Critical Impact of Solvent Evaporation on the Resolution of Inkjet

Jun 25, 2018 - To confirm our hypothesis, we adjusted the evaporation rate gradient along ... This work brings us a step closer to resolving one of th...
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Letter Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Critical Impact of Solvent Evaporation on the Resolution of Inkjet Printed Nanoparticles Film Ruiqiang Tao,† Zhiqiang Fang,‡ Jianhua Zhang,§ Honglong Ning,*,† Jianqiu Chen,† Caigui Yang,† Yicong Zhou,† Rihui Yao,*,† Weixi Lin,† and Junbiao Peng*,† State Key Laboratory of Luminescent Materials and Devices and ‡State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou 510640, China § Key Laboratory of Advanced Display and System Applications of Ministry of Education, Shanghai University, Shanghai 200072, China Downloaded via UNIV OF SUSSEX on June 27, 2018 at 02:58:22 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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S Supporting Information *

ABSTRACT: We first verify the critical role of solvent evaporation on the resolution of inkjet printing. To confirm our hypothesis, we adjusted the evaporation rate gradient along the surface of adjacent droplets by controlling the drying microenvironment. Uneven solvent evaporation flux caused thermocapillary surface flow inward the space of micrometer-sized droplets and increase the air pressure, which prevented the neighboring droplets from coalescence. When reducing the droplet distance by the solvent evaporation-based method, a uniform profile could be obtained at the same time. This work brings us a step closer to resolving one of the critical bottlenecks to commercializing printed electronic goods.

KEYWORDS: inkjet printing, high resolution, evaporation, air pressure, uniform profile

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noticed the significant effect of the unavoidable evaporation on the resolution of inkjet printing. Existing studies on evaporation are mainly only focused on the morphology of the final deposits,10,11 and research on its effect on the resolution is unavailable. The study of droplet coalescence kinetics seems to bring insights to improve the resolution of inkjet printing,12−14 but very limited work has been focused on microscale droplets as its unattainable demands for measurement.15−17 Accordingly, the major influence of droplets evaporation on the resolution of inkjet printing has long time been ignored. Figure 1a presents the coalescence of inkjet printed droplets (diameter ∼50 μm) on unmodified glass substrate after solidification with continuously increased drop space. For such tiny droplets, the distance increased from coalescence to noncoalescence is intermittent. The drop space of the minimum distance ( p2), thus the periphery surface of droplets descends and retracts quickly with a smaller dynamic contact angle (θ1 < θ2), leaving the fixed nanoparticles more scattered. The schematic is presented in Figure 3d. The reverse motion of nanoparticles is induced by the capillary force of the retracting droplet surface, and will increase the distance of periphery nanoparticles (L1 > L2) when the contact angle is smaller. Further demonstration of the existence of the air film between droplets deposited on the same substrate is shown in Figure S4, in which a developed silver precursor ink is used to strengthen the air flow, and larger size droplets (d ≈ 5 mm) are released by a syringe for the observing of distinct self-aligned phenomenon. Besides the air film, the wetting is another important factor attributing to the self-aligned droplets coalescence. The wetting region (residual area) of the former released droplet, which is generated during droplet impinging process, will draw the later released droplet closer,28 as the overlapping of their maximum spreading states.29 This effect reduces the force and

Figure 2. Air film prevents the coalescence of two neighboring droplets. B

DOI: 10.1021/acsami.8b06519 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Letter

ACS Applied Materials & Interfaces

Figure 3. Scattered periphery nanoparticles induced by the air film. The surface profiles of (a) a single dot and (b) two neighboring dots indicate the outward increased evaporation flux of the printed droplets during drying process. (c) Closer droplets have more scattered nanoparticles at the periphery region. (d) Schematic of the periphery nanoparticles varies with the air pressure.

Figure 4. Droplets evaporation influenced by the drying microenvironment. (a) Location based droplets evaporation in an isometric array. (b) Simplified vapor diffusion model of a single droplet and uneven solvent vapor distribution induced between two droplets, i.e. the drying microenvironment, which will suppress the evaporation of droplets placed in it. (c) Surface profiles of single dots regulated by the drying microenvironment.

environment and the solvent vapor evaporation of another adjacent droplet (as the source of vapor distribution). Thus, it can be reasonably deduced that the drying process of a droplet varies with its location in an isometric droplets array deposited by inkjet printing all at once. Figure 4a shows the optical photo of an intermediate drying state of such droplets array, in which the droplets evaporate much slower and more symmetric near the center area. The drying microenvironment regulation method is powerful as large drop space (∼200 μm) and small droplet size (r0 ≈ 25 μm) was adopted in the experiment. The drying microenvironment has it is affected area, as the vapor concentration difference decreases with the increasing of droplets distance (Figure S5). The evaporation rate is determined by the surrounding vapor concentration distribution. Compared to the edge droplets, the droplets in the center area are surrounded by more droplets, thus the vapor concentration near the surface is higher, and the droplet

increases the drop space for droplets coalescence, thus making the induced air pressure enough to prevent the contacting of micrometer-sized droplets. Accordingly, the minimum distance of two droplets can be achieved with an extensive range of drop space, which means that the resolution of directly printed patterns with high precision cannot be further regulated by its drop space. Evaporation control is an effective way to regulate the strength of the induced air film between droplets, thus varying droplets distance after self-aligning can be obtained. Our previous report has demonstrated that the evaporation process of printed patterns can be continuously regulated by the drying microenvironment, which is the vapor distribution induced by the solvent evaporation of simultaneously deposited adjacent patterns.30 Up to this work only asymmetrical deposition patterns of two neighboring droplets was explored. This is a special case that the drying microenvironment of one droplet is influenced merely by atmospheric C

