Organic solvent–based paintings are still widely used in the coating industry. However, growing awareness of environmental impact and safety concerns has accelerated the transition toward waterborne paintings, whose demand continues to increase each year. In waterborne paintings, polymer binders must be finely dispersed in a liquid medium, and a robust coating film is formed as the solvent evaporates and the polymer chains entangle each other. Because many polymers are poorly soluble in water, the addition of organic solvents remains indispensable for stabilizing the dispersion, and optimizing this balance remains a major challenge.
In this study, molecular dynamics simulations were employed to directly track the motion of polymer chains and to compare their dispersion and aggregation behaviors in aqueous, organic, and mixed-solvent environments. By systematically varying the interaction strength between polymers and solvents, it is verified how organic solvents influence the conformation of polymer chains. It is found that weak polymer–solvent interactions lead to polymer aggregation, whereas stronger interactions stabilize the dispersed state. Furthermore, in mixed water–organic solvent systems, organic molecules tend to phase-separate into small organic-rich domains within water. These simulations revealed that polymer chains become locally concentrated in these domains, demonstrating that polymer aggregation is strongly dependent on the organic solvent fraction. These insights provide a molecular-level understanding of dispersion stability and aggregation mechanisms during the early stages of film formation in water-based paints. They also offer valuable guidelines for designing polymer–solvent systems, ultimately contributing to the development of environmentally friendly, low–organic solvent coatings.
Molecular dynamics simulation of polymer dispersion in binary (aqueous + organic) solvents.
Papers
Journal: ACS Omega
Title: Molecular Dynamics Study of Polymer Coiling in a Water−Organic Binary Solvent System
Authors: Shinya Kawakami, Ryuhei Sato*, Hirotaka Ejima, Takahiro Ujii, Koichi Sato, Takanori Ichiki, Yasushi Shibuta
Elucidating the Relationship between the Strength and Structure of Polymer Materials: Development of New Painting Materials Combining Molecular Dynamics Simulations and Mathematical Science
Molecular Dynamics Simulation of Adhesion of Additive Molecules in Paint Materials toward Enhancement of Anticorrosion Performance
