251
immiscibility was reduced on a microscopic scale, and for 5 wt.% PEG-PDMS
block copolymer, the permittivity was increased up to 60% with low dielectric
losses and high dielectric breakdown strengths (~100 V/μm). Meanwhile, Risse
et al. (2012a) used cyanopropyl-functional silicone as a high permittivity filler and
as a plasticizer in mixtures with PDMS matrix. The dielectric permittivity increased
considerably, but the dielectric E BD decreased by 75% (~20 V/μm).
Fluorosilicones are also very interesting polymers to use in mixtures, which give
good results in some cases (Pelrine et al. 1998; Böse et al. 2012; Biggs et al. 2013).
For a trifluoropropyl-functional divinylpolydimethylsiloxane crosslinked into an
elastomer and mixed with 40 or 45 wt.% fluorinated silicone oil, the actuation
strains were higher by a factor of five, the dielectric permittivity values were around
5.4 and lower Y values were achieved (0.07 MPa) (Böse et al. 2012). Chloropropyl
dipole attached onto the main backbone or on crosslinking nodes, was also used in
silicone oil (commercially available as LMS-152) as additives for a commercial silicone elastomer (LR3043/50) (Madsen et al. 2015c, 2016b). For a 30 phr additive
content, a modest value of dielectric permittivity was obtained (4.4) with a decreasing loss tangent and a plasticizing effect (reducing the Y from 2 to 1.35 MPa). Even
if a high percentage of polar additive was used and the Y decreased, the dielectric
E BD values were higher (130 V/μm). In addition, this chloropropyl-based additive
provided a low dielectric loss when used in TiO 2 -filled silicone elastomer.
Racles et al. (2015a) recognized phase separation, when cyanopropyl-modified
polysiloxanes were used as a high ε’ component in mixtures or co-networks with
PDMS, resulting in negative effects on the final properties. As an alternative, the
same materials were mixed in polymer-polymer composites, where submicron particles were first obtained from the polar material with a specially designed siloxane
surfactant and then used as the disperse phase into PDMS matrix. The mechanical
properties were improved as a result of a more controlled sub-microscopic phase
separation. Asandulesa et al. (2018) reported an in-depth dielectric investigation of
these materials focused on interfacial phenomena in co-networks and mixtures with
a similar composition and a different morphology in terms of domain size and
nature of the interface.
Following the same strategy, Racles et al. (2017a) processed silicones with CN
or Cl-propyl groups as submicron particles, stabilized with a hydrophobic commercial surfactant and crosslinked, then the particles were mixed into a high Mw PDMS
matrix. These authors obtained E BD up to 63 V/μm, dielectric permittivity up to 4.7
at 10
4
Hz and soft elastomeric materials with low Y, which also showed an atypically high piezoelectric coefficient (d 33 ) at ambient temperature without poling.
Similarly, the polyazomethine (PAZ) submicron particles were obtained by Racles
et al. (2015b) via polycondensation reactions occurring in reverse micelles of an
amphiphilic siloxane oligomer, and then dispersed into a high Mw PDMS. The
dielectric and mechanical properties can thus be largely tuned depending on the
structure of the dispersed phase (containing or not siloxane units) and their
proportion.
The high dielectric constant of metal complexes of bis-azomethines containing
dimethyl siloxane segments makes them candidates to be considered as fillers for
11 Reactive and Functional Silicones for Special Applications
immiscibility was reduced on a microscopic scale, and for 5 wt.% PEG-PDMS
block copolymer, the permittivity was increased up to 60% with low dielectric
losses and high dielectric breakdown strengths (~100 V/μm). Meanwhile, Risse
et al. (2012a) used cyanopropyl-functional silicone as a high permittivity filler and
as a plasticizer in mixtures with PDMS matrix. The dielectric permittivity increased
considerably, but the dielectric E BD decreased by 75% (~20 V/μm).
Fluorosilicones are also very interesting polymers to use in mixtures, which give
good results in some cases (Pelrine et al. 1998; Böse et al. 2012; Biggs et al. 2013).
For a trifluoropropyl-functional divinylpolydimethylsiloxane crosslinked into an
elastomer and mixed with 40 or 45 wt.% fluorinated silicone oil, the actuation
strains were higher by a factor of five, the dielectric permittivity values were around
5.4 and lower Y values were achieved (0.07 MPa) (Böse et al. 2012). Chloropropyl
dipole attached onto the main backbone or on crosslinking nodes, was also used in
silicone oil (commercially available as LMS-152) as additives for a commercial silicone elastomer (LR3043/50) (Madsen et al. 2015c, 2016b). For a 30 phr additive
content, a modest value of dielectric permittivity was obtained (4.4) with a decreasing loss tangent and a plasticizing effect (reducing the Y from 2 to 1.35 MPa). Even
if a high percentage of polar additive was used and the Y decreased, the dielectric
E BD values were higher (130 V/μm). In addition, this chloropropyl-based additive
provided a low dielectric loss when used in TiO 2 -filled silicone elastomer.
Racles et al. (2015a) recognized phase separation, when cyanopropyl-modified
polysiloxanes were used as a high ε’ component in mixtures or co-networks with
PDMS, resulting in negative effects on the final properties. As an alternative, the
same materials were mixed in polymer-polymer composites, where submicron particles were first obtained from the polar material with a specially designed siloxane
surfactant and then used as the disperse phase into PDMS matrix. The mechanical
properties were improved as a result of a more controlled sub-microscopic phase
separation. Asandulesa et al. (2018) reported an in-depth dielectric investigation of
these materials focused on interfacial phenomena in co-networks and mixtures with
a similar composition and a different morphology in terms of domain size and
nature of the interface.
Following the same strategy, Racles et al. (2017a) processed silicones with CN
or Cl-propyl groups as submicron particles, stabilized with a hydrophobic commercial surfactant and crosslinked, then the particles were mixed into a high Mw PDMS
matrix. These authors obtained E BD up to 63 V/μm, dielectric permittivity up to 4.7
at 10
4
Hz and soft elastomeric materials with low Y, which also showed an atypically high piezoelectric coefficient (d 33 ) at ambient temperature without poling.
Similarly, the polyazomethine (PAZ) submicron particles were obtained by Racles
et al. (2015b) via polycondensation reactions occurring in reverse micelles of an
amphiphilic siloxane oligomer, and then dispersed into a high Mw PDMS. The
dielectric and mechanical properties can thus be largely tuned depending on the
structure of the dispersed phase (containing or not siloxane units) and their
proportion.
The high dielectric constant of metal complexes of bis-azomethines containing
dimethyl siloxane segments makes them candidates to be considered as fillers for
11 Reactive and Functional Silicones for Special Applications