Langmuir 2004, 20, 9075-9079
9075
Changing Surface Hydro- and Oleophobicity with Resorcinarene MultilayerssA Simple Water/Oil Proofing Process Frank Davis,*,† Elaine Frary,‡ and Charles J. M. Stirling‡ Institute of Bioscience and Technology, Cranfield University at Silsoe, Silsoe, MK45 4DT United Kingdom, and Department of Chemistry, The University, Sheffield, S3 7HF United Kingdom Received June 23, 2004 Resorcinarenes (resorcinol-aldehyde tetramers) of appropriate structures have been shown to change the hydro- and oleophilicities of a variety of surfaces. The phenomenon results from attachment of the rim of the bowl-like molecules to hydrophilic surfaces. Hydrophobic (alkyl) and oleophobic (perfluoro alkyl) “legs” attached to the bowls then determine the immediate surface property. Amounts required to modify surfaces are only between 2 and 10 mg m-2 treated, and there is evidence of multilayer formation. Penetration of surfaces by a variety of liquids has been studied and cannot easily be understood as a function of density, viscosity, or surface tension.
1. Introduction Calixarenes have been intensively studied with regard to their synthesis,1-5 bulk properties, and ability to form complexes with a wide variety of species.6 In addition, recent work has focused on the behavior of calixarenes in general and on resorcinarenes in particular when located in ultrathin organic films.7-13 Much of this work has been based on adsorbing thiol- or sulfide-modified calixarenes onto gold surfaces,7-12 but other workers have used sugarsubstituted resorcinarenes to bind to hydrophilic surfaces13 or to bind calixarenes to silica surfaces.14,15 Resorcinarenes containing azobenzene side chains have been shown to bind strongly to silica particles via strong head group interactions.16 Similar work17 by the same group studied a wider range of resorcinarenes and showed adsorption * Correspondence should be addressed to Dr. Frank Davis: phone +44(0)1525 863455, fax +44 (0)1525 863533, e-mail
[email protected]. † Cranfield University at Silsoe. ‡ The University. (1) Bo¨hmer, V. Angew. Chem., Int. Ed. Engl. 1995, 34, 713. (2) Timmerman, P.; Verboom, W.; Reinhoudt, D. N. Tetrahedron 1996, 52, 2663. (3) Gutsche, C. D. Calixarenes Revisited; The Royal Society of Chemistry: London, U.K., 1998. (4) Asfari, Z., Ed. Calixarenes 2001; Kluwer Academic Publishers: Dordrecht, 2001. (5) Mandolini, L., Ungaro, R., Eds. Calixarenes in Action; Imperial College Press: London, U.K., 2000. (6) Aoyama, Y.; Tanaka, Y.; Sugahara, S. J. Am. Chem. Soc. 1989, 111, 5397. (7) Van-Velzen, E. U. T.; Engbersen, J. F. J.; Delagne, P. J.; Mahy, J. W.; Reinhoudt, D. N. J. Am. Chem. Soc. 1995, 117, 6853. (8) Adams, H.; Davis, F.; Stirling, C. J. M. Chem. Commun. 1994, 2527. (9) Davis, F.; Stirling, C. J. M. J. Am. Chem. Soc. 1995, 117, 10385. (10) Davis, F.; Stirling, C. J. M. Langmuir 1996, 12, 5365. (11) Raible, S.; Pfeiffer, J.; Weiss, T.; Goepel, W.; Schurig, V.; Kern, D. P. Appl. Phys. A 2000, 70, 607. (12) Faull, J. D.; Gupte, V. K. Langmuir 2002, 18, 6584. (13) Hayashida, O.; Shimizu, C.; Fujimoto, T.; Aoyama, Y. Chem. Lett 1998, 13-14. (14) Wang, Z.; Chen, Y.; Yuan, H.; Huang, Z.; Liu, G. Electrophoresis 2000, 21, 1620. (15) Katz, A.; Da Costa, P.; Lam, A. C. P.; Notestein, J. M. Chem. Mater. 2002, 14, 3364. (16) Ueda, M.; Fukushima, N.; Hudo, K.; Ichimura, K. J. Mater. Chem. 1997, 7, 641. (17) Kurita, E.; Fukushima, N.; Fujimaki, M.; Matsuzawa, Y.; Hudo, K.; Ichimura, K. J. Mater. Chem. 1998, 8, 297.
