Polyelectrolyte multilayer hollow capsules studied by small-angle neutron scattering (SANS)

Silica-templated polyelectrolyte (PE) hollow capsules with various template diameters and PE layer numbers were fabricated by using the layer-by-layer technique and subsequent core dissolution in hydrofluoric acid. The properties of the resulting freestanding polyelectrolyte multilayers (PEM) were characterized in an aqueous environment by means of SANS and compared with scanning force microscopy (SFM) data. The thickness of the capsule wall was found to be about 25% thicker and with correspondingly higher water content than the template-supported PE layers. The wall thickness increase as a result of core dissolution was anisotropic. The average single layer thickness of hollow capsules was independent of the surface curvature and decreased slightly with increasing PE layer number. SANS was used to determine whether the capsules were empty or contained the rest of the core. An annealing at 70 °C for 4 h induced capsule shrinking by about 20% at an ionic strength of 1 mol L⁻¹. Furthermore, the capsule wall upon annealing increased in thickness by about 38%. These changes corresponded to a wall densification of about 13%.