The temperature-dependence characterization of insoluble films at the air-water interface

The Temperature-Dependence Characterization of Insoluble Films at the Air-Water Interface In studies of monomolecular films at the air/water interface, it is frequently desirable to compare the temperature dependence of different substances. Hitherto, this has most commonly been done by means of a comparison of the respective "half-expansion temperatures" (1), generally at a pressure of 1.4 dynes/cm (T1/2). This method was popularized by Adam (2) and does provide an approximate method of comparing temperature-dependent monolayer behavior. It has, however, several drawbacks. One obvious problem lies in the fact that, for any substance which does not achieve a fully condensed isotherm above 0°C, it is physically impossible to measure T~:2. In fact, for most substances, very few isotherms are obtained at temperatures more than about 2°C below the half-expansion temperature, since they generally are devoid of interesting features. This results in some difficulty in plotting the data in the form necessary to determine the precise half-expansion temperature. A second problem lies in the fact that the use of such a half-expansion temperature only allows a comparison at the temperature of the half-expansion temperature itself. This is true since different compounds have different temperatures dependences, i,e., the rate at which they expand with increasing temperature varies. It is proposed here that an improved method of tabulating temperature dependence data be used. This method is based on the experimentally determined fact that the pressure for the liquid-expanded (or gaseous-expanded)/llquid-condensedphase change is a linear function of temperature, i.e., can be expressed in the general form y = m x + b.

[1]

Here y is the pressure for the onset of the stated phase transition (rh) 1 and x is the temperature. The slope m is d~t/dT, and the Y intercept b is 7rt at T = 0°C. Of more practical interest is the X intercept To, which is the temperature at which ~t extrapolates

1 The onset of the phase transition (~t) is not always well defined. Here, we adopt the procedure of extrapolating linear portions of the liquid-expanded and intermediate regions, taking ~rt as the point of intersection.

to zero, i.e., the temperature at which the phase transition disappears (at its lower temperature limit). The linear dependence of 7rt on temperature has previously been remarked on [e.g., Ref. (3)], and was, in fact, used as a test of a theoretical equation of state by Smith (4), but the general usefulness of this linearity for the tabulation of experimental results has somehow never been taken advantage of. In Smith's case, its use was restricted to a series of straight alkane chain fatty acids (4). Tables I through IV present the constants To, m, and b for a number of substances whose monolayer temperature dependence was available. These values were obtained by means of a linear regression fit to the experimental values for 7rt and T. As can be seen from the correlation coefficient r, an excellent fit is obtained in essentially all cases. Where similar data have been obtained by differing groups for the same compound, the values ofT0 and m are not always within experimental agreement. All other factors being equal, the data having the highest correlation coefficient for a maximum number of isotherms are clearly the most self-consistent. In many instances, the differences observed may be due to differing substrate compositions, and it is for this reason that the substrate composition, when known, is stated. It should, of course, be realized that impurities, in either the film or the substrate, can produce similar effects. Use of the procedure presented here obviates to a large extent the problems associated with the use of half-expansion temperatures. Consideration is no longer limited to compounds whose phase transition has a critical temperature above 0°C. As long as the phase change occurs at a minimum of two experimentally accessible temperatures, it is possible to obtain To by extrapolating the 7rt-T data. Second, in the form of dTrt/dt, one now has a direct measure of the rate at which the substance in question expands with temperature, which can itself be of interest since it is a measure of the thermodynamics of the phase change (35). The values in Tables I and II reveal some interesting trends, only two of which will be mentioned here by way of example. (1) For fatty acid-based compounds, m decreases in the order hydroxy fatty acids (pseudomonopolar) (18) > odd-numbered fatty acids > even-numbered fatty acids > hydroxy fatty acids (bipolar) (18). In all cases, m for the ester is lower

597 0021-9797/78/0663-0597502.00/0 Journal of Colloid and Interface Science, Vol. 66, No. 3, October 1, 1978

Copyright © 1978 by Academic Press, Inc. All rights of reproduction in any form reserved.

