@article{kleinert_srinivasan_rival_delattre_velev_pamula_2015, title={The dynamics and stability of lubricating oil films during droplet transport by electrowetting in microfluidic devices}, volume={9}, ISSN={["1932-1058"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84930221924&partnerID=MN8TOARS}, DOI={10.1063/1.4921489}, abstractNote={The operation of digital microfluidic devices with water droplets manipulated by electrowetting is critically dependent on the static and dynamic stability and lubrication properties of the oil films that separate the droplets from the solid surfaces. The factors determining the stability of the films and preventing surface fouling in such systems are not yet thoroughly understood and were experimentally investigated in this study. The experiments were performed using a standard digital microfluidic cartridge in which water droplets enclosed in a thin, oil-filled gap were transported over an array of electrodes. Stable, continuous oil films separated the droplets from the surfaces when the droplets were stationary. During droplet transport, capillary waves formed in the films on the electrode surfaces as the oil menisci receded. The waves evolved into dome-shaped oil lenses. Droplet deformation and oil displacement caused the films at the surface opposite the electrode array to transform into dimples of oil trapped over the centers of the droplets. Lower actuation voltages were associated with slower film thinning and formation of fewer, but larger, oil lenses. Lower ac frequencies induced oscillations in the droplets that caused the films to rupture. Films were also destabilized by addition of surfactants to the oil or droplet phases. Such a comprehensive understanding of the oil film behavior will enable more robust electrowetting-actuated lab-on-a-chip devices through prevention of loss of species from droplets and contamination of surfaces at points where films may break.}, number={3}, journal={BIOMICROFLUIDICS}, author={Kleinert, Jairus and Srinivasan, Vijay and Rival, Arnaud and Delattre, Cyril and Velev, Orlin D. and Pamula, Vamsee K.}, year={2015}, month={May} }
 @article{kleinert_kim_velev_2012, title={Electric-Field-Controlled Flow in Nanoscale-Thin Wetting Films}, volume={28}, ISSN={["0743-7463"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84863050366&partnerID=MN8TOARS}, DOI={10.1021/la204774s}, abstractNote={A novel nanofluidic system based on electroosmotic flow in nanoscale-thin aqueous wetting films is reported. The water films formed spontaneously on mica substrates in a saturation humidity environment. The film thickness was determined to be a few tens of nanometers by optical interference and fluorescence intensity measurements and was consistent with a theoretical evaluation of the thickness of a film based on the competing forces of electrostatic repulsion and capillary pressure. Lateral flow was induced by applying a dc electric field tangential to the film and characterized by tracking the position of a fluorescent probe. The mobilities of the thin fluid layer and the flow marker were lower than the predictions of the electrokinetic theory, which may be a result of adsorption of the fluorescent molecules to the mica. Confinement of the film to two-dimensional "channels" was achieved by microcontact printing of patterned hydrophobic monolayers onto the substrate. This system has the advantage of simple and inexpensive fabrication in comparison to nanofluidic devices made by traditional lithography techniques.}, number={5}, journal={LANGMUIR}, author={Kleinert, Jairus and Kim, Sejong and Velev, Orlin D.}, year={2012}, month={Feb}, pages={3037–3044} }
 @article{kleinert_kim_velev_2010, title={Electric-Field-Assisted Convective Assembly of Colloidal Crystal Coatings}, volume={26}, ISSN={["0743-7463"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78649279091&partnerID=MN8TOARS}, DOI={10.1021/la100119m}, abstractNote={A new technique that combines evaporative convective deposition of colloidal crystal coatings with an electric field to achieve more rapid assembly and reduce the defects in the crystal structure is reported. When an ac voltage is applied across the particle suspension and the substrate in the convective assembly process, a longer film spreads from the meniscus by the electrowetting-on-dielectric (EWOD) effect. The data suggest that the EWOD-increased liquid surface area results in increased evaporation-driven particle flux and crystal assembly that is up to five times more rapid. The extended drying film also provides more time for particle rearrangement before the structure becomes fixed, resulting in formation of crystal domains an order of magnitude larger than those deposited by convective assembly alone. The results demonstrate that EWOD is a facile tool for controlling particle assembly processes in wetting films. The technique could be used in improved large-scale colloidal crystal coating processes.}, number={12}, journal={LANGMUIR}, author={Kleinert, Jairus and Kim, Sejong and Velev, Orlin D.}, year={2010}, month={Jun}, pages={10380–10385} }