Influence of Ionic Strength and Specific Ion Effects on Polyelectrolyte Multilayer Films with pH-Responsive Behavior

Abstract

Layer-by-layer assembled multilayer films have shown great potential for different applications owing to their responsive behavior. Herein, we systematically investigated the effects of composition, salt concentration, and ion specificity on the pH responsiveness of covalently crosslinked chitosan and alginate dialdehyde multilayer films. The changes in film swelling were measured using ellipsometry from low (0.01 mM) to high (3 M) salt (NaCl or NaSCN) concentrations at pH 3, 6, and 9. The swelling responses to increasing ionic strength matched the swelling responses observed for polyzwitterionic and weak monocomponent polyelectrolyte films and depended on the multilayer composition, pH, and ion specificity. Finally, we used the ellipsometric data to demonstrate that the pH responsiveness of such multilayer films, as measured using a quartz crystal microbalance with dissipation monitoring, strongly depends on the ionic condition under which the responses were measured. We thus show that erroneous conclusions about the pH responsiveness of polyelectrolyte multilayer films can be easily obtained if the ionic environment of the application does not closely resemble the ionic condition under which the pH responsiveness is tested.

Fabrication of Fully Negatively Charged Layer-by-Layer Nanofilms with pH-Induced Remarkable Swelling–Shrinking Properties

“…The pH stability of FNC nanofilms might be attributed to the triazole linkages between adjacent layers, which can resist the pH changes . PE nanofilms are simply cohered by electrostatic interactions, which can be easily destroyed when the charges are eliminated in harsh pH conditions . Without the main electrostatic interactions between polycations and polyanions, the PE nanofilms can be easily dissociated.…”

Nanostructured Flame-Retardant Layer-by-Layer Architectures for Cotton Fabrics: The Current State of the Art and Perspectives

“…The construction of the LbL assembly proceeds until the intended number of layers has been deposited on the substrate: in this context, ten to fifty (or even more) layers can be placed on the polymer substrate, depending on the design of the LbL architecture. Additionally, several experimental parameters may significantly affect the structure, morphology, and final performance of the layer-by-layer assemblies, namely as follows: adsorption time [50,51], the pH of the solutions/suspensions [52], ionic strength [53,54], temperature [55,56], and the structure/conformation/molecular weight of the employed polyelectrolytes [57][58][59].…”

The pH responsiveness of fluorescein loaded in polysaccharide composite films

“…In general, the pH responsiveness of film-like materials composed of polyions depended on the ionic strength of the buffer solution. 41,[47][48][49] The CS/CHI films in the high ionic strength buffer such as phosphate buffer saline (PBS, pH 7.4, I = 0.16) reduced electrostatic interactions between polysaccharides. 41 To clarify the effect of the ionic strength of PB, the calculation of the ionic strength of PB was performed and the order was as follows; pH 8.0 (I = 0.027) 4 7.4 (I = 0.022) 4 5.8 (I = 0.011) 4 3.0 (I = 0.010) 4 2.0 (I = 0.007).…”