Influence of hydrophobic and electrostatic interactions on counterion-dissociation in sodium carboxymethylcellulose - polyethylene glycol (PEG) solutions

Counterion dissociation/condensation and related phenomena of sodium carboxymethylcellulose have been investigated in water with varying hydrophobicity by conductance measurements. Alteration of the hydrophobicity of the media was accomplished by adding varying amounts of polyethylene glycol with different molar masses to the solutions. Analyses of the specific conductances measured as a function of sodium carboxymethyl-cellulose concentration were performed taking into account the de Gennes scaling model which describes the configuration of polyion chains in semidilute solutions. Results indicate that polyions are the chief transporter of the electricity in the investigated solutions and that a major fraction of the counterions is accompanied by the polyion chains and performs concerted movement towards the positive electrode. Increasing molar mass of the polyethylene glycol samples added to aqueous sodium carboxymethylcellulose solutions containing a given amount of the additive promotes counterion-dissociation, whereas increasing amount of the additive with a given molar mass promotes counterion-condensation. Relative influences of electrostatic and hydrophobic forces have been taken into consideration in order to elucidate the observed dissociation/condensation behavior of counterions of aqueous sodium carboxymethylcellulose solutions. Analyses of the results provided important insight regarding the possible alterations of the conformation of the polyions originating from the subtle balance of hydrophobic and electrostatic interactions in these solutions. (C) 2020 Elsevier B.V. All rights reserved.