Force Measurements between Semifluorinated Thiolate Self-Assembled Monolayers: Long-Range Hydrophobic Interactions and Surface Charge

Ederth, Thomas; Tamada, Kaoru; Claesson, Per M.; Valiokas, Ramūnas; Colorado, Ramon; Graupe, Michael; Shmakova, Olga E.

doi:10.1006/jcis.2000.7318

Cited by 17 publications

(13 citation statements)

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“…The accumulated experimental and theoretical results imply that there are at least two kinds of hydrophobic surface forces of nonelectrostatic physical origin: (i) due to the gaseous capillary bridges (cavitation) between the hydrophobic surfaces − and (ii) due to hydrogen-bond-propagated ordering of water molecules in the vicinity of such surfaces; − a review was recently published by Christenson and Claesson . In the former case, the formation of the gaseous capillary bridges leads to jumps in the experimental force−distance dependence, and, moreover, the strength of the interaction increases with the concentration of gas dissolved in water. − For the second kind of hydrophobic force, the attraction is monotonic and decays exponentially at long distances, with a decay length of about 15.8 nm. , In principle, the two kinds of hydrophobic surface forces could act simultaneously, and it is not easy to differentiate their effects.…”

Section: Introductionmentioning

confidence: 99%

Detection of the Hydrophobic Surface Force in Foam Films by Measurements of the Critical Thickness of the Film Rupture

et al. 2004

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At sufficiently high electrolyte concentrations (at suppressed electrostatic repulsion), the free foam films thin gradually, until reaching a certain critical thickness, and then they break. The value of this critical thickness is sensitive to the magnitude of the attractive surface forces acting in the film. We experimentally investigated the rupture of the films formed from aqueous solutions of sodium dodecyl sulfate (SDS) in the presence of 0.3 M NaCl added. The theoretical fits of the data indicate that the van der Waals interaction, alone, is insufficient to explain the measured critical thickness, especially for the lower SDS concentrations. If the difference is attributed to the hydrophobic attraction, then a very good agreement between the theory and experiment is achieved. From the best fit, we determine that the decay length of the hydrophobic force is about 15.8 nm, which coincides with the value obtained by other authors for hydrophobized mica surfaces. The strength of the hydrophobic interaction increases with the decrease of the SDS concentration, which can be explained with the fact that between the adsorbed surfactant molecules greater areas of bare hydrophobic air-water interface are uncovered. In the investigated concentration range, the strength of the hydrophobic force is found to be inversely proportional to the surface density of the adsorbed ions.

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Section: Introductionmentioning

confidence: 99%

Detection of the Hydrophobic Surface Force in Foam Films by Measurements of the Critical Thickness of the Film Rupture

et al. 2004

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“…39 Selfassembled monolayers of semifluorinated alkanethiols on gold have been examined by direct force measurements in aqueous solutions. 40 The structure of similar systems has also been investigated with AFM, X-ray photoelectron spectroscopy (XPS), and surface plasmon resonance spectroscopy. 41 Layers of fluorosilane moieties grown on silicon surfaces were characterized by ellipsometry.…”

Section: Introductionmentioning

confidence: 99%

“…Hydrophobic surfaces produced with fluorinated acids adsorbed/reacted on alumina from aqueous solution were investigated using classical adsorption isotherms, contact angle measurements, and colloid probe atomic force microscopy . Self-assembled monolayers of semifluorinated alkanethiols on gold have been examined by direct force measurements in aqueous solutions . The structure of similar systems has also been investigated with AFM, X-ray photoelectron spectroscopy (XPS), and surface plasmon resonance spectroscopy …”

