含盐胶体液滴的蒸发图案形成机理

Pattern Formation Mechanism via Evaporation of Colloidal Droplet Containing PTFE Particles and NaCl

研究了聚四氟乙烯(PTFE)胶粒与NaCl混合液滴的蒸发过程及其图案形成机理.结果表明,PTFE颗粒对接触线具有强烈的钉扎作用,胶体液滴蒸发伴有显著的'咖啡环'效应.由于液滴中心液相区表面张力法向分力的作用,使得凝胶区存在辐射状应力,进而产生从液滴边缘向中心的辐射状裂纹,裂纹数量随胶粒的体积分数增大而减少.NaCl与PTFE胶粒的混合液滴出现了复杂多样的蒸发图案.盐的加入抑制了向外的毛细补偿流,从而有利于获得宏观上厚度均匀的沉积膜.NaCl与PTFE胶粒耦合形成了凹凸不平的枝晶状形貌,这可能是释放蒸发应力的结果.

The pattern formation via the evaporation of colloidal droplet containing polytetrafluoroethene （PTFE） particle and NaCl salt were investigated. Due to the pinning of the contact line caused by the PTFE particles, a notable “coffee ring” effect was observed in the drying of droplets containing only colloidal parti-cles. Furthermore, because of the stress field built between the inner liquid zone and outside solid zone which is induced by the azimuthal component of the surface tension of the liquid zone, cracks start to emerge in the gel zone and propagate from the edge of the droplet to the centre. The quantity of the cracks decreases with increasing volume fraction of particles. With the presence of NaCl, the outward capillary flow was greatly restricted, leading to a more homogeneous deposition of the colloidal particles. Interestingly, a rough dendrite structure containing both salt and PTFE particles was formed. It was resulted from the release of stress induced by evaporation.