Membrane Osmometry Alfredo Clemente CH 392 N Prof

Membrane Osmometry Alfredo Clemente CH 392 N Prof. Grant Willson. The University of Texas Austin

Membrane Osmometry n n n Molecular Weight and polymer properties Methods Used to determine Mn, Mw Membrane Osmometry ØIntroduction and Theory ØMeasuring Mn by osmotic pressure n Conclusions: Advantages and disadvantages n Questions The University of Texas at Austin

Relative fraction Representative differential weight distribution curves 1 Molecular weight The University of Texas at Austin

Relationship of polymer properties to molecular weight. 1 The University of Texas at Austin

Typical Molecular Weight Determination Methods 1 Method Type of mol. Range wt. avg. To ∞ Light scattering (LS) Membrane osmometry 2 x 104 to 2 x 106 Vapor phase osmometry Electron and X-ray microscopy To 4 x 104 102 to ∞ Ebulliometry To 4 x 104 Cryoscopy To 5 x 104 End Group Analysis To 2 x 104 Osmodialysis 500 -2500 To ∞ Centrifugation SEC, with c detector Relative SEC, with c and LS detectors Viscometry Relative Info. Shape, dist To ∞ Mol w Dist To ∞ The University of Texas at Austin

Membrane Osmometry Introduction and Theory Osmosis and Osmotic Pressure Osmosis and Chemical Potential h The University of Texas at Austin

Equilibrium of Chemical Potential 2 The University of Texas at Austin

Osmotic Pressure The University of Texas at Austin

Osmotic Pressure and The University of Texas at Austin

Osmotic Pressure and The University of Texas at Austin

Osmotic Pressure and 2 The University of Texas at Austin

Measuring by osmotic pressure Membrane osmometers used: ØStatic osmometer 2 • Equilibrium by natural diffusion • Large cell volumes • Long equilibrium times The University of Texas at Austin

Measuring by osmotic pressure Membrane osmometers used: ØDynamic osometer 3 • Equilibrium by reducing pressure on solution reservoir • Small cell volumes • Short equilibrium times The University of Texas at Austin

Measuring by osmotic pressure Membrane osmometers used: ØDynamic osometer 3 The University of Texas at Austin

Osmotic Pressure and 5 20. 0°C: Slope = A 2 = -2. 0 x 10 -4 cm 3 mol/g 2 1/intercept = Mn = 1. 97 x 104 g/mol 34. 5°C: Slope = A 2 = 1. 7 x 10 -5 cm 3 mol/g 2 1/intercept = Mn = 2. 02 x 104 g/mol 50. 0°C: Slope = A 2 = 1. 7 x 10 -5 cm 3 mol/g 2 1/intercept = Mn = 2. 00 x 104 g/mol The University of Texas at Austin

Conclusion: Advantages and disadvantages Disadvantages ØMembrane problems: leakage, asymmetry and ballooning ØOverestimation of molecular due low molecular weight molecules ØNot suitable for electrolytes Advantages ØAbsolute value of Mn ØNo calibration with standards required ØIndependent of chemical heterogeneity ØApplicable to polymers with broad range of molecular weights ØMeasurement of Mn within 10, 000 to 2 x 106 The University of Texas at Austin

Questions? The University of Texas at Austin

References 1. Carraher, C. E. , Jr Polymer Chemistry: An Introduction, 4 th Ed. , Marcel Dekker, NY: 1996. 2. Young, R. J. ; Lovell, P. A. Introduction to Polymers, 2 nd Ed. , Chapman & Hall, New York: 1991. 3. Lipták B. G. ; Brodgesell, A. Instrument Engineers' Handbook, Process measurement and analysis. CRC Press, Florida: 1995 4. W. R. Krigbaum and L. H. Sperling, J. Phys. Chem. , 64, 99 (1960) 5. Hiemenz, Paul C. , Lodge, Timothy P. ; Polymer Chemistry, 2 nd Ed. , CRC Press, Boca Raton: 2007. 6. http: //www. engga. uwo. ca/people/pcharpentier/3922004/MW%20 Measurement. pdf 7. http: //www. chem. ufl. edu/~polymer/instrumentation/vpo. html 8. http: //www. chem. ufl. edu/~polymer/instrumentation/vpo. html 9. http: //www. eng. uq. edu. au/files/course/files/CHEE 2006%20 Week% 2012_2. pdf The University of Texas at Austin

References 10. http: //www. humancorp. co. kr/catalog/272 -277. pdf 11. http: //www. gonotec. com/content. OSMO_090. PRODUCTS_CHEM. OSMO_090. USA. ENG. html 12. http: //www. princeton. edu/~pccm/facilities-polymersynth-eq. htm 13 Chalmer, John M. ; Meier, Robert J. , Molecular Characterization and Analysis of polymers, Elsevier Science, Burlington: 2008 The University of Texas at Austin