A review on emulsification via microfluidic processes

Abstract

Emulsion is a disperse system with two immiscible liquids, which demonstrates wide applications in diverse industries. Emulsification technology has advanced well with the development of microfluidic process. Compared to conventional methods, the microfluidics-based process can produce controllable droplet size and distribution. The droplet formation or breakup is the result of combined effects resulting from interfacial tension, viscous, and inertial forces as well as the forces generated due to hydrodynamic pressure and external stimuli. In the current study, typical microfluidic systems, including microchannel array, T-shape, flow-focusing, co-flowing, and membrane systems, are reviewed and the corresponding mechanisms, flow regimes, and main parameters are compared and summarized.

Key words： microfluidics; emulsification; capillary number; droplet breakup

Acknowledgements

This work was supported by the National Key Research and Development Program of China (Grant Nos. 2017YFB1103002 and 2018YFB0604304), Federal Ministry for Economic Affairs and Energy, Germany (No. 03ET1093C), Fundamental Research Funds for the Central Universities, China (No. 2017MS011), and the National Natural Science Foundation of China (Grant No. 51821004).

References

1 Zhao C X. Multiphase flow microfluidics for the production of single or multiple emulsions for drug delivery. Advanced Drug Delivery Reviews, 2013, 65(11-12): 1420–1446

2 Ran R, Sun Q, Baby T, Wibowo D, Middelberg A P, Zhao C X. Multiphase microfluidic synthesis of micro-and nanostructures for pharmaceutical applications. Chemical Engineering Science, 2017, 169: 78–96

3 Maeki M. Microfluidics for pharmaceutical applications. Microfluidics for Pharmaceutical Applications. Amsterdam: Elsevier, 2019, 101–119

4 Muijlwijk K, Berton-Carabin C, Schroën K. Cross-flow microfluidic emulsification from a food perspective. Trends in Food Science & Technology, 2016, 49: 51–63

5 Gunes D Z. Microfluidics for food science and engineering. Current Opinion in Food Science, 2018, 21: 57–65

6 Gilbert L, Picard C, Savary G, Grisel M. Rheological and textural characterization of cosmetic emulsions containing natural and synthetic polymers: Relationships between both data. Colloids and Surfaces. A, Physicochemical and Engineering Aspects, 2013, 421: 150–163

7 Ferreira A, Vecino X, Ferreira D, Cruz J, Moldes A, Rodrigues L. Novel cosmetic formulations containing a biosurfactant from Lactobacillus paracasei. Colloids and Surfaces. B, Biointerfaces, 2017, 155: 522–529

8 Preetika R, Mehta P S, Kaisare N S, Basavaraj M G. Kinetic stability of surfactant stabilized water-in-diesel emulsion fuels. Fuel, 2019, 236: 1415–1422

9 Sun G, Zhang J, Ma C, Wang X. Start-up flow behavior of pipelines transporting waxy crude oil emulsion. Journal of Petroleum Science Engineering, 2016, 147: 746–755

10 Zhang M, Wang W, Xie R, Ju X, Liu Z, Jiang L, Chen Q, Chu L. Controllable microfluidic strategies for fabricating microparticles using emulsions as templates. Particuology, 2016, 24: 18–31

11 Parker A P, Reynolds P A, Lewis A L, Hughes L. Semi-continuous emulsion co-polymerisation of methylmethacrylate and butylacrylate using zwitterionic surfactants as emulsifiers: Evidence of coagulative nucleation above the critical micelle concentration. Colloids and Surfaces. A, Physicochemical and Engineering Aspects, 2005, 268(1): 162–174

12 Wang L Y, Ma G H, Su Z G. Preparation of uniform sized chitosan microspheres by membrane emulsification technique and application as a carrier of protein drug. Journal of Controlled Release, 2005, 106(1-2): 62–75

13 Choi C H, Jung J H, Kim D W, Chung Y M, Lee C S. Novel one-pot route to monodisperse thermosensitive hollow microcapsules in a microfluidic system. Lab on a Chip, 2008, 8(9): 1544

