Madhusudan Tyagi NIST Center for Neutron Research Tyagi NIST Center for Neutron Research Spectroscopy Summer School 2011 06/13/2011 Typical Scans on HFBS I: Elastic Scan 0 0.2 0.4

06/13/2011

High Flux Backscattering Spectrometer

Madhusudan TyagiNIST Center for Neutron Research

Spectroscopy Summer School 2011

06/13/2011

Typical Scans on HFBS I: Elastic Scan

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200 250 300 350 400

Normalized Intensities for PVME

I/I0

T(K)

Elastic scans scan the motions that are slower than instrumental resolution.

The two step relaxation in a typical polymer system:

Low-T step –

methyl group rotations

High-T step –

α-relaxation of PVME-[CH-CH2 -] n

O-CH3

-

><−=

3exp/

22

0eff

el

rQII

Energy resolution = 0.8 µev


06/13/2011

Typical Scans on HFBS II: Dynamic scan

Need a dynamic window? Turn ON the Doppler!

i

D

i

D

v

v

E

E2≈δ

maximum vD will determinethe maximum energy transfer

Doppler dynamicfrequency range

15Hz ±11µeV24Hz ±17µeV50Hz ±35µeV

Accessible dynamic range for HFBS

Velocity of monochromator

Relaxation time is inverselyproportional to the broadening!

PMMA/PEO


Garcia-Sakai, Macromolecules 2004

06/13/2011

Small Molecules and Biology….


Free volume and mobility in glass formers Proto-type glass former Glycerol

Available free volume to drive the molecular motions and relaxations

PALS is sensitive to available free volumeand preferentially probes these regions

MSD is sensitive to the mobility on the molecular scale.

Higher free volume in the confined glycerol and the lower molecular mobility!

06/13/2011 Spectroscopy Summer School 2011

Kilburn et al in Applied Physics Letters 92, 033109 (2008)

06/13/2011

Thermodynamic transition in water

−−=

KT

BDD

170exp0

good above 242K

4.12/1

0 1220

−=K

TTDD below 242K

Paradox in excess entropy!

Solution: A transition at 220K!

Angell, J. Chem. Phys. 77, 3092 (1973)

DSC Pulse gradient NMR

Price, J. Phys. Chem. A 103, 448 (1999)


06/13/2011

−=

00 exp

TT

Bττ

=RT

Eexp0ττ

VFT:

Arrhenius:

Fragile-to-Strong transition at around 222K inrelaxation time of water!

Confined water in silica

Liu et al., J. Phys: Cond. Matter 18, S2261 (2006)

T

strong

fragile

crossover 222K


06/13/2011

Two temperature laws:

i) 270K – 230K VFT power law

ii) 220K and below Arrhenius law

−=

00 exp

TT

Bττ

=RT

Eexp0ττ

Fragile

Strong

dynamic transition in DNA/Lysozyme is driven by fragile-to-strong transition in water!

Relation with transition in DNA/Lysozyme hydration water

Chen et al., J. Chem. Phys. 125, 171103 (2006)


Dynamic transition of protein

ps - nsTd = 200 K

Substrate

SubstrateM

ean

squa

red

disp

lace

men

t of

H-a

tom

s in

pro

tein

[Å

2 ]

Methyl rotations

at T = 100 K

0 50 100 150 200 250 3000.0

0.5

1.0

1.5

T [K]Hydration water enables dynamic transition.

Wet protein

Dry protein

Anharmonic

Onset of biological function


Hydration dependence of dynamical transition

50 100 150 200 250 300

0.0

0.5

1.0

1.5

200 250 300

0.0

0.5

1.0

1.5

<r2

> - <

r2 >D

ry [Å

2 ]

T [K]

0.65 h 0.50 h 0.35 h 0.20 h Dry

tRNA

<r2 >

[Å2 ]

T [K]

50 100 150 200 250 300

0.0

0.5

1.0

1.5

200 250 300

0.0

0.5

1.0

<r2

> - <

r2 > Dry [Å

2]

T [K]

Lysozyme

<r2 >

[Å2 ]

T [K]

0.45 h 0.35 h 0.30 h 0.20 h Dry

� Larger amplitude of motions, <r2>Wet - <r2>Dry , in tRNA than in lysozyme.

Å ÅRoh J. H., et al. PRL 2005, 95, 038101. Roh J. H., et al. Biophysical J. 2009, 96, 2755.

