磁场对疏水表面铁磁流体液滴浸润性的影响及调控

欧阳奕; 温明富; 王娅萍; 杜玥蒨; 王誉乔; 牛小东

doi:10.11729/syltlx20220086

磁场对疏水表面铁磁流体液滴浸润性的影响及调控

欧阳奕^{1, 2,},
温明富^{1, 2, ,},
王娅萍^{1, 2},
杜玥蒨^{1, 2},
王誉乔^{1, 2},
牛小东^{1, 2}

1.
汕头大学智能制造技术教育部重点实验室，汕头　515063
2.
汕头大学工学院，汕头　515063

基金项目: 国家自然科学基金（12172203）

详细信息

作者简介:
欧阳奕: （1998—），女，广东深圳人，硕士研究生，研究方向：磁流体实验。通信地址：广东省汕头市金平区鮀江街道大学路243号汕头大学（515063）。E-mail：20youyang@stu.edu.cn

通讯作者:
温明富: E-mail：mfwen@stu.edu.cn

中图分类号: O361.3
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出版历程
- 收稿日期: 2022-08-29
- 修回日期: 2022-11-03
- 录用日期: 2022-11-26
- 网络出版日期: 2023-02-28

Influence and regulation of magnetic field on wettability of ferrofluid droplet on hydrophobic surface

OUYANG Yi^{1, 2,},
WEN Mingfu^{1, 2, ,},
WANG Yaping^{1, 2},
DU Yueqian^{1, 2},
WANG Yuqiao^{1, 2},
NIU Xiaodong^{1, 2}

1.
Key Laboratory of Intelligent Manufacturing Technology　(Shantou University), Ministry of Education, Shantou　515063, China
2.
College of Engineering, Shantou University, Shantou　515063, China

摘要

摘要: 利用铁磁流体液滴在磁场作用下的可控动态行为机制，实现微小部件甚至气泡等的定向输运，在微流控器件、抗结冰、滴状凝结及矿物浮选等领域都具有广泛的应用前景，但目前对于铁磁流体在超疏水表面的场辅助润湿行为机理、影响因素及调控方法等尚不明确。本文通过实验研究了外加磁场作用下水基铁磁流体在非磁疏水表面的润湿行为和液滴形态动态演变过程。在垂直方向磁场的激励下，通过控制磁感应强度及铁磁流体液滴体积，实验观测液滴的接触线直径和接触角变化。结果表明：在弱磁场作用下，铁磁流体液滴表观接触角由90°以上降至90°以下；在磁场作用下，铁磁流体液滴中的纳米磁性颗粒沿磁力线方向形成链状结构，液滴接触角发生变化。根据接触角、接触线直径、液滴高度和液滴体积对铁磁流体液滴润湿行为进行量化，采用标度分析方法建立磁场与接触角之间的理论预测关系。本文研究结果有助于理解磁场调控下铁磁流体在超疏水表面的可逆浸润性机制。
- 铁磁流体 /
- 液滴 /
- 润湿性 /
- 接触角 /
- 磁场 /
- 磁感应强度
Abstract: The controllable dynamic behavior of ferrofluid droplets under the magnetic field can be used to realize directional transport of small droplets or bubbles in microfluidic devices, anti-icing, droplet condensation, mineral flotation and other fields. At present, the mechanism, influencing factors and regulation methods of the field-assisted wetting behavior of magnetic fluid on the superhydrophobic surface are not clear. The wetting behavior and droplet shape evolutions of water-based ferrofluid on a hydrophobic surface under an external magnetic field are studied experimentally. Under the vertical magnetic field, the effects of the magnetic induction intensity and ferrofluid droplet size on the droplet wetting behaviors are investigated, and the contact line diameter and contact angle of the droplet are measured experimentally. The experimental results show that the apparent contact angle of the ferrofluid droplets decreases from above 90° to below 90° under the action of the weak magnetic field. Under the magnetic field, the nanomagnetic particles in the magnetic fluid form a chain structure along the direction of the magnetic field line and the droplet contact angle changes. Through a scaling analysis, the theoretical relationship of the magnetic field and the contact angle is established and it successfully predicts our experimental results. The work is valuable for controlling the wetting properties of the ferrofluid droplets on the solid surfaces under the magnetic field.
- ferrofluid /
- droplet /
- wettability /
- contact angle /
- magnetic field /
- magnetic induction density

