The size and weight fraction of crystals of pure ice or dimethylsulfoxide (DMSO) in poly(vinyl alcohol) (PVA) gel prepared from a mixed solvent of DMSO/water were determined from melting peaks observed by differential...The size and weight fraction of crystals of pure ice or dimethylsulfoxide (DMSO) in poly(vinyl alcohol) (PVA) gel prepared from a mixed solvent of DMSO/water were determined from melting peaks observed by differential scanning calorimetry (DSC). The depression of the melting point with respect to the equilibrium melting point and the melting enthalpy gave the crystal size and weight fraction, respectively. The sizes were in the range of a few nm to tens of nm, depending on the composition ratio of the mixed solvent (DMSO/water) and the polymer concentration. Based on the weight fraction, the critical condition at which the whole solvent became non-freezable was estimated, and it was found to depend on both the PVA concentration and the DMSO/water ratio. When the solvent was pure water, the critical PVA concentration was as high as 86.4 wt%, while for pure DMSO solvent it was 50.1 wt%.展开更多
The mechanical properties of polyvinyl alcohol (PVA) films prepared by evaporating water from freeze/thaw cycled gel were investigated as a function of the number of freeze/thaw cycles. The maximum stress of the PVA f...The mechanical properties of polyvinyl alcohol (PVA) films prepared by evaporating water from freeze/thaw cycled gel were investigated as a function of the number of freeze/thaw cycles. The maximum stress of the PVA film prepared by freeze/thaw cycling was larger than that prepared without the freeze/thaw cycle process. The largest maximum stress was 46.2 MPa for a film prepared with 10 freeze/thaw cycles, which was twice as large as that for a cast PVA film without freeze/thaw cycling (22.3 MPa). This is due to the formation of small crystallites during the freeze/thaw cycle process. Furthermore, when the film was annealed at 130°C, the maximum stress was as high as 181 MPa which was comparable to that for PVA films prepared using additives. The crystallinity is not the main factor that determines the maximum stress for either the non-annealed or annealed freeze/thaw cycled films, but the glass transition temperature is well correlated with the maximum stress, irrespective of the annealing process. This is due to the different molecular morphology;the non-annealed freeze/thaw cycled film consists of many small crystallites, but the annealed film consists of larger crystallites formed during the annealing process.展开更多
文摘The size and weight fraction of crystals of pure ice or dimethylsulfoxide (DMSO) in poly(vinyl alcohol) (PVA) gel prepared from a mixed solvent of DMSO/water were determined from melting peaks observed by differential scanning calorimetry (DSC). The depression of the melting point with respect to the equilibrium melting point and the melting enthalpy gave the crystal size and weight fraction, respectively. The sizes were in the range of a few nm to tens of nm, depending on the composition ratio of the mixed solvent (DMSO/water) and the polymer concentration. Based on the weight fraction, the critical condition at which the whole solvent became non-freezable was estimated, and it was found to depend on both the PVA concentration and the DMSO/water ratio. When the solvent was pure water, the critical PVA concentration was as high as 86.4 wt%, while for pure DMSO solvent it was 50.1 wt%.
文摘The mechanical properties of polyvinyl alcohol (PVA) films prepared by evaporating water from freeze/thaw cycled gel were investigated as a function of the number of freeze/thaw cycles. The maximum stress of the PVA film prepared by freeze/thaw cycling was larger than that prepared without the freeze/thaw cycle process. The largest maximum stress was 46.2 MPa for a film prepared with 10 freeze/thaw cycles, which was twice as large as that for a cast PVA film without freeze/thaw cycling (22.3 MPa). This is due to the formation of small crystallites during the freeze/thaw cycle process. Furthermore, when the film was annealed at 130°C, the maximum stress was as high as 181 MPa which was comparable to that for PVA films prepared using additives. The crystallinity is not the main factor that determines the maximum stress for either the non-annealed or annealed freeze/thaw cycled films, but the glass transition temperature is well correlated with the maximum stress, irrespective of the annealing process. This is due to the different molecular morphology;the non-annealed freeze/thaw cycled film consists of many small crystallites, but the annealed film consists of larger crystallites formed during the annealing process.
