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建立了直流电场作用下协流式微流控装置中单乳液液滴乳化生成过程的非稳态理论模型，并开展了数值模拟研究，揭示了电场对液滴乳化生成动力学行为的调控机理，阐明了流场/电场参数对液滴乳化生成特性的影响规律.研究结果表明：沿流体流动方向施加静电场可在电物性参数不同的两相流体界面法线方向上产生指向内相流体的电场力，进而强化了内相流体界面的颈缩和断裂，提升了液滴生成速率和形变程度，减小了液滴生成尺寸；在同一毛细数下，随着电毛细数的增大，乳液乳化流型由每周期仅有单一液滴生成的滴式流型转变为每周期有一个主液滴并伴随有卫星液滴生成的滴式流型；随着毛细数和电毛细数的增大，黏性拖曳力以及电场力作用增强，使内相流体颈缩过程后期更容易形成细长型液线，从而有助于诱发液线上产生Rayleigh-Plateau不稳定现象，继而促进卫星液滴的形成.Applying the active control of electric field to the preparation of micro-droplets via the traditional microfluidic technology has attracted great attention because it can effectively improve the controllability of the preparing process. Therefore, a full understanding of mechanism for the regulation and control of microdroplets's generation by the microfluidic technology and electric field will provide interesting possibilities for the active control of producing required microdroplets in the practical applications. A transient theoretical model is developed via the coupling of phase-field method and electrostatic model to numerically investigate the generation of the single-phase droplets in a co-flow microfluidic device under the control of a uniform direct-current electric field. Via the numerical simulations based on the transient model, the control mechanisms of the electric field on dynamic behaviors of the droplets generation are revealed, and the influences of flow and electric parameters on the droplets generation characteristics are elucidated. The results indicate that the electrostatic field is able to generate an electric field force toward the inner phase fluid in the normal direction of the interface between two-phase fluids with different electric parameters. The electric field force enhances the necking and breaking of the inner fluid interface, which accelerates the droplets' generation, increases droplet deformation degree, and reduces droplet size. As the electric capillary number increases under the same hydrodynamic capillary number, the droplet formation pattern is transformed from dripping regime with only a single droplet formed per cycle to another dripping regime with one main droplet formed together with the following satellite droplets per cycle. In addition, according to the numerical results in this work, we organize a regime diagram to quantitatively represent the respective regime of these two flow patterns as a function of hydrodynamic capillary number and electric capillary number. The regime diagram indicates that with the increase in hydrodynamic capillary number and electric capillary number, the viscous drag force and electric field force are strengthened, which induces the formation of a slender liquid thread of inner fluid at the later stage of the necking process. This contributes to triggering the Rayleigh-Plateau instability on the liquid thread of inner fluid, and thus facilitating the generation of satellite droplets via the breakup of the liquid thread.
