McNamee Cathy E, Yamamoto Shinpei, Higashitani Ko
Department of Chemical Engineering, Kyoto University-Katsura, Nishikyo-ku, Kyoto, Kyoto 615-8510, Japan.
Langmuir. 2007 Apr 10;23(8):4389-99. doi: 10.1021/la063512l. Epub 2007 Mar 17.
We prepared pure and mixed monolayers of methoxy-terminated poly(ethylene glycol)s (m-PEG's) chemically attached to silica surfaces by using m-PEG silane coupling agents of three different molecular weights. These films were subsequently characterized in water by atomic force microscopy (AFM). Images of pure m-PEG monolayers showed the formation of polymer brushes on silica. Force curves between two modified surfaces suggested that an increase in the number of oxyethylene (OE) groups from 6 (PEG6 surface) to 43 (PEG43 surface) to 113 (PEG113 surface) decreased the flexibility of the m-PEG chains in the m-PEG brushes. Frictional force measurements also showed that the friction increased in the order PEG6 < PEG43 <PEG113. Because PEG113 had a molecular weight that was greater than the critical molecular weight for entanglement in a PEG melt and displayed the least stretching of its chain, a chain in the PEG113 brush was thought to participate in entanglements or interchain hydrogen bonding. Mixed monolayers of PEG6 and PEG113 were prepared using various fractions of PEG6 and PEG113. Images of mixed PEG6 and PEG113 monolayers showed that the size of the PEG113 islands in the film decreased as the fraction of PEG113 decreased. The force curves between two modified surfaces suggested that the flexibility of the mixed monolayers decreased as the fraction of PEG113 increased. Frictional force measurements also showed that the friction decreased as the fraction of PEG6 in the PEG6-PEG113 mixed film increased. Entanglements were therefore thought to decrease as the fraction of PEG113 in the mixed monolayer decreased.
我们使用三种不同分子量的甲氧基封端聚乙二醇（m-PEG）硅烷偶联剂，制备了化学附着在二氧化硅表面的纯m-PEG单分子层和混合单分子层。随后通过原子力显微镜（AFM）在水中对这些薄膜进行了表征。纯m-PEG单分子层的图像显示在二氧化硅上形成了聚合物刷。两个改性表面之间的力曲线表明，氧化乙烯（OE）基团的数量从6（PEG6表面）增加到43（PEG43表面）再到113（PEG113表面），会降低m-PEG刷中m-PEG链的柔韧性。摩擦力测量还表明，摩擦力按PEG6 < PEG43 < PEG113的顺序增加。由于PEG113的分子量大于PEG熔体中缠结的临界分子量，且其链的伸展程度最小，因此认为PEG113刷中的链参与了缠结或链间氢键作用。使用不同比例的PEG6和PEG113制备了PEG6和PEG113的混合单分子层。PEG6和PEG113混合单分子层的图像显示，随着PEG113比例的降低，薄膜中PEG113岛的尺寸减小。两个改性表面之间的力曲线表明，混合单分子层的柔韧性随着PEG113比例的增加而降低。摩擦力测量还表明，随着PEG6-PEG113混合薄膜中PEG6比例的增加，摩擦力降低。因此，认为随着混合单分子层中PEG113比例的降低，缠结会减少。
