مرکزی صفحہ Colloids and Surfaces Miscibility of dodecylammonium chloride and octylsulfinylethanol in the adsorbed film and micelle
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Colloir/s trrrtl S~trficws. 67 (1992) 53-59 Elscvier Scicncc Publishers B.V., Amsterdam 53 Miscibility of dodecylammonium chloride and octylsulfinylethanol in the adsorbed film and micelle Kinsi Motomura, Makoto Aratono Tomoko (Received 23 December Kanda, Koji Abe, Natsuko Todoroki, Norihiro Ikeda and 199 I; accepted 6 March 1992) Abstract The surface tension or an aqueous solution of a dodecylammonium chloride (DAC) and octylsulfinylethanol (OSE) mixture was mcasurcd as a function of the total molality of surfactants and the molt fraction of OSE in the solution. By analyzing the experimental results using thermodynamic relations developed previously, a phase diagram of adsorption rcprcscnting the cquiiibrium bct\vccri the adsorbed film and solution was obtained at a given surt%cc tension. At a low surface tension, the mixture was found to rorm a negative azcotropic mixed film. It was also observed that the phase diagram of miccllc rormation has a distinct minimum. Such behavior was attributed to the attractive interaction between DAC and OSE molcculcs in the oricntcd states. Further, the molecular interaction was round to be more attractive in the miccllar state than in the adsorbed state. Ke_ww~ls: Dodccylammonium chloride: film: miccllc: miscibility: Introdrrction A strong interaction between ionic and nonionic surfactants has been disclosed by surface tension measurements [I-22]. Meguro and )workers have shown that these surfactants form mixed micelles and mixed adsorbed films at interfaces [S-IO]. The present authors have established that the non-ideal mixing of decytammonium chloride (De.4C) and octylsuIfinylethanoI (OSE) in the adsorbed and mIcelIar states can be investigated advantageously with the aid of the phase diagrams of adsorption and micelle formation obtained by tise of their thermodynamic method [23,24]. It is now useful to consider a mixture of surfactants interacting so as to form an azeotrope. For this purpose, we chose dodecylammonium chloride (DAC) and OSE (which have co; mparable values Corrcspmdam lo.- K. Motomura. Dept. ol Chemistry, Faculty of Science, Kyt!shu University 33, Fukuoka 812,3apan. 01 GG-6622/92/505.00 0 1992 - Elsevicr Science Publishers octylsulfinylcthanol: surface tension. of the critical micelle concentration CMC and surface tension at the CMC) as the surfactants because the azeotropic behavior is expected for a mixture of components whicir have similar physical properties . The surface tension of an aqueous solution of a DAC and OSE mixture is measured and comas ;L function of the total concentration position. of the mixture, and the data are analyzed thermodynamically by \he equations developed previously [23,24]. The results are compared with those obtained for the DeAC and OSE mixture. Materials and methods DAC and OSE were synthesized and purified by methods described previously by Aratono et al.  and Motomura et al. . Water was distilled three times from alkaline permanganate solution. The equilibrium surface tension was measured within an experimental error of 0.05 mN m-l at B.V. All rights reserved. 53 298.15 K under the drop-volume Results atmospheric pressure method . by means of and discussion Sime DAC and OSE are expected to interact so strongly as to show azcotropic behavior, it is appropriate to adopt the total molality lit of surfactants and the mole fraction 22 of OSE in the total surfactant as the experimental variables: rir and _?? are defined, respectively, as (1) 9J 2, = rlI,/riJ (2) where rrrr and III-, arc the molalities of DAC and OSE respectively [23,24]. The surface tension ;* of an aqueous solution of the DAC and OSE mixture .vas measured as a function of rir at constant k2. he ;t vs lir curves obtained arc presented together with those of pure DAC and OSE in Fig. I. It is seen that the curve has an obvious break point at the CMC (c’). However, it is difficult to see how the curve varies with 2i,. In order to visualize the dependence of ;I on Rz, the values of ;’ at a given iir were read from Fig. I and plotted against ki, in Fig. 2. The surIW.Z tension ;B’ at the CMC vs gZ curve is also shown in this figure. It is seen that the ;I value decreases gradually with j;12 at a low