14 Shah R K, Kim J W, Agresti J J, Weitz D A, Chu L Y. Fabrication of monodisperse thermosensitive microgels and gel capsules in microfluidic devices. Soft Matter, 2008, 4(12): 2303

15 Singh D, Sharma R. Post harvest wax coating of kinnow fruits to retain quality during. Storage Agricultural Engineering Today, 2007, 31(2): 232–238

16 Cameron J C, Fischer C A, Lehman N C, Lindquist J S, Olson C E, Fox S A. Hot melt adhesive pellet comprising continuous coating of pelletizing aid. US Patent, 6120899, 2000-09-19

17 Kabal’Nov A S, Pertzov A V, Shchukin E D. Ostwald ripening in two-component disperse phase systems: Application to emulsion stability. Colloids and Surfaces, 1987, 24(1): 19–32

18 Bibette J, Mason T G, Gang H, Weitz D A, Poulin P. Structure of adhesive emulsions. Langmuir, 1993, 9(12): 3352–3356

19 Mason T G. New fundamental concepts in emulsion rheology. Current Opinion in Colloid & Interface Science, 1999, 4(3): 231–238

20 Tiwary C, Kishore S, Vasireddi R, Mahapatra D, Ajayan P, Chattopadhyay K. Electronic waste recycling via cryo-milling and nanoparticle beneficiation. Materials Today, 2017, 20(2): 67–73

21 Fernández-Ávila C, Escriu R, Trujillo A. Ultra-high pressure homogenization enhances physicochemical properties of soy protein isolate-stabilized emulsions. Food Research International, 2015, 75: 357–366

22 Trujillo-Cayado L A, Alfaro M C, García M, Muñoz J. Comparison of homogenization processes for the development of green O/W emulsions formulated with N, N-dimethyldecanamide. Journal of Industrial and Engineering Chemistry, 2017, 46: 54–61

23 McClements D J. Food Emulsions: Principles, Practices, and Techniques. 3rd ed. Florida: CRC Press, 2015, 245–288

24 Squires T M, Quake S R. Microfluidics: Fluid physics at the nanoliter scale. Reviews of Modern Physics, 2005, 77(3): 977–1026

25 Geczy R, Agnoletti M, Hansen M F, Kutter J P, Saatchi K, Häfeli U O. Microfluidic approaches for the production of monodisperse, superparamagnetic microspheres in the low micrometer size range. Journal of Magnetism and Magnetic Materials, 2019, 471: 286–293

26 Li Y, Wengerter M, Gerken I, Nieder H, Scholl S, Brandner J J. Development of an efficient emulsification process using miniaturized process engineering equipment. Chemical Engineering Research & Design, 2016, 108: 23–29

27 Li Y, Gerken I, Hensel A, Kraut M, Brandner J J. Development of a continuous emulsification process for a highly viscous dispersed phase using microstructured devices. Green Processing and Synthesis, 2013, 2(5): 499–507

28 Wennerstrom H, Balogh J, Olsson U. Interfacial tensions in microemulsions. Colloids and Surfaces A—Physicochemical and Engineering Aspects, 2006, 291(1-3): 69–77

29 Diez J, Gratton R, Thomas L, Marino B. Laplace pressure-driven drop spreading: Quasi-self-similar solution. Journal of Colloid and Interface Science, 1994, 168(1): 15–20

30 Lyklema J. Fundamentals of Interface and Colloid Science. 1st ed. Amsterdam: Elsevier, 2005, 1.1–1.1.6

31 Kenis P J A, Ismagilov R F, Whitesides G M. Microfabrication inside capillaries using multiphase laminar flow patterning. Science, 1999, 285(5424): 83–85

32 Stone H A. Dynamics of drop deformation and breakup in viscous fluids. Annual Review of Fluid Mechanics, 1994, 26(1): 65–102

33 Stewart W E Jr, Dona C L G. Low Rayleigh number flow in a heat generating porous media. International Communications in Heat and Mass Transfer, 1986, 13(3): 281–294

34 Tadros T, Izquierdo P, Esquena J, Solans C. Formation and stability of nano-emulsions. Advances in Colloid and Interface Science, 2004, 108-109: 303–318

