The Properties Of Polyethylene Glycol Aqueous Solution And The Influence Of Small Molecules

The use of PEG has been involved in all aspects of life,and these applications are inseparable from the water environment,so it is particularly important to study the effect of PEG on water.So far,people have research through different experiments and theories,and obtained that the value of the bound water of each PEG circulation unit is vaired from 1 to 4.In this dissertation,the relationship between the crystallization and vitrification of PEG aqueous solutions has been mainly studied by differential scanning calorimetry and Raman spectroscopy.The molecular weight of PEG used varies from200 to 20000.The PEG solutions mixing some small molecules have been studied as well.The main research content is as follows:（1）At present,there are different definitions to the number of bonded water molecules of PEG.We find a universal relationship between the glass transition temperature and water mass fraction to different molecular weight PEG aqueous solutions.Similar to an aqueous solution of an aqueous electrolyte solution and glycerol,PEG solution with different molecular weight even as high as 20,000 can also be divided into three concentration ranges.Blue shift occurs for the peak position of the CH₂ Raman vibration of the PEG molecule in aqueous solution when water content increases.However,when the molar ratio of water content is larger than n_cr,the vibrational Raman peak position of the CH₂ does not change with the water content.When n=n_cr,there is an inflection point for the relation between the CH₂ Raman peak position of PEG with water content.Many of the properties of PEG×nH₂O have an inflection point at the point n=n_cras the aqueous solution concentration changes.n_crincludes number of bound water n_h and number of confined water confined n_confined.The main reason existing an inflection point is caused by the changing process from Ⅲ zone with higher water content to Ⅱ zone with corresponding small water content.There are both bound water and free water existing in the aqueous solution Ⅲ zone,while there are only bound water and confined water in Ⅱ zone.However,this inflection point can not be regarded as a evidence to quantifying the bound water number.（2）Ternary mixed aqueous solution composed of short-chain PEG molecules and monosaccharides or DMSO have been measured as well.Through quantification of the amount of bound water and free water,no evident interaction between PEG and other solute has been found in a ternary mixed aqueous solution.This proves that each kind of solute molecule keeps their ability to bound water separately.Consequently,the bound water content of the mixed solute solution equals the sum of the hydration numbers of the two solutes.