Biomedical Engineering Reference
In-Depth Information
for the same polymer system. More approximately, they are also in accord
with those of Sato et al. [137] for a copolymer system of poly(vinyl octanal
acetal) and poly(vinyl alcohol). Most of these methods can indeed extract
viscoelastic moduli, i.e., storage and loss moduli. Most extensive in apply-
ing a full complement of various methods to span as wide a frequency
range as possible are the efforts by the Monroy-Rubio group, exemplified
by their efforts with poly(vinyl acetate) and poly(
p
-hydroxystyrene) in good
and poor solvent conditions, respectively. The oscillatory barrier method of
this group has undergone some refinement in the data analysis by Fourier
transform, and a review appeared recently [151]. A caveat is offered in the
examination of these efforts for viscoelastic properties of polymer monolay-
ers with respect to surface mass density. Once the monolayer collapse state
has set in as revealed by the surface pressure isotherm, different sorts of
non-linear behavior are observed. Such should not be included in the dis-
cussion of monolayer properties since the persistence of the monolayer state
is rarely proven or offered. Multilayers of polymer chains can scarcely be
construed as two-dimensional objects in light of difficulty for strict ther-
modynamic specification of monolayers to be two-dimensional as we stated
in the Introduction.
7
Conclusions
Insoluble polymer monolayers as confined to A/W have received significant
attention in the past few decades. While the initial driving force might have
been fabrication of Langmuir-Blodgett films, it has now been transformed
into a field of polymer dynamics in a reduced dimension, having its own sig-
nificance in fundamental science. This is further buttressed by the current
preoccupation with nanoscience and nanotechnology in the scientific com-
munity in the context of a monolayer being a primordial interface object of
nanometer thickness. Thus, a review of this sort dealing with the dynamics
of 2D objects affords a singular value in the contemporary milieu of science
and technology. In the foregoing, we summarized how the capillary wave dy-
namics of a polymer monolayer covered air/water interface are interpreted to
extract their viscoelastic characteristics. The process is to make use of the dis-
persion equation for the capillary wave propagation under the condition of
resonant mode coupling between the transverse and lateral dilational waves.
In the final analysis, we describe how elastic and loss components of the dila-
tional modulus are deduced, and their relative proportion depends intimately
on the chemical structure of monolayer constituents. Since the static struc-
ture of a monolayer as gleaned by the surface pressure isotherm is closely
related to the chemical structure of a chain unit, it is entirely predictable that
the dynamics probed by the capillary wave propagation should correspond
