the contents are released in response to a stimulus such as mechanical damage,
temperature, pH, ionic strength, electric field, magnetic field, irradiation with
light, etc. The light as stimulant finds applications in the fields of intelligent
microstructures and microsystems, phase-change materials, self-healing composites, etc. The release of core by light irradiation has specific demand for application
in agricultural and cosmetic field. Although UV and visible lights are mostly
used, near-IR absorbing capsules are more suitable for applications in biological
systems.
LCPs are known to form efficient chain packing, which imparts excellent barrier
properties to the LCP film. This state can be changed reversibly by disturbing the
orientation to isotropic phase. Obviously, the result is the change of permeability of
the film. Thus, by incorporating photoresponsive groups as guest or as a part of the
polymer chain make it smart which can be controlled by clean energy. As an example,
azo-containing monomer is used, along with trifunctional cross-linker, to react with
diamine in interfacial polycondensation of an oil-in-water dispersion to make lightly
cross-linked main-chain LC polyamide microcapsules (Tylkowski et al. 2009). By
beaming UV light continuously on the microcapsules, the encapsulated β-carotene is
released quickly to reach maximum within 5 min. Poly(α-methylstilbenesebacoateco-α-methylstilbeneisophthalate), containing chloroform or chloroform/vanillin as a
filler, is sprayed on methanol so that precipitation of polymer occurs immediately to
form the microcapsule (Bogdanowicz et al. 2013). The condition of microcapsule
formation is maintained such that the polymer remained in trans-state. During
UV-irradiation, the roughness of the microcapsule decreases by about 24%. The
surface skewness, which describes the asymmetry of the height distribution, changes
from a negative value to a positive one during UV irradiation. The negative value
indicates a surface-porous sample, while the positive value indicates lack of surface
porosity and smoothening of the microcapsule surface (Raulio et al. 2008).
The smoothing of the surface is due to photoisomerization of α-methylstilbene
moieties. The moiety is in the E form with a molecular length of 9.1 Å and after UV
irradiation, they convert into Z isomers having length of 6.8 Å. This leads to
substantial modification and smoothing of film morphology, in response to the
contraction of the polymer main chain. The release of core liquid is accelerated to
large extent during irradiation of UV light.
After microencapsulation, nanoencapsulation approach has been initiated,
which enables producing particles with size in the nanoregion. Nanosizing of the
capsules results in a dramatically increased interfacial area with the surrounding
environment, which offers great advantages in pharmaceutics and material science
significantly by assisting in controlling the release kinetics. Along with more
efficient drug detoxification and intracellular uptake, the nanoparticles can be
biocompatible with tissue and cells when synthesized from biocompatible or
biodegradable materials. The UV-responsive nano-sized capsules, based on a
lightly cross-linked polyamide-containing azobenzene moieties in the main
chain, are prepared by oil-in-water miniemulsion interfacial polycondensation
(Marturano et al. 2015). The UV-responsive polyamide nanocapsules find applications in the encapsulation and release of photo protective agents that can protect
14 Photoactive Liquid Crystalline Polymers
413
temperature, pH, ionic strength, electric field, magnetic field, irradiation with
light, etc. The light as stimulant finds applications in the fields of intelligent
microstructures and microsystems, phase-change materials, self-healing composites, etc. The release of core by light irradiation has specific demand for application
in agricultural and cosmetic field. Although UV and visible lights are mostly
used, near-IR absorbing capsules are more suitable for applications in biological
systems.
LCPs are known to form efficient chain packing, which imparts excellent barrier
properties to the LCP film. This state can be changed reversibly by disturbing the
orientation to isotropic phase. Obviously, the result is the change of permeability of
the film. Thus, by incorporating photoresponsive groups as guest or as a part of the
polymer chain make it smart which can be controlled by clean energy. As an example,
azo-containing monomer is used, along with trifunctional cross-linker, to react with
diamine in interfacial polycondensation of an oil-in-water dispersion to make lightly
cross-linked main-chain LC polyamide microcapsules (Tylkowski et al. 2009). By
beaming UV light continuously on the microcapsules, the encapsulated β-carotene is
released quickly to reach maximum within 5 min. Poly(α-methylstilbenesebacoateco-α-methylstilbeneisophthalate), containing chloroform or chloroform/vanillin as a
filler, is sprayed on methanol so that precipitation of polymer occurs immediately to
form the microcapsule (Bogdanowicz et al. 2013). The condition of microcapsule
formation is maintained such that the polymer remained in trans-state. During
UV-irradiation, the roughness of the microcapsule decreases by about 24%. The
surface skewness, which describes the asymmetry of the height distribution, changes
from a negative value to a positive one during UV irradiation. The negative value
indicates a surface-porous sample, while the positive value indicates lack of surface
porosity and smoothening of the microcapsule surface (Raulio et al. 2008).
The smoothing of the surface is due to photoisomerization of α-methylstilbene
moieties. The moiety is in the E form with a molecular length of 9.1 Å and after UV
irradiation, they convert into Z isomers having length of 6.8 Å. This leads to
substantial modification and smoothing of film morphology, in response to the
contraction of the polymer main chain. The release of core liquid is accelerated to
large extent during irradiation of UV light.
After microencapsulation, nanoencapsulation approach has been initiated,
which enables producing particles with size in the nanoregion. Nanosizing of the
capsules results in a dramatically increased interfacial area with the surrounding
environment, which offers great advantages in pharmaceutics and material science
significantly by assisting in controlling the release kinetics. Along with more
efficient drug detoxification and intracellular uptake, the nanoparticles can be
biocompatible with tissue and cells when synthesized from biocompatible or
biodegradable materials. The UV-responsive nano-sized capsules, based on a
lightly cross-linked polyamide-containing azobenzene moieties in the main
chain, are prepared by oil-in-water miniemulsion interfacial polycondensation
(Marturano et al. 2015). The UV-responsive polyamide nanocapsules find applications in the encapsulation and release of photo protective agents that can protect
14 Photoactive Liquid Crystalline Polymers
413