Exceptionally slow motion of nanoparticles in liquid
Liquid-phase electron microscopy (LP-EM) offers unique options to study the nanometer-scale dynamic processes occurring at the solid-liquid interface. We have recently studied the electron beam induced electrochemistry of gold nanoparticles under varied liquid conditions. New fundamental insights can possibly be gained in nanoscale dynamics, and local van der Waals interactions. We discovered that nanoparticles in close proximity of a surface do not move as predicated by Brownian motion but many orders of magnitude slower, possibly explained by the presence of an interface layer of ordered liquid with exceptionally high viscosity (see figure).
This research is funded by the DFG in the project: “Probing nanoscale interactions at the solid-liquid interface via liquid-phase electron microscopy”.
Figure at the left: LP-EM of gold nanoparticles in a thin liquid layer. (a) Schematic of the experimental setup consisting of a microfluidic chamber with electron transparent windows. (b) The first nanometers of liquid consist of an ordered liquid layer with nanoparticles. (c) Mean square displacement versus time of twenty moving nanoparticles in the image shown. From: Pfaff et al.2015
Nanoparticle self-assembly studied in liquid
We are partner in the MARIE SKLODOWSKA-CURIE ACTIONS Innovative Training Network (ITN) project “A multiscale approach towards mesostructured porous material design, MULTIMAT“.
MULTIMAT will make the next step in mesoscale science by combining experimental approaches to build materials by bottom-up assembly in combination with multiscale modelling and in-situ analysis in order to unravel the mechanisms of multiscale assembly
Our role is to develop and demonstrate new technology to expand the application area of LP-EM to multiscale self-assembly. To this end, the LP-EM visualisation of the formation, mineralisation and self-organisation of bicontinuous polymer nanoparticles (BPN) will be studied. The studies will include the implementation of a new chip design that allows flow of a relatively large volume through a thin imaging segment (US Patent Application 13,299,241 (2011), as needed for high resolution imaging of low density materials, and for liquid mixing. With LP-TEM we aim to image the development of BPNs from PEO-POEGMA block copolymers, and visualise the effect of their interaction with silicification agents. Manipulation of the solution conditions will be used to observe in situ the effects on the assembly pathways. The influence of the electron beam on the experiment will be considered particularly carefully by repeating experiments at different electron doses and by determining the critical dose above which structural damage occurs.