Dependence of Contact Angles on Temperature: Polar Liquids on

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NOTES

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the change from phenol to phenolate to increase JrneI, while affecting Jm,,,’ only slightly. This behavior is noted in all three phenol systems in Table I, and it is reasonable to assume that the values listed as J,,, are for protons adjacent to the phenolic hydroxyl. A reverse behavior would be expected for the coupling between the protons ortho to the amine group in going to the conjugate acid. The values for the sets JmeiaJ,,,,’ for p-nitroaniline and its conjugate acid, as listed in Table I, either indicate no change in these values or else an increase in Jmeia’ upon protonation. No such change in Jm,,‘ was noted in the phenolphenolate series. In view of the wide range of solvent conditions necessitated in this study, no conclusions regarding changes in chemical shifts seem warranted.

Experimental Section Spectra were determined on a Varian A-60 operating at ambient temperature. Six or more sweeps were made on each compound, and the line positions were averaged. Typically, the standard deviations of the line positions were 0.04-0.07 cps, and often lower values were obtained. The spectra were typical AA‘BB’ spectra and were analyzed according to the procedure of Grant, Hirst, and Gutowsky.6 Values of the spectral parameters were refined with the aid of the FREQINT IV A 1620 program until all lines fit to better than 0.1 cps. Empirically, we noted that variation in any of the coupling constants by 0.1 cps from the optimum values determined by this procedure resulted in perceptibly poorer fit of the observed and calculated lines. It was felt that the coupling constants so determined were, therefore, good to h0.l cps. The aromatic compounds were all commercially available samples. The 4-methyl-4-trichloromethyl2,5-cyclohexadienonewas kindly supplied by Dr. M. G. Reinecke of these laboratories. Fuchsone w m synthesized by the method of Bistrzycki and Herbst.’ The phenols were determined in 10% solutions of methanol, arid the phenolates were run in the same solvent containing about 10% excess dissolved potassium hydroxide. p-Nitroaniline was run as a 20y0 solution in acetone as was the cyclohexadienone. A 16% solution of p-nitroaniline in trifluoroacetic acid served as the source of the anilinium spectrum. Fuchsone was determined as a 20% solution in deuteriochloroform. Tetramethylsilane was used as an internal standard in each case. (6) D. M. Grant, R. C. Hirst, and H. S. Gutowsky, J . Chem. Phys., 38, 470 (1963). (7) A. Bistrzycki and C. Herbst, Ber., 36, 2333 (1903).

The Journal of P h y s h l Chemistry

Aclcnowledgment. We wish to express our gratitude to the Robert A. Welch Foundation for its generous support of this work.

Dependence of Contact Angles on Temperature : Polar Liquids on Polypropylene

by Harold Schonhorn Bell Telephone Laboratories, Incorporated, Murray HiU, New Jersey (Receized June 17, 1966)

Recently, experimental results for the temperature dependence of the contact angle of liquids on nonpolar solids have been presented by Phillips and Riddiford,’ Johnson and Dettre,2Brewis,*and this a ~ t h o r . ~ In this note we shall present the results for the polar liquid-polypropylene (melt crystallized film) systems based on the reported surface tension measurements for polypropylene.6 Assuming that ysvd = ( ~ L v ) P ~Fowkes’ , modifications of the Young equation yields

YLV

where subscript P refers to polymer and superscript d refers to the dispersion component of the surface tension. For polypropylene, where only dispersion forces are assumed operative, YSVd = ( ~ L v ) P . Further, assuming the ratio Y L V ~ / ~ L to V be temperature invariant, we obtain

where k = y ~ v ~ / y t v .The calculated and experimental results are shown in Table I. Experimental details are given el~ewhere.~As has been observed in the polar liquid-polyethylene ~ y s t e m sthe , ~ contact angles of these liquids on polypropylene appear to be in(1) M. C. Phillips and A. C. Riddiford, Nature, 205, 1005 (1965). (2) R. E. Johnson, Jr., and R. H. Dettre, J, Colloid Sci., 20, 173 (1965). (3) D. M. Brewis, presented a t the 22nd Annual Technical Conference, S.P.E., March 1966. (4) H. Schonhorn, Nature, 210, 896 (1966). (5) H. Schonhorn and L. H. Sharpe, J. Polymer Sci., B3,235 (1965). (6) F. M. Fowkes, J. Phys. Chem., 66, 1863 (1962); 67,2538 (1963); Advances in Chemistry Series, No. 43, American Chemical Society, Washington, D. C., 1964, p 99.

