Wetting Transition on Hydrophobic Surfaces Covered by Polyelectrolyte Brushes

Abstract

We study the wetting by water of complex "hydrophobic-hydrophilic" surfaces made of a hydrophobic substrate covered by a hydrophilic polymer brush. Polystyrene (PS) substrates covered with polystyrene- block-poly(acrylic acid) PS- b-PAA diblock copolymer layers were fabricated by Langmuir-Schaefer depositions and analyzed by atomic force microscopy (AFM) and ellipsometry. On bare PS substrate, we measured advancing angles theta A = 93 +/- 1 degrees and receding angles theta R = 81 +/- 1 degrees . On PS covered with poorly anchored PS- b-PAA layers, we observed large contact angle hysteresis, theta A approximately 90 degrees and theta R approximately 0 degrees , that we attributed to nanometric scale dewetting of the PS- b-PAA layers. On well-anchored PS- b-PAA layers that form homogeneous PAA brushes, a wetting transition from partial to total wetting occurs versus the amount deposited: both theta A and theta R decrease close to zero. A model is proposed, based on the Young-Dupre equation, that takes into account the interfacial pressure of the brush Pi, which was determined experimentally, and the free energy of hydration of the polyelectrolyte monomers Delta G PAA (hyd), which is the only fitting parameter. With Delta G PAA (hyd) approximately -1300 J/mol, the model renders the wetting transition for all samples and explains why the wetting transition depends mainly on the average thickness of the brush and weakly on the length of PAA chains.

Contact angle dynamics on pseudo-brushes: Effects of polymer chain length and wetting liquid

“…That good solvents make a finite contact angle with the polymer has already been observed and explained [39][40][41].…”

Temperature effects on spreading of water nano‐droplet on poly(methyl methacrylate): A molecular dynamics simulation study

“…Second, the wetting of polymer surfaces which have been examined from the early ages of CA studies . Furthermore, recent researches have been concerned with the effect of surface roughness and the transition to extreme cases of super‐hydrophilicity/hydrophobicity …”

“…30,31 Furthermore, recent researches have been concerned with the effect of surface roughness 32,33 and the transition to extreme cases of super-hydrophilicity/ hydrophobicity. 34,35 On this premise, this study addresses the nonreactive spreading process of a water nano-droplet on poly(methyl methacrylate) (PMMA) using molecular dynamics simulation. The hydrophilic PMMA was chosen based on its wide range of use in the industry along with especial applications in microfluidic studies.…”

Adsorption of modified dextrins to a hydrophobic surface: QCM-D studies, AFM imaging, and dynamic contact angle measurements

“…There have been some studies that have been performed on surfactant coated model hydrophobic surfaces [13] that have indicated that adsorbed molecules can affect film thinning and rupture, and three-phase contact line movement when a bubble is pressed against a surface. In addition, the effect of adsorbed polymers on the wetting/dewetting of surfaces has been studied theoretically [14] and experimentally [15,16], with patchy coverage of polymers and bridging between adsorbed layers and an approaching bubble surface both seen to affect the movement of the three-phase contact line. In this work, we have set out to further investigate the effect of polymers on the dynamic contact angle of a bubble attaching to a hydrophobic surface, using the quartz crystal microbalance with dissipation monitoring (QCM-D) to characterize the polymer adsorption (adsorbed amount, conformation, kinetics of adsorption, water content) [17,18], atomic force microscopy to characterize the adsorbed layer morphology, and novel measurements of dewetting using bubble-surface collisions monitored using high speed video capture techniques [19].…”