Applications of Fluorescence
Photobleaching Recovery
ACS Polymer Group
Raleigh, North Carolina
Thursday, November 8
Gelation of “sticky” rods
O
PBLG is “sticky”
but not very.
O
PBLG: poly(benzyl-L-glutamate)
Helical a-polypeptide backbone,
persistence length > 1000 Å
PSLG: a stickier wicket.
PSLG: poly(stearyl-L-glutamate)
O
O
Waxy Sidechains
C18 = Stearyl
Very rigid a-helical
polypeptide
backbone
Intramolecular
Hydrogen Bonds
Why everyone cares about these molecules again.
•Self-solvating (well, sorta): Molten Rods—easier processing.
•Oriented Films/waveguides/chiral separation
•Polymer Physics of Rods in Solution, Gel & Melt
•More rigid and more soluble than those high-$$$ Air Force &
NASA polymers
•Hey…they don’t have to be rigid—helix-to-coil transition
Idealized Rod Phase Diagram
fa
T
ISO
fb
LC
f
Very rigid rods!
Mw/Mn
x=
L/d
fa
(%)
fb
(%)
favg
(%)
Onsager
4/x
Flory
239,000
1.13
28
13.5
2
15.0
1.5
14.3
1
14
27
208,000
1.08
24
15.2
1.3
17.8
1.3
16.5
2.6
17
30
127,000
1.12
15
16.2
2.1
25.3
1.3
20.8
3.4
27
46
Mw
by GPC/LS
Hypothetical Rod Phase Diagram
With Gelation Transitions Overlaid
Iso
LC
S1
T
S2
P1
LL2
LL1
P2
f
DSC can detect ISO-LC transition. Heat
per molecule gives no trend.
sarah file: s.conave
sarah file: s.conave
55
60
T
m
50
T
55
H (mJ/mg PSLG)
c
45
Temperature (C)
40
35
30
50
45
40
35
30
25
25
20
20
Ordered
Isotropic
15
0
10
20
30
40
15
50
0
Weight % PSLG
Schmidtke et al.
Figure 4a
10
20
30
Weight % PSLG
40
50
Schmidtke et al.
Figure 4b
Annealing perfects but does not alter
gel structure. Suggests motion!
sarah file: s.annave
55
50
50
45
Temperature (oC)
H (mJ/mg PSLG)
sarah file: s.annave
45
40
35
40
35
30
30
25
0
100
200
300
400
Time cured (minutes)
Schmidtke et al.
Figure 5b
0
100
200
Time cured (minutes)
300
400
Schmidtke et al.
Figure 5a
Labeling Does Not
Bug the Helix




Computer Simulation
Intrinsic Viscosity
Static Light Scattering
Dynamic Light
Scattering
 Phase boundary
determinations
 Temperaturedependent studies
Modulation FPR Device
PA
TA/PVD
PMT
*
OS
*
D
S
*
M
DM
OBJ
RR
*
M
L
AOM
20
700
Temperature-ramped
modulation FPR
30
40
scan1062
combinehigh
50
2
DDSC
4
Contrast (AC/DC)
500 3
2040 s
DSC
start ramp @
0.3oC/min
400
AC/DC
DSC (W) or DDSC+600 ( W/ oC)
600
2
300
TRFPR: 30.7oC
200 1
1
Melt at 30.9oC
100
0
0 0
20
1000
2000
30 t (seconds)
T/ oC
3000
40
Schmidtke et al.
50
Figure 6
Schmidtke et al.
Figure 7
Everything can move,
yet the structure remains
Sticky rods—remaining challenges
•Crosslink ‘em to lock in liquid crystal structure
•Solution behavior above the gel transition
•Rheological response
•EM’s of these gels
•Supercritical fluid drying of gels and LC’s
Problems related to entanglement
Bulk polymers: welding, processing,
phase separation, failure
Solutions: rate of dissolving,
intracellular transport, separations for
genomics, joining PVC pipe!
Reptation—a theory to describe
random snaking in polymer tangles
There 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
Need: better diffusion methods
Problem: lots of things appear to obey this scaling law
Suggests: look at the ignored systems, especially RODS
*With apologies to Walter Stockmayer
Entanglement in solution?
Collander
To isolate spaghetti in "solution" with a fork is
difficult: hydrodynamic interactions interfere
with entanglement. After solvent is drained to
obtain a "melt" the entire blob is easily handled.
See, e.g., Lodge & Muthukumar, J. Phys. Chem. 1996, 100, 13275-13292
Our Hypothesis
Solutions containing rodlike diffusers may
provide evidence for entanglement-like
phenomena in solution…or at least prove
interesting, fun and challenging.
Evidence would be: sudden drop-offs in
mobility with concentration, failure to
follow continuum mechanics.
Rods should make
effective probes. But very challenging:
Early de Gennes paper on
rod/coil diffusion: 19 citations
Same era de Gennes paper
on coil/coil reptation: 479 citations
We may expect some problems!
Why it’s worth it: composite precursor
fluids, dissolution rate, phase sep’n rate,
relation to GPC, CGE of rods, intracellular
transport.
Studying “entangled” rods by
Optical Methods
Fluorescently
labeled probe rod
Unlabeled rods
Solvent
Doi-Edwards-Onsager Reference Volumes for Rods
 = number density = # of rods per unit volume
d
LC formation
* = 4/A2  5/dL2
L
Reduced # Density
/*  dL2/5
2
3
dL
L

