Single-Particle Tracking Studies of Poly(Ethylene Glycol) Diacrylate Solutions: How Polymer Concentration and Particle Size Define the Nanoscale Mass Transport Properties of an Unentangled Polymer Network

Single-particle tracking studies of the nanoparticle diffusion behaviors in unentangled poly(ethylene glycol) diacrylate (PEGDA, M_n = 700 g mol^-1) solutions are reported. The impacts of the PEGDA concentration (10 – 40% weight%) and the size of carboxylate-modified fluorescent microspheres (FluoSpheres, diameter: 30 – 200 nm) on the nanoparticle diffusion in unentangled polymer networks are systematically investigated. The fluorescence videos recorded on our home-built widefield fluorescence microscope show that for one given probe size, the nanoparticle diffusivity is observed to decrease with increasing PEGDA concentration. Similarly, the recorded dynamics of nanoparticles for one fixed PEGDA concentration are observed to decrease as the probe size increases. Quantitative data analysis of the recorded fluorescence video data using established computer routines (e.g., Particle Tracker) provides a wealth of useful quantitative measures such as the single-particle trajectories, mean-squared displacements, and single-particle diffusion coefficients. These metrics are employed to access the details of the probe diffusion behaviors revealing the reduced particle diffusivity in PEGDA (vs. bulk liquid). This is primarily linked to the significant probe-host interactions present in unentangled PEGDA. Our experiments are also used to confirm or reject an existing multi-scale mass-transport model proposed by our lab (J. Phys. Chem. B 2023, 127, 7091 – 7102) based on this work’s outcome.