| 摘要: | 工業程序與生化系統中常涉及水溶性高分子與界劑的混合物。此外許多工業成品例如清潔劑、洗髮精、油漆等，亦常含高分子與界劑的混合物。大多數在應用上的主題是找出合適的高分子與界劑種類，在適當的比例下配合產品的使用調整產品溶液的黏度。本研究中我們主要的研究目標是線性高分子，(聚乙二醇)。由於聚乙二醇在水中有很好的溶解度，因此在製藥界與工業界被廣泛地使用。 對於中性(neutral)高分子與離子型界劑的作用機制，過去的研究常採用項鍊-珍珠模式(pearl-necklace model)來描述。此模式將高分子鏈視為項鍊長線(string)，同時將界劑所形成的微胞看作一顆顆的珍珠(necklace)，兩者之間的作用如同珍珠附著在長線上。過去的實驗結果包含電導度、表面張力、黏度等量測結果都相當支持項鍊-珍珠模式。在溶液中添加PEG後，會導致界劑微胞提早生成，但組成微胞的界劑分子數目較少且其大小較無添加高分子的微胞小。雖然項鍊-珍珠模式已被提出將近三十年，但我們對於高分子與界劑作用的認識仍不完整。舉例而言，若採用低分子量的高分子(其迴旋半徑大小與微胞相差不多時)，項鍊-珍珠模式是否仍合理？另外，當系統中含有中性高分子與中性界劑時，一般咸信兩者之間的作用不存在，然而我們的實驗結果發現溶液黏度會顯著增加。此現象無法以項鍊-珍珠模式(聚電解質效應)來解釋。為了釐清上述問題，我們必須先了解中性高分子在水溶液中的構形特性，即其分子量與高分子大小的關係。由於本研究主要以電導度法探討高分子/界劑的作用，而電導度與離子泳動度之間為線性關係，因此高分子鏈對離子在溶液中的泳動度的阻礙亦必須加以暸解。 本論文分為三個部份︰第一部份我們以冰點下降法測量分子量600-10000 PEG高分子的第二維里係數，它可代表高分子的特徵(硬球)半徑。B12 為兩種不同分子量的PEG所產生的第二維里係數，實驗證實B11可符合M3 Mixtures of water-soluble polymers and surfactants in aqueous solutions are common in industrial applications and biological systems. Moreover, many end-products such as shampoos, detergents, and paints contain polymer/surfactant mixtures. An important issue in most applications is the fine-tuning of the solution viscosity by a suitable polymer/surfactant combination. In the present study, we focus on the linear homopolymer poly (ethylene glycol), which is the most commonly used substances in pharmaceutical and other industrial formulations, due to its high water solubility. The polymer-surfactant interaction leads to the formation of polymer-surfactant complex. The well-accepted morphology of the complex is the necklace model. In this scenario, a "necklace" is formed by the micelles (beads) and the uncharged, water-soluble polymer (string). It is evident that in this model the micelle size must be small compared to the characteristic size of the polymer, which corresponds to high molecular weight. Despite many studies on interactions between neutral polymer and anionic surfactant have supported the necklace scenario, the understanding of the nature of the neutral polymer-surfactant interaction is still incomplete. For example, the radius of gyration of a polymer with molecular weight of O (10³) is less than about 5 nm. One may ask how the necklace model be modified when the "string" is comparable to or smaller than the "bead." To explore the interaction of low molecular weight polymer with surfactant, we have to know the polymer size. Since the conductometry is used to study the polymer solution, we also have to understand the hindrance to ion mobility due to polymer. Hence, this thesis divided into three topics. In the first topic, we determine the second virial coefficients Bij (nm³) of poly(ethylene glycol) with molecular weight M=600-104 in water by freezing point depression. B12 represents the virial cross coefficient for two PEG solutes with different molecular weights M1 and M2. B11 can be well described by the scaling law M3ν with ν≃0.60. That is, the good solvent behavior is observed even for such low molecular weight. In terms of the hard-sphere model, the effective diameter of PEG ranges from 1.3 to 7.9 nm. Since the second virial coefficient is generally increased with decreasing temperature, our results at freezing point provide an upper bound. We also observe the effective hard-sphere picture is reasonable for dilute solutions of different polymer molecules in good solvents. In the second topic, we investigate the ion migration in polymer solutions of different molecular weights by conductometry for various inorganic salts. The electric conductivity |
