Dynamic Light Scattering based microrheology of End-functionalised triblock copolymer solutions

TL;DR

This study uses dynamic light scattering and microrheology to explore how end-functionalisation of triblock copolymer F108 with azide or DNA affects its phase behavior and structural properties, revealing new insights into hybrid micellar systems.

Contribution

It introduces a detailed analysis of how end-functionalisation alters the phase behavior and rheological properties of F108 micellar solutions, advancing understanding of hybrid self-assembling systems.

Findings

Azide functionalisation induces flower-micelles at lower temperatures.

DNA attachment enables temperature-dependent 'stickiness' due to hybridisation.

Functionalisation significantly changes the mechanical and structural properties of micellar fluids.

Abstract

'Soft' patchy surfactant micelles have become an additional building tool in self-assembling systems. The triblock copolymer, Pluronic F108, forms spherical micelles in aqueous solutions upon heating leading to a simple phase diagram with a micellar crystalline solid at higher temperatures and concentrations. Here we report the strong influence of end-functionalising the chain ends either with an azide or azide-DNA complex on the systems' phase behaviour. We find that the azide(N3)- functionalisation renders the chain ends weakly hydrophobic at lower temperatures, causing them to self-assemble into flower-micelles. This hydrophobicity increases with increasing temperature and poses a competing self-assembling mechanism to the solvent induces hydrophobic interactions between the middle-blocks of F108 at higher temperatures and leads to a macroscopic phase separation that is absent in the pure F108 system. However, when we attached short, hydrophilic single-stranded (ss)DNA to the azide groups via click chemistry the chain ends became 'sticky' due to DNA hybridisation below the melting temperature of the complementary ssDNA ends while reverting to hydrophilic behaviour above. We characterise their structural and rheological properties via Dynamic Light Scattering (DLS) and DLS-based passive microrheology with an improved time-frequency domain inversion step. We present the structural behaviour of dilute and semi-dilute solutions of the original F108 system and compare the results with solutions containing either the F108- azide (F108-N3) or partially DNA-functionalised F108-azide chains. Our DLS and microrheology studies inform us on how the attachment of azide groups on F108 changes the mechanical and structural properties of micellar fluids pioneering further characterisation and design of these hybrid systems.