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Anomalous toluene transport in model segmented polyurethane-urea/clay nanocomposites

Abstract

The kinetics of liquid solvent sorption in polymeric systems and their nanocomposites often deviate from normal Fickian behaviour. This needs to be understood and interpreted, in terms of their underlying mechanistic origins. In the present study, the results of time dependant toluene sorption measurements in model segmented polyurethane-urea/clay nanocomposites have been analysed at room temperature. The studies revealed pronounced S-shaped sorption curves and unusually higher swelling of the nanocomposites compared with the neat polyurethane-urea matrix. Dynamic mechanical analysis (DMA) and small angle x-ray scattering (SAXS) measurements on the nanocomposites in the dry and liquid toluene saturated state have been carried out. The DMA studies revealed significant decrease in the α relaxation temperature and storage modulus of the nanocomposites in the swollen state compared to the dry samples. SAXS results showed that the nanoclay dispersion morphology transformed from intercalation in the dry state to exfoliation in the swollen state and the interdomain distance between hard segments increased upon swelling. Thermodynamic analysis of the Flory-Huggins interaction parameter (χ) of the nanocomposite/toluene system revealed increasingly negative χ values with increased clay loading. These results imply significant plasticization effect of toluene on the nanocomposites. An interpretation of these data, which relates the abovementioned results, is presented in the framework of differential swelling stress (DSS) induced deviation from Fickian transport characteristics. This framework emphasizes the interplay between diffusion and changes in the state of the material as it undergoes plasticization. We expect that these findings and methods may provide new insight in the analysis of the process of solvent diffusion in heterogeneous polymers and their nanocomposites.

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Publication details

The article was received on 09 Nov 2017, accepted on 13 Apr 2018 and first published on 17 Apr 2018


Article type: Paper
DOI: 10.1039/C7SM02202F
Citation: Soft Matter, 2018, Accepted Manuscript
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    Anomalous toluene transport in model segmented polyurethane-urea/clay nanocomposites

    S. Rath, J. Bahadur, H. S. Panda, D. Sen, T. U. Patro, P. S, M. Patri and D. V. Khakhar, Soft Matter, 2018, Accepted Manuscript , DOI: 10.1039/C7SM02202F

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