NOTES
Dec., 1961 I .o
0.9 -
due to the effect of steric hindrances and restricted flexibility of these linear polymer molecules. The - C F r and -CFa groups thus are prevented from being distributed in the same arrangement along the free surface of the solid as they are in any individual polymer molecule. The necessity of pressures from 2000 to 10,000 atmospheres and temperatures above 200' in the preparation of the poly HFP3 are a strong indication that restrictions arise from the steric configurations and the limited accessibility of the bonds of the monomers.
\
0.5-
----
2267
HEAT CONTENTS, HT - H298.10K, FOR SOME HALIDES OF MERCURY, CADMIUM AND BISMUTH AT THEIR MELTING POINTS' BY L. E.TOPOL A N D L. I>. RANSOM
\
23% H F P - T F E COPOLYMER 100% T F E I
I
L
I
120
1
o--WATER
Research Division, Atomics Internotzonal. -4 Dinision of North American Avzatoon, Inc., Canoga Park, Calzfornzo Receioed June 6. 1961
In previous investigations2 the heats of fusion and heat capacities of BiC4, BiBra, HgC12, CdCl2, CdBrz and CdIz near the melting point were measured. However, the heat contents relative PEXACHLORO- ' /PROPYLENE to 298.15'K. were not published for these halides ----(-DIcYcL~~HExYL 1 at the melting point. Since it recently was pointed out3 that such data would be of value, the Hm,p, - Hzgs 1 ° increments ~ as well as the heat capacities (assuming they are constant) of the solid salts for , I the same temperature range are listed in Table I. 0 20 40 63 80 100 MOLE FERCENT HEXAFLUOAOPROPYLENE IN COPOLYMER. Although the agreement between the heat content Fig. 2.-Wetting of HFP polymer and HFP-TFE copoly- increment of this study and that of an earlier work4 mers by miscellaneous liquids. for CdCIzis poor, the present value as well as those that of -CF2- groups,lJ the yc value of a 100% of all the other salts except the bismuth halides hexafluoropropylene polymer shows the lowest sur- are in excellent agreement with literature estimates5 (Table I). Included in Table I with the face energy encountered to date in a bulk solid. It was predicted by extrapolating the results heat capacities for the temperature range 298OK. of wetting studies on TFE-HFP copolymers,2 to the melting point are those values found near that a 100% H F P polymer will exhibit a yc of the melting points of the salts. As can be seen, 15.5 dynee/cm. The actual value obtained in this TABLE I study is 16.2 dynes/cm. This is in reasonably HEATCONTENTS, HT H ~ W J ~ATKMELTINQ , POINTAND good agreement with the predicted value, if one HEAT CAPACITY DATAFOR HgC12, BiCl,, BiBra, CdC12, considers the extent of extrapolation from 23 CdBr2 AND CdIl to 100 mole % HFP. (A 23 HFP mole % was the Heat capacity Ifm.g. - ~ z 8 8 . 1 O K (cal./deg.mole) highest available in the studies of TFE-HFP M.P., (kcal./mole) m.p. to copolymers.) The extrapolation was made with Salt OK. This work Lit.# 2981.OK. near m.p. the assumption that a graph of contact angle us. HgClz 552.7 19.4 19.2 4.93 5.1 mole yo H F P for any given liquid mill continue in BiClr 506.6 5.27 4.6 25.3 26.1 a straight line throughout the total mole yorange, as BiBra 492.2 5.11 4.3 26.3 26.0 it did for polymers containing up to 23 mole yo CdClr 842.1 11.21 10.9, 13.14 20.6 28.5 HFP.2 This linearity was considered only a con- CdBrp 841.2 20.4 22.8 11.06 10.9 venient approximation. Figure 2 shows the com- CdIi 20.3 21.5 661.2 7.36 7.3 plete graph obtained when the observed 0 values for the 100% H F P also are plotted. It can be there is virtually no change in the heat capacity seen that slight deviations from a straight line with temperature for any of the solid salts except resulted with each alkane liquid, and greater CdC12 and CdBr2. Since these two halides have deviations with the hydrogen-bonding liquids, (1) This work was performed under contract to the U. 9. Atomic such as formamide and ethylene glycol. This is Enerw Commission. L. E. Topol, S. W. &layerand L. D. Ransom, J . Phys. Chem., in general accordance with the earlier investiga- 64,(2)862(a)(1960); (b) L. E. Topol and L. D. Ransom, ibid.. 64, 1339 tion of halogenated organic solid surfaces.6 (1960). That the actual value of yc of the 100% H F P (3) L. Brewer, private communication. (4) A. N. Krestovnikov and G . A. Karetnikov. Legkie Metal.. 4, 35 is so close to the predicted one, and not to the calculated one of 13.3 dynes/cm.2, is undoubtedly (1935). (5) L. Brewer, el aZ., "The Chemistry and Metallurgy of MisceUane1
-
( 5 ) H. W. Fox and W.A. Zisman, J . Colloid Sei., 7 , 228 (1952). ( 6 ) A. H. Ellison and W. A. Zisman, J . Phys. Chem., 68, 260 (1954).
ous Materials: Thermodynamics," ed. by L. L. Quill, McGraw-Hill Book Co., New York, N. Y., 1950.
NOTES
2268
Vol. 65
much higher melting points than do the others, the occurrence of an increase in heat capacity over this larger temperature interval is not unexpected. However, the reason for the much larger change for CdClz than for CdBrz is not clear in view of the similar nature of these salts.
