Surface Forces between Titanium Dioxide Surfaces in the Presence of Cationic Surfactant as a Function of Surfactant Concentration, Electrolyte Concentration, and pH (original) (raw)

Adsorption Isotherms and Structure of Cationic Surfactants Adsorbed on Mineral Oxide Surfaces Prepared by Atomic Layer Deposition

Langmuir, 2013

The adsorption isotherms and aggregate structures of adsorbed surfactants on smooth thin-film surfaces of mineral oxides have been studied by optical reflectometry and atomic force microscopy (AFM). Films of the mineral oxides of titania, alumina, hafnia, and zirconia were produced by atomic layer deposition (ALD) with low roughness. We find that the surface strongly influences the admicelle organization on the surface. At high concentrations (2 × cmc) of cetyltrimethylammonium bromide (CTAB), the surfactant aggregates on a titania surface exhibit a flattened admicelle structure with an average repeat distance of 8.0 ± 1.0 nm whereas aggregates on alumina substrates exhibit a larger admicelle with an average separation distance of 10.5 ± 1.0 nm. A wormlike admicelle structure with an average separation distance of 7.0 ± 1.0 nm can be observed on zirconia substrates whereas a bilayered aggregate structure on hafnia substrates was observed. The change in the surface aggregate structure can be related to an increase in the critical packing parameter through a reduction in the effective headgroup area of the surfactant. The templating strength of the surfaces are found to be hafnia > alumina > zirconia > titania. Weakly templating surfaces are expected to have superior biocompatibility.

The influence of ionic and nonionic surfactants on aggregative stability and electrical surface properties of aqueous suspensions of titanium dioxide

Journal of Colloid and Interface Science, 2006

The influence of concentration of nonionic TRITON X-100 and anionic ATLAS G-3300 surfactants, and pH of medium on the size and zetapotential of TiO 2 particles in the water suspensions has been studied. Suspensions have been prepared by mixing of the titanium dioxide in the suitable mediums at 10 min and 6 h correspondingly. It was established, that the duration of mixing of the suspensions has an essential influence on the dependence of zeta-potential and size of particles versus concentration of surfactant. However, the duration of mixing does not influence the dependence of electrical conductivity and pH of the suspensions on concentration of surfactant. It is shown that anionic ATLAS G-3300 surfactant is more effective stabilizator of aqueous suspensions of titanium dioxide, than nonionic surfactants of TRITON X-100. It is found that hydrophobic interaction has important role in the processes of stabilization of suspensions for nonionic surfactant, and for anionic surfactant-moving of ψ δ-planes into solution's depth.

Adsorption of cationic ?gemini? surfactants at the TiO2/solution interface

Surface and Interface Analysis, 2002

Adsorption isotherms of cationic pyridinium surfactants at the solid/liquid interface were obtained on aqueous dispersions of titanium dioxide as a function of the electrification features of the adsorbent. The surfactants, prepared in the laboratory, were a symmetric 'gemini-like' dimer (1,1 -bidodecyl-4,4bipyridinium chloride) and its related simple monomeric salt (1-dodecyl-4-methylpyridinium chloride). X-ray photoelectron spectroscopy analyses were performed both on the bare adsorbent and in the presence of the adsorbates. The XPS regions of Ti 2p, O 1s, N 1s and C 1s were specifically investigated. The nature of the interactions supporting the adsorption and the molecule orientation/co-area are discussed in the light of the different experimental evidence.

Examination of Surface Adsorption of Soluble Surfactants by Surface Potential Measurement at the Air/Solution Interface

Journal of Physical Chemistry C, 2008

Surface potential (∆V) of the air/surfactant-solution interface was measured by using an ionizing 241 Am electrode method at 298.2 K, where the effect of the head groups on ∆V was also examined. Hexadecyltrimethylammonium bromide (CTAB) and its homologous head group tetramethylammonium bromide (TAB) were used for examination of a cationic surfactant, sodium dodecyl sulfate (SDS), sodium methylsulfate (CH 3 -SO 4 Na), and sodium hydrogensulfate (NaHSO 4 ) for an anionic surfactant, and octaethylene glycol mono-ntetradecyl ether (C14E8) and octaethylene glycol (E8) for a nonionic surfactant. For the cationic and nonionic systems, the surface potential of the homologous solutions gradually changed with concentration, whereas that of the corresponding surfactant solutions steeply increased up to 420 mV for CTAB at a concentration far below the critical micelle concentration (CMC), CMC/9, and up to 480 mV for C14E8 at CMC/18. For the anionic system, the surface potential traced a more complex variation with concentration. The above results indicate that the molecular arrangement of CTAB and C14E8 near the interfacial region becomes established at a concentration far below the CMC. The molecular dipole moment at the surface, derived from the surface potential, was also discussed. Change of surface tension with concentration was discussed with change in the surface potential and with preceding observations depending upon the concentrations. Finally, the Brewster angle microscopy (BAM) images of the surfactant solutions below and above the CMC and that of pure water are quite the same in darkness, which strongly indicates no adsorption of the surfactants at the air/solution interface contrary to an insoluble monolayer at the interface. This fact is substantiated by the distinct change of the BAM images in darkness for a small change in refractive index increment of the substrate. * Corresponding author. Phone/fax: +81-956(20)5686.

