Marcinko Stephen, Fadeev Alexander Y
Department of Chemistry and Biochemistry, Seton Hall University, South Orange, New Jersey 07079, USA.
Langmuir. 2004 Mar 16;20(6):2270-3. doi: 10.1021/la034914l.
The hydrolytic stability of C18 monolayers supported on TiO2 and ZrO2 was studied. Three types of monolayers were prepared from the following octadecyl modifiers: (1) octadecyldimethylchlorosilane (C18H37Si(CH3)2Cl); (2) octadecylsilane (C18H37SiH3); and (3) octadecylphosphonic acid (C18H37P(O)(OH)2). The hydrolysis of the surfaces prepared was studied under static conditions at 25 and 65 degrees C at pH 1-10. On the basis of the loss of grafted material, the stability of the monolayers fall in the following range: C18H37P(O)(OH)2 > or = C18H37SiH3 >> C18H37Si(CH3)2Cl. At 25 degrees C, monolayers from C18H37P(O)(OH)2 showed only approximately 2-5% loss in grafting density after one week at pH 1-10. The high stability of these monolayers was explained because of the strong interactions of the phosphonic acids with the substrates. Monolayers from C18H37Si(CH3)2Cl showed poor hydrolytic stability at any pH, which was explained because of the low stability of Ti-O-Si and Zr-O-Si bonds. Unlike monofunctional silanes, trifunctional silane (C18H37SiH3) yielded surfaces that showed good hydrolytic stability. This suggests that the stability of the monolayers from trifunctional silanes is primarily due to "horizontal" bonding (Si-O-Si or Si-OH...HO-Si) rather than due to bondingwith the matrix (M-O-Si). At 65 degrees C, all C18 surfaces become more susceptible to hydrolysis; however, the trend observed for 25 degrees C remained unchanged. Low-temperature nitrogen adsorption was used to study the adsorption properties of the monolayers as a function of their grafting density. The energy of adsorption interactions showed a significant increase as the grafting density of the monolayers decreased. The order of the alkyl groups in the monolayers, as assessed from CH2 stretching, decreased as the grafting density of the monolayers decreased.
研究了负载在二氧化钛和氧化锆上的C18单分子层的水解稳定性。由以下十八烷基改性剂制备了三种类型的单分子层：（1）十八烷基二甲基氯硅烷（C18H37Si(CH3)2Cl）；（2）十八烷基硅烷（C18H37SiH3）；（3）十八烷基膦酸（C18H37P(O)(OH)2）。在25℃和65℃、pH值为1 - 10的静态条件下研究了所制备表面的水解情况。基于接枝材料的损失，单分子层的稳定性顺序如下：C18H37P(O)(OH)2 ≥ C18H37SiH3 >> C18H37Si(CH3)2Cl。在25℃时，来自C18H37P(O)(OH)2的单分子层在pH值为1 - 10的条件下放置一周后，接枝密度仅损失约2 - 5%。这些单分子层的高稳定性归因于膦酸与底物之间的强相互作用。来自C18H37Si(CH3)2Cl的单分子层在任何pH值下都表现出较差的水解稳定性，这归因于Ti - O - Si和Zr - O - Si键的低稳定性。与单官能硅烷不同，三官能硅烷（C18H37SiH3）产生的表面表现出良好的水解稳定性。这表明三官能硅烷单分子层的稳定性主要归因于“横向”键合（Si - O - Si或Si - OH...HO - Si），而不是与基质的键合（M - O - Si）。在65℃时，所有C18表面都更容易发生水解；然而，在25℃时观察到的趋势保持不变。采用低温氮吸附法研究了单分子层的吸附性能与其接枝密度的关系。随着单分子层接枝密度降低，吸附相互作用能显著增加。从CH2伸缩振动评估，单分子层中烷基的顺序随着单分子层接枝密度降低而降低。
