Lama, Giuseppe Cesare
(2017)
Shape Memory Polymers Charged with Modified Carbon-Based
Nanoparticles.
[Tesi di dottorato]
Collection description
In this thesis, shape memory nanocomposites were prepared and characterized. The
polymer matrix consisted in an epoxy-based liquid crystalline elastomer (LCE). Multi-walled
carbon nanotubes (MWCNT) and graphite nanoplatelets (GNP) were selected as fillers. The
influence of different contents of nanofillers on mechanical, thermal and shape memory
properties was evaluated.
In order to disperse and homogeneously distribute the nanofillers within the polymer
matrix an in-depth evaluation on the optimal conditions to synthesize the materials was
carried out. These conditions had a substantial influence on the final distribution of the
nanofillers within the epoxy-based matrix, which was analyzed from a macroscopic and
microscopic point of view. The best results were obtained through a chemical surface
modification of the nanoparticles.
The chemical modification of MWCNTs consisted in grafting the selected epoxy
monomers on the surface. The obtained adducts were characterized in terms of chemical,
thermal and morphological features.
Concerning GNP, a similar protocol based on surface modification was carried out. In
this case, a preliminary oxidation process was performed in order to promote the
exfoliation of graphene sheets, in form of graphene oxide (GO), and to favour their
dispersion within the polymer matrix. Different degrees of oxidation were attempted.
GO nanoparticles were successively modified with epoxy monomers. Also in this case,
chemical, morphological, structural and thermal characterization was carried out.
Surface modified carbonaceous nanoparticles were then dispersed in varying amounts
in the organic matrix. The obtained nanocomposite systems were characterized in their
chemical-physical and morphological properties. The adopted compatibilization strategies
used for both MWCNTs and GNP were found to be extremely effective to get homogeneous
samples and to enable a dramatic enhancement of the actuation extent at low nanofiller
content. Moreover, the stress threshold required to trigger the reversible
thermomechanical actuation was significantly decreased. The effect of nanoparticles on
thermomechanical properties of the materials was correlated to the microstructure and
the phase behavior of the host system. Results demonstrated that the incorporation of
carbon nanofillers amplified the soft-elastic response of the liquid crystalline phase to
external stimuli. Tunable thermomechanical properties of these systems make them
suitable for a variety of potential advanced applications ranging to robotics, sensing and
actuation, and artificial muscles.
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