Å

Å


Slaving and biomolecular influence

3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.010-11

10-9

10-7

10-5

10-3

10-1 Myoglobinh = 0.4

tRNAh = 0.65

Lysozymeh = 0.4

τ [s

]

1000/T [K-1]

Combined dielectric data (solid) and neutron scattering (open)

� Weaker temperature dependence of faster relaxation time in protein� Contradicts the concept of “solvent-slaved” dynamics

Each h = full first hydration layer

Khodadadi S., et al. Biophysical J. 2010, 98, 1321.

DNAh = 0.65


Effect of electrostatic interactions

150 200 250 300 3500.0

0.5

1.0

1.5

2.0

T [K]

Roh J. H., Tyagi M. To be submitted

� Electrostatic stabilization seems to play an important role in facilitating the coupled dynamics of biological macromolecules and hydration water.

Td

Tm<

r2>

[Å2 ]

Neutral folded tRNA

Negative unfolded tRNA

-- ---- -

- - - ------

- --- -- - --- -

-

Difference of the amount of water composing first hydration shell ~ 4 %

Unfolded tRNA seems more fragile!


06/13/2011

Polymers….


Liquid electrolytes

Leakage, decomposition, flammability and tendency to short circuit

Solution?

Polymer electrolyte that can solvate and transport Li+ ions

PEO

Liquid/solid electrolytes as battery material

Highly mobile amorphous regions transport Li+

at faster pace leading to higher Li+-conductivity as PEO showshigh conductivity just above the melting temperature.

issues? (semi-crystalline)

Battery requirements: σ=10-3 S/cm


PEO based solid electrolytes (with LiClO4)

Combined HFBS and DCS data

Conductivity measurements

•PEO crystallization generally lowers theconductivity at temperature of interest.

•At 50C, a partially crystalline shows, maxconductivity despite being less mobile!

• Ionic conductivity and polymer segmentaldynamics are decoupled!

max conductivity at 50C ~ 10-5 S/cm

crystallinePEO

Fullerton-Shirey, Macromolecules 42, 2142 (2009)


Move to a different kind of PEO > hyper-branched PEO

HB PEO

linear PEO

•Hyper-branched structure can be controlled and varying degree ofcrystallinity can be achieved.

•At 50C, conductivity is 10-4 S/cm.improvement by a factor of 10! At RT, an increase of 100!

•50% HB sample shows considerable reduced conductivity and mobility in NS experiment.

PEO segmental motion and Li+transport seem to be coupled.

Lee et al, Accepted in Chemistry of Materials


LiN(CF3SO2)2

06/13/2011

Different segmental dynamics (α(α(α(α−−−−relaxation)for each component in the blend

50/50

100% 100%

1/T

log ττττ

TgA TgB

Chain connectivityeffects

Segmental Dynamics in Polymers and Polymer Blends

PIPI in PI/ PVEPVE in PI/PVEPVE


06/13/2011

-10

-9

-8

380 400 420 440 460 480

∆T=34K

Tg T

g

log[

a(T

)τΜ

(Q=

1Å

-1)(

s)]

blend(DSC)

T,T+∆T (K)

-10

-9

-8

380 400 420 440 460 480

log[

a(T

)τΜ

(Q=

1Å-1

)(s)

]

T, T+∆T (K)

∆T=23K

Tg T

g,eff

PVAc,LML

A shift in glass transition temperatureor equivalently, concentration effectscan be used to explain the dynamicsof high-Tg component.

Lodge McLeish ModelTyagi, Macromolecules, 2007


-0.7

-0.6

-0.5

-0.4

200 250 300 350

hea

t flo

w (

W/g

)

T (K)

Tg = 280 K

blend

Tg - 220 K

PEO

Tg = 315 K

PVAc

PVAc (high-Tg) in BLEND

06/13/2011

Backscattering Measurements: PEO in hPEO/dPVAc

Gaussian distribution of log ττττ

1

10 270K290K350K375K400K

σ

-11

-10

-9

-8

-7

0.1 1

log[

τ o(s)]

Q (Å-1)

Q-4

(b)

1

10

100

I(Q

,ω)

(a.u

.)

T = 270 K

Q = 1Å-1

1

10

100T = 290 K

I(Q

,ω)

(a.u

.)

1

10

100T = 350 K

I(Q

,ω)

(a.u

.)

1

10

100

T = 375 K

I(Q

,ω)

(a.u

.)

1

10

100

-15 -10 -5 0 5 10 15

T = 400 K

hω(µeV)

I(Q

,ω)

(a.u

.)

