perpendicular to the substrate material. Complex structures can be formed when
liquid crystal melts are passed through the capillary filling. This leads to the
formation of splayed and twisted nematics. Figure 10 shows the scanning electron
microscope image of a fractured film of a chiral nematic liquid crystal acrylate
polymeric network showing the molecular orientation present therein.
When the desired structure is generated, the liquid crystal monomers are exposed
to light to initiate the polymerization process. Depending on the types of photoinitiators, the polymerization may proceed under UV or visible light source. For
liquid crystal acrylate polymerization, the free radical polymerization proceeds by
avoiding oxygen attack. Photopolymerization is, in general, a high-conversion
method, specifically when performed at the elevated temperatures. However, if the
curing process is pursued at room temperature, vitrification may proceed during
polymerization. This restricts the mobility of the monomers and further reaction is
hampered. In these cases, post-curing at or around glass transition temperature may
be helpful. In practice, curing at 120
C for 10 min after the UV exposure is sufficient
for the full polymerization process (Liu and Broer 2014). Figure 11 represents a
typical example of surface dynamics of patterned nematic networks.
Mostly all commercial LCPs contain p-hydroxybenzoic acid ( p-HBA) as a
monomeric unit in its structure. These LCPs are synthesized by condensation of
p-HBA with other monomers. A homopolymer composed of only p-HBA generates
liquid crystals of flowability below 500
C (Linstid et al. 2000). The processing
temperature can be reduced further by the addition of different monomers such as
bisphenols, terephthalic acid, isophthalic acid, hydroquinone, etc. As, for example, a
O
O
O
O
O
O
O
O
O
O
H CH 3
CH 3 H
= 180 nm
p
Fig. 10 Scanning electron microscope image of a fractured film, cross section of a chiral nematic
liquid crystal acrylate polymeric network. (Reprinted with permission from Liu and Broer 2014)
12
S. Banerjee and K. K. Kar
liquid crystal melts are passed through the capillary filling. This leads to the
formation of splayed and twisted nematics. Figure 10 shows the scanning electron
microscope image of a fractured film of a chiral nematic liquid crystal acrylate
polymeric network showing the molecular orientation present therein.
When the desired structure is generated, the liquid crystal monomers are exposed
to light to initiate the polymerization process. Depending on the types of photoinitiators, the polymerization may proceed under UV or visible light source. For
liquid crystal acrylate polymerization, the free radical polymerization proceeds by
avoiding oxygen attack. Photopolymerization is, in general, a high-conversion
method, specifically when performed at the elevated temperatures. However, if the
curing process is pursued at room temperature, vitrification may proceed during
polymerization. This restricts the mobility of the monomers and further reaction is
hampered. In these cases, post-curing at or around glass transition temperature may
be helpful. In practice, curing at 120
C for 10 min after the UV exposure is sufficient
for the full polymerization process (Liu and Broer 2014). Figure 11 represents a
typical example of surface dynamics of patterned nematic networks.
Mostly all commercial LCPs contain p-hydroxybenzoic acid ( p-HBA) as a
monomeric unit in its structure. These LCPs are synthesized by condensation of
p-HBA with other monomers. A homopolymer composed of only p-HBA generates
liquid crystals of flowability below 500
C (Linstid et al. 2000). The processing
temperature can be reduced further by the addition of different monomers such as
bisphenols, terephthalic acid, isophthalic acid, hydroquinone, etc. As, for example, a
O
O
O
O
O
O
O
O
O
O
H CH 3
CH 3 H
= 180 nm
p
Fig. 10 Scanning electron microscope image of a fractured film, cross section of a chiral nematic
liquid crystal acrylate polymeric network. (Reprinted with permission from Liu and Broer 2014)
12
S. Banerjee and K. K. Kar