The self-assembly of nanoparticles (NPs) attracts great attention for its potential application in the design of hybrid composites with collective properties from different types of materials. Here, the in-situ liquid TEM with liquid cell made from a pair of SiN membranes was employed to study the self-assembly of Au NPs with positively charged cetyltrimethylammonium ions (CTA+) and negatively charged citrate ions surfactants in aqueous in order to unravel the mechanism of NPs self-assembly. Under electron illumination in TEM, the solvated electrons will neutralize the positive charge on CTA+ coated NPs to reduce the repulsive electrostatic forces among them, resulting in the assembly of individual NPs into quasi one dimensional chains. The individual particles show a preference to on-axis attachment with the existing dimers, trimers to form trimer and tetramer. The anisotropic forces from dipolar interaction (long distance) and Van der Waals interactions (short distance) are the major driving factors for the anisotropic attachment. We found that positively charged Au NPs self-assembled only when the electron beam intensity exceeds a threshold, while negatively charged particles do not move due to the charging effect from high energy electron beam interaction with insulator SiN membranes.<br/>We further use the in-situ liquid TEM technique to study the self-assembly of Au nanoparticles under biased/current flow conditions in aqueous. At biased condition, once there is liquid suspension with CTA+ coated Au nanoparticles across between the electrodes, there can be current through the NPs suspension. We adjusted the beam intensity lower than the threshold to trigger the nanoparticle movement. Under this condition, all the particles are steady without bias voltage applied. Then the different biased voltage was applied to the NPs suspension. It was found that the nanoparticles movement took place. By statistics, we found the nanoparticle displacement is roughly the same under different biased voltage from 0V to 3V. But there were more NPs start moving along with higher biased voltage/bigger current. Over all, the self-assembly dynamics under biased condition is the same as the non-biased condition.

Study of Au nanoparticles self-assembly by in-situ transmission electron microscopy

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.