Yilmaz Neval, Mizukami Masashi, Kurihara Kazue
Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, 2-1-1 Katahira, Aobaku, Sendai 980-8577, Japan.
Langmuir. 2007 May 22;23(11):6070-5. doi: 10.1021/la0700366. Epub 2007 Apr 18.
The adsorption of phenol, an aromatic compound with a hydrogen-bonding group, onto a silica surface in cyclohexane was investigated by colloidal probe atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and adsorption isotherm measurements. ATR-FTIR measurements on the silica surface indicated the formation of surface macroclusters of phenol through hydrogen bonding. The ATR-FTIR spectra were also measured on the H-terminated silicon surface to observe the effect of the silanol groups on the phenol adsorption. The comparison of the ATR-FTIR spectra for both the silicon oxide and H-terminated silicon surfaces proved that the silanol groups are necessary for the formation of phenol clusters on the surface. The surface force measurement using colloidal probe AFM showed a long-range attraction between the two silica surfaces in phenol-cyclohexane mixtures. This long-range attraction resulted from the contact of the adsorbed phenol layers for the phenol concentrations below 0.6 mol %, at which no significant phenol clusters formed in the bulk solution. The attraction started to decrease at 0.6 mol % phenol due to the exchange of the phenol molecules between the clusters in the bulk phase and on the surface. The surface density of phenol in the adsorbed layer was calculated on the basis of the long-range attraction and found to be much smaller than the liquid phenol density. The plausible structure of the adsorbed phenol layer was drawn by referring to the crystal structure of the bulk phenol and orientation of the phenol molecules on the surface, estimated by the dichroic analysis of ATR-FTIR spectroscopy. The investigation of the phenol adsorption on the silica surface in a nonpolar solvent using this novel approach demonstrated the effect of the aromatic ring on the surface packing density.
通过胶体探针原子力显微镜（AFM）、衰减全反射傅里叶变换红外光谱（ATR-FTIR）和吸附等温线测量，研究了具有氢键基团的芳香族化合物苯酚在环己烷中在二氧化硅表面的吸附情况。对二氧化硅表面的ATR-FTIR测量表明，通过氢键形成了苯酚的表面大聚集体。还对氢终止的硅表面进行了ATR-FTIR光谱测量，以观察硅醇基团对苯酚吸附的影响。氧化硅表面和氢终止硅表面的ATR-FTIR光谱比较证明，硅醇基团是表面形成苯酚聚集体所必需的。使用胶体探针AFM进行的表面力测量表明，在苯酚-环己烷混合物中，两个二氧化硅表面之间存在长程吸引力。这种长程吸引力是由于在苯酚浓度低于0.6 mol%时，吸附的苯酚层之间的接触引起的，此时本体溶液中没有形成明显的苯酚聚集体。由于本体相和表面上聚集体之间苯酚分子的交换，在苯酚浓度为0.6 mol%时吸引力开始下降。根据长程吸引力计算了吸附层中苯酚的表面密度，发现其远小于液态苯酚的密度。通过参考本体苯酚的晶体结构和通过ATR-FTIR光谱的二向色性分析估计的表面上苯酚分子的取向，绘制了吸附苯酚层的合理结构。使用这种新方法对非极性溶剂中二氧化硅表面上苯酚吸附的研究证明了芳香环对表面堆积密度的影响。
