SYNERESIS OF SODIUM OLEATE GELS IN ORGANIC SOLVENTS

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1 SYNERESIS OF SODIUM OLEATE GELS IN ORGANIC SOLVENTS Part V. Syneress of Sodum Oleate Gels n Mxtures of Organc Solvents BY MATh, PRASAD, F.A.Sc. AND V. SUNDA.M (From the Chemcal Laboratores, The Insttute of Scence, Bombay) Receved September 23, 1950 VARIOUS nvestgators have ponted out the mportance of the nature of the dsperson medum on the syr..ercss of gels. Usually the dsperson medum has been changed by the addton of other substances, such as acds, alcohols and others. Very few nvestgators have studed the syneress of the same gel-formng substance n dfferent meda. Hard/observed that the syneress of azomethne gels starts n a fcw mnutes n an ether gel, n a few hours n an alcohol or an aldehyde gel and n a few days n a carbon tetrachlorde gel. Le Blanc and Kroger 2 have notced that the syneress of caoutchouc gels n benzene starts earler than n carbon tetrachlorde; the velocty of the man amount exuded n both the solvents s the same but the fnal amount exuded by the gel n carbon tetrachlorde s somewhat greater. It has been observed n a prevous communcaton 3 that gels of sodum oleate n xylene synerse more rapdly than those n pnene. In the present nx, estgaton, an attempt has been made to study the syneress of sodum oleate gels n mxtures of (a) xylene and toluene and (b) xylene and pnene. EXPERIMENTAL (a) g. of sodum oleate was weghed out nto fve dfferent testtubes of the same nternal dameter (1.65 cm.) whch were flled wth several mxtures of xytene (A) and toluene (B). It was observed that f the mxtures contaned more than 70% by volume of toluene, the soap does not dssolve completely and the gels obtaned are not homogeneous. Hence mxtures contanng more than 70 toluene were not used. (b) g. of sodum oleate was weghed out nto seven dfferent testtubes of the same nternal dameter (1.65 cm.) whch were flled wth several mxtures of xylene (A) and pnene (C). The test-tubes were placed n an ol-bath, the temperature of whch was mantaned at C. n the case of mxtures of xylene and toluene and at C. n the case of mxtures of xylene and pnene, and the 344

2 Synertss of Sodum Oleate Gels n Organc Solvenls--V 345 contents of the test-tubes strred tll all the soap had dssolved. Then a long condensng tube was attached to each test-tube and the test-tubes were allowed to stand n the bath tll all the bubbles had dsappeared. The testtubes were then tghtly corked and transferred to a thermostat or a thermos flask dependng on the temperature at whch readngs were taken. At defnte ntervals of tme (t) after the gels had set, the amount of syneretcum (X) n each test-tube was measured by the method followed n Part II. n The temperatures used were 30 C. and 40 C. n the thermostat and 20 C. n the thermos flask. Sodum oleate used was of the B.D.H. qualty and the xylene used was obtaned from S. B. Penck & Co., New York. Toluene was obtaned from May & Baker, Ltd., and pnene from the Cty Chemcal Corporaton, New York. The results obtaned are gven n Tables I and II. DISCUSSION OF RESULTS It s seen from Table I that n the case of gels n mxtures of xylene and toluene the syneress ncreases wth an ncrease n the amount of toluene n the mxture. Ths fact s seen at all the temperatures. Also, the amount of syrteress at any one composton of the mxture s greatest at 20 C. and decreases as the temperature s ncreased. The effect of temperature on gels n mxtures of solvents s therefore smlar to that on gels n these pure solvents (cf. Part III of ths seres'). The graphs of syneress aganst composton of the mxture are more or less straght lnes for all the tme ntervals TABLE I Values of X for gels n mxtures of xylene and toluene at varous ntervals Composton Temperature '20 C. Temperature 30* C. Temperature 40 C. o[ the mxtare f A ] B 15 ran.; ' 30 ran, 1 hr I 2 hr. 15ran. 30 mm.l " ' I hr. 2 hrs. 15 ran. 30 mn.[ I hr. 2 hr ]0c.c. 8c. fc.c 4c.c. 3c.c. 0cc: 2c.c. 4c.c. 6c.c. 7c. I ! I o J [ , l , t I *

