Title:	Salt-induced swelling transitions of a lamellar amphiphile—Polyelectrolyte complex
Authors:	Thomas, Meera Swamynathan, K. Raghunathan, V.A.
Issue Date:	18-Feb-2019
Publisher:	American Institute of Physics
Citation:	Journal of Chemical Physics, 2019, Vol.150, p 094903
Abstract:	We report salt-induced swelling transitions of a lamellar complex of the anionic polyelectrolyte, poly(acrylic acid sodium salt) (PAANa), and the cationic amphiphile, didodecyldimethylammonium chloride (DDAC). Increasing the concentration of NaCl in the solution is found to lead to a collapsed􀀀swollen􀀀collapsed transition of the complex. The swelling transition is driven by an abrupt increase in PAANa adsorption on DDAC bilayers above a threshold salt concentration. The lamellar periodicity of the swollen phase is not determined by the thickness of the adsorption layer, and additional mechanisms have to be invoked to understand the extent of its swelling. The swelling transition is not observed for the highest molecular weight of PAANa used, but a gradual transformation between the two collapsed structures is seen on increasing the salt concentration. The polyelectrolyte chains desorb from the bilayers at a very high salt concentration, in a process similar to the well-known destabilization of complexes of oppositely charged polyelectrolytes. However, unlike the PAANa chains, the polymer-free bilayers do not disperse uniformly in the solution. Instead, they form a collapsed lamellar stack containing very little water due to the van der Waals attraction between them. The occurrence of an abrupt swelling transition at intermediate salt concentrations in this system contrasts sharply with the gradual swelling reported in other complexes with increasing salt concentration. Furthermore, this behavior does not seem to have been anticipated by theories of complexation of oppositely charged macroions. More experiments are required for a clear understanding of the interactions stabilizing the different phases observed in this system.
Description:	Restricted Access.
URI:	http://hdl.handle.net/2289/7181
ISSN:	0021-9606 1089-7690 (Online)
Alternative Location:	https://doi.org/10.1063/1.5063964
Copyright:	2019 American Institute of Physics
Appears in Collections:	Research Papers (SCM)

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