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Effects of Substrate Heating and Wettability on Evaporation Dynamics and Deposition Patterns for a Sessile Water Droplet Containing Colloidal Particles
Langmuir ( IF 3.7 ) Pub Date : 2016-11-01 00:00:00 , DOI: 10.1021/acs.langmuir.6b02769 Nagesh D. Patil 1 , Prathamesh G. Bange 1 , Rajneesh Bhardwaj 1 , Atul Sharma 1
Langmuir ( IF 3.7 ) Pub Date : 2016-11-01 00:00:00 , DOI: 10.1021/acs.langmuir.6b02769 Nagesh D. Patil 1 , Prathamesh G. Bange 1 , Rajneesh Bhardwaj 1 , Atul Sharma 1
Affiliation
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Effects of substrate temperature, substrate wettability, and particle concentration are experimentally investigated for evaporation of a sessile water droplet containing colloidal particles. Time-varying droplet shapes and temperature of the liquid–gas interface are measured using high-speed visualization and infrared thermography, respectively. The motion of the particles inside the evaporating droplet is qualitatively visualized by an optical microscope and the profile of the final particle deposit is measured by an optical profilometer. On a nonheated hydrophilic substrate, a ring-like deposit forms after the evaporation, as reported extensively in the literature, while on a heated hydrophilic substrate, a thinner ring with an inner deposit is reported in the present work. The latter is attributed to Marangoni convection, and recorded motion of the particles as well as measured temperature gradient across the liquid–gas interface confirms this hypothesis. The thinning of the ring scales with the substrate temperature and is reasoned to stronger Marangoni convection at larger substrate temperature. In the case of a nonheated hydrophobic substrate, an inner deposit forms due to very early depinning of the contact line. On the other hand, in the case of a heated hydrophobic substrate, the substrate heating as well as larger particle concentration helps in the pinning of the contact line, which results in a thin ring with an inner deposit. We propose a regime map for predicting three types of deposits—namely, ring, thin ring with inner deposit, and inner deposit—for varying substrate temperature, substrate wettability, and particle concentration. A first-order model corroborates the liquid–gas interface temperature measurements and variation in the measured ring profile with the substrate temperature.
中文翻译：
基质加热和润湿性对含胶粒无水水滴蒸发动力学和沉积模式的影响
通过实验研究了底物温度，底物可湿性和颗粒浓度对含胶体颗粒的无水水滴蒸发的影响。时变液滴形状和液-气界面温度分别通过高速可视化和红外热像仪测量。通过光学显微镜定性地观察蒸发液滴内的颗粒运动，并通过光学轮廓仪测量最终颗粒沉积物的轮廓。如文献中广泛报道的那样，在未加热的亲水性基材上，蒸发后形成环状沉积物，而在加热的亲水性基材上，本发明报道了具有内部沉积物的较薄环。后者归因于Marangoni对流，记录下来的颗粒运动以及在液-气界面上测得的温度梯度证实了这一假设。环的变薄随基材温度的升高而变化，这是由于在较高的基材温度下更强的Marangoni对流所致。在未加热的疏水性基材的情况下，由于接触线的过早钉扎而形成了内部沉积物。另一方面，在加热的疏水性基材的情况下，基材的加热以及较大的颗粒浓度有助于固定接触线，从而形成带有内部沉积物的薄环。我们提出了一种状态图，用于预测三种类型的沉积物，即环形，带内部沉积物的细环和内部沉积物，以改变基材温度，基材润湿性和颗粒浓度。
更新日期：2016-11-01
中文翻译：
基质加热和润湿性对含胶粒无水水滴蒸发动力学和沉积模式的影响
通过实验研究了底物温度，底物可湿性和颗粒浓度对含胶体颗粒的无水水滴蒸发的影响。时变液滴形状和液-气界面温度分别通过高速可视化和红外热像仪测量。通过光学显微镜定性地观察蒸发液滴内的颗粒运动，并通过光学轮廓仪测量最终颗粒沉积物的轮廓。如文献中广泛报道的那样，在未加热的亲水性基材上，蒸发后形成环状沉积物，而在加热的亲水性基材上，本发明报道了具有内部沉积物的较薄环。后者归因于Marangoni对流，记录下来的颗粒运动以及在液-气界面上测得的温度梯度证实了这一假设。环的变薄随基材温度的升高而变化，这是由于在较高的基材温度下更强的Marangoni对流所致。在未加热的疏水性基材的情况下，由于接触线的过早钉扎而形成了内部沉积物。另一方面，在加热的疏水性基材的情况下，基材的加热以及较大的颗粒浓度有助于固定接触线，从而形成带有内部沉积物的薄环。我们提出了一种状态图，用于预测三种类型的沉积物，即环形，带内部沉积物的细环和内部沉积物，以改变基材温度，基材润湿性和颗粒浓度。
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