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微小液滴在不同能量表面上的润湿状态对于准确预测非均相核化速率和揭示界面效应影响液滴增长微观机理具有重要意义. 通过分子动力学模拟, 研究了纳米级液滴在不同能量表面上的铺展过程和润湿形态. 结果表明, 固液界面自由能随固液作用强度增加而增加, 并呈现不同液滴铺展速率和润湿特性. 固液作用强度小于1.6的低能表面呈现疏水特征, 继续增强固液作用强度时表面变为亲水, 而固液作用强度大于3.5的高能表面上液体呈完全润湿特征. 受微尺度条件下非连续、非对称作用力影响, 微液滴气液界面存在明显波动, 呈现与宏观液滴不同的界面特征. 统计意义下, 微小液滴在不同能量表面上铺展后仍可以形成特定接触角, 该接触角随固液作用强度增加而线性减小, 模拟结果与经典润湿理论计算获得的结果呈现相似变化趋势. 模拟结果从分子尺度为核化理论中的毛细假设提供了理论支持, 揭示了液滴气液界面和接触角的波动现象, 为核化速率理论预测结果和实验测定结果之间的差异提供了定性解释.The wetting characteristic of micro-droplets on surfaces with different free energies is crucial to heterogeneous nucleation theory and the growth mechanism of micro-droplets during vapor condensation. In this paper, the spreading processes and wetting characteristics of nanoscale water droplets on various surfaces are explored by molecular dynamics simulation method. The surfaces are constructed from face centered cubic copper-like atoms with different Lennard-Jones potential parameters. The Lennard-Jones interaction energy well-depth of the surface atoms is adjusted to acquire different surface free energies, and the ratio of surface-water interaction energy well-depth to the water-water interaction energy well-depth is defined as the interaction intensity. In the present study, the relationship between interfacial free energies and solid-liquid interaction intensities is evaluated using molecular dynamics simulations. The wetting characteristics of TIP4P/2005 water droplets on surfaces with various free energies are simulated and analyzed as well, using molecular dynamics simulations under an NVT ensemble. Results indicate that the solid-liquid interfacial free energy increases as the solid-liquid interaction intensity increases, with different spreading processes and wetting characteristics achieved for the water droplets on these surfaces. For the surfaces with lower interaction intensities, water cannot spread on the solid surfaces and hydrophobic surfaces are obtained when the interaction intensity ratio between surface atoms and water molecules is lower than 1.6. As the interaction intensity increases, the surface translates from hydrophobic into hydrophilic, and finally into a complete wetting state as the interaction intensity reaches up to 3.5. Due to the limitation of nanoscale dimensions, the forces that exert on droplet surface are non-continuous and asymmetric. As a result, significant fluctuations of liquid-vapor interface and local solid-liquid contact line can be observed for the droplet in nanoscale. The transient contact angle of nano-droplets is also fluctuating within a certain range, which is different from that observed for macro-droplets. From the viewpoint of statistics, an apparent contact angle can be obtained for the droplet on each surface. The contact angle decreases with solid-liquid interaction intensities linearly, which is in accordance with the calculated results of classic Young's theory using the interfacial free energies obtained from molecular dynamics simulations. The fact that an apparent contact angle is already established for a droplet in nanoscale, supporting the capillary assumption that is widely adopted in classic nucleation theory. The fluctuation of liquid-vapor interface and contact angle also provides a qualitative explanation for the discrepancy between experimental nucleation rates and predictions in classic nucleation theory.
