Resumen de Room-Temperature Synthesis of Size-Uniform Polystyrene Latex and Characterization of Its Properties: Third-Year Undergraduate Teaching Lab
Nimer Murshid, Nicole Cathcart, Vladimir Kitaev
Teaching emulsion polymerization is an important benchmark in undergraduate polymer courses. However, the introduction of hands-on experiments in undergraduate polymer laboratories is challenging: experimental time, reagents, and equipment involved are the primary restraints. We report a practical emulsion polymerization laboratory experiment for undergraduate students that includes the synthesis of polystyrene (PS) latex and exposure to multiple methods of characterization. Using a room-temperature redox initiation system of ascorbic acid (vitamin C) and hydrogen peroxide, and scaling the reaction down to ca. 10 mL, simplifies stirring and degassing and alleviates the aforementioned challenges. To prepare latex samples with different sizes and low size dispersity, students explore an effect of a steric stabilizer (polyvinylpyrrolidone, PVP). For effective time management, students perform characterization of previously prepared latex, while qualitatively and quantitatively monitoring particle growth during polymerization stages. Latex characterization performed by students includes measurements of average particle size and zeta potential, estimating conversion and preparation of latex films with determination of glass transition temperature (Tg). Other characterization methods that can be incorporated in the extended experiments include electron microscopy, atomic force microscopy, and other techniques of colloidal and polymer characterization. Additionally, the prepared latex is able to form colloidal photonic crystal films, enabling size evaluation by color or UV–vis measurements, where selective reflection of blue, green, and red corresponds to latex with particle diameters of 185, 240, and 300 nm, respectively. On the basis of the lab evaluation survey, students performing the experiment have an overall positive learning experience with 94% satisfaction rate.
