聚乙二醇、聚丙二醇和环氧乙烷-环氧丙烷嵌段共聚物在固-液界面上的吸附——Ⅲ.硅烷化活性炭/水和甲基化硅胶/水界面

Adsorption of Polyethylene Glycols, Polypropylene Glycols and Polyoxyethylene-Polyoxypropylene Block co-Polymer on Solid/Liquid Interfaces Ⅲ. Silanized Active Carbon/Water and Methylated Silica Gel/Water Interfaces

测定了25℃时硅烷化不同时间(1至30天)的活性炭及甲基化硅胶自水溶液中吸附四种聚乙二醇(PEG)、三种聚丙二醇(PPG)和环氧乙烷(EO)-环氧丙烷(PO)嵌段共聚物pluronic-L64的等温线.结果表明,在各活性炭样品上的等温线均为Langmuir型的;同一炭样对不同PEG的极限吸附量(g·g^(-1))与分子量无关;极限吸附时每个PEG分子所占面积(A)与分子中所含EO数(n_(EO))间有直线关系,直线的斜率与硅烷化时间有关,这一结果可用硅烷化时间延长时吸附分子的EO基可能以其氧原子向水,碳氢链节靠近固体表面取向的模型解释.根据PPG的极限吸附量与分子量有关和极限吸附时的分子面积推断PPG分子不是以平躺方式吸附.甲基化硅胶对PEG的吸附量极小,对PPG的吸附量随分子量减小急剧降低,而对L64的吸附量明显大于在亲水硅胶上的.文中对所得结果给出了初步的解释.

The adsorption isotherms of polyethylene glyools(PEG, molecular weights of 1000, 4000, 6000 and 20000), polypropylene glycols (PPG, M. W. of 425, 1000 and 2025) and pluronie-L64 from water onto the ailanized active carbon and methylated silica gel (at 25℃) have been debermined. The results indicate that all the isotherms of PEG, PPG, pluronic-L64 on various active carbons with different degree of silanization are Langmuir-type; the limiting adsorption (g·g^(-1)) of PEG on the same carbon is essentially constant, and the molecular areas at limiting adsorption (A) decrease linearly with the increasing number of ethylene oxide units (n_(EO)), showing a slop decreased greatly with the lapse of the silanization time. From these results, it is suggested that the -CH_2CH_2-groups of PEG molecule are bound to the solid surface, and the oxygen atoms are directed to the water. On the basis of the limiting adsorption, molecular area at limiting adsorption and the adsorbed layer thickness of PPG, it is suggested that the molecules of PPG do not lie 'flat' on the active carbon surface. The adsorption of PEG onto the methylated silica gel is quit weak. With the increasing molecular weight of PPG the adsorption decreases markedly and the adsorption of pluronic-L64 onto the methylated silica gel is more than that onto the hydrophilic silica gel.