Positron annihilation spectroscopy study of polyethyleneimine-modified mesoporous cellular foam under different atmospheres

A novel mesoporous cellular foam (MCF) was prepared and modified with polyethyleneimine (PEI, 60 wt%) with varying molecular weights (M.W. 600, 1800, 10,000). The effects of PEI-modified MCF on nano-scale pore structure were systematically studied by positron annihilation lifetime spectroscopy (PALS), coincidence Doppler broadening spectroscopy (CDB) and conventional characterization methods, such as N 2 adsorption and desorption, Fourier transform infrared spectroscopy, small angle X-ray scattering (SAXS) and CO 2 adsorption analysis. Positron annihilation CDB test of PEIs/MCF were performed under vacuum conditions and N 2 , CO 2 , air, O 2 atmospheres respectively. Samples MCF and MCF-20–600 (20 wt% of PEI), which are sensitive to atmospheric changes, were selected for PALS test, the annihilation mechanism of positrons in different atmospheres was investigated, and it was found that the long-lifetime of ortho-positronium (o-Ps) decreased obviously in O 2 atmospheres, which may be related to the spin conversion quenching of o-Ps, and calculate the mesoporous size with theoretical models, and it was found that after the impregnation of PEI into MCF, the mesopore size decreases. The results show that the MCF modified with lower molecular weight PEI showed higher CO 2 adsorption capacity. This will provide a new idea for exploring the pore structure characterization of PEI modified MCF.