From Rubinstein & Colby Polymer Physics Here is a nice example of scaling: 3 different types of polymers, all normalized sround the entanglement molecular weight and viscosity at that molecular weight.

From Rubinstein & Colby Polymer Physics The best experiments do not match the reptation prediction exactly.

From Rubinstein & Colby Polymer Physics What has this got to do with our creep compliance plot? 12 decades of time!!!??? In a mechanical experiment???

From Rubinstein & Colby Polymer Physics

From Rubinstein & Colby Polymer Physics It is easier for a camel to pass through the eye of a needle than for an octopus to escape a fishnet. Can you think of an experiment?

No one knows if reptation really happens in solutions; these diffusion results from an obscure group in Baton Rouge suggest not. Figure 1: Diffusion of fluorescently tagged dextran in unlabeled d extran matrix of M w = 2,000,000 Da. No Matrix ( ), 5% w/w Matrix ( ■ ), 10% w/w Matrix (  ), 15% w/w Matrix (  ), 20% w/w Matrix ( ○ ), and 25% w/w (  ).

Figure 5. Representative spectra calculated by CONTIN and chosen by the user showing the detection of FD20 and FD70 in a mixture. The weight percent of the matrix solutions was Spurious peaks at low and high M not shown. We are putting probe diffusion to work. This molecular weight distribution was obtained without GPC, without AF4, without any separation at all. Molecules were just put under a “speed gun” as they diffuse around In a constraining solution.

Figure 6: GPC-MALS separation of FD20 and FD70 (circles; two different injections are shown). Also shown are individual runs for FD20 (-) and FD70 (+). GPC is actually LESS effective in this case.

Rheology plays a role in figuring out why our “non- separation” method doesn’t work even better. Figure 7: Illustration of the change of G′ over the range of dextran matrix concentrations at oscillation frequencies 2 Hz ( ■ ), 5 Hz ( ● ), 10 Hz ( ▲ ), 20 Hz (  ).

This figure demonstrates the absence of a rheological plateau modulus in the measured frequency range for the matrix dextran. Figure 7: Example of storage modulus, G′, as a function of frequencies for different dextran matrix concentrations: w = 5% ( ■ ), 10%( ▲ ), 15%(  ), 20%( ○ ), and 25%(  )