598

NOTES TABLE I

Linear Regression Constants a for the Temperature Dependence of the Expanded/Condensed Phase Change in Monolayers of Fatty Acid-Based Compounds r

Number of points

20.7

0.947

7

pH 2 HCI, 2 M NaC1

5

4.9 8.2 7.5

0.999 0.955 0.980

7 4 8

pH 2 HC1 pH 2 HC1, 2 M NaC1 H20

6 4 4

1.10 1.16 1.29 1.10

-7.5 -8.2 -11.0 -7.3

0.999 0.994 0.996 0.997

8 7 8 23

pH 2 HC1 pH 2 H2SO4 H20 pH 2 HC1

7 8 4 9

-5.6 5.2

0.77 0.82

4.3 -4.3

0,983 0.999

9 6

pH 2 HC1 H20

9 10

18.0 17.5 19.7 17.7

1.21 1.10 1.37 1.17

-21.7 -19.2 -26.8 -20.7

0.997 0.997 1.000 0,999

7 9 5 4

pH 2 HCI pH 2 H~SO4 HzO H20

11 8 12 4

Compound

To

m

Dodecanoic acid

-20.9

0.99

Tridecanoic acid

-4.0 -8.3 -8.1

1.24 0.99 0.93

6.8 7.1 8.5 6.7

Tetradecanoic acid

Methyl tetradecanoate Pentadecanoic acid

b

Substrate

Ref.

6.0

0.87

-5.2

1.000

2

pH 2 HC1

11

Hexadecanoic acid

21.7 26.8 29.6

1.03 1.12 1.17

-22.4 -30.0 -34.8

0.998 0.991 0.998

6 6 9

H20 pH 2 HC1 H20

4 13 12

Methyl hexadecanoate

23.3 21.6 24.8

0.81 0.70 1.09

- 18.8 -15.0 -26.9

0.999 0.995 0.993

3 3 11

H20 pH 2 HCI pH 2 HCI

14 15 9

Ethyl hexadecanoate

11.4 9.8 12.6 14.7 11.8

0.68 0.46 0.79 0.74 0.59

-7.7 -4.5 - 10.0 - 10.9 -6.9

1.000 0.998 1.000 0.992 0.992

2 3 2 7 15

pH 2 HC1 pH 2 HC1 pH 5.5 H20 pH 2 HC1

11 7 16 12 9

pH 2 HC1

Ethyl pentadecanoate

1.9

0.44

0.8

1.000

2

17

Butyl hexadecanoate

-5.8 -6.1

0.47 0.43

2.7 2.6

1.000 1.000

2 2

17 15

Heptadecanoic acid

30.2

0.86

-26.1

0.999

5

H20

4

Octadecanoic acid

38.1 44.5

1.09 1.10

-41.5 -49.2

0.986 0.999

3 7

H20 H20

4 12

Methyl octadecanoate

33.9 39.1

0.87 1.05

-29.5 -40.9

1.000 0.999

2 3

3 M NaC1 H20

10 12

-40.5

18

Propyl hexadecanoate

2-Hydroxyhexadecanoic acid Methyl 2-hydroxyhexadecanoate 3-Hydroxyhexadecanoic acid

-

28.6

1.41

0.988

3

3 M NaC1

-11.7

1.38

16.1

1.000

5

3 M NaC1

19

10.0

1.47

- 14.7

0.997

8

3 M NaC1

18

-8.9

0.59

5.3

0.997

7

3 M NaCI

19

4-Hydroxyoctadecanoic acid

8.2

0.83

-6.8

0.992

6

pH 2 HCI

20

9-Hydroxyhexadecanoic acid

18

Methyl 3-hydroxyhexadecanoate

-45.7

0.24

10.9

0.998

6

3 M NaC1

12-Hydroxyoctadecanoic acid

5.2

0.35

- 1.8

0.998

3

3 M NaCI

10

16-Hydroxyhexadecanoic acid

-60.6

0.14

8.7

0.995

7

3 M NaCI

18

Diethyl ester of octadecanedioic acid Divinyl 1-12 dodecyl dicarboxylate acid 2-Ethyl octadecanoic acid

trans-9-Octadecenoic

-8.0

0.17

1.4

0.999

3

21

-4.6

0.23

1.08

0.993

3

22

-2.4

1.07

2.5

0.999

3

pH 2 HC1

23

-18.3

0.28

5.07

0.997

3

pH 2 HC1

24

" To = X intercept of a plot of 7rt vs T (°C); m = slope of a plot of 7rt vs T (dynes/cm/deg); b = Y intercept of a plot of 7rt vs T (dynes/cm); r = correlation coefficient. Journal of Colloid and Interface Science, Vol. 66, No. 3, October 1, 1978

