( SDS ) were selected as the cationic and anionic surfactants, respectively. The formed coacervate was extracted with chloroform and then dried. 0.01 - 0. 04 g of the dry coacervate was mixed with 0.20 - 0.50 g of low molecular weight PVC and 1.0 - 1. 2 g of dioctylphthalate and the entire mass of the mixture was dissolved carefully in cyclohexanone6 maintained at an elevated temperature of around 40° - 60°C The clear, transparent liquid was then spread over clean mercury surface contained in a petri - dish of around 10cm diameter. The whole mass was air dried for 2 days. A thin and elastic membrane was obtained which was stored under water in a suitable container. After evaporation of the solvent the mass turned into a thin film or membrane which was carefully lifted off the mercury surface, cut into pieces and attached to one open end of a Teflon tube by means of rubber band. The tube with membrane was conditioned and set up as a membrane electrode in the manner as described below in example 2. Example 2 Experimental set - up of the membrane electrode for electrochemical measurements Small pieces of the prepared membrane were fixed on one end of a Teflon tube by using the PVC + cyclohexanone solution as the glue. To each tube 0.1 M CTAB solution was added through the other open end and they were kept overnight. The tubes were then washed with doubly distilled conductivity water and equilibrated with a fixed and low concentration (less than critical micellar solution) of the experimented surfactant solution for an hour. An electrochemjcaljtof the type calomel electrode / reference surfactant solution (lower than CMC) // experimental solution / calomel electrode was set up and the cell e. m. f was measured with a digital multimeter at increasing concentration of the experimental surfactant solution under the condition of equilibrium in a temperature controlled thermostated water bath. A calibration curve was constructed by plotting e. m. f vs. [ surfactant ]. for an unknown solution, the concentration can be determined by using the solution as the experimental solution in the set - up and measuring the cell e. m. f and from the calibration curve. Electrochemical response of different surfactants is evidenced from the plot of e. m. f vs. log [ surfactant ], as shown in Fig 1 for cationic surfactant and Fig. 2 for anionic surfactants in the drawings accompanying the provisional specification. The results are summarised in Tables 1 and 2 hereinbelow: 7 Table 1: Electrochemical response of cationic surfactants at 25°C Surfactant CMC /mM observed slope of e. m. f vs log [surfactant] Observed Reported Using ( CTAB + TTAB + DTAB + SDBS) as coacervate : ~ see Fig.1 CTAB 0.86 0.80 0.043 TTAB 3.70 4.00 0. 028 DTAB 14.50 14.00 0.030 Using (CTAB + SDS H H SDBS + AOT + /VaDC + NaTDC ) as coacervate:- See Fig.2 SDS 9.70 8.00 0.053 SDBS 1.12 1.20 0.036 AOT 2.00 2.70 0.053 NaDC 3.23 5.00 0.025 NaTCDC 1.35 - 0.016 8 Table 2 : Electrochemical response of surfactants in solid Ion selective membranes at different time intervals at 303K. Surfactant Type of ion Time CMC Slope of e. t n. f vs loa l pair (davs) (m mol dm"3) surfactant I curve complex used Observed Expected Observed Expected (/>m 2 0.708 0.043 _____ + 4 0.851 •DTA 10 0.631 0.044 CTAB 14 0.760 0. 80 30 0.813 0.051 60 0.759 0.048 |CO 2 4 8.511 _____——— 0.060 SDS CD __ 15 8.710 8. 00 (13> 30 8.610 75 9.772 8.623 90 Legend to the figures : Fig. 1 : Plot of e. m. f vs log[ surfactant ] for cationic surfactants using ( CTAB + TTAB + DTAB + SDBS) as coacervate. _ - CTAB; 0 - TTAB; D - DTAB Fig. 2 : Plot of e. m. f vs log[ surfactant ] for anionic surfactants using {CTAB + SDS + SDBS + AOT + NaDC + NaTCDC ) as coacervate. 0 - SDS; A - SDBS; o - AOT; m - NaDC; * - NaTCDC. 9 As mentioned earlier, membranes prepared according to this invention have been found to have wider and better activities than those obtained according to prior art, the latter being far more costly and of limited durability. The membranes of subject invention gave long durability, retaining activity for over 1 year. Such membranes are obtainable from indigenously available, low cost material. The membrane electrodes are also easily made and can be stored under ambient conditions for considerable length of time. Preparation of membranes and electrodes from indigenous material will result in considerable saving of foreign exchange. The advantages of the present invention may briefly be outlined as under: i. The process for preparing the membrane is simple and economical and the chemicals used in such preparation are all indigenously available, ii. Long shelf - life and durability of the membrane activity is extremely advantageous from the viewpoint of usability and economy, iii. The process of this invention opens a new horizon for easy determination and estimatbn of surfactant concentration in solution which was hitherto not possible, iv. The process would result in considerable saving of valuable foreign exchange. While the invention has been described in detail and with reference to the specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without deviating or departing from the spirit and scope of the invention. Thus the disclosure contained herein includes within its ambit the obvious equivalents and substitutes as well. Having described the invention in detail with particular reference to the drawings accompanying the Provisional Specification and illustrative Examples given above, it will now be more particularly defined by means of claims appended hereinafter. 10 We claim: 1. A process for preparing surfaction ion - selective membranes and membrane electrodes, which comprises: i. reacting together a predetermined set of anionic and cationic surractants such as herein described in around equimolar ratio; iii, extracting the product with a non - aqueous solvent and drying the extract;iiii, mixing the dried product with water insoluble organo polymer and an ongano, diester such as herein described; iv. cleaning and drying the clear liquid obtained in step (iii); v. attaching a section / piece of the dried product to a tubular body and V'I, making an electrochemical set - up with standard electrodes as herein described. 2. A process as claimed in Claim 1, wherein the coacervate formed in step (i) is extracted with chloroform and dried. 3. A process as claimed in Claim 1, wherein the dry coacervate is mixed with low molecular weight PVC and an organo - diester. 4. A process as claimed in Claim 3, wherein the organo - diester is selected form the group of dioctjl phthalate ( DOP ), dibutyl phthalate ( DBP ), dipropyl phthalate ( DPP ) and is used as a plasticiser. 5. A process as claimed in Claim 1, wherein the mixture obtained in step (iii) is dissolved in a non - polar solvent like cyclohexanone or tetrahydrofuran at an elevated temperature of between 40° and 60°C. 6. A process as claimed in Claims 1 and 5, wherein the clear solution is poured into a receptacle made of inert material like glass or porcelain. 7. A process as claimed in Claim s 1, 5 and 6, wherein the clear solution is poured over mercury surface kept in a petri - dish of suitable diameter and allowed to dry, resulting in a thin sheet or membrane - like product. 11 8. A process as claimed in any of the preceding claims, wherein small pieces of said membrane are fixed on one end of a Teflon tube by use of PVC and chlorohexanone solution as the adhesive or glue, to each is added 0. 1 M CTAB solution through the open end and kept overnight, the tubes are washed with conductivity water and equilibrated with a fixed and low concentration of the experimental surfactant solution for an hour. 9. A process as claimed in Claim 8, wherein an electrochemical cell of the type calomel electrode / reference surfactant solution // experimental solution / calomel electrode is set up and the concentration of the experimental ( unknown) surfactant solution is lower than critical micellarv solution. 10. A process as claimed in Claims 8 and 9, wherein the cell e. m. f is measured with a digital multimeter at increasing concentration of the experimental surfactant solution under condition of equilibrium. 11. A process as claimed in Claim 10, wherein the measurements are carried out in a temperature controlled thenmostatic water bath.and the data obtained are converted into a 'calibration cuve" by plotting e.m.f's aganist logrithmic values of surfactor concentraction 12. A process for preparing/ion - selective membranes and membrane electrodes, substantially as hereinbefore described with particular reference to the Examples given 12

