Mundra Manish K, Donthu Suresh K, Dravid Vinayak P, Torkelson John M
Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
Nano Lett. 2007 Mar;7(3):713-8. doi: 10.1021/nl062894c. Epub 2007 Feb 9.
Poly(methyl methacrylate) (PMMA) nanostructures embedded with a fluorescence tag are fabricated using electron beam lithography on oxidized silicon substrates. The glass transition temperatures (Tgs) of these one-dimensional (1-D) nanostructures (parallel lines) are measured by monitoring their temperature-dependent fluorescence intensities, revealing substantial differences between the Tgs of the nanostructures and the thin films from which they were fabricated. For example, the Tg of 50-nm-wide PMMA nanolines on silica is approximately 15 K lower than that of a PMMA film on silica of the same 18 nm thickness. Attractive PMMA-silica interfacial interactions increase the Tg, while free surfaces decrease the Tg of PMMA in ultrathin films relative to bulk PMMA. Thus, the significant differences between the Tgs of the 1-D and two-dimensional (2-D) forms of PMMA on silica are the result of a substantial increase in the ratio of free-surface area to interfacial area in the PMMA nanolines relative to ultrathin films.
通过电子束光刻技术在氧化硅衬底上制备了嵌入荧光标签的聚甲基丙烯酸甲酯（PMMA）纳米结构。通过监测这些一维（1-D）纳米结构（平行线）随温度变化的荧光强度来测量其玻璃化转变温度（Tg），结果表明纳米结构的Tg与其制备所用薄膜的Tg存在显著差异。例如，二氧化硅上50纳米宽的PMMA纳米线的Tg比相同18纳米厚度的二氧化硅上的PMMA薄膜的Tg低约15K。有吸引力的PMMA-二氧化硅界面相互作用会提高Tg，而相对于本体PMMA，自由表面会降低超薄膜中PMMA的Tg。因此，二氧化硅上PMMA的一维（1-D）和二维（2-D）形式的Tg之间的显著差异是由于PMMA纳米线中自由表面积与界面面积之比相对于超薄膜大幅增加所致。
