(398c) The Determination of the Critical Concentrations of Aqueous Polymeric Solutions Using the Fingerprint of Impacting Drops

Drop impact and the subsequent capillary wave propagation at lower Weber numbers allows for the top surface of the drop to invert due to peripheral waves meeting at the apex. The degree of deformation depends on the aqueous polymer concentration and type, where the nano-microscale deformations are measured during the initial impact stages utilizing a high-speed total internal reflection and interference microscopy technique. The initial impact stages involves the formation of a dimple and an interstitial air layer, which strongly decelerates the drop impact over a thin viscous oil film. The changes in this deformation at a fixed Weber number for various polymers including polyethylene oxide, xanthan gum and a Boger fluid are demonstrated and the rheometer-predicted critical overlap, semidilute and entangled concentrations are compared with the drop impact-derived setup with good agreement between the two. We suggest that this method may be used to inexpensively characterize aqueous polymeric solutions for various commercial applications.