PARTIAL MOLAL VOLUMES IN LIQUTDLIQUID MIXTURES BY RYOICHIFUJISHIRO, Kbz6 SHINODA AND J. H. HILDEBRAND
Department
OJ
Fig. 1.-Partial
Chemistry, Unirersity of CaliJornia, Berkeley 4 , CaE. Receiiied J u n e 19, 1061
The work here report,ed is part of a study of the role of expansion in the theory of solution. The magnitude of this factor first became strikingly evident by the observation of Glew' that the partial molal volume, Vz, of iodine in f-heptane a t 25' and a t virtually infinite dilution (mole fraction 1.8 X is 100 cc., a 70% expansion over its (extrapolated) liquid molal volume, 59 cc. Its partial molal volumes in a number of other solvents were measured by Shinoda and Hildebrand. Smith, Walkley and Hildebrand3 obtained figures for the partial molal volumes of bromine and stannic iodide at high dilution in the same series of solvents. Jolley and Hildebrand4 published values of the partial molal volumes of gases. Walkley and Hildebrand6 found that VZ for Hz in benzene and in toluene exceeds that of Dzby 10%. The paper by Smith, Walkley and Hildebrand compared the partial molal volumes of one solute in a series of solvents; this research compares a series of solutes in the same solvent. The method used was t.he simple, rapid, accurate one described in ref. 2. A long, thin glass capsule containing a small, weighed amount of a solute is drop ed into a large bulb filled with a solvent through its capilkry stem. The capsule is broken and the solute dissolved by means of a large glass ball within the bulb. The partial molal volume is calculated from the rise of the liquid in the capillary stem. The amounts of the solvent and solute are such that the values of ?n are virtually those for infinite dilution (mole fraction M 10-3). The materials used were purified by methods previously described.2
The values of V2 thus obtained are given in Table I, together with t'he molal volumes, Vzo, and the solubility parameters of the pure components, 6. The values of Vz are the means of two or more determinations agreeing well within 1%. Figure 1 is a plot of [(Vz - V Z O ) / V ~ ~ ] 'us. / ~ solubility parameters in the two solvents, CC14 and CSz. This method of plotting is suggested by the equation 02
- vP
=
nfllRT In
y2
(1)
where is the compressibility of t,he solvent when the solute is very dilute, as in these experiments; yz is the activity coefficient of the solute, and n is (1) D. N. Glew and J. H. Hildebrand, J. Phys. Chem., 60, 618 (1956). (2) I(. Shinoda and J. H. Hildebrand, ibid.,62, 272 (1958). (3) E. B. Smith. J. Walkley and J. H. Hildebrand, ibid., 63, 703 (19591. (4) J. E. Jolley m d J. H. Hildebrand. J . A m . Phern. Soc., 80, 1050 ( 1 958). ( 5 ) J. IVdkIey and J . If. IIildebrand, ibid., 81, 4139 (1959).
excess volumes at high dilution and solubility psrameters.
the ratio (bEl/bV1)p,~to AE~"/VL E is energy in cal./mole, AE" is energy of vaporization. Equation l, without the factor, n, was given by Hildebrand and Scott.6 Inclusion of the factor, n, is explained in a more detailed derivation to be given in a book now in press.7 Upon combining equation 1 with the simple equation for regular solutions R T In
y2 =
v20912(6n -~ 3 ~ ) ~
(2)
where cpl is the volume fraction of the solvent, here -1, we obtain (3)
We see from Fig. 1 that the left-hand member is closely proportional t'o f (62 - 61) except in the cases Of n-C7H1tj1 i-CsHu, C6H6 and 1,2,3-CeH~(CH,):, the points for which are designated by crosses. The slopes of the lines are almost exactly 4 5 O , hence the proportionality constant is close to 0.1. The wide range of expansion covered by this regularity, up t o 9%, is especially noteworthy. TABLE I PARTIAL MOLALVOLUMES OF SOLUTES, V2, AT 25" A N D HIGH DILUTION -vZ
Solute
6
C7F16 c-C~FUCF~ i-CsHn c-CdClnFs n-C~Hls CClzF.CClF2 c-CsHiz
5.85 6.0 6.85 7.1 7.45 7.5 8.2 8.6 8.8 9.15 9.5 10.0 10.5 11.5
cc1,
s-CsHs(CHt)r CsH6 CsHsC1
csn CHBr3 Brz
V1'
225.5 195.8 166.1 142.5 147.5 119.8 108.8 97.1 139.6 89.3 102.1 60.7 87.8 51.5
cs2
... .., 172.2 155.5 154.4 127.7 112.1 99.2 144.5 91.6
... ... 88.1 52.6
In----CCl4
246.5 211.6 167.5 146.6 149.1 120.9
n-CIHl6
... ...
254.6 218.3 167.4 153.6 ... 124.5 ... 98.2
,
...
. .
... .. .
91.0 105.5 62.0 63.4 90.9 92.1 54.75 . . .
This empirical constant does not agree very 'Iz. The compressibilities well with values of (np) of CC14 and CS2 are 1.11 X and 0.93 X atm.-',, respectively, and the n-values are, respectively,8 1.07 and 0.89. The figures for p are (6) J. H. Hildebrand and R. L. Soott, "Solubility of Nonelectrolytes," Reinhoid Publ. Corp., New York, N. Y., 1950, p. 141. (7) J. H. Hildebrand and R. L. Scott, "Regular Solutions," Prentice-Hall, New York, N. Y.,1962, i n press. (8) Ref. 6, p. 97.
