Structure and Dynamics at the Nanoscale Probed by XPCS Alec Sandy X-Ray Science Division Argonne National Laboratory
Outline Motivation XPCS XPCS at beamline 8-ID at the APS Selected XPCS results from 8-ID at the APS Complex glass dynamics Bimodal suspension dynamics Future Directions Protein Dynamics Conclusions
Motivation Copolymer Dynamics as a probe of the energy landscape or stability of complex so6 materials Hierarchical order in so6 ma9er results from narrowly- separated, compe>ng length and energy scales Resul>ng behavior is intermediate between that of fluids and crystalline solids Melt Physical nature of slow equilibrium and non- equilibrium dynamics of complex nano- structured materials vis- à- vis stability Jamming aging glass dynamics Consumer and industrial products Foods, personal care products, Energy Oil recovery, Copolymer phases Pictures courtesy of N. Balsara, UC- Berkeley
XPCS Malvern Technical Note MRK- 656-01 Dynamic light sca9ering (DLS) or photon correla>on spectroscopy (PCS) but with x- rays rather than laser light: 1. Illuminate a disordered sample with a (par>ally) coherent x- ray beam 2. Collect the speckled sca9ered beam with a high resolu>on detector
XPCS 3. Monitor speckle pa9ern as a func>on of >me so that changes in the speckle pa9ern can be observed Large Particles Small Particles Intensity Time Time 4. Calculate the >me auto- correla>on of the fluctua>ng signal at a par>cular wave vector to yield informa>on about the nature and >me scale of sample fluctua>ons at that length scale Intensity g ( Q, τ ) (, ) (, + τ ) I Q t I Q t 2 2 I g2( Q, τ ) "
XPCS Why XPCS as opposed to PCS? Smaller length scales than PCS Natural length scale of many technologically and scientifically relevant emerging materials Flexibility per sample or solvent combinations such as opaque and translucent samples Light scattering in similar systems is state-of-the-art
XPCS at 8-ID Most measurements in small-angle geometry with direct detection area detectors Polymers, colloids, filled polymers Simple but effective pinhole SAXS set-up Very good at small Q scattering with minimal parasitic scattering near USAXS pinhole SAXS Set-up naturally complementary with time-resolved SAXS pink-beam capable Mono or 8-ID-I Pink beam Small-angle XPCS 65 m 8-ID-D 8-ID-E Mono beam GISAXS G large Q XPCS E 51 m Undulator A 0 m 8-ID-A FOE 30 m > 4X10 9 ph/s/(20 x 20 um) 2 > 1013 ph/s/2%
Complex Glass Dynamics Motivation Understanding the glass transition remains a grand challenge in condensed matter physics What is the nature of dynamics in the glassy state? Are there distinct glassy phases? R U R F. Sciortino, Nature Materials 1, 145 (2002)
Complex Glass Dynamics repulsive glass Increasing attractive potential liquid attractive glass F. Sciortino, Nature Materials 1, 145 (2002) Mode coupling theory phase diagram for sticky hard spheres plotted vs. stickiness and volume fraction (φ) From L Fabbian, W Götze F Sciortino, P Tartaglia, F Thierry, Phys. Rev. E 59, R1347 (1999).
Complex Glass Dynamics n Summary of theoretical predictions for glass behavior: n A colloidal glass with hard-sphere (HS) repulsions (repulsive glass) may be melted by switching on a short-ranged attractive interaction n Density fluctuations decay logarithmically versus time, in the liquid where attractive and repulsive arrest mechanisms compete n Such a melted glass may be re-vitrified upon further increase in the attraction and become an attractive glass.
Complex Glassy Dynamics How are weakly attractive potentials added to colloidal systems Depletion-like interactions R" More excluded volume less entropy Slide courtesy of B. Leheny, JHU Less excluded volume more entropy effective attraction
Complex Glassy Dynamics Experimental realization at 8-ID is concentrated 200 nm radius silica spheres in a 2-component fluid: water and lutadine Vary temperature and silica sphere concentration to move through glass phase diagram 200 nm radius silica spheres V. Gurfein, D. Beysens and F. Perrot, Phys. Rev. A 40, 2543 (1989)
Complex Glassy Dynamics SAXS (and transmission) measurements and single parameter fits to a theoretically predicted model for S(Q) provide information on the phase diagram Model for S(Q) for sticky hard spheres from K. Dawson et al., Phys. Rev. E 63, 011401 (2000) One parameter, the product of the attractive potential and depth, was varied in the fits. R determined in the repulsive glass and Φ determined from transmission
Complex Glassy Dynamics Dynamics probed via XPCS (5 fps) ΔT = +0.06 K Liquid or glass? Liquid or glass?
