Preparation of Sol-Gel Films by Dip-Coating in Extreme Conditions
Preparation of Sol-Gel Films by Dip-Coating in Extreme Conditions
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DOI：
10.1021/jp9114755
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发表时间：
2010-05-06
影响因子：
3.7
通讯作者：
Grosso, David
中科院分区：
文献类型：
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作者：
Faustini, Marco;Louis, Benjamin;Grosso, David
溶胶-凝胶溶液的浸涂是一个复杂的动态过程，难以建模，因为它与时间相关的蒸发诱导的浓度和粘度梯度的溶液。然而，它在涂层技术中被高度使用，因为它简单并且提供优异的再现性。几十年前就已经提出了现有的公平模型来描述这种方法，但它们是基于牛顿和非蒸发液体，需要几个重要的假设和简化。在这项工作中，我们提出了一个简单的实验研究溶胶-凝胶膜形成的浸涂，通过我们提出了一个通用的半经验模型来预测最终的膜厚。采用椭圆偏振光谱法测量了不同浸涂工艺条件下薄膜的物理厚度和光学密度（抽取速度为0.01至20 mm.s（-1），温度为25至60 ℃）和几种不同的化学溶液（TiCl 4、TEOS和MTEOS，全部在EtOH/H2O中存在或不存在嵌段PEO-b-PPO共聚物模板的情况下，浓度为10（-1）至10（-3）mol.L-1）。我们发现，沉积过程中难以评估的现象，如粘度变化，蒸发冷却，化学反应和热Marangoni流，可能不必考虑。各种实验参数的影响一起讨论的局限性和浸涂技术的全部潜力。我们发现，两个制度的膜形成独立存在于极端的撤回速度，而他们联合收割机在中间速度成第三个制度。虽然第一个制度是众所周知的，是由重力引起的粘性阻力在较高的速度，第二个几乎没有使用，是由相互依赖的蒸发和毛细作用上升在较低的速度。我们表明，这两个制度可以选择建立一个可调的厚度和最小厚度存在于每个给定的解决方案在一个临界速度，我们认为，毛细上升效应完全抵消了粘性阻力。我们还表明，毛细管制度是非常适合当需要从高度稀释的溶液存款厚膜。
Dip-coating of sol-gel solutions is a complex dynamic process that is difficult to model because it is associated with time-dependent evaporation-induced concentration and viscosity gradients in the solution. It is, however, highly used in the coating technology because it is simple and provides excellent reproducibility. Existing fair models have been proposed some decades ago to describe this method, but they are based on Newtonian and nonevaporating liquids and require several important assumptions and simplifications. In this work, we present a simple experimental study of sol-gel film formation by dip-coating, through which we propose a general semiexperirnental model to predict the final film thickness. Spectroscopic ellipsometry was used as the main technique to obtain the film physical thickness and optical density for various dip-coating processing conditions (withdrawal speeds from 0.01 to 20 mm.s(-1) and temperatures from 25 to 60 degrees C) and for several different chemical solutions (TiCl4, TEOS, and MTEOS, all in the presence, or not, of block PEO-b-PPO copolymer templates in EtOH/H2O, with concentrations from 10(-1) to 10(-3) mol.L-1). We show that phenomena that are difficult to assess during deposition, such as viscosity variation, evaporation cooling, chemical reaction, and thermal Marangoni flow, may not have to be taken into account. The influences of various experimental parameters are discussed together with the limitations and the full potentiality of the dip-coating technique. We show that two regimes of film formation independently exist at extreme withdrawal speeds, while they combine into a third regime at intermediate speeds. Although the first regime is well-known and is governed by gravity-induced viscous drag at higher speeds, the second one is barely used and is governed by interdependent evaporation and capillarity rise at lower speeds. We show that both regimes can be selected to build up films with a tunable thickness and that a minimum thickness exists for each given solution at a critical speed for which we believe that the capillarity rise effect perfectly counterbalances the viscous drag. We also show that the capillarity regime is well-suited when one needs to deposit thick films from highly diluted solutions.