Engineered polymeric com posites for flexible electronics [619680]

Engineered polymeric com posites for flexible electronics
Problems
The development of electrical composites is motivated by the need of new properties, not
available in single -phase materials. Their design needs a deep understanding of the ways in which
composite properties depend upon the component properties, composition and composite
micro/nanostructure (phase interconnectivity, filler size & shape). Metallic particles (MPs) – based
nanostructures are currently of high interest for a broad range of app lications, because of their
remarkable electric, magnetic, optical an d catalytic properties . The combination of conductive particles
with magnetic and/or plasmonic components or with multifunctional character ( e.g. ferro, piezo,
pyroelectric) with a polyme r matrix may induce new electromagnetic properties, with potential use in
light-weight flexible electronic components as supercapacitors, sensors, memo ries, electromagnetic
shielding. In relation to these needs, there are multiple possible material and str ucture combinations to
be explored. For example, dielectrics acquire a field -induced polarisation generated by dipole or
bounded charges re -distribution, while isolated metallic particles embedded into a dielectric matrix, also
polarize under electric fiel ds, by the confined displacement of their free electrons. In metal -dielectric
composites (MDCs), the properties are dominated by the dielectric matrix at low filler concentration.
When increasing the metallic addition, local clustering of fillers takes pla ce and permittivity increases
by the formation of a large number of local micro/nanocapacitors. At a critical concentration
(percolation threshold), the pattern of conductive particles creates a network of conductive channels and
a sharp increase of permit tivity with few orders in magnitude (giant permittivity) can be achieved. The
percolation threshold is dependent on the geometry, shape, size, and distributi on of the conducting
fillers . Metal -polymer composites ( MPolCs ) are studied for static or electroma gnetic interference
shielding, supercapacitors and sensors/actuators . Mostly the dependence of the effective conductivity
and permittivity on filler concentration was reported to date, while the role of filler size and /or shape
was less investigated. As matrices, various polymers were employed, according to their flexibility, their
dielectric response and glass transition tem perature: epoxies, polystyrene or polyvinylidene fluoride
(PVDF). Among them, PVDF has the advantage of high permittivity (above 10) due to its ferroelectric
character . Although the polarization of metallic fillers contribute to the enhancement of permittivity
towards giant values near the percolation threshold, the risk of percolation and high loss should be
considered for practical a pplications. Therefore, a strict control of the phase assemblage to ensure the
full isolation of the metallic particles (e.g. 0 -3 connectivity) is necessary. This aim can be accomplished
by us ing the core -shell approach , in which the metallic particle is f ully coated by a thin dielectric layer
and then dispersed into the dielectric matrix. The present project will use as fillers Ag@dielectric oxide
core-shell fillers (e.g. Ag@TiO 2 or Ag@BaTiO 3) embedded into fl exible polymer, as PVDF . We
propose here a novel approach in order to control and exploit the sub -percolative region for increasing
permittivity to giant values: Ag particles (cores) fully isolated by a dielectric oxide shell prepared in the
powder state will be embedded into a polymer matrix, close belo w to the percolation limit. B eside the
giant permittivity, one interesting aspect far less investigated in MDCs, represents the field
concentration in the dielectric regions adjacent to the metal -dielectric interfaces, as demonstrated by
calculations wi th finite element method (FEM) . The FEM prediction of tunability increase in polar
dielectrics by adding metallic NPs was confirmed by our group for Au NPs -chitosan composites . Such
effects are only scarcely reported and this idea deserves a further attention , since it may be exploited in
devices, if suitable combinations of materials and phase assemblage are appropriate engineered. The
project is aimed to produce innovative core -shell metallic -based composites with sub -percolative
compositions in flexible matrices, to understand the role of composition, microstructure, nature and
properties of the components and of the interfaces on their functional properties (dielectric,
ferro electric , dc-tunability) .

Objectives
The main goal of the project is to produce sub -percolative innovative polymer based composites, to
understand the role of composition, microstructure, nature, and properties of the components and of the
interfaces on their electrical properties and to describe them by realistic model s. The specific objectives

are: OI: Synthesis and micro/nanostructural characterization of polymer -based composites. Ag
particles will be coated with TiO 2 and with BaTiO 3 by a combined wet/solid state method from
Ag@TiO 2@BaCO 3. The process will be optimised in order to ensure homogeneous coating, accurate
control of size, shape and crystallinity of the oxide shell. OII: Study of the functional properties of
polymer -based composites with different filler content. The role of hig h conductive filler (Ag) and
of the dielectric shell in the polymer matrix on the functional properties (frequency dependence and high
field non -linear properties ) will be investigated and the o ptimum structures will be proposed for possible
applications.

Methodology
Task I. Synthesis by Ag @ dielectric oxide (TiO 2 and/or BaTiO 3) core -shell structures . The effect
of processing parameters (time, pH, supersaturation) on the morphology, particle size, coating, mixing,
should be optimized such as the final aim being to produce good quality powders with metallic -oxide
core-shell structures.
Task II . Preparation of flexible composites using selected Ag particles, Ag@TiO 2 and/or
Ag@BaTiO 3 core-shell particles embedded into polymer matrix . PVDF -based c omposites will be
produced from solution and/or by thermal casting in order to result in various microstructures to be
compared .
Task III . Structural, n anoscale and mesoscopic characterization of polymer -based composites
(XRD, SEM/EDX, TEM). Phase purity, structural parameters, particle & grain size d istributions in
powders , the characteristics of interfaces and filler dispersion within the matrices will be determined as
a basis for understanding the functional properties and for building realistic models. Samples with the
same compositions and micro/nanostructural differences will be comparatively investigated to discl ose
the role of microstructures on the functional properties.
Task IV. Complex functional characterization of polymer -based composites will be performed by
broadband impedance spectroscopy analysis from 1Hz -1 GHz , in order to find the role of composition
around the percolation limit, of particle/grain size, phase assemblage and other micro/nanostructural
parameters on the effective electrical properties of composites. The role of high conductive filler (Ag)
and of the dielectric shell (TiO 2, BaTiO 3) in th e polymer matrix on the high field non -linear properties
will be checked (non -linear dielectric character: tunability (E), ferroelectric P(E), FORC) and
pyroelectric characteristics. Optimum structures possible interesting for enhanced non -linear character
in polymer -based flexible composites will be selected.

Collaboration with the research group
The project requires multidisciplinary expert ise in fundamental and A pplied Physics and
Chemistry, in the complex micro – and macroscopic characterization and in multiscale modeling. For
choosing the more suitable composition and microstructures for composites I will collaborated with my
colleague dr. Leontin Padurariu that will simulate different microstructures and will calculate the
functional properties of composites using 3D FEM modeles. For preparation part , Task I&II – I will
used my international collaboration with our partner ICMATE -CNR, Genoa (dr. V. Buscaglia). With
this group, I collaborated since 2008, when I learned the coating of particles by c ore-shell approach.
Task III – will be achieved together with dr. Cristina Ciomaga, e xpert in XRD and SEM characterisation.
Contribution of the program
The budget will be used for acquisition of consumable materials necessary for preparations
tasks, consumable for some equipments , one research stage at ICMATE -CNR for preparation task and
some salary expenses. If the obtained results will be accepted to publication in a high impact factor
journal open access will be pay for increase their visibility.