Biomedical Engineering Reference
In-Depth Information
72 mol % PVP mixtures, there is a significant increase in
κ
around Limit II,
0.38 nm
2
monomer
-1
,
0.2 mN m
-1
,
6 mN m
-1
and
when
<A>
≈
Π
≈
ε
d
≈
κ
·
10
5
6 mN s m
-1
. Additionally, the maximum damping coefficient seems to
be depressed which is consistent with an increase in
≈
κ
. Another differ-
ence is the decrease in
Π
at the maximum damping coefficient at Limit III:
Π
PVAc
>
= 4.8, 4.3, 1.5
and 0.35 mN m
-1
.ThisissimilartothetrendobservedforPVAc,PEOand
PtBMA, again suggesting poorer hydrodynamic coupling between the mono-
layer and liquid motion. Finally, there is a dramatic change in the collapse
behavior of these films. As mol% of PVP increases, the collapse behavior
changes from that of pure PVAc, where the maximum elasticity roughly cor-
responds to Limit IV, the minimum velocity of a perfectly elastic surface, and
collapse proceeds back along a path slightly more viscous than a perfectly
elastic film to lower elasticity values (Fig. 18D). Rather than collapsing back
to lower elasticities, the higher PVP content films proceed onto the infinite
lateral modulus, Limit V, forming an essentially infinitely rigid film. This is
attributable to the enhanced lateral interactions of the packed hydrophobic
side chains which lead to higher film viscosities. For the case of 72 mol % PVP,
Π
27%PVP
>
Π
55%PVP
>
Π
72%PVP
, corresponding to
Π
f
s,c
vs.
f
s
for PVP/PVAc mixed monolayers on water at 25
◦
C(27 mol % PVP).
Values for different surface pressures and wave vectors have been normalized and aver-
aged to the conditions and limits of Fig. 4 with one standard deviation error bars. Surface
pressure increases counterclockwise around the contours. Departure from pure liquid dy-
namics occurs at
<A>
is less than around 0.6 nm
2
monomer
-1
,and
Π >
0.6 mN m
-1
.
The mixture approaches Limit II(A,
Fig. 20
∆
10
5
)
≈
0.36 nm
2
monomer
-1
, 2 mN m
-1
,
Π
,
ε
d
,
κ
·
7 mN m
-1
, 2 mN s m
-1
, Limit III(A,
10
5
)
0.27 nm
2
monomer
-1
, 4.3 mN m
-1
,
Π
,
ε
d
,
κ
≈
13 mN m
-1
, 2 mN s m
-1
,andLimitIV(
A<
,
Π >
)
≈
0.17 nm
2
monomer
-1
, 13 mN m
-1
of
a perfectly elastic surface film
