液滴蒸发残留溶质图案的理论研究
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- 英文论文题名：Ring to Mountain Transition in Deposition Pattern of Drying Droplets
- 论文作者：满兴坤 ; 土井正男
- 英文论文作者：Xingkun Man ; Masao Doi ; Center of Soft Matter Physics and its Applications ; Beihang University ; School of Physics and Nuclear Energy Engineering ; Beihang University
- 年：2016
- 作者机构：北京航空航天大学软物质物理及应用研究中心;北京航空航天大学物理科学与核能工程学院;
- 论文关键词：Onsager变分模型 ; 液滴蒸发 ; 咖啡环
- 会议召开时间：2016-08-25
- 会议录名称：中国化学会2016年软物质理论计算与模拟会议论文摘要集
- 语种：中文
- 分类号：O552.6
- 学会代码：ZGHY
- 会议名称：中国化学会2016年软物质理论计算与模拟会议
- 会议地点：中国天津
- 主办单位：中国化学会
- 学会名称：中国化学会
- 页数：2
- 文件大小：187k
- 原文格式：D
- 会议级别：全国
摘要
含有非挥发性溶质的液滴干燥后,会产生丰富多样的沉积图案。最著名的就是"咖啡环"图案,既液滴中大部分颗粒在液滴干燥后会集中在液滴初始接触线附近。另外,液滴干燥后颗粒还可能会沉积在液滴中心而形成"山状"的图案。实验上还观察到"多环"、"火山状"等等各种各样的沉积图案。怎样控制液滴蒸发后残留溶质在衬底上的图案是工业制造中一个关键问题之一,尤其是在喷墨打印技术上。然而到目前为止,还没有一个普适的对此类问题的理论解释。我们基于Onsager变分原理,提出了包含液滴内部流体运动模式和液滴接触线运动模式的理论模型,成功预测了在各种不同条件下,非挥发性溶质在衬底上的密度分布情况[1]。理论研究表明,可以通过调控液滴接触线与衬底的摩擦系数以及液滴蒸发速率,来实现沉积图案连续的从"咖啡环"到"火山状"再到"山状"结构的变化。当接触线与衬底的摩擦系数很大时,接触线几乎不会动,以至于液滴内部流体把溶质带到接触线附近沉积而形成"咖啡环";相反,当接触线与衬底无摩擦时,接触线可以自由滑动,并且导致液滴内部流体流向中心。此时,流体的速度大于接触线收缩的速度,以至于流体可以把大部分的溶质带到中心而形成"山状"结构;当接触线摩擦系数介于零和无穷大之间时,接触线收缩速度会在某一时刻赶上流体的运动速度,导致液滴中间成环而形成"火山状"。火山形状的顶点位置还取决于液滴蒸发速率的快慢,既随着蒸发速率的减慢,顶点的位置往液滴中心运动。
When a droplet containing a nonvolatile component is dried on a substrate,it leaves a ringlike deposition the substrate.We propose a theory that predicts the deposit distribution based on a model of fluid flow and the contact line motion of the droplet.It is shown that the deposition pattern changes continuously from a coffee ring to volcanolike and to mountainlike depending on the mobility of the contact line and the evaporation rate.An analytical expression is given for the peak position of the distribution of the deposit left on the substrate.Our understanding for the deposition pattern in droplets having a moving contact line is still at a primitive stage.We propose a simple Onsager principle model for a drying droplet that accounts for the contact line motion and the solvent evaporation simultaneously.We have clarified how the contact line friction and the evaporation rate affect the final deposition pattern,especially the transition from coffee ring to volcanolike and then to mountainlike patterns.We have shown that the peak position of the deposit profile shifts to inward with the decrease of the friction constant between contact line and the substrate,k_(cl).When it is large,100k_(cl)(28),the contact line does not move much from its initial position,and the coffee-ring pattern appears.On the other hand,when 0k_(cl)(28),most solute is accumulated at the center of the droplet,and a mountainlike pattern appears.Moreover,when the evaporation rate,k_(ev),is too fast,the peak position is independent of k_(ev),while it becomes a function of k_(ev) for slow evaporation rate.Our study gives insight to control the deposition pattern of drying droplets,which has various applications in industry.
When a droplet containing a nonvolatile component is dried on a substrate,it leaves a ringlike deposition the substrate.We propose a theory that predicts the deposit distribution based on a model of fluid flow and the contact line motion of the droplet.It is shown that the deposition pattern changes continuously from a coffee ring to volcanolike and to mountainlike depending on the mobility of the contact line and the evaporation rate.An analytical expression is given for the peak position of the distribution of the deposit left on the substrate.Our understanding for the deposition pattern in droplets having a moving contact line is still at a primitive stage.We propose a simple Onsager principle model for a drying droplet that accounts for the contact line motion and the solvent evaporation simultaneously.We have clarified how the contact line friction and the evaporation rate affect the final deposition pattern,especially the transition from coffee ring to volcanolike and then to mountainlike patterns.We have shown that the peak position of the deposit profile shifts to inward with the decrease of the friction constant between contact line and the substrate,k_(cl).When it is large,100k_(cl)(28),the contact line does not move much from its initial position,and the coffee-ring pattern appears.On the other hand,when 0k_(cl)(28),most solute is accumulated at the center of the droplet,and a mountainlike pattern appears.Moreover,when the evaporation rate,k_(ev),is too fast,the peak position is independent of k_(ev),while it becomes a function of k_(ev) for slow evaporation rate.Our study gives insight to control the deposition pattern of drying droplets,which has various applications in industry.
引文
[1]Zhang,S.;Li,S.;Zhou,W.;Zheng,L.Chem.Phys.2011,135:14304.Man,X.K.;Doi,M.Phys.Rev.Lett.2016,116,066101.