Plate43.A TGBA*phase with relatively long pitch at planar anchoring conditions in the Grandjean orientation.The helix axis is parallel to the direction of light propagation and different colors are due to different twist states develop-ing during cooling.
Plate44.A short pitch TGBA*phase in Grandjean orientation due to planar an-choring conditions.Different twist states are observed on cooling with the helix axis perpendicular to the boundary plates and parallel to the di-rection of light propagation.
Plate45.TGBA*phase under planar anchoring conditions in a wedge cell preparation. The helical superstructure with twist axis parallel to the direction of light propagation can clearly be observed by the formation of Grandjean-like steps.(Courtesy of
W.Kuczynski.)
Plate46.Sample on cooling under homeotropic boundary conditions at the transition from N*(fingerprint texture at the right)to TGBA*(filament texture at the left).
Plate47.Sample on heating under homeotropic boundary conditions at the transition from SmA*(black pseudo-isotropic texture)to TGBA* (filament texture).
Plate48.Fingerprint texture of the TGBA*phase under homeotropic anchoring con-ditions.The pitch of the heli-cal superstructure can be es-timated from twice the dis-tance between adjacent dark lines,due to the identity peri-od of L P/2for the TGBA* helix.
Plate49.Fingerprint texture of the TGBA*phase subjected to homeotropic boundary conditions.(Reproduced by permission of T aylor&Francis, I.Dierking et al.,Liq.Cryst.,17, (1994),17h www.tandf.-co.uk/journals i.)
Plate50.Same sample area
as in Plate49at a slightly lower temperature.The TGBA*phase can be observed by its typical filament texture, while the pseudo-isotropic texture of the SmA*phase is seen as black areas,because here the optic axis is oriented along the direction of light propagation.(Reproduced by permission of T aylor&Francis, I.Dierking et al.,Liq.Cryst.,17, (1994),17h www.tandf.-co.uk/journals i.)
Plate51.Planar wedge cell
preparation of a N*ÀTGBA*ÀSmA*sample under a tem-perature gradient.In the right part of the photograph,at lower temperatures,the texture of the uniform planar SmA* phase can be brought into an extinction position.The TGBA*phase exhibits a texture with Grandjean steps and cannot be brought
to extinc-tion by rotation of the sample between crossed polarizers, due its helical superstructure. The cholesteric N*phase at higher temperatures can be seen at the top left of the photograph with an oily streaks texture.(Reproduced by per-mission of T aylor&Francis, I.Dierking,S.T.Lagerwall,Liq. Cryst.,26,(1999),83h uk/journals i.)
Plate52.Homeotropic
wedge cell preparation of the
same N*ÀTGBA*ÀSmA*
sample as depicted in Plate
51,also subjected to a tem-
perature gradient.In the right
part of the photograph the
pseudo-isotropic SmA*tex-
ture can be observed,which
appears black for all orienta-
tions of the sample between
crossed polarizers.The
TGBA*phase exhibits a typi-
cal filament texture at the
SmA*ÀTGBA*transition area
and a fan-like texture at
slightly higher temperatures.
At still higher temperatures a cholesteric fan-like texture is observed in the left top part of the photograph,which can clearly be distinguished from TGBA*by a change in birefringence. (Reproduced by permission of T aylor&Francis,I.Dierking,S.T.Lagerwall,Liq.Cryst.,26,(1999), 83h uk/journals i.)
Plate53.Droplet preparation
of the cholesteric phase,
which shows a fingerprint-like
texture at elevated tempera-
tures.The cholesteric helix
axis exhibits no preferred di-
rection in the substrate plane.
(Reproduced by permission of
T aylor&Francis,I.Dierking et
al.,Liq.Cryst.,17,(1994),17
h uk/
journals i.)
Plate54.Same droplet pre-
paration as Plate53at a
slightly lower temperature,
showing the TGBA*phase.
The smectic layers are or-
iented in concentric circles
with the TGBA*helix axis or-
iented along the smectic layer
plane.This leads to a radial
symmetric line pattern.(Re-
produced by permission of
T aylor&Francis,I.Dierking et
al.,Liq.Cryst.,17,(1994),17
h uk/
journals i.)
Plate55.Same droplet pre-
paration as Plates53and54
at still lower temperature in
the SmC*phase.The smectic
layers are still oriented in a
concentric fashion,but the
helix axis orientation is now
radially symmetric.This re-
sults in a concentric line pat-
tern,because the SmC*helix
lines are observed parallel to
the smectic layer plane.(Re-
produced by permission of
T aylor&Francis,I.Dierking et
al.,Liq.Cryst.,17,(1994),17
h uk/
journals i.)
Plate56.In thin cells with
planar boundary conditions,
the appearance of the helical
TGBA*phase can be sup-
pressed by surface induced
unwinding of the helical
superstructure.The texture
photograph shows the same
sample as Plates53À55with a
bulk phase sequence
N*ÀTGBA*ÀSmC*.In thin
cells with planar anchoring
conditions,the bulk TGBA*
phase is now observed as a narrow uniform planar SmA*phase(right),mediating the N*and the SmC*phase(left),which can be identified by the partial development of helix lines along the smectic layer planes. (Reproduced by permission of T aylor&Francis,I.Dierking,S.T.Lagerwall,Liq.Cryst.,26,(1999), 83h uk/journals i.)
Plate57.Square grid texture
of the TGBC#*phase under
planar boundary conditions.
The TGB helix is oriented
perpendicular to the bounding
subjectionparallel to the di-
rection of light propagation.
The square grid pattern is
presumed to be due to a heli-
cal director configuration
within the individual SmC*
blocks,with the helix axis
being in the plane of the sub-
strate and mutually perpen-
dicular in adjacent smectic
blocks.Another model of the
square grid texture is that of
the undulated twist grain
boundary C*phase. (Reproduced by permission of T aylor&Francis,I.Dierking,Liq.Cryst.,28,(2001),165h uk/journals i.)
Plate58.TGBC#*phase
(square grid texture at the
right)at the transition to the
common surface stabilized
SmC*phase(left),which ex-
hibits a ferroelectric domain
texture(see also Chapter7).
(Reproduced by permission of
T aylor&Francis,I.Dierking,
Liq.Cryst.,28,(2001),165
h uk/
journals i.)
*phase
Plate59.The TGBC
prepared in a wedge cell with
planar boundary conditions.
(Courtesy of S.K.Prasad.)The
twist grain boundary helix axis
is oriented perpendicular to
the substrate plates and thus
parallel to the direction of
light propagation,leading to
the observed Grandjean steps.
The additional square grid
pattern corresponds to a two
dimensional director modula-
tion in the plane of the sub-
strate.This is due to either a SmC*helix within local smectic blocks,exhibiting a helix axis that is perpendicular in adjacent slabs,or a director configuration as proposed for the UTGBC*phase.
Plate60.Growth of SmA(*)
bâtonnets(bright)from the
isotropic melt(black).Note
the pronounced growth ani-
sotropy.