35 Kawakatsu T, Kikuchi Y, Nakajima M. Regular-sized cell creation in microchannel emulsification by visual microprocessing method. Journal of the American Oil Chemists’ Society, 1997, 74(3): 317–321

36 Kawakatsu T, Komori H, Nakajima M, Kikuchi Y, Yonemoto T. Production of monodispersed oil-in-water emulsion using crossflow-type silicon microchannel plate. Journal of Chemical Engineering of Japan, 1999, 32(2): 241–244

37 Kobayashi I, Takano T, Maeda R, Wada Y, Uemura K, Nakajima M. Straight-through microchannel devices for generating monodisperse emulsion droplets several microns in size. Microfluidics and Nanofluidics, 2008, 4(3): 167–177

38 Kobayashi I, Uemura K, Nakajima M. CFD analysis of generation of soybean oil-in-water emulsion droplets using rectangular straight-through microchannels. Food Science and Technology Research, 2007, 13(3): 187–192

39 Kobayashi I, Mukataka S, Nakajima M. Effect of slot aspect ratio on droplet formation from silicon straight-through microchannels. Journal of Colloid and Interface Science, 2004, 279(1): 277–280

40 Kobayashi I, Nakajima M, Nabetani H, Kikuchi Y, Shohno A, Satoh K. Preparation of micron-scale monodisperse oil-in-water microspheres by microchannel emulsification. Journal of the American Oil Chemists’ Society, 2001, 78(8): 797–802

41 Kobayashi I, Nakajima M, Chun K, Kikuchi Y, Fukita H. Silicon array of elongated through-holes for monodisperse emulsion droplets. AIChE Journal. American Institute of Chemical Engineers, 2002, 48(8): 1639–1644

42 Sugiura S, Nakajima M, Tong J H, Nabetani H, Seki M. Preparation of monodispersed solid lipid microspheres using a microchannel emulsification technique. Journal of Colloid and Interface Science, 2000, 227(1): 95–103

43 Sugiura S, Nakajima M, Seki M. Effect of channel structure on microchannel emulsification. Langmuir, 2002, 18(15): 5708–5712

44 Sugiura S, Nakajima M, Iwamoto S, Seki M. Interfacial tension driven monodispersed droplet formation from microfabricated channel array. Langmuir, 2001, 17(18): 5562–5566

45 Sugiura S, Nakajima M, Kumazawa N, Iwamoto S, Seki M. Characterization of spontaneous transformation-based droplet formation during microchannel emulsification. Journal of Physical Chemistry B, 2002, 106(36): 9405–9409

46 Sugiura S, Nakajima M, Seki M. Preparation of monodispersed emulsion with large droplets using microchannel emulsification. Journal of the American Oil Chemists’ Society, 2002, 79(5): 515–519

47 Treesuwan W, Neves M A, Uemura K, Nakajima M, Kobayashi I. Preparation characteristics of monodisperse oil-in-water emulsions by microchannel emulsification using different essential oils. LWT, 2017, 84: 617–625

48 De Menech M, Garstecki P, Jousse F, Stone H A. Transition from squeezing to dripping in a microfluidic T-shaped junction. Journal of Fluid Mechanics, 2008, 595: 141–161

49 Okushima S, Nisisako T, Torii T, Higuchi T. Controlled production of monodisperse double emulsions by two-step droplet breakup in microfluidic devices. Langmuir, 2004, 20(23): 9905–9908

50 Xu Q Y, Nakajima M. The generation of highly monodisperse droplets through the breakup of hydrodynamically focused microthread in a microfluidic device. Applied Physics Letters, 2004, 85(17): 3726–3728

51 Xu J H, Li S W, Tan J, Wang Y J, Luo G S. Controllable preparation of monodisperse O/W and W/O emulsions in the same microfluidic device. Langmuir, 2006, 22(19): 7943–7946

52 Mora A E M, de Lima e Silva A L F, de Lima e Silva S M M. Numerical study of the dynamics of a droplet in a T-junction microchannel using OpenFOAM. Chemical Engineering Science, 2019, 196: 514–526

