The Influence of Surface Hydrophobicity on Polyacrylamide Adsorption

Abstract

The adsorption of a modified polyacrylamide on gold surfaces coated with varying proportions of -CH3- and -OH-terminated alkanethiols (producing substrates of varying hydrophobicity: thetac=75, 98, and 119 degrees), was investigated using quartz crystal microbalance with dissipation (QCM-D), tapping-mode atomic force microscopy (TM-AFM), and captive bubble contact angle measurements. The QCM-D data for the polymer adsorbing on the different substrates indicates that the polymer adsorbs faster and to a greater extent on surfaces with higher hydrophobicity. Dissipation data from the QCM-D suggests that the adsorbed polymer undergoes a conformational change when adsorbing onto the substrates of higher hydrophobicity, forming a less rigid extended layer as the adsorption progresses toward the maximum adsorbed amount. AFM imaging of the adsorbed layer illustrates that the polymer layer is incomplete on all three substrates, and that the underlying substrate hydrophobicity has a role in determining the morphology (distribution, coverage, and thickness) of the adsorbed layer. Contact angle measurements of the polymer-coated substrates show variation in the ability of the polymer to reduce the hydrophobicity of the substrates. The role of coverage and distribution of adsorbed polymer on the surface hydrophobicity reduction is discussed.

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

“…Nevertheless, the fitting confirms that the polymers have varying affinity for the surface with PS and SO Dextrin adsorbing much faster (at least five times faster) than Dextrin TY. Deviation from pseudo-first order behavior for adsorption steplimited polymer adsorption has been reported by this group [18] and by other researchers [37]. In the case of our earlier work (on polyacrylamide adsorption onto the same substrate type as used here) the observation of two rate constants for adsorption was attributed to a second stage in the adsorption/attachment step that is also rate limiting, such as a conformation rearrangement step that is necessary before further polymer can adsorb.…”

“…For PS Dextrin, the hydration water content at equilibrium for adsorption from 100 mg/L solution is significantly smaller (50%). A value of around 50% is what would be expected for polyacrylamide adsorption [18]. This low water content was unexpected given that the polymer has a carboxyl functionality (expected to enhance hydration water content).…”

“…The advancing contact angle of the thiol-coated QCM sensors was measured to be 97°. The formation and structure of the mixed thiol layers have been confirmed using external reflectance infrared spectroscopy, with all substrates composed of ordered self-assembled monolayers [18]. The substrates for the dewetting experiment were prepared using glass slides.…”

“…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]. The polymers (regular wheat dextrin -Dextrin TY; phenyl succinate dextrin -PS Dextrin; and styrene oxide dextrin -SO Dextrin) have been selected to enable us to investigate subtle effects in adsorption and dewetting due to minor variation in the substitution chemistry of a commonly studied flotation depressant [5,20,21].…”

Hydrogel Microparticles as Sensors for Specific Adhesion: Case Studies on Antibody Detection and Soil Release Polymers

“…This confirms the extraordinary antiadhesive properties of the PEG part, which could be attributed to the comparatively firm hydration shell around PEG resulting in excluded volume effects [32]. Although generally considered as a hydrophilic polymer, polyacrylamide is known to show strong interactions with hydrophobic surfaces which was also confirmed in this study [33]. Overall, the significant differences in adhesion of the hydrophilic polymers investigated to hydrophobic materials are quite intriguing and still not well understood [34,35].…”