Small-angle X-ray scattering - Hasylab - Desy

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$Grazing Incidence X-ray Diffraction - Hasylab$

Form factor & structure factor of particles • Intensity = form factor x structure factor I(q) = P(q)S(q) – This equation works if you have spherical monodisperse particles, otherwise the factors may be more mixed • Structure factor S(q) is related to the ordering and distance between particles • Form factor tells about the shape and size of the particles – In a very dilute solution of particles I(q) = P(q) because S(q) = 1 P(q) Form factor More on form factors of differently shaped particles: Jan Skov Pedersen: Analysis of small-angle scattering data from colloids and polymer solutions: modeling and least-squares fitting. Advances in Colloid and Interface Science 70 (1997) 171-210. q P(q)S(q) S(q) q Structure factor q Total scattering
Far from ideal Real systems have nasty effects which disturb the perfect SAXS measurement of particles • “Concentration effect”: The contribution of the structure factor increases when the particle concentration increases (order is increased) •Concentration series is usually needed and then one can extrapolate to 0concentration and determine the particle shape and size • “Polyelectrolyte effect”: Charged particles (negative or positive) in solution give always a structure factor •Add salt to suppress the interaction caused by charges (but this can make the particles willing to aggregate!) Problem 1: Why measuring very dilute solutions is not usually possible? Problem 2: Why you cannot measure forever long a sample with a synchrotron beam? Intensity / concentration Concentration effect Concentration increases Concentration increases q Polyelectrolyte effect
Page 1 and 2: The very basics of Small-angle X-ra
Page 4 and 5: 20 40 60 80 Small is big & big is s
Page 6 and 7: Oriented samples (example) Organocl
Page 8 and 9: Example of a SAXS beamline, B1 SAXS
Page 10 and 11: 0 200 400 600 800 Scattering from a
Page 12 and 13: Intensity (arbitrary units) 10 10 1
Page 14 and 15: Surface fractal Koch snowflake, sur
Page 18 and 19: Scattering from particles Distance
Page 20 and 21: N(R) = number size distribution R =
Page 22 and 23: Example: Ontime chemistry at beamli
Page 24 and 25: Example: Spinodal decomposition in
Page 26 and 27: Two-phase approximation • Only me
Page 28 and 29: Lignosulfonate, the brown stuff in
Page 30 and 31: SAXS beamlines at DORIS III • SAX
Page 32: Programs to analyze SAXS data But b

Small-angle X-ray scattering - Hasylab - Desy

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