53 Thorsen T, Roberts R W, Arnold F H, Quake S R. Dynamic pattern formation in a vesicle-generating microfluidic device. Physical Review Letters, 2001, 86(18): 4163–4166

54 Zheng B, Ismagilov R F. A microfluidic approach for screening submicroliter volumes against multiple reagents by using preformed arrays of nanoliter plugs in a three-phase liquid/liquid/gas flow. Angewandte Chemie International Edition, 2005, 44(17): 2520–2523

55 Günther A, Khan S A, Thalmann M, Trachsel F, Jensen K F. Transport and reaction in microscale segmented gas-liquid flow. Lab on a Chip, 2004, 4(4): 278–286

56 Sabri F, Lakis A A. Hydroelastic vibration of partially liquid-filled circular cylindrical shells under combined internal pressure and axial compression. Aerospace Science and Technology, 2011, 15(4): 237–248

57 Xu J H, Li S W, Tan J, Wang Y J, Luo G S. Preparation of highly monodisperse droplet in a T-junction microfluidic device. AIChE Journal. American Institute of Chemical Engineers, 2006, 52(9): 3005–3010

58 Garstecki P, Fuerstman M J, Stone H A, Whitesides G M. Formation of droplets and bubbles in a microfluidic T-junction—scaling and mechanism of break-up. Lab on a Chip, 2006, 6(3): 437–446

59 Zhao C X, Middelberg A P J. Two-phase microfluidic flows. Chemical Engineering Science, 2011, 66(7): 1394–1411

60 Stone H A, Stroock A D, Ajdari A. Engineering flows in small devices: Microfluidics toward a lab-on-a-chip. Annual Review of Fluid Mechanics, 2004, 36(1): 381–411

61 Oishi M, Kinoshita H, Fujii T, Oshima M. Confocal micro-PIV measurement of droplet formation in a T-shaped micro-junction. Journal of Physics: Conference Series, 2009, 147: 012061

62 De Menech M, Garstecki P, Jousse F, Stone H. Transition from squeezing to dripping in a microfluidic T-shaped junction. Journal of Fluid Mechanics, 2008, 595: 141–161

63 Van der Graaf S, Steegmans M, Van Der Sman R, Schroën C, Boom R. Droplet formation in a T-shaped microchannel junction: A model system for membrane emulsification. Colloids and Surfaces. A, Physicochemical and Engineering Aspects, 2005, 266(1-3): 106–116

64 Oishi M, Kinoshita H, Oshima M, Fujii T. Investigation of micro droplet formation in a T-shaped junction using multicolor confocal micro PIV. In: Proceedings of MNHT2008. ASME, 2008, 297–301

65 Li X B, Li F C, Yang J C, Kinoshita H, Oishi M, Oshima M. Study on the mechanism of droplet formation in T-junction microchannel. Chemical Engineering Science, 2012, 69(1): 340–351

66 Seemann R, Brinkmann M, Pfohl T, Herminghaus S. Droplet based microfluidics. Reports on Progress in Physics, 2012, 75(1): 016601

67 Rayleigh L. On the capillary phenomena of jets. Proceedings of the Royal Society of London, 1879, 29(196-199): 71–97

68 Xu J H, Luo G S, Li S W, Chen G G. Shear force induced monodisperse droplet formation in a microfluidic device by controlling wetting properties. Lab on a Chip, 2006, 6(1): 131–136

69 Lignel S, Salsac A V, Drelich A, Leclerc E, Pezron I. Water-in-oil droplet formation in a flow-focusing microsystem using pressure-and flow rate-driven pumps. Colloids and Surfaces. A, Physicochemical and Engineering Aspects, 2017, 531: 164–172

70 Hamlington B D, Steinhaus B, Feng J J, Link D, Shelley M J, Shen A Q. Liquid crystal droplet production in a microfluidic device. Liquid Crystals, 2007, 34(7): 861–870

71 Yobas L, Martens S, Ong W L, Ranganathan N. High-performance flow-focusing geometry for spontaneous generation of monodispersed droplets. Lab on a Chip, 2006, 6(8): 1073–1079

