pubs.acs.org/Langmuir © 2010 American Chemical Society
Wettability of a Quartz Surface in the Presence of Four Cationic Surfactants Lei Zhang,† Zeng-Lin Wang,† Zhen-Quan Li,† Lu Zhang,*,‡ Zhi-Cheng Xu,‡ Sui Zhao,‡ and Jia-Yong Yu‡ †
Geological Scientific Research Institute, Shengli Oilfield Company of SINOPEC, Dongying 257015, Shandong, P. R. China, and ‡Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China Received September 14, 2010. Revised Manuscript Received November 5, 2010 Advancing contact angle (θ) measurements were carried out for aqueous solutions of four cationic surfactants, hexadecanol glycidyl ether ammonium chloride (C16PC), guerbet alcohol hexadecyl glycidyl ether ammonium chloride (C16GPC), hexadecanol polyoxyethylene(3) glycidyl ether ammonium chloride (C16(EO)3PC), and guerbet alcohol hexadecyl polyoxyethylene(3) glycidyl ether ammonium chloride (C16G(EO)3PC), on the quartz surface using the sessile drop analysis. The influences of surfactant type and bulk concentration on contact angle were expounded, and the changes in adhesional tension and adhesion work were discussed. The contact angle increases up to a maximum with the increasing concentration for all cationic surfactants. Surfactants with branched chain have more hydrophobic group density on the quartz surface, which results in higher values of maxima in contact angle curves. When ethylene oxide groups CH2CH2O were incorporated in the hydrophobic group, the decrease in contact angle maximum was observed for C16(EO)3PC and C16G(EO)3PC. Moreover, an increase in quartz-water interfacial free energy (γSL) has been observed due to the adsorption of four cationic surfactants. The four cationic surfactants can form a monolayer with alignment structure on the quartz surface through electrostatic interaction and then form the bilayer with increasing bulk concentration. In contrast with literature, the maximal contact angles may not necessarily correspond to the beginning of the formation of bilayer for cationic sufactants at the quartz-water interface. Moreover, the concentrations corresponding to maximal contact angles for C16PC and C16(EO)3PC were much lower than their CMC. The contact angle passes through a maximum at a concentration obviously higher than CMC for C16G(EO)3PC.
1. Introduction Wettability is of special importance for many technological applications such as oil recovery, coating, adhesion, flotation, printing, detergency, and cosmetics industry.1-6 The extent of wettability can be modified by the addition of surfactants to water because they reduce the high surface tension of water and also change solid-water interfacial free energy, which may cause contact angles to decrease or increase in solid-water drop-air system. *To whom correspondence should be addressed. E-mail: luyiqiao@ hotmail.com. Tel: 86-10-82543587. Fax: 86-10-62554670. (1) Robert, A.; Bernard, P. B.; John, H. C. Adv. Colloid Interface Sci. 2003, 100-102, 503. (2) Wilson, A. J. Foams: Physics, Chemistry, and Structure; Springer-Verlag: London, 1989; p 1. (3) Brookes, G. F. Powder Technol. 1984, 40, 207. (4) Sabia, A. J. Text. Chem. Color. 1980, 12, 22. (5) Chau, T. T.; Bruckard, W. J.; Koh, P. T. L.; Nguyen, A. V. Adv. Colloid Interface Sci. 2009, 150, 106. (6) Otami, M.; Saito, M.; Yabe, A. Textile Res. J. 1985, 55, 582. (7) Pisaev, I. V.; Soboleva, O. A.; Ivanova, N. I. Colloid J. 2009, 71, 246. (8) Harkot, J.; Janczuk, B. Appl. Surf. Sci. 2009, 255, 3623. (9) Chaudhuri, R. G.; Paria, S. J. Colloid Interface Sci. 2009, 337, 555. (10) Szymczyk, K.; Janczuk, B. J. Adhes. Sci. Technol. 2008, 22, 1145. (11) Szymczyk, K.; Janczuk, B. Langmuir 2007, 23, 8740. (12) Harkot, J.; Janczuk, B. Appl. Surf. Sci. 2007, 253, 7166. (13) Szymczyk, K.; Zdziennicka, A.; Janczuk, B.; Wojcik, W. J. Colloid Interface Sci. 2006, 293, 172. (14) Szymczyk, K.; Janczuk, B. J. Colloid Interface Sci. 2006, 303, 319. (15) Ferrari, M.; Ravera, F.; Rao, S.; Liggieri, L. Appl. Phys. Lett. 2006, 89, 053104. (16) Zdziennicka, A.; Janczuk, B.; Wojcik, W. J. Colloid Interface Sci. 2005, 281, 465. (17) Karakashev, S. I.; Phan, C. M.; Nguyen, A. V. J. Colloid Interface Sci. 2005, 291, 489. (18) Zdziennicka, A.; Janczuk, B.; Wojcik, W. Colloids Surf., A 2004, 249, 73. (19) Zdziennicka, A.; Janczuk, B.; Wojcik, W. J. Colloid Interface Sci. 2003, 268, 200.
