Multi-Scale Structural Insights Into Amphiphilic Model PEG–PCL Co-Networks From LS and SANS

Abstract

This work investigates the structural characteristics of model amphiphilic polymer co-networks formed by hetero-complementary crosslinking of 2-(4-nitrophenyl)-benzoxazinone-terminated tetra-poly(ε-caprolactone) (t-PCL) and amino-terminated tetra-poly(ethylene glycol) (t-PEG) in nonselective and selective solvents using simultaneous dynamic and static light scattering (DLS & SLS) and small-angle neutron scattering (SANS). In addition, time-resolved dynamic light scattering (TRDLS) is employed to follow the real-time gelation in a nonselective solvent. Simultaneous DLS/SLS measurements yield dynamic and static correlation lengths, providing insight into thermally driven and frozen-in concentration fluctuations, respectively. The static correlation length increases with the polymer volume fraction, indicating growing structural inhomogeneities arising from partial PEG/PCL immiscibility, while the mean-square refractive index fluctuations decrease, suggesting reduced local contrast and enhanced overall homogeneity. In contrast, the dynamic correlation length decreases with increasing polymer volume fraction according to ξ ∼ Φ^{−0.95 ± 0.15}, consistent with faster cooperative segmental dynamics. Complementary SANS measurements on water-swollen APCNs confirm the presence of microphase-separated PCL clusters, well described by a polydisperse Percus–Yevick hard-sphere model with consistent core–corona architecture independent of the network polymer volume fraction at preparation. Comparison with a purely hydrophilic PEG–PEG reference network highlights the influence of amphiphilicity on the structural features of the networks.