Determination of
Molecular Weight of Polyacrylamide by Dilute Solution Viscosity Method
Abstract: To learn and master the Ubbelohde
viscometer viscosity measurement method; to understand the statistical
significance of the molecular average molecular weight and polymer dilute
solution of the intrinsic viscosity of the characterization method; master the
determination of polymer dilute solution viscosity experiment Technology and
viscosity method to characterize the molecular weight of polymer; the viscosity
of polyacrylamide aqueous solution to reflect the molecular weight of
polyacrylamide;
Experimental principle
Liquid flow is due to external force molecules irreversible displacement
process. Liquid molecules exist between the interaction force, so when the
polymer liquid flow, the polymer molecules to produce internal friction between
the performance of the liquid viscosity characteristics.
According to Newton's law of viscous flow, the viscous resistance of the liquid
to the flow is caused by the flow gradient between the two layers of flowing
liquid (with A) due to intermolecular friction.
In the
Ubbelohde viscometer capillary, it is assumed that the force that causes the
polymer dilute solution to flow is all used to overcome the internal friction
f:
For most flexible polymer - good dilute solution
solvent system, protraction
with c. Extrapolated intercepts coincide with the value of the point 
Instrument: Ubbelohde viscometer constant
temperature water bath, electronic scales, stopwatch, pipettes, flasks, ear
cleaning ball, glass sand funnel;
Reagents: polyacrylamide samples, sodium
chloride, purified water;
Experimental steps:
1. Solution preparation
2. Viscosity meter cleaning and drying
3. Viscometer installation: check the
viscometer, with a clamp carefully fixed viscometer, into the constant
temperature sink. The viscometer should be kept vertical, and the constant
temperature surface should be immersed in the two balls above the capillary and
the temperature remains constant.
4. Determine the elution time of the solution:
Remove the 10 ml solution from the self-volumetric flask and inject it from the
A tube into the viscometer. The clip holds the C tube and draws the solution
from the B tube to the top of the a The ball volume of half of the time until
the release of the ear ball, release the C tube clip, the air into the C tube,
immediately horizontally watching the decline in the liquid level with a
stopwatch recorded liquid flow through the a and b line time is Out of time.
5 ml, 5 ml, 10 ml and 10 ml of solvent were
added to the same solution for 2/3, 1/2, 1/3, 1/4 of the original solution, and
the respective elution times (t2, t3 , T4, t5).
Determination of pure solvent elution time: The
solution in the viscometer was poured out and washed several times with solvent
to determine the elution time t0 of the pure solvent.
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