Abstract
The layer-by-layer (LbL) method of polyelectrolyte multilayer (PEM) fabrication is extremely versatile. It allows using a pair of any oppositely charged polyelectrolytes. Nevertheless, it may be difficult to ascribe a particular physicochemical property of the resulting PEM to a structural or chemical feature of a single component. A solution to this problem is based on the application of a polycation and a polyanion obtained by proper modification of the same parent polymer. Polyelectrolyte multilayers (PEMs) were prepared using the LbL technique from hydrophilic and amphiphilic derivatives of poly(allylamine hydrochloride) (PAH). PAH derivatives were obtained by the substitution of amine groups in PAH with sulfonate, ammonium, and hydrophobic groups. The PEMs were stable in 1 M NaCl and showed three different modes of thickness growth: exponential, mixed exponential-linear, and linear. Their surfaces ranged from very hydrophilic to hydrophobic. Root mean square (RMS) roughness was very variable and depended on the PEM composition, sample environment (dry, wet), and the polymer constituting the topmost layer. Atomic force microscopy (AFM) imaging of the surfaces showed very different morphologies of PEMs, including very smooth, porous, and structured PEMs with micellar aggregates. Thus, by proper choice of PAH derivatives, surfaces with different physicochemical features (growth type, thickness, charge, wettability, roughness, surface morphology) were obtained.
Highlights
Surface modification is one of the strategies used to tailor the properties of objects, with sizes spanning several orders of magnitude, to make them suitable for practical applications
Five derivatives of poly(allylamine hydrochloride) (PAH) were obtained by substitution of its amine groups to obtain ionic polymers of both hydrophilic and amphiphilic character
This film is the most compact and tangled among all tested films with low permeability which may be due to the micellar structure of the films [47]. This may be presumed as polyelectrolyte multilayer (PEM) coatings composed of at least one amphiphilic polyelectrolyte, polycation or polyanion, are rougher than the others as evidenced by higher value of C parameter in formulas of Cauchy model, and confirmed by Atomic force microscopy (AFM). These results suggest that hydrophobic anchor present in both polymeric chains may inhibit their diffusion through the film because of higher molecular weight of amphiphilic polyelectrolytes, and due to the formation of mixed micellar structures
Summary
Surface modification is one of the strategies used to tailor the properties of objects, with sizes spanning several orders of magnitude, to make them suitable for practical applications. Such modification may change the chemical, biological, physical properties of the materials, allowing their use, e.g., as drug-delivery systems, cosmetics, textiles, adsorbents, membranes, self-healing and anticorrosive materials, to mention just a few examples [1,2,3]. Pairs of oppositely charged polymers (polyelectrolytes) are suitable for this method because of their ability to form polyelectrolyte multilayers (PEMs) on any charged surface due to the strong electrostatic attraction. The most often studied synthetic polyanions include poly(acrylic acid) (PAA) [6,7,8], poly(methacrylic acid) (PMA) [9,10], and poly(sodium 4-styrenesulfonate) (PSSS) [11,12,13,14,15,16,17,18,19,20], while the typical synthetic polycations are poly(allylamine hydrochloride) (PAH) [6,8,17,19,21,22], polyethyleneimine (PEI) [7], poly-L-lysine (PLL) [18,23,24,25,26], and poly(diallyldimethylammonium chloride)
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