Interpretation of a Specific Point in the Relationship between Zero‐Angle Intensity and Contrast Observed by X‐ray Small‐Angle Scattering

The iso‐zero‐angle‐intensity point (abbreviated as isoZAI point) is a specific point at which X‐ray zero‐angle intensities of samples with different structures take a constant value. The isoZAI point was first observed in X‐ray contrast‐variation studies of a homologous series of micelles. The condition for appearance of the isoZAI point has been theoretically derived by consideration of samples with inhomogeneous internal structure. The condition is given bywhere ν ij and ρ ij are the volume and electron density of j th internal domain of the i th sample (1 ≤ i ≤ N , 1 ≤ j ≤ M ), respectively. ρ 0 * denotes the position of the isoZAI point on the electron‐density scale. The isoZAI point was found to give useful information for analysis of X‐ray or neutron small‐angle scattering data measured by the contrast‐variation method.