molecular weight and polymer properties methods used to determine mn, mw membrane osmometry
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Molecular Weight and polymer properties Methods Used to determine Mn, Mw Membrane Osmometry Conclusions: Advantages and disadvantages Questions. Introduction and Theory Measuring Mn by osmotic pressure. Relative fraction. Molecular weight. - PowerPoint PPT PresentationTRANSCRIPT
Membrane Osmometry
Alfredo Clemente
CH 392NProf. Grant Willson.
The University of Texas Austin
Membrane Osmometry
The University of Texas at Austin
Molecular Weight and polymer propertiesMethods Used to determine Mn, MwMembrane Osmometry
Conclusions: Advantages and disadvantagesQuestions
Introduction and TheoryMeasuring Mn by osmotic pressure
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Molecular weight
Rel
ativ
e fra
ctio
n
Representative differential weight distribution curves1
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Relationship of polymer properties to molecular weight.1
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Typical Molecular Weight Determination Methods1
Method Type of mol. wt. avg. Range Info.
Light scattering (LS) To ∞ Shape
Membrane osmometry 2x104 to 2x106
Vapor phase osmometry To 4x104
Electron and X-ray microscopy 102 to ∞ Shape, dist
Ebulliometry To 4x104
Cryoscopy To 5x104
End Group Analysis To 2x104
Osmodialysis 500-2500Centrifugation To ∞SEC, with c detector Relative To ∞ Mol w Dist
SEC, with c and LS detectors To ∞ Mol w Dist
Viscometry Relative To ∞
nM
nMzwnM ,,
nMnMnMnMwzM ,
wnM ,
wM
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Membrane OsmometryIntroduction and Theory
Osmosis and Osmotic Pressure
Osmosis and Chemical Potential
h
011
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Equilibrium of Chemical Potential2
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Osmotic Pressure
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Osmotic Pressure and
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Osmotic Pressure and
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Osmotic Pressure and nM
Typical plot of osmometry experimental data
12
14
16
18
20
0 2 4 6 8 10 12
c/ g dm-3
(п/c
) / J
kg-
12
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Measuring by osmotic pressurenMMembrane osmometers used:
Static osmometer2
h•Equilibrium by natural diffusion
•Large cell volumes
•Long equilibrium times
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Measuring by osmotic pressurenMMembrane osmometers used:
Dynamic osometer3
•Equilibrium by reducing pressure on solution reservoir
•Small cell volumes
•Short equilibrium times
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Measuring by osmotic pressurenMMembrane osmometers used:
Dynamic osometer3
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Osmotic Pressure and nM 5
20.0°C:Slope = A2 = -2.0x10-4 cm3 mol/g2
1/intercept = Mn = 1.97x104 g/mol34.5°C:Slope = A2 = 1.7x10-5 cm3 mol/g2
1/intercept = Mn = 2.02x104 g/mol50.0°C:Slope = A2 = 1.7x10-5 cm3 mol/g2
1/intercept = Mn = 2.00x104 g/mol
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Conclusion: Advantages and disadvantages
DisadvantagesMembrane problems: leakage, asymmetry and ballooningOverestimation of molecular due low molecular weight moleculesNot suitable for electrolytes
AdvantagesAbsolute value of MnNo calibration with standards requiredIndependent of chemical heterogeneityApplicable to polymers with broad range of molecular weightsMeasurement of Mn within 10,000 to 2x106
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Questions?
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References1. Carraher, C. E., Jr Polymer Chemistry: An Introduction, 4th Ed., Marcel Dekker, NY: 1996.2. Young, R. J.; Lovell, P. A. Introduction to Polymers, 2nd Ed., Chapman & Hall, New York: 1991.3. Lipták B. G.; Brodgesell, A. Instrument Engineers' Handbook, Process measurement and analysis. CRC Press, Florida: 19954. W. R. Krigbaum and L. H. Sperling, J. Phys. Chem., 64, 99 (1960)5. Hiemenz, Paul C., Lodge, Timothy P.; Polymer Chemistry, 2nd Ed., CRC Press, Boca Raton: 2007.6. http://www.engga.uwo.ca/people/pcharpentier/392-2004/MW%20Measurement.pdf7. http://www.chem.ufl.edu/~polymer/instrumentation/vpo.html8. http://www.chem.ufl.edu/~polymer/instrumentation/vpo.html9. http://www.eng.uq.edu.au/files/course/files/CHEE2006/CHEE2006%20Week%2012_2.pdf
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References10. http://www.humancorp.co.kr/catalog/272-277.pdf11. http://www.gonotec.com/content.OSMO_090.PRODUCTS_CHEM.OSMO_090.USA.ENG.html12. http://www.princeton.edu/~pccm/facilities-polymersynth-eq.htm13 Chalmer, John M.; Meier, Robert J., Molecular Characterization and Analysis of polymers, Elsevier Science, Burlington: 2008