NOTES

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Table I : The Temperature Dependence of the Wettability of Polypropylene by Water, Glycerol, and Formamide T,

(YLV)P,

OC

dynes/cm

dynes/cm

I-

0 10 20 30 40 50 60 70 80 100

29.2 28.8 28.4 28.0 27.6 27.2 26.8 26.4 26.0 25.2

75.60 74.22 72.75 71.18 69.56 67.91 66.18 64.40 62.60 58.90

0.300

20 90

28.4 25.6

63.4 58.6

0 20 50

29.2 28.4 27.2

59.9 58.2 55.7

YLV.

YLVd, dynes/om

COB

e

Water-Poly propylene 22.7 -0.3302 22.2 -0.3283 21.8 -0.3155 21.3 -0.3144 20.8 -0.3099 20.3 -0.3079 19.8 -0.3049 19.3 -0.2981 18.7 -0.2971 17.6 -0.2869

109 108 108 108 108 108 108 107 107 107

...

0.584

G1y cerol-Pol ypropylene 37.0 0.0221 34.2 0.0102

89 89

91-92 90-91

87

0.679

FormamidePolypropylene 40.7 0.1519 39.5 0,1512 37.8 0,1526

81 81. 81

83

...

...

... 95

...

...

...

*.. ... ,..

...

...

... ...

...

...

E. Wolfram, KolloziZ-Z., 182, 75 (1962).

sensitive to temperature. Again, as observed for the polar liquid-polyethylene systems, the experimental and calculated contact angles agree well except for the results with water. It is possible that the choice of 21.8 dynes/cm for ( Y L V ~ ) E ~ Oat 20’ needs some revision to obtain better agreement with the experimental contact angle. The apparent insensitivity of the contact angle to temperature is related to the relative constancy of [(~Lv>P/YLv]’/’ in eq 2. However, this is probably not general with respect to all liquids in contact with low energy polymers. Since the test liquid and polymer probably have different critical temperatures (To), the temperature where YLV = 0, there should be an intermediate temperature where ( ~ L V ) P = YLV. When this condition is fulfilled, 8 = 0. From the critical temperatures of low molecular weight n-hydrocarbons, it was estimated? that T, of polyethylene is 1031OK, considerably higher than any of the polar liquids included in this study. A similar value of T , is expected for polypropylene based on the work of Frisch and Rogers.8 Therefore, at some temperature below the T , of the polymer, assuming no polymer degradation, 8 = 0. However, wetta-

(7) H. Schonhorn, Makronaol. Chem., 93,262(1966). (8) H. L. Frisch and C. E. Rogers, Jr., J . Polymer Sei., C12. 297 (1966).

temperatures, well below the T, of both liquid and polymer, but, as shown in Table I, there is a general trend to a lower value of 8 as T increases.

Solvent Effects in the Proton Chemical Shifts of Acetonitrile and Malononitrile’

by Taku Matsuo and Yasushi Kodera Department of Organic Synthesis, Faculty of Engineering, Kyuahu University, Hakozaki, Fukuoka-Shi, Japan (Received July 18, 1966)

Since the original suggestion of the “reaction field theory”2 and its experimental application to the proton chemical shifts of acetonitrile in various solventsla the Buckingham formula has been widely used in the investigation of the polar effect of solvent on the chemical shift of solute molecule. Buckingham’s formula gives the change in nuclear screening constant of a proton held by an X-H bond in terms of the reaction field R of the media in the form thesis, Faculty of Engineering, Kyushu University. (2) A. D. Buckingham, Can. J . Chem., 38,300 (1960). (3) A. D. Buckingham, T. Schaefer, and W. G. Schneider, J . Chem. Phya., 32, 1227 (1960).

Volume 70, Number 12 Decembm 1966