Molecular confinement of solid and gaseous phases of self-standing bulk nanoporous polymers inducing enhanced and unexpected physical properties

Dielectric behavior of porous PMMA: From the micrometer to the nanometer scale

“…This behavior was previously observed by J. Pinto and coworkers [14], who demonstrated the appearance of an electrical conductivity component and an interfacial polarization phenomena (or MWS) in nanocellular PMMA based foams at low frequencies. MWS occurs in heterogeneous materials, such as blends or composites, at the interfaces, leading to a separation of charges ( Fig.…”

“…Furthermore, experimental results have confirmed the confinement of the polymer chains along the temperature domain (from À20 to 110 C), showing a great stability up to temperatures close to the glass transition temperature (T g ) of the solid material. Finally, some dynamic mechanical properties previously published of nanocellular materials as well as the dielectric spectrum of PMMA foams have been verified and confirmed [14,20]. Nowadays, the unexpected conductive mechanism found at low frequencies in nanocellular foams is not a problem for the implementation of nanocellular polymeric systems as low dielectric constant materials (since they have to work at high frequencies), but it has to be taken into account to study these systems in more detail and to develop new models to predict its complex behavior.…”

“…This reduction of Dε/Dε solid was previously observed only at room temperature [14] and is was related to a progressive decrease of the number of free dipoles able to rotate, i.e., it is related to the confinement effect of the solid phase in the nanocellular system. Therefore, this results proves that the modifications of the dielectric behavior of PMMA foams induced by the pore size are stable in the temperature domain; a relevant result from an applied point of view.…”

“…Therefore, according to the literature, these required cell sizes are merely the result of the dimensions of the devices and it is not expected a significant difference between the well-known dielectric behavior of conventional, or microcellular foams, and that of the recently developed nanocellular foams [13]. However, a preliminary work by the authors has showed the emergence of a Maxwell Wagner Sillars (MWS) phenomenon in PMMA-based nanocellular foams at room temperature [14].…”

“…Further research to analyze this unexpected behavior as a function of temperature and frequency could provide important information for the application of nanocellular foams in microelectronic devices [14], where thermal stability is critical and one of the main drawbacks of polymer-based materials [15]. Therefore, the aim of the present study was to investigate in detail the dielectric behavior of both micro and nanocellular foams as a function of frequency and temperature showing the main differences between the behaviors of the two type of materials when cell size is reduced to the nano-scale.…”