Crystallization Mechanisms in Convective Particle Assembly
Crystallization Mechanisms in Convective Particle Assembly
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DOI：
10.1021/la2048618
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发表时间：
2012-06-05
期刊：
影响因子：
3.9
通讯作者：
Kraus, Tobias
中科院分区：
文献类型：
--
作者：
Born, Philip;Munoz, Andres;Kraus, Tobias
使用对流流体流动将胶体颗粒连续组装成结晶颗粒涂层。组装发生在润湿储液器上的弯月面内。弯月面的形状限定了对流的轮廓和颗粒的运动。我们使用光学干涉显微镜，粒子图像测速仪，和粒子跟踪分析的粒子的轨迹从液体水库的薄膜生长前沿和内部的沉积膜作为温度的函数。我们的研究结果表明，在高沉积温度下的静态膜生长前沿组装在低沉积温度下的前体膜与高颗粒迁移率的组件的过渡。一个简单的模型，比较对流阻力的颗粒的热搅拌解释了这一行为。对流组装机制表现出明显的温度依赖性，并且需要提供足够蒸发的温度。毛细管机制几乎与温度无关，并在较低温度下控制组装。该模型拟合的实验数据与温度和颗粒尺寸作为可变参数，并允许预测的转变温度。虽然这两种机制是显着不同的，干燥的颗粒膜从两个组件制度表现出六边形颗粒包装。我们发现，由对流机制组装的膜比由毛细管机制组装的膜具有更大的规律性。
Colloidal particles are continuously assembled into crystalline particle coatings using convective fluid flows. Assembly takes place inside a meniscus on a wetting reservoir. The shape of the meniscus defines the profile of the convective flow and the motion of the particles. We use optical interference microscopy, particle image velocimetry, and particle tracking to analyze the particles' trajectory from the liquid reservoir to the film growth front and inside the deposited film as a function of temperature. Our results indicate a transition from assembly at a static film growth front at high deposition temperatures to assembly in a precursor film with high particle mobility at low deposition temperatures. A simple model that compares the convective drag on the particles to the thermal agitation explains this behavior. Convective assembly mechanisms exhibit a pronounced temperature dependency and require a temperature that provides sufficient evaporation. Capillary mechanisms are nearly temperature independent and govern assembly at lower temperatures. The model fits the experimental data with temperature and particle size as variable parameters and allows prediction of the transition temperatures. While the two mechanisms are markedly different, dried particle films from both assembly regimes exhibit hexagonal particle packings. We show that films assembled by convective mechanisms exhibit greater regularity than those assembled by capillary mechanisms.