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Self-propellant Janus microsphere is a special class of active particles with a regular shape and irregular surface characteristic. With the self-propulsion of 2 μm diameter Pt-SiO2 Janus microsphere near the wall, we have measured the relationship of self-propellant velocity VJanus versus the observed time Δtobs. A diffusiophoretic force-dominated motion, which can be deemed as a quasi-1 D motion with the characteristics of both force free and torque free, is distinguished from the entire motion process. At the same time, it is also observed that the Janus microsphere is deflected about the vertical direction with an angle ψ. The deflection angle ψ is found to decrease with the increase of H2O2 concentration in the solution. For the 2.5%-10% H2O2 solution in this experiment, the angle ψ ranges from 20° to 7° approximately. A numerical model, involving viscous force, diffusiophoretic force and the effective gravity, is created with a reference frame, this quasi-1 D self-propellant motion can be solved to satisfy the conditions of the force and torque balance simultaneously. We have studied the changes of angle ψ and separation distance δ of the microsphere from the substrate under different conditions, including the concentrations of H2O2 solution, the material density, and the diameter of the microsphere. For the self-propulsion velocity VJanus and the deflection angle ψ, numerical results show good agreement with the published experimental observation results. Moreover, it is found that the lower density or the smaller diameter of the microsphere will generate the smaller distance δ, while the higher concentration of H2O2 in the solution will result in a larger distance δ. The predicted δ is 2-8 μm. With the obtained data, we further discuss the effect of near wall on the characteristic time τR of rotational diffusion of the Janus microsphere. Because the predicted values of δ are relative high, the near wall effect can be neglected, indicating that this effect should not be a significant factor to cause a big discrepancy of τR in different references. The present work will be beneficial to the understanding of the mechanism of self-propulsion and the development in its potential applications.
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Keywords:
- Janus microsphere /
- self-propulsion /
- near wall effect /
- rotational diffusion
[1] Jiang S, Granick S, Schneider H J 2012 Janus Particle Synthesis, Self-assembly and Applications (USA: RSC Publishing Press) pp1-25
[2] Zhang C L, Wei W, Liang F X, Yang Z Z 2013 Scientia Sinica: Chimica 42 1616 (in Chinese) [张成亮, 韦玮, 梁福鑫, 杨振忠 2013 中国科学:化学 42 1616]
[3] Chernyak V G, Starikov S A, Beresnev S A 2001 Journal of Applied Mechanics and Technical Physics 42 445
[4] Wang W, Duan W, Ahmed S, Mallouk T E, Sen A 2013 Nano Today 8 531
[5] Wang D, Zhang W, Jiang X Y 2011 Physics 40 588 (in Chinese) [王栋, 张伟, 蒋兴宇 2011 物理 40 588]
[6] Kapral R 2013 The Journal of Chemical Physics 138 020901
[7] Golestanian R, Liverpool T B, Ajdari A 2007 New Journal of Physics 9 126
[8] Howse J R, Jones R A L, Ryan A J, Gough T, Vafabakhsh R, Golestanian R 2007 Physical Review Letters 99 048102
[9] Ke H, Ye S, Carroll R L, Showalter K 2010 The Journal of Physical Chemistry A 114 5462
[10] Zheng X, Ten Hagen B, Kaiser A, Wu M L, Cui H H, Silber-Li Z H, Hartmut L 2013 Physical Review E 88 032304
[11] Crowdy D 2014 4th Micro and Nano Flows Conference on UCL, London, UK, Septemper 7-10, 2014
[12] Crowdy D, Lee S, Samson O, Lauga E, Hosoi A E 2011 Journal of Fluid Mechanics 681 24
[13] Wu M L, Zhang H Y, Zheng X, Cui H H 2014 AIP Advances 4 1326
[14] WU M L, Zheng X, Cui H H, Li Z H 2014 Chinese Journal of Hydrodynamics, (A) 274 (in Chinese) [武美玲, 郑旭, 崔海航, 李战华 2014 水动力学研究与进展: A辑 274]
[15] Yan Z Y 1996 Low Reynolds Number Flow Theory (Beijing: Peking University Press) pp92-112 (in Chinese) [严宗毅 1996 低雷诺兹数流动理论 (北京: 北京大学出版社)第92-112页]
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[1] Jiang S, Granick S, Schneider H J 2012 Janus Particle Synthesis, Self-assembly and Applications (USA: RSC Publishing Press) pp1-25
[2] Zhang C L, Wei W, Liang F X, Yang Z Z 2013 Scientia Sinica: Chimica 42 1616 (in Chinese) [张成亮, 韦玮, 梁福鑫, 杨振忠 2013 中国科学:化学 42 1616]
[3] Chernyak V G, Starikov S A, Beresnev S A 2001 Journal of Applied Mechanics and Technical Physics 42 445
[4] Wang W, Duan W, Ahmed S, Mallouk T E, Sen A 2013 Nano Today 8 531
[5] Wang D, Zhang W, Jiang X Y 2011 Physics 40 588 (in Chinese) [王栋, 张伟, 蒋兴宇 2011 物理 40 588]
[6] Kapral R 2013 The Journal of Chemical Physics 138 020901
[7] Golestanian R, Liverpool T B, Ajdari A 2007 New Journal of Physics 9 126
[8] Howse J R, Jones R A L, Ryan A J, Gough T, Vafabakhsh R, Golestanian R 2007 Physical Review Letters 99 048102
[9] Ke H, Ye S, Carroll R L, Showalter K 2010 The Journal of Physical Chemistry A 114 5462
[10] Zheng X, Ten Hagen B, Kaiser A, Wu M L, Cui H H, Silber-Li Z H, Hartmut L 2013 Physical Review E 88 032304
[11] Crowdy D 2014 4th Micro and Nano Flows Conference on UCL, London, UK, Septemper 7-10, 2014
[12] Crowdy D, Lee S, Samson O, Lauga E, Hosoi A E 2011 Journal of Fluid Mechanics 681 24
[13] Wu M L, Zhang H Y, Zheng X, Cui H H 2014 AIP Advances 4 1326
[14] WU M L, Zheng X, Cui H H, Li Z H 2014 Chinese Journal of Hydrodynamics, (A) 274 (in Chinese) [武美玲, 郑旭, 崔海航, 李战华 2014 水动力学研究与进展: A辑 274]
[15] Yan Z Y 1996 Low Reynolds Number Flow Theory (Beijing: Peking University Press) pp92-112 (in Chinese) [严宗毅 1996 低雷诺兹数流动理论 (北京: 北京大学出版社)第92-112页]
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