Abstract
AbstractSelf‐diffusion of poly(acrylic acid) (PAA) in dilute solution is studied by pulsed field gradient (PFG)‐NMR, also known as DOSY, and correlated to molecular weight with scaling laws at varying pH. Fitting a diffusion coefficient distribution model to PFG‐NMR data, the molecular weight polydispersity of commercial PAA samples is quantified. Due to good agreement with GPC data, diffusion measurements offer a viable alternative to estimate chain length properties with minimal sample preparation. Similar results are achieved by dynamic light scattering (DLS), however, with lower precision. The evolution of the scaling exponent with increasing pH indicates a transition from a globular state in highly acidic conditions (ν = 0.46) to a partially stretched conformation with a maximum at pH 5 (ν = 0.67). At higher pH, counterion screening counteracts chain expansion, while an unexpected increase in the width of the diffusion coefficient distribution occurs. A universal scaling law of the diffusivity applies for a chain length range of 25 ≤ N ≤ 1585, albeit with distinctly different scaling exponents. While opposing arguments are brought forward in recent literature concerning the pH‐dependence of short‐chain conformations, analysis supports the view that chain conformation is significantly affected by pH, even for short chains.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.