72 Moon B U, Abbasi N, Jones S G, Hwang D K, Tsai S S. Water-in-water droplets by passive microfluidic flow focusing. Analytical Chemistry, 2016, 88(7): 3982–3989

73 Anna S L, Bontoux N, Stone H A. Formation of dispersions using “flow focusing” in microchannels. Applied Physics Letters, 2003, 82(3): 364–366

74 Anna S L, Mayer H C. Microscale tipstreaming in a microfluidic flow focusing device. Physics of Fluids, 2006, 18(12): 121512

75 Lee W, Walker L M, Anna S L. Impact of viscosity ratio on the dynamics of droplet breakup in a microfluidic flow focusing device. In: Co A, Leal L G, Colby R H, Giacomin A J, eds. XV^th International Congress on Rheology—the Society of Rheology 80th Annual Meeting. American Institute of Physics, 2008, 994–996

76 Lee W, Walker L M, Anna S L. Role of geometry and fluid properties in droplet and thread formation processes in planar flow focusing. Physics of Fluids, 2009, 21(3): 032103

77 Anna S L. Droplets and bubbles in microfluidic devices. Annual Review of Fluid Mechanics, 2016, 48(1): 285–309

78 Garstecki P, Stone H A, Whitesides G M. Mechanism for flow-rate controlled breakup in confined geometries: A route to monodisperse emulsions. Physical Review Letters, 2005, 94(16): 164501

79 Zhou C, Yue P, Feng J J. Formation of simple and compound drops in microfluidic devices. Physics of Fluids, 2006, 18(9): 092105

80 Christopher G F, Anna S L. Microfluidic methods for generating continuous droplet streams. Journal of Physics D: Applied Physics, 2007, 40(19): R319–R336

81 Nunes J K, Tsai S S H, Wan J, Stone H A. Dripping and jetting in microfluidic multiphase flows applied to particle and fibre synthesis. Journal of Physics D: Applied Physics, 2013, 46(11): 114002–114020

82 Fu T, Wu Y, Ma Y, Li H Z. Droplet formation and breakup dynamics in microfluidic flow-focusing devices: From dripping to jetting. Chemical Engineering Science, 2012, 84: 207–217

83 Wu P, Luo Z, Liu Z, Li Z, Chen C, Feng L, He L. Drag-induced breakup mechanism for droplet generation in dripping within flow focusing microfluidics. Chinese Journal of Chemical Engineering, 2015, 23(1): 7–14

84 Utada A S, Lorenceau E, Link D R, Kaplan P D, Stone H A, Weitz D A. Monodisperse double emulsions generated from a microcapillary device. Science, 2005, 308(5721): 537–541

85 Utada A S, Fernandez-Nieves A, Stone H A, Weitz D A. Dripping to jetting transitions in coflowing liquid streams. Physical Review Letters, 2007, 99(9): 094502

86 Gañán-Calvo A M. Jetting-dripping transition of a liquid jet in a lower viscosity co-flowing immiscible liquid: The minimum flow rate in flow focusing. Journal of Fluid Mechanics, 2006, 553: 75–84

87 Deng C, Wang H, Huang W, Cheng S. Numerical and experimental study of oil-in-water (O/W) droplet formation in a co-flowing capillary device. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2017, 533: 1–8

88 Cramer C, Fischer P, Windhab E J. Drop formation in a co-flowing ambient fluid. Chemical Engineering Science, 2004, 59(15): 3045–3058

89 Suryo R, Basaran O A. Tip streaming from a liquid drop forming from a tube in a co-flowing outer fluid. Physics of Fluids, 2006, 18(8): 082102

90 Villermaux E, Hopfinger E. Periodically arranged co-flowing jets. Journal of Fluid Mechanics, 1994, 263: 63–92

91 Wu L, Chen Y. Visualization study of emulsion droplet formation in a coflowing microchannel. Chemical Engineering and Processing: Process Intensification, 2014, 85: 77–85

92 He Y, Battat S, Fan J, Abbaspourrad A, Weitz D A. Preparation of microparticles through co-flowing of partially miscible liquids. Chemical Engineering Journal, 2017, 320: 144–150

