Download - Viscosity measurement
Ubbelohde Viscometer, for measuring viscocity of dilute solution
upper and lower level
(measure the flow time t, of solution, drop from upper level to lower level)
= kt
k = viscometer constant = density of solution t = flow time
If, t = time for solution to = time for solvent
= o dilute solution o = solvent density
VISCOSITY MEASUREMENT
Dilute Solution Viscosity Designationsa
oorel t
t
1
relo
o
o
osp t
tt
CCrelsp
red
1
Crel
inh
ln
0)(][
CC inh
oc
sp
Relative viscosity Viscosity ratio
Specific viscosity -
Reduced viscosity Viscosity number
Inherent viscosity Logarithmic viscosity number
Intrinsic viscosity Limiting viscosity number
aConcentrations (most commonly expressed in grams per 100 mL of solvent) of about 0.5 g/dL
Common name IUPAC name Definition
All Dilute Solution Viscosity Designations can be obtained for dilute polymer solution using viscometer by measuring the flow time between the two level for dilute polymer solution and the solvent.
c co c1 c2 c3 c4 c5
t to t1 t2 t3 t4 t5
sp / c
{ln r}/ c
Huggins (a ) & Kramer (b) Equations
(a)sp / c = [] + k1 []2C
(b){ln r}/ c = [] + k2 []2 C
Graph,:
k1 + k2 = 1/2
[]
(a)
(b)
x
xx
x
x
xx
xxx
sp / c
or{ln r}/ c
C
Concentration C x 10-2 (g cm-3)
Intrinssic visscosity is the most useful of the variousViscosity designations because it can be related to molecular weight by the Mark-Houwink-Sakurada equation:
a
vMK
][
where ,vM
is the viscosity average molecular weight, defined as
a
ii
aii
vMN
MNM
/11
Log [ ŋ ] = log K + a log Mv
Log K and a are the intercept and slope, respectively, of a plot of log [] versus log Mv
Log [ ŋ ] = log K + a log Mv
Value of K between 0.001 – 0.5 and a between 0.5 – 0.8
…………. Mv can be calculated (approximation value)
Value of [ ŋ ] can be calculated using the following equation
Ŋsp / C
[ ŋ ] =
1 + kn Ŋsp
Measurement of [ ŋ ], just for estimation, can also be conducted from a value of one solution concentration using Schulz dan Blaschke Equation
For most of polymer solvent system, kn = 0.28
During measurement:
Viscometer: Vertical no dirt or suspension Temperature. Should be constant
Importance of Molecular Weight, why?
Properties of polymers are closely related to their molecular weight
Hard, soft, impact resistance, tensile strenght etc.