Photothermal Waterborne Polydopamine/Polyurethanes with Light-to-Heat Conversion Properties

Abstract

A polydopamine-polyurethane (PDA-WPU)-based polymeric matrix with efficient light-to-heat conversion properties that can initiate light-activated temperature elevations is presented. The polymerization of dopamine monomer in a pre-synthesized aqueous polyurethane dispersion resulted in hybrid polyurethane-polydopamine particles via the coating of discrete waterborne polyurethane (WPU) particles with photothermal polydopamine. The resulting polydopamine-polyurethane (PDA-WPU) dispersions presented a unimodal particle-size distribution and particle sizes that increased as a function of the initial dopamine concentration and polymerization time. Films cast from PDA-WPU dispersions were black-colored and presented a homogeneous morphology with contact angles that decreased with increasing PDA content. While the thermal decomposition behavior and thermal conductivity values of hybrid PDA-WPU films were improved relative to neat WPU films, the glass transition temperatures remained unaffected and the films presented acceptable mechanical properties. PDA-WPU films prepared with the highest amount of polydopamine reached 105.8 °C when irradiated with solar light at 3 sun for 20 min. Five min of irradiation with NIR laser light at 800 mW/cm2 elevated the temperatures of the PDA-WPU films from room temperature to 138.6 °C. Moreover, PDA-WPU dispersions were molded in the form of a container to investigate their potential in solar-driven water-evaporation applications. The hybrid PDA-WPU polymer matrix prepared via a facile postsynthesis modification of WPU dispersions with polydopamine synergistically possesses the features of both components and presents strong photothermal activity along with its easy-to-apply, nanoparticle-free, and environmentally friendly nature; thus, this matrix can be viewed as a promising candidate for a wide range of photo-driven applications.