NOTES

599

TABLE II Linear Regression Constants a for the Temperature Dependence of the Expanded/Condensed Phase Change in Monolayers of Glycerol-Based Compounds Compound

1-Monolaurin

To

m

-26.6

b

r

Number of points

Substrate

Ref.

1,03

27.3

0.992

7

pH 2 HC1, 2 M NaC1

5

1-Monomyristin

1.7 1.04 - 4 . 8 0.64

-1.8 3.1

0.996 1.000

6 2

pH2HC1,2MNaC1

5 25

1-Monopalmitin

23.5 1 . 5 9 -37.4 19.6 1 . 0 5 -20.6

0.994 0.996

4 3

pH 2 HC1, 2 MNaC1

5 25

2-Monopalmitin

1.0 1.19 - 0 . 2 0.86

1.000 1.000

3 2

pH2HCI, 2MNaCI H~O

5 26

1-Tetradecyl glyceryl ether

-1.1

1.4 0.998

3

pH 2 HC1, 2 M NaCI

5

H~O

1.26

-1.2 0.2

1-Hexadecyl glyceryl ether

18.4 0.85

-15.6

0.975

3

1-Octadecyl glyceryl ether

28.0

0.49

-13.7

0.999

3

28

2-Octadecyl glyceryl ether

10.8 0.79

-8.6

0.994

3

29

1.0

1.000

2

H~O

30 31

27

1,2-Dilaurin

-0.8

1,2-Dimyristin

25.0

1 . 2 0 -30.1

0.980

6

1-/20

1,3-Dimyristin 1,2-Dipalmitin 1,3-Dipalmitin

8.6

0.83

-7.2

0.992

4

HzO

31

40.4

1.49

-60.1

0.993

3

HzO

31

29.5 0.84 -24.9 28.1 1 . 2 6 -35.4

0.998 1.000

3 2

H20

31 15

1-Palmitoyl-2-oleoyl diglyceride

1.24

1.0

1.15

-1.1

1.000

2

H20

31

L-c~-Dimyristoyl phosphatidylcholine

-2.8 2.2

1.26 1.90

3.6 -4.2

1.000 0.999

3 6

H20 H20

32 33

L-c~-Dipalmitoyl phosphatidylcholine

17.7 15.2 19.5 19.8 16.8

1.65 1.71 1.97 1.72 1.77

-29.1 -26.1 -38.4 -34.0 -29.7

1.000 0.997 0.996 0.992 0.989

4 5 5 8 9

H~O 0.1 MNaC1 H20 0.1 MNaC1 10mMNaCI, 0.1 mM EDTA, 2 mM histidine, 2 mM TES, pH 7.4

34 35 33 36

L-/3-Dipalmitoyl phosphatidylcholine

8.1

1 . 3 4 -10.9

0.992

3

H20

33

L-a-Dipalmitoyl phosphatidylethanolamine L-a-Dipalmitoyl phosphatidylglycerol

-5.4 16.2 15.6 32.9 24.5

2.12 1.05 1.23 1.42 1.10

ll.5 -17.0 -19.1 -46.6 -26.9

0.997 0.990 1.000 0.999 0.993

4 9 2 8 9

H~O 0.1 M NaCI H20 H20 HzO

12 36 32 38 12

L-a-Dimyristoyl phosphatidic acid -~

25.0

1 . 0 3 -25.8

0.998

6

pH 5.5, BrittonRobinson II buffer

33

L-c~-Dimyristoyl phosphatidic acid -z

-3.7

1.51

0.994

8

pH 11.5, BrittonRobinson II buffer

33

L-c~-Dielaidoylphosphatidylcholine L-a-Dimyristoylphosphatidylethanolamine

5.6

37

a For definitions, see Table I, footnote a. than for the corresponding free acid (2). Among the glycerol-based compounds, the 1,2-diglycerides exhibit a significantly higher value of m than do the 1,3-diglycerides. It might also be noted that the treatment can be extended to substances which behave abnormally.