Complex Glassy Dynamics Answers: ΔT = +0.06 K Glassy liquid Attractive glass
Complex Glassy Dynamics Intermediate scattering functions determined via XPCS Repulsive glass Revitrification Attractive glass Melted phase logarithmic correlation decays Melted phase liquid-like correlation decays Logarithmic relaxation in glass-forming systems, W. Götze and M. Sperl, Phys. Rev. E 66, 011405 (2002)
Complex Glassy Dynamics Experimentally-determined phase diagram for water, lutadine, silica spheres Log. decay Liquid Attractive Glass Stretched Exp. Repulsive Glass Summary XPCS used to probe complex glassy dynamics Re-entrant glass transition Fluid with unusual correlation decays X. Lu, S. G. J. Mochrie, S. Narayanan, A. R. Sandy, and M. Sprung, Phys. Rev. Lett. 100, 045701 (2008). X. Lu, S. G. J. Mochrie, S. Narayanan, A. R. Sandy, and M. Sprung, Soft Matter 6, 6160 (2010).
Bimodal Suspension Dynamics Mo>va>on Bimodal suspensions occur frequently in nature Explosive (and non- explosive) ash from Spring 2010 Icelandic volcano erup>on Milk BBC News S. Gislason et al., PNAS 108, 7307 (2011) Model system for exploring structure and dynamics versus poly- dispersity 18
Bimodal Suspension Dynamics Sample Mixtures of sulfate latex spheres suspended in glycerol: R B = 54.6 nm and R S = 11 nm Fixed total volume frac>on Φ = Φ B + Φ S = 0.4 Mixture composi>on, ε B, defined by: ε φb φ + φ B = = B S φb φ Bimodal suspensions examined: ε B = 0.00, 0.04, 0.17, 0.28, 0.48, 0.68, 0.77, 1.00! = R LARGE R SMALL! 5 19
Bimodal Suspension Dynamics SAXS results well- described by addi>on of a spheroid term: ε B a 0.00 b 0.04 c 0.17 ε B =0.68 u Sticky Hard Spheres Model R B r d 0.28 e 0.48 f 0.68 g 0.77 u 0 Δ h 1.00 I( q) φ S ( q) f ( q) + φ S ( q) f ( q) + φ f ( q) B BB B S SS S Spheroid (R Sticky Hard Sphere Model Hard Sphere Model M ) With increasing ε B, large spheres are less sticky M M 20
Bimodal Suspension Dynamics Dilute mixtures of large spheres exhibit dynamics slower than large- sphere suspensions Deple>on induced aggregates of large (and small spheres) diffuse slowly and dominate measurements 21
Bimodal Suspension Dynamics Summary M. Sikorski, A.R. Sandy, S. Narayanan, PRL 106, 188301 (2011). 22
Future Directions Extensions to biologically- relevant materials like proteins Brighter sources Harder x- rays More sensi>ve and faster detectors Extensions to sample variables other than temperature and composi>on Brighter sources Harder x- rays More sensi>ve and faster detectors Figure courtesy of M. Spannuth Figure courtesy of W. Burghardt
Protein Dynamics XPCS to probe the dynamics of eye- lens- protein mixtures (L. Lurio, J. DeBartolo, G. Thurston, Nuwan K.) Physiological mo>va>on Cold cataract is due to reversible liquid- liquid phase separa>on in young, mammalian eye lenses S>ffening of eye- lens presbyopia (far- sightedness) possibly associated with liquid- glass transi>on in protein mixture Dynamics measurements provide informa>on on rate of phase separa>on, elas>city X- rays provide informa>on on local nanoscale diffusion and diffusion of clusters of proteins (cf. light sca9ering) NSSRC Users Meeting Oct. 2011 24
Protein Dynamics XPCS to probe the dynamics of eye- lens proteins (L. Lurio, J. DeBartolo, G. Thurston, Nuwan K.) Physics mo>va>on Dynamics of concentrated s>cky spheres Technical mo>va>on Extend XPCS to biological materials in aqueous solu>on Faster >me scales Higher x- ray energies Detector usability and robustness Experienced and local user group Intermi9ent trials over the years as test of state- of- the- art XPCS 25
Conclusions XPCS can now be used to measure complex dynamics in a range of physically interesting systems There is significant room for additional growth with: Brighter sources New and improved 3 rd generation light sources 4 th generation light sources Additional users from outside traditional communities Biophysics, geophysics, Faster, more efficient detectors
Acknowledgements 8-ID Personnel Jin Wang, Time-Resolved Research Group Leader at the APS Suresh Narayanan Post-doc Marcin Sikorski (now at LCLS) Partner Users Prof. Larry Lurio, Northern Illinois University Prof. Simon Mochrie, Yale University Graduate Students Xinhui Lu, Yale (now at BNL)