Cross-linked amphiphilic polyelectrolyte colloidal gels: Green synthesis and chemical and microstructure analysis

A cross-linked amphiphilic polyelectrolyte colloidal gel (CG) exhibits significant potential for diverse applications, including hydrophobic drug delivery and oil recovery, owing to its enhanced functionality. However, the synthesis of these CGs demands a sustainable, eco-friendly, and cost-effective approach, posing both interest and challenges. This study addresses these considerations by synthesizing model cross-linked amphiphilic CGs using both direct and indirect methods in green solvents. Various macromolecular and colloidal characterization techniques were employed to investigate the chemical composition, internal structure, size distribution, colloidal and structural stability, and pH-, electrolyte-, and composition-dependent swelling and morphology transitions of the CGs. The successful synthesis of monodisperse dual cross-linked CGs containing up to 94 mol% of hydrophilic acrylic acid was achieved through a practical pathway that avoids the use of toxic organic solvents. This involved incorporating a low content of a hydrophobic component (e.g., 6 mol % of butyl acrylate) via seeded semi-batch emulsion polymerization under low pH conditions. The CGs exhibited a logarithmic size dependence on ionic strength across a wide range of electrolyte concentrations (0.1–500 mM) and demonstrated a distinctive pH-dependent morphological transition influenced by the hydrophobic content. This study provides a profound insight into the interplay between hydrophobic interactions, swelling-driven forces, and chemical linking, highlighting the impact of composition on the internal structure and size distribution of the CGs.