Formation of liquid‐crystalline morphologies in dilute solutions of a charged random terpolymer

Abstract

Formation of micellar morphologies in aqueous solutions of charged random copolymers has been reported in several studies. This paper reports on liquid crystallization of the cationic random acrylic terpolymer i.e., poly[(dimethylaminoethyl methacrylate)-co-(methyl methacrylate)-co-(butyl methacrylate)] containing no mesogenic groups. The viscometric behaviour of the terpolymer solutions deviated in several ways from ordinary behaviour of polyelectrolytes supporting the possibility of self-assembly of this cationic random terpolymer in a solvent mixture containing acetone, ethanol and 1-propanol or each of these solvents separately. The existence of nano-sized liquid-crystalline structures was demonstrated using small-angle X-ray scattering (SAXS) analysis of the terpolymer solutions. Morphology and sizes of the liquid-crystalline structures were determined according to the SAXS results and confirmed by dynamic light scattering and atomic force microscopy findings. Liquid crystallization was reasoned on the basis of the existence of a segregated chain microstructure as for polyelectrolytes containing folded parts connected to each other by monomer strings. In a random amphiphilic copolymer or the terpolymer under investigation, the folded parts and strings must be hydrophilic and hydrophobic, respectively. The role of alcohol aggregates should be considered in self-assembly of the terpolymer chains. The alcohol aggregates can act as physical crosslinkers leading to the formation of more compact liquid-crystalline structures. The deviations observed in the viscometric behaviour of the terpolymer solutions are suggested as the result of the ability of terpolymer chains to self-assemble.

Solvent-dependent rheological behavior of concentrated solutions of a cationic acrylic terpolymer containing self-assembled chains

“…It can be concluded that stronger self-assembled structures in the solvent mixture cannot be dissociated during the strain sweep test. This can be confirmed by our previous findings on the dilute solutions of the terpolymer (13). According to the SAXS results, the terpolymer self-assembled structures in the solvent mixture were much more compact than those in acetone.…”

“…Often, the formation of such regular morphologies is not the result of the drying process (16). These lamellar morphologies are similar to those related to terpolymer dilute solutions (13) and can indicate the existence of self-assembled structures in concentrated solutions. The complex viscosity curves resulting from the strain sweep tests for the terpolymer solutions in acetone and the solvent mixture are shown in Figure 2.…”

“…According to the SAXS results, the terpolymer self-assembled structures in the solvent mixture were much more compact than those in acetone. This finding is based on the existence of alcoholic aggregates in the solvent mixture acting as physical cross-linkers (13).…”

“…poly[dimethylaminoethyl methacrylateco-methyl methacrylate-co-butyl methacrylate]) in a solvent mixture composed of acetone, ethanol and 1-propanol at a ratio of 60:33.4:6.6 (v/v/v) and in each of the constituting solvents separately (13). The solvent mixture composition is according to the terpolymer manufacturer recommendation.…”