Molecular and colloid chemical characterization

Membrane osmometry


  • Suitable for the method are polymers or nanoparticles that are soluble or dispersible in aqueous media or organic solvents. The required sample quantity is 100-500 mg. The method covers approximately the molar mass range from 104 to 105.



  • GONOTEC OSMOMAT 090 membrane osmometer
  • Membranes: cellulose triacetate (cut-off 5000, 10000 and 20000 g/mol), regenerated cellulose (cut-off 20000 g/mol)
  • Solvents: water and aqueous salt solutions as well as organic solvents like tetrahydrofuran, toluene, chloroform etc.



  • Measurement of the osmotic pressure p as a function of the polymer concentration and extrapolation of the reduced osmotic pressure to the concentration zero
    • Numerical average molar mass Mn and 2nd virial coefficient A2,o



  • Example: Poly-DADMAC standard materials (see PDF)


Methods of comparison and supplementation

  • Aqueous size exclusion chromatography (Mn; MW; D)
  • Organic size exclusion chromatography
  • Static light scattering (MW; RZ; A2
  • Analytical ultracentrifugation (MZ; D)
  • Differential refractometry (dn/dc)
  • Dynamic light scattering (dH)
  • Vapor pressure osmometry (Mn)