...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Journal of Non-Crystalline Solids: A Journal Devoted to Oxide, Halide, Chalcogenide and Metallic Glasses, Amorphous Semiconductors, Non-Crystalline Films, Glass-Ceramics and Glassy Composites >Polymers in nanoconfinement: What can be learned from relaxation and scattering experiments?
【24h】

Polymers in nanoconfinement: What can be learned from relaxation and scattering experiments?

机译：纳米约束中的聚合物：可以从弛豫和散射实验中学到什么？

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Dielectric spectroscopy in combination with temperature modulated differential scanning calorimetry and quasielastic/inelastic neutron scattering are employed to investigate the molecular (glassy) dynamics of poly(dimethyl siloxane) (PDMS) and poly(methyl phenyl siloxane) (PMPS) confined to random nanoporous glasses with nominal pore sizes between 2.5 nm and 20 nm. Inside the pores PDMS and PMPS have faster molecular dynamics than in the bulk state. Down to a pore size of 7.5 nm the temperature dependence of the relaxation times (or rates) obeys the Vogel/Fulcher/Tammann (VFT) equation where the data obtained from dielectric and thermal spectroscopy agree quantitatively. At a pore size of 5 nm this VFT-like temperature dependence changes to an Arrhenius behavior. At the same confining length scale the increment of the specific heat capacity at T-g normalized to the weight of the confined polymer vanishes. The results indicate that a minimal length scale seems to be relevant for glassy dynamics in both polymers although the estimated length scale of about 5 nm seems to a bit too large in comparison to other experimental results and theoretical approaches. Neutron scattering is employed to investigate methyl group reorientation and the fast segmental dynamics of both polymers in confinement. Although the methyl group rotation is a localized process these experiments show that a part of the methyl groups is immobilized by the confinement whereas the effects for PDMS are much more pronounced than for PMPS. With regard to the segmental dynamics, neutron scattering reveals a big difference in the behavior of both polymers. Whereas the data obtained for PMPS are in accord with a boundary layer formed at the surfaces of the nanopores, for PDMS a considerable amount of elastic scattering is observed. To explain this result it is assumed that some structure formation of PDMS takes place in the nanopores, although the thermal data show no crystallization or melting effects. (c) 2005 Elsevier B.V. All rights reserved.
机译：介电谱结合温度调制差示扫描量热法和准弹性/非弹性中子散射技术，用于研究局限于随机纳米多孔玻璃中的聚二甲基硅氧烷（PDMS）和聚甲基苯基硅氧烷（PMPS）的分子（玻璃态）动力学标称孔径在2.5 nm至20 nm之间。在孔内部，PDMS和PMPS的分子动力学比在本体状态下要快。孔径降至7.5 nm时，弛豫时间（或速率）的温度依赖性符合Vogel / Fulcher / Tammann（VFT）方程，其中从介电和热光谱学获得的数据在数量上是一致的。在孔径为5 nm时，这种类似于VFT的温度依赖性会变为Arrhenius行为。在相同的限制长度范围内，标准化为受限制聚合物重量的T-g处的比热容增量消失了。结果表明最小长度尺度似乎与两种聚合物中的玻璃态动力学有关，尽管与其他实验结果和理论方法相比，约5 nm的估计长度尺度似乎太大了。用中子散射法研究两种聚合物在限制条件下的甲基取向和快速节段动力学。尽管甲基旋转是一个局部过程，但这些实验表明，部分甲基被限制固定，而PDMS的作用比PMPS的作用明显得多。关于分段动力学，中子散射揭示了两种聚合物在行为上的巨大差异。尽管从PMPS获得的数据与在纳米孔表面形成的边界层一致，但是对于PDMS，观察到了相当数量的弹性散射。为了解释该结果，假定了PDMS的一些结构形成在纳米孔中发生，尽管热数据没有显示出结晶或熔融作用。 （c）2005 Elsevier B.V.保留所有权利。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号