I prepared a certain concentration of the polymer and I want to know its molecular weight from its viscosity.
Thanks.
You need to specify the type of viscosity that your referred to. If you referred to intrinsic viscosity, then you can use the Mark Houwink equation. From the Mark-Houwink equation the relationship among the molecular weight and viscosity are given below:
[Ƞ] = KMα
Where Ƞ is the intrinsic viscosity , M is Molecular weight, K and α are constants for a particular polymer solvent system.
Dear Mohamed, there are some group contribution methods to predict the viscosity of polymers based on their structure. You might find some approaches in "The Properties of Gases and Liquids". If you have some measured results an interpolation of ln(viscosity) = c * Molecular Weight gives reasonable results.
You need to specify the type of viscosity that your referred to. If you referred to intrinsic viscosity, then you can use the Mark Houwink equation. From the Mark-Houwink equation the relationship among the molecular weight and viscosity are given below:
[Ƞ] = KMα
Where Ƞ is the intrinsic viscosity , M is Molecular weight, K and α are constants for a particular polymer solvent system.
Please have a look at the following introductory text: http://www.agilent.com/cs/library/primers/public/5990-7196EN.pdf
Hi Mohamed, Norazwani's answer is accurate, and I just want to add that if you're working with dilute solutions, you can use one set of Kappa and alpha values, but if you are working with a polymer melt, you will have a different k and a value. Normally you'd get three different samples of a polymer type with different MW's and measure their viscosity (either zero shear for a melt, or intrinsic for a solution) and plot log viscosity vs Log MW and that will give you a straight line with the gradient being "a" and the intercept being K. The preliminary MW's would be from a GPC measurement.
Dear sir,
You need to specify the type of viscosity that your referred to. If you referred to intrinsic viscosity, then you can use the Mark Houwink equation. From the Mark-Houwink equation the relationship among the molecular weight and viscosity are given below:
[Ƞ] = KMα
Where Ƞ is the intrinsic viscosity , M is Molecular weight, K and α are constants for a particular polymer solvent system.
Hello Mohamed Esmat I want to know how you calculated the molecular weight of the polymer? please answer me .. i have polymer and i want to calculate the Mw of it .
Dear Norazwani Muhammad Zain I have determined the intrinsic viscosity by the cupriethylendiamine method. From Henriksson et al. (2008) the relation between degree of polymerization (DP) and molecular weight is given by:
η = 0.42 DP for DP < 950 and η = 2.28 DP^0.76 for DP > 950
At this point I still don't know the DP of my polymer, reason why I don't know how to proceed with the calculation.
By applying the Mark-Houwink equation, [η] = KMα, I'm not aware of the K and α values for my polymer solvent system... How can I get these constants values?
I have the same problem measuring the Mw of alginate and I have its viscosity value at 1 wt% and 3 wt% separately. Does anyone know how the concentration can be integrated into the equation? Obviously it matters. Thanks.
Hanxiao Huang You have to measure intrinsic viscosity , by measuring a series of viscosity using Ubbelohde Viscometer, 0.1M Nacl will be the solvent, You can try with 0.05, 0.1, 0.15 , 0,2, 0.25 % solution, then find the specific viscosity and relevant viscosity , the intercept will be the intrinsic viscosity in dl/g , in general K=7.3*10ˆ3 and α= 0.92 for alginate, but this constant depend on the M/G ratio o alginate, you can find lots of literature regarding this.
Hanxiao Huang
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