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Neutrons and Soft Matter

Neutrons and Soft Matter. Aurel RADULESCU Jülich Centre for Neutron Science JCNS, Outstation at MLZ, 85747 Garching, Germany 7 July 2014. Outline. Soft Matter – definition , examples , applications Soft Materials – structural and dynamical properties

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Neutrons and Soft Matter

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  1. Neutrons and Soft Matter Aurel RADULESCU Jülich Centrefor Neutron Science JCNS, Outstation at MLZ, 85747 Garching, Germany 7 July 2014

  2. Outline • Soft Matter – definition,examples, applications • Soft Materials – structuralanddynamicalproperties • Relevanceof Neutron Scattering • Small-Angle Neutron Scattering (SANS) • Neutron Spin-Echo (NSE) • SANS and NSE at JCNS and FZJ • Conclusions

  3. Soft Matter – Definition Soft Materials • “molecular systems giving a strong response to very weak command signal” PG deGennes (1991) • - easily deformed by small external fields, including thermal stresses and thermal fluctuations • - relevant energy scale comparable with RT thermal energy • - subtle balance between energy and entropy  rich phase behavior and spontaneous complexity crystallinestate Soft Matter liquid state structure: shortrangetolongrange order dynamicresponse: elasticandviscousproperties

  4. Soft Materials Soft Matter materials: common features • structural units: much larger than atoms • large molecules, assemblies of molecules that move together • large, nonlinear response to weak forces • slow, non-equilibrium response mechanicalresponserubbers elongatedseveralhundred % ofinitiallenght no linear relationbetween stress andstrain response time liquid ~ 10-9 s polymer orcolloidalsolution ~ 1 … 10-4 s

  5. Soft Matter – qualitative and quantitative “Soft” – qualitative property shear modulus G – quantitative parameter restoring force of a deformed material which tends to recover its own shape (elastic materials) “softness” – smallness of G bulk modulus K of soft mater same order as for metals shearmodulus ShearmodulusG metals: some 10 GPa soft matter: < 0.1 GPa liquids: 0 Gpa Bulk modulus K metalsand soft matter: >1 GPa bulkmodulus

  6. Example: molecularvsmacromolecularcrystals macromolecular (colloidal) crystals: molecule size ~1mm molecular crystals (NaCl): unit size ~ 1Å unit size molecular crystal << unit size colloidal crystal F – shearingforce DL – crystaldeformation G ~ energy/(length)3 typicalinteractionenergy ~ kBT Gcolloidalcrystalis 12 ordersof magn. smallerthanGusualcrystal S. Kaufmann et al. J Mater Sci (2012) 47:4530–4539

  7. Examplesof soft matter systems • Complexfluidsincludingcolloids, polymers, surfactants, foams, gels, liquid crystals, granular andbiologicalmaterials. Y. Roiter and S. Minko AFM biological membrane

  8. Soft-Matter Triangle

  9. Applications– everydaylife

  10. Soft Matter – high-techapplications polymericand soft compositematerialsas additives foroilindustry tyrescontainingnanostructuredaggregates: lessenergyto roll → save fuel understandingformationofnanoparticles: keyfornewproductsfromdetergentstocosmetics environmentallyfriendlycleaners

  11. Staticproperties – statisticalparameters statistical „randomwalk“ effect segmentlength: a numberofsegments: N contourlength: Na End-to-end length Fulllengthcontour: lengthofthestretched polymer L=((bondlength)*(cos(109.47°-90°)/2))*(#C-1) Radius ofgyration (averageextensionfromthecenterofmass)

  12. Polymer architecture homopolymer heteropolymer (diblock)

  13. Polymer aggregates – shape distance distribution function for different shapes

  14. Polymer conformation long-range repulsion R L  aN good solvent R  aN3/5 q-solvent R aN1/2 poor solvent R aN1/3 Monomer size a~0.1nm Number of monomers N~102 – 1010 Contour length L~10nm – 1m homopolymer star-like block copolymer: n and m – number of repetitive units for the blue-solvophilic and the red solvophobic blocks

  15. Polymer morphology Morphologycal behavior of PEP-PEO in solution

  16. Dynamicalproperties A. Wischnewski & D. Richter, Soft Matter vol. 1, 2006 Ed. G. Gompper & M. Schick polymer chains in the melt 3D Fickiandiffusion localreptation each chain can be considered to be constrained within a tube – topological constraints Rousedynamics center-of-massdiffusion

  17. Dynamicalproperties – tubeconcept Lateral confinement Rousemodel – dynamicsofGaussianchain at intermediate scale Localreptation – randomwalk Diffusion alongthetube - reptation

  18. Neutron Scattering – key in Soft-Matter

  19. Lengthscale – Time scale

  20. Neutrons exhibitveryspecialproperties • Organicandbiologicalcompoundsconsistofprimarily C, H, N, O • Hydrogen (H) and Deuterium (D) scatterverydifferently • Simple H/D substitutionallowshighlighting / maskingstructures Ideal for Soft Matter

  21. ScatteringTheory

  22. Small-angle neutronscattering

  23. Small-angle neutronscattering

  24. The form factor intraparticlecorrelations

  25. Contrast Variation hPS-dPBmicelles (Fpol=0.25%) in different solventsfor different contrasts R. Lund et al., 2013

  26. Experimental aspects – resolutionandpolydispersity

  27. SANS - Examples PEP-PEO J. Stellbrink et al., 2005 structure factor effect effect of asymmetry in MW L. Willner et al., 2010

  28. Neutron Spin-Echo Dl/l=10-20% decouplingdetectabilityoftinyvelocitychangescausedbythescatteringprocessfromthewidthoftheincomingvelocitydistribution thekeyistheneutronspin

  29. Neutron Spin-Echo • relaxation-type scattering, functionof time • J – integral ofthemagneticinduction • – gyromagneticratio D. Richter et al., 1994 • meaningofthescatteringfunction • deuterated polymer matrixcontaining a few % protonatedchains → coherentsinglechaindynamicsin the SANS regime • sample containingonlyprotonatedchains → incoherentscatteringfunction– self-correlationofprotonsofchainsegments → segmental mean-squaredisplacement <r2(t)> fit – Rousemodel Q=1nm-1

  30. Neutron Spin-Echo A. Wischnewski et al., 2003 plateau – topologicalconstraints theonlyfreeparameter – thetubediameter: d=6nm PEP melt, 492K Tube concept – pair correlationfunctionof a singlechain in themelt

  31. SANS and NSE at JCNS@MLZ KWS-2 SANS diffractometerl=4.5 .. 20Å; Dl/l=2%..20% max. flux 2x108 ncm-2 s-1 Q-range: 1x10-4 .. 0.5Å-1 (withlenses) J-NSE spectrometer l=4.5 .. 16Å; Dl/l=10% Fourier time ranget=2ps.. 350ns

  32. Phase behaviorof C28H57-PEO M. Amann et al., 2014 expected change in aggregation number Nagg → exploring the phase diagram usingchopper at KWS-2: solid-solid phasetransition fcc→ bcc observed f=15% f=30% fcc

  33. Conclusions • Soft Matter Systems – greatrichnessofproperties, complexsystems • SANS – uniquemethodforstructuralinvestigation • NSE – uniquemethodfordynamicalinvestigation • KWS-2 & J-NSE – dedicatedneutronscatteringinstrumentsto soft-matter systems

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