Biomedical Engineering Reference
In-Depth Information
a polarization ei ciency up to 95.2%. h e resulting thin i lm showed good
adhesion strength to various substrates, superior surface hardness, better
thermal stability and good solvent resistance with respect to polarizing i lms
made from aqueous solution of the same system.
Tam-Chang
et al.
[53] designed molecules for the fabrication of broad
spectrum polarizing materials that were composed of a mixture of chro-
monic mesogens. h is approach employed multicomponent LC materials
which allowed the generation of anisotropic i lms that linearly polarized
light over large wavelength range and broadens their potential utility such
as display technologies.
9.2.2.2
Monolayer and Multilayer Deposition of Chromonic LCs
By using a combination of electrostatic layer-by-layer deposition and shear
orientation technique, plane oriented i lms (mono- and multi-) of chro-
monic materials were prepared in presence of polycations with a nano-
meter scale topography. h e approach relies on the coating of chromonic
N phase such as violet 20 (V20) onto the polycation layer supported on
a glass substrate through mechanical shearing. Excess liquid crystal was
then removed to give an oriented chromonic monolayer. It has been
demonstrated that orientationally ordered chromonic aggregates (par-
allel to the substrates) were preserved in the dried i lms by this method
(Figure 9.7), coni rmed through atomic force microscopy and X-ray pho-
toelectron spectroscopy [45]. Boiko
et al.
[62] demonstrated and prepared
thin chromonic i lms of ~1-10 nm with alternating monolayers of posi-
tively charged (Red 2316) and negatively charged (Red 2304) chromonic
LCs (Figure 9.8) by the electrostatic layer-by layer technique.
9.2.2.3
Micropatterned Anisotropic Chromonic Films
Tam-Chang
et al.
[46] developed a new approach to generate micropatterns
of anisotropic perylenebis(dicarboximide) in aqueous solutions using a
micropatterned template which exploits the self-organization and driven
by noncovalent interactions such as π-π stacking and hydrophobic inter-
actions. An isotropic solution of disc-shaped perylenebis(dicarboximide)
dye was introduced between a polydimethylsiloxane (PDMS) template
with regular line features (~9 μm wide, ~2 μm deep and ~11 μm apart)
and a cover glass, followed by slow evaporation of the solvent so that the
entire solution became completely LC and anisotropic. At er the sample
was dried, the PDMS template was peeled of leaving patterned solid onto
cover slip which can exhibit anisotropic optical properties and can serve as
micro-sized polarizers.
