Defining the Conformation of Water-Soluble Poly(vinyl alcohol) in Solution: A SAXS, DLS, and AFM Study

This study examines the conformation of soluble poly(vinyl alcohol) (PVA) in aqueous solution using small angle X-ray scattering (SAXS), dynamic light scattering (DLS), and atomic force microscopy (AFM). The focus is on PVA grades used in industrial water-soluble detergent films, comparing their behavior to nanometer-sized polystyrene (PS) beads. SAXS analysis indicates that soluble PVA chains adopt a single molecule random Gaussian coil conformation with a radius of gyration (<i>R_g</i> ) of approximately 14 nm, consistent across various grades, dissolution temperatures, and water hardness. DLS corroborates this single-molecule behavior, and AFM imaging confirms separated PVA chains. SAXS, DLS, and AFM collectively enhance understanding of PVA's behavior in solution. They provide distinguishing features (e.g., SAXS form factors, <i>q</i> ^-4 decay, <i>q</i> ^-2 decay; SAXS- and DLS-derived <i>R_g</i> /<i>R_h</i> ratio, AFM images) to aid in visualizing and differentiating between water-soluble polymers and micro- or nanoplastic polymers, which exhibit a hard interface. The study concludes that soluble PVA grades used in the detergent films maintain a stable single molecular chain conformation in water with a nonsolid interface, hence very different from known microplastics. This study also provides a basis for a methodology to differentiate the behavior of water-soluble polymers from microplastics.