Feng Fengfeng, Guo Dong, Shao Yu, Yan Xiang, Yue Kan, Pan Zhipeng, Li Xiangqian, Xiao Dongcheng, Jin Liang, Zhang Wen-Bin, Liu Hao
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Center for Advanced Low-Dimension Materials, College of Materials Science and Engineering, Donghua University Shanghai 201620 P. R. China
Department of Polymer Science, College of Polymer Science and Polymer Engineering, The University of Akron Akron Ohio 44325 USA.
Chem Sci. 2021 Feb 26;12(14):5216-5223. doi: 10.1039/d1sc00021g.
The performance of 2D nanomaterials hinges on both the chemical compositions and the morphological structures across different length scales. Among all the three dimensions, thickness is the only one that falls into the nanometer scale and, to some extent, determines the intrinsic properties of 2D nanomaterials. In this study, we report the preparation and precise thickness control of 2D nanosheets assembled from a library of monodispersed amphiphilic giant molecules composed of functional polyhedral oligomeric silsesquioxanes (POSSs) as the side groups. Solution self-assembly of such giant molecules resulted in 2D nanosheets with similar structural configurations, where a bilayer of hydrophobic isobutyl POSS (BPOSS) is sandwiched by two monolayers of hydrophilic POSS bearing carboxylic acid groups (APOSS). The thickness of the obtained nanosheets could be tuned through adjusting the chemical compositions of the pendant POSS cages. Intriguingly, we found that the thickness of the 2D nanosheets was not necessarily proportional to the contour length of the giant molecule nor the total number of POSS cages tethered to the main chain. Indeed, the number ratio of BPOSS to APOSS, rather than the exact number, played a deterministic role in the thickness control. To explain the unusual thickness dependence, we built up a structure model with an in-plane orientation of the giant molecules in the nanosheets, from which a formula was further deduced to semi-quantitatively describe the inverse relationship between the overall thickness and the number ratio of BPOSS to APOSS.
二维纳米材料的性能取决于其化学成分和不同长度尺度下的形态结构。在所有三个维度中，厚度是唯一处于纳米尺度的维度，并且在一定程度上决定了二维纳米材料的固有属性。在本研究中，我们报道了由一系列以功能性多面体低聚倍半硅氧烷（POSS）作为侧基的单分散两亲性巨型分子组装而成的二维纳米片的制备及精确厚度控制。此类巨型分子的溶液自组装产生了具有相似结构构型的二维纳米片，其中疏水性异丁基POSS（BPOSS）的双层被两层带有羧酸基团的亲水性POSS（APOSS）单层夹在中间。通过调节悬垂POSS笼的化学成分，可以调整所得纳米片的厚度。有趣的是，我们发现二维纳米片的厚度不一定与巨型分子的轮廓长度或连接到主链上的POSS笼的总数成比例。实际上，BPOSS与APOSS的数量比而非确切数量在厚度控制中起决定性作用。为了解释这种不寻常的厚度依赖性，我们构建了一个纳米片中巨型分子呈面内取向的结构模型，并由此进一步推导出一个公式，以半定量地描述总厚度与BPOSS与APOSS数量比之间的反比关系。
