Determination
of relative molecular mass of water soluble polymer by viscosity method
Abstract:
in the study of polymers, the relative molecular
mass is an indispensable important data Because it not only reflects the size
of polymer molecules, but also directly related to the physical properties of
polymers.
In the study of polymers, the relative
molecular mass is an important data. Because it not only reflects the size of
polymer molecules, but also directly related to the physical properties of
polymers. However, unlike ordinary inorganic or low molecular organic matter,
the polymer is a mixture of different molecular weight, so the relative
molecular mass is usually an average value. There are many methods to determine
the relative molecular weight of polymer. Compared with other methods, the
viscosity method is simple and convenient to operate.
The viscosity of polymer solution is
particularly large, because its molecular chain length is much larger than that
of the solvent molecule, and the solvent is added to make it more resistant to
friction.
In the flow of viscous liquid, it is
necessary to overcome the internal friction resistance and work. The size of
the coefficient of resistance available viscosity of viscous liquid in the flow
process (the viscosity) to express (kg M-1 S-1).
The viscosity of dilute polymer solution is
a reflection of the size of the internal friction force. The pure solvent
viscosity reflects the internal friction between the solvent molecules, denoted
ETA 0, polymer solution viscosity is high internal friction between the
molecules, polymer molecules and solvent molecules and internal friction
between three and 0. At the same temperature, usually ETA > ETA 0, relative
to the solvent, the viscosity of the solution increases the fraction called
viscosity, denoted as SP, i.e.
1）The ratio of the
viscosity of the solution and the pure solvent viscosity called relative
viscosity, denoted R, i.e.
2）The viscosity
behavior of ETA R is also reflected in the solution, and SP means has been
deducted from the solvent internal friction between the molecules effect only
reflects the polymer molecules and solvent molecules and polymer molecules
between the internal friction effect.
The polymer solution viscosity eta SP
tended to increase with increasing concentration of C. For comparison, the unit
concentration shows the specific viscosity of SP / C is called viscosity, R / C
and LN ETA is known as logarithmic viscosity. When the solution is diluted, the
polymer molecules are far apart from each other, and their interaction can be
ignored
3）[η] called intrinsic viscosity, it reflects the polymer molecules and
solvent molecules in dilute solution of infinite internal friction between the
size and shape, its value depends on the properties and polymer molecules of
solvent. Because R and SP are both ETA ETA dimensionless quantity, so their
unit is the reciprocal of concentration of C units.
In the dilute polymer solution is
sufficient, SP / C and C / C and LN R and C respectively conform to the
following formula:
4）
5）The two and the
Huggins and Kramer are the constants in the. This is the two linear equations,
the SP / C ETA on C or ln / C ETA r in C mapping, extrapolated to C=0 is the
intercept []. Obviously, for the same polymer, the two linear equations are
extrapolated to the same point, as shown in figure 1.
Figure 1: extrapolation method [η] Figure 2: viscometer
The relationship between intrinsic
viscosity and polymer molar mass of polymer solution, usually expressed with
two parameters of Mark - Houwink equation:
6) In
the formula 
means the average molecular
weight of viscosity, K is the proportionality constant, and alpha is an
empirical parameter related to the molecular shape. The value of K and alpha is
related to the temperature, the properties of the polymer and the solvent. The
value of K is affected by temperature obviously, alpha value mainly depends on
the polymer coils in a certain temperature, the degree of a stretch of solvent.
K and alpha can be determined by some absolute experimental methods (such as
membrane osmotic pressure, light scattering, etc.).
The
capillary tube method was used to determine the viscosity, and it was obtained
by measuring the time required for a certain volume of liquid to flow through a
capillary with a certain length and radius. Ubbelohde viscometer used in the
experiment as shown in figure 2. When the liquid passes through the capillary
under gravity, it follows Poiseuille's law:
7) Type
of eta (kg M-1 s-1) is the viscosity of the liquid; liquid density; capillary
length; capillary radius; outflow time; the average height of liquid column of
liquid flows through the capillary; for the acceleration of gravity; V is the
volume of liquid flows through the capillary; and the geometric shape of the
instrument is constant. When take m=1.
For a
specified viscometer, many parameters are specified, so that
,
.
So 7)
can be changed as
,
8) In
the Formula 
, when
,the equation on the right side of the second can be ignored. The
density of the solution
is approximately equal to the
solvent density
. In this way, the T and t0 of the solution and solvent can be
calculated
:
9) So
the only solution was determined and solvent in capillary outflow time can be
obtained by ηr.
