Role of Poly(Ionic Liquid) in Aggregation Behavior of Micro‐Particles in Aqueous Solvent

ABSTRACT Microplastic (MP) pollution in marine environments remains difficult to mitigate because conventional coagulants often lose effectiveness under high‐salinity conditions. In this study, two poly(isobutylene)‐derived poly(ionic liquid) (PIL) flocculants; polyisobutylene‐trihexyl(tetradecyl)phosphonium decanoate (PIB‐t‐TPD) and polyisobutylene‐1‐methyl‐3‐octylimidazolium tetrafluoroborate (PIB‐ImTFB), were synthesized and systematically evaluated for the aggregation of polypropylene (PP) and polystyrene (PS) microplastics in natural seawater collected from Penang National Park. Sodium dodecyl sulfate (SDS) was employed to enhance PIL dispersion and modulate interfacial interactions under saline conditions. Both PILs induced pronounced aggregation of PP and PS microplastics, with optimal performance observed at intermediate dosages (0.5–1.0 wt.% PIL in the presence of 1 wt.% SDS). Under these conditions, large and rapidly settling flocs were formed, with average aggregate sizes reaching ~142 μm for PS and ~198 μm for PP. Thorough analysis revealed that aggregation was governed by a synergistic interplay between surface charge attenuation toward the point of zero charge and hydrophobic polymer bridging mediated by the PIB backbone. At higher SDS or PIL dosages, charge reversal and steric stabilization led to partial particle restabilization and reduced aggregation efficiency. Compared with conventional polyaluminum chloride (PAC), the PIB‐derived PILs demonstrated superior aggregation efficiency, larger floc sizes, and enhanced turbidity removal in high‐ionic‐strength seawater. These results highlight PIB‐based PILs as tunable, metal‐free flocculants and promising candidates for microplastic remediation in marine environments.