Biomedical Engineering Reference
In-Depth Information
ing that
did not depend on wave vector
k
,whereassuchwasnot
thecasewithPVAc.ThetransverseviscosityofPnBMAshowedananoma-
lous temperature dependence, and was interpreted in terms of the relaxation
model of Mann and Du [112]. On the other hand, Rubio's group have ex-
amined the temperature dependence over 1-25
◦
Cwithfourdifferenttech-
niques [113, 114] including SLS. They found a transition temperature from
a soft solid-like state at low temperature to a fluid state that is commonly
observed.
ε
d
and
κ
5.2
Copolymers
5.2.1
Alternating Copolymers
We now turn to an intriguing alternating copolymer system [115]. It is the
system of poly(1-alkylene-co-maleic acid), thus having the same hydrophilic
head group while varying the length of hydrophobic side chain, from
n
-butyl
to
n
-hexadecyl. The polymer system is designated as PXcMA, where X varies
from 1-hexylene to 1-octadecylene. Thus, the side chain R varies from the
n
-butyl to
n
-hexadecyl group with 4
≤
m
≤
16. It is synthesized by copoly-
merization of
-olefin with maleic anhydride, and subsequently hydrolyzed
to a maleic acid moiety in the chain, constituting the hydrophilic component.
We present the results for four polymers: they are (1)
m
=4,thestarting
α
α
-
olefin is 1-hexene, hence designated as PHcMA, (2)
m
=6,
α
-olefin=1-octene,
POcMA, (3)
m
=8,
-olefin = 1-
octadecene, PODcMA. The central focus here is to probe how the side chain
length R influences the viscoelastic characteristics of the monolayers of these
polymers.
As in the earlier section, we briefly present the static properties first. The
results obtained with pH 2 water (with 10 mM HCl) as the subphase are
displayed in Fig. 22, where
α
-olefin = 1-decene, PDcMA, and (4)
m
= 16,
α
ε
s
-
A
isotherms for all four polymer
monolayers are plotted together in each. With the exception of PHcMA, the
Π
Π
-
A
and
-
A
isotherms of the polymer monolayers are nearly identical and they are
consistent with the expected isotherms of condensed films. Each isotherm is
shown in two regions: the dilute regime where
1 mN m
-1
Π
≤
(open sym-
