Diffusive probe penetration for characterization of diffusion-governing length scales in amphiphilic PEG–PCL co-networks

We investigate the penetrative probe diffusion in a model amphiphilic polymer co-network (APCN) synthesized <i>via</i> a hetero-complementary coupling reaction between 2-(4-nitrophenyl)-benzoxazinone-terminated tetra-poly(<i>ε</i>-caprolactone) (t-PCL) and amino-terminated tetra-poly(ethylene glycol) (t-PEG) using isorefractive dynamic light scattering (DLS). We employ spherical silver nanoparticles (AgNPs) and esterified dextrans of varying molecular weights in the APCN swollen in toluene to get insights about the diffusion-governing length scales, namely the correlation length and the hydrodynamic screening length of the network. The diffusion data are analyzed using hydrodynamic and obstruction models, with the hydrodynamic model proving more suitable for such networks. Our results reveal scaling laws for the correlation length as a function of the polymer volume fraction, matching previous theoretical simulations and experimental findings, alongside the determination of the hydrodynamic screening length, marking the transition from the Rouse to the Zimm regime. Additionally, we demonstrate how structural length scales evolve with swelling, offering more profound insights into the structure-property relationships of APCNs. Comparative diffusion measurements in non-crosslinked t-PEG/t-PCL solutions reveal that network crosslinking significantly affects both the characteristic length scales and the scaling behavior of diffusion.