Background: Due to the integration of the advantages of the inorganic filler phase and the polymer phase

the organic-inorganic hybrid membrane

which can overcome the trade-off effect between permeability and selectivity

is widely used in many areas. Purpose: The aim is to study the microstructure of the PDMS-MIL-101(Cr) (Poly (dimethyl siloxane)-Material Institute Lavoisier-101(Cr))

which is a polymer-metal organic framework (MOFs) materials hybrid membrane. Methods: Positron annihilation lifetime spectroscopy (PALS) and coincidence Doppler broadening energy spectroscopy (CDBES) were used. Results: PALS results showed that the size of both the space at cross linking site and the free volume of polymer matrix decreased when the MIL-101(Cr) keep increasing

which indicates that MOFs penetrated into the free volume of polymer. Moreover

according to the CDB ratio spectra of hybrid membranes to single silicon crystal

it can be found that the effect of positron preferential annihilation with oxygen atoms was weakened with much more MIL-101(Cr) in hybrid membranes

and a fraction of positrons annihilated with the electrons of metal atoms locating at the center of subnanometer particles of MIL-101(Cr). It is inferred that after entering the free volume of polymer

MIL-101(Cr) particles may interact with oxygen atoms

thus partly block the way for positron’s access to oxygen atoms. Conclusion: Positron annihilation technique is proved to be effective to characterize the microstructure of organic-inorganic hybrid membranes. Abstract