Recent Developments in Polymer Characterization And how we may have to modify them for nanoparticles

Obligatory Equation SEC = GPC = GFC Size Exclusion Chromatography Gel Permeation Chromatography Gel Filtration Chromatography

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

GPC 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 ?

Simple SEC degas pump injector DRI VeVe log 10 M c c c

Osmometry: Real Science Semipermeable membrane: stops polymers, passes solvent. h  V = n R T n = g/M c = g/V  = c R T

Light Scattering: Osmometer without the membrane 100,000  x c 

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

SEC/MALLS degas pump injector DRI MALLS

SEC/MALLS Scattering angle VeVe Scattered intensity

Scattering Envelope for a Single Slice

SEC/MALLS in the Hands of a Real Expert a p  15 nm Much less than PBLG Macromolecules, 29, (1996)

Midpoint The new power of SEC/Something Else experiments is very real. SEC is now a method that even the most skeptical physical chemist should embrace. For example, our results (not shown) favor higher rather than lower values for persistence length of one polymer (PBLG). This helps to settle about 30 years of uncertainty. So, SEC is good enough for physical measurements, but is it still good enough for polymer analysis? What about nanoparticles, especially large ones, in GPC?

They were young when GPC was.

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…

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.

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

Sizing by Dynamic Light Scattering — a 1970 ’ s advance in measuring motion, driven by need to measure sizes, esp. for small particles. t IsIs It’s fluctuations again, but now fluctuations over time! DLS diffusion coefficient, inversely proportional to size. Large, slow molecules Small, fast molecules

Molecular Weight Distribution by DLS/Inverse Laplace Transform--B.Chu, C. Wu, &c. Where: G(  ) ~ cMP(qR g )  = q 2 D  q 2 kT/(6  R h ) R h = XR g g(t) log 10 t ILT  q 2 D G(  ) CALIBRATE MAP M c log 10 M log 10 D 

Hot Ben Chu / Chi Wu Example MWD of PTFE Special solvents at ~330 o C Macromolecules, 21, (1988) Problems: Only “works” because MWD is broad Poor resolution. Low M part goofy. Some assumptions required.

Reptation: inspired enormous advances in measuring polymer speed … and predicts More favorable results for polymers in a matrix. T here once was a theorist from France Who wondered how molecules dance. "They're like snakes," he observed, "as they follow a curve, the large ones can hardly advance."* D ~ M -2 deGennes More generally, we could write D ~ M -  where  increases as entanglements strengthen *With apologies to Walter Stockmayer

Matrix Diffusion/Inverse Laplace Transformation Goal: Increase magnitude of  Difficult in DLS because matrix scatters, except special cases. Difficult anyway: dust-free matrix not fun! Still nothing you can do about visibility of small scatterers DOSY not much better Replace DLS with FPR. Selectivity supplied by dye. Matrix = same polymer as analyzed, except no label. No compatibility problems. G(  ) ~ c (sidechain labeling) G(  ) ~ n (end-labeling) log 10 M log 10 D Stretching  Solution:   Matrix:  

Painting Molecules* Makes Life Easier *R. S. Stein Small Angle Neutron Scattering ForcedRayleighScattering Fluorescence Photobleaching Recovery Index-matched DLS match solvent & polymer refractive index can't do in aqueous systems Depolarized DLS works for optically anisotropic probes works for most matrix polymers

Fluorescence Photobleaching Recovery 1. An intense laser pulse photobleaches a striped pattern in the fluorescently tagged sample. 2. A decaying sine wave is produced by moving the illumination pattern over the pattern written into the solution. 3. An exponential decay is produced by monitoring the amplitude of the decaying sine wave. Fitting this curve produces  from which D can be calculated.

FPR for Pullulan (a polysaccharide) Probe Diffusion: Polymer physicsCalibration: polymer analysis

FPR Chromatogram  Indicates targeted M.

GPC vs. FPR for a Nontrivial Case 20,000 & 70,000 Dextran PL Aquagel 40A & 50A User-chosen CONTIN 25% Matrix

 Indicates targeted M.

Examples of Separation Results from Simulation Data  Indicates targeted M.

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

Field Flow Fractionation, that’s how! In FFF, large nanoparticles are made to flow between plates.

One plate is porous, and a cross- flow is arranged.

What happens? Little nanoparticles come out first!

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

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

Thank you! LSULSU