18834 DOI: 10.1021/la1036822
The important ability of surfactants to change wetting of low-energy solids has been studied extensively for decades.7-21 However, research about the influence of surfactants on the quartz plate is rare, especially for cationic surfactants. Quartz is a high-energy hydrophilic solid that is used in many branches of industry. Bogdanova stated that nonionic polyoxyenthylene surfactants absorbed via hydrogen bonding between their ethylene oxide groups and SiO2 surface.22 Zdziennicka presented an overview that nonionic and anionic surfactants interact with hydrophobic groups on quartz surface predominantly through Lifshitz-van der Waals interactions and that the water molecules interact stronger than those of surfactants with quartz surface.23 A water film forms on the quartz surface as a result of water vapor adsorption or water molecules diffusion from the drop. Therefore, surface properties of the quartz depend not only on the density of the silanol group but also on the number of the water molecules physically adsorbed on this surface. Janczuk and his group have been dealing with the mechanism of the surfactants adsorption at the quartz-water interface and have tried to establish the correlation between surface free energy of quartz at a given condition of the environment in which quartz was found and its wettability by aqueous solution of nonionic, anionic, and cationic surfactants. The cationic surfactants employed were linear molecules cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPyB).23 (20) Kumar, N.; Varanasi, K.; Tilton, R. D.; Garoff, S. Langmuir 2003, 19, 5366. (21) Kjellin, U. R. M.; Claesson, P. M.; Linse, P. Langmuir 2002, 18, 6745. (22) Bogdanova, Y. G.; Dolzhikova, V. D.; Summ, B. D. Colloid J. 2003, 65, 290. (23) Zdziennicka, A.; Szymczyk, K.; Janczuk, B. J. Colloid Interface Sci. 2009, 340, 243.
Published on Web 11/17/2010
Langmuir 2010, 26(24), 18834–18840
Zhang et al.
Article Scheme 1. Formula and Abbreviations of the Surfactants
Cationic surfactants have a very wide applicability from both biological and technical points of view. Compared with nonionics and anionics, cationic surfactants have a positive charge and thus adsorb strongly onto most solid surfaces (which are usually negatively charged) and can impart special characteristics to the substrate.24 In the present work, the purpose of our studies was to determine the adsorption properties at water-air and quartz-water interfaces in relation to quartz wettability by a series of cationic surfactant solutions. Four cationic surfactants containing similar polar groups and different nonpolar groups were used in this work. For this purpose, measurements of the surface tension of aqueous solutions and of the contact angle in the quartz-drop of aqueous four cationic surfactants solution-air system were carried out.
2. Experimental Section 2.1. Materials. The series of fatty alcohol hexadecyl polyoxyethylene glycidyl ether ammonium chloride was two pairs of isomeric compound, which was synthesized in our laboratory.25 Each isomer bears an identical polar group and an identical number of carbon atoms, differing only by the structure of the hydrophobic chain (See Scheme 1). The purity of the compounds was checked by elemental analysis and 1H NMR spectroscopy. The structures and abbreviations of the four surfactants are shown in Scheme 1. The synthesis and characterization of the surfactants are reported elsewhere.26 Ultra pure water with 18.0 MΩ cm-1 resistivity was used for the experiment. 2.2. Surface Tension Measurements. The surface tension measurements of surfactant aqueous solutions were measured by the Wilhelmy plate method using the Kr€ uss K100 tensiometer under atmospheric pressure. The platinum plate was burned after wash under alcohol flame to remove the adsorbed surfactants completely before each measurement. Next, it was dipped in the solution to measure its surface tension. Measurements of the surface tension of pure water at 303 K were performed to calibrate the tensiometer and to check the cleanliness of the plate and glassware. The measurements were conducted until constant surface tension values indicated that equilibrium had been reached. In all cases, more than three successive measurements were carried out, and the standard deviation did not exceed 0.2 mN/m. 2.3. Contact Angle Measurements. Because of the adsorption of surfactant on the surface of quartz plates, there was a fluctuation in reading between first and second measurements; to avoid that, the surface was properly cleaned after each measurement. The surface was first washed with pure water and acetone, treated with freshly prepared chromic acid and then in doubly (24) Rosen, J. M. Surfactants and Interfacial Phenomena; Wiley-Interscience: New York, 2004. (25) Xu, Z. C. Ph.D. Dissertation, Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 2009 (26) Xu, Z. C.; Zhou, C. H.; Jin, Z. Q.; Zhao, S.; Yu, J. Y. Fine Chemicals 2009, 26, 248.
Langmuir 2010, 26(24), 18834–18840
Figure 1. Dependence of the measure values of the surface tension (γLV) of surfactant solutions and log C (C is the surfactant concentration). distilled water, and washed in a water ultrasonic bath for 20 min. Next, these surfaces were heated at 378 K for 1 h. The measurements of contact angles for the water and aqueous solutions of surfactants on quartz plates were carried out via the sessile drop method with the SCA20 from Dataphysics Instruments GmbH, Stuttgart, Germany. The contact angle measurements on both sides of the drop of a given solution were carried out immediately after depositing the drop on the quartz plate (within about 1 to 2 min after depositing the drop). The measurements were repeated several times by settling other drops on the new parts of the same plate. The results are means of five measurements, and the standard deviation of the contact angle values was
