Structure of Nonionic Surfactant Layers Adsorbed at the Solid/Liquid Interface on Self-Assembled Monolayers with Different Surface Functionality:  A Neutron Reflection Study

Abstract

The adsorption of a series of nonionic surfactants, C n H2 n +1(OC2H4) m OH (C n E m ), from aqueous solution onto a self-assembled monolayer (SAM) before and after chemical modification has been studied by neutron reflection. On a SAM consisting of a layer of undecenyl trichlorosilane with the ethylenic group at the aqueous interface all the surfactants adsorbed to form a monolayer whose thickness compared with the length of the molecule suggests that the molecules are tilted at angles in the region of 60° away from the surface normal. There was some penetration of the SAM layer by the alkyl chains of the surfactants. When the SAM was hydroxylated, the pattern of adsorption was found to be quite different and, for all the surfactants, the layer was only about 4 Å thick with a segmental surface density constant within experimental error, and there was no penetration of the SAM. The structure of this layer is attributed to hydrogen bonding between the ethylene glycol groups in the surfactant and the OH groups on the surface of the SAM. For comparison the adsorption of the same set of surfactants was studied on the bare silica surface. In all cases the adsorption was in the form of a defective bilayer, quite different again from the adsorption pattern on the two SAMs.

Structure of self-assembled layers on silicon: Combined use of spectroscopic variable angle ellipsometry, neutron reflection, and atomic force microscopy

“…The silicon blocks were cleaned in a surfactant ͑Decon-90͒ followed by rinsing in water, immersing in a 7:1 H 2 SO 4 /H 2 O 2 solution at about 110°C, and lastly rinsing in high purity water. 21 Then the samples were treated with ozone ͓generated by an oxygen flow in ultraviolet ͑UV͒ radiation͔ for 1 h. 22 The thickness of the native oxide layer was measured using ellipsometry, AFM and neutron reflection for each sample prior to the chemical grafting of OTS to the surface. OTS ͑Aldrich, UK͒ was used as received.…”

“…For the solid/liquid NR experiments a special sample cell was used. 21 Fitting of the NR data involved the calculation of the reflectivity profile for a model interfacial structure using the optical matrix method. A model typically consists of several layers that are characterized by their thickness and scattering length density.…”

Surface treatment and characterization: Perspectives to electrophoresis and lab‐on‐chips

“…Finally, we note that adsorption of nonionic surfactants (with various lengths and corresponding to the general formula C n H 2n11 (OC 2 H 4 ) m OH) on undecenyl trichlorosilane and hydroxyl-terminated trichlorosilane SAMs was investigated by neutron reflectivity [146]. The thickness of the adsorbed surfactant layer is thinner (about 4 Å) on hydroxylated SAM than what could be obtained on alkyl SAM.…”

Adsorption of Ethoxylated Nonionic Surfactants From Siloxane-Based Solvent and Aqueous Systems: Use of QCM and Model Polymeric Surfaces

“…Most of these applications involve adsorption of the surfactants from their solutions onto various interfaces. Studies have been conducted to understand the adsorption behavior of the surfactants at various interfaces in aqueous environment (Blom et al, 2005;Brinck et al, 1999;Cai et al, 2003;Caruso et al, 1995;Desbene et al, 1997;Geffroy et al, 2000;Gilchrist et al, 2000;Grant et al, 2000;Kharitonova et al, 2005;Kjellin et al, 2002;Kumar and Tilton, 2004;Lindheimer et al, 1990;Portet et al, 1996;Somasundaran et al, 1991;Tahani et al, 1996;Thirtle et al, 1997;Torn et al, 2005). Parameters governing the adsorption behavior include morphology and chemistry of solid surface, functional groups involved, solute-solvent interactions, intermolecular forces between adsorbed molecules, pH, and temperature.…”

“…Parameters governing the adsorption behavior include morphology and chemistry of solid surface, functional groups involved, solute-solvent interactions, intermolecular forces between adsorbed molecules, pH, and temperature. Characteristics of the adsorption process were studied using various techniques like fluorescence decay (Levitz and Van Damme, 1986), calorimetry (Lindheimer et al, 1990;Denoyel and Rouquerol, 1991), neutron reflection (Thirtle et al, 1997;Lee at al., 1989), ellipsometry (Gilchrist et al, 2000;Kjellin et al, 2002;Stalgren et al, 2002;Tiberg et al, 1994), surface plasmon resonance (Caruso et al, 1995), quartz crystal microbalance (Caruso et al, 1995;Stalgren et al, 2002), high-performance liquid chromatography (Desbene et al, 1997;Portet et al, 1996), and gravimetry (Caruso et al, 1996). Silica-water interface is the most studied surface for ethoxylated surfactant adsorption (Blom et al, 2005;Brinck et al, 1999;Desbene et al, 1997;Kharitonova et al, 2005;Kjellin et al, 2002;Portet et al, 1996;Thirtle et al, 1997;Stalgren et al, 2002).…”