Operation steps
1
cleaning equipment
The
viscometer with lotion, tap water and distilled water clean, pay special
attention to the capillary, rinse with ethanol, and then dried standby.
It takes
longer to dry the viscometer, especially for a long period of time. After
drying, the viscometer is placed in a constant temperature bath and is clamped
vertically with an iron clamp.
2
polyvinyl alcohol solution
Accurate
weighing about 1g solid polyvinyl alcohol, into the beaker, add 60mL distilled
water to dissolve, can be properly heated to accelerate the dissolution, to be
solid polyvinyl alcohol completely dissolved, the solution (solution after
cooling) into 100mL volumetric flask volume.
1.0111g
polyvinyl alcohol is said to be solid and dissolved in an electric furnace.
After the dissolution of polyvinyl alcohol 10min. Transferred to the capacity
of the bottle at 35 degrees Celsius under constant temperature and volume, the
volume of the solution was found to have some foam.
3
constant temperature
Open the
thermostat, set the temperature of 35 + 0.01. The viscometer (Figure 2) in the
thermostat temperature 10min (note that vertically). Pure water as well as samples
to be measured at 35 degrees C.
In
addition, the utility model can be conveniently placed in a constant
temperature water tank with a conical bottle filled with distilled water.
4
Determination of solvent outflow time t0
The
water is injected into the viscometer 20mL, and the temperature is measured
after 2 minutes. The method is as follows: the C tube is not ventilated. Wash
the ear with a ball at the upper end of the suction pipe B, the water from the
F ball by D ball, E ball, capillary pumped to G at 2/3; the clip on the release
of C tube, the ventilation, the D solution in the ball back into the F ball,
the capillary suspended above the liquid; the liquid falls above the capillary.
When the concave surface the lowest scale a flows through the line, immediately
press the stopwatch start time, stop time to B. Note the time required for the
liquid to flow through a, B. Repeated measurement three times, the deviation is
less than 0.3s, the average value is t0.
Distilled
water is taken from the 3 in the conical flask, to ensure that the liquid drops
when the liquid level does not bubble, the data recorded in 5.
5
Determination of time of solution outflow
Drying
viscometer, with the pipette has been a good solution in advance of 10mL, the A
tube into the viscometer, in 25 degrees of water temperature for about 2
minutes, the determination of the outflow time of three times, the average.
Pure
solution viscosity is very large, with the ear when the ball to slowly inhale
to rise to the surface of the G ball, otherwise the bubble will be a lot of.
6
Determination of the outflow time of different concentration solution
2, 3, 10
mL distilled water was added to the viscometer, and the T values of different
concentrations were measured by the above methods, respectively. After each
dilution, the liquid is mixed (2min) with an ear washing ball, and the E ball,
G ball and capillary part of the viscosity are repeatedly washed.
In
accordance with the steps in the operation 3-4 times after the solution is
roughly mixed. Data records see 5.
7
cleaning equipment
Turn off
the power supply, clean the viscometer 3 times, fill it with water. To ensure
that the viscometer is not used when it is clean, otherwise there is a foreign
body for a long time to clean up the impact of experimental results.
Matters
needing attention
1 the
use of black viscosity timing, in the same viscometer to determine a series of
concentrations into a simple proportional relationship between the outflow time
of the solution. In order to avoid the volume change caused by the temperature
change, the solution and the solvent should be removed at the same temperature.
2 every
time when adding solvent dilution solution, the viscometer must be mixed in the
liquid, but also to the solution to the E line above the ball two times, wash
capillary, otherwise the time of the solution is poor repeatability.
3 in the
use of organic matter as a solvent for the polymer, the polymer solution
contained a glass instrument, should be the first to use this solvent soaking
and washing to be washed and moist, dry polymer organic material such as
solvent, can be used to soak chromic acid, or organic materials are made of
chromium in pickling solution of potassium dichromate reduction, lotion will
fail.
4
viscometer must be clean, such as hanging on the capillary wall with water,
blowing dryer.
5
Determination of the viscometer to be placed vertically, otherwise affect the
accuracy of the results.
6 in
this experiment, the dilution of the solution is carried out directly in the
viscometer, so the solvent must be in constant temperature with the solution in
the same temperature tank, and then accurately measured with the pipette and
fully mixed can be measured.
Coyp right by @Hangzhou Zhongwang Technology CO.,LTD
.
Among them, η0, it’s the pure solvent viscosity. η is the viscosity of
solutions at the same temperature. ηr is a dimensionless quantity.
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