Suppressing the Hofmeister Anion Effect by Thermal Annealing of Thin-Film Multilayers Made of Weak Polyelectrolytes

Abstract

Thin films made of weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) have been fabricated on silicon wafers using the layer-by-layer (LbL) method. To study the influence of counteranion type on the growth and properties of PAH/PAA multilayers, the nature of the supporting sodium salt was varied from cosmotropic to chaotropic anions (F–, Cl–, and ClO4 –). Results of ellipsometry and AFM measurements indicate that the film thickness and surface roughness systematically increase on the order F– < Cl– < ClO4 –. Furthermore, we found that the hydrophobicity of the PAH/PAA multilayer also follows the described trend when a polycation is the terminating layer. However, the heating of PAH/PAA multilayers to 60 °C during the LbL assembly suppressed the influence of background anions on the multilayer formation and properties. On the basis of the obtained results, it could be concluded that thermal annealing induces changes at the polymer–air interface in the sense of reorientation and migration of polymer chains.

Self-Patterning of Polyelectrolyte Multilayer Films: The Roles of PSS Molecular Weight, the Top Layer, and Post-Preparation Treatment

“…In an aqueous solution, the increased total area has few energetic consequences because the surface tension γ (or surface energy) is approximately zero. This was shown by surface force measurements with PE-covered surfaces. , However, in the air, the surface tension γ is between 15 and 25 mN/m, as adhesion and contact angle measurements show. ,, …”

“…34,51 However, in the air, the surface tension γ is between 15 and 25 mN/m, as adhesion and contact angle measurements show. 21,52,53 We suggested that pattern formation in PEMs is caused by minimizing mechanical stresses within the film. 18 Figure 6 demonstrates that the increased surface energy from exposure to air does not affect the surface pattern of PSS-terminated films.…”

Chemical Structure–Physicochemical Property Relationships of Copolymers Utilizable for Negative-Tone Photoimaging via Chemical Amplification

“…The water contact angle of F-532-10.4k also reached the contact angles of the atoms of O-532-11.6k and A-532-12.2k at 128 mJ/cm 2 , which is also unexpected. Unlike the solubility parameter, the wetting by water is a quite complex behavior that can be affected by many different parameters such as surface roughness and chain conformations. − Especially during the PEB process, the surface concentrations of polar moieties, including carboxylic acid in the copolymer chains and generated acid molecules, can be varied, resulting in unexpected surface wetting properties with water molecules regardless of the variation in the comonomer structure. Therefore, these results suggest that the water contact angle is beneficial to catch if the deprotection reaction occurs by acid catalysis in the CAR mechanism, although the prediction of the patterning capability relying on it should be carefully considered.…”

Ion-Specific Effects on the Structure, Size, and Charge of Polymers Applied in Enhanced Oil Recovery

“…The role of the ionic environment present in the reservoirs is of particular importance since ion-specific effects are responsible for the structural and physicochemical properties of polymer or polymer–surfactant solutions . The effect of the chemical composition of the electrolyte on the structure of polymers (or their charged version called polyelectrolytes) has already been reported in the past and was explained with the Hofmeister series of ions. − Accordingly, the presence of kosmotropes (or water-structure-forming ions) stabilizes the conformation of well-hydrated polymeric chains, while chaotropes (or water-structure-breaking ions) disturb the hydrogen bonding pattern in polymer solutions and, hence, lead to the unfolding of the macromolecules . Despite its clear importance, such an ion-specific effect induced by dissolved salt constituents has rarely been studied and compared for EOR polymers.…”