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Keywords:
- micro droplet /
- surface free energy /
- wetting /
- molecular dynamics simulation
[1] Wenzel R N 1936 Industrial and Engineering Chemistry 28 988
[2] Cassie A B D, Baxter S 1944 Transactions of the Faraday Society 40 546
[3] Yang Z, Wu Y Z, Ye Y F, Gong M G, Xu X L 2012 Chin. Phys. B 21 126801
[4] Gong M G, Liu Y Y, Xu X L 2010 Chin. Phys. B 19 106801
[5] Liu S S, Zhang C H, Zhang H B, Zhou J, He J G, Yin H Y 2013 Chin. Phys. B 22 106801
[6] Gong M G, Xu X L, Yang Z, Liu Y S, Liu L 2010 Chin. Phys. B 19 056701
[7] Cui S W, Zhu R Z, Wei J A, Yang H X, Xu S H, Sun Z W 2015 Acta Phys. Sin. 64 116802 (in Chinese) [崔树稳, 朱如曾, 魏久安, 杨洪秀, 徐升华, 孙祉伟 2015 64 116802]
[8] Xu W, Lan Z, Peng B L, Wen R F, Ma X H 2015 RSC Adv. 5 812
[9] Zang D Y, Lin K J, Wang W K, Gu Y X, Zhang Y J, Geng X G, Binks B P 2014 Soft Matter 10 1309
[10] Volmer M, Weber A 1926 Z. Phys. Chem. 119 277
[11] Fisher J C, Hollomon J H, Turnbull D 1948 J. Appl. Phys. 19 775
[12] Laaksonen A, Ford I J, Kulmala M 1994 Phys. Rev. E 49 5517
[13] Talanquer V, Oxtoby D W 1995 Physica A 220 74
[14] Kashchiev D 2000 Nucleation: Basic Theory with Applications (Burlington: Butterworth-Heinemann) p32
[15] Carey V P 2008 Liquid-vapor Phase-Change Phenomena (New York: Taylor and Francis)
[16] Abyzov A S, Schmelzer J W P 2013 J. Chem. Phys. 138 164504
[17] Xu W, Lan Z, Peng B L, Wen R F, Ma X H 2014 RSC Adv. 4 31692
[18] Jian Z Y, Gao A H, Chang F E, Tang B B, Zhang L, Li N 2013 Acta Phys. Sin. 62 056102 (in Chinese) [坚增运, 高阿红, 常芳娥, 唐博博, 张龙, 李娜 2013 62 056102]
[19] Wang J Z, Chen M, Guo Z Y 2003 Chinese Science Bulletin 48 623
[20] Tsuruta T, Tanaka H, Masuoka T 1999 Int. J. Heat Mass Tran. 42 4107
[21] Tsuruta T, Nagayama G 2005 Energy 30 795
[22] Yang T H, Pan C 2005 Int. J. Heat Mass Tran. 48 3516
[23] Tanaka K K, Kawano A, Tanaka H 2014 J. Chem. Phys. 140 114302
[24] Merikanto J, Vehkamäki H, Zapadinsky E 2004 J. Chem. Phys. 121 914
[25] Diemand J, Angélil R, Tanaka K K, Tanaka H 2013 J. Chem. Phys. 139 074309
[26] Ge S, Chen M 2013 Acta Phys. Sin. 62 110204 (in Chinese) [葛宋, 陈民 2013 62 110204]
[27] Khan S, Singh J K 2014 Molecular Simulation 40 458
[28] Niu D, Tang G H 2014 Int. J. Heat Mass Tran. 79 647
[29] Hu H B, Chen L B, Bao L Y, Huang S H 2014 Chin. Phys. B 23 074702
[30] Zhang M K, Chen S, Shang Z 2012 Acta Phys. Sin. 61 034701 (in Chinese) [张明焜, 陈硕, 尚智 2012 61 034701]
[31] Toxvaerd S 2002 J. Chem. Phys. 117 10303
[32] Abascal J L F, Vega C 2005 J. Chem. Phys. 123 234505
[33] Vega C, Abascal J L F, Conde M M, Aragones J L 2009 Faraday Discuss. 141 251
[34] Heinz H, Vaia R A, Farmer B L, Naik R R 2008 J. Phys. Chem. C 112 17281
[35] Allen M P, Tildesley D J 1987 Computer simulation of liquids (Oxford: Clarendon Press) p20
[36] Phillips J C, Braun R, Wang W, Gumbart J, Tajkhorshid E, Villa E, Chipot C, Skeel R D, Kale L, Schulten K 2005 Journal of Computational Chemistry 26 1781
[37] Humphrey W, Dalke A, Schulten K 1996 J. Molec. Graphics 14 33
[38] Tyson W R, Miller W A 1977 Surf. Sci. 62 267
[39] Osman M A, Keller B A 1996 Appl. Surf. Sci. 99 261
[40] Angélil R, Diemand J, Tanaka K K, Tanaka H 2014 J. Chem. Phys. 140 074303
[41] Pérez A, Rubio A 2011 J. Chem. Phys. 135 244505
[42] Boda D, Henderson D 2008 Mol. Phys. 106 2367
[43] Gunton J D 1999 Journal of Statistical Physics 95 903
