Langmuir 1992,8, 763-764
763
Reduction of Surface Tension of Pure m-Xylene by Novel Fluorinated Surfactants Masahiko Abe,*ptv*Kimio Morikawa,t and Keizo Oginot** Faculty of Science and Technology, Science University of Tokyo, 2641 Yamazaki, Noda, Chiba 278, Japan, and Institute of Colloid and Interface Science, Science University of Tokyo, 1-3 Kagurazaka, Shinjuku, Tokyo 162, Japan
Hideo Sawada, Takeo Matsumoto, and Masaharu Nakayama Tsukuba Research Laboratory, Nippon Oil and Fat Co., Ltd., 6-10 Tokodai, Tsukuba, Ibaraki 300-26, Japan Received October 28, 1991.In Final Form: December 27, 1991 We have measured the reduction of surface tension by novel fluorinated surfactants having different ether linkages. The surfactants having fluoroalkyl chains including ether linkages were able to reduce the surface tension of m-xylene to about 10 dyn/cm. Moreover, the surfactant having a fluoroalkyl chain containing only one ether linkage was particularly effective in reducing the surface tension. Recently, it has become generally known that organic compounds containing fluorocarbon chains are harmless and show unique physical properties such as heat resistance, chemical resistance, water repellance, and oil repellance.' A number of recent papers have described the synthesis and characteristics of water-soluble fluorinated surfactants,2v3 but there have been only a few studies of oil-soluble fluorinated surfactant^.^ In this paper, we report the effectiveness of novel fluorinated surfactants (fluoroalkylated benzene: CsHsRf, Rf = CnFzn+l, n = 3, 4,6,8;Rf = CF(CF~)O(CF~CF(CF~)O),C~FT, m = 0 , l ) in reducing the surface tension of pure m-xylene. The fluorinated surfactants used in this experiment were fluoroalkylated benzenes roughly equivalent in chain length to the normal fluoroalkyl chains (Rf = CnF~n+l,n = 3,4, 6, 8), and having nearly equivalent chain length to fluoroalkyls containing one or two ether linkages (Rf = CF(CF3)0(CF&F(CF3)0),C3F,, m = 0, 1). They were synthesized by the reaction of benzene with fluoroalkanoyl peroxides having different fluoroalkyl chains as shown in Scheme I. Details of the synthesis and preparation of fluoroalkylated benzenes were described in our previous paper^.^-^ The solvent used in this experiment was pure m-xylene (Wako Pure Chemical Industries, Ltd.). The surface tensions of solutions of fluorinated surfactants were measured at 30 f 0.1 "C by using a Wilhelmy-type surface tensiometer (ST-1, Shimadzu Co.) with a glass plate. The effect of varying concentrations of the fluorinated surfactants on surface tension is shown in Figure 1. The surface tension decrease of m-xylene caused by the surfactants having normal fluoroalkyl chains (0) in Figure 1 is quite small and does not greatly increase with increasing surfactant concentration. However, the effectiveness in surface tension reduction of m-xylene by the surfactants having fluoroalkyl chains containing ether linkages be+ Faculty
of Science and Technology.
* Institute of Colloid and Interface Science.
(1) Banks, R. E. Organofluorine Chemicals and their Industrial Application; Ellis Horwood: London, 1979. (2) Ishikawa, N. J. Jpn. Oil Chem. SOC.1977, 26, 613. (3) Ono, Y.; Ohtoshi, S. J. J p n . Oil Chem. SOC.1985, 34, 1035. (4) Ishikawa, N.; Sasabe, M. J.Fluorine Chem. 1984, 25, 241. (5) Sawada, H.;Nakayama, M.; Yoshida, M.; Kamigata, N. J. J p n . Oil Chem. SOC.1989, 38, 32. (6) Sawada, H.; Nakayama, M. J. Fluorine Chem. 1991, 51, 117. (7) Sawada, H.; Akuzawa, K.; Mitani, M.; Nakayama, M. Mass Spectrosc. Jpn. 1991, 39, 63.
0743-1463/92/2408-0163$03.00/0
n=3 n=4
n=6 n=8
0
Lf-----J 0
105
104
lo-'
IO'
102
Concentration (mol/l)
Figure 1. Variation of surface tension with concentration for CeH&f at 30 OC: (0) Rf = CnF2n+l (n = 3, 4, 6, 8); ( 0 ) Rf = CF(CF3)0(CF&F(CF3)0),C3F7(m = 0,l).
Scheme I 0 Reaction
formula
o f )
RfCOOCRf
40-70 "C
+
CFzClCFC12
R
f
a
+
0
RfCOH
+
C(h
Rf=Cbzn+I (n=3,4,6,8)
Rf=CF(CF3)0{CF2ff(CF3)O}mC3F7 (m=O, I)
comes greatly enhanced at higher concentrations. These surfactants decrease the surface tension of m-xylene from about 28 dynlcm to about 10dynlcm. Although solubility limitations prevent the measurement of surface tension for the surfactant having fluoroalkyl chains with two ether linkages (m = 1)at concentrations greater than lo9 mol/ L, the efficiency8 of the surfactants in reducing surface tension is enhanced by increasing the fluoroalkyl chain lengths of the surfactants. The behavior of the surfactants having fluoroalkylchains containing ether linkages (m = 0, 1) are of particular interest because they exhibit surface activity not shown by the ordinary hydrocarbon surfactants and the other fluorinated surfactants used in this experiment. The sur(8)Rosen, M. J. Surface and Interfacial Phenomena, 2nd ed.; John Wiley and Sons, Inc.: New York, 1989.
0 1992 American Chemical Society
764 Langmuir, Vol. 8,No. 3,1992
factant having a fluoroalkylchain containingonly one ether linkage ( m = 0)has a surface tension vs log concentration curve showing a break at a specific surfactant concentration, above which the surface tension remains nearly constant. This is analogous to the behavior of a watersoluble surfactant, for which there is also a discontinuity in the slope of a surface tension vs log concentration plot at the critical micelle concentration (cmc), where micelles first form. For the surfactant having fluoroalkyl chains with one ether linkage ( m = 0), the concentration at the break in surface tension is about 5 X lo9 mol/L. The unique surface tension reduction caused by surfactants having particular numbers of trifluoromethyl groups and ether linkages cannot be explained in detail at this time.
Letters Further studies are in progress and the reeulta will be published in the near future. However, application of the Gibba adsorption equation indicates that the thermodynamic activity of the surfactant containing one ether linkage (m= 0) remains practically constant in the bulk solution phase at total concentrations above the break point in the curve in Figure 1. This can only be interpreted as an indication that relatively large aggregates of surfactant molecules form, while the monomer concentration remains nearly constant. -#try NO. C&C$’,, 378-98-3; C&CJ?s, 239876-6; awu,664-4@9~& (%&817,87406.83-2; csHscF(cFs)W~, 133414-83-2; CsHsCF(CF3)0CF*CF(CFs)OCaF7,133414-78-6;mxylene, 108-38-3.
