Subscriber access provided by YONSEI UNIV Article Influence of Fluid Physical Properties on Ink-Jet Printability Daehwan Jang, Dongjo Kim, and Jooho Moon Langmuir, 2009, 25 (5), 2629-2635• DOI: 10.1021/la900059m • Publication Date (Web): 05 February 2009 Downloaded from http://pubs.acs.org on February 25, 2009 More About This Article Additional resources and features associated with this article are available within the HTML version: • Supporting Information • Access to high resolution figures • Links to articles and content related to this article • Copyright permission to reproduce figures and/or text from this article Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Langmuir 2009, 25, 2629-2635 2629 Influence of Fluid Physical Properties on Ink-Jet Printability Daehwan Jang, Dongjo Kim, and Jooho Moon* Department of Materials Science and Engineering, Yonsei UniVersity 134 Shinchon-dong Seodaemun-gu, Seoul 120-749, Korea ReceiVed August 21, 2008 Ink-jet printing is a method for directly patterning and fabricating patterns without the need for masks. To achieve this, the fluids used as inks must have the capability of being stably and accurately printed by ink-jetting. We have investigated the inter-relationship between ink-jet printability and physical fluid properties by monitoring droplet formation dynamics. The printability of the fluids was determined using the inverse (Z) of the Ohnesorge number (Oh) which relates to the viscosity, surface tension, and density of the fluid. We have experimentally defined the printable range as 4 e Z e 14 by considering characteristics such as single droplet formability, positional accuracy, and maximum allowable jetting frequency. Introduction of ink-jet dynamics is recently emerging.14,15 The important physical parameters of printing fluids are viscosity, density, and Ink-jet printing is an emerging technology with many surface tension. These fluid properties influence the drop applications being explored beyond its image transfer capability, 1-5 formation mechanism and subsequent drop size at a given voltage. including microdispensing and materials assembly. Recently Fromm obtained an approximate solution to the Navier-Stokes it has been used to fabricate polymeric electroluminescent devices, equations for the case of droplet ejection.16 He used characteristic controlled-release drug delivery devices, and refractive micro- dimensionless numbers representing fluid physical properties. lenses made of hybrid organic-inorganic materials.2,6,7 The drop- The Reynolds number (NRe) is the ratio of inertial to viscous on-demand (DOD) method is most commonly used for modern forces, and the Weber number (NWe) is a balance between inertial industrial applications. It deposits precise quantities of functional and capillary forces:17 inks in the form of droplets on an arbitrary surface by applying - a short pressure pulse through a nozzle which is typically 20 50 VaF 8 N ) (1) µm diameter. The jetting operation mechanism involves the Re η generation of pressure waves in a fluid-filled pathway behind an orifice. At the end of the orifice, the fluid meniscus is maintained and by surface tension. A piezoelectrically induced pressure wave V2 F can propagate against the surface tension of the fluid, forming ) a NWe (2) a small droplet which is ejected from the nozzle. Under suitable γ electrical conditions, the ejected fluid develops into a single droplet where V, F, γ, and η are the average travel velocity, the density, for quality ink-jetting. surface tension, and viscosity of the fluid, and a is a characteristic However, appropriate functional ink materials are limited in dimension (the radius of the printing orifice). Another dimen- availability. Inappropriate ink will lead to unstable ink-jetting in sionless number is the inverse (Z) of the Ohnesorge number which long-lived filaments form, connecting the ejected droplet (Oh), which is defined as the ratio between the Reynolds number to the nozzle.9 The length and lifetime of the filament influence and a square root of the Weber number, and is independent of the positional accuracy and resolution of the printing as well as fluid velocity: the printability of the inks. Fluid dynamics involved in the ink- - jet printing have been studied10 13 and an atomistic understanding 1⁄2 (aFγ) NRe Z ) ) (3) η (N )1⁄2 * To whom correspondence should be addressed. E-mail: jmoon@ We yonsei.ac.kr. Tel.: +82-2-2123-2855. Fax: +82-2-365-5882. On the basis of a numerical analysis using complete incom- (1) Derby, B.; Reis, N. MRS Bull. 2003, 28, 815–18. (2) Gans, B.-J.; Duineveld, P. C.; Schubert, U. S. AdV. Mater. 