Dynamic Light Scattering Based Microrheology of End-Functionalised Triblock Copolymer Solutions

Nano-sized particles functionalised with short single-stranded (ss)DNAs can act as detectors of complementary DNA strands. Here we consider tri-block-copolymer-based, self-assembling DNA-coated nanoparticles. The copolymers are chemically linked to the DNA strands via azide (N-3) groups. The micelles aggregate when they are linked with complementary ssDNA. The advantage of such block-copolymer-based systems is that they are easy to make. Here we show that DNA functionalisation results in inter-micellar attraction, but that N-3-groups that have not reacted with the DNA detector strands also change the phase behaviour of the tri-block polymer solution. We studied the triblock copolymer, Pluronic((R)) F108, which forms spherical micelles in aqueous solutions upon heating. We find that the triblock chains ending with either an N-3 or N-3-DNA complex show a dramatic change in phase behaviour. In particular, the N-3-functionalisation causes the chain ends to cluster below the critical micelle temperature (CMT) of pure F108, forming flower-micelles with the N-3-groups at the core, while the PPO groups are exposed to the solvent. Above the CMT, we see an inversion with the PPO chains forming the micellar core, while the N-3-groups are now aggregating on the periphery, inducing an attraction between the micelles. Our results demonstrate that, due to the two competing self-assembling mechanisms, the system can form transient hydrogels.