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Keywords:
- microfluidics /
- droplets /
- emulsification and generation /
- electric control
[1] Mcclements D J, Li Y 2010 Adv. Colloid Interface Sci. 159 213
[2] Wan J 2012 Polymers 4 1084
[3] Sander J S, Erb R M, Denier C, Studart A R 2012 Adv. Mater. 24 2582
[4] Lee D, Weitz D A 2008 Adv. Mater. 20 3498
[5] Liang H, Chai Z H, Shi B C 2016 Acta Phys. Sin. 65 204701 (in Chinese)[梁宏, 柴振华, 施保昌 2016 65 204701]
[6] Chen Y P, Shen C Q, Peterson G P 2015 Ind. Eng. Chem. Res. 54 9257
[7] Chen Y P, Deng Z L 2017 J. Fluid Mech. 819 401
[8] Wu L Y, Liu X D, Zhao Y J, Chen Y P 2017 Chem. Eng. Sci. 163 56
[9] Liu X D, Wang C Y, Zhao Y J, Chen Y P 2018 Int. J. Heat Mass Transfer 121 377
[10] Liu X D, Chen Y P 2013 Appl. Therm. Eng. 58 585
[11] Utada A S, Fernandez-Nieves A, Stone H A, Weitz D A 2007 Phys. Rev. Lett. 99 094502
[12] Freiberg S, Zhu X X 2004 Int. J. Pharm. 282 1
[13] Baret J C, Miller O J, Taly V, Ryckelynck M, El-Harrak A, Frenz L, Rick C, Samuels M L, Hutchison J B, Agresti J J, Link D R, Weitz D A, Griffiths A D 2009 Lab on Chip 9 1850
[14] Chen Q, Qi X B, Chen S F, Liu M F, Pan D W, Li B, Zhang Z W 2017 Acta Phys. Sin. 66 046801 (in Chinese)[陈强, 漆小波, 陈素芬, 刘梅芳, 潘大伟, 李波, 张占文 2017 66 046801]
[15] Liu X, Chen Y, Shi M 2013 Int. J. Therm. Sci. 65 224
[16] Wu J, Shi M, Chen Y, Li X 2010 Int. J. Therm. Sci. 49 922
[17] Chen Y P, Liu X D, Shi M H 2013 Appl. Phys. Lett. 102 051609
[18] Chen Y P, Liu X D, Zhao Y J 2015 Appl. Phys. Lett. 106 141601
[19] Chen Y P, Wu L Y, Zhang L 2015 Int. J. Heat Mass Transfer 82 42
[20] Mohseni K, Dolatabadi A 2006 Ann. N. Y. Acad. Sci. 1077 415
[21] Zagnoni M, Cooper J M 2009 Lab on Chip 9 2652
[22] Hohman M M, Shin M, Rutledge G, Brenner M P 2001 Phys. Fluids 13 2201
[23] Hohman M M, Shin M, Rutledge G, Brenner M P 2001 Phys. Fluids 13 2221
[24] Zhai S L, Luo G S, Liu J G 2001 Chem. Eng. J. 83 55
[25] Luo G S, Jiang W B, Lu Y C, Zhu S L, Dai Y Y 1999 Chem. Eng. J. 73 137
[26] Zhang X, Basaran O A 1996 J. Fluid Mech. 326 239
[27] Kim H, Luo D, Link D, Weitz D A, Marquez M, Cheng Z 2007 Appl. Phys. Lett. 91 133106
[28] Tan S H, Semin B, Baret J C 2014 Lab on Chip 14 1099
[29] Wang X X, Ju X J, Sun S X, Xie R, Wang W, Liu Z, Chu L Y 2015 RSC Adv. 5 34243
[30] Ju X, Wang X, Liu Z, Xie R, Wang W, Chu L Y 2017 Particuology 30 151
[31] Notz P K, Basaran O A 1999 J. Colloid Interface Sci. 213 218
[32] Li Y, Jain M, Ma Y, Nandakumar K 2015 Soft Matter 11 3884
[33] Gong S, Cheng P, Quan X 2010 Int. J. Heat Mass Transfer 53 5863
[34] Wehking J D, Chew L, Kumar R 2013 Appl. Phys. Lett. 103 054101
[35] Liu X D, Wang C Y, Zhao Y J, Chen Y P 2018 Chem. Eng. Sci. 183 215
[36] Nie Z, Seo M S, Xu S, Lewis P C, Mok M, Kumacheva E, Whitesides G M, Garstecki P, Stone H A 2008 Microfluid. Nanofluid. 5 585
[37] O'Konski C T, Jr H C T 1953 J. Phys. Chem. 57 955
[38] Tomar G, Gerlach D, Biswas G, Alleborn N, Sharma A, Durst F, Welch S W J, Delgado A 2007 J. Comput. Phys. 227 1267
