No abstract

The microstructure and mechanical properties of β-nucleated iPP before and after being annealed at different temperatures (90-160 °C) have been analyzed. Annealing induced different degrees of variation in fracture toughness of β-nucleated iPP samples, namely, slight enhancement at relatively low annealing temperatures (<110 °C) and great improvement at moderate temperatures (120-130 °C), whereas dramatic deterioration at relatively high temperatures (>140 °C) has been observed. The variation of fracture toughness of β-nucleated iPP is observed to be dependent on the content of β-NA. Experiments, including scanning electronic microscope (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA), are performed to study the variations of microstructures as well as the toughening mechanism of the β-nucleated iPP after being annealed. The results indicate that the decreased number of chain segments in the amorphous region and the formation of microvoids, which is easily triggered by the secondary crystallization at 120-130 °C, are mainly responsible for the great improvement of toughness through promoting the lamellae to slip or elongate along the impact direction and inducing the intense plastic deformation during the fracture process.

Capillary condensation of water is ubiquitous in nature and technology. It routinely occurs in granular and porous media, can strongly alter such properties as adhesion, lubrication, friction and corrosion, and is important in many processes employed by microelectronics, pharmaceutical, food and other industries [1][2][3][4] . The century-old Kelvin equation 5 is commonly used to describe condensation phenomena and shown to hold well for liquid menisci with diameters as small as several nm [1][2][3][4][6][7][8][9][10][11][12][13][14] . For even smaller capillaries that are involved in condensation under ambient humidity and so of particular practical interest, the Kelvin equation is expected to break down because the required confinement becomes comparable to the size of water molecules . Here we take advantage of van der Waals assembly of two-dimensional crystals to create atomic-scale capillaries and study condensation inside. Our smallest capillaries are less than 4 Å in height and can accommodate just a monolayer of water. Surprisingly, even at this scale, the macroscopic Kelvin equation using the characteristics of bulk water is found to describe accurately the condensation transition in strongly hydrophilic (mica) capillaries and remains qualitatively valid for weakly hydrophilic (graphite) ones. We show that this agreement is somewhat fortuitous and can be attributed to elastic deformation of capillary walls [23][24][25] , which suppresses giant oscillatory behavior expected due to commensurability between atomic-scale confinement and water molecules 20,21 . Our work provides a much-needed basis for understanding of capillary effects at the smallest possible scale important in many realistic situations.The Kelvin equation predicts that capillaries become spontaneously filled with water at the relative humidity RHK = exp (-2σ/kBTdρN)where σ ≈ 73 mJ m -2 is the surface tension of water at room temperature T, ρN ≈ 3.3×10 28 m -3 is the number density of water, kB is the Boltzmann constant, and d is the diameter of the meniscus curvature. For a two-dimensional (2D) confinement created by parallel walls separated by a distance h, d = h/cos(θ) where θ is the contact angle of water on the walls' material. For capillary condensation to occur at relative humidity (RH) considerably below 100%, equation 1 dictates that d must be comparable to 2σ/kBTρN ≈ 1.1 nm. For example, under typical ambient RH of 40-50%, water is expected to condense in slits with h < 1.5 nm and cylindrical pores with diameters < 3 nm, if θ is close to zero. Even stronger confinement is required for capillaries involving less hydrophilic materials. So far, a broad consensus has been reached that the Kelvin equation remains accurate for menisci with d ≥ 8 nm [1][2][3][4][6][7][8][9][10][11] and can also describe condensation phenomena in hydrophilic pores as small as 4 nm in diameter 12-14 . To achieve agreement with the experiments at this scale, the Kelvin equation is usually modified to account for so-called wetting films that are adsorbed on...

No abstract

A new method is introduced for the preparation of graphene/polyaniline hybrids using a one-step intercalation polymerization of aniline inside the expanded graphite. The structural and morphological characterizations were performed by X-ray diffraction analysis, transmission electron microscopy and field emission scanning electron microscopy. Both the experimental and first-principles simulated results show that the aniline cation formed by aniline and H(+) tends to be drawn towards the electron-enriched zone and to intercalate into the interlayer of graphite. Subsequently, an in situ polymerization leads to the separation of graphite into graphene sheet, resulting from the exothermic effect and more vigorous movements of the chain molecules of polyaniline. The interactions between polyaniline and graphene were confirmed by Fourier transform infrared spectroscopy and Raman spectra. In addition, the graphene/polyaniline hybrid exhibited a breakthrough in the improvement of microwave absorption.