| Summary: | 碩士 === 國立臺北科技大學 === 有機高分子研究所 === 102 === Xanthan gum (XG) is a natural high molecular weight extracellular polysaccharide. Due to its exceptional properties this polymer is actually employed in many industrial processes such as food, textile, pharmaceutical, cosmetics and other industries. The effects of temperature, pH value of xanthan solutions are of great importance. The XG has different properties in different polymer concentrations. XG in gel condition still has the properties of liquid crystal. XG, which possesses lyotropic properties, was confirmed by optical studies that showed samples in this region to consist of a nematic liquid crystalline phase dispersed in an isotropic phase.
In this work, two topical subjects were investigated. The first topic was the phase diagram of the XG/water/phosphoric acid tertiary system. The second topic was the phase diagram of the XG/water/acetic acid tertiary system. The experimental technique used was polarizing optical microscope assembling with a hot stage and a heat controller. The difference in phase formation and transition of these two systems at room temperature were compared and discussed.
The phase diagram composed of three distinct phases- the completely separated (S) phase, the liquid crystalline (LC) miscible phase, and the isotropically miscible (I) phase. Besides, an intermediate or transition region formed from the overlapping of LC and S phase was identified as LC plus S region in this system. The phase diagram of the XG/water/phosphoric acid tertiary system was affected by temperature and annealing time or relaxation time.
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