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.