Charges and Potentials in Liquid Phase Transmission Electron Microscopy

Liquid phase transmission electron microscopy (LPTEM) has enabled us to visualize and analyze nanostructures in liquids and even the liquids themselves on a fundamental level in the last two decades.
In this thesis, I explore combining LPTEM with another TEM method, electron holography (EH), that allows us to measure the mean inner potential (MIP) of a material, where the MIP can be understood as the refractive index for high energy electrons. When MIP contributions are accounted for in an EH image, then EH can furthermore be used to map out electrical or magnetic fields on the nanoscale. Combined, this form the basis of a new method we coin Liquid Phase Transmission Electron Holography (LPTEH).
In this thesis, I will investigate to what extent we can use LPTEH to measure the electrostatic potential in a liquid.
I will firstly give a proper foundation of EH and LPTEH through a detailed study on the methods.
Later I will be using LPTEH to measure the MIP of liquid mixtures of the liquids with different MIPs. This allow direct measurement of liquid composition in the TEM, creating a nanoscale electron-based version of the traditional optical refractometer often used to assess liquid composition. The electron refractometer method will also be used to measure the hydration level of polymers in liquids. Understanding of the hydration level is of high importance, where the functionalization of nanoparticles form the basis of how they interact with their surroundings, which is useful if one wants to further optimize the nanoparticle for specific applications such as in medicine.
One of the main forces in liquids is the electrostatic force, which forms the basis of liquid-solid interactions through the electric double layer (EDL) of charged ion species surrounding any charged interface. We will investigate to what extent LPTEH can be used to quantify the electrostatic potential of the EDL for different structures in liquids, such as nanoparticles with a certain surface potential and biased electrodes in electrochemical systems, where the surface potential is controlled by the external bias. Visualizing the electrostatic potential of the EDL in the solid-liquid interface has high importance, since it is a crucial parameter in electrochemistry and particle dynamics in liquids. The underlying question is: To what extent can we map out a potential distribution around a biased interfaces in an electrochemical system?
Finally we will explore how the EDL may affect experiments carried out in LPTEM. LPTEM experiments are carried out using highly energetic electrons, which for long only has been investigated in terms of the electron-liquid reaction. The interaction between the electrons and the membrane encapsulating the liquid has not yet been studied much. We use electrokinetic methods to investigate how these highly energetic electrons may alter the surface charge density of the membrane, thereby altering the solid-liquid interface, and how this may be quantified and may affect measurements such as LPTEH.
The final discussion will summarize the findings to assess how much new information LPTEH can provide about liquid mixtures, nanoparticles, charged interfaces and electrochemical systems, both by the demonstrated capabilities and with an outlook to future improvements.