1
3
L
L3  1

A2 
1
2
dL
dL2  1

dL2
1
A2
A2  1
4
Desirable rod properties
Stiff—no bending
Monodisperse (all the same size)
Non-aggregating
Water-soluble
We don’t have to make ‘em!
Let mother nature do the work: plants make
viruses (unwillingly) with most of these qualities.
Doing our Part to Keep the “A” in LSU A&M
Seedlings
Sick Plants 
And close-up
of mosaic
pattern.
Two TMV’s in Transmission
Electron Microscopy
An ear of corn has about as many kernels as TMV
has protein subunits (ca. 2130). The protein
subunits enfold a spiral-wound strand of RNA which
will encode the next generation. TMV is more
extended than an ear of corn.
Better Views
http://www.uct.ac.za/depts/mmi/stannard/linda.html
TMV Characterization
Sedimentation, Electron Microscopy & DLS
Most TMV is intact.
Some TMV is fragmented.
 weaker, faster mode in CONTIN decay analysis
 Intact TMV is easy to identify
 stronger, slower mode in CONTIN
 It is easy to measure at low concentrations
that avoid TMV-TMV interactions in DLS and we
can use small amounts in FPR after dye
attached.
Huh?
Tobacco from the Carolinas to Connecticut
If tobacco goes away…
“Traditionally in Kentucky great mounds of brush are piled and
burned in February to prepare a bed for tobacco seedlings. I
remember spending most of the day hauling and piling brush. My
dad would start the fire in late afternoon and we would sit up most
of a cold February or March night stoking the fire, watching the
stars, and roasting hot dogs or marshmallows over the bonfire.
Many times neighbors would stop by and sit with us for a spell
around the fire, talking into the night.”
From: http://www.webcom.com/duane/farm2.html
Measuring Translational Diffusion
Modulation FPR Device a’la Lanni & Ware
PA
TA/PVD
PMT
*
OS
SCOPE
*
D
S
*
M
DM
OBJ
RR
*
M
L
AOM
FPR Data for TMV Solution: very low dye content.
Contrast
4
0.040
0.035
3
0.030
/Hz
0.025
0.020
0.015
2
0.010
DC Signal
0.005
0.000
0
2
4
6
8
10
12
14
K2 / 105cm-2
1
0
0
200
400
600
t/s
800
1000
Dtracer self of TMV vs. cTMV
Source: Cush Monthly Report (5/1/01)
7
1/L3
1/dL2
5
4
3
D
self
/ 10 -8 cm 2 s -1
6
2
1
0.1
1
10
c
TMV
/ mg mL-1
100
Rotation & Diffusion of TMV in
Polymer Solutions
Matrix
Polymer
TMV
Probe
Solvent
– – – Hard to see rotation in FPR; try scattering
+ + + Fabulous new autocorrelators for scattering
10 decades of time in one measurement!
– – – Contrast for scattering stinks: everything
scatters, esp. in aqueous systems where
refractive index matching cannot hide matrix.