272
Azo-modified silicones have also been intensively studied with respect to their
photoresponsive behavior for biology, solar energy conversion or plasmonic applications (Hurduc et al. 2013, 2014; Damian et al. 2014). These materials exhibit
surface relief grating (SRG) generation ability, as a consequence of athermal photofluidisation (Hurduc et al. 2014), a phenomenon based on the concept of conformational instability, thus explaining the sharp modification of the surface properties.
The proposed mechanism for the SRG formation follows three steps: (1) photofluidization of polymers in illuminated regions, (2) the mass displacement from
illuminated regions to dark regions and (3) the inverse mass displacement from dark
to illuminated regions.
Organosilicones are also interesting as solvent-free liquid electrolytes for lithium
batteries, being a promising alternative to commercial carbonyl-based electrolytes
due to their electrochemical and thermal stability, as well as their low flammability
and vapor pressure and relatively low viscosity (Zhang et al. 2008; Rossi and West
2009). The siloxane segment may contain functionalities capable of coordinating
lithium such as PEO moieties, and its highly flexible chain provides a complete
amorphous state of the polymer (Zhang et al. 2005). Recently, cyclic and linear
methylsiloxanes having carboxyl groups attached to each of the silicon atoms which
behave as thermally stable liquids over a wide temperature range have shown a
higher conductivity and dielectric permittivity compared to the original unmodified
compounds (Turcan-Trofin et al. 2019). Following Turcan-Trofin et al. (2019) these
increases were even more significant when the products were doped with lithium
salt, creating the premise for use as solvent-free liquid electrolytes for ionic batteries.
A photo-crosslinked polymer based on the siloxane backbone containing cyanide pendant groups showed an increased conductivity (up to 3.38 × 10
−5
S/cm)
attributed to the dissociation and increased mobility of the ion pairs, promoted by
the polarity and solvation power of the cyano group and the flexibility of the siloxane chain. This is of high potential as a solid electrolyte for Li batteries (Lee
et al. 2003).
Pyridyl-siloxanes have also been tested as phase transfer agents (PTAs), being
able to transfer hydro-soluble organic molecules from water into chloroform or
toluene. The proposed applications are cold-dying of polymers (e.g. transparent colored silicones were obtained) or the preparation of removable and reusable pH indicators (Racles et al. 2018).
11.9 Conclusions
The introduction of functional groups onto the silicon atom is continuously explored,
which generates an unlimited variety of structures, improves the already special
properties of silicones and adapts them to specific requirements. Several synthetic
pathways have been well established and used for a long time, such as hydrolysiscondensation of silane precursors, hydrosilylation and ROP of cyclosiloxanes.
Other methods have been less addressed but gained more recently attention, such as
C. Racles et al.
Azo-modified silicones have also been intensively studied with respect to their
photoresponsive behavior for biology, solar energy conversion or plasmonic applications (Hurduc et al. 2013, 2014; Damian et al. 2014). These materials exhibit
surface relief grating (SRG) generation ability, as a consequence of athermal photofluidisation (Hurduc et al. 2014), a phenomenon based on the concept of conformational instability, thus explaining the sharp modification of the surface properties.
The proposed mechanism for the SRG formation follows three steps: (1) photofluidization of polymers in illuminated regions, (2) the mass displacement from
illuminated regions to dark regions and (3) the inverse mass displacement from dark
to illuminated regions.
Organosilicones are also interesting as solvent-free liquid electrolytes for lithium
batteries, being a promising alternative to commercial carbonyl-based electrolytes
due to their electrochemical and thermal stability, as well as their low flammability
and vapor pressure and relatively low viscosity (Zhang et al. 2008; Rossi and West
2009). The siloxane segment may contain functionalities capable of coordinating
lithium such as PEO moieties, and its highly flexible chain provides a complete
amorphous state of the polymer (Zhang et al. 2005). Recently, cyclic and linear
methylsiloxanes having carboxyl groups attached to each of the silicon atoms which
behave as thermally stable liquids over a wide temperature range have shown a
higher conductivity and dielectric permittivity compared to the original unmodified
compounds (Turcan-Trofin et al. 2019). Following Turcan-Trofin et al. (2019) these
increases were even more significant when the products were doped with lithium
salt, creating the premise for use as solvent-free liquid electrolytes for ionic batteries.
A photo-crosslinked polymer based on the siloxane backbone containing cyanide pendant groups showed an increased conductivity (up to 3.38 × 10
−5
S/cm)
attributed to the dissociation and increased mobility of the ion pairs, promoted by
the polarity and solvation power of the cyano group and the flexibility of the siloxane chain. This is of high potential as a solid electrolyte for Li batteries (Lee
et al. 2003).
Pyridyl-siloxanes have also been tested as phase transfer agents (PTAs), being
able to transfer hydro-soluble organic molecules from water into chloroform or
toluene. The proposed applications are cold-dying of polymers (e.g. transparent colored silicones were obtained) or the preparation of removable and reusable pH indicators (Racles et al. 2018).
11.9 Conclusions
The introduction of functional groups onto the silicon atom is continuously explored,
which generates an unlimited variety of structures, improves the already special
properties of silicones and adapts them to specific requirements. Several synthetic
pathways have been well established and used for a long time, such as hydrolysiscondensation of silane precursors, hydrosilylation and ROP of cyclosiloxanes.
Other methods have been less addressed but gained more recently attention, such as
C. Racles et al.