Chemistry Reference
In-Depth Information
0.60
Crystallization
Isotropic
transition
0.45
0.30
PMA(Az)
SmA-SmC
0.15
PEO
SmC-SmA
0.00
PMA(Az)
PEO
−
0.15
Melting
−
0.30
240
260
280
300 320
Temperature [K]
340
360
380
400
Fig. 17 DSC heating and cooling curves (heat flux in mW mg
1
vs temperature) for PEO
114
b
PMA(Az)
20
showing the high temperature isotropic transition
(Az)
n
generate at the interface between PEO and PMA(Az) moieties well-ordered
structures of one in the other, depending on their respective volume fractions
f
i
. The
ordered structures can be of three different types: spheres, cylinders, or lamellae, as
illustrated in Fig.
18
for an AB-type diblock copolymer [A and B standing,
respectively, for PEO and PMA(Az) components].
Obtaining a given molecular organization of these structures as regards their
type, size, and arrangement is directly controlled by the thermodynamic conditions,
i.e.,
p
,
T
, and the nature of the hydraulic fluid used to pressurize. To this end, the
isotropic transition of the diblock copolymer at which well-defined self-organized
nanoscale structures form is the main thermodynamic property to document.
In the series of PEO
m
-
b
-PMA(Az)
n
copolymers, PEO self-organized entities in
the form of highly ordered periodic hexagonal-packed PEO cylinders are formed in
the PMA domain by annealing at the isotropic state. This shows that controlling the
phase changes at the interface allows tailoring of the nanoscale structures, as
illustrated in Fig.
19
.
Scanning transitiometry has been used to evaluate the pressure dependence of
the isotropic transition temperature
T
tr
, as well as the transition enthalpy
D
H
tr
and