of these materials from solution onto silica particles, poly(vinyl alcohol) film, or quartz plates and confirmed that under the correct condtions tightly packed monolayers and multilayers can be formed. An azobenzene-containing resorcinarene has been immobilized at an amino-substituted glass surface and has been shown to display irradiation-dependent wetting properties.18 Resorcinarenes have been shown to bind strongly to gold nanoparticles, aiding their stabilization in organic solvents.19,20 Besides self-assembly techniques, Langmuir-Blodgett films of resorcinarenes have been studied by us21 and other workers. Monolayers of resorcinarenes have been transferred onto solid substrates, their spectra have been studied,22 and similar monolayers of ester- or amidesubstituted resorcinarenes have been shown to selectively bind metal ions.23 Azobenzene-substituted resorcinarenes have been immobilized on silica slides and have been shown to undergo cis-trans isomerization,24 leading to controllable photomodification of surface wetting properties and light-driven motion of liquids on the surface. We now report novel work on the modification of surface hydrophobicity and oleophobicity by films of resorcinarenes. Earlier work from our laboratories has been concerned with the formation of self-assembled gold-thiol monolayers (SAMs) of resorcinarene 1a (Chart 1), which show differential adsorption of a number of carbonyl compounds from water and from polar solvents.8,10 Work by us and other workers has shown that in apolar solvents, resorcinarenes form aggregates in solution where the bowls of the resorcinarenes are hydrogen bonded together.25,26 For example, in chloroform stable hexamers of both resor(18) Oh, S.-K.; Nakagawa, M.; Ichimura, K. J. Mater. Chem. 2001, 11, 1563. (19) Wei, A.; Kim, B.; Pusztay, S. V.; Tripp, S. L.; Balasubramanian, R. J. Inclusion Phenom. Macrocyclic Chem. 2001, 41, 83-86. (20) Balasubramanian, R.; Kim, B.; Tripp, S. L.; Wang, X. J.; Lieberman, M.; Wei, A. Langmuir 2002, 18, 3676. (21) Davis, F.; Lucke, A. J.; Smith, K. A.; Stirling, C. J. M. Langmuir 1998, 14, 4180. (22) Moreira, W. C.; Dutton, R.; Aroca, P. J. Langmuir 1994, 10, 4148. (23) Moreira, W. C.; Dutton, R.; Aroca, P. J. Langmuir 1995, 11, 3137. (24) Ichimura, K.; Oh, S. K.; Nakagawa, M. Science 2000, 288, 1624.