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[1] Wenzel R N 1936 Industrial and Engineering Chemistry 28 988
[2] Cassie A B D, Baxter S 1944 Transactions of the Faraday Society 40 546
[3] Yang Z, Wu Y Z, Ye Y F, Gong M G, Xu X L 2012 Chin. Phys. B 21 126801
[4] Gong M G, Liu Y Y, Xu X L 2010 Chin. Phys. B 19 106801
[5] Liu S S, Zhang C H, Zhang H B, Zhou J, He J G, Yin H Y 2013 Chin. Phys. B 22 106801
[6] Gong M G, Xu X L, Yang Z, Liu Y S, Liu L 2010 Chin. Phys. B 19 056701
[7] Cui S W, Zhu R Z, Wei J A, Yang H X, Xu S H, Sun Z W 2015 Acta Phys. Sin. 64 116802 (in Chinese) [崔树稳, 朱如曾, 魏久安, 杨洪秀, 徐升华, 孙祉伟 2015 64 116802]
[8] Xu W, Lan Z, Peng B L, Wen R F, Ma X H 2015 RSC Adv. 5 812
[9] Zang D Y, Lin K J, Wang W K, Gu Y X, Zhang Y J, Geng X G, Binks B P 2014 Soft Matter 10 1309
[10] Volmer M, Weber A 1926 Z. Phys. Chem. 119 277
[11] Fisher J C, Hollomon J H, Turnbull D 1948 J. Appl. Phys. 19 775
[12] Laaksonen A, Ford I J, Kulmala M 1994 Phys. Rev. E 49 5517
[13] Talanquer V, Oxtoby D W 1995 Physica A 220 74
[14] Kashchiev D 2000 Nucleation: Basic Theory with Applications (Burlington: Butterworth-Heinemann) p32
[15] Carey V P 2008 Liquid-vapor Phase-Change Phenomena (New York: Taylor and Francis)
[16] Abyzov A S, Schmelzer J W P 2013 J. Chem. Phys. 138 164504
[17] Xu W, Lan Z, Peng B L, Wen R F, Ma X H 2014 RSC Adv. 4 31692
[18] Jian Z Y, Gao A H, Chang F E, Tang B B, Zhang L, Li N 2013 Acta Phys. Sin. 62 056102 (in Chinese) [坚增运, 高阿红, 常芳娥, 唐博博, 张龙, 李娜 2013 62 056102]
[19] Wang J Z, Chen M, Guo Z Y 2003 Chinese Science Bulletin 48 623
[20] Tsuruta T, Tanaka H, Masuoka T 1999 Int. J. Heat Mass Tran. 42 4107
[21] Tsuruta T, Nagayama G 2005 Energy 30 795
[22] Yang T H, Pan C 2005 Int. J. Heat Mass Tran. 48 3516
[23] Tanaka K K, Kawano A, Tanaka H 2014 J. Chem. Phys. 140 114302
[24] Merikanto J, Vehkamäki H, Zapadinsky E 2004 J. Chem. Phys. 121 914
[25] Diemand J, Angélil R, Tanaka K K, Tanaka H 2013 J. Chem. Phys. 139 074309
[26] Ge S, Chen M 2013 Acta Phys. Sin. 62 110204 (in Chinese) [葛宋, 陈民 2013 62 110204]
[27] Khan S, Singh J K 2014 Molecular Simulation 40 458
[28] Niu D, Tang G H 2014 Int. J. Heat Mass Tran. 79 647
[29] Hu H B, Chen L B, Bao L Y, Huang S H 2014 Chin. Phys. B 23 074702
[30] Zhang M K, Chen S, Shang Z 2012 Acta Phys. Sin. 61 034701 (in Chinese) [张明焜, 陈硕, 尚智 2012 61 034701]
[31] Toxvaerd S 2002 J. Chem. Phys. 117 10303
[32] Abascal J L F, Vega C 2005 J. Chem. Phys. 123 234505
[33] Vega C, Abascal J L F, Conde M M, Aragones J L 2009 Faraday Discuss. 141 251
[34] Heinz H, Vaia R A, Farmer B L, Naik R R 2008 J. Phys. Chem. C 112 17281
[35] Allen M P, Tildesley D J 1987 Computer simulation of liquids (Oxford: Clarendon Press) p20
[36] Phillips J C, Braun R, Wang W, Gumbart J, Tajkhorshid E, Villa E, Chipot C, Skeel R D, Kale L, Schulten K 2005 Journal of Computational Chemistry 26 1781
[37] Humphrey W, Dalke A, Schulten K 1996 J. Molec. Graphics 14 33
[38] Tyson W R, Miller W A 1977 Surf. Sci. 62 267
[39] Osman M A, Keller B A 1996 Appl. Surf. Sci. 99 261
[40] Angélil R, Diemand J, Tanaka K K, Tanaka H 2014 J. Chem. Phys. 140 074303
[41] Pérez A, Rubio A 2011 J. Chem. Phys. 135 244505
[42] Boda D, Henderson D 2008 Mol. Phys. 106 2367
[43] Gunton J D 1999 Journal of Statistical Physics 95 903
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