濃高分子凝膠在溫度梯度下的熱泳動與受力

Abstract

近年來，微流體控制技術使實驗室晶片有廣泛的應用，微流道、外加電場、磁場、溫度場都是常見的控制方法，其中用雷射加熱來控制微流體的方法是屬於非接觸性且易於控制。隨著許多對於高分子溶液、膠體溶液等複雜系統的液體熱泳研究，使得液體熱泳現象的物理機制陸續被提出來。本文由雷射加熱高分子並觀察高分子在溫度梯度下的變形，來推測熱泳動與受力之間的關係，以更深入的了解高分子的熱泳性質。 本實驗的研究方法是在聚環氧乙烷 (PEO, polyethylene oxide)與瓊脂糖 (agarose)的混合凝膠中加入螢光聚苯乙烯粒子，並以紅外雷射照射產生一溫度梯度場，藉由觀察螢光粒子的位移，並利用PIV的方式來分析凝膠受熱後變形的位移場，希望可以藉由這個位移場來觀察溫度梯度下熱泳與受力的關係。濃高分子在結構上交結而會有彈性材料的性質，實驗上發現濃高分子置於溫度梯度下會結構有變形，且變形幅度遠大於熱膨脹的尺度，顯示應該有一個與溫度梯度有關的力作用於此高分子上，且這個力可能與熱泳現象有關。 本研究觀察到濃高分子在溫度梯度場下受力最大的位置在溫度梯度最大值附近的位置，溫度梯度高的區域受力較大，而受力大小也與高分子濃度有關，顯示出在同樣溫度下高分子密度越高則受力越大。

In recent years, many researches for complex system of thermophoresis in liquid has been reported, such as thermophoresis of polymer and colloid solution. Thermophoresis in liquid has been widely used in different fields, such as control of microfluidics and biological engineering. We plan to study thermophoretic properties of polymer by observing the mechanical behavior of polymer under temperature gradient. Concentrated polymer solution is a partial elastic material with entangling of structure. We observe structure of concentrated polymer solution also deform under temperature gradient. The degree of deformation from thermophoresis under temperature gradient is much larger than the degree of deformation from thermal expansion. This result indicates that a force applied on the polymer solution which is related to temperature gradient. In our experiment, we add PS fluorescent particle in to the gel which is a mixture of PEO and agarose, and we use IR laser to generate a temperature gradient. To study the relation between thermophoresis and mechanical behavior, we analysis the displacement field of deformation under temperature gradient by PIV method. According to our experiment, the force acts on polymer solution which is positively relative to temperature gradient and concentration of polymer.