Stepwise Fabrication and Characterization of Ultrathin Hydrogels Prepared from Poly(vinylamine-co-N-vinylformamide) and Poly(acrylic acid) on a Solid Substrate

Abstract

Sequential amide formation between poly(vinylamine-co-N-vinylformamide)s [poly(VAmco-NVF)s] with VAm contents of 20, 28, and 42 mol % plus polyAAc using a water-soluble carbodiimide was studied to prepare ultrathin hydrogels on a solid substrate. The analysis of assembly amounts at each assembly step using a quartz crystal microbalance revealed that at least 28 mol % of VAm was essential for stepwise reaction of both polymers on the substrate. The assembly amount was regulated not only by the VAm content but also by the concentration of the copolymer in the reaction solution. Reflection-absorption spectra of the assemblies showed typical peaks assigned to both polymers. The thickness of the assemblies, which was analyzed in the scratching mode using atomic force microscopy, increased in water to form ultrathin hydrogels. The increase in thickness was dependent on the VAm content, and the assembly prepared from poly(VAm-co-NVF) with a 42 mol % VAm content swelled with more water molecules compared to that with a 28 mol % VAm. Analysis using cyclic voltammetry revealed that Fe(CN) 6 3readily permeated the ultrathin hydrogels by the process of diffusion. The permeability was also dependent on the VAm content. Collectively, these results indicated that ion-permeable ultrathin hydrogels were successfully prepared on a solid substrate.

Ultrathin Hydrogels Prepared from Poly(acrylic acid-co-acrylamide) and Poly(vinylamine) on a Solid Substrate

“…These swelling ratios were similar to those reported for ultrathin hydrogels previously prepared using copolymers of N-vinylalkylamides. 5,6 Even in the absence of EDC, the film obtained swelled slightly with water molecules, possibly due to the presence of monomer units that did not related to the noncovalent interactions between the polymers. The percent incremental increase in assembly thickness was dependent on the amount of EDC, and increased with the amount of EDC.…”

“…This hypothesized assembly mechanism is also supported by the assembly of poly(VAm-co-NVF) and polyAAc. 6 The amount of assembled polymer was also regulated by the concentration of poly(AAc-co-AAm). An increase in the polymer concentration resulted in an increase in the total assembly amount.…”

“…5,6 The crystal (9 mm in diameter) was coated on both sides with gold electrodes 4.5 mm in diameter, the mean roughness of which was 1.7 nm. The frequency was monitored by an Iwatsu frequency counter (Model SC7201).…”

“…In our previous papers, sequential formation of amide linkages in LbL assemblies between primary amine containing copolymers of N-vinylalkylamides such as poly(vinylamine-co-N-vinylisobutyramide) (poly(VAm-co-NVIBA)) 5 or poly(vinylamine-co-Nvinylformamide) (poly(VAm-co-NVF)), 6 plus poly-(acrylic acid) (polyAAc) in the presence of a watersoluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) was used in the fabrication of ultrathin films on a solid substrate. Subsequent immersion into aqueous phase resulted in an increase in the film thickness as a result of swelling with water molecules due to the presence of hydrophilic N-vinylalkylamide units, thus fabricating ultrathin hydrogels.…”

“…These findings indicated that ultrathin hydrogels could be prepared by sequential chemical reaction of certain copolymers having hydrophilic neutral units. Although copolymers of Nvinylalkylamides are potentially available for the preparation of ultrathin hydrogels in conjunction with polyAAc, at least approximately 40 mol% 5 and 30 mol% 6 of VAm content in poly(VAm-co-NVIBA) and poly(VAm-co-NVF), respectively, were necessary for stepwise deposition with polyAAc. Otherwise, the films were not deposited in an LbL manner.…”