concentration, while at a high concentration the ;’ vs 2, curve has a shallow minimum. Such a regular variation in the shape of the curve with rir indicates that DAC and OSE molecules mix homogeneously and interact strongly with each other in the adsorbed film. It is worthwhile to note that the ;” vs ri, curve has an unambiguous maximum. The difference in shape between the ;’ vs 82 and ;” vs ji2 curves suggests that the mutual interaction between DAC and OSE molcculcs in the micclle differs considerably from that in the adsorbed film. Similar information is provided by plotting the 1i1 values read at constant ;’ from Fig. 1 against 2,. The !jr vs kZ curves are shown together with the e vs _?iz curve 8 I I f 6 / mmoI Fig. I. Surkm knsion constant composilions. 0.17(,: 0.538: curve curve I 20 10 vs 22: lot:tl curve I I 30 kg-’ molality curves at various 1, 0: curve 7. 0.1 16: curve 3. 4. 0.333: curve 5. 0.43: CUFVC 6. 0.489: curve 7, X. O.GG7: curve Y, 0.X 19: curve 10. 0.880; curve I I. I. in Fig. 3. As expected, the curve shows a shallow minimum at a low ;’ value. However, it is important to note that the c vs 2Z curve clearly has a distinct minimum. It may be said, therefore, that the DAC and OSE molecules interact strongly with each other in the micellar state. Now let us analyze the above experimental rcsu”I; thermodynamically to clarify the behavior of L1rc surfactant mixture in the adsorbed and miccllar states. The total surface density of the surfactants and the composition in the adsorbed film corresponding to rig and 2, are defined, respectivcl:? , as f-u = 2r;’ + 1-y and (3) Fig. 2. Surhcc tension vs composition stattt total molalitics. rig (mmol kg-‘): curves at various curve I. 4; curve curve 3, 8: curve 4, 10: curve 5, 12: curve curve 8. IS: curve 9, 20: curve 10. 22: curve 6. 14: curve con2, 6: 7. f6: I I, -f vs ,V2. Fig. T. Total mololity vs composition c~urvcs at various cons!ant values of lhc surhx Icnsion ;’ (mN m- I): curve i. 60: curve 2. 55: curve 3. 50; curve 4. -16; curve -IO: curve 8. 3X: curve 9. 36: curw 5. 44: curve IO, 34: curve 6, 41: curve 7. ! i. 32: curve I?. s vs 2,. where I-7 and I-y arc the surface excess numbers of moles of DAC and OSE w,th reference to the two dividing planes chosen so as to make the surface excess numbers of moles of water and air equal to zero, respectively. The values of F” ai temperature 7T pressure p and composition X1 are evaluated by app!ying the following equation to the ;I vs fir curves given in Fig. 1: P” = - (G/R T)(?;/L7rit),e,,ex (5) where the subscript X denotes Xz [23,24-j. Here the aqueous solution has been assumed to bc ideal. because it is sufficiently dilute. The results are shown in the form of a p’r vs iit plot in Fig. 4. It is seen that the 7”’ value increases gradually with rir and approaches the saturation value at a concen- tration I: ‘at- the SMC. This supports the view that are miscible with the DAC and 03% molecules each other over the whole composition range in the adsorbed film. In order to examine the miscibility of the surfactants, we proceeded to estimate the composition 2;. Its values are calculated by making use of the equation [23,24] X’,’ = .Qz - (~,~,/ril)(L?ri1/~ji~j~.~,~ (6) Applying Eq (6) to the sir vs 2, curve depicted in Fig. 5 Fig. 3, the lit vs j2-y curve was obtained; shows the total molality vs composition diagram at constant surface tension. It is seen from Fig. 5 that the ril vs 2; curve deviates negatively from 56 straight line connecting the ril values of pure DAC and OSE and its deviation is large enough to have a minimum at a low ;’ value. Both the curves are found to coincide with each other at the minimum point. Therefore the total modality vs composition diagram can be called the phase diagram of adsorption, which rcprescnts the equilibrium between the adsorbed film and solution. In the case of the DeAC and OSE mixture, the liz vs ?y curve was observed to deviate negatively, though not significantly. from a straight line. The diagram is compared with that of the DAC and OSE mixture at ;1=40 mN m-I in Fig. 6; the difference in shape between the diagrams seems tc, be one of degree. Takinp into account that the to?31 molaIity vs compnc (1 diagram for a mixed adsorbed film is a thcri, Jynamic analog of the vapor pressure vs composition diagram for a twocomponent mixture [293, DAC and OSE are said the I I I I 61 / mmol Fig. 4. Total constant curve 0.176; surhcc density compositions, 4. 