Department of Chemistry & Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 5290002, Israel.
School of Materials Science and Engineering, Nanyang Technological University, 639798 Singapore; Singapore-HUJ Alliance for Research and Enterprise (SHARE), Nanomaterials for Energy and Energy-Water Nexus (NEW), Campus for Research Excellence and Technological Enterprise (CREATE), 138602, Singapore.
J Colloid Interface Sci. 2019 Feb 15;536:701-709. doi: 10.1016/j.jcis.2018.10.100. Epub 2018 Oct 30.
Directed-assembly by standing surface acoustic waves (SSAWs) only requires an acoustic contrast between particles and their surrounding medium. It is therefore highly attractive as this requirement is fulfilled by almost all dispersed systems. Previous studies utilizing SSAWs demonstrated mainly reversible microstructure arrangements from nanoparticles. The surface chemistry of colloids dramatically influences their tendency to aggregate and sinter; therefore, it should be possible to form permanent microstructures with intimate contact between nanoparticles by controlling this property. Dispersed silver nanoparticles in a microfluidic channel were exposed to SSAWs and reversibly accumulated at the pressure nodes. We show that addition of chloride ions that remove the polyacrylic capping of the nanoparticles trigger their sintering and the formation of stable conducting silver microstructures. Moreover, if the destabilizing ions are added prior to nanoparticle assembly while continuously streaming the dispersion through the acoustic aperture, the induced aggregation leads to formation of significantly thinner microstructures, which are (for the first time) unlimited in length by the acoustic apparatus. This new approach overcomes the discrepancy between the need for organic dispersants to prevent unwanted aggregation in the dispersion, and the end product's requirement for intimate contact between the colloidal particles.
定向组装通过静止表面声波（SSAW）只需要颗粒与其周围介质之间的声对比度。因此，它具有很大的吸引力，因为几乎所有分散系统都满足这一要求。以前利用 SSAW 的研究主要展示了来自纳米颗粒的可逆微观结构排列。胶体的表面化学显著影响其聚集和烧结的趋势；因此，通过控制这一特性，应该有可能形成具有纳米颗粒之间紧密接触的永久性微观结构。在微流道中的分散银纳米颗粒暴露于 SSAW 并在压力节点处可逆地积累。我们表明，添加去除纳米颗粒的聚丙烯酸包覆的氯离子会触发它们的烧结和稳定导电银微观结构的形成。此外，如果在纳米颗粒组装之前添加了破坏稳定的离子，同时将分散体连续流通过声孔径，所诱导的聚集会导致形成明显更薄的微观结构，这些微观结构（首次）由声设备无限延长。这种新方法克服了分散体中防止不需要的聚集所需的有机分散剂与胶体颗粒之间需要紧密接触之间的差异。
