Influence of the Particle Concentration and Marangoni Flow on the Formation of Cellulose Nanocrystal Films
Influence of the Particle Concentration and Marangoni Flow on the Formation of Cellulose Nanocrystal Films
复制标题
DOI：
10.1021/acs.langmuir.6b03724
复制
发表时间：
2017-01-10
期刊：
影响因子：
3.9
通讯作者：
Thielemans, Wim
中科院分区：
文献类型：
--
作者：
Gencer, Alican;Schutz, Christina;Thielemans, Wim
纤维素纳米晶体（CNC），带状结晶纳米颗粒，是一种生物基材料，可以是一个伟大的替代获得薄膜具有可调的光学性能。通过干燥这些纤维素纳米晶体的悬浮液可以容易地获得虹彩和光衍射膜。颗粒沉积过程的特性以及在排除悬浮液中的自组装对所获得的膜的光学性质具有直接影响。沉积到基底上的颗粒受到固着液滴内部的流动动力学的影响，并且通常产生通常称为咖啡环效应的环形沉积图案。我们着手测量和描述不同条件下的干燥动力学。我们发现，Marangoni流内的液滴是太小，以抵消毛细流动沉积在边缘的CNCs，导致咖啡环效应，无论大气湿度。通过改变大气中乙醇的量，我们能够找到（1）液滴中的胶体稳定性（其通过乙醇扩散到液滴中而降低）与（2）通过改变液滴表面张力来增加相对于液滴内部的毛细流动的马兰戈尼流动之间的平衡。这样我们就可以制作出厚度均匀的彩虹色薄膜。
Cellulose nanocrystals (CNCs), ribbonlike crystalline nanoparticles, are a biobased material that can be a great alternative to obtaining films with tunable optical properties. Iridescent and light-diffracting films can be readily obtained via the drying of a suspension of these cellulose nanocrystals. The characteristics of the particle deposition process together with the self-assembly in the precluding suspension has a direct effect on the optical properties of the obtained films. Particle deposition onto a substrate is affected by the flow dynamics inside sessile droplets and usually yields a ring shaped deposition pattern commonly referred to as the coffee-ring effect. We set out to measure and describe the drying kinetics under different conditions. We found that the Marangoni flow inside the droplet was too small to counteract the capillary flow that deposits CNCs at the edges, resulting in the coffee-ring effect, irrespective of the atmospheric humidity. By varying the amount of ethanol in the atmosphere, we were able to find a balance between (1) colloidal stability in the droplet, which is reduced by ethanol diffusion into the droplet, and (2) increasing Marangoni flow relative to capillary flow inside the droplet by changing the droplet surface tension. We could thus make iridescent films with a uniform thickness.