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首页> 外文期刊>Journal of advanced dielectrics >HIGH DIELECTRIC CONSTANT COMPOSITE BASED ON CHLOROPHYLL A ENTRAPPED NANOPOROUS SILICA GEL
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HIGH DIELECTRIC CONSTANT COMPOSITE BASED ON CHLOROPHYLL A ENTRAPPED NANOPOROUS SILICA GEL

机译：基于叶绿素包裹的纳米多孔硅凝胶的高介电常数复合材料

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摘要

Chlorophyll a (naturally occurring Mg porphyrene) has been entrapped in nano/porous silica gel using sol-gel method at room temperature, producing a stable composite. HRTEM observation reveals regular nanoscale [around 15-20 nm diameter] distribution of aggregated polycrystalline chlorophyll a within porous silica matrix. UV-vis study also corroborates the presence of various aggregated chlorophyll a species within the system. Low field measurement shows almost 400 times enhancement of dielectric constant (1700) with incorporation of only 0.125 mg/ml of chlorophyll and the loss is 0.5 at room temperature at 100 Hz. The dielectric constant of the composite reaches 2500 as chlorophyll concentration becomes 1 mg/ml. Observed strong space charge response to the external field and strong frequency dispersion of the dielectric properties of the composite can be attributed to the long-range electron delocalization [nomadic polarization] in chlorophyll a aggregates. The electric modulus (M*) formalism used in this study enabled us to distinguish and separate various relaxation processes. It is found that with increasing chlorophyll concentration D.C. relaxation time decreases exponentially at room temperature. It is shown that observed relaxations do not perfectly follow the Debye response in high frequency region due to heterogeneous distribution of chlorophyll aggregates. The low values of room temperature activation energy calculated from Arrhenius plot reveal that polaronic hopping phenomena is absent at grain-interfacial region due to low thermal energy.
机译：在室温下，使用溶胶-凝胶法将叶绿素a（天然存在的镁卟啉）截留在纳米/多孔硅胶中，从而生成稳定的复合材料。 HRTEM观察显示多孔二氧化硅基质中聚集的多晶叶绿素a的规则纳米级[直径约15-20 nm]分布。紫外线可见研究还证实了系统中存在各种聚集的叶绿素a物种。低场测量显示，仅掺入0.125 mg / ml的叶绿素，介电常数（1700）几乎提高了400倍，并且在室温和100 Hz下损耗为0.5。当叶绿素浓度变为1 mg / ml时，复合材料的介电常数达到2500。观察到的对外部电场的强空间电荷响应和复合材料介电性能的强频率色散可以归因于叶绿素a聚集体中的远距离电子离域[游动极化]。在这项研究中使用的电模量（M *）形式主义使我们能够区分和分离各种松弛过程。已经发现，随着叶绿素浓度的增加，DC的弛豫时间在室温下呈指数下降。结果表明，由于叶绿素聚集体的分布不均，在高频区域观察到的弛豫并不完全遵循德拜响应。根据Arrhenius曲线计算得出的室温激活能的低值表明，由于低的热能，在晶界区域不存在极化子跳跃现象。

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  • 来源
    《Journal of advanced dielectrics》 |2012年第3期|p.1230016.1-1230016.9|共9页
  • 作者

    J. S. MANNA; M. K. MITRA; S. MUKHERJEE; G. C. DAS;

  • 作者单位

    Department of Metallurgical and Material Engineering School of Material Science and Nanotechnology Jadavpur University, Kolkata 700032, India;

    Department of Metallurgical and Material Engineering School of Material Science and Nanotechnology Jadavpur University, Kolkata 700032, India;

    Department of Metallurgical and Material Engineering School of Material Science and Nanotechnology Jadavpur University, Kolkata 700032, India;

    Department of Metallurgical and Material Engineering School of Material Science and Nanotechnology Jadavpur University, Kolkata 700032, India;

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  • 关键词

    nanoporous silica gel; chlorophyll a; dielectric; dipole relaxation; activation energy;

    机译：纳米多孔硅胶叶绿素a;电介质偶极弛豫活化能;

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