Surface mixed films of cationic surfactants at aqueous solution/air interface

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1994

The results are presented of experimental studies of the adsorption of surfactants at the solution/air interface from an aqueous binary cationic surfactant mixture: n-dodecyltrimethylammonium bromide-n-dodecylpyridinium chloride (DT MAB-DPC). The surface properties of the above-mentioned mixture were studied by surface tension and surface potential measurements. These measurements were carried out as a function of the concentration of DTMAB aqueous solution at a constant concentration of DPC. Using the results obtained, the mixed adsorbed film composition, Gouy's potential of the monolayer, the effective dipole moment of the adsorbed molecule, and the interaction between the adsorbed molecules and the CMC of the solutions were determined. To this purpose, Gibbs adsorption equation, the Gouy and Helmholtz formulae and the Rosen method were applied.

An electrostatic-surface stability interpretation of the “hydrophobic” force inferred to occur between mica plates in solutions of soluble surfactants

Chemical Physics, 1991

We analyse the data on the "hydrophobic" forces between mica surfaces immersed in solutions of the surfactant CTAB. For the particular regime where these "attractive" forces are not directly seen but are only inferred to exist because of a deviation from expected reputsive forces, we find that there is a strong correlation between the surface electrostatic potential that appears to be the source of electrostatic rep&ion and the force at collapse that is used to infer the hy~theti~ attractive hyd~phobic interaction. A simple phenomenol~~ model is presented that takes note of this pfeviousfy neglected internal correlation. From this model we suggest that, at least in the case of CTAB, the collapse is probably not due to the balance between eIectrostatic and Van der Waals or "hydrophobic" attractive forces; it is due rather to a shift in the balance between the inter-and intra-surface forces' that govern surfactant deposition. Such a view, based on the critical desorption or rearrangement of lipids or other solutes, is consonant with recent reports that the earlier experimental results of Pashley and Israelachvili are not reproduced when one uses purified CTAB. Recognition of solute desorption and adsorption might provide a key to the puzzling data where very long-range net attractive forces are observed but where these forces change with the activity of solutes in the intervening solution.

Forces between silica surfaces with adsorbed cationic surfactants: influence of salt and added nonionic surfactants

Langmuir : the ACS journal of surfaces and colloids, 2005

Forces have been measured between silica surfaces with adsorbed surfactants by means of a bimorph surface force apparatus. The surfactants used are the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) and the nonionic surfactant hexakis(ethylene glycol) mono-n-tetradecyl ether (C(14)E(6)) as well as mixtures of these two surfactants. The measurements were made at elevated pH, and the effect of salt was studied. At high pH the glass surface is highly charged, which increases the adsorption of TTAB. Despite the low adsorption generally seen for nonionic surfactants on silica at high pH, addition of C(14)E(6) has a considerable effect on the surface forces between two glass surfaces in a TTAB solution. The barrier force is hardly affected, but the adhesion is reduced remarkably. Also, addition of salt decreases the adhesion, but increases the barrier force. In the presence of salt, addition of C(14)E(6) also increases the thickness of the adsorbed layer. The force barrier...

Aggregate structures of the sorbitan monooleate (SPAN80) surfactant at TiO2 (rutile)/water interfaces by computer simulations

Revista Mexicana De Fisica, 2013

Molecular dynamics simulations were carried out to study the behavior fo a nonionic surfactant close to TiO_(2) surfaces at three different crystallographic orientations of rutile, (001), (100) and (110). Sorbitan Monooleate (SPAN80) molecula was used as nonionic surfactant and it was observed that these molecules seemed to aggregate in similar ways. Namely, the hydrocarbon chains of the surfactant molecules were attached at the solid surfaces. Structure of the molecules and surfactant adsorption on the surfaces were studied in terms of tails and head groups density profiles as well as surface coverage. From density profiles and angular distributions it was possible to determine the influence of the solid surface. For instance, on the three surfaces the surfactant molecules formed molecular layers parallel to the surface. Besides, it was found that in the solids (100) and (110), where there were oxygen atoms exposed on the surface, surfactant were attached to the surfaces along the ...

Adsorption Isotherms of Aqueous C12E6 and Cetyltrimethylammonium Bromide Surfactants on Solid Surfaces in the Presence of Low Molecular Weight Coadsorbents

Langmuir, 2009

In this work, we evaluate the effects of the low molecular weight compounds toluene, phenol, and 1-hexanol on the adsorption of two surfactants on one solid surface. The surfactants are cetyltrimethylammonium bromide (CTAB, cationic) and hexaethylene glycol monododecyl ether (C 12 E 6 , nonionic). The surface is gold, although X-ray photoelectron spectroscopic analysis reveals the presence of a large number of oxygenated sites that render the surface hydrophilic (contact angle 10°). Adsorption isotherms are measured using a quartz crystal microbalance with dissipation monitoring (QCM-D). Although our measurements do not allow the determination of the morphology of the aggregates directly, we rationalize our results by referring to AFM images from the literature. On the basis of primarily the dissipative signal and on AFM studies done by others, our results are consistent with CTAB forming a patchy cylindrical structure and C 12 E 6 likely yielding a monolayer structure. The presence of cosolutes almost doubles the mass of surface aggregates and increases the rigidness of the aggregates for CTAB, consistent with a morphological change from cylinders to flat bilayers. Part of the increase in adsorbed mass is likely due to increased surface area covered by admicelles. For C 12 E 6 , cosolutes cause small changes in the mass adsorption and essentially no change in the flexibility of surface aggregates.