DOI: 10.1021/acsami.8b06519 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Letter

ACS Applied Materials & Interfaces

Figure 5. Resolution of inkjet printing regulated by the drying microenvironment. (a) Solvent vapor distribution along the surface of two neighboring droplets with the decreased S and the increased r of the frame patterns. (b) Surface profiles and resolution of two neighboring droplets varies with the drying microenvironment. (c) Distance of the droplets regulated by the drop space and the drying microenvironment.

evaporation is slower. When the drop space of droplets at the array periphery area is sufficiently decreased to form wet film, the effect of the induced drying microenvironment can be strengthened on the evaporation process of the center droplets, which can be indicated by the suppressed coffee-ring profiles of the solidified droplets. The schematic of the drying microenvironment and its impact on suppressing the coffee-ring effect is shown in Figure 4b. The two-dimensional model is proposed based on the simplified vapor distribution model, in which hemispherical cap of droplets deposited on glass substrate is assumed due to its small capillary length (2r0
0, the coffee-ring effect is inhibited or figured out by the decreasing of d as well as the increasing of r. Figure 4c presents the evolution process of the surface profiles of a single droplet with various drying microenvironment (different d). The designed pattern for the regulation of the drying microenvironment of a single droplet is shown in Figure S6. The experimental result is consistent with the theory proposed above. This research issue reveals the significance of pattern design in controlling the evaporation process of wet film and its surface profile after solidification. On the basis of the drying microenvironment regulation model, the resolution of inkjet printing is not only dominated by the evaporation of droplets themselves, but also influenced by the solvent vapor diffusion during the drying process of adjacent printed patterns, which is designed here as a frame pattern with inner circled area of S (S = (d − 2r)2) and line width of r (Figure S7). As the decreasing of S and the increasing of r, the vapor concentration gradient (∇c) is increased from situations A to D, which is schematically shown in Figure 5a. The circled droplets in all situations are printed with the same drop space (58 μm), however, the distance of them varies regularly from A to D. The higher ∇c, the smaller D

DOI: 10.1021/acsami.8b06519 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Letter