Section: Introductionmentioning

confidence: 99%

Fluorosurfactant Self-Assembly at Solid/Liquid Interfaces

et al. 2002

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Fluorosurfactants have some unique properties that are advantageously used in a range of applications. Their solutions are commonly in contact with solid surfaces onto which the molecules adsorb. Despite this, the adsorption behavior of fluorosurfactants at solid/liquid interfaces is not sufficiently understood, and there is a need for more information. In this study we focus on cationic fluorosurfactant adsorption on negatively charged hydrophilic surfaces, especially with respect to the adsorbed layer structure, long-range interactions, and adhesion forces. To this end we combined results obtained from bimorph and interferometric surface force instruments and ellipsometry techniques. The initial adsorption to the oppositely charged surfaces occurs due to the electrostatic attraction between the charged headgroups and the surface. Further adsorption, driven by hydrophobic interactions, occurs readily as the surfactant concentration is increased. Surface force and ellipsometric experiments indicate that the surfactants self-assemble in the form of bilayer aggregates. The thickness of the bilayer aggregates was found to be consistent with the molecular structure. Further, ellipsometric measurements indicate that no complete bilayers were formed but rather that bilayer aggregates were present on the surface even at concentrations well above the cmc. Surface force data for low fluorosurfactant concentrations demonstrate that upon compression the bilayer aggregates assembled on the isolated surfaces are transformed, and as a result monolayer structures build up between the surfaces in contact. The force required to attain bilayer−bilayer contact increases with the surfactant bulk concentration due to an increase in the repulsive double-layer force. The force required to drive out surfactant molecules to achieve monolayer−monolayer contact also increases with surfactant concentration. Above the cmc some additional aggregates are present on top of the bilayer aggregates coating the surface. The adhesion found between the monolayer aggregates is an order of magnitude larger than between the bilayer aggregates. However, it is an order of magnitude lower than the corresponding value for Langmuir−Blodgett monolayer films of similar fluorosurfactants.

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“…The surface tension along the liquid-vapor interface creates the long range hydrophobic force. The bridging bubble can be formed by cavitation of the liquid when the two surfaces approach each other (Berard, Attard et al 1993; or by stable nano-bubbles that have previously adhered to the hydrophobic surface (Carambassis, Jonker et al 1998;Ederth, Tamada et al 2001;. Arguments against microscopic bridging bubbles state that they are thermodynamically unstable (Eriksson and Ljunggren 1995;Eriksson and Ljunggren 1999) and too short lived to have a noticeable effect on experimental measurements (Ljunggren and Eriksson 1997).…”

Section: Surface Forces (Energies)mentioning

confidence: 99%

Establishment of the Center for Advanced Separation Technologies

Hull¹

2006

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INTRODUCTIONThe U.S. is the largest producer of mining products in the world. In 1999, U.S. mining operations produced $66.7 billion worth of raw materials that contributed a total of $533 billion to the nation's wealth. Despite these contributions, the mining industry has not been well supported with research and development funds as compared to mining industries in other countries. To overcome this problem, the Center for Advanced Separation Technologies (CAST) was established by Virginia Tech and West Virginia University to develop technologies that can be used by the U.S. mining industry to create new products, reduce production costs, and meet environmental regulations. This endeavor is supported through U.S. DOE Cooperative Agreement No. DE-FC26-01NT41091: Establishment of the Center for Advance Separation Technologies.Much of the research to be carried out at CAST will be longer-term, high-risk, basic research, and will be carried out in four broad areas: a) Solid-solid separation b) Solid-liquid separation c) Chemical/Biological extraction, and d) Sensor and control development.Distribution of funds has been handled via competitive solicitation of research proposals through Site Coordinators at the two universities. Two RFP's have been issued to date. The first of these, referred to as the CAST I -Round 1 RFP, was issued on August 17, 2001 and closed October 15, 2001. A total of 12 proposals were received in response to this first RFP. These were first reviewed and ranked by a group of technical reviewers (selected primarily from industry). Based on these reviews, and an assessment of overall program requirements, the CAST Technical Committee made an initial selection/ranking of proposals and forwarded these proposals to the DOE/NETL Project Officer for final review and approval. This process took some 6 months to complete but 8 projects were in place at the constituent universities (5 at Virginia Tech and three at West Virginia University) by May 17, 2002. This was followed, on June 1, 2002 with the CAST I -Round 2 RFP, which closed on July 19, 2002. A total of 12 proposals were received in response to this second RFPfive were selected for funding. These were in place at the constituent universities (2 at Virginia Tech and 3 at West Virginia University) by March 1, 2003.All thirteen of these projects are listed below by category, along with brief abstracts of their aims and objectives. The recovery of coarse particles by flotation is a common problem in the coal and minerals processing industry. The objective of this project is to develop methods of extending the upper particle size limit for flotation. The availability of such a technology will improve processing efficiency and greatly simplify the plant flowsheet. Two different complementary approaches will be used to achieve the project objective. One is to use novel flotation reagents that will help increase the attachment force between air bubbles and coarse particles, and the other is to develop new flotation machines specifically de...

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Force Measurements between Semifluorinated Thiolate Self-Assembled Monolayers: Long-Range Hydrophobic Interactions and Surface Charge

Cited by 17 publications

References 45 publications

Detection of the Hydrophobic Surface Force in Foam Films by Measurements of the Critical Thickness of the Film Rupture

Detection of the Hydrophobic Surface Force in Foam Films by Measurements of the Critical Thickness of the Film Rupture

Fluorosurfactant Self-Assembly at Solid/Liquid Interfaces

Establishment of the Center for Advanced Separation Technologies

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