Multimodal Particle-Size Distribution or Fractal Surface of Acrylic Acid Copolymer Nanoparticles: A Small-Angle X-ray Scattering Study using Direct Fourier and Indirect Maximum-Entropy Methods

Acrylic acid copolymers are potential carriers for drug delivery. The surface, surface rugosity and the absolute dimension of the particles are parameters that determine the binding of drugs or detergents, diffusion phenomena at the surface and the distribution of the carrier within the human body. The particle-size distribution and surface rugosity of the particles have been investigated by small-angle X-ray scattering and dynamic light scattering. Direct Fourier transform as well as a new strategy for the indirect maximum-entropy method MAXENT are used for data evaluation. Scattering equivalence of a pure multimodal distribution of hard spheres (five populations) and a mixed multimodal-surface-fractal model (four populations) was found. Model calculations and dynamic light-scattering experiments gave evidence of the multimodal particle-size distribution combined with the fractal surface of the carrier. The main moiety consists of particles 90 nm in diameter which are surface fractals in the 10 nm region.