Diaz Alfredo J, Noh Hanaul, Meier Tobias, Solares Santiago D
Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, United States.
Beilstein J Nanotechnol. 2017 Oct 4;8:2069-2082. doi: 10.3762/bjnano.8.207. eCollection 2017.
Bioinspired design has been central in the development of hierarchical nanocomposites. Particularly, the nacre-mimetic brick-and-mortar structure has shown excellent mechanical properties, as well as gas-barrier properties and optical transparency. Along with these intrinsic properties, the layered structure has also been utilized in sensing devices. Here we extend the multifunctionality of nacre-mimetics by designing an optically transparent and electron conductive coating based on PEDOT:PSS and nanoclays Laponite RD and Cloisite Na. We carry out extensive characterization of the nanocomposite using transmittance spectra (transparency), conductive atomic force microscopy (conductivity), contact-resonance force microscopy (mechanical properties), and SEM combined with a variety of stress-strain AFM experiments and AFM numerical simulations (internal structure). We further study the nanoclay's response to the application of pressure with multifrequency AFM and conductive AFM, whereby increases and decreases in conductivity can occur for the Laponite RD composites. We offer a possible mechanism to explain the changes in conductivity by modeling the coating as a 1-dimensional multibarrier potential for electron transport, and show that conductivity can change when the separation between the barriers changes under the application of pressure, and that the direction of the change depends on the energy of the electrons. We did not observe changes in conductivity under the application of pressure with AFM for the Cloisite Na nanocomposite, which has a large platelet size compared with the AFM probe diameter. No pressure-induced changes in conductivity were observed in the clay-free polymer either.
仿生设计一直是分级纳米复合材料发展的核心。特别是，仿珍珠母的砖-灰浆结构表现出优异的机械性能、气体阻隔性能和光学透明度。除了这些固有特性外，这种层状结构还被应用于传感设备。在此，我们通过设计一种基于聚（3,4-乙撑二氧噻吩）：聚苯乙烯磺酸盐（PEDOT:PSS）以及纳米黏土锂皂石RD和有机改性蒙脱石钠的光学透明且导电的涂层，扩展了仿珍珠母材料的多功能性。我们使用透射光谱（透明度）、导电原子力显微镜（导电性）、接触共振力显微镜（机械性能）以及结合多种应力-应变原子力显微镜实验和原子力显微镜数值模拟的扫描电子显微镜（内部结构），对该纳米复合材料进行了广泛表征。我们进一步利用多频原子力显微镜和导电原子力显微镜研究了纳米黏土在压力作用下的响应，结果表明锂皂石RD复合材料的电导率会出现增加和降低的情况。我们通过将涂层建模为电子传输的一维多势垒势，提供了一种可能的机制来解释电导率的变化，并表明在压力作用下，当势垒之间的间距发生变化时电导率会改变，且变化方向取决于电子的能量。对于有机改性蒙脱石钠纳米复合材料，我们在使用原子力显微镜施加压力时未观察到电导率的变化，该复合材料的片状颗粒尺寸与原子力显微镜探针直径相比很大。在无黏土聚合物中也未观察到压力诱导的电导率变化。