Documents:

00556-cal-2000-abstract.pdf

00556-cal-2000-claims.pdf

00556-cal-2000-correspondence.pdf

00556-cal-2000-description(complete).pdf

00556-cal-2000-drawings.pdf

00556-cal-2000-form-1.pdf

00556-cal-2000-form-19.pdf

00556-cal-2000-form-2.pdf

00556-cal-2000-form-3.pdf

00556-cal-2000-form-5.pdf

00556-cal-2000-letters patent.pdf

00556-cal-2000-others.pdf

00556-cal-2000-p.a.pdf

556-cal-2000-granted-abstract.pdf

556-cal-2000-granted-acceptance publication.pdf

556-cal-2000-granted-claims.pdf

556-cal-2000-granted-correspondence.pdf

556-cal-2000-granted-description (complete).pdf

556-cal-2000-granted-drawings.pdf

556-cal-2000-granted-examination report.pdf

556-cal-2000-granted-form 1.pdf

556-cal-2000-granted-form 18.pdf

556-cal-2000-granted-form 2.pdf

556-cal-2000-granted-form 3.pdf

556-cal-2000-granted-form 5.pdf

556-cal-2000-granted-letter patent.pdf

556-cal-2000-granted-pa.pdf

556-cal-2000-granted-reply to examination report.pdf

556-cal-2000-granted-specification.pdf