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Viscosity Data Equations

Application Note: Molecular Weight Estimation From Viscosity Data - Nylon 66 Solutions

Access Application Note!

This application note presents an analysis of concentration dependent viscosity data for solutions of nylon 66 in formic acid previously measured with the fully automatic VROC® Initium.  The intrinsic viscosity is first extracted from the viscosity data in the semi-dilute concentration regime with the Martin equation.  Coefficients found in the literature are then used to estimate the molecular weight of the polymer from the intrinsic viscosity with the Mark-Houwink-Sakurada equation. 



  • viscosity
  • intrinsic viscosity
  • molecular weight
  • Martin equation
  • Mark-Houwink-Sakurada exponents
  • formic acid
  • nylon 66
  • polyamide
  • engineering thermoplastic
  • polymer concentration


1. Are volatile solvents compatible with VROC® powered viscometers?
Yes and it really helps when you're working with RheoSense viscometers as they are all closed systems. This will keep the original composition of the sample and also protect the end users. 
2. Is Nylon 66 miscible in formic acid?

When you download the application note, you will be able to see that we use nylon 66 in formic acid and our preparation time is by rotating for a minimum of 2 hours. According to ASTM D789, it is recommended to shake for a minimum of 1 hour. There are many users who even rotate for 2 weeks. 

Overall, nylon 66 and formic acid are not immediately miscible. It takes quite a long time for the two solutions to interact and often results in a cloudy solution which is the key indicator that the the two are just not miscible. However, after 2 hours or even 2 weeks of rotation, the solution becomes a lot more homogenous enabling a more smooth solution to work with.

Slow rotation also helps with preventing bubble formation which is another reason to use the rotator for a given period of time.


About the Viscometer

Learn more about the automated viscometer that compliments Clariti™, VROC® initium.

  • 26 µL of Sample
  • Sample Retreival initium (no bdg)
  • Sample Recovery
  • Measurement temperatures 4 - 70 ºC
  • Sample storage temperature
  • Intrinsic Viscosity
  • Injectability 
VROC initium