Biomedical Engineering Reference
In-Depth Information
Figure 2.11
Speciicviscosityofalginatesolutionversusconcentration:thedotscorrespondtothe
experimentalvalues,thecurvetothepowerlaw(alginateKeltoneHV1%).Insert:valuesof[
η
]and
n
havebeendeterminedbytakingthelogarithmofrelation(3.8)andittingwithastraightline.
Keltone HV alginates, it has been found that [
η
]
sp
= (
c
[
η
])
4.1
and [
η
] = 450 mL/g
(Figure 2.11).
Using relations (2.17) and (2.19), the viscosity of the solution is given by
é
n
ù
(
[ ]
)
η η
=
1
+
a c
η
(2.23)
s
ê
ú
ë
û
2.2.2.4
ViscosityVariationwithTemperature
As a general rule, the viscosity of a polymeric liquid decreases with temperature.
The Vogel-Fulcher-Tamman-Hess (VFTH) hyperbolic relation is often used to de-
scribe the thermal dependency of the viscosity [11] (Figure 2.12) and writes
B
log
η
=
A
+
(2.24)
T T
-
0
where
A
and
B
are experimentally determined coefficients.
The VFTH law stems from the fact that the density of the polymeric solution
depends linearly on temperature and intermolecular distance. The VFTH relation
states that the logarithm of the viscosity depends on the intermolecular distance
d
as
B
¢
log
η
=
A
¢
+
(2.25)
d d
-
0
The change of viscosity with temperature of a polymeric liquid is such that it
is important to always check the temperature before performing experiments with
polymeric liquids.
