Wąsik Patryk, Redeker Christian, Dane Thomas G, Seddon Annela M, Wu Hua, Briscoe Wuge H
School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K.
The European Synchrotron (ESRF) 71, Avenue des Martyrs, Grenoble, France.
Langmuir. 2018 Jan 30;34(4):1645-1654. doi: 10.1021/acs.langmuir.7b03854. Epub 2018 Jan 17.
Surface structures with tailored morphologies can be readily delivered by the evaporation-induced self-assembly process. It has been recently demonstrated that ZnO nanorods could undergo rapid chemical and morphological transformation into 3D complex structures of Zn(OH) nanofibers as a droplet of ZnO nanofluid dries on the substrate via a mechanism very different from that observed in the coffee ring effect. Here, we have investigated how the crystallinity and morphology of ZnO nanoparticles would affect the ultimate pattern formation. Three ZnO particles differing in size and shape were used, and their crystal structures were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Their dispersions were prepared by sonication in a mixture of isobutylamine and cyclohexane. Residual surface patterns were created by drop casting a droplet of the nanofluid on a silicon substrate. The residual surface patterns were analyzed by scanning electron microscopy (SEM) and microfocus grazing incidence X-ray diffraction (μGIXRD). Nanofluid droplets of the in-house synthesized ZnO nanoparticles resulted in residual surface patterns consisting of Zn(OH) nanofibers. However, when commercially acquired ZnO powders composed of crystals with various shapes and sizes were used as the starting material, Zn(OH) fibers were found covered by ZnO crystal residues that did not fully undergo the dissolution and recrystallization process during evaporation. The difference in the solubility of ZnO nanoparticles was linked to the difference in their crystallinity, as assessed using the Scherrer equation analysis of their XRD Bragg peaks. Our results show that the morphology of the ultimate residual pattern from evaporation of ZnO nanofluids can be controlled by varying the crystallinity of the starting ZnO nanoparticles which affects the nanoparticle dissolution process during evaporation.
具有定制形态的表面结构可以通过蒸发诱导自组装过程轻松实现。最近有研究表明，当一滴ZnO纳米流体在基底上干燥时，ZnO纳米棒会通过一种与咖啡环效应中观察到的机制截然不同的方式，快速发生化学和形态转变，形成Zn(OH)纳米纤维的三维复杂结构。在此，我们研究了ZnO纳米颗粒的结晶度和形态如何影响最终的图案形成。使用了三种尺寸和形状不同的ZnO颗粒，并通过粉末X射线衍射（XRD）和透射电子显微镜（TEM）对其晶体结构进行了表征。它们的分散体是通过在异丁胺和环己烷的混合物中超声处理制备的。通过将一滴纳米流体滴铸在硅基底上来形成残留表面图案。通过扫描电子显微镜（SEM）和微聚焦掠入射X射线衍射（μGIXRD）对残留表面图案进行分析。内部合成的ZnO纳米颗粒的纳米流体滴产生了由Zn(OH)纳米纤维组成的残留表面图案。然而，当使用由各种形状和尺寸的晶体组成的市售ZnO粉末作为起始材料时，发现Zn(OH)纤维被ZnO晶体残留物覆盖，这些残留物在蒸发过程中没有完全经历溶解和重结晶过程。通过对其XRD布拉格峰进行谢乐方程分析评估，发现ZnO纳米颗粒溶解度的差异与它们结晶度的差异有关。我们的结果表明，通过改变起始ZnO纳米颗粒的结晶度，可以控制ZnO纳米流体蒸发后最终残留图案的形态，这会影响蒸发过程中纳米颗粒的溶解过程。
