Basavaraj M G, Fuller G G, Fransaer J, Vermant J
Department of Chemical Engineering, K.U. Leuven, W. de Croylaan 46, B-3001 Leuven, Belgium.
Langmuir. 2006 Jul 18;22(15):6605-12. doi: 10.1021/la060465o.
The behavior of monolayers of monodisperse prolate ellipsoidal latex particles with the same surface chemistry but varying aspect ratio has been studied experimentally. Particle monolayers at an air-water interface were subjected to compression in a Langmuir trough. When surface pressure measurements and microscopy observations were combined, possible structural transitions were evaluated. Ellipsoids of a sufficiently large aspect ratio display a less abrupt increase in the compression isotherms than spherical particles. Microscopic observations reveal that a sequence of transitions is responsible for this more gradual increase of the surface pressure. When a percolating aggregate network is used as the starting point, locally ordered regions appear progressively. When it reaches a certain surface pressure, the system "jams", and in-plane rearrangements are no longer possible at this point. A highly localized yielding of the particle network is observed. The compressional stress is relieved by flipping the ellipsoids into an upright position and by expelling particles from the monolayer. The latter does not occur for spherical particles with similar dimensions and surface chemistry. In the final stage of compression, buckling of the monolayer as a whole was observed. The effect of aspect ratio on the pressure area isotherms and on the obtained percolation and packing thresholds was quantified.
对具有相同表面化学性质但纵横比不同的单分散长椭球形乳胶颗粒单层的行为进行了实验研究。在Langmuir槽中对空气-水界面处的颗粒单层进行压缩。结合表面压力测量和显微镜观察，评估了可能的结构转变。纵横比足够大的椭球体在压缩等温线上的增加比球形颗粒的增加更不突然。显微镜观察表明，一系列转变导致了表面压力的这种更逐渐的增加。当以渗流聚集体网络作为起点时，局部有序区域逐渐出现。当达到一定表面压力时，系统“卡住”，此时面内重排不再可能。观察到颗粒网络有高度局部化的屈服。通过将椭球体翻转到直立位置并从单层中排出颗粒来缓解压缩应力。对于具有相似尺寸和表面化学性质的球形颗粒，后者不会发生。在压缩的最后阶段，观察到整个单层的屈曲。量化了纵横比对压力-面积等温线以及所获得的渗流和填充阈值的影响。
