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Macromolecular Chemistry. Lecture 10 . Midterm Exam. Where: Right here….in the lecture room WEL 3.502 When: Next Tuesday 2/24/09 at 3:30 – 5PM What: Covers lectures through Thursday 2/18 Bring: Pencil, eraser, Calculator only…closed book! - PowerPoint PPT Presentation
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Chemistry 367L/392N
Macromolecular ChemistryMacromolecular Chemistry
Lecture 10 Lecture 10
Chemistry 367L/392N
Midterm ExamMidterm Exam Where:Where: Right here….in the lecture room WEL 3.502 When:When: Next Tuesday 2/24/09 at 3:30 – 5PM What:What: Covers lectures through Thursday 2/18 Bring:Bring: Pencil, eraser, Calculator only…closed book! Do:Do: Study lecture notes, homework, reading
assignments and graduate presentations Do not: Do not: Memorize the free radical kinetics equations…
but do know the principles! Go over homework problems.
Please: Please: Do a good job!
Chemistry 367L/392N
Measuring Molecular WeightMeasuring Molecular Weight Membrane Osmometry AlfredoAlfredo Vapor Phase Osmometry LindaLinda Viscometry GWGW Gel Permeation Chromatography
– Size exclusion Chromatography Light Scattering MALDI Others
– End group analysis YouYou
GWGW
GWGW
GWGW
Setting the Standard for GPC.
Grubisic, Rempp & Benoit, Grubisic, Rempp & Benoit, JPS Pt. B, 5, 753 (1967JPS Pt. B, 5, 753 (1967))
Setting the Standard for GPC.
Chemistry 367L/392N
Light scatteringLight scattering
4
Scattering(Mie, Rayleigh)
Absorption
Emission(Fluorescence)
Incident BeamsIncident Beams
Particles
The interaction of light with a particle in terms of scattering, absorption, and emission.
Chemistry 367L/392N
Rayleigh ScatterRayleigh Scatter Molecules and very small particles do not
absorb, but scatter light in the visible region (same freq as excitation)
Rayleigh scatteringRayleigh scattering is directly proportional to the electric dipole and inversely proportional to the 4th power of the wavelength of the incident light The sky looks blue because the The sky looks blue because the
gas molecules scatter more gas molecules scatter more light at shorter (blue) rather light at shorter (blue) rather than longer wavelengths (red)than longer wavelengths (red)
Chemistry 367L/392N
Building a detectorBuilding a detector
In the lab…
Chemistry 367L/392N
Basic light scattering principlesBasic light scattering principlesPrinciple 1Principle 1The amount of light scattered is directly proportional to the product of the polymer molar mass and concentration.
Principle 2Principle 2The angular variation of the scattered light is
directly related to the size of the molecule.
Chemistry 367L/392N
Rayleigh ScatteringRayleigh Scattering
●
)cos1(8 2
24
24
raI
Io
Io
Iθr
r = distance from particle a = polarizabilityλ = wavelength
particles much smaller than the wavelength of the light
Chemistry 367L/392N
Some nasty math later……Raleigh gets the average scattering intensity as a function of the (particle) molecular weight and the 2nd virial coefficient.
K = Optical constant C = ConcentrationM = Molecular weight Rθ = Rayleigh ratio A2 = 2nd Virial coefficient P(θ) = Shape (or form) factor
Static Light ScatteringStatic Light Scattering
Rayleigh EquationRayleigh Equation
KCKC))((
11221122
PPccAA
MMRR
Chemistry 367L/392N
IA = lntensity of analyte (sample I – solvent I)no = Solvent RIIT = Intensity of standard (toluene)nT = Standard (toluene) RIRT = Rayleigh ratio of standard (toluene)
KCKC))((
11221122
PPccAA
MMRR
22
0044
00
2222
dcdc
dndnnn
NNKK
AA
λo = laser wavelengthNA = Avogadros numberno = Solvent RIdn/dc = differential RI increment
22sinsin
331616
11 22
22
00
2222
00
22
ggRRnn
PP
Rg = Radius of gyrationθ = Measurement angle
TT
TTTT
AA RRnnIInnIIRR 22
22
00
Chemistry 367L/392N
Light ScatteringLight Scattering
Therefore a “Debye plot” of KC/Rθ versus c should give a straight line whose intercept at zero concentration will be 1/M and whose slope will be A2!
KCKC))((
11221122
PPccAA
MMRR
For Rayleigh scatterers, P(θ) = 1 and the equation is simplified to
KCKC2211
22
ccAAMMRR
(y = b + mx)(y = b + mx)
Chemistry 367L/392N
Molecular Weight ExampleMolecular Weight Example
Chemistry 367L/392N
Molecular Wt ExampleMolecular Wt Example
Chemistry 367L/392N
Light Scattering ExperimentLight Scattering Experiment
MeasureI/I0 = f(θ)
Chemistry 367L/392N
For SECFor SEC This concept has been embodied in detectorsThis concept has been embodied in detectors These measurements give an absolute value for MwThese measurements give an absolute value for Mw Remember that there are some assumptions made that Remember that there are some assumptions made that
limit the utility of the “simple” detectors to Molecular limit the utility of the “simple” detectors to Molecular weights below abut 150,000 Daltonsweights below abut 150,000 Daltons
dn/dc can be measured with an RI detectordn/dc can be measured with an RI detector A “significant” difference in the refractive index of the A “significant” difference in the refractive index of the
sample and the solvent is required for good signal. sample and the solvent is required for good signal.
Chemistry 367L/392N
Study HardStudy Hard