Mechanical reinforcement of gellan-alginate hydrogels using commercial functionalized silica particles and mild...

Hydrogels offer tunable mechanical properties that can be enhanced through tailored polymer-colloidal filler interactions. This work examines the interfacial behavior in gellan gum/sodium alginate soft polymeric networks reinforced with commercial polydisperse amine-functionalized mesoporous silica particles, and glutaraldehyde (GTA) or genipin (GN) as bifunctional surface activators. The reinforcement mechanism was elucidated through quantitative in-line pH kinetics and surface charge evolution analysis. A critical 'electrostatic window' was identified where the surface charge of the amino-functionalized silica transitions from +20.9 mV to -11.5 mV, minimizing particle-polymer repulsion and facilitating interfacial anchoring. Furthermore, particle-size heterogeneity was found to broaden the linear viscoelastic regime by creating a distributed, particle-bridged interfacial network. Surface activation by GTA or GN introduced additional stiffening. While both activators reduce surface charge, GN produced the largest mechanical enhancement due to its slower, more controlled reaction pathway. Scanning electron microscopy (SEM) revealed the growth of rod-like structures at the particle-polymer interface in GN-activated systems, providing a physical interlocking mechanism that substantiates the observed 15% increase in storage modulus, G'. While FT-IR detected only subtle chemical changes, X-ray diffraction revealed a significant shift in the amorphous silica reflection from 23° to 13°, indicating structural rearrangements consistent with covalent interfacial coupling. These results demonstrate that synchronizing reaction kinetics with the electrostatic landscape provides a data-backed strategy to optimize the robustness of hybrid polymeric networks.