| From integrated circuits to DNA hybridization micro arrays, many areas of research require flexible and reliable, high resolution surface patterning tools. A new surface patterning technique, electrohydrodynamic printing (EHDP) [1] provides high resolution and speed at the same time, which was not attainable with the existing direct surface patterning techniques. Stability of electrohydrodynamic (EHD) jets determines the accuracy of deployment in EHD printing [1-3]; therefore, understanding non-axisymmetric instability of the jet, which is caused by the surface charges, is crucial to successful operation.; In this thesis, fast imaging and image analysis techniques are used to determine non-axisymmetric disturbance growth rates experimentally. Comparison of experimental instability growth rates with the theoretical estimations based on total current reveals a big discrepancy. It is also found that instability growth rates decrease and stability of EHD filaments is enhanced either by decreasing the electrode separation or by changing the surrounding gas. After considering all possible mechanisms, it is concluded that the main reason for stabilization is the increased ionization of the surrounding gas. Gas ionization results in partial neutralization of surface charges on the filament by the oppositely charged ions in the gas phase and stabilizes the jet. A new current balance including the charge transfer through the gas is developed to estimate the charge density left on the filament. Experimental and theoretical instability growth rates agree much better when the estimated charge density is used for the instability growth rate calculations.; The second part of the thesis focuses on pattern formation on the surfaces. The final pattern produced with a colloidal suspension by EHDP depends on not only the stability of the jet but also the dynamics of the suspension and the stability of printed lines after the deployment. Rivulet instability, which causes deployed filament to break up into islands, depends on the contact angle of the deployed liquid on the substrate. Patterns produced on hydrophobic surfaces differ greatly compared to those on hydrophilic surfaces. Pre-patterning of the substrate with hydrophilic and hydrophobic regions prior to deployment of the liquid generates new types of patterns such as rectangular arrays. EHD Printing of colloidal suspensions on hydrophobic substrates followed by self-assembly of particles produces unique three dimensional clusters. Finally, it is shown that rod-like particles are aligned along printed patterns during EHDP process but unless prevented, rotational Brownian motion of the particles disturbs the alignment after deployment.; 1 Poon, H.F., "Electrohydrodynamic Printing", PhD Thesis, Princeton University, 2002. 2 Kameoka, J., Orth, R., Yang, Y., Czaplewski, D., Mathers, R., Coates, G.W., Craighead, H.G., Nanotech . 14, 1124 (2003). 3 Sun, D., Chang, C., Li, S., Lin, L., Nanolett. 6 (4), 839 (2006). |
