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Nanotube-Matrix Interplay and Tunability in Ultrahigh Volume-Fraction Aligned Carbon Nanotube Poly(Urethane-urea) Nanocomposites

机译：纳米管-基质相互作用和超高体积分数排列的碳纳米管聚（尿烷-脲）纳米复合材料的可调谐性

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摘要

The present dissertation seeks to better understand the nature of biphasic poly(urethane-urea) (PUU) interactions in materials with densely packed, aligned carbon nanotubes (CNTs). Of particular interest are the CNT-matrix interactions with in-situ polymerized PUU of various stoichiometric ratios. A novel synthesis method for PUU which permits fabrication of PUU-based polymer nanocomposites (PNCs) has been developed. Study of the thermal and multiscale mechanical behavior of stoichiometrically varied PUU materials has been conducted to demonstrate significant interaction between the matrix and CNTs, both in terms of morphology and mechanical reinforcement.;PNCs with CNT Vf up to 30% have been achieved with excellent wetting confirmed via Micro-CT. TGA and DSC have revealed that CNTs stabilize thermal degradation of PUU by inducing crystallinity and reducing phase-mixing. AFM confirmed this by visualizing the crystals present in the matrix materials. CNT-induced crystallinity and phase-separation are attributed to the binding of CNTs to hard segments, which limit chain mobility during polymerization. Higher CNT Vf PNCs were found to increase soft-segment crystallinity, though with diminishing returns. Extreme crystallinity was found at 10% V f CNTs which is though to arise due to an optimized spacing to permit ordered crystal formation of the PUU.;Enhancements to indentation modulus of up to 1600% in the transverse orientation and 3500% in the axial orientation have been recorded via quasi-static nanoindentation. Greater CNT Vf and greater hard-segment composition lead to reduced chain mobility, and in some instances, can reduce CNT effectiveness in mechanical enhancement. The 10% CNT Vf exhibits greater indentation and storage moduli arising which is thought to arise from an optimized balance of inter-CNT spacing and chain mobility. Furthermore, PUU with higher hard-segment content is highly anisotropic and highly rate-sensitive, indicating significant morphological interactions with inter-CNT spacing of ~18nm. Degradation and increased loss modulus are seen in similar PUU with 20% loading, pointing to weak chain interactions and reduced hydrogen, likely do to confinement and reduced mobility. A model has also been developed which sheds light on the evolution of CNT-matrix interactions across a wide range of CNT volume-fractions.
机译：本论文旨在更好地理解具有密集排列的碳纳米管（CNTs）的材料中双相聚（尿烷-脲）（PUU）相互作用的性质。特别令人感兴趣的是CNT与各种化学计量比的原位聚合PUU的相互作用。已经开发了允许用于制造基于PUU的聚合物纳米复合材料（PNC）的PUU的新颖合成方法。已经对化学计量变化的PUU材料的热和多尺度力学行为进行了研究，以证明基体与CNT之间在形态和机械增强方面都具有显着的相互作用; CNT Vf高达30％的PNC具有优异的润湿性通过Micro-CT确认。 TGA和DSC已显示CNT通过诱导结晶度和减少相混合来稳定PUU的热降解。 AFM通过观察基质材料中存在的晶体证实了这一点。 CNT诱导的结晶度和相分离归因于CNT与硬链段的结合，这限制了聚合过程中的链迁移率。发现较高的CNT Vf PNC可以增加软段的结晶度，但收益却有所降低。在10％V f CNTs处发现了极高的结晶度，但这是由于优化间距以允许PUU的有序晶体形成而产生的;横向压痕模量提高了1600％，轴向压模量提高了3500％已经通过准静态纳米压痕记录了。较大的CNT Vf和较大的硬段组成会导致链迁移率降低，并且在某些情况下会降低CNT在机械增强方面的有效性。 10％的CNT Vf表现出更大的压痕和储能模量，这被认为是由CNT间间距和链迁移率的最佳平衡引起的。此外，具有较高硬段含量的PUU具有高度的各向异性和较高的速率敏感性，表明CNT间间距约为18nm时，形态学相互作用显着。在负载量为20％的类似PUU中会看到降解和增加的损耗模量，这表明链相互作用弱且氢减少，很可能会限制和降低迁移率。还开发了一个模型，该模型阐明了在宽范围的CNT体积分数中CNT与基质相互作用的演变。

著录项

  • 作者

    Gair, Jeffrey L., Jr.;

  • 作者单位

    University of Maryland, College Park.;

  • 授予单位 University of Maryland, College Park.;
  • 学科 Mechanical engineering.;Materials science.;Nanotechnology.
  • 学位 Ph.D.
  • 年度 2017
  • 页码 287 p.
  • 总页数 287
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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