Axial Drop Mechanism Design For Carbopol Jet Dynamics Analysis

Abstract

A common phenomenon when dropping a container of water axially is the formation of a jet. This is due to the pressure of the impact travelling upwards and collapsing the curvature of the meniscus. The meniscus or cavity is created because the “outer layer” of water satisfies the wetting condition: the water is attracted to the test tube and the water molecules are attracted to each other. In Non-Newtonian, yield stress gels like Carbopol, however, this cavity can be artificially created. Carbopol has the ability to liquefy into a viscoelastic liquid due to high stress, allowing it to form a jet, but can also stay firm and hold its shape under low stress which allows the formation of a cavity. Similar to water, when this test tube of Carbopol is dropped, the cavity collapses on itself a creates a strong jet upwards. In this study, an axial drop mechanism is designed. Then, the rheometry of a specific formulation of Carbopol is explored. Aided by highspeed videography and image analysis, the jet phenomenon is then examined by investigating the effect of drop height and different cavity shapes and sizes on jet speed. An uncertainty analysis is done on the straightness of the dropping mechanism to assess the accuracy of results.