Pore size and volume effects on the incorporation of polymer into macro- and mesoporous zirconium titanium oxide membranes.

Macro- and mesoporous hybrid materials have applications in the fields of drug delivery, catalysis, biosensing, and separations. The pore size requirements must be well-understood to maximize the performance (e.g., load capacity and accessibility) of such materials. Hybrid materials were prepared by coating five distinct macroporous commercial membranes with zirconium titanium oxide through sol-gel chemistry. Calcination of these templated materials produced oxide membranes which had a suite of macropore and mesopore architectures, pore volumes, and surface areas. These differences in physical properties were used to conduct a fundamental study on the relationship between the pore size and volume and the polymer incorporation. Metal oxide membranes were postsynthetically modified with poly(ethyleneimine) (PEI) ranging in molecular weight from 1300 to 1 000 000 Da (1.2-11 nm in hydrodynamic diameter). The incorporation of the polymer from a 9 wt % solution at pH 10 was highly dependent on the pore size and pore volume. As the surface area increased, loading capacity decreased, indicating that much of the increased internal surface, due to small pore diameters (< or = 8 nm), was inaccessible to the macromolecules. Exclusion of PEI from small mesopores was apparent even for the lowest molecular weight polymer. A high maximum loading of 1.25 mg m(-2) of 600 000-1 000 000 Da PEI was achieved in the metal oxide with the largest minimum mesopore diameter. Thus, mesopore diameter and pore volume must be considered when designing a mesoporous solid support.