One-point method measuring viscosity
by using Ubbelohde Viscometer
Experiment details:
A flask of 10ml, pipet two or high precision
pipetting devices, a Ubbelohde viscometer (capillary diameter are obtained
according to the choice of solvent), a thermostat (temperature control accuracy
is better than 0.1 DEG C), a two stopwatch, a rubber tube, a syringe, a sucking
ball.
Steps:
1，Solution: take a certain amount
of polymer, add 10mm solvent, make it dissolve completely, heating if
necessary.
2，Constant temperature: installed device, stable temperature,
fluctuation no more than 0.1 degrees centigrade.
3，Add solution
balance 5min, suck capillary three times.
4，Determination of
solvent flow time t0: measuring three sets of data, so that deviation is less
than 0.2s.
5，Take out the
pipette, absorb the solution 10ml which has been pre isothermal, and inject it
into the viscometer. With the same method, install the viscometer and measure
the flow time of the solution t.
Data processing
Relative viscosity ηr=t/t0(t represent the flow time of solution, t0 represent solvent
time)
Specific viscosity ηsp＝ηr－1
Intrinsic viscosity [η]=【2( ηsp-ηr)】/C(C represent concentration units g/ml)
[η] = (ηSP/C)c=0 = (ln ηr/ C)c=0 [η]=KMα
Ubbelohde viscometer
viscosity test principle and matters needing attention
When the fluid is flowing by external forces,
there is a tangential internal friction between the flowing liquid layers, and
if the liquid is to pass through the tube, a portion of the work must be
consumed to overcome the resistance of the flow. When the flow rate is low, the
liquid in the pipe is advanced in a straight line parallel to the pipe wall.
The liquid closest to the pipe wall is actually stationary, and the distance
from the wall is farther and the speed of flow becomes larger. The tangential force f between the flow layers is
proportional to the contact area A between the two layers and the velocity
difference Δv, which is inversely proportional to the distance Δx between the
two layers: where η is the proportional coefficient, called the viscosity
coefficient of the liquid, Referred to as viscosity.
The molar mass of the polymer not only reflects the size of the
polymer molecule, but also directly related to its physical properties, is an
important basic parameter. Unlike conventional inorganic or low molecular organic
compounds, polymers are mostly macromolecules with different molar masses.
Therefore, the molar mass of polymers is usually a statistical average.
There are many ways to determine the mass of high
moles, and the average molar mass of the different methods is different. In
comparison, the viscosity method is simple, easy to operate, and has a good
experimental accuracy, is one of the commonly used methods. The molar mass
obtained by this method becomes the viscosity average molar mass.
Common Viscosity Symbols, Name and Physical
Meaning：
η0：The viscosity of the pure
solvent, and the internal friction between the solvent molecule and the solvent
molecule.
η ：The
viscosity of the solution, the interaction between the solvent molecule and the
solvent molecule, between the polymer and the polymer, and between the polymer
and the solvent molecule.
ηr ：Relative viscosity，ηr=η/η0，The relative
value of solution viscosity versus solvent viscosity.
ηsp：Increased viscosity，ηsp= (η-η0) / η0 = (η / η0)-1 = ηr -1,Reflecting the
polymer and polymer, pure solvent and polymer between the internal friction
effect.ηsp/C：Viscosity
expressed at a unit concentration.
[η] ：Intrinsic viscosity
reflects the internal friction between polymers and solvent molecules.
The definition of intrinsic viscosity of polymers [η]=lim ηsp/c 【c->0】。It is the use of Ln (ETA sp/c) in C
mapping，The extrapolated value of the line is
characteristic viscosity [η]，as
dl/g. ηsp as specific viscosity，c as the concentration of polymer solution，as
g/ml. specific viscosity ηsp=（η-η0）/η =（t-t0）/t0 。In the foruma，η、η0 Viscosity of
polymer solution and pure solvent, respectively；t、t0 The concentration of polymer solution and the outflow time of
pure solvent measured by viscometer. Respectively,
with the viscosity of the polymer solution concentration and pure solvent out
of the time, the unit is s. In the analysis test, the sample was dissolved in a
specific solvent and formulated into a concentration of polymer solution. Keep
the body temperature, with the viscometer were measured pure solvent and
solution out of time, you can get the ratio of viscosity and relative
viscosity.
