Molecular and colloid chemical characterization

Analytical ultracentrifugation

Analyte

The method is suited for polymers and nanoparticles, which can be dissolved or dispersed in aqueous media or organic solvents. The required amount of sample is in the range between 100 and 500 mg. The method covers the molar mass range from 103 to approx. 1014 and particle sizes from 1 nm to approx. 500 nm.

 

Equipment

  • Instrument: Optima XL-I (Beckman-Coulter, USA)
  • Rotation speed: 2000 to 60000 rpm
  • Solvents: Solvents: water and aqueous saline solutions, organic solvents, such as THF, Toluene, DMF, DMF+LiCl, DMAc etc.
  • Cells: double-sector cells from reinforced Epon, aluminium, or titan; multi-channel cells for sedimentation equilibria; boundary-forming cells
  • Detection: absorption (200 - 800 nm), interference optics (if appropriate Schlieren optics MOM 3180)

 

Evaluation methods and targets

  • Measurement of the sedimentation speed
  • Sedimentation coefficients s and s-distribution g (s)

  • Average molar masses / molar mass distributions via s-M-calibration
  • Size distribution of nanoparticles
  • Measurement of concentration distribution in sedimentation-distribution equilibrium

  • Average molar masses Mw, Mz (absolute values) and 2nd virial coefficient A2,o
  • Layering experiment at low rotation speeds
  • Diffusion coefficient Dx
  • Density gradient centrifugation
  • Density ρ and density distribution g (ρ) of polymer particles

 

Application examples

  • Molar mass determination by evaluation of the sedimentation equilibrium (→ PDF)
  • Evaluation of the sedimentation speed (→ PDF)
  • Analysis of particle sizes in polymer dispersions (→ PDF)
  • Determination of particle densities by density gradient centrifugation (→ PDF)