Effects of Surfactants and Polyelectrolytes on the Interaction between a Negatively Charged Surface and a Hydrophobic Polymer Surface

Abstract

ABSTRACT:We have measured and characterized how three classes of surface-active molecules self-assemble at, and modulate the interfacial forces between, a negatively charged mica surface and a hydrophobic end-grafted polydimethylsiloxane (PDMS) polymer surface in solution. We provide a broad overview of how chemical and structural properties of surfactant molecules result in different self-assembled structures at polymer and mineral surfaces, by studying three characteristic surfactants: (1) an anionic aliphatic surfactant, sodium dodecyl sulfate (SDS), (2) a cationic aliphatic surfactant, myristyltrimethylammonium bromide (MTAB), and (3) a silicone polyelectrolyte with a long-chain PDMS midblock and multiple cationic end groups. Through surface forces apparatus measurements, we show that the separate addition of three surfactants can result in interaction energies ranging from fully attractive to fully repulsive. Specifically, SDS adsorbs at the PDMS surface as a monolayer and modifies the monotonic electrostatic repulsion to a mica surface. MTAB adsorbs at both the PDMS (as a monolayer) and the mica surface (as a monolayer or bilayer), resulting in concentration-dependent interactions, including a long-range electrostatic repulsion, a shortrange steric hydration repulsion, and a short-range hydrophobic attraction. The cationic polyelectrolyte adsorbs as a monolayer on the PDMS and causes a long-range electrostatic attraction to mica, which can be modulated to a monotonic repulsion upon further addition of SDS. Therefore, through judicious selection of surfactants, we show how to modify the magnitude and sign of the interaction energy at different separation distances between hydrophobic and hydrophilic surfaces, which govern the static and kinetic stability of colloidal dispersions. Additionally, we demonstrate how the charge density of silicone polyelectrolytes modifies both their self-assembly at polymer interfaces and the robust adhesion of thin PDMS films to target surfaces.

Influence of Perfluorooctanoic Acid on the Transport and Deposition Behaviors of Bacteria in Quartz Sand

“…The presence of steric repulsion in the presence of PFOA is well supported by the higher breakthrough curves observed in treated bacteria with PFOA in suspension (Figure a, solid squares and Table S1) compared with untreated bacteria (Figure a, solid triangles and Table S1)which is consistent with the adsorption test results (Figure S3), which indicate that greater PFOA adsorption occurs for treated bacteria relative to untreated bacteria. Previous studies also reported that the density of the adsorbed brush layers influences the steric repulsive force. , The result of interaction energy calculation at 10 mM NaCl is presented in Figure as a representative since a similar trend is observed in other conditions (Figure S1). The clear difference in the total interaction energy between the presence and absence of PFOA indicates that the addition of PFOA in cell suspensions increases the repulsive interaction between bacteria and quartz sand.…”

Bubble Attachment to Cellulose and Silica Surfaces of Varied Surface Energies: Wetting Transition and Implications in Foam Forming

“…Electrostatic repulsion explains the negligible adsorption of negatively charged SDS on hydrophilic silica below the CMC (Figure S4). Increased SDS adsorption with an increase in SDS concentration on a hydrophilic surface could be caused by electrostatic screening of the charges in the presence of counterions (Na + ) in solution. ,, However, most of the mass gains are explained by the hydration water, which correlated with the observed high dissipation.…”

Specific Ion Effects on the Interaction of Hydrophobic and Hydrophilic Self-Assembled Monolayers

“…Although −CH 3 surfaces have no specific charge, interaction of water with the aliphatic chain of the SAM could lead to a slightly negative charge over the surface. It has been reported − that air bubbles, oily groups, and hydrophobic surfaces spontaneously acquire a diffuse negative charge in water as a result of hydroxide ion adsorption. This behavior is a result of suppression of the dipole moment of water molecules, which induces an increase in hydroxide ion affinity to surfaces where dipole moment fluctuations are smaller than in bulk water .…”