Experiments on the spreading of droplets on rotating plates and their stability

液滴在旋转板上的铺展及其稳定性实验

• 批准号: 194067256
• 负责人: Professor Dr. Peter Ehrhard
• 金额: --
• 依托单位: Professur für Strömungsmechanik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2011
• 资助国家: 德国
• 起止时间: 2010-12-31 至 2016-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/194067256?language=en
• 关键词: Experiments; spreading; droplets; rotating; plates

The spreading of liquids on rotating substrates, on the one hand, is the basis of the spin-coating process. This process is often engaged, if a solid coating of plane substrates is needed. Examples include semi-conductors, solar panels, or liquid-crystal displays (LCDs), where in all cases numerous solid layers of defined electrical or optical properties have to be added. In most cases, this coating applies initially a homogeneous liquid layer, which transform due to solidification or evaporation of the solvent into a solid layer. On the other hand, the modelling of such coating flows and their stability presents a scientific challenge, since at least one moving contact line is involved, a region where the fluid-layer thickness becomes very small. Hence, continuum mechanics is expected to touch its limit of validity within those regions. Even a secondary moving contact line may occur, if the liquid layer ruptures at the centre of rotation and creates a dewetting front.During the last decades, the theoretical modelling of this process has significantly advanced. Particularly, adequate models are available which capture the rotationally-symmetric spreading base flow and its (linear) stability against small disturbances which are periodic in the circumferential direction. Nevertheless, careful experiments on this process remain rare, which makes it hard to validate the theoretical models. The few published experiments focus on liquid contours during continuous liquid pouring at the rotation centre, on liquid contours during spreading across non-plane substrates, and on the finger instability of the contact line. Our proposed experiments aim to provide a broad data basis for the spreading of perfectly- and partially-wetting, Newtonian liquids on plane rotating substrates. We shall capture the dynamics of the (mean) drop radius, the speed of the contact line, and particularly contours of spreading droplets in time. This allows also to infer the history of the contact angle. Moreover, the rupture of the liquid film at the centre of rotation and the dynamic behavior of the corresponding dewetting front is an important aspect of our investigations. Finally, the systematic investigation of the stability of the wetting front is within our focus.

一方面，液体在旋转基板上的铺展是旋涂工艺的基础。如果需要在平面基材上进行固体涂层，则通常采用该工艺。例子包括半导体、太阳能电池板或液晶显示器（LCD），在所有情况下，必须添加具有限定的电或光学特性的许多固体层。在大多数情况下，该涂层最初施加均匀的液体层，其由于溶剂的固化或蒸发而转变成固体层。另一方面，这种涂层流动及其稳定性的建模提出了科学挑战，因为至少涉及一个移动接触线，流体层厚度变得非常小的区域。因此，预计连续介质力学将在这些区域内触及其有效性的极限。如果液体层在旋转中心破裂并产生去湿锋，甚至可能出现二次移动接触线。在过去的几十年中，这一过程的理论模型有了很大的发展。特别是，适当的模型是可用的，它捕获的旋转对称的扩展基流和它的（线性）稳定性对小扰动是周期性的周向方向。然而，对这一过程的仔细实验仍然很少，这使得很难验证理论模型。几个公布的实验集中在液体轮廓在连续液体倾倒在旋转中心，液体轮廓在整个非平面基板上传播期间，和手指的接触线的不稳定性。我们提出的实验的目的是提供一个广泛的数据基础上的完全润湿和部分润湿，平面旋转基板上的牛顿液体的传播。我们将捕捉动态的（平均）滴半径，速度的接触线，特别是轮廓的蔓延液滴的时间。这也允许推断接触角的历史。此外，在旋转中心的液膜的破裂和相应的去湿前的动态行为是我们的调查的一个重要方面。最后，润湿锋的稳定性的系统调查是在我们的重点。