261
A surfactant was specifically designed by Loudet and Poulin (2002), suitable for
stabilizing silicone oil/LC nonaqueous emulsions, composed of PDMS and cyanobiphenyl groups. Depending on the size of the PDMS segment, silicone in LC emulsions or LC in silicone emulsions were stabilized. The materials obtained were not
optimal for electrooptical applications because of the poor mismatch between the
optical indexes of the LC and silicones used, but they were presented as an alternative for chemically bonding LC onto siloxane chain, and coatings, cosmetics or
thermal sensors applications were proposed.
Organic-inorganic LC materials containing siloxane moieties have also been
investigated. NPs (magnetic NPs, nanotubes, photo-isomerisable dyes) incorporated into LCE networks have been shown to increase their sensitivity to external
stimuli (i.e. electrical, electro-thermal, magnetic, optical, strain or stress). For
example, carbon black NPs integrated at surfaces can be used for electrothermal
heating of LCE systems (Chambers et al. 2009). Fujisawa et al. (2018) reported LC
gold complexes containing siloxane units in the flexible segment and phenylisocyanide complexing groups. These materials exhibited a special photoluminescence behavior in condensed phase, i.e. different luminescence colors were observed
depending on the aggregate structure due to the effect of intermolecular interactions, while said effect was not observed in the solution. LC-grafted silica NPs have
also been tested by Rachet et al. (2007) in photoinduced phase separation experiments to prepare PDLC with droplets of submicron size.
Micrometre-sized ‘artificial muscles’ are desirable for applications involving
surface-responsive materials, such as microfluidics, and present an alternative to
more classic responsive materials. The Zentel’s group reported a procedure for producing LCE actuator microparticles based on a microfluidic device (Ohm et al.
2011; Hessberger et al. 2018). To avoid the need for mechanical manipulation during curing conventional LCEs, another original method was proposed for the preparation of PDLC elastomers (Rešetič et al. 2016), which offers the advantage of
imprinting the thermal shape memory anisotropy by curing in external magnetic
field. The method is based on crushing the starting bulk LCE into microparticles,
dispersing these in uncured PDMS elastomer, aligning of LCE microparticles in a
magnetic field and subsequent thermal curing of the silicone matrix.
11.5 Functional Silicones as Surfactants
The colloidal phenomena associated with the silicon element have been observed
for a long time being considered a science in itself (Hauser 1955). In this context,
the ability of the polysiloxane-based materials for the formation of nano-aggregates
and their utility in practical applications have been extensively studied (Hill 1998,
1999, 2002; Schlachter and Feldmann-Krane 1998; Iwakiri et al. 2009).
Silicone surfactants are used for agricultural adjuvants, cosmetic formulations,
paint additives, PU foams, textile conditioning and (more recently) in nanotechnology and drug delivery systems. They are unique because of a series of
11 Reactive and Functional Silicones for Special Applications
A surfactant was specifically designed by Loudet and Poulin (2002), suitable for
stabilizing silicone oil/LC nonaqueous emulsions, composed of PDMS and cyanobiphenyl groups. Depending on the size of the PDMS segment, silicone in LC emulsions or LC in silicone emulsions were stabilized. The materials obtained were not
optimal for electrooptical applications because of the poor mismatch between the
optical indexes of the LC and silicones used, but they were presented as an alternative for chemically bonding LC onto siloxane chain, and coatings, cosmetics or
thermal sensors applications were proposed.
Organic-inorganic LC materials containing siloxane moieties have also been
investigated. NPs (magnetic NPs, nanotubes, photo-isomerisable dyes) incorporated into LCE networks have been shown to increase their sensitivity to external
stimuli (i.e. electrical, electro-thermal, magnetic, optical, strain or stress). For
example, carbon black NPs integrated at surfaces can be used for electrothermal
heating of LCE systems (Chambers et al. 2009). Fujisawa et al. (2018) reported LC
gold complexes containing siloxane units in the flexible segment and phenylisocyanide complexing groups. These materials exhibited a special photoluminescence behavior in condensed phase, i.e. different luminescence colors were observed
depending on the aggregate structure due to the effect of intermolecular interactions, while said effect was not observed in the solution. LC-grafted silica NPs have
also been tested by Rachet et al. (2007) in photoinduced phase separation experiments to prepare PDLC with droplets of submicron size.
Micrometre-sized ‘artificial muscles’ are desirable for applications involving
surface-responsive materials, such as microfluidics, and present an alternative to
more classic responsive materials. The Zentel’s group reported a procedure for producing LCE actuator microparticles based on a microfluidic device (Ohm et al.
2011; Hessberger et al. 2018). To avoid the need for mechanical manipulation during curing conventional LCEs, another original method was proposed for the preparation of PDLC elastomers (Rešetič et al. 2016), which offers the advantage of
imprinting the thermal shape memory anisotropy by curing in external magnetic
field. The method is based on crushing the starting bulk LCE into microparticles,
dispersing these in uncured PDMS elastomer, aligning of LCE microparticles in a
magnetic field and subsequent thermal curing of the silicone matrix.
11.5 Functional Silicones as Surfactants
The colloidal phenomena associated with the silicon element have been observed
for a long time being considered a science in itself (Hauser 1955). In this context,
the ability of the polysiloxane-based materials for the formation of nano-aggregates
and their utility in practical applications have been extensively studied (Hill 1998,
1999, 2002; Schlachter and Feldmann-Krane 1998; Iwakiri et al. 2009).
Silicone surfactants are used for agricultural adjuvants, cosmetic formulations,
paint additives, PU foams, textile conditioning and (more recently) in nanotechnology and drug delivery systems. They are unique because of a series of
11 Reactive and Functional Silicones for Special Applications