Controlling Nanoparticle Diffusion via the Length of the Hydrophilic Side Chain in Gel Networks

The local structures of temperature-responsive poly(oligo ethylene glycol methyl ether methacrylate) (pOEG) gels were investigated by analyzing the dynamics of probe nanoparticles using dynamic light scattering (DLS). The probe diffusion depends on the number of ethylene oxide (EO) units, i.e., the length of the hydrophobic side chains, due to the increased steric hindrance and increased network density (volume fraction) with increasing length of the EO side chain. The temperature dependence of the probe diffusion was also examined, and anomalous diffusion behavior was observed in the pOEG-based gels. This was attributed to the phase separation between the polymer and water in the pOEG gels, which causes an expansion of the diffusion area available to the nanoparticles and creates a local environment conducive to nanoparticle movement. Furthermore, we established precise control over the temperature where anomalous diffusion occurs by copolymerizing pOEG with varying side-chain length. These results should facilitate the development of synthetic strategies to control the transport and activity of functional molecules in soft matrices for advanced applications, including catalysis, chaperone functions, and drug-delivery systems.