聚乙二醇（polyethylene glycol）是一種直鏈狀高分子，由於其分子本身不具有毒性，且具有抗蛋白質吸附的特性，因此聚乙二醇被廣泛應用於生物科技和醫學領域當中。而目前認為聚乙二醇能夠抗蛋白質吸附的主因，為聚乙二醇分子在溶液中所產所的立體排除（steric exclusion）效應，以及其良好的水合能力，使得聚乙二醇分子周圍形成類似保護膜的水籠結構，造成其它物質不易吸附於其上。
　　本研究利用恆溫滴定卡計（ITC）和modified segment-based NRTL model，探討聚乙二醇單體於水合程序的熱力學性質變化。結果顯示出聚乙二醇單體於水中傾向於聚集，且其水合過程為enthalpy driven的自發程序。而當分子量超過500時，聚乙二醇分子鏈段開始因償熵效應發生摺疊的現象。且隨著分子量的增加，聚乙二醇片段（segment）的親水性也因不同因素而遞減。
　　此外，我們也利用熱力學模式來估算聚乙二醇溶液的稀釋焓，對於聚乙二醇－水的雙成分系統而言，計算結果與實驗值的趨勢相符合，但準確度仍差了一個級數（order）以上，而對於聚乙二醇─鹽類─水三成分系統，則難以利用model預測其放熱量及趨勢。

Polyethylene glycol (PEG) is linear and neutral polymer. The characteristic of low toxicity and preventing nonspecific adsorption of protein provides PEG extensive usage in biomaterials and biomedical application. The prevalent viewpoint to non-fouling phenomenon of PEG is due to the steric exclusion PEG produces in the solution as well as the hydrophilic chain of PEG. The hydration water structure around PEG molecule provides more energy barrier in the adsorption process of other solutes.
In this study, we probe into the change of thermodynamic properties during the hydration process of PEG by ITC and modified segment-based NRTL model. The result shows the monomers of PEG tend to aggregate in the solution in order to reduce the water accessible surface area. When the molecular weight is over 500 (g/mole), PEG starts to fold because of entropy compensation. Besides, the hydrophilic of PEG segment decreases with the increasing of molecule weight for different factors.
We also estimate the heat of dilution of PEG solution by modified segment-based NRTL model. For PEG-water binary system, although there is similar trend between predicted and experimental data, the accuracy is different by an order. For PEG-salt-water ternary system, we found it hard to predict the result by thermodynamic model.

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