CSIRO, Earth Science and Resource Engineering, Wealth from Oceans Flagship, 26 Dick Perry Avenue, Kensington, WA, 6151, Australia.
Anal Chem. 2012 Oct 16;84(20):8564-70. doi: 10.1021/ac301458e. Epub 2012 Oct 5.
Chemical sensors based on a polymer coated quartz crystal microbalance (QCM) generally present poor molecular selectivity for compounds that contain similar functional groups and possess the same chemical properties. This paper shows for the first time that the selectivity and sensitivity of a poly(methyl methacrylate) (PMMA) based QCM sensor can be significantly enhanced for aromatic hydrocarbons by incorporating a plasticizer into the polymer film. The sensor was fabricated by spin coating PMMA onto a quartz crystal, and the influence of plasticizer type and amount on the response was evaluated. It was shown that the hydrocarbon sensitivity of plasticizer-free PMMA is negligible, while the sensitivity of plasticized PMMA was similar to or in some cases greater relative to highly responsive rubbery polymers such as polyisobutylene (PIB). Detection limits of 4.0, 1.5, 0.4, 0.6, and 0.1 ppm were obtained on a PMMA film containing 25% w/w di(2-ethylhexyl) phthalate for benzene, toluene, ethylbenzene, p-xylene, and naphthalene, respectively. We found that at low plasticizer levels (∼10% w/w) the PMMA film was more sensitive toward ethylbenzene and p-xylene over naphthalene when compared to a PIB film under similar measurement conditions. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) measurements were performed to understand the sensing mechanism, and these studies confirmed a higher hydrocarbon uptake by PMMA in the presence of plasticizer. Positron annihilation lifetime spectroscopy (PALS) studies detected variations in the free volume properties of the polymer films as a function of plasticizer content. The accessible free volume as measured by PALS was significantly less in the PMMA films compared to the PIB, and this result correlates favorably with differences in the QCM response pattern. The QCM results have been rationalized in terms of free volume theory which is responsible for the higher hydrocarbon diffusion/sorption with increased plasticizer content.
基于聚合物涂覆石英晶体微天平（QCM）的化学传感器通常对含有相似官能团和具有相同化学性质的化合物表现出较差的分子选择性。本文首次表明，通过在聚合物膜中加入增塑剂，可以显著提高基于聚甲基丙烯酸甲酯（PMMA）的 QCM 传感器对芳烃的选择性和灵敏度。该传感器是通过将 PMMA 旋涂在石英晶体上来制备的，并评估了增塑剂类型和含量对响应的影响。结果表明，不含增塑剂的 PMMA 对烃类的灵敏度可以忽略不计，而增塑 PMMA 的灵敏度与高响应性橡胶状聚合物（如聚异丁烯（PIB））相似，在某些情况下甚至更高。在含有 25wt%二（2-乙基己基）邻苯二甲酸酯的 PMMA 膜上，分别获得了苯、甲苯、乙苯、对二甲苯和萘的检测限为 4.0、1.5、0.4、0.6 和 0.1ppm。我们发现，在低增塑剂水平（约 10wt%）下，与类似测量条件下的 PIB 膜相比，PMMA 膜对乙基苯和对二甲苯的灵敏度高于萘。进行了衰减全反射傅里叶变换红外光谱（ATR-FTIR）测量以了解传感机制，这些研究证实了在存在增塑剂的情况下 PMMA 对烃类的吸收更高。正电子湮没寿命光谱（PALS）研究检测到聚合物膜中自由体积特性随增塑剂含量的变化。与 PIB 相比，PALS 测量的 PMMA 膜中的可及自由体积明显更小，这一结果与 QCM 响应模式的差异很好地相关。根据自由体积理论对 QCM 结果进行了合理化，该理论负责随着增塑剂含量的增加提高烃类的扩散/吸附。
