Adsorption mechanisms in layer-by-layer films

Abstract

Adsorption processes in layer-by-layer lms are discussed using polyo-methoxyaniline POMA as a case study and also comparing with results for other polymers from the literature. This follows a brief overview of the materials and characterization techniques employed for self-assembled lms, including their possible applications. The original paradigm of the self-assembly method is associated with spontaneous adsorption of oppositely charged polymer layers. While this rationale has been successful in explaining adsorption mechanisms for some polyelectrolytes, for polyanilines other interactions must be included. For POMA, in particular, at least three types of interactions are identi ed, namely van der Waals forces, ionic interactions and H-bonding. Furthermore, H-bonding is responsible for a number of e ects even for charged POMA where electrostatic attraction was expected to predominate. Such e ects include POMA dedoping upon contact with a glass substrate at early stages of adsorption, and the non-linear increase in the adsorbed amount with the number of POMA polyethenesulfonic acid PVS bilayers deposited in a multilayer structure. Adsorption of a POMA layer on a glass substrate or on an already formed POMA PVS lm occurs in two steps: a fast, rst-order kinetics process with a characteristic time of a few seconds and a slower process represented by a Johnson-Mehl-Avrami function with a characteristic time of hundreds of seconds. These correspond basically to nucleation and growth mechanisms which is corroborated by atomic force microscopy measurements. The amount of material adsorbed in any given layer depends on experimental parameters, especially polymer concentration and pH, owing to the di erent extents of H-bonding that may allow POMA to adsorb on itself or on PVS molecules.

Ultrathin polymer coatings by complexation of polyelectrolytes at interfaces: suitable materials, structure and properties

“…Still, mostly used polyelectrolytes are commercially available ones, like poly(ethyleneimine) (9), poly(allylamine) (10), poly(diallyldimethylammonium chloride) (16), poly(styrene sulfonate) 6, poly(vinylsulfate) (3), poly(acrylic acid) (1), and (poly[N-vinyl-(4-(39-carboxy-49-hydroxyphenylazo)benzenesulfonamide)] (25) ("PAZO") (cf. Fig.…”

“…(9), and by the UV-absorbance maximum of the viologene group at about 270 nm ( 6 ). Right: shift of the absorbance maximum with ongoing film growth for the azobenzene chromophore (9) and for the viologene chromophore ( 6 ) 147) Fig. 12.…”

Morphological Structure Characterization of PAH/NiTsPc Multilayer Nanostructured Films

“…This model gives a phenomenological description of the adsorption kinetics without revealing molecular details; it has been used to explain growth processes due to its mathematical simplicity and proper description of the experimental data of polymeric systems [34]. The results of the phenomenological analysis of the growth of the PAH/ NiTsPc LbL films employing the JMA model were summarized in Table 1.…”

“…A two-stage adsorption process was also pro posed by Raposo [34] and Tsukruk [35]. It is possible to use the Avrami parameter n to distinguish between growth on the interface or by diffusion.…”

Influence of the pH and substrate immersion time on the adsorption of poly(o-ethoxyaniline) in self-assembled films

“…16 In general, repeatedly immersions in short times followed up of washing/drying increase the amount of material deposited. For this system, the polymer adsorption process may not reach a saturation plateau if successive short-time immersion steps are adopted instead of long-time ones.…”