3 346 Mata Prasad and V. S u n d a r a m TABLE II Values of J( for gels n mxtures of xylene and pnene at varous ntervals omposton of the mxture A C Temperature 20 C. 15 mn.] 30 ran Temperature 30* C. 1 hr. ] 2 h r s. 15 ran 30mn. hr. F 0 c.c cc. I e,c c.c. 2c.c. 2" c. 4c.c c.c0 6c.c. 2 e x. 8c.c. I0 c. 0c.c.l 10c.c.! I Temperature40* C. 2 hrs, 15 mn. 30 ran. I hr. 2 hrs I " ! " O , ' J Oo studed, ndcatng the possblty of an addtvty law. The graphs of syneress aganst composton at 20 C. are shown n Fg. 1. Snce no gels are formed n pure toluene wth 0.10 g. of the soap, the valdty of the addtvty law cannot be tested n any case. It s seen from Table II that on ncreasng the percentage of pnene n the mxture of xylene and pnene, the amount of syneress of gels at frst ncreases, reaches a maxmum n a mxture contanng 80 xylene and 20 pnene, and then gradually falls off. The graphs of syneress aganst composton of the mxture are S-shaped for all the tme ntervals and temperatures studed; those n the case of syneress at 20 C. are shown n Fg. 2. The amount of syneretcum gven out by a gel n pure xylene s greater than that gven out by the same gel n pure pnene. Hence, t would be expected that on ncreasng the amount of pnene n the mxture the amount of syneretcum should contnually decrease. Palt and co-workers have shown that n the case of organc mxtures contanng a glycol as one component, the solublty of soap reaches a maxmum value at ntermedate compostons of the mxture. Probably n the mxtures of pnene and xyene me solu0lty has an optmum value n the mxture contanng 80 xylene and 20% pnene. Snce the same amount of soap s used n all the mxtures the amount of supersaturaton wll be teast n the mxture of 80 o xylene and 2 0 pnene and hence the gel formed wll be weaker (cf Part IV"). Therefore the syneress of the gel n the

4 Syneress ot; Sodum Oleage Gels n Organc Solvents--V 347 3") Z.*70 ' -,)o -Z,4O X X Z.-IO..Io ao 2.,4. 6 FIo. oe 1 L'I)O,-4o 2-40 I)... -_ j,, r A j. g 6 l F I G. = ) mxture of 80% ylene and 20 pnene would be maxmum. Such an effect s not observed n the mxtures of toluene and xylene, probably because both these solvents belong to the same homologous seres and the solublty n these solvents probabi fouows the addtvt law,

5 348 Mata Prasad and V. Sundaram It s also observed, as n the case of gels n mxtures of xylen and toluene, that syneress at a lower temperature s greater than at hgher ones. Further work for the examnaton of the behavour of soap gels n mxtures of organc lquds s n progress. One of the authors (V. S.) s grateful to the authortes of the Unversty of Bombay for the award of a Research Studentshp whch enabled hm to carry out ths nvestgaton. SUMMARY The rates of syneress n mxtures of (1)xylcnc and toluene and (2) xylenc and pnenc have becn nvestgated. In the case of xylene-toluene mxtures, syneress seems to be addtve whcreas n the case of xylenepnene mxtures, synercss shows a maxmum value n a mxture of 80 xylene and 20 pnene. REFERENCES 1. Hardy.. Proe. Roy. Soe., 1912, 87 A, Le Blanc and Kroger.. Z Elektrochem., 1921, 27, Prasad and Sundaram.. Part II, Communcated for publcaton Part Ill,,,,, 5. PaIR and Co-workers..... Indan Chem. Sac., 1942, 19, 271 ; 1949, 26, 12; jr Am. Chem. Soc., 1947, 69, 3120 ; 3". Am. Ol Chem. Sot., 1947, 24, Prasad and Sundaram.. Part IV, Communcated for publcaton.

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