Typically, hexadecyl and octadecyl ureas (45) (Table IV) condense with increasing temperature, with the result that the m values are negative and the To values represent the m a x i m u m temperature at which a phase change is observed. Also included in Table IV are data for D(+)-tetracosanol-2-acetate, where a simiJournal of Colloid and Interface Science, Vol.66, No. 3, October1, 1978

600

NOTES TABLE III

Linear Regression Constants a for the Temperature Dependence of the Expanded/Condensed Phase Change in Monolayers of Miscellaneous Compounds

Compound

To

m

b

r

Number of points

Substrate

Ref.

Octadecane nitrile N-Octadecylnaphthyl-2-amino-6-sulfonic acid N-octadecylamine

23.3

1.95

-43.5

0.988

4

H~O

39

23.1 16.9

0.47 1.28

- 10.8 -21.6

1.000 1.000

2 2

40 41

Octadecyl methacrylate Poly(n-hexadecyl methacrylate) Dodecyl phenol DL-Tetracosanol-2 trans-9-Octadecanol

23.3 10.2 19.9 -3.0 12.2

0.87 1.24 1.77 1.99 0.94

-20.2 - 12.6 -35.1 5.9 - 11.4

0.997 0.985 0.991 0.999 0.998

4 6 3 14 9

H20 10-3 M H2SO4 H20 H20 pH 2 HC1 H~O

42 43 25 3 44

a For definitions, see Table I, footnote a. lar negative temperature dependence is indicated (3). We have also included the values for 12-doxyl octadecanoic acid, one of a series of spin-labeled (oxazolidine ring) fatty acids and esters (46, 47), where 1rt, in spite of a gradual phase transition, can be precisely defined with the definition given here. ACKNOWLEDGMENT W e wish to acknowledge the financial assistance of the Heart, Lung and Blood Institute in the completion of this work through Grant No. HL-12760. REFERENCES 1. Gaines, G. L., Jr., "Insoluble Monolayers at Liquid-Gas Interfaces," p. 182. Interscience, New York, 1966. 2. Adam, N. K., "The Physics and Chemistry of Surfaces," p. 61. Dover, New York, 1968. 3. Lundquist, M., Ark. Kemi 17, 183 (1961). 4. Smith, T., J. Colloid Interface Sci. 23, 27 (1967). 5. I, C. S., unpublished. 6. Boyd, G. E., J. Phys. Chem. 62, 536 (1958).

7. Adam, N. K., and Jessop, G., Proc. Roy. Soc. London Ser. A 112, 362 (1926). 8. Nutting, G. C., and Harkins, W. D., J. Amer. Chem. Soc. 61, 2040 (1939). 9. Joos, P., Bull. Soc. Chim. Belg. 79, 655 (1970). 10. Miiller-Landau, F., unpublished. 11. Harkins, W. D,, and Boyd, E., J. Phys. Chem. 45, 20 (1941). 12. Kellner, B. M. J., unpublished. 13. Harkins, W. D., Young, T. F., and Boyd, E., J. Chem. Phys. 8, 954 (1940). 14. Kellner, B. M. J., and Rice, D. K., unpublished. 15. Phillips, M. C., unpublished. 16. Phillips, M. C., and Joos, P., Kolloid-Z. Z. Polym. 238, 499 (1970). 17. Adam, N. K., Proc. Roy. Soc. London Ser. A 126, 366 (1930). 18. Kellner, B. M. J., and Cadenhead, D. A., J. Colloid Interface Sci. 63, 452 (1978). 19. Kellner, B. M. J., and Cadenhead, D. A., Chem. Phys. Lipids, in press. 20. Fosbinder, R. J., and Rideal, E. K., Proc. Roy. Soc. London Ser. A 143, 61 (1933).

