# Presentation: 184928

## XPCS and Science Opportunities at NSLS-II

- Bob Leheny
- Johns Hopkins University

## X-ray Photon Correlation Spectroscopy

- Dynamic light scattering with x-rays

- Autocorrelation of intensity...

- Gives dynamic structure factor:

- I(Q,t’)

- t’

- g2(Q,t)

- t

- _X-ray Photon Correlation Spectroscopy_

## Examples of XPCS topics to date:

- _Soft matter:_

- _Hard matter:_

- • Polymers

- • Antiferromagnetic domain motion

- • Charge density wave motion

- • surface & interfacial fluctuations

- • reptation

- • phase separation and mesophase ordering

- • Smectic liquid crystals

- • Colloids

- • gels

- • glass transitions

- • Order-disorder transitions in alloys

## Prospects for NSLS-II

- = accumulation time (≈ minimum delay time t)

- = source brilliance

- = cross section per volume

- Signal-to-Noise in g2(Q,t):

- (Falus et al., JSR 2006)

- • Optimization of coherent flux

- x 10

- • Intrinsic brilliance

- Consequences:

- • Minimum delay time shortens substantially:

- Potential improvement at NSLS-II over APS (8-ID)

- - vertical focusing

- x 30

- • Weaker scatterers become accessible.

- = energy bandpass

- - wider

## What occurs in 100 ns? 

- E.g., a 6 nm sphere in water diffuses its diameter

- Nanoscale dynamics in aqueous solution become accessible to XPCS

- Suggests studies of:
- 	• nanoparticle motion/self-assembly in low-viscosity solutions
- 		in bulk and on surfaces
- 	• biologically relevant systems

- Overlap with Neutron Spin Echo in reach!

- S(Q,t) from 10-11 s < t < 104 s

## Fluctuations in lipid membranes

- protein
- conformation

- NSE of higher Q dispersion indicates:

- Potentially interesting range of length scales could be accessible at NSLS-II

-  ≈ 10-6 s

- at   Q ≈ 0.03 - 0.1 nm-1

- membrane
- elastic modulus

- protein
- conformation

- active fluctuations driven by protein dynamics

- •

- •

## Another membrane system: bicontinuous microemulsions

- • Numerous such nanostructured soft materials have intrinsic dynamics in the window that NSLS-II will fill.

- oil

- water

- Long-standing theoretical predictions for dynamical
- behavior.

- Important in applications

- Fluctuations at relevant wave vectors (~2/d):
- 		too slow for NSE, too short for DLS
- 		well suited for XPCS at NSLS-II

- e.g. unique nanostructured materials through polymerization

- d ~ 10 nm

- templates for chemical reactions

- Others likely include lamellar phases (smectics), ringing gels, etc.

- Gompper et al.

## Protein & protein complex conformational fluctuations

- _Protein & protein complex conformational fluctuations_

- • Potentially important for function.

- • Deviations of diffusion from rigid-body behavior

- • Fluctuations involving large-scale conformational changes can occur on microseconds to milliseconds.

- e.g. enzymatic activity

- - Demonstrated with NSE for domain-scale fluctuations ( ~ 10 ns)

- • Potential strategies to access fluctuations with XPCS:

- • Time dependence of diffuse scattering around bragg peaks of protein crystals (???)

- Enzyme from *E. coli*

- H. Yang, UC Berkeley

- (Z. Bu et al., PNAS 2005)

-  ~ 100 s

## Other interesting opportunities with XPCS at NSLS-II

- 1) Expanding polymer research:

- Surface fluctuations

- Reptation

- • Highly successful phenomenological model

- • Motion accessible to XPCS (Lumma et al,. PRL, 2001)

- • Broader dynamic range will illuminate:

- - Rouse-to-reptation crossover

- - Specific nature of relaxation (e.g., constraint release)

- • Well suited for XPCS (Kim et al., PRL, 2003)

- - probe nature of fluctuations at molecular scales: Rg, entanglement length

## 2) Local dynamics in glassy materials

- Approach to glass transition characterized by growing separation of time scales:

- “” and “” relaxations

- slow, terminal
- relaxation

- fast, localized
- motion

- Eg., gelation and aging in nanocolloidal suspensions

- accessed
- experimentally

- inferred

- NSLS-II will have dynamic range to track full relaxation spectrum.

- APS, 8-ID

## Analysis beyond g2(Q,t) required.

- Systems far from equilibrium characterized by:

- Spatial and/or temporal heterogeneity

- Intermittent (non-Gaussian) dynamics

- Eg., “degree of correlation”:

- dilute colloidal gels

- Duri & Cipelletti, EPL (2006)

- Large, non-Gaussian fluctuations

- temporal heterogeneity

## Other ideas from DLS for characterizing intermittent dynamics :

- • Higher order moments:

- • Speckle-visibility spectroscopy

- NSLS-II should make these (and other) analysis approaches feasible for XPCS.

- ,

- etc.

- (Lemieux and Durian, Appl. Opt. 2001)

- (Bandyopadhyay et al., RSI 2006)

- Measure variance in speckle intensity as a function of exposure time.

- (Note:

- )

## Conclusion

- NSLS-II will _revolutionize_ XPCS.

- But,

- Realizing many of these advancements will require a corresponding improvement in detector technology...

## K = detector efficiency

- T = total experiment duration
-  = accumulation time
-  = angle subtended by Q of interest
-  = scattering cross section per unit volume
- W = sample thickness
- = 1/attenuation length
- B = source brilliance
- E/E = normalized energy spread
- r = factor depending on source size, pixel size, and slit size