Forces between Two Glass Surfaces with Adsorbed Hexadecyltrimethylammonium Salicylate (original) (raw)
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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...
Time-dependent adhesion between glass surfaces in dilute surfactant solutions
Langmuir, 1993
Measurements of surface forces between glass surfaces in very dilute cationic surfactant solutions at pH 10 are presented. As the surfaces approach the forces are purely repulsive and correspond exactly to the interaction of glass surfaces in aqueous solution at the same pH. However, a small adhesion is observed on separation, the magnitude of which is dependent on the time the surfaces are left in contact. The adhesion arises due to adsorption of surfactant in a narrow gap around the contact area and is induced by the favorable interaction of hydrophobic tails across the gap. The time dependence of the adhesion suggests that the adsorption is diffusion limited.
Forces between surfaces in the presence of a cationic polyelectrolyte and an anionic surfactant
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999
An atomic force microscope has been used to investigate the interaction forces between a mica surface and a colloidal glass sphere in the presence of a high molecular weight cationic polyelectrolyte, and the anionic surfactant sodium dodecylbenzenesulfonate (SDbS). The effect of addition of SDbS on the interaction forces between the polyelectrolyte coated surfaces was investigated. At low concentrations of SDbS the electrostatic repulsion initially present was progressively neutralized as a function of increasing surfactant concentration. Neutralization resulted in a strong attraction between the surfaces. As the SDbS concentration was increased further, additional surfactant association took place and the surfaces were recharged. At these surfactant concentrations the surfaces became less attractive at small separations. At high SDbS concentrations the interaction profile became purely repulsive as the surfaces were recharged. Diffuse double layer potentials derived from the direct force measurement data correlated well with zeta-potential measurements of silica particles treated with the polyelectrolyte and surfactant. Particulate stability behaviour was also seen to compare well with the force measurement and electrostatic potential data.
Forces between Glass Surfaces in Mixed Cationic−Zwitterionic Surfactant Systems
Langmuir, 2004
We report atomic force microscopy (AFM) measurements of the forces between borosilicate glass solids in aqueous mixtures of cationic and zwitterionic surfactants. These forces are used to determine the adsorption of the surfactant as a function of the separation between the interfaces (proximal adsorption) through the application of a Maxwell relation. In the absence of cationic surfactant, the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS) undergoes little adsorption to glass at concentrations up to about 2 /3 critical micelle concentration (cmc). In addition, DDAPS does not have much effect on the forces over the same concentration range. In contrast, the cationic surfactant dodecylpyridinium chloride (DPC) does adsorb to glass and does affect the force between glass surfaces at concentrations much lower than the cmc. In the presence of a small amount of DPC (0.05 mM) cmc/300), the net force between the glass surfaces is quite sensitive to the solution concentration of DDAPS. A model-independent thermodynamic argument is used to show that the surface excess of DDAPS depends on the separation between the glass interfaces when the cationic surfactant is present and that the surface excess of the cationic surfactant is more sensitive to interfacial separation in the presence of the zwitterionic surfactant. The change in adsorption of the zwitterionic surfactant is explained in terms of an intermolecular coupling between the long-range electrostatic force acting on the cationic surfactant and the short-range hydrophobic interaction between the alkyl chains on the cationic and zwitterionic surfactants. The adsorptions of cationic and zwitterionic surfactants in mixtures were measured independently and simultaneously by attenuated total internal reflection infrared spectroscopy (ATR-IR). The adsorption of the zwitterionic surfactant is enhanced by the presence of a small amount of cationic surfactant.
The Journal of Physical Chemistry B, 2006
Cylindrical micelles prepared in aqueous solutions from cationic surfactants octadecyl trimethylammonium (OTA + ) or cetyltrimethylammonium (CTA + ) and parachlorobenzoate (PCB) counterion were successfully imaged after evaporation of water using tapping mode atomic force microscopy (TM-AFM) onto very smooth gold and glass substrates. With the help of the obtained topography AFM images, it was shown that the micellar structures are preserved on gold substrates after evaporation of the solvent despite the new set of stresses due mainly to capillary forces and dehydration. The influence of the substrate on the resulting micellar morphology observed in air was investigated for these two materials: cylindrical micelles were evidenced as loosely adherent on gold surface in the presence of parachlorobenzoate (PCB) and identical, geometrically speaking, to those known to exist in aqueous solutions. In this situation, topographic AFM images allowed us to determine accurately their geometrical characteristics such as diameter and length in the nanometer range. On the other hand, AFM images obtained in air on glass surfaces revealed micellar structures that are different from those existing in the bulk of the solution. Indeed, bilayer-type micelles with a thickness close to twice the surfactant monomer expected length were observed, indicating that the well-established and strong influence of glass on micelle geometry at the glass/solution interface is maintained after evaporation of water. These results have been analyzed on the basis of positive charge of gold deduced from electrochemical impedance spectroscopy (EIS) and Raman spectroscopy measurements on one hand and of the negative charge of glass on the other hand. Although these results appeal to new theoretical considerations dealing with dynamics of evaporation of micellar solution drops and/or with counterion contributions to macromolecular interactions in aqueous solutions and in air, this new AFM imaging method appears to be the more adequate one to image and measure the micelles formed in the presence of water.
