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Polyimide (PI)/nano-SiO 2 composites were successfully fabricated via a novel in-situ polymerization. Microstructure, thermal properties, mechanical performance and tribological behaviors of these composites were investigated. The results indicate that nano-SiO 2 dispersed homogeneously. Compared with pure PI, thermal stability and heat resistance are higher about 10℃ with the addition of 5 wt% nano-SiO 2. Compressive strength and modulus of composite with 5 wt% nano-SiO 2 increase by 42.6 and 45.2%, respectively. The coefficient of friction (COF) of composite with 5 wt% nano-SiO 2 decrease by 6.8% owing to the thick and uniform transfer films. Excess nano-SiO 2 could adversely affect the COF of PI/nano-SiO 2 composite. Additionally, wear resistance deteriorates obviously since transfer film exfoliates easily and nano-SiO 2 aggregates on the surface of transfer films.

Mesoporous silica (MPS) with tunable mesopore channels can be used to reinforce polymers and has great potential in tribological applications, which is rarely investigated by research community. In this study, comprehensive properties of polyimide (PI)/MPS composites were investigated. Specially, the tribochemistry of PI/MPS composites in dry sliding against bearing steel was explicitly studied by the combined use of X-ray photoelectron spectroscopy (XPS) and Raman analysis. The results demonstrated a slightly decreased tensile strength but increased modulus, microhardness and thermal stability of the PI/MPS composites. The incorporation of 1.5 wt.% MPS increased the anti-wear resistance of PI by more than 14-fold. This was highly associated with the formation of high-quality transfer film on the bearing steel counterpart surface. Relevant tribochemistry was thoroughly revealed by XPS analysis on the transfer film and Raman analysis on the worn surfaces. This study confirmed the high efficiency of using MPS to reinforce PI polymer for tribological applications and elaborated tribochemistry to further better understand tribochemical reactions in polymer-metal rubbing systems.

In this article, the effects of different silane coupling agents: 3-glycidyloxypropyltrimethoxysilane (GOTMS), 3aminopropyltriethoxysilane (APTES), and 3-methacryloxypropyltrimethoxysilane (MPTS), on the interface between polyimide (PI) and silica (SiO 2 ), were investigated using molecular dynamic simulation. The results indicate that binding energy between PI molecules and SiO 2 surface mainly comes from van der Waals interaction. Proper silane coupling agents generate a thin membrane on the surface of SiO 2 , which improves the thickness of the transition layer between PI molecules and SiO 2 surface. And density of the transition layer was enhanced by APTES significantly. In addition, amino group (ANH 2 ) improves the electrostatic interaction between PI molecules and SiO 2 surface rather than epoxy group (ACHACH 2 AO) and methacrylic oxide group (AOACOAC(CH 3 )@CH 2 ). As a result, APTES enhances the binding energy effectively. However, excessive silane coupling agent increases the distance between PI matrices and SiO 2 , which deteriorates performance of the interface. In addition, GOTMS and MPTS generate a thick and dense membrane on SiO 2 surface, which induces the loose transition layer and poor binding energy. Overlap parameter between PI molecules and SiO 2 surface grafted with silane coupling agent can be employed to evaluate the transition layer successfully. V C 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45725.

The effects of polyimide with silica (SiO 2 -PI) and pores (porous PI) on the morphology, thermal, mechanical, and tribological properties of polytetrafluoroethylene (PTFE) composites were investigated. SiO 2 -PI and porous PI fillers decrease the compactness of PTFE matrices within PTFE/SiO 2 -PI composites and PTFE/porous-PI composites. In addition, SiO 2 -PI fillers improve the interfacial bonding between PI fillers and PTFE matrices, which is opposite to the detrimental effect of porous PI fillers. Thermal and mechanical properties of PTFE composites were deteriorated apparently. The friction coefficients of PTFE/SiO 2 -PI and PTFE/porous-PI composites are 9.5% and 8.5% lower than that of PTFE/PI, respectively. The wear resistance of PTFE/SiO 2 -PI and PTFE/porous-PI composites is enhanced by 77.8% and 70.1%, respectively. Scanning electron microscopy (SEM) of worn surface indicates that SiO 2 -PI and porous PI fillers protect PTFE matrices from counterpart ball, which inhibits the plastic flow of PTFE matrices effectively. In addition, the uneven worn surface decreases the contact area between PTFE composites and counterpart ball. Compared with SiO 2 -PI fillers, the extension of porous PI fillers in friction process increases the contact area between PTFE composites and counterpart, which induces the relatively poor tribological performance of PTFE/porous-PI. Furthermore, SiO 2 -PI and porous PI fillers contribute to the formation of smooth and uniform transfer films, which improve the tribological performance of PTFE composites effectively. In addition, compared with adding SiO 2 -PI into PTFE, the addition of SiO 2 nanoparticles into PTFE/PI induces the rough and uniform transfer films, which is bad for tribological performance of PTFE/PI/-SiO 2 composites. POLYM. COMPOS., 40:3438-3452, 2019.