93 Hua J, Zhang B, Lou J. Numerical simulation of microdroplet formation in coflowing immiscible liquids. AIChE Journal. American Institute of Chemical Engineers, 2007, 53(10): 2534–2548

94 Castro-hernández E, Gundabala V, Fernández-nieves A, Gordillo J M. Scaling the drop size in coflow experiments. New Journal of Physics, 2009, 11(7): 075021

95 Vladisavljevic G T, Williams R A. Manufacture of large uniform droplets using rotating membrane emulsification. Journal of Colloid and Interface Science, 2006, 299(1): 396–402

96 Joscelyne S M, Tragardh G. Membrane emulsification—a literature review. Journal of Membrane Science, 2000, 169(1): 107–117

97 Charcosset C, Limayem I, Fessi H. The membrane emulsification process—a review. Journal of Chemical Technology & Biotechnology: International Research in Process. Environmental & Clean Technology, 2004, 79(3): 209–218

98 De Luca G, Sindona A, Giorno L, Drioli E. Quantitative analysis of coupling effects in cross-flow membrane emulsification. Journal of Membrane Science, 2004, 229(1-2): 199–209

99 Drioli E, Giorno L. Membrane operations. Simulation, 2009, 1: 1

100 Sharma S, Shukla P, Misra A, Mishra P R. Chapter 8. Interfacial and colloidal properties of emulsified systems: Pharmaceutical and biological perspective. In: Colloid & Interface Science in Pharmaceutical Research & Development. Amsterdam: Elsevier, 2014, 149–172

101 Schroder V, Behrend O, Schubert H. Effect of dynamic interfacial tension on the emulsification process using microporous, ceramic membranes. Journal of Colloid and Interface Science, 1998, 202(2): 334–340

102 Wang K, Lu Y C, Xu J H, Luo G S. Determination of dynamic interfacial tension and its effect on droplet formation in the T-shaped microdispersion process. Langmuir, 2009, 25(4): 2153–2158

103 Mozafarpour R, Koocheki A, Milani E, Varidi M. Extruded soy protein as a novel emulsifier: Structure, interfacial activity and emulsifying property. Food Hydrocolloids, 2019, 93: 361–373

104 van Dijke K, Kobayashi I, Schroen K, Uemura K, Nakajima M, Boom R. Effect of viscosities of dispersed and continuous phases in microchannel oil-in-water emulsification. Microfluidics and Nanofluidics, 2010, 9(1): 77–85

105 Wu N, Zhu Y, Leech P W, Sexton B A, Brown S, Easton C. Effects of surfactants on the formation of microdroplets in the flow focusing microfluidic device. In:  Proceedings of SPIE—The International Society for Optical Engineering. Bellingham: SPIE2007, 6799: U84–U91

106 Vlahovska P M, Danov K D, Mehreteab A, Broze G. Adsorption kinetics of ionic surfactants with detailed account for the electrostatic interactions. Journal of Colloid and Interface Science, 1997, 192(1): 194–206

107 Sasaki M, Yasunaga T, Satake S, Ashida M. Kinetic studies on double relaxation of surfactant solutions using a capillary wave method. Bulletin of the Chemical Society of Japan, 1977, 50(12): 3144–3148

108 El-Abbassi A, Neves M A, Kobayashi I, Hafidi A, Nakajima M. Preparation and characterization of highly stable monodisperse argan oil-in-water emulsions using microchannel emulsification. European Journal of Lipid Science and Technology, 2013, 115(2): 224–231

109 Eggleton C D, Tsai T M, Stebe K J. Tip streaming from a drop in the presence of surfactants. Physical Review Letters, 2001, 87(4): 048302

110 Bracco G, Holst B. Surface Science Techniques. 1st ed. Berlin: Springer, 2013, 3–34

111 Hu S, Ren X, Bachman M, Sims C E, Li G P, Allbritton N L. Surface-directed, graft polymerization within microfluidic channels. Analytical Chemistry, 2004, 76(7): 1865–1870 doi:10.1021/ac049937z

112 Barrat J L, Bocquet L. Influence of wetting properties on hydrodynamic boundary conditions at a fluid/solid interface. Faraday Discussions, 1999, 112: 119–127