TABLE IV Linear Regression Constants a for Substances Exhibiting a Negative Temperature Dependence Compound

To

m

b

r

Number of points

D(+)-Tetracosanol-2 acetate Hexadecyl urea Octadecyl urea 2-(10-Carboxydecyl-2-hexyl-4,4-dimethyl-3-oxazolidinyloxyl)[12-doxyl octadecanoic acid]

29.9 27.1 33.3

-1.88 -1.67 - 1.62

56.2 45.4 53.9

-0.994 -0.999 - 1.000

89.2

-0.23

20.5

-0.996

a For definitions, see Table I, footnote a. Journal of Colloid and Interface Science, Vol. 66, No. 3, October 1, 1978

Substrate

Ref.

8 7 6

pH 2 HC1

3 45 45

5

H~O

46

NOTES 21. Adam, N. K., and Jessop, G., Proc. Roy. Soc. London Ser. A 112, 376 (1926). 22. Dubault, A., Casagrande, C., Veyssie, M., Caille, A., and Zuckerman, M. J. J. Colloid Interface Sci. 62, 290 (1978). 23. Cadenhead, D. A., and Demchak, R. J., J. Colloid Interface Sci. 24, 483 (1967). 24. Izawa, M.,Bull. Chem. Soc. Japan. 25, 182 (1952). 25. Adam, N. K., Berry, W. A., and Turner, H. A., Proc. Roy. Soc. London Ser. A 117, 532 (1928). 26. Merker, D. R., and Daubert, B. F.,J. Amer. Chem. Soc. 80, 516 (1958). 27. Knight, B. C. J. G., Biochem. J. 24, 257 (1930). 28. Adam, N. K., J. Chem. Soc. 1933, 164 (1933). 29. Davies, W. H., Heilbron, I. M., and Jones, W. E., J. Chem. Soc. 1934, 1232 (1934). 30. Caruso, S. C., Ph.D. Thesis. Chemistry Department, University of Pittsburgh, 1954. 31. Koval, V. A., M. A. Thesis. Chemistry Department, State University of New York at Buffalo, 1978. 32. Cadenhead, D. A., Demchak, R. J., and Phillips, M. C., Kolloid Z. Z. Polym. 220, 59 (1967). 33. Albrecht, O., Gruler, H., and Sackmann, E., J. Phys. 39, 301 (1978). 34. Ries, H. E., Jr., Matsumoto, M., Uyeda, N., and Suito, E., Advan. Chem. Ser. 144, 286 (1975). 35. Phillips, M. C., and Chapman, D., Biochim. Biophys. Acta 163, 301 (1968). 36. Tr/iuble, H., Eibl, H., and Sawada¢:~H~., Naturwissenschaften 61, 344 (1974). 37. Hui, S. W., Cowden, M., Papahadjopoulos, D.,

601

38. 39. 40.

41. 42. 43. 44. 45. 46. 47.

and Parsons, D. F., Biochim. Biophys. Acta 382, 265 (1975). Rice, D. K., unpublished. Copeland, L. E., and Harkins, W. D., J. Amer. Chem. Soc. 64, 1600 (1942). Kellner, B. M. J., Ph.D. Thesis. Chemistry Department, State University of New York at Buffalo, 1977. See reference 1, p. 231. Naegele, D., and Ringsdorf, H., J. Polymer Sci. 15, 2821 (1977). Nakahara, T., Motomura, K., and Matuura, R., Bull. Soc. Chem. Japan 40, 495 (1967). Glazer, J., and Goddard, E. D., J. Chem. Soc. 1950, 3406 (1950). Glazer, J., and Alexander, A. E. Trans. Faraday Soc. 47, 401 (1951). Cadenhead, D. A., and M011er-Landau, F., J. Colloid Interface Sci. 49, 131 (1974). Cadenhead, D. A., and Mfiller-Landau, F., Advan. Chem. Ser. 144, 294 (1975). B. M. J. KELLNER F. MOLLER-LANDAU D. A. CADENHEADz

Department o f Chemistry State University o f New York at Buffalo Buffalo, New York 14214 Received April 18, 1978; accepted May 4, 1978

2 TO whom all correspondence should be addressed.

Journal of Colloidand Interface Science, Vol.66, No. 3, October 1, 1978