Influence of the carbon nanofiller surface curvature on the initiation of crystallization in thermoplastic polymers

Abstract

Experimental results have shown that graphitizated carbon nanofibers initiate crystallization in R-BAPB polyimides twice as fast as single-wall carbon nanotubes (CNT) leading to the hypothesis that nanofiller curvature influences polyimide crystallization. Therefore, atomistic molecular-dynamics simulations have been performed for R-BAPB in the presence of a flat graphene sheet and the results were compared with those obtained in the presence of a small-radius CNT. The polyimide chain segments tend to lie parallel to the nanofiller surface and this tendency is stronger and the segments are closer to the graphene surface than to the CNT one. Moreover, the density of the polyimide in the near-surface layer is higher for composites filled with graphene than with CNT. This confirms the assumption that the nanofiller surface curvature is indeed a factor influencing the polymer patterning structure, and that a smaller curvature (i.e. flat surface) provides an enhanced initiation of polymer ordering. A IntroductionOne of the most promising ways to improve the performance of polymeric materials consists of developing polymer composites.1-3 Signicant changes aer addition of a ller are inuenced by the polymer and ller properties, but also by the interface interactions between both components. The use of nanoscalereinforcing llers leading to a considerable increase in the interaction area between the composite components has driven the interest of researchers in last years.4-11 Allotropic carbon compounds (carbon black, fullerenes, single-and multiwall nanotubes, nanobers and graphene sheets) are among the popular nanollers. 4,7,9,[11][12][13][14][15][16][17] Polymers with a relatively simple or complicated molecular structure have been and are currently used as matrices in nanocomposite materials. 4,[17][18][19] By combining different types of matrices and nanollers, it is possible to obtain composites with a wide range of physical properties. In some cases, a nanoller can initiate the crystallization of the polymer matrix, 18,20-25 signicantly accelerating the formation of crystallites, or even initiating their formation in the polymer under conditions which do not normally favor the crystallization, as in the case of ODPA-P3 polyimide.26 Crystallization of a polymer matrix in a nanocomposite may signicantly impact its mechanical and thermophysical properties, which should be taken into account when developing new composite materials.18,27,28 The advantage of using nanoparticles for initiation of crystallization is that the formation of a large number of nanoscale crystallites improves the strength of the nanocomposite preventing the typical failure on the boundary area between crystalline regions, thus improving the performance of the material. Therefore, the question arises on how the physical properties of carbon nanollers affect the initiation of crystallization in semicrystalline thermoplastic matrices.Yudin et al. 17,[23][24][25]29 investigated the crystallization initiation of the semicrystalline ther...

Influence of the carbon nanotube surface modification on the microstructure of thermoplastic binders

“…52,53 Similar to our previous paper 52 carbon nanotubes of 4.7 nm long with chirality (5, 5) were used as fillers with carboxyl groups attached to the CNTs. 52,53 Similar to our previous paper 52 carbon nanotubes of 4.7 nm long with chirality (5, 5) were used as fillers with carboxyl groups attached to the CNTs.…”

“…52,53 The computer simulation of the systems under the study was performed in the Gromacs computational package 71 using the Gromos53a5 force field. 52,53 The computer simulation of the systems under the study was performed in the Gromacs computational package 71 using the Gromos53a5 force field.…”

“…To maintain the set lengths of the bonds between the atoms, the LINCS algorithm was used. 52,53,[60][61][62][63][64][65] The equilibration procedure included stages of the system compression from the initial low-density configuration (polymer gas), cyclic annealing within the temperature range of 600 to 290 K, equilibration at a high temperature for 1.5 μs, and further production run during 1 μs. Parametrization of the charges in this force field was done using the HF/6-31G* method.…”

“…The changes observed are attributed to the decrease in the filler surface area available for the contact with polymer chains, which is related to the steric effect of functional groups coupled with the nanotube. 1), 52,53 resulting from the interaction with the filler surface. Such simulation enables us to explore structural properties of the systems under scrutiny on the atomistic scale, and establish the mechanisms stipulating the changes in the polymer properties after nanofiller loading.…”

Degree of Crystallinity and Phase Fraction of Polyvinylidene Fluoride Nanocomposites Containing Ionic Liquid and Graphene/Carbon Nanotube

“…This reduction in the degree of crystallinity could be attributed to the different crystallization mechanisms on the surface of the graphene flakes and the SWNTs , as well as the different geometry parameters of SWNTs and the graphene flakes. A SWNT is a one dimensional nanostructure with 1–4 nm in diameter and high curvature that results in a significant decrease of the interfacial crystallization and hence smaller . In addition, decreases because of the highly dense tangled CNTs which confine the free growth of crystalline regions , and the effect of DMAc solvent on the interfacial crystallization .…”