Counterion Effects on Hexadecyltrimethylammonium Surfactant Adsorption and Self-Assembly on Silica
Langmuir, 2000
Combining optical reflectometry and atomic force microscopy (AFM), we have studied the effects of the surfactant counterion on the adsorption isotherms, kinetics, and layer structure for cationic hexadecyltrimethylammonium (C16TA + ) surfactants on negatively charged silica surfaces. The adsorption kinetics suggest that the adsorption mechanism changes at the critical micelle concentration (cmc). A change in mechanism is also suggested by differences observed in the state of interfacial self-assembly on either side of the cmc. Above the cmc, increasing the binding affinity of the counterion (from chloride to bromide) increased the surface excess concentration by approximately 60% and changed the structure of the adsorbed surfactant layer from aggregates with circular projections to wormlike micelles. The addition of 10 mM KCl or KBr increased the surfactant surface excess concentration for both counterions. Below the cmc, the counterion has only a small effect on the structure of the adsorbed layer, and the isotherms are similar, provided the surfactant concentration is scaled by the appropriate cmc. By quantitatively analyzing the AFM images and comparing this to the surface excess concentration measured by reflectometry, we determined that surfactants pack differently in adsorbed aggregates than they do in aggregates formed by self-assembly in solution. Finally, we show that an impurity present in poly(vinyl chloride) tubing explains anomalous adsorption behavior previously reported for C16TAB on silica.
Journal of Colloid and Interface Science, 1996
forces are referred to as hydrophobic forces, whose origin Hydrophobic forces were measured using a Mark IV surface is a subject of considerable debate. The hydrophobic forces force apparatus with mica surfaces in equilibrium with dodecylammeasured with water-soluble surfactants are relatively short ine hydrochloride (DAHCl) solutions at pH 5.7. With DAHCl ranged, being discernible at separation distances in the 0alone, only ''short-range'' hydrophobic forces were observed with to 15-nm range. The measured hydrophobic forces (F) are decay lengths of 1.3 nm. In the presence of dodecanol, long-range usually described using an exponential force law hydrophobic forces were observed with the decay length as large as 9.0 nm, which represents the strongest ever recorded hydrophobic force with soluble single-chain surfactants. The appearance
Hofmeister Solute Effects on Hydrophobic Adhesion Forces in SFM Experiments
Langmuir, 2001
One of the chief problems currently facing surface scientists is determining the relationship between mechanical forces, such as those measured by surface forces apparatus (SFA) or scanning force microscopes (SFM), and chemical driving forces, such as those governing interactions between molecules. Hydrophobic forces are important at both levels, but there is no clear relationship between their manifestation at molecular and supramolecular scales. To help bridge this gap, we have used an SFM to measure detachment forces between untreated silicon nitride SFM tips, which are moderately hydrophobic, and the highly hydrophobic surfaces paraffin and octadecylsilane-mica in the presence of various 2.0 and 3.0 M salt solutions. The salts were chosen for their strong abilities to promote or inhibit hydrophobically driven phenomena, according to their positions in the Hofmeister series. Thus, this is the first systematic assessment of Hofmeister salt effects on supramolecular hydrophobic adhesion in solution-phase chemical terms. NaCl has no effect on hydrophobic adhesion force relative to pure water, which agrees with previous SFM and SFA work but lies in contrast with the effects of NaCl on solution-phase behavior such as aqueous nonpolar compound solubility. Chaotropes such SCNand guanidinium + , which promote exposure of molecular nonpolar surfaces to water, decrease adhesion force, whereas kosmotropes such as NH4 + and SO4 2-, which promote sequestration of nonpolar molecular surfaces from water, enhance adhesion force. Our results suggest that solvent structures near molecular and supramolecular hydrophobic surfaces are fundamentally different but that the nonideal effects embodied by the Hofmeister series have similar mechanisms in both length scales. Preferential interactions of solutes with hydrophobic surfaces and potential sources of hydrophobic adhesion, such as cavitation, van der Waals interactions, and solvent ordering, are discussed.
Use of atomic force microscope for the measurements of hydrophobic forces
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1994
An atomic force microscope (AFM) was used to measure the short-and long-range hydrophobic attractive forces between a silanated silica plate and a glass sphere. Octadecyltrichlorosilane (ODTCS) and trimethylchlorosilane (TMCS) were used to render the surfaces hydrophobic with advancing contact angles (8,) in the 88-115" range. The forces measured with surfaces coated with TMCS ((1. = 88") are comparable to those obtained previously using the surface force apparatus (SFA). On the other hand, the hydrophobic forces measured with ODTCS-coated surfaces are much larger than those measured with mica surfaces coated with other long-chain surfactants such as dimethyldioctadecylammonium bromide. The long-range hydrophobic force increases sharply at (I, > 95 '. The AFM images show that the surfactants adsorb on the silica surface forming domains (or molecular clusters). With ODTCS. elliptical domains begin to form at relatively low coverages. their size and the distance between them remaining relatively constant with increasing 0.. At the same time, the decay length of the long-range hydrophobic force does not change significantly with U.. while its strength increases sharply at (I, > 95". These findings suggest that the decay lengths of long-range hydrophobic forces vary with the domain size and the distance between them, with their strength increasing with increasing packing density and hence the ordering of the hydrocarbon chains in the domains. The AFM force measurements conducted in the present work also show that the hydrophobic force significantly increases in argon-saturated water, suggesting that the cavitation mechanism may play a role. Only short-range hydrophobic forces have been observed between hydrophilic silica and hydrophobic (silanated) glass. The adhesion forces measured by AFM show a strong dependence on II,, which can be explained by the Young-Dupri equation with appropriate corrections.