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[1] Mcclements D J, Li Y 2010 Adv. Colloid Interface Sci. 159 213
[2] Wan J 2012 Polymers 4 1084
[3] Sander J S, Erb R M, Denier C, Studart A R 2012 Adv. Mater. 24 2582
[4] Lee D, Weitz D A 2008 Adv. Mater. 20 3498
[5] Liang H, Chai Z H, Shi B C 2016 Acta Phys. Sin. 65 204701 (in Chinese)[梁宏, 柴振华, 施保昌 2016 65 204701]
[6] Chen Y P, Shen C Q, Peterson G P 2015 Ind. Eng. Chem. Res. 54 9257
[7] Chen Y P, Deng Z L 2017 J. Fluid Mech. 819 401
[8] Wu L Y, Liu X D, Zhao Y J, Chen Y P 2017 Chem. Eng. Sci. 163 56
[9] Liu X D, Wang C Y, Zhao Y J, Chen Y P 2018 Int. J. Heat Mass Transfer 121 377
[10] Liu X D, Chen Y P 2013 Appl. Therm. Eng. 58 585
[11] Utada A S, Fernandez-Nieves A, Stone H A, Weitz D A 2007 Phys. Rev. Lett. 99 094502
[12] Freiberg S, Zhu X X 2004 Int. J. Pharm. 282 1
[13] Baret J C, Miller O J, Taly V, Ryckelynck M, El-Harrak A, Frenz L, Rick C, Samuels M L, Hutchison J B, Agresti J J, Link D R, Weitz D A, Griffiths A D 2009 Lab on Chip 9 1850
[14] Chen Q, Qi X B, Chen S F, Liu M F, Pan D W, Li B, Zhang Z W 2017 Acta Phys. Sin. 66 046801 (in Chinese)[陈强, 漆小波, 陈素芬, 刘梅芳, 潘大伟, 李波, 张占文 2017 66 046801]
[15] Liu X, Chen Y, Shi M 2013 Int. J. Therm. Sci. 65 224
[16] Wu J, Shi M, Chen Y, Li X 2010 Int. J. Therm. Sci. 49 922
[17] Chen Y P, Liu X D, Shi M H 2013 Appl. Phys. Lett. 102 051609
[18] Chen Y P, Liu X D, Zhao Y J 2015 Appl. Phys. Lett. 106 141601
[19] Chen Y P, Wu L Y, Zhang L 2015 Int. J. Heat Mass Transfer 82 42
[20] Mohseni K, Dolatabadi A 2006 Ann. N. Y. Acad. Sci. 1077 415
[21] Zagnoni M, Cooper J M 2009 Lab on Chip 9 2652
[22] Hohman M M, Shin M, Rutledge G, Brenner M P 2001 Phys. Fluids 13 2201
[23] Hohman M M, Shin M, Rutledge G, Brenner M P 2001 Phys. Fluids 13 2221
[24] Zhai S L, Luo G S, Liu J G 2001 Chem. Eng. J. 83 55
[25] Luo G S, Jiang W B, Lu Y C, Zhu S L, Dai Y Y 1999 Chem. Eng. J. 73 137
[26] Zhang X, Basaran O A 1996 J. Fluid Mech. 326 239
[27] Kim H, Luo D, Link D, Weitz D A, Marquez M, Cheng Z 2007 Appl. Phys. Lett. 91 133106
[28] Tan S H, Semin B, Baret J C 2014 Lab on Chip 14 1099
[29] Wang X X, Ju X J, Sun S X, Xie R, Wang W, Liu Z, Chu L Y 2015 RSC Adv. 5 34243
[30] Ju X, Wang X, Liu Z, Xie R, Wang W, Chu L Y 2017 Particuology 30 151
[31] Notz P K, Basaran O A 1999 J. Colloid Interface Sci. 213 218
[32] Li Y, Jain M, Ma Y, Nandakumar K 2015 Soft Matter 11 3884
[33] Gong S, Cheng P, Quan X 2010 Int. J. Heat Mass Transfer 53 5863
[34] Wehking J D, Chew L, Kumar R 2013 Appl. Phys. Lett. 103 054101
[35] Liu X D, Wang C Y, Zhao Y J, Chen Y P 2018 Chem. Eng. Sci. 183 215
[36] Nie Z, Seo M S, Xu S, Lewis P C, Mok M, Kumacheva E, Whitesides G M, Garstecki P, Stone H A 2008 Microfluid. Nanofluid. 5 585
[37] O'Konski C T, Jr H C T 1953 J. Phys. Chem. 57 955
[38] Tomar G, Gerlach D, Biswas G, Alleborn N, Sharma A, Durst F, Welch S W J, Delgado A 2007 J. Comput. Phys. 227 1267
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