Electrostatic force microscopy for the accurate characterization of interphases in nanocomposites

Abstract

The unusual properties of nanocomposites are commonly explained by the structure of their interphase. Therefore, these nanoscale interphase regions need to be precisely characterized; however, the existing high resolution experimental methods have not been reliably adapted to this purpose. Electrostatic force microscopy (EFM) represents a promising technique to fulfill this objective, although no complete and accurate interphase study has been published to date and EFM signal interpretation is not straightforward. The aim of this work was to establish accurate EFM signal analysis methods to investigate interphases in nanodielectrics using three experimental protocols. Samples with well-known, controllable properties were designed and synthesized to electrostatically model nanodielectrics with the aim of “calibrating” the EFM technique for future interphase studies. EFM was demonstrated to be able to discriminate between alumina and silicon dioxide interphase layers of 50 and 100 nm thickness deposited over polystyrene spheres and different types of matrix materials. Consistent permittivity values were also deduced by comparison of experimental data and numerical simulations, as well as the interface state of silicone dioxide layers.

Polymer Nanocomposite Dielectrics: Understanding the Matrix/Particle Interface

“…The topography and frequency shift Δ f (used to calculate the force gradient) signal of the detection are shown in Figure b–e, and Figure e is the average profile of the signal shown in Figure b,c. It can be seen clearly that the signal difference generated by the 50-nm-thick, totally different interface is equivalent to the error in the test . The results in that study imply that even a great change of interface polarization has a very weak impact on the electrostatic force measured by EFM.…”

“…It can be seen clearly that the signal difference generated by the 50-nm-thick, totally different interface is equivalent to the error in the test. 211 The results in that study imply that even a great change of interface polarization has a very weak impact on the electrostatic force measured by EFM. Recently, in the topic of interface detection by EFM, the influence of the morphology, polarization, and charge in the interfacial region on measurement was analyzed by FEM simulation (Figure 13f).…”

“…Average profiles of (d) topography profiles and (e) EFM signal in subgraphs of (b) and (c). Adapted with permission from ref under a Creative Commons CC BY 4.0 License. Copyright 2018 published by Beilstein.…”

Dielectric Properties of Polymer Nanocomposite Interphases Using Electrostatic Force Microscopy and Machine Learning

“…Because a precise value for tip size is essential for quantifying electrostatic force gradients, we independently calibrated the tip. Two fitting parameters are generally used to model a tip: the tip apex radius, R apex , and the half an gle of the cone, θ, and there are several potential approaches. , Similar to Fumagalli et al, the capacitive force gradient was measured at various lift heights, z , for a gold-coated steel substrate. The results were fitted to the analytical equation: C m e t a l ( z ) = 2 π ϵ o R a p e x ln ( 1 + R a p e x z false( 1 − sin .25em θ false) ) Based on that fitting, we calculated θ = 12° and R apex = 29 nm, which correspond well with the manufacturer’s claim of a 25 nm tip radius and side angle of 12°.…”

Dielectric polymer nanocomposites: Past advances and future prospects in electrical insulation perspective

“…Furthermore, DSC and NMR studies revealed that local permittivity is linked to interphase, and TiO 2 nanoparticles inhibit local chain segment mobility. Khoury et al [ 137,138 ] investigated interphase using EFM and DC or AC gradient detection. The main goal of this work was to create an experimental protocol for analyzing and calibrating EFM signals for use in interphase studies.…”