Fanlin Zeng

A molecular dynamics simulation study to investigate the elastic properties of PVDF and POSS nanocomposites

The effects of the polyhedral oligomeric silsesquioxanes compound (3, 3, 3-trifluoropropyl)8Si8O12 (FP-POSS) on the elastic properties of poly(vinylidene difluoride) (PVDF) are investigated using molecular dynamics (MD) simulations. The volume–temperature properties and elastic constants for four different systems (PVDF-0, neat PVDF; PVDF-I, with 3.1 wt% FP-POSS; PVDF-II, with 5.85 wt% FP-POSS; PVDF-III, with 8.52 wt% FP-POSS) in the temperature range 100–400 K are studied. Simulation results show that (1) the calculated volume–temperature behavior and elastic constants for PVDF-0 matched well with experimental results; (2) the glass transition temperature of PVDF is significantly improved with FP-POSS; (3) the moduli of PVDF are improved and the improvement effect, in general, nearly always decreases with the increase in the mass ratio of FP-POSS. Furthermore, the possible mechanism of the difference in the modulus improvement effects is discussed.

Molecular simulations of the miscibility in binary mixtures of PVDF and POSS compounds

The miscibility behavior of binary mixtures of poly(vinylidene difluoride) (PVDF) and six different kinds of polyhedral oligomeric silsesquioxanes (POSS) compounds ((ethylic)8Si8O12 (E-POSS), (phenyl)8Si8O12 (P-POSS), (3, 3, 3-trifluoropropyl)8Si8O12(FP-POSS), (1H, 1H, 2H, 2H-nonafluorohexyl)8Si8O12 (FH-POSS), (1H, 1H, 2H, 2H-tridecafluorooctyl)8Si8O12 (FO-POSS) and (1H, 1H, 2H, 2H-heptadecafluorodecyl)8Si8O12 (FD-POSS)) was studied using molecular simulations and the extended Flory–Huggins model. First, the pairwise binding energies Eij and coordination numbers Zij were computed by means of a Monte Carlo approach. Then the mixing energies Emix, the Flory–Huggins interaction parameters χ and the free energies ΔGmix in the temperature range 100–600 K and phase diagrams of the six different mixtures were obtained. All these results indicate that PVDF/FP-POSS, PVDF/FH-POSS, PVDF/FO-POSS and PVDF/FD-POSS are fully miscible at any temperature. PVDF/E-POSS and PVDF/P-POSS are immiscible except at very high temperatures. The lowest energy frames and the frame energies show that the miscibility of PVDF and the four kinds of fluorinated POSS compounds is derived from the polar C–F bonds and the electrostatic interactions in their molecules.

Reactive Molecular Dynamics Simulations on the Disintegration of PVDF, FP-POSS, and Their Composite during Atomic Oxygen Impact.

Poly(vinylidene fluoride) (PVDF) is a kind of important piezoelectric polymer used in spacecraft industry. But the atomic oxygen (AO) is the most abundant element in the low Earth orbit (LEO) environment. AO collision degradation is an important issue in the application of PVDF on spacecrafts. To investigate the erosion behaviors of PVDF during AO impacts and how to improve the stability of PVDF against AO impacts, the temperature evolution, mass loss, and erosion yields of neat PVDF, neat polyhedral oligomeric silsesquioxanes compound (3,3,3-trifluoropropyl)8Si8O12 (FP-POSS) and the PVDF/FP-POSS composite under AO impacts, as well as some key disintegrated structures and separated chemical compositions, were researched using the molecular dynamics (MD) simulations and the reactive ReaxFF force field. The simulation erosion yield result of PVDF is very close to the experiment results, which shows our simulations are reliable. The results of the temperature evolution, mass loss, and erosion yield of three materials show that the antierosion performance of PVDF is not outstanding. However, incorporating FP-POSS into PVDF matrix enhances the stability of PVDF against AO impact greatly and reduces the temperature rise, mass loss, and the erosion yield of PVDF rapidly. A detailed analysis on the flight chemical compositions and key snapshots of the structures reveals that the erosion process on PVDF and PVDF/FP-POSS is continuous and should be derived from the same PVDF matrix in two materials. In contrast, the erosion process on FP-POSS is stepped. The erosion will not take place until the number of AO reaches a specific value. There is a barrier for the erosion of high-energy AO because of the stable cagelike Si-O frame in FP-POSS molecules. This should be chiefly responsible for the high stability of FP-POSS and the reinforcement mechanism of FP-POSS on PVDF against AO impacts. This work is helpful for people to understand the erosion details of PVDF and POSS and provides valuable information to design effective protective structure for PVDF against AO impacts in LEO environment.

Study on different behaviour of poly(vinylidene fluoride)-polyhedral oligomeric silsesquioxane nanocomposites in mechanical properties and nano-tensile testing

Nanocomposites consisting of a poly(vinylidene fluoride) (PVDF) matrix and 0, 3, 5 and 8 wt-% fluoropropyl polyhedral oligomeric silsesquioxane (FP-POSS) were prepared using the solvent evaporation method. The mechanical properties of nanocomposites were investigated by universal mechanical testing and nano-tensile testing. The results derived from two different scales testing both indicated that a small addition of FP-POSS exhibited a positive reinforcement effect of mechanical properties. Meanwhile the reason of the different variation trend of mechanical properties derived from testing standards under different scales was analysed, and the specific role and multi-performance of POSS were estimated.

Ferroelectric performance, surface and mechanical properties of poled PVDF sheet with metal coating: Assessing through PFM, FTIR, and nanoindentation and nanoscratch

ABSTRACT In this work, the poled PVDF with metal coating was prepared. The microscopy characterization and crystalline phase were studied. The piezoresponse force microscope (PFM) test, nanoindentation and nanoscratch tests were carried out. The focus of this work is on the morphology, local piezoelectric deformation, and the key properties of PVDF sheet with coating, such as the hardness, roughness, critical load and so on. The aim is to determine surface characteristic, ferroelectric domain and mechanical properties of PVDF sheet and can avoid the unfavorable effect that the sample served as an actuator broke during the bending deformation.

Molecular Mechanics Simulation on the Deformation Behaviors and the Mechanical Properties of Nano Composite of Polyethylene and POSS

The influence of polyhedral oligomeric silsesquioxane (POSS) on nano-hybrid materials has caused widespread attentions. In the current work, we investigate the deformation behaviors and the mechanical properties of the two kinds of polymers, polyethylene (PE) and PE copolymerized with vinyl-POSS (POSS-PE) by using molecular mechanics simulations. First, the nano scale atomistic models of the PE and POSS-PE incorporated with 25 wt% vinyl-POSS are built. With the aids of the COMPASS force field, the mechanical behaviors of the two kinds of polymers under different tensile strains are then simulated and the stress-strain curves are obtained. From the curve, the stresses and strains of PE keep approximately linear before the yield point. The corresponding tensile modulus is in good agreement with the experimental data. In addition, the simulation results show that the localized necking deformation appears during the yield process. It is believed that the slippage between the adjacent molecule chains is the chief source of such localized deformation. However, the necking phenomenon is not found in POSS-PE nano-composite. It seems that the POSS cages prevent the macromolecule chains from wide-spread slipping. The deformation is restrained locally around POSS monomers, thus leading to the formation of micro voids. We finally analyze the mechanical properties of the two kinds of polymers. The elastic modulus and tensile strength of POSS-PE have been remarkably improved. This work is significant to understand the reinforcement mechanism of POSS and provides important referential message to the applications of POSS.