Effects of mixed solvent on solution properties and gelation behavior of polyvinyl alcohol

• Main Authors: Shi-jie Hong, 洪士傑
• Other Authors: Po-Da Hong
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/02974989541297568844

碩士 === 國立臺灣科技大學 === 高分子工程系 === 92 === In this thesis, the solution properties of PVA were first investigated in a wide range of solvent compositions for the PVA/DMSO/water ternary systems. Ubbelohde viscometer was first used to get some apparent information on the polymer-co-solvent interaction in the present work. The viscometric result showed that the affinity to PVA for DMSO is higher than that for water. The original Flory-Huggins expression for free energy of mixing, which is traditionally used to analyze the experimental results in mixed solvents, led to a very poor agreement between theoretical and experimental data. Therefore, we modified Read’s formalism, which is generally applied to the weaker interaction systems, to calculate preferential adsorption coefficients, αa, when the solvent complexes are comparatively stable in the present systems. The theoretical preferential adsorption coefficients could be calculated for discussing the results of polymer-co-solvent interaction (cC3). The inversion of the preferential adsorption was confirmed for a mixture of a marginal solvent (water) with a good one (DMSO) at DMSO mole fraction (X1) = 0.33. For X1<0.33 and X1>0.33, PVA chains preferentially adsorb water molecules and DMSO molecules, respectively. Typically, this co-solvent mixture could form hydrogen bonded DMSO / (water) 2 complexes, involving one DMSO and two water molecules. Besides, the measurements of dynamic light scattering (DLS) were carried out to elucidate the effect of molecular interactions on the properties of PVA dilute solutions. DLS analysis could provide many information on the properties of diluted solution such the average relaxation rate of a single coil ( ), the hydrodynamic radius (Rh) and the additional dynamic second virial coefficient (Kd) and diffusion coefficient at infinite dilute, D0. All of the results reveal a critical value around X1=0.28~0.33. Finally, a study on the relationship between phase separation and gelation was carried out through kinetic analyses. The present study has primarily focused on such solvent compositions where gelation and liquid-liquid phase separation occur easily (i.e., X1=0.2~0.33). Due to various interactions between PVA and co-solvent mixtures, the gelation behavior is significantly affected by the formation of co-solvent complex.