One-point method measuring viscosity by using Ubbelohde Viscometer

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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