engleski

Influence of relative humidity on the swelling of chitosan/poly(acrylic acid) nanofilms

Polyelectrolytes are macromolecules in which a significant proportion of functional groups are ionic or easily ionizing. Given the charge of polyelectrolytes in solution, they are divided into polycations and polyanions, and given the degree of ionization in a solution, they are classified as weak and strong polyelectrolytes. By alternating adsorption of positively and negatively charged polyelectrolytes on a solid surface, polyelectrolyte multilayers are formed. This procedure is called layer-by-layer (LbL) method which allows the precise design of nanofilms with desired properties. The main reason that multilayers have been increasingly researched in recent years is their application, for example, in fruit protection, drug delivery, membrane technology, etc. One of the interesting properties of polyelectrolyte coatings is self-healing. For example, a multilayer of chitosan (CS) and poly(acrylic acid) (PAA), was recently prepared and after treatment in an aqueous medium, it healed inflicted mechanical damage. A key factor in this effect is the swelling of the film which is strongly influenced by multilayer interactions. In order to investigate the swelling of CS/PAA thin films, a chamber for controlling the relative humidity of the atmosphere was designed, constructed, and tested using saturated salt solutions which control the relative humidity inside the chamber. In the next step, the LbL method was used to prepare films with different numbers of layers on silica substrate from CS and PAA solutions. The formation and thickness of the LbL film after each adsorbed layer was monitored by ellipsometry. By measuring the thickness of the prepared film during its swelling and drying, the reversibility of these processes, i.e. swelling hysteresis, was examined. After that, the thickness of the prepared samples at different humidities was determined. It was found that the thickness of the multilayers increased with increasing humidity and that the swelling of the nanofilms is more pronounced for the films with a higher number of layers.

Polyelectrolyte ; Polyelectrolyte multilayer ; Film swelling ; Self-healing

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