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This presentation exemplifies the latest Power Point dogma. 1 A full sentence at the top tells the main point. Vertically aligned lists are avoided in.

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Presentation on theme: "This presentation exemplifies the latest Power Point dogma. 1 A full sentence at the top tells the main point. Vertically aligned lists are avoided in."— Presentation transcript:


2 This presentation exemplifies the latest Power Point dogma. 1 A full sentence at the top tells the main point. Vertically aligned lists are avoided in favor of diagonal arrangement to create visual tension. A page number helps reader ask questions. Tasteful use of animation helps. Occasionally, put in something strange or fun to keep professors and other tired listeners awake. dogma, n. A settled or established opinion, belief, or principle

3 “You cannot measure absolute molecular weights” Dow manager, 1983 Wrong! Correct, even in 1983: you NEED NOT always measure ABSOLUTE molecular weights…but you could have. Correct in 2005: it is almost always essential to measure absolute M s. 2

4 So, how would you analyze polymers and nanoparticles for polydispersity?

5 Here is the easiest equation in this talk. SEC = GPC = GFC Size Exclusion Chromatography Gel Permeation Chromatography Gel Filtration Chromatography 4

6 A riddle: After a hurricane, many trees fall over and bend into a river. Also, a cow and a dog fall into that flooded river. Which one reaches the ocean first, cow or dog? Moo! Woof! 5

7 In GPC, as when throwing a cat through a tree, the big things come out first.. Solvent flow carries molecules from left to right; big ones come out first while small ones get caught in the pores. It is thought that particle volume controls the order of elution. But what about shape ? 6

8 Simple SEC is only simple when you don’t have to do it yourself. degas pump injector DRI VeVe log 10 M c c c 7

9 In simple GPC, you first make a map (calibrate), then follow it. VeVe log M VoVo VeVe A DRI VeAVeA DRI A MAMA 8

10 Are you straight? 9

11 Use the right tool (column) for the job. 10

12 OK, but how did you get the M values for the standards? Osmometry Scattering MALDI Analytical ultracentrifugation End group analysis Goal in this class: make it seem reasonable that it IS possible to measure M values. 11

13 Osmometry is Real Science because it is tied closely to thermodynamics. Semipermeable membrane: stops polymers, passes solvent. h  V = n R T n = g/M c = g/V  = c R T 12

14 Light scattering operates on thermodynamics; think of it as an osmometer without the membrane. 100,000  x c  Teaching Light Scattering to Exemplify and Reinforce Basic Principles, D. S. Poche', P. S. Russo, B. Fong, E. Temyanko and H. Ricks, J. Chem. Ed., 1999, 76 (November), 1534-1538. 13

15 LS adds optical effects  Size. q = 0 in phase I s maximum q > 0 out of phase, I s goes down 14

16 Just add LS detector…and much complexity. degas pump injector DRI MALLS 15

17 This waterfall plot shows many “slices” of a chroma- togram: 13 angles were recorded ~8 times per second as the sample flowed by the MALS detector. Scattering angle VeVe Scattered intensity 16

18 The scattering “envelope” for a single slice shows how I s decreases with angle. Intercept  Molecular weight Slope  Size 17

19 We add a viscometer in some cases. degas pump injector DRI LS90 o  P   viscometer 18

20 Intrinsic viscosity is a secondary molecular weight method so good it’s almost like the real thing. Mark-Houwink-Sakurada relationship between the intrinsic viscosity and the molecular weight. K and a are constants for a given polymer, not strongly dependent on solvent or temperature, as long as we’re talking about a “good solvent”. These words have special meaning in polymer science. 19

21 Grubisic, Rempp & Benoit, JPS Pt. B, 5, 753 (1967) One of of the most important papers in polymer science. Imagine the work involved! 6 pages long w/ 2 figures. Selected for JPS 50 th Anniv. Issue. Universal Calibration lets you get the molecular weight of one kind of polymer knowing only the Mark-Houwink- Sakurada values of a standard (look it up) and your unknown (uh-oh). 20

22 Universal Calibration says that whatever comes out at a particular volume has the same product, [  ]M. [  ] = KM a [  ] A  M A = [  ] S  M S = f (V e ) Mark-Houwink Relation Universal Calibration A = analyte; S = standard Combine to get these two equations, useful only if universal calibration works! 21

23 They were young when GPC was.

24 They were young when GPC hit middle age.

25 Here is a small subset of GPC spare parts. To say nothing of unions, adapters, ferrules, tubing (low pressure and high pressure), filters and their internal parts, frits, degassers, injector spare parts, solvent inlet manifold parts, columns, pre-columns, pressure transducers, sapphire plunger, and on it goes… 24

26 Other SEC Deficiencies 0.05 M salt at 10 am, 0.1 M salt at 2 pm? 45 o C at 8 am and 50 o C at noon? Non-size exclusion mechanisms: binding. Big, bulky and slow (typically 30 minutes/sample). Temperature/harsh solvents no fun. You learn nothing by calibrating. Columns are expensive, easily damaged. 25

27 Must we separate ‘em to size ‘em? Your local constabulary probably doesn’t think so. Atlanta, GA I-85N at Shallowford Rd. Sat. 1/27/01 4 pm 26

28 Matrix Fluorescence Photobleaching Recovery* is an LSU-invented method designed to compete with GPC for certain systems (aqueous commodity polymers).  Indicates targeted M. *G. J. Doucet, D. Dorman, R. Cueto, D. Neau, P. S. Russo, D. DeKee, J. Pople Macromolecules 2006, 39(26), 9446 – 9455. 27

29 Ultimate Goal: A Black Box for MWD Matrix FPR Easily Maintained Accurate Precise Simple Concept Expedient Easy System Switch Basic Info Obtained Miniaturizable Detect Large Masses Labeling Required GPC Accurate Simple Concept Miniaturizable No Labeling Required Broad Distributions Pumps Parts Press for MWD DLS Form Factor Index Matching Long Acquisition for Multiangle Experiments Precise Accurate DOSY Easy System Switch Precise Accurate Obtain Basic Info Labeling Required 28

30 In other words, the search continues. Two promising contenders are discussed next. MALDI-TOF: most effective when the molecules are small, biological and not very polydisperse. Can be coupled to GPC! FFF: like GPC only a flowing field replaces the stationary phase, stuff comes out backwards, and big stuff can be handled as well as small. 29

31 MALDI-TOF stands for Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry. 30

32 These data obtained at LSU: click the figure to analyze these results.  Guess what M w /M n is. 31

33 Patience is a virtue. You 4010 students will get to practice with a MALDI dataset, but …. that’s enough MALDI for now. 32

34 What about separating cows and elephants? Either will float around the trees. How do you separate them then? Moo! Eeee! 33

35 Field Flow Fractionation, that’s how! In FFF, large nanoparticles are made to flow between plates; a field is applied to separate them by size. 34

36 The most commonly used field is flow itself: one or both plates are porous, and a cross-flow is arranged. 35

37 What happens because of the cross-flow? Little nanoparticles come out first! At LSU, only one plate is porous. 1.Everyone calls it AF4 = Asymmetric Flow Field Flow Fractionation 2.How to you get a crossflow then? 36

38 Potential Advantages of FFF Handles a wider range of particles. May be easier for some aggressive solvents. 37

39 AF4 can even separate large PTFE latex particles. 38

40 Conclusion GPC is essential in any Nano Lab GPC may eventually get replaced. Matrix FPR FFF 39

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