Nanoscale Characterization of the Mechanical and Electrical Properties of a Nanodielectric:
the Case Study of Silver Nanoparticles dispersed in a Poly(styrene) Matrix
Thomas De Muijlder1, Michel Voué2, Philippe Leclère*
1 Laboratory for Physics of Nanomaterials and Energy (LPNE)
2 Laboratory for Physics of Materials and Optics (LPMO)
Research Institute for Materials Science and Engineering (UMONS)
* Corresponding author: philippe.leclere@umons.ac.be
During the last decades, nanodielectrics (i.e. nanocomposite materials based on a polymer matrix mixed with an inorganic filler) have shown a great potential for electronic applications. In particular, they show clear improvements in electrical properties (capacitance, electric field concentration, dielectric breakdown) as well as mechanical properties (tensile strength, flexibility) for a wide range of temperatures. These improvements are promising for the design of energy harvesting devices or electrical insulation systems.
More and more studies highlighted the major role of the interphase between the matrix and the filler. Because of its nanoscopic nature, the characterization of the interphase properties requires cutting-edge tools as scanning probe microscopy (SPM).
As model polymer matrix, we choose poly(styrene) (PS), a well-known polymer, easy to handle and one of the most used in this context. As inorganic filler, we selected silver nanoparticles since silver is known to show the highest electrical and thermal conductivity. They are produced by laser photoablation in toluene as organic solvent. The laser photoablation is known to produce nanoparticles with good colloidal stability while the use of toluene aims to add an extra carbonic shell surrounding the silver nanoparticles.
For the analysis of our samples, we used optical measurements at different steps of the thin film fabrication process: reflectometry to determine the thickness of the polymer matrix, UV-VIS spectroscopy to monitor the production of the silver particles, and finally ellipsometry to characterize the optical properties of the composite films.
For the measurements at the nanoscale, on one hand, we used PeakForce Tapping (PFT) and Intermodulation AFM (ImAFM) methods, to systematically analyze and quantitatively map the mechanical properties (rigidity modulus, adhesion, deformation) of the thin films. On the other hand, for their electrical properties (contact potential difference, capacitance, and its derivatives) we used Intermodulation EFM (ImEFM).
In fine, we compared the different existing interphase models with the data to explain the dielectric properties of our samples.