Abhijit S. Joshi

Effect of relative humidity on contact angle and particle deposition morphology of an evaporating colloidal drop

The deposition behavior of inkjet-printed aqueous colloidal drops on a glass substrate has been investigated by using fluorescence microscopy and a high resolution goniometer. Real-time side-view images of a pinned colloidal drop show that the contact angle during evaporation is a function of the relative humidity (RH). The RH also affects the extent to which the drop is able to spread after impacting a substrate, the evaporation rate at the drop surface, and the evaporatively driven flow inside the drop that drives the suspended particles toward the contact line. Results show that the particle deposition area and pattern change significantly with the RH.

Numerical Simulation of Colloidal Drop Deposition Dynamics on Patterned Substrates for Printable Electronics Fabrication

One of the major challenges in printable electronics fabrication is the print resolution and accuracy for high precision applications such as printable displays. In this paper, the lattice Boltzmann method (LBM) is used for the direct numerical simulation of an inkjet-printed colloidal drop wetting on a patterned substrate for confined deposition. The two-dimensional multiphase particle suspension LBM model previously developed by the authors is extended to three-dimensional with the addition of the particle rotational dynamics and an improved treatment of particle-particle forces. The model is used to study the contact angle hysteresis and the stick-slip behavior of the contact line motion as a liquid drop wetting and evaporating on a patterned substrate. Finally, the dynamics of a colloidal drop containing many suspended particles are examined with and without evaporation. Results show that colloidal jamming occurs at the liquid-vapor interface as the drop preferentially wets and evaporates on a patterned substrate. This model development is an important first step towards understanding the complex transport phenomena present in an inkjet-printed evaporating drop for printable electronics fabrication.

Lattice boltzmann simulation of colloidal drop dynamics on patterned substrates for printable electronics fabrication

In this paper, the lattice Boltzmann method (LBM) is used for the direct numerical simulation of an inkjet-printed colloidal drop wetting on a patterned substrate. The single component multiphase (SCMP) model of Shan and Chen is used for the liquid-vapor multiphase flow and the particle suspension model is modified to incorporate adhesive forces between the suspended particle and the surrounding fluid phases. Several validation problems are presented to test the separate sub-models and the combined model. The combined multiphase particle suspension model is then used to study the contact angle hysteresis and the stick-slip behavior of the contact line motion as a liquid drop wetting and evaporating on a patterned substrate. Finally, the dynamics of a colloidal drop containing many suspended particles are examined with and without evaporation. Results show that colloidal jamming occurs at the liquid-vapor interface as the drop preferentially wets and evaporates on a patterned substrate. This model development is an important first step towards understanding the complex transport phenomena present in an inkjet-printed evaporating drop for printable electronics fabrication.