Insights into the stability of polytetrafluoroethylene aqueous dispersion: Role of surfactant

Polytetrafluoroethylene (PTFE) has attracted significant interest from both industry and academia owing to its remarkable properties such as wear and corrosion resistance, low surface energy and low dielectric constant. High stability and high solid content (~60%) are primary criteria for PTFE aqueous dispersions toward preparing various end-use articles; however, they are difficult to be achieved simultaneously. Additionally, the stabilization mechanism has not been clearly unraveled and understood till date. Herein, four types of surfactants including cationic dodecyltrimethylammonium bromide (DTAB), anionic sodium dodecylsulfate, zwitterionic lauryl betaine (LB), and nonionic lauryl alcohol polyoxyethylene Brij 30, are used to stabilize 60% PTFE dispersions from the as-polymerized dilute mixture. The stabilities of these dispersions are quantitatively and objectively characterized for the first time using a Turbiscan analyzer based on multiple light scattering technology. While DTAB causes flocculation, the other three surfactants can formulate concentrated dispersions. The dispersion with LB loses the stability in a short time, whereas Brij 30-stabilized dispersion exhibits high stability due to the formation of a network of wormlike micelles. It is determined that the instability of surfactant-stabilized dispersion stems from particle sedimentation rather than coalescence or aggregation. The size of dispersed particle and dispersion viscosity play dominant roles in controlling the particle settling rate, thereby affecting the stability. This study affords useful insights into the stability of concentrated PTFE dispersion, which can guide the selection of suitable surfactants to prepare PTFE dispersions with desired stabilities.