Laboratoire Matière et Systèmes Complexes

Spreading and Arrest of Molten Liquid on a Cold Solid Substrate

Pirouz Kavehpour Department of Mechanical & Aerospace Engineering University of California, Los Angeles

ATTENTION LIEU EXCEPTIONNEL/UNUSUAL LOCATION salle 646A

The physics of non-isothermal liquid spreading followed by phase change, unlike universal equations established for isothermal spreading, is still a mystery. The motivation for the study stems from industrial applications such as thermal spray coating, rapid prototyping, 3D printing, plastic electronics and solder jetting in microelectronics. This presentation will focus on the dynamic and thermal characteristics of liquid spreading and subsequent arrest on a cold solid substrate. Spreading of liquid was recorded and the evolution of liquid spread diameter and liquid-solid contact angle were measured from the recordings of a high-speed digital camera. After solidification initiation at the basal plane, a liquid drop is pinned to a solid substrate showing fixed footprint (D*) and contact angle (θ*). For theorization of our data, we present a new hypothesis for spreading drop solidification. We assume that drop stops because a finite volume of ice (nuclei) forms at the contact point vicinity. Stable nuclei forms when enough energy from thermal activation is provided. This region emerges under an arbitrary isotherm adjacent to solid-liquid-gas contact point. A physical theory using scaling law analysis was provided to explain the relationship between arrested base diameter and Stefan number. Our proposed hypothesis was further corroborated by free fall impact and inclined wedge experiments.