10.1021/la048455f CCC: $27.50 © 2004 American Chemical Society Published on Web 09/15/2004
9076
Langmuir, Vol. 20, No. 21, 2004 Chart 1. Structures of Resorcinarenes
Davis et al. chased from Fluorochem. Compounds 1a,8,10 1b,6,32 1c,7 1d,30 1e,32 1f,32 1g,10 and 1h33 have been previously reported and were synthesized by refluxing the appropriate commercially available aldehyde with an equimolar amount of resorcinol or pyrogallol in ethanol6 except for 1h, which was synthesized by reaction of the fluorinated acetal with resorcinol in chloroform/trifluoroacetic acid.33 All compounds used gave suitable Fourier transform infrared, NMR, fast atom bombardment mass spectra, and elemental analyses. Samples of paper, cotton, wool, wood, glass wool, leather, and sugar were treated by soaking for a brief period (60 h >2 h 2h 30 h 10 h
80 260 172 >700 570 170 170 170 60
1 >60 h 40
a
The test material was standard commercial kitchen paper with the same batch being used for all tests. The standard procedure for water penetration was (i) weigh impregnated sample, (ii) immerse in water for 15 s at 20-25 °C, (iii) shake off in a standard fashion, and (iv) reweigh. b For oil penetration testing, a 5-µL drop of liquid paraffin was placed on the surface. c In this case the impregnated sample has been irradiated with UV light (254 nm) at 60 °C for 16 h. d C8F17Si(OMe)3 was supplied by Sivento Chemie Rheinfelden, Germany, and applied according to the manufacturer’s instructions. We thank Sivento Chemie for samples. e A mixture of perfluoroaromatics were supplied in solution in perfluorohexane by BNFL, Ltd. We thank Mr. D. Ross for a specimen of this material. f Supplied by Ronseal, Ltd., Sheffield, U.K. Table 2. Absorption of Liquids by Resorcinarene-Impregnated Cellulosea liquid water ethanol ethylene glycol glycerol CF3CH2OH hexane dodecane liquid paraffin diiodomethane CF3(CF2)9If nitromethane benzaldehyde formamide
surfaceb tension (dyn cm-1)
viscosityb (cp)
densityb (g cm-3)
72 22.7 48 63
0.89 1.1 20 1490
18.4 21.8
0.34 1.35
1 0.8 1.1 1.26 1.39 0.66 0.75 0.85 3.3
50 37 40 58
0.62 1.39 3.3
1.13 1.04 1.13
untreated
solution 1b
solution 1h
yesc yes yes yes yes yes yes yes yes yes yes yes yes
no yes yes nod yes yes yes yes yes yes yes yes yes
no yes no noe yes yes no no no yes no no yes
a In the form of cotton wool balls (boots) impregnated with 1% (w/v) solutions of 1b in hexane and 0.04% (w/v) solutions of 1h in acetone. At 25 °C. c Yes indicates absorption within about 10 s. d Absorbed in 40 min but not 1 min. e Absorbed in 1 h but not 40 min. f Mp 40-43 °C, supercooled liquid used.
b
or 1% Waterseal. Although none of the hydrocarbon-type treatments render the surface oleophobic, a 0.1% solution of 1h prevents oil ingress for over 60 h, similar behavior only being equalled by a 10% Flutec solution. The effects of various further treatments on hydrophobized materials were analyzed to investigate the stability of the layers. Samples of paper and cotton treated with either 1b or 1h remained hydrophobic after prolonged washing with hydrophobic solvents, for example, hexane or water. Prolonged washing with ethanol removed the layers. Samples of cloth treated with 1b or 1h lost their hydrophobicity after being put through a commercial washing machine cycle. Samples appeared to be stable to physical abrasion, and cotton and paper remained hydrophobic even after being ground in a mortar and pestle whereas samples on evaporated aluminum or gold could not be removed by abrasion; rather, the metal was first removed from the glass substrate. We have also briefly investigated absorption of other liquids by cellulose in the form of cotton wool impregnated with resorcinarenes 1b or 1h. Results are in Table 2. Resorcinarene 1b specifically excludes water or glycerol
but not a range of other liquids irrespective of viscosity, density, or surface tension. The fluororesorcinarene 1h is much more selective for reasons that do not appear to depend on any one of these parameters. Adsorption of water, glycerol, di-iodomethane, and long chain aliphatic hydrocarbons is prevented, which because flurocarbons are immiscible with those substances is not surprising. No protection is noted against fluorocarbons or aromatic hydrocarbons or against the polar liquid formamide. The resorcinarenes described provide a simple, inexpensive-solution-based method for modifying the surface properties of a wide variety of materials. These observations are clearly of potential commercial application33 arising from the understanding of the molecular interactions involved. This, surely, is the paradigm of invention. Acknowledgment. We thank Dr. Jeremy Holmes and Zeneca plc for their interest in this work. This work was supported by the University of Sheffield. We thank Mr. Barry Evans for the photographs. LA048455F
