In polymer matrix nano-composite, the interphase is the region around the fiber reinforcement, and its local morphology and properties are different from the bulk matrix. The practical use of CNT particles in polymer matrix nano-composites has been limited to less than 5 wt%. Assembling CNTs into a thin film Buckypaper (BP) is an effective way of creating high CNT content nano-composites. BP consist of entangled CNT networks with a porous mesh structure in which CNTs are randomly distributed. The interaction between the CNT network and the surrounding polymer and between BP and the surrounding polymer occurs via interphase with different morphology than the bulk matrix. This interphase's properties have not been given enough attention in the literature, and the purpose of this study is to investigate the stochastic nature of these properties experimentally.&nbsp;Atomic Force Microscopy based Peak Force Quantitative Nanomechanics Mapping (PFQNM) technique has been used for characterization of the CNT network interphase at the nano-scale with high lateral resolution. Details of the calibration parameters include probe stiffness, real spring constant, tip radius, tapping force, deformation level, synchronous distance, drive3 amplitude sensitivity (DDS3), and deflection sensitivity for heterogeneous polymer matrix carbon fiber composites will be discussed. The nano-scale material properties will be extracted from Trace and retrace curves of force vs. deformation response. Reduced modulus, adhesion, and deformation results are used to examine the interphase zone thickness and properties.Biaxial carbon fiber and Bisphenol-A/F type epoxy with amine hardener with a mix ratio of 100:22 was used as the fabric and polymer matrix.&nbsp; Nonfunctionalized multiwall carbon nanotube (MWCNT) with an average outer diameter of 10-30nm, an average length of 15-30µm, and a purity of 90%, produced with chemical vapor deposition technique, was used as the nano-reinforcement. &nbsp;The AFM samples are 1 mm in thickness and are polished to 0.1 µm. AFM Multimode 8, scanner type J with a maximum scanning window of 125µm × 125µm, is used. An indentation depth of up to ~4nm is used during peak force tapping to avoid any damage to the sample and guarantee repeatable results. Since the Deformation is less than or equal to the tip radius; therefore, the Derjaguin, Muller, Toropov (DMT) equation is applied to the retract curve to calculate the elastic modulus.For the statistical analysis, the authors use the Weibull model to examine material properties' distribution. Weibull statistics shows the probability of the occurrence of an interphase thickness or its modulus. Linear regression, the method of moments, and the maximum likelihood method are common techniques for evaluating the Weibull parameters. These techniques are currently examined to investigate the applicability and suitability for interphase properties of CNT networks. The scale parameter and the Weibull modulus (shape parameter) of the distribution characterize the data's scattering. A lower Weibull modulus means a higher dispersion of the data. The Weibull analysis results will show the interphase thickness of small and large CNT networks in 3-phase nanocomposites.

Experimental Approach and Conventional Analytical Techniques to the Carbon Nanotube Network Interphase in 3-Phase Polymer Matrix Nano-Composites

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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