Biomedical Engineering Reference
In-Depth Information
Fig. 28
Π
-
Γ
isotherms (
a
)and
ε
-
Γ
for sample II on the air/water interface at various
temperatures; 7
◦
C(
), 23
◦
C, (
)and32
◦
C(
Γ
∗
•
).
stands for the same as in Fig. 29
A qualitative interpretation of this contrasting behavior is offered as follows.
Unlike with sample I where PEO blocks in both ends of PPO are conforma-
tionally free to respond to temperature changes here the PEO block in the
middle is conformationally pinned by PPO blocks at both ends by the nature
of segment connectivity, PPO-PEO-PPO.
We come to the dynamics of these polymer monolayers. At the risk of
repetition,wenoteagainthatthepolarplothasauniquefeaturerelativeto
resolution. As the surface viscoelasticity increases, the spacing between grids
decreases, resulting in broadening of imprecision for the viscoelastic param-
eters. Thus, clear specifications of viscoelastic parameters are hard to come
by when
10
-4
mN s m
-1
, respectively.
Pluronics copolymers under study here pose an intriguing question by virtue
of their architectural difference in the hydrophilic EO versus hydrophobic PO
moieties. Sample I (with PEO-PPO-PEO) has a greater amount of hydrophilic
PEO blocks which conformationally have greater freedom than that in sample
exceed 20 mN m
-1
ε
d
and
κ
and 3
×
