Tleugabulova Dina, Duft Andy M, Brook Michael A, Brennan John D
Department of Chemistry, McMaster University, Hamilton, Ontario, L8S 4M1, Canada.
Langmuir. 2004 Jan 6;20(1):101-8. doi: 10.1021/la035333z.
The fluorescence-based nanosize metrology approach, proposed recently by Geddes and Birch (Geddes, C. D.; Birch, D. J. S. J. Non-Cryst. Solids 2000, 270, 191), was used to characterize the extent of binding of a fluorescent cationic solute, rhodamine 6G (R6G), to the surface of silica particles after modification of the surface with the hydrophilic polymer poly(ethylene oxide) (PEO) of various molecular weights. The measurement of the rotational dynamics of R6G in PEO solutions showed the absence of strong interactions between R6G and PEO chains in water and the ability of the dye to sense the presence of polymer clusters in 30 wt % solutions. Time-resolved anisotropy decays of polymer-modified Ludox provided direct evidence for distribution of the dye between bound and free states, with the bound dye showing two decay components: a nanosecond decay component that is consistent with local motions of bound probes and a residual anisotropy component due to slow rotation of large silica particles. The data showed that the dye was strongly adsorbed to unmodified silica nanoparticles, to the extent that less than 1% of the dye was present in the surrounding aqueous solution. Addition of PEO blocked the adsorption of the dye to a significant degree, with up to 50% of the probe being present in the aqueous solution for Ludox samples containing 30 wt % of low molecular weight PEO. The addition of such agents also decreased the value and increased the fractional contribution of the nanosecond rotational correlation time, suggesting that polymer adsorption altered the degree of local motion of the bound probe. Atomic force microscopy imaging studies provided no evidence for a change in the particle size upon surface modification but did suggest interparticle aggregation after polymer adsorption. Thus, this redistribution of the probe is interpreted as being due to coverage of particles with the polymer, resulting in lower adsorption of R6G to the silica. The data clearly show the power of time-resolved fluorescence anisotropy decay measurements for probing the modification of silica surfaces and suggest that this method should prove useful in characterization of new chromatographic stationary phases and nanocomposite materials.
基于荧光的纳米尺寸计量方法是由格迪斯和伯奇最近提出的（格迪斯，C.D.；伯奇，D.J.S.《非晶态固体杂志》2000年，270卷，191页），该方法用于表征在二氧化硅颗粒表面用不同分子量的亲水性聚合物聚环氧乙烷（PEO）进行改性后，荧光阳离子溶质罗丹明6G（R6G）与颗粒表面的结合程度。对R6G在PEO溶液中的旋转动力学测量表明，在水中R6G与PEO链之间不存在强相互作用，并且该染料能够感知30 wt%溶液中聚合物聚集体的存在。聚合物改性的卢多克斯的时间分辨各向异性衰减为染料在结合态和游离态之间的分布提供了直接证据，结合态染料呈现出两个衰减分量：一个与结合探针的局部运动一致的纳秒衰减分量，以及由于大二氧化硅颗粒缓慢旋转导致的残余各向异性分量。数据表明，该染料强烈吸附在未改性的二氧化硅纳米颗粒上，以至于周围水溶液中存在的染料不到1%。添加PEO在很大程度上阻止了染料的吸附，对于含有30 wt%低分子量PEO的卢多克斯样品，高达50%的探针存在于水溶液中。添加此类试剂还降低了纳秒旋转相关时间的值并增加了其分数贡献，这表明聚合物吸附改变了结合探针的局部运动程度。原子力显微镜成像研究没有提供表面改性后颗粒尺寸变化的证据，但确实表明聚合物吸附后颗粒间发生了聚集。因此，这种探针的重新分布被解释为是由于聚合物覆盖了颗粒，导致R6G对二氧化硅的吸附减少。数据清楚地显示了时间分辨荧光各向异性衰减测量在探测二氧化硅表面改性方面的作用，并表明该方法在表征新型色谱固定相和纳米复合材料方面应会很有用。