113 Dreyfus R, Tabeling P, Willaime H. Ordered and disordered patterns in two-phase flows in microchannels. Physical Review Letters, 2003, 90(14): 144505

114 Nie Z, Seo M, Xu S, Lewis P C, Mok M, Kumacheva E, Whitesides G M, Garstecki P, Stone H A. Emulsification in a microfluidic flow-focusing device: Effect of the viscosities of the liquids. Microfluidics and Nanofluidics, 2008, 5(5): 585–594

115 Fournanty S, Guer Y L, Omari K E, Dejean J P. Laminar flow emulsification process to control the viscosity reduction of heavy crude oils. Journal of Dispersion Science and Technology, 2008, 29(10): 1355–1366

116 Farokhirad S, Lee T, Morris J F. Effects of inertia and viscosity on single droplet deformation in confined shear flow. Communications in Computational Physics, 2015, 13(3): 706–724

117 Eggers R. Industrial High Pressure Applications, Processes, Equipment and Safety. 1st ed. Weinheim: Wiley-VCH Verlag & Co. KGaA, 2012, 97–122

118 Chwalek J M, Trauernicht D P, Delametter C N, Sharma R, Jeanmaire D L, Anagnostopoulos C N, Hawkins G A, Ambravaneswaran B, Panditaratne J C, Basaran O A. A new method for deflecting liquid microjets. Physics of Fluids, 2002, 14(6): L37–L40

119 Xu J H, Li S W, Tan J, Luo G S. Correlations of droplet formation in T-junction microfluidic devices: From squeezing to dripping. Microfluidics and Nanofluidics, 2008, 5(6): 711–717

120 Hong Y, Wang F. Flow rate effect on droplet control in a co-flowing microfluidic device. Microfluidics and Nanofluidics, 2007, 3(3): 341–346

121 Wright P. The variation of viscosity with temperature. Physics Education, 1977, 12(5): 323–325

122 Wengerter M, Li Y, Nieder H, Brandner J J, Schoenitz M, Scholl S. Energy and resource efficient continuous production of a binder emulsion using microstructured devices. Chemical Engineering and Processing: Process Intensification, 2017, 122: 319–329

123 Fujiu K B, Kobayashi I, Neves M A, Uemura K, Nakajima M. Effect of temperature on production of soybean oil-in-water emulsions by microchannel emulsification using different emulsifiers. Food Science and Technology Research, 2011, 17(2): 77–86

124 Mahajan R K, Chawla J, Bakshi M S. Depression in the cloud point of Tween in the presence of glycol additives and triblock polymers. Colloid & Polymer Science, 2004, 282(10): 1165–1168

125 Shinoda K, Arai H. The correlation between phase inversion temperature in emulsion and cloud point in solution of nonionic emulsifier. Journal of Physical Chemistry, 1964, 68(12): 3485–3490

126 Shinoda K, Saito H. The stability of O/W type emulsions as functions of temperature and the HLB of emulsifiers: The emulsification by PIT-method. Journal of Colloid and Interface Science, 1969, 30(2): 258–263

127 Stan C A, Tang S K Y, Whitesides G M. Independent control of drop size and velocity in microfluidic flow-focusing generators using variable temperature and flow rate. Analytical Chemistry, 2009, 81(6): 2399–2402

128 Tice J D, Lyon A D, Ismagilov R F. Effects of viscosity on droplet formation and mixing in microfluidic channels. Analytica Chimica Acta, 2004, 507(1): 73–77

129 Nguyen N T, Ting T H, Yap Y F, Wong T N, Chai J C K, Ong W L, Zhou J, Tan S H, Yobas L. Thermally mediated droplet formation in microchannels. Applied Physics Letters, 2007, 91(8): 084102

130 Zhou Z, Kong T, Mkaouar H, Salama K N, Zhang J M. A hybrid modular microfluidic device for emulsion generation. Sensors and Actuators. A, Physical, 2018, 280: 422–428

131 Kanai T, Tsuchiya M. Microfluidic devices fabricated using stereolithography for preparation of monodisperse double emulsions. Chemical Engineering Journal, 2016, 290: 400–404