Effect of dissolution pathways of polyacrylonitrile on the solution homogeneity: Thermodynamic- or kinetic-controlled dissolution

초록

Dissolution behavior of polyacrylontrile (PAN) in N,N-dimethylformamide (DMF) and dimethylsulfoxide (DMSO) is investigated in terms of dipole-dipole interactions at polymer-solvent interface. Fourier-transformed infrared (FTIR) imaging of polymer-solvent interface under static dissolution condition at 25 degrees C and 60 degrees C exhibits the gel-like swollen layer in the early stage of dissolution for both solvents. This layer readily disappears in PAN-DMSO and DMSO molecules penetrate deep into the polymer phase, whereas that in PAN-DMF is still observed until 12 h even at 60 degrees C. The better dissolving ability of DMSO is interpreted by higher intrinsic viscosity and lower Huggins' constant. The solubility (solution homogeneity) is also evaluated by rheological analysis in a wide concentration range of 8-20 wt%. At above 15 wt%, DMSO produces homogeneous solution at 60 degrees C even without stirring, showing the lower Newtonian flow region. On the other hand, it is necessary to apply vigorous stirring and heating for PAN-DMF system in order to prepare concentrated solution. DMSO provides greater slope of the Cole-Cole plot by rheological measurement than DMF, indicating better solution homogeneity in PAN-DMSO. The FTIR spectra and 2D correlation analysis show that both DMSO and DMF dissolve PAN in a way of sequential contributions of enthalpic and entropic factors. However, DMSO exhibits predominant contribution by enthalpic factor, suggesting that enthalpy change of mixing is a driving force of PAN dissolution in DMSO, whereas dissolution of PAN-DMF is governed by kinetic control.

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