On the maximum spreading of liquid droplets impacting on soft surfaces
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摘要: 采用高速摄影与计算机图像识别技术，研究了单个液滴撞击不同厚度、不同弹性模量的聚二甲基硅氧烷（PDMS）样品表面后的动态铺展过程，获得了液滴与柔性材料表面的移动接触线直径随时间的变化规律。实验结果表明：柔性材料在撞击过程中受压变形所导致的固体材料粘性能量耗散与系统的总能量相比很小，不会对液滴的铺展过程产生明显影响；在较低的撞击速度下，柔性材料表面形成的润湿脊所导致的粘弹性能量耗散是系统能量耗散的重要因素，且随着柔性材料弹性模量的减小而增大，因此液滴撞击弹性模量较小的PDMS表面时的最大铺展系数相对较小；当撞击速度增大后，粘弹性能量耗散在总能量耗散中所占的比例降低，液滴铺展过程中的液体粘性能量耗散所占比例逐渐升高，柔性材料弹性模量对液滴铺展行为的影响逐渐降低。Abstract: With the method of the high-speed camera and image recognition, the spreading procedure of the liquid droplet impacting on the surface of Polydimethylsiloxane (PDMS) with different thickness and different modulus is obtained. The variation curves of between the spread factor with time are also plotted. Compared with the total energy of the system, the viscous energy dissipation caused by the compression deformation of the PDMS substrate is too small to affect the spreading procedure. In the case of lower impact velocity, the viscoelastic energy dissipation caused by the wetting ridge, which is formed on the surface of PDMS, is the major component of the total energy dissipation of the system. It increases with the decrease of the modulus of flexible materials. For this reason, the spread factor shows a decrease trend with the decrement of the modulus of PDMS. When the impact velocity increases, the viscous energy dissipation becomes the major component of the total energy dissipation and the spread factor remains unchanged with the change of the modulus of the flexible material.
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Key words:
- droplet /
- flexible material /
- contact line /
- energy balance /
- maximum spreading dia-meter
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图 2 高速摄影照片(Ratio=10:1, v0=0.623m/s)
Figure 2. Photos of impact procedure (Ratio=10:1, v0=0.623m/s)
表 1 PDMS样品的主要参数
Table 1. Parameters of PDMS substrates
No. Ratio b/mm G/kPa 1 10:1 0.03 710 2 10:1 0.09 710 3 10:1 0.30 710 4 10:1 1.00 710 5 10:1 3.60 710 6 40:1 0.03 36 7 40:1 0.09 36 8 40:1 0.30 36 9 40:1 1.00 36 10 40:1 3.60 36 
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表 2 3种不同表面的接触角
Table 2. Summary of different contact angles
Surfaces θe θa θr PDMS 10:1 120°±2° 116°±2° 88°±2° PDMS 40:1 125°±3° 123°±2° 24°±2° Silicon 80°±2° 92°±2° 74°±2°
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表 3 实验所用液滴参数
Table 3. Parameters of liquid droplets in the study
D0/mm H/mm v0/(m·s-1) Re We 2.36±0.07 6 0.216±0.006 481±18.0 1.52±0.09 12 0.409±0.002 899±14.5 5.39±0.10 25 0.623±0.007 1429±26.3 13.05±0.36 50 0.881±0.007 1954±29.2 25.23±0.52 100 1.311±0.018 2882±56.4 55.38±1.63 200 1.864±0.009 4099±43.1 111.96±1.52 400 2.602±0.017 6017±90.4 229.44±3.99 800 3.544±0.057 7995±210.0 415.18±20.90 1600 4.743±0.142 10 520±301.0 731.12±48.70
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表 4 粘弹性能量耗散、初始总能量及其比值
Table 4. Ev, Etotal and the ratio of Ev to Etotal
We PDMS 10:1 PDMS 40:1 Etotal Ev Ψ Etotal Ev Ψ 1.5 1.43×10-6 3.78×10-8 2.64% 1.43×10-6 4.94×10-7 34.5% 5.4 1.86×10-6 4.74×10-8 2.55% 1.85×10-6 6.16×10-7 33.3% 13.1 2.61×10-6 7.16×10-8 2.74% 2.61×10-6 9.31×10-7 35.7% 25.2 3.93×10-6 9.19×10-8 2.34% 3.94×10-6 1.19×10-6 30.3% 55.4 7.18×10-6 1.45×10-7 2.02% 7.20×10-6 1.89×10-6 26.2% 112.0 1.31×10-5 2.46×10-7 1.87% 1.32×10-5 3.20×10-6 24.2% 229.0 2.55×10-5 3.82×10-7 1.50% 2.51×10-5 4.97×10-6 19.8% 415.0 4.69×10-5 4.81×10-7 1.03% 4.72×10-5 6.26×10-6 13.3% 731.0 7.34×10-5 5.61×10-7 0.76% 7.48×10-5 7.29×10-6 9.74%
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