Non-Contact Rolling Bond Stiffness Characterization of Polyvinylpyrrolidone (PVP) Particles

Abstract

Two techniques, based on a contact lateral pushing and a noncontact base excitation, were utilized to characterize the adhesion behavior of polyvinylpyrrolidone (PVP) particles. The micro-spherical PVP particles deposited on silicon substrates were excited by an ultrasonic transducer and the transient particle response was acquired by an interferometer. The natural frequencies of the particle rocking motion were extracted by comparing the vibrational spectra of the particles to those of the substrate. The obtained frequencies were then used to determine the work of adhesion of the contact. Rolling resistance moment-based lateral pushing experiments were also conducted on similar PVP particles. The resulting slopes of force–displacement curves were utilized to obtain the work of adhesion. The work of adhesion results determined from the noncontact measurements and lateral pushing measurements were in good agreement. In order to characterize the particle/substrate adhesion bond, different contact modes (i.e., rigid contact, neck-shaped contact, and an equivalent torsional spring) in the contact area were considered. For each case, the expected natural frequencies of the rocking motion were extracted from the slopes of force–displacement curves obtained in the contact lateral pushing experiments. The existence of all possible modes of the particle/substrate bond was verified because all expected natural frequencies were observed in the noncontact acoustic measurements.