19 research outputs found
Small-angle scattering behavior of thread-like and film-like systems
A film-like or a thread-like system is a system such that one of its
constituting homogeneous phases has a constant thickness or a constant
normal section of largest diameter . The stick probability function of
this phase, in the limit , naturally leads to the definition of
the correlation function (CF) of a surface or a curve. This CF fairly
approximates the generating stick probability function in the range of
distances larger than . The surface and the curve CFs respectively
behave as and as . In the two cases, this result implies
that small-angle scattering intensities of the relevant samples respectively
behave as and in an intermediate range of the scattering vector
and as in the outermost one. One reports the analytic expressions
of the pre-factors of these behaviors. It may happen that a sample looks
thread-like at large scale resolution and film-like at smaller one. The surface
and the curve CFs have explicitly been evaluated for some simple geometrical
shapes. Besides, it is also reported the algebraic expression of the circular
cylinder CF in terms of two elliptic integral functions, and it is shown that
the limits of this CF, as the height or the radius of the cylinder approaches
to zero, coincide with the CF of a disk or a linear segment, respectively.Comment: 37 pages, 18 figure
Diffuse Interfaces and Small-Angle Scattering Intensity Behaviour
The contributions corresponding to the Porod, the oscillatory O(h−4) and the Kirste–Porod O(h−6) terms, present in the asymptotic expansion of the small-angle scattering (SAS) intensities, are numerically evaluated, in the presence of diffuse interfaces generated by different smoothing functions (Gaussian, spherical or Helfand–Tagami). It is shown that SAS experiments are generally unable to distinguish among different profiles, because any smoothing can be made to coincide with another type by scaling its thickness parameter. The oscillatory deviations are observable in the Porod plot of the intensities when the typical distance between parallel diffuse interfaces is greater than 50 A and the ratio of the thickness to this distance is less than 1/4. The same conclusion applies to the infinite-slit intensities