ACS Applied Materials & Interfaces

(3) Ko, S. H., Chung, J., Choi, Y. H., Grigoropoulos, C. P., Bieri, N. R., Choi, T. Y., Dockendorf, C., Poulikakos, D. Laser Based Hybrid Inkjet Printing of Nanoink for Flexible Electronics. In Proceedings of SPIE: Photon Processing in Microelectronics and Photonics IV; Fieret, J., Herman, P. R., Okada, T., Arnold, C. B., Bachmann, F. G., Hoving, W., Washio, K., Lu, Y. F., Geohegan, D. B., Trager, F., Dubowski, J. J., Eds.; SPIE: Bellingham, WA, 2005; Vol. 5713, pp 97−104. (4) Mahajan, A.; Hyun, W. J.; Walker, S. B.; Lewis, J. A.; Francis, L. F.; Frisbie, C. D. High-Resolution, High-Aspect Ratio Conductive Wires Embedded in Plastic Substrates. ACS Appl. Mater. Interfaces 2015, 7 (3), 1841−1847. (5) Ning, H.; Zhou, Y.; Fang, Z.; Yao, R.; Tao, R.; Chen, J.; Cai, W.; Zhu, Z.; Yang, C.; Wei, J.; Wang, L.; Peng, J. UV-Cured Inkjet-Printed Silver Gate Electrode with Low Electrical Resistivity. Nanoscale Res. Lett. 2017, 12 (1), 546. (6) Sirringhaus, H.; Kawase, T.; Friend, R. H.; Shimoda, T.; Inbasekaran, M.; Wu, W.; Woo, E. P. High-Resolution Inkjet Printing of All-Polymer Transistor Circuits. Science 2000, 290, 2123−2126. (7) Bromberg, V.; Ma, S.; Singler, T. J. High-Resolution Inkjet Printing of Electrically Conducting Lines of Silver Nanoparticles by Edge-Enhanced Twin-Line Deposition. Appl. Phys. Lett. 2013, 102 (21), 214101. (8) Noh, Y. Y.; Zhao, N.; Caironi, M.; Sirringhaus, H. Downscaling of Self-Aligned, All-Printed Polymer Thin-Film Transistors. Nat. Nanotechnol. 2007, 2 (12), 784−789. (9) Doggart, J.; Wu, Y.; Liu, P.; Zhu, S. Facile Inkjet-Printing SelfAligned Electrodes for Organic Thin-Film Transistor Arrays with Small and Uniform Channel Length. ACS Appl. Mater. Interfaces 2010, 2 (8), 2189−2192. (10) Harris, D. J.; Hu, H.; Conrad, J. C.; Lewis, J. A. Patterning Colloidal Films Via Evaporative Lithography. Phys. Rev. Lett. 2007, 98 (14), 148301. (11) Deegan, R. D.; Bakajin, O.; Dupont, T. F.; Huber, G.; Nagel, S. R.; Witten, T. A. Capillary Flow as the Cause of Ring Stains From Dried Liquid Drops. Nature 1997, 389 (6653), 827−829. (12) Sarojini KG, K.; Dhar, P.; Varughese, S.; Das, S. K., Coalescence Dynamics of PEDOT: PSS Droplets Impacting at Offset on Substrates for Inkjet Printing. Langmuir 2016, 32 (23), 5838− 5851. (13) Castrejón-Pita, J. R.; Betton, E. S.; Kubiak, K. J.; Wilson, M. C. T.; Hutchings, I. M. The Dynamics of the Impact and Coalescence of Droplets On a Solid Surface. Biomicrofluidics 2011, 5 (1), 014112. (14) Ristenpart, W. D.; McCalla, P. M.; Roy, R. V.; Stone, H. A. Coalescence of Spreading Droplets On a Wettable Substrate. Phys. Rev. Lett. 2006, 97 (6), 064501. (15) Loudet, J. C.; Yodh, A. G.; Pouligny, B. Wetting and Contact Lines of Micrometer-Sized Ellipsoids. Phys. Rev. Lett. 2006, 97 (1), 018304. (16) Liu, M.; Wang, J.; He, M.; Wang, L.; Li, F.; Jiang, L.; Song, Y. Inkjet Printing Controllable Footprint Lines by Regulating the Dynamic Wettability of Coalescing Ink Droplets. ACS Appl. Mater. Interfaces 2014, 6 (16), 13344−13348. (17) Zhou, W.; Loney, D.; Fedorov, A. G.; Degertekin, F. L.; Rosen, D. W. Shape Evolution of Multiple Interacting Droplets in Inkjet Deposition. RAPID PROTOTYPING J. 2015, 21 (4), 373−385. (18) Ning, H.; Tao, R.; Fang, Z.; Cai, W.; Chen, J.; Zhou, Y.; Zhu, Z.; Zheng, Z.; Yao, R.; Xu, M.; Wang, L.; Lan, L.; Peng, J. Direct Patterning of Silver Electrodes with 2.4 Μm Channel Length by Piezoelectric Inkjet Printing. J. Colloid Interface Sci. 2017, 487, 68−72. (19) Monti, R.; Savino, R.; Lappa, M.; Tempesta, S. Behavior of Drops in Contact with Pool Surfaces of Different Liquids. Phys. Fluids 1998, 10 (11), 2786−2796. (20) Dell Aversana, P.; Banavar, J. R.; Koplik, J. Suppression of Coalescence by Shear and Temperature Gradients. Phys. Fluids 1996, 8 (1), 15−28. (21) Hu, S.; Wang, Y.; Man, X.; Doi, M. Deposition Patterns of Two Neighboring Droplets: Onsager Variational Principle Studies. Langmuir 2017, 33 (23), 5965−5972.

droplets surface, can be suppressed by the drying microenvironment through pattern design. The surface tension gradient will cause thermocapillary surface flow inward the space of droplets and increase the air pressure. That is, the air pressure can be adjusted by the drying microenvironment, then reduces the droplets distance, and a uniform profile could be obtained at the same time. Although the miniaturization of electronics is demanded in high-end applications, the channel length of directly printed electrodes will be shorter when they are constructed by more droplets, due to the increased vapor concentration near the channels. An effective way to resolve this contradiction may be fabricating devices with higher integration. This work brings referential significance for highresolution films directly patterned by inkjet printing.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b06519. Materials and methods, rheological behavior of the ink change during and after the printing process, direct patterning of short channel electrodes, coalescence of multidroplets, materials preparing and characterization of distinct self-aligned phenomenon, designed pattern for the drying microenvironment, profiles of two neighboring droplets, resolution of inkjet printing affect by ink concentration, nanoparticles size, solvent types, substrates, and temperature (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. ORCID

Ruiqiang Tao: 0000-0002-4096-3966 Honglong Ning: 0000-0001-9518-5738 Junbiao Peng: 0000-0003-1671-2750 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by National Key R&D Program of China (2016YFB0401504), National Natural Science Foundation of China (Grant 51771074, 51521002, and U1601651), National Key Basic Research and Development Program of China (973 program, Grant 2015CB655004) Founded by MOST, National Science Foundation for Distinguished Young Scholars of China (Grant 51725505), Guangdong Natural Science Foundation (2016A030313459 and 2017A030310028), Guangdong Science and Technology Project (2016B090907001, 2016A040403037, 2016B090906002, 2017B090907016, and 2017A050503002), Guangzhou Science and Technology Project (201804020033).

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REFERENCES

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DOI: 10.1021/acsami.8b06519 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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DOI: 10.1021/acsami.8b06519 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX