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Impact of Interfacial Roughness on the Sorption Properties of Nanocast Polymers

Sridhar, Manasa, Gunugunuri, Krishna R., Hu, Naiping, Motahari, Ahmad, Zuo, Xiaobing, Schaefer, Dale W., Thiel, Stephen W., Smirniotis, Panagiotis G.
Macromolecules 2016 v.49 no.7 pp. 2663-2670
X-ray diffraction, foams, fractal dimensions, lysozyme, models, nitrogen, polymers, roughness, small-angle X-ray scattering, sorption, sorption isotherms, transmission electron microscopy
Nanocasting is an emerging method to prepare organic polymers with regular, nanometer pores using inorganic templates. This report assesses the impact of imperfect template replication on the sorption properties of such polymer castings. Existing X-ray diffraction data show that substantial diffuse scattering exists in the small-angle region even though TEM images show near perfect lattices of uniform pores. To assess the origin of the diffuse scattering, the morphology of the phenol–formaldehyde foams (PFF) was investigated by small-angle X-ray scattering (SAXS). The observed diffuse scattering is attributed to interfacial roughness due to fractal structures. Such roughness has a profound impact on the sorption properties. Conventional pore-filling models, for example, overestimate protein sorption capacity. A mathematical framework is presented to calculate sorption properties based on observed morphological parameters. The formalism uses the surface fractal dimension determined by SAXS in conjunction with nitrogen adsorption isotherms to predict lysozyme sorption. The results are consistent with measured lysozyme loading.