Solidification Properties of Certain Waxes

Gao and Sonin (1994) have proposed a method for rapid prototyping and microfabrication by precise deposition and solidification of molten microdrops. Objects can be fabricated by a drop-on-demand, computer-controlled droplet generator. To understand the fundamentals of droplet deposition and solidification, experiments have been conducted using microcrystalline wax droplets (Schiaffino and Sonin, 1997a-d). One of the objectives of this thesis is to determine the solidification properties of the microcrystalline wax and to characterize its solidification. First, we determined the enthalpy and specific heat of the wax as a function of temperature and found that the wax releases latent heat over an extended temperature range, 30-90 'C. Next, we obtained a value for the thermal conductivity of the wax, 0.073 W/m K, by performing a transient solidification experiment and matching the data with the results of a numerical model. These measurements allowed us to formulate a model for characterizing the wax's solidification. In addition, we carried out a general theoretical investigation of solidification of materials that, like wax, release latent heat over a temperature range. Finally, we performed molten droplet deposition experiments with octacosane, a paraffin with properties similar to those of wax except for its distinct melting point. We were particularly concerned with the contact angles after solidification, which were mostly larger than 900 even at target temperatures close to the melting point. The solidification angle data were compared to those of previous investigators who used waxes in their experiments. Thesis Supervisor: Dr. Ain A. Sonin Title: Professor of Mechanical Engineering