2004, 16, 203– pressible flow equations, Fromm predicted that stable drop 16 13. formation in DOD systems is permitted only when Z > 2. (3) Jeong, S.; Woo, K.; Kim, D.; Lim, S.; Kim, J.; Shin, H.; Xia, Y.; Moon, Later Reis and Derby determined that a printable fluid should J. AdV. Funct. Mater. 2008, 18, 679–86. (4) Jeong, S.; Kim, D.; Moon, J. J. Phys. Chem. C 2008, 14, 5245–9. have a Z value between 1 and 10. They explored the influence (5) Kim, D.; Jeong, S.; Park, B.; Moon, J. Appl. Phys. Lett. 2006, 89, 264101 of fluid properties on ink-jet printing behavior using computational 1–3. fluid dynamics that modeled the free-surface flow characteristics (6) Xu, T.; Jin, J.; Gregory, C.; Hickman, J. J.; Boland, T. Biomaterials 2005, 26, 93–9. of drop formation in conjunction with a parallel experimental (7) Tekin, E.; Smith, P. J.; Hoeppener, S.; Berg, A. M. J.; Susha, A. S.; Rogach, study. They found that the lower limit of Z is governed by the A. L.; Feldmann, J.; Shubert, U. S. AdV. Funct. Mater. 2007, 17, 23–8. (8) Le, H. P. J. Imaging Sci. Technol. 1998, 42, 49–62. dissipation of the pressure pulse by fluid viscosity, and that the (9) Gans, B.-J.; Kazancioglu, E.; Meyer, W.; Schubert, U. S. Macromol. Rapid Commun. 2004, 25, 292–6. (14) Li, F. I.; Leo, P. H.; Barnard, J. A. J. Phys. Chem. C 2008, 112, 14266–73. (10) Dong, H.; Carr, W. W.; Morris, J. F. Phys. Fluids 2006, 18, 072102–16. (15) Lugli, F.; Zerbetto, F. J. Phys. Chem. C 2008, 112, 10616–10621. (11) Xu, Q.; Basaran, O. A. Phys. Fluids 2007, 19, 102111–12. (16) Fromm, J. E. IBM J. Res. DeV. 1984, 28, 322–33. (12) Zhang, X.; Basaran, O. A. Phys. Fluids 1995, 7, 1184–1203. (17) Bergeron, V.; Bonn, D.; Martin, J. Y.; Vovelle, L. Nature 2000, 405, (13) Notz, P. K.; Chen, A. U.; Basaran, O. A. Phys. Fluids 2001, 13, 549–52. 772–5. 10.1021/la900059m CCC: $40.75 2009 American Chemical Society Published on Web 02/05/2009 2630 Langmuir, Vol. 25, No. 5, 2009 Jang et al. Table 1. Summary of Physical Properties and Dimensionless Numbers for Each Fluid a inverse (Z) density viscosity surface tension Reynolds number Weber number of Ohnesorge 3 solvent type (volume fraction) (Kg/m ) (mPa · s) (mN/m) (NRe) (NWe) number (Oh) ethylene glycol (0.15) + water (0.85) 1059 3.11 54.8 51.08 8.69 17.32 ethylene glycol (0.25) + ater (0.75) 1068 3.69 47.8 43.42 10.07 13.68 ethyl alcohol (0.75) + ethylene glycol (0.25) 866 4.83 28.9 26.89 13.47 7.32 ethylene glycol (0.5) + water (0.5) 1094 7.61 45.8 21.56 10.76 6.57 ethylene glycol (0.75) + water (0.25) 1106 12.3 45.6 13.49 10.91 4.08 glycerol (0.66) + Water (0.33) 1172 16.05 56.2 10.95 9.37 3.57 diethylene glycol (0.5) + water (0.5) 1111 22.0 41.4 7.58 12.08 2.17 diethylene glycol 1118 35.1 44.8 4.78 11.23 1.43 a Droplet diameter and its travel velocity are assumed to be 50 µm and 3 m/s, respectively. upper limit is determined by the point at which a satellite forms Results and Discussion instead of single droplet.18 Droplet formation behavior during piezoelectric DOD ink-jet In this study, we redefine the printable range of Z by in situ printing is influenced by the system’s response to an applied monitoring of droplet formation dynamics for various fluids pressure stimulus on the fluid.20,21 Drop ejection is the result of having different Z values. We can determine the printable range the superposition of consecutive acoustic waves that generate by considering characteristics of printability such as single droplet pressure pulses large enough to overcome viscous dissipation formability, the minimum stand-off distance (i.e., the distance and the energy associated with forming a new surface. Reis et from the nozzle tip to the substrate), positional accuracy, and al. found that drop velocity and volume exhibit a linear relation maximum allowable jetting frequency. These can be used to with driving voltage, but show a more complicated and periodic reduce the number of experiments needed to determine the optimal behavior with changing frequency and pulse width (i.e., dwell ink-jetting conditions for each fluid. time).16 This periodic dependence is determined by the acoustic properties of the fluid-filled chamber in the piezoelectric droplet Experimental Section generator, which is a function of the fluid properties, print head To investigate drop formation dynamics during ink-jet printing, design, and constituent materials. Hence, each individual fluid we set up an ink-jet printing system consisting of a nozzle, a jetting with different physical properties may have specific optimum driver (pressure pulse generating system), a charge-coupled-device printing conditions where the desired superposition of the acoustic (CCD) camera, and a system computer.