From Rubinstein & ColbyPolymer Physics

Here is a nice example of scaling: 3 different types of polymers, all normalizedsround the entanglement molecular weight and viscosity at that molecular weight.

From Rubinstein & ColbyPolymer Physics

The best experiments do not match the reptation prediction exactly.

From Rubinstein & ColbyPolymer Physics

What has this got to do with our creep compliance plot?

12 decades of time!!!???In a mechanical experiment???

From Rubinstein & ColbyPolymer Physics

From Rubinstein & ColbyPolymer 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.

10000 100000

0.1

1

10

Ds /

10-7

cm

2 s-1

Mw / Da

Figure 1: Diffusion of fluorescently tagged dextran in unlabeled dextran matrix of Mw = 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 ().

10000 100000

0

2

4

6

8

10

12%

Am

plitu

de

M

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 0.25. 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.

10000 1000000.0

0.2

0.4

0.6

0.8

1.0

MIX

FD70

FD20

Rel

ativ

e C

once

ntra

tion

M / g mol-1

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.

0.00 0.05 0.10 0.15 0.20 0.250.01

0.1

1

10

20 Hz

10 Hz

5 Hz

2 Hz

G' /

Pa

w

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.

1 10 1000.01

0.1

1

10

100G

' / P

a

/ Hz

Figure 7: Example of storage modulus, G′, as a function of frequencies for different dextran matrix concentrations: w = 5% (■), 10%(▲), 15%(), 20%(○), and 25%()