Q-independent timescales at high Q

270K

350K

400K

dynamicconfinement

standardscenario


-0.7

-0.6

-0.5

-0.4

200 250 300 350

hea

t flo

w (

W/g

)

T (K)

Tg = 280 K

blend

Tg - 220 K

PEO

Tg = 315 K

PVAc

PEO (low-Tg) in BLEND

06/03/2010 HFBS/DCS Tutorial

-12

-10

-8

-6

-4

-2

2 2.5 3 3.5 4 4.5 5

log

[τm

ax(s

), Q

~1.

5Å-1]

1000 / T(K-1

)Glass-forming liquid

-like dynamics

0

0.1

0.2

0.3

0.4

0.5

-15 -14 -13 -12 -11 -10 -9

g(lo

gτ)

log [τ(s)]

<σσσσ>400K

=0.71 ββββ=0.5

-11

-10

-9

-8

-7

0.1 1Q(Å

-1)

log

< τ(

s) > T = 400 K

~ Q-4

~ Q-independent σσσσ

pure

PEO

Tg

blend

0

0.1

0.2

0.3

0.4

0.5

-14 -12 -10 -8 -6 -4log [τ(s)]

1.16Å-1

0.65Å-1

0.29Å-1g[lo

g(τ

)]

ββββ=0.5

-11

-10

-9

-8

-7

-6

0.2 0.4 0.6 0.8 1

T = 350 K

log

< τ(

s) >

Q(Å-1

)

l c ~1nm

Q-dependent σ!σ!σ!σ!

τ∗

0

0.1

0.2

0.3

0.4

0.5

-15 -10 -5 0

g(lo

gτ)

log [τ(s)]

ββββ=0.5

1.16Å-1

0.76Å-1

0.43Å-1

T = 270 K

Q-dependent σσσσ

-10

-9

-8

-7

-6

0.4 0.6 0.8 1

log

[τo(s

)]

Q (Å-1

)

~ Q-4

270 K

290 K

crossover confined

Overall Picture Tyagi, Macromolecules, 39 (2008)


Confinement Effects in Polymer Blends

Logτ

1/T

ττττ∼∼∼∼111100000000s

Glass-forming liquid-like dynamics

Glassydynamics

TgA Tg

B

<Tg>

TgeffA/AB Tgeff

B/AB

Equilibrium two componentGlass-forming system

Confineddynamicscrossover

Confined dynamics of B-component

Glassy systemfrozen


Logτ

1/T

ττττ∼∼∼∼111100000000s

Glass-forming liquid-like dynamics

Confineddynamics

Glassydynamicscrossover

TgA Tg

B

<Tg>

TgeffA/AB Tgeff

B/AB

Equilibrium two componentGlass-forming system

Confined dynamics of B-component

Glassy systemfrozen

Confinement Effects in Polymer Blends

06/13/2011

…even inelastic neutron scattering…


06/13/2011

Low-T dynamics of confined CH3I molecule

Full pore = bulk-like peaks + new at 4 µeV

Origin: i) low energy peaks → core ii) high energy peaks → surface

full porepartially filledbulk

T=5K

Dimeo et al., Phys. Rev. B 63, 014301 (2000)

Porous glasspore diameter 58Å

Overall picture:1) Core → high degree of local order (5%)2) Peaks at 4µeV: surface moleculesi) strongly disordered 70%ii) weakly disordered 25%


06/13/2011

Rotational tunnelingof the ammonium ions

0 20 400.000

0.005

0.010

Neutron Energy Transfer / µeV

a.

b.

c.

A

T

E

-20 -10 0 10 20 30

4 K

20 K

25 K

40 K

30 K

Neutron Energy Transfer / µeV

Inel

astic

Sca

tterin

g In

tens

ity

50 K

60 K

Thermally activatedjumps

NaBH4

KBH4

(NH4)2B12H12


Recent examples of Tunneling and Rotational motions probed by HFBS

2-site/3-site jump

High-T arrangementsof H atoms around B

Verdal, Submitted to J. Chem. Phys.Verdal, J. Phys. Chem. C 2010, 114, 10027–10033

06/13/2011

….Thank you!


Documents

Madhusudan Tyagi NIST Center for Neutron Research Tyagi NIST Center for Neutron Research Spectroscopy Summer School 2011 06/13/2011 Typical Scans on HFBS I: Elastic Scan 0 0.2 0.4