Incorporating Spherical and Rod-Shaped Gold Particles into Polymeric Coacervates 

In aqueous solution, oppositely charged polyelectrolytes undergo associative liquid–liquid phase separation, forming a dense coacervate phase in equilibrium with a dilute supernatant. This behavior is highly sensitive to external factors, especially salt concentration, which can weaken inter-polyelectrolyte interactions by introducing counterions that disrupt charge pairing. Such effects significantly alter the structure and mechanical properties of the resulting complexes. Incorporating nanoparticles into soft materials offers a promising route to enhance their mechanical performance. Among various additives, gold nanoparticles (AuNPs) are of particular interest due to their tunable morphology, surface chemistry, and catalytic properties. In this study, we explore the integration of AuNPs into complex coacervates formed by poly(diallyldimethylammonium chloride) (PDADMAC) and sodium poly(acrylate) (PANa). Our objectives were to understand the mechanism of nanoparticle incorporation, evaluate their dispersion, and assess their effect on the mechanical behavior of the coacervate matrix. Both spherical and rod-shaped AuNPs were synthesized and embedded within the coacervate phase. Small-angle X-ray scattering (SAXS), coupled with a refined fitting model, was employed to analyze the nanoparticle distribution and the internal structure of the polymer matrix. Results show that the coacervate enables stable, homogeneous dispersion of the nanoparticles. Rheological measurements reveal that AuNPs enhance the mechanical strength of the coacervate, with rod-shaped particles having a greater effect due to their higher aspect ratio. The resulting nanocomposite system also shows promise as a recoverable catalytic platform, demonstrating the versatility of coacervate-based materials for functional applications.