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图 1 疏水表面上铁磁流体液滴接触角等基础参数的实验测量装置

Fig. 1 Schematic diagram of the experimental device for measuring the contact angle and other basic parameters of the ferrofluid droplets on a hydrophobic substrate

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图 2 永磁铁和疏水表面垂直距离与液滴中心磁感应强度的关系

Fig. 2 Relationship between vertical distance from permanent magnet to hydrophobic base and magnetic induction intensity at droplet center

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图 3 铁磁流体液滴在强磁场作用下分离“子液滴”

Fig. 3 Ferrofluid droplets separate "daughter droplet" under the action of strong magnetic field

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图 4 3种体积铁磁流体液滴的基础参数随液滴中心磁感应强度的变化

Fig. 4 The variation of basic parameters of three kinds of fixed ferrofluid droplets with the magnetic induction intensity at the droplet center

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图 5 3种体积的铁磁流体液滴在磁感应强度增大过程中的阴影图

Fig. 5 Shadow graphs of three volumes of ferrofluid droplets in the process of magnetic induction intensity increase

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图 6 铁磁流体液滴气–液–固三相交界点受力示意图

Fig. 6 Schematic diagram of force on gas-liquid-solid three-phase tri-junction of ferrofluid droplet

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图 7 9 μL铁磁流体液滴的接触角随磁感应强度的变化

Fig. 7 The change of contact angle and magnetic induction intensity of 9 μL ferrofluid droplet

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图 8 4种磁感应强度下铁磁流体液滴的接触角、接触线直径及高度随时间的变化

Fig. 8 The contact angle, the diameter of the contact line and the droplet height change with time under four different magnetic induction intensities

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图 9 铁磁流体液滴的初始接触角和最终接触角随磁感应强度的变化

Fig. 9 Change of the initial contact angle and the final contact angle of the droplet with the magnetic induction intensity

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图 10 4种磁感应强度下铁磁流体液滴的接触角、接触线直径及高度随时间的变化

Fig. 10 The contact angle, contact line diameter and droplet height change with time under four different magnetic induction intensities

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图 11 铁磁流体液滴初始接触角和最终接触角随磁感应强度的变化

Fig. 11 Change of the initial contact angle and final contact angle of the droplet with the magnetic induction intensity

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图 12 对数坐标下铁磁流体液滴接触角实验拟合和理论拟合

Fig. 12 Experimental and theoretical fitting of ferrofluid droplet contact angle in logarithmic coordinates

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表 1 MFW铁磁流体的物理特性

Table 1 Physical characteristics of MFW magnetic fluid

基液	水
饱和磁化强度	2 × 10⁴ A/m
密度	1.18 × 10³ kg/m³
黏度（25℃）	1 × 10⁻² Pa·s
载液饱和蒸气压（20℃）	2.3 kPa
起始磁化率	0.6
表面张力	2.6 × 10⁻⁴ N/cm
热导率	0.59 W/(m·K)
比热容	4184 J/(kg·K)

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表 2 KYN–100 PDMS薄膜的物理特性

Table 2 Physical properties of KYN–100 PDMS films

硬度/（邵氏A）	65
拉伸强度	6 Mpa
撕裂强度	20 kN/m
透光率	>95%
适用温度范围	−40～200 ℃
介电强度	12 kV/mm
介电常数	2.7 F/m
体积电阻率	1 × 10¹⁴ Ω·cm

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