Dielectric properties of polymers with lateral resolution using an AFM approach: nanoDielectric Spectroscopy

Presentation given at the "Polymat seminar series 2018/2019"

Abstract:

The study of the physical properties at the nanometer scale is becoming a key aspect for understanding the relations between the molecular organization and physical behavior in nanostructured polymer materials. Atomic Force Microscopy (AFM) based techniques can provide useful information on the surface morphology as well as quantitative information of physical properties, with lateral resolution usually below 50 nm. This aims to achieve a one-to-one relationship between the physical origins of different processes to their particular structures at the molecular scale. For example, using the AFM probe as a nanoelectrode, it is possible to study the topographical and electrical properties of polymers, simultaneously. This is the idea behind nanoDielectric Spectroscopy (nDS), a technique that allows the electrical mapping of surfaces to obtain information related to the components of the complex dielectric permittivity (*), at a fixed electric field frequency (f). In addition, it is possible to carry out broadband dielectric spectroscopy measurements (f = 1 Hz – 100 kHz) at fixed points on the sample’s surface. [1,2] These measurements can be analyzed under the framework of classical electrodynamics and allow the study of polymers molecular dynamics and transport properties. As a case of study, I’ll present nDS experiments on poly(ethylene oxide) (PEO) thin films. PEO is a semicrystalline polymer that at room temperature shows a dielectric signal related to charge trapping between amorphous/crystalline interfaces. This phenomenon is directly related to the ionic conductivity of the material. Using nDS I’ll present dielectric images of PEO at room temperature, with 40 nm lateral resolution, and in a humidity range of 15 – 60%. The nDS results were analyzed taking into consideration the role of the tip/sample geometry and allowed to obtain the complex dielectric permittivity function. These results will be discussed by taking into consideration the presence of water on the PEO surface and on the AFM probe, as well as taking into account the different molecular organizations of PEO.