The intrinsic viscosity of the ηsp / c = [η] + k '[η] ^ 2 * c can be
calculated by the Hagans equation. Where k 'is the Harkins constant. In
addition, the intrinsic viscosity can be determined by the measured relative
viscosity ηr, which is calculated as [η] = F / M, where
m is the mass of the polyester sample to be weighed. For the convenience of
calculation, the corresponding relative viscosity ηr corresponding to the F
value list, through the look-up table can be different ηr value corresponding
to the F value. The intrinsic viscosity is related to the mass of the polymer
molecule. The relationship is: [η] = K * M. The molecular weight of the polymer
can be calculated from the intrinsic viscosity. Among them, K and a are the
characteristic indices of a polymer solute system at a certain temperature, and
they depend on the form of the polymer in the form of the radical, which is a
reflection of the intermolecular interaction between the polymer chains. K and
a values need to be determined experimentally.
Viscosity
measurement considerations
1. Temperature of the measured liquid: Many users ignore this point, that the
temperature difference does not matter, our experiments show that: when the
temperature deviation of 0.5 ℃, some liquid viscosity value of more than 5%
deviation, the temperature deviation on the viscosity of a great temperature
Increased, viscosity decreased. So pay special attention to the measured liquid
temperature is constant in the vicinity of the specified temperature, the
precise measurement can not exceed 0.1 ℃, it is best not to exceed 0.05 ℃.
2. Capillary
Umbrella Viscometer cleaning degree: U wall Viscometer before and after each
experiment must be thoroughly cleaned and dried to ensure that the viscosity of
the process of Wu's viscometer clean.
3.
Dissolution of the sample: The solution sample used for the viscosity determination
test must be completely dissolved without fine particles.
4. Viscosity of the experimental staff of the
operating practices: the process of the Uptel viscometer must be kept upright,
the solution or pure solvent into the Uygur viscometer Note that the product cannot
bubble, the process of constant temperature tank within the constant
temperature medium (usually water) Must be higher than the U-Viscometer
measurement of the ball and so on.
U-viscometer use precautions
1. When using a U-viscometer, the elution time of a
series of solutions with a simple proportional ratio is determined within the
same viscometer. The volume of the liquid drawn and added is accurate. In order
to avoid changes in the volume caused by temperature changes, the solution and
solvent should be removed at the same temperature.
2. Each time the
solvent dilution solution is added, the liquid in the viscometer must be mixed
evenly, and the solution should be sucked into the ball above the E line twice,
and the capillary is rinsed. Otherwise, the repeatability of the solution is
out of time.
3. When using
organic substances as the solvent of the polymer, the glass instrument
containing the polymer solution should be soaked and rinsed with this solvent,
and the organic matter such as the solvent is allowed to be washed away.
Chromic acid wash solution to soak, or organic matter will chromate lotion in
the reduction of potassium dichromate, lotion will fail.
4. Viscometer
must be clean, such as capillary wall hanging water droplets, need to use a
hair dryer to dry.
5. The viscometer
should be placed vertically, otherwise it will affect the accuracy of the
results.
6. The dilution of
the solution in this experiment is carried out directly in the viscometer.
Therefore, the solvent used must be constant in the same bath as the solution,
and then measured with the pipette accurately and thoroughly mixed.
Kent Yuan (Mr.)
Hangzhou Zhongwang Technology Co., LTD. |
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Coyp right by @Hangzhou Zhongwang Technology CO.,LTD
with c. Extrapolated intercepts coincide with the value of the point 
