Download Figure 1 shows the photomicrograph images acquired for pure BP

Figure 1 shows the photomicrograph images acquired for pure BP and AuNRs doped BP samples. It
was observed that colored domains in pure BP were smaller in size and nucleated at lower
temperatures in comparison to the doped BP samples, while the temperature of the appearance of the
cholesteric phase were approximately the same. Figure 1 shows red colored domains in BPI of the
AuNRs doped BP samples, a sign of deformation of the cubic lattice, which is not observed in the pure
BP sample. The photomicrographs of Fig. 1 shows that colored domains gradually grew to fill in the
field of view as the temperature decreased in the AuNRs doped BPLC.
Figure 1. (a) TEM image of organo-thio monolayer protected AuNR in DCM. POM images of (b) pure
BP, and (c) 0.06% AuNR BP. The BP sample with 0.06% AuNR shows red domains indicating the
perturbation of BP cubic lattice by AnNRs. The dark bars in (b) and (c) are the 10 micron glass rod
spacers.
The temperature range of the BPLC can be estimated according to Meiboom’s defect model.2 Based on
the defect theory, the free energy of blue phase can be written as
(1)
where coefficient can be estimated from the latent heat of the cholesteric-isotropic phase transition.
From de Gennes’ book,16 we adopted the value of
; is the transition
temperature of the BP-isotropic phase transition, is the transition temperature of the BP-cholesteric
phase transition, is the interfacial tension, which is about
, is the radius of the
disclination core, and
is the radius of the double twist cylinders, and K is the typical elastic
constant of bend of the BP mixture (
). In general, the bend distortion energies at larger angles
prevent diameters greater than the length of a single twist. The blue phase would be stable when the
equation (1) becomes negative. Because
term is much smaller compared with other terms, for
simplicity we ignore this term. Thus, minimal free energy (F) can be obtained when
(2)
From a provided estimate,15 we can get the estimation of R in BP I,
(3)
where p is the pitch of the blue phase liquid crystal, HTP is the helix twisting power of the chiral dopant
(defined as a combination of the reciprocal pitch and concentration of each enantiomer concentration);
and C is the weight concentration of the chiral dopant. The practical use of this is that, roughly
speaking, adding more of a chiral dopant to an achiral nematic material will result in a more highly chiral
mixture. Substituting equation (3) into equation (2), we can get the estimation of BP temperature range,
(4)
Take a blue phase mixture BPLC-1 as an example, where
, then the
temperature range is around
. The theoretically predicted value validates the value of 12oC of the
pure BPLC. In the AuNRs doped samples, the BP phase range transition expands to 3.2C with 0.06%
AuNR doping. Further increase in AuNRs concentration counters the BP phase expansion. This
phenomenon may arise from saturation due to the amount of AuNRs that can fit in the defect regions,
thus destabilizing the defects.
Broadening of spectra peaks was noted as the increase in concentration of AuNR as shown in
Fig. 2. This may be attributed to the non-uniform distribution of AuNRs in the samples which causes a
large deformation of blue phase lattice.
Figure 2. Reflection spectra for pure BP (a) and 0.06% AuNR BP (b) showing a shift to longer
wavelengths as a function of the temperature. (c) A plot of peak wavelength as a function of
temperature for all concentrations of AuNRs doped BPs.
According to Gleeson and Cole,3 the rise and fall times can be expressed as equations (5) and (6),
respectively.
(5)
(6)
Here, Vc is the critical voltage to unwind the cholesteric pitches,
critical electric field (
cholesteric phase),
the BPLC.
1
is the rotational viscosity, Ec is the
, where p is the pitch and k is the twist elastic constant of the
o
is the dielectric permittivity at vacuum (~1) and
is the dielectric anisotropy of
Figure 3. The transmittance-voltage (TV) curve of pure BP (square) and 0.06% AuNR BP (circle)
device (a) the plot of the TV curve shows the 0.06% AuNR BP sample having a decrease in the
threshold voltage (Vth), (b) The plot of transmittance versus response time of BP (square) and 0.06%
AuNR BP (triangle), and (c) the POM images of BPLC cells of  pure BP samples and  0.06% AuNR
BP under applied voltages from 0V to 50 V at the same BP temperature (50C).
1. Reinitzer, F., Monatsh. Chem. 1988, 9, 421-441.
2. Johnson, P. L., Flack, J. H. and Crooker, P. P., Phys. Rev. Lett.1980, 45, 641-644.
3. Gleeson, H. F. and Coles, H. J., Liq. Cryst., 1989, 5, 917–926.
4. J. M. Wong, J.-Y. Hwang and L.C. Chien, To be submitted (2011).