Amphiphilic Copolymers as Flexible Macromolecular Surfactants: Design Principles and Performance in Inkjet Applications

Amphiphilic copolymers, functioning as macromolecular surfactants or dispersants, play a crucial role in modern dispersion technology. In the inkjet industry, ink performance and print quality strongly depend on dispersant properties. Although various dispersants are used for ink dispersion, comprehensive guidelines on molecular design and performance evaluation remain limited. Establishing such guidelines is essential for improving ink performance and advancing inkjet technology. This study focuses on the development of polymeric dispersants as key components of inkjet inks. Amphiphilic copolymers with different monomer compositions and architectures (random vs block) were synthesized and evaluated using hydrophobic dye models. Random copolymers exhibited lower viscosity and rheology closer to Newtonian fluid behavior compared to block copolymers. Newtonian fluids, characterized by constant viscosity across shear rates, are ideal for stable and consistent inkjet dispensing. However, random copolymers showed poor dispersion stability, leading to sedimentation. To address this, electrostatic repulsion was explored by incorporating cationic groups. While this modification further reduced viscosity relative to anionic or nonionic systems, stable dispersion was not achieved. We hypothesize that the hydrophobic pyridinium salt moieties impeded dye particle dispersion in water. Redispersibility─the ability of dried ink to redisperse in water─is essential for preventing nozzle clogging. To improve this property, we enhanced the hydrophilicity of random copolymers by incorporating sulfonic acid groups. These dispersants exhibited markedly improved redispersibility; however, the dye dispersions still displayed non-Newtonian behavior, indicating the need for further molecular optimization. Our findings highlight two key outcomes: random copolymers lower viscosity, and sulfonic acid groups significantly enhance redispersibility. Future work will aim to achieve Newtonian fluid characteristics while further improving dispersion stability. Given the broad relevance of dispersion technology, these insights are expected to contribute well beyond the inkjet field.