Surface forces measurement polyelectrolyte adsorption

The aim of this review is to demonstrate the potential of surface forces measurement as a novel means for investigating surfaces and complex soft systems by describing our recent studies, which include cluster formation of alcohol, polyion adsorption, and polyelectrolyte brushes. 

The process of adsorption of polyelectrolytes on solid surfaces has been intensively studied because of its importance in technology, including steric stabilization of colloid particles [3,4]. This process has attracted increasing attention because of the recently developed, sophisticated use of polyelectrolyte adsorption alternate layer-by-layer adsorption [7] and stabilization of surfactant monolayers at the air-water interface [26], Surface forces measurement has been performed to study the adsorption process of a negatively charged polymer, poly(styrene sulfonate) (PSS), on a cationic monolayer of fluorocarbon ammonium amphiphilic 1 (Fig. 7) [27],... 

In the latter case the total interaction, which is what can be measured, is affected by the net charge of the surface and the adsorbed layer, ion-ion correlations, bridging interactions and steric confinement of the polymer chain [116]. We note that polyelectrolytes are often present as additives in colloidal dispersions and the character of the forces generated by the polyelectrolyte adsorption layers has a paramount influence on stability of these colloidal systems. With the aim to illustrate what can be learnt about polyelectrolyte adsorption layers using the SFA, we will look at the influence of the polyelectrolyte charge density on the forces acting between surfaces coated with polyelectroytes. We will consider an example where the polyelectrolyte charge density is varied by a systematic... 

Table 3 lists some ionization properties of functionalized gold-thiol monolayers and relevant alkylsiloxane monolayers together with the appropriate bulk values. Monolayers with carboxylate terminal groups show abnormal wetting behaviour, which makes it difficult to determine accurately their surface pKa values308. Apart from contact angle titration, other methods were also used to study proton transfer equilibria at the mono-layer surfaces, such as quartz crystal microbalance (Table 3, line 1), measurements of the adhesion force between the monolayer deposited at the surface of an AFM tip and the same monolayer deposited on the substrate (chemical force microscopy, Table 3, lines 3, 4, 15), FT-IR spectroscopy (Table 3, line 7), adsorption of polyelectrolytes (Table 3, line 5) and differential capacitance measurements (Table 3, lines 12, 13). 

The experiments were started by bringing the surfaces into contact first in dry air and then in pure water or 10 MKBr. This establishes the zero separation, and from the adhesion force and from the shape of the interference fringes it can be judged that the surfaces are clean. In the next step, polyelectrolytes were added to the solution to a concentration of 20 ppm (PCMA and AM-MAP-TAC-30) or 50 ppm (AM-PCMA-10). These conditions were used since the adsorption of the polyelectrolytes at these concentrations results in a close to net zero charge of the polyelectrolyte coated mica surface [11,16,17]. After allowing at least 12 h for the adsorption to take place the force-distance curve was measured and then the polyelectrolyte containing solution was replaced with a polyelectrolyte-free aqueous solution. This does not result in any significant desorption of the polyelectrolyte [11,16,17]. In the final step, SDS was added to the solution. Hence, no polyelectrolytes are present in the solution in these experiments, except for the data presented in Fig. 8 where a different experimental procedure was used. 

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