液体弹珠的微流体操作及工程应用

微流体技术是一种精确操控和检测微量流体的新兴技术,广泛应用于生物、化学、材料等领域的实验及工程中.液体弹珠作为一种新兴的数字微流体平台在近几年快速发展.它是一种将疏水的微纳米级颗粒包裹在液滴表面形成的软物质,体积通常在几微升到几百微升之间.区别于构建特殊表面微结构或化学改性制备的超疏水表面,液体弹珠是通过颗粒层阻隔内部液体与载体的微观接触,构建类似于莱顿弗罗斯特液滴的结构来实现微量液体在固体或液体表面不润湿且稳定存在的目的.目前的研究已经证明液体弹珠拥有独特优越的物理性能,如液体弹珠表面的颗粒层将固-液接触转化为固-固和固-气接触,因此具有不粘的特性,与载体表面的摩擦很小,在很小的外力作用下就可以实现灵活移动且不污染弹珠内的液体和载体.当表面颗粒呈多层且致密分布时也并非完全阻隔外界环境,在很大程度上能够减缓内部液体的蒸发且具有良好的气体渗透性,而且液体弹珠具有较好的稳固性,往往能够承受30％的可逆线性弹性形变,这些性能使液体弹珠可以作为理想的数字微流体平台.液体弹珠的原材料十分丰富,从而决定了其性状具有灵活的可调控性,所用颗粒的疏水性和形状会直接影响液体弹珠的力学性能,例如棒状颗粒包裹的液体弹珠具有更大的刚度,链状颗粒包裹的液体弹珠具有优越的弹性性能.颗粒的化学性质可以按需赋予液体弹珠不同的响应特性,从而衍生出多种操控手段,主要方式包括静电力、磁力、自推进、光辐射、温度、超声等,完成液体弹珠的精确移动、定位、颗粒层开启和关闭以及释放内部液体的操作.以上特性使液体弹珠能够应用于各种工程中,在细胞组织和微生物的培养以及微型化学反应器方面具有很好的应用前景,同时还被广泛应用于传感器、制药和精密仪器等领域,例如光电传感、污水检测、微型胶囊制备、构建纳米复合透镜以及精准电化学沉积等.同时液体弹珠制备方法较简单,无需复杂仪器设备,具有很高的经济效益.本文结合近年来液体弹珠相关研究的发展现状介绍了液体弹珠的制备方法、结构特点、材料和不同于纯液滴的性质主要包括有效表面张力、力学稳定性和蒸发速率,归纳了几种主流操作控制液体弹珠移动和释放的手段并分析优势与不足,总结了目前液体弹珠在工程上的主要应用并对其未来的发展趋势和应用前景进行展望.

Microfluidics Operational Techniques and Engineering Applications of Liquid Marbles

Liquid marbles are a soft matter formed by wrapping hydrophobic microscale particles on the surface of a droplet, and the volume is usuallybetween a few microliters and hundreds of microliters, and is constructed by a structure separating the internal liquid and the carrier through a particle layer in achieving the non-wetting and stable existence of trace liquid on solid or liquid surface effect, which is similar to Leidenfrost drop-lets but differs from the preparation of super-hydrophobic surfaces by construction of special surface microstructures or chemical modification. Current research has proven that liquid marbles have unique superior physical properties, such as non-viscosity, high elasticity, low friction, slow evaporation, and the ability to interact with external environment. These superior properties enable liquid marbles as the ideal digital microflui-dic platform. It has potential applications in microreactors, sensors, pharmaceuticals and other related fields. The preparatory method of liquid marble is relatively simple and does not require complicated instruments or equipment, yet it brings high economic benefits. This paper reviewed and discussed the methods of preparation, structural characteristics and properties of different materials of the liquid mar-bles, inclusive of the effective surface tension, mechanical stability and evaporation rate. Several mainstream techniques to control the movement and release of liquid marbles had been reviewed and assessed their advantages and disadvantages. The current main applications of liquid mar-bles in engineering had been reviewed and summarized with their prospects, potential applications and future development trends.