Biomedical Engineering Reference
In-Depth Information
Fig. 21
∆
f
s,c
vs.
f
s
for PVP/PVAc mixed monolayers on water at 25
◦
C(72 mol % PVP by
successive addition). Values for different surface pressures and wave vectors have been av-
eraged and normalized to the conditions and limits of Fig. 4 with 1 standard deviation
error bars. Surface pressure increases counterclockwise around the contours
there is actually significant deviation even from this limit as the data actually
fall outside the contours. Here,
σ
d
, however, it
is clear this region corresponds to a collapsing film as lens formation occurs
during spreading, and the long stabilization times in this region would make
further study difficult.
A binary monolayer of another kind was examined by means of the me-
chanical relaxation technique in conjunction with SLS by Rivillon et al. [110].
The system was PVAc and poly(
p
-hydroxystyrene) (P4HS). They have studied
over a broad range of frequency (0.1 mHz-200 kHz) and finer composition
resolution. Their conclusion is somewhat the same as our example of the
PVP-PVAc system, but they can advance further details of the composition-
dependent relaxation modes, after having established that the P4HS mono-
layer is in a poor solvent condition with the same set of two techniques [111].
µ
may be significant, or
σ
=
s
5.1.3
Temperature Dependence
Although an accessible temperature range is restricted by complication of
subphase water evaporation, there have been some reports on temperature-
dependent investigations with homopolymers. Yoo and Yu [105] studied
PVAc and poly(
n
-butyl methacrylate)(P
n
BMA) as the prototype of good sol-
vent and poor solvent cases. Both were over a range of 15
◦
C, 10-25
◦
C
and 15-30
◦
C respectively, and PnBMA required the inclusion of
µ
assum-
