Positron Age-Momentum Correlation Studies of Free Volumes in Polyethylenimine-Modified Mesoporous Cellular Foam

By varying the mass ratio of the amphiphilic triblock copolymer (P123) to 1,3,5-trimethylbenzene (TMB), alongside the content and molecular weight of polyethylenimine (PEI) and the incorporation of catalyst ammonium fluoride (NH₄F), four distinct types of polyethylenimine-modified siliceous mesostructured cellular foam (PEIs-MCF) are prepared. To elucidate the annihilation mechanism of positrons and positronium within the amorphous porous materials, we perform positron age-momentum correlation techniques (AMOC). The Doppler broadening spectroscopy results obtained from AMOC indicated differences in electronic momentum across porous materials with varying free volume holes following PEI impregnation. Based on the differentiation of the S parameters for samples with different free volume hole sizes, -NH₂ concentrations and the structural forms of -NH₂ in the branches of PEI, various annihilation processes of positrons within the age domain were explored. Employing positron annihilation lifetime spectroscopy (PALS), the study examined the relationship between PEI content and the pick-off annihilation rate of o-Ps as PEI was introduced. According to the examination of correlation of the positron annihilation linear parameter S derived from DBS data extracted from AMOC and the o-Ps intensity from PALS measurements (S-I_o-Ps) and the discussion in the authors' previous work, the chemical environments of PEIs-MCF modified with low content of PEI differ from those of PEIs-MCF modified with high PEI content.