Network Formation in Poly(diallyldimethylammonium chloride)/Polyphosphoric Acid Polyelectrolyte Complexes and Their Role in Sand Stabilization

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Soil erosion remains a pressing global environmental challenge, and polyelectrolyte complexes (PECs) have emerged as promising stabilizing agents for soil erosion control. However, the mechanistic basis of their performance, particularly the complex interplay between the structure of PECs, rheological behavior, and the associated flow field within the surrounding environment, remains poorly understood. In this study, we constructed PECs by combining a short-chain polyanion and a long-chain polycation to form a polymeric network, using polyphosphoric acid (PPA) and poly(diallyldimethylammonium chloride) (PDDA) as the model components. Electrophoretic mobility (EPM) measurements, hydrodynamic diameter analysis by dynamic light scattering (DLS), and quartz crystal microbalance with dissipation (QCM-D) collectively reveal an electrostatically driven self-assembly process in which long-chain PDDA provides the scaffold while short-chain PPA acts as a molecular connector. Rheological measurements show that the shear resistance of the PDDA/PPA network, characterized by the effective shear rate γ̇ and the characteristic shear stress τ at the G′ maximum, can be tuned by adjusting the PPA dosage. Macroscale hydrodynamic shear tests further demonstrate a strong positive correlation between consolidated-sand stability and the rheology-derived network strength, with both γ̇ and τ at the G′ maximum reaching a maximum at a PDDA:PPA monomer molar ratio of 1:5. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) directly visualizes interparticle physical bridging that promotes sand aggregation. Collectively, these results suggest that the PPA-regulated strength of the PECs network is an important factor influencing sand-stabilization performance. Such findings shift the design philosophy of sand stabilizers from conventional surface adhesion toward the internal structural engineering of particle-bridging networks.