Charge Modification as a Mechanism for Tunable Properties in Polymer-Surfactant Complexes.

Christopher Hill,Robert Dalgliesh,Peter Charles Griffiths,Martin Crossman,Wasiu Abdullahi

doi:10.3390/polym13162800

Abstract

Oppositely charged polymer–surfactant complexes are frequently explored as a function of phase space defined by the charge ratio Z, (where Z = [), commonly accessed through the surfactant concentration. Tuning the phase behaviour and related properties of these complexes is an important tool for optimising commercial formulations; hence, understanding the relationship between Z and bulk properties is pertinent. Here, within a homologous series of cationic hydroxyethyl cellulose (cat-HEC) polymers with minor perturbations in the degree of side chain charge modification, phase space is instead explored through at fixed C. The nanostructures were characterised by small-angle neutron scattering (SANS) in DO solutions and in combination with the oppositely charged surfactant sodium dodecylsulfate (h- or d-SDS). Scattering consistent with thin rods with an average radius of ∼7.7 Å and length of ∼85 Å was observed for all cat-HEC polymers and no significant interactions were shown between the neutral HEC polymer and SDS (C < CMC). For the charge-modified polymers, interactions with SDS were evident and the radius of the formed complexes grew up to ∼15 Å with increasing Z. This study demonstrates a novel approach in which the Z phase space of oppositely charged polymer–surfactant complexes can be controlled at fixed concentrations.

Highlights

Many industrial processes rely on controlling the tunable behaviour of formulated products through an appropriate blending of oppositely charged polymer–surfactant mixtures
The nanostructures formed by the series of cationic hydroxyethyl cellulose (cat-HEC) PEs at a practical concentration of 1 wt% are investigated individually before discussions of mixed cat-HEC/sodium dodecylsulfate (SDS) complexes
PEs in the semidilute regime, weak scattering is observed for all cat-HEC polymers in this study [15,16,17,18,25], being consistent with the presence of thin, rodlike solution structures

Summary

Introduction

Many industrial processes rely on controlling the tunable behaviour of formulated products through an appropriate blending of oppositely charged polymer–surfactant mixtures. As a result of this relative ease of control over such properties, oppositely charged polymer–surfactant mixtures have had great success as formulated products in applications such as, but not limited to, detergency [1,2,3], drug delivery [4,5,6,7], and rheological modifiers [8,9]. One series of polysaccharide-based polyelectrolytes (PEs) that have received particular attention due to their commercial relevance and interesting rheological properties are cationic hydroxyethyl cellulose (cat-HEC) polymers, in particular, JR400 [14,15,16,17,18,20,23,25] More recently, polysaccharides have emerged as an important component in commercially formulated products as a result of their biocompatibility, biodegradability, bioadhesivity, and nontoxicity [14,15,16,17,18,19,20,21,22,23,24].

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