0.333: I I 20 10 kg-’ vs total molality gy2: curve curve 30 curves at various I. 0: curve 2, 0.1 16; curve 3. 5. 0.428: curve 0.538: curve 8. 0.067: curve 9, 0.X19: curve 6, 0.489; curve IO. 0.880: curve 7. I I. I. \ 80 _t\ \ \ \ \ \ \ \ \ \\ \\ ,\ \\ 20 \ \ 10 0’0 Fig. 5. Total --- I 0.2 molality * rig vs jiy) curves I 1 0.4 0.6 22 ,x; vs composition at constant surface I. 50; curves 2, 40; curves 3. 32. diagrams tension I 3.8 (-, I 1 ril vs ,fiiz: ;’ (mN m-l): 0 I I 0.2 I I O-4 0.6 xhz ,2; I 0.8 Fig. 6. Total molality vs cowpositIon diugrams (---, tin vs 2;II: --. rif vs A?‘, at 7=40 mN m-‘: curves I. DAC and OSE mixture: curves 1. DcAC and OSE mixture. K. Maronrrtra 57 er q~~.~Colloid.s 5 trj2~cc.s G7 ( 1992) 53-59 form a negative azcotropic mixed film at a low surface tension. Accordingly, we can conclude that the interaction between DAC and OSE molecules are attractive in the adsorbed film. Now we are interested in exploring the miscibility of DAC and OSE in the micellar state. The mole fraction _%y of OSE in the micelle particle is dehned by to j;ly = NJ(‘N, + NJ (7) of where N1 and N, are the excess numbers molecules of DAC and OSE with reference to the dividing spherical interface which makes the excess number of molecules of water equal to zero. respectively. The numerical value is estimated by applying the following equation C23,24] lo the r? vs ki, c11I’vc: ‘P’;: L- ?-: - (.C _ P,/i;i;:~i~;:~~;!;;_,,, The va.lues form of a 2’: curve diagram is where both the curves coincide. Therefore it can be said that the DAC and OSE molecules interact attractively with each other in the micellar state and form a significant negative azectrope. In Fig. 8, the above phase diagram of micelle formation representing the equilibrium between the micelle and solution is compared with the corresponding one for the DcAC and OSE mixture. At first glance, there seems to be a discrepancy in shape between them. However, noting that the difference in c between pure DAC and OSE is extremely small compared with that between pure DeAC and OSE, the discrepancy is thought to be not so large. By drawing the ;” vs 2;’ curve with the use of Figs 3 and 8, anr: comparing it with the ;” vs _%;‘curve, we can infer 101: :_)$:pendcncc of ;’ on rir in the concentration range Grave the CMC; this inference is in fair agrccm~:nt with the cxpcrimental (8) o!;;:li:::?:. ?r’ton. “ig. 3 are shown in the I? vs 2;’ cur. :‘ together bvvrth the c vs in Fig. 7. The C.:‘GY vs cclin;:+)si.‘ion clearly seen to have a ~c.:i;:ite minimuin I ‘0 I 0.2 1 I 0.6 08 I 0.4 - $2 , ay Fig. 7. CMC I’$ ,vy. vs cnmposition d:agram: --, i- vs 2?: - - - , i? Fig. 8. CMC vs composition diagrams (-, e vs 2:‘): cwves I. DAC ad OSE mixture; and OSE misture. c vs ‘v2: ---, curves 2, DcAC result seen in Fig. I. Furthermore, the ;” vs 2, curve carries useful information concerning the relationship of the composition of the micelfc to that of the adsorbed film %?!j.’ ht the CMC [23,24-J (9) where fHnC is the total surface density of DAC and OSE at the CMC. Thus the value of z’,‘*’ at a given 2, is obtained by estimating the slope of the ;” vs .%2 curve given in Fig. 2 and by reading the values of .@ and p H*Cfrom Figs S and 4 respectively. The result is shown in Fig. 9 whcrc the ;qc vs a:*’ curve is drawn together with the ;” vs 2;’ curve. This figure may be referred to as the phase diagram representing the equilibrium between the micellc and adsorbed film at the CMC. It is seen that the curves have a maximum a; which they agree with each other. This is in accordance with the theoretical cxpcctations of Rosen and Murphy , although their theory is based on regular solution theory and is inapplicable to ionic and non-ionic surfactant mixtures 1231. Therefore we conclude that the molecular interaction between DAC and OSE is more attractive in the micellar state than in the adsorbed state. The conclusion is consistent with the fact that the s vs 2, curve has a deeper minimum than the ril vs .%2 curve at 32 mN m - ‘, as seen in Fig. 3. Finally, we notice that the DeAC and OSE mixture has no cxtremum in the diagrams L-241. From this WC may mfcr that the interaction between DAC and OSE molecules is siightly stronger than that bekveen DeAC and OSE molecules in the micellar and adsorbed states. 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