Mechanisms of dual-core-coalescence in double-emulsion droplets via photothermal manipulation

doi:10.11949/0438-1157.20250476

Abstract

Abstract:

Double-emulsion droplets are droplets that contain smaller droplets inside which are often used as reaction units to achieve various functions and have attracted much attention due to their unique core-shell structure. In this paper, we propose to use laser photothermal effect to induce thermocapillary flow to achieve core-droplet coalescence of double emulsion droplets. We use couple level set and volume of fluid method (CLSVOF) to track phase interface and study its characteristics of core coalescence. The results show that when the laser irradiates the centers of two internal droplets, the local thermal effect of the laser induces the formation of thermal capillary flow at the internal and external interfaces, which together drive the internal droplets closer to each other for coalescence. When the radius of laser increases from 20 μm to 50 μm, the thermal capillary migration is stronger due to the increase in heat absorbed by the internal droplets, leading the coalescence-begin gradually shortened. As the spot radius increases further, the onset of coalescence gradually delays. Lower laser power leads to later coalescence. The larger the radius of the internal droplet, the earlier the internal droplet coalesces due to the increased absorbed heat and the shorted initial interface distance.

Key words: double-emulsion droplet, photothermal manipulation, coalescence, microfluidics, CFD, multiphase flow

摘要：

双重乳液滴是指液滴内部还包含更小液滴，因其独特的壳核结构而备受关注，常被作为反应单元实现诸多功能。本研究提出利用激光光热效应诱导热毛细流动实现双核双重乳液滴核聚并，并采用CLSVOF方法追踪相界面研究其核聚并特性。结果表明：当激光照射两个内液滴中心时，激光局部热效应会在内外界面诱导形成热毛细流动，共同驱动内液滴相互靠近发生聚并；当光斑半径从20 μm增加至50 μm时，内液滴吸收热量增多，温差增大使热毛细流动更强，聚并发生时间逐步提前；当光斑半径进一步增大，内液滴聚并发生时间又逐步推迟；激光功率越小，内液滴聚并发生时间越晚；内液滴半径越大，由于吸收热量增多及初始界面距离缩短，内液滴越早聚并。

关键词: 双重乳液, 光热操控, 聚并, 微流体学, CFD, 多相流

CLC Number:

TQ 050

Guirong PENG, Yilin WANG, Jingyi QIN, Zhibin WANG, Songping MO, Ying CHEN. Mechanisms of dual-core-coalescence in double-emulsion droplets via photothermal manipulation[J]. CIESC Journal, 2025, 76(11): 5764-5775.

彭桂荣, 王奕淋, 覃静沂, 王智彬, 莫松平, 陈颖. 光热操控双核双重乳液滴核聚并特性[J]. 化工学报, 2025, 76(11): 5764-5775.

Figures/Tables 12

Fig.1 Physical model

Table 1 Physical properties of water and hexadecane

工质	密度/(kg/m³)	比热容/(J/(kg·K))	热导率/(W/(m·K))	黏度/(Pa·s)	表面张力/(N/m)
水	998.2	4996.047-5.29412T+0.00858T²	-0.6028+0.00658T-8.42644×10^-6T²	0.06225-5.09763×10^-4T+1.41113×10^-6T²-1.3137×10^-9T³	0.02-1×10^-4(T-300)
十六烷	773.4	28994.24-244.7219T+0.73241T²-7.17898×10^-4T³	0.18745-1.32437×10^-4T-8.53221×10^-8T²	0.153593-1.22841×10^-3T+3.33586×10^-6T²-3.05677×10^-9T³	0.02-1×10^-4(T-300)

Table 2 Results of grid independence verification

网格数量/个	上峰值速度偏差/%	计算成本/%
791864	2.90	66.29
967032	2.28	51.86
1213056	0.13	35.05
1432448	—	—

Fig.2 Model validation

Fig.3 Dynamic behavior of core-coalescence in a double-emulsion droplet driven by photothermal effect

Fig.4 Temperature gradient and migration velocity with time

Fig.5 Effect of laser beam radius

Fig.6 Influence of laser beam radius on temperature gradient and migration velocity

Fig.7 Effect of heating power

Fig.8 Influence of laser power on temperature gradient and migration velocity

Fig.9 Effect of right internal droplet diameter

Fig.10 Influence of right internal droplet diameter on temperature gradient and migration velocity

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