Glassy maltodextrins are amorphous carbohydrates characterized by very high barrier properties for low molecular weight gases. Although they are commonly used for the encapsulation of active ingredients in food and pharmaceutics, the microscopic description of the processes which limit the diffusion of molecules inside the polymeric glassy matrix is still not fully understood. In this paper, we study sorption and diffusion of nitrogen molecules in glassy maltodextrins at negligible water content. The solution-diffusion model for the transport of small molecules is combined with recent positron annihilation lifetime spectroscopy data on the microscopic structure of the matrices. We find that both sorption and diffusion are strongly suppressed by the reduced size of the hole volumes and by the enhanced rigidity of the glassy carbohydrates matrices. Values of the diffusion coefficient of nitrogen gas in glassy maltodextrin calculated using the transition state theory were found to correspond well with experimentally obtained values. Also, our calculations can explain the recently observed remarkably high stability of pressurized nitrogen encapsulated in maltodextrin.
- Glassy polymers