Yongri Liang

High Performance Graphene Oxide Based Rubber Composites

In this paper, graphene oxide/styrene-butadiene rubber (GO/SBR) composites with complete exfoliation of GO sheets were prepared by aqueous-phase mixing of GO colloid with SBR latex and a small loading of butadiene-styrene-vinyl-pyridine rubber (VPR) latex, followed by their co-coagulation. During co-coagulation, VPR not only plays a key role in the prevention of aggregation of GO sheets but also acts as an interface-bridge between GO and SBR. The results demonstrated that the mechanical properties of the GO/SBR composite with 2.0 vol.% GO is comparable with those of the SBR composite reinforced with 13.1 vol.% of carbon black (CB), with a low mass density and a good gas barrier ability to boot. The present work also showed that GO-silica/SBR composite exhibited outstanding wear resistance and low-rolling resistance which make GO-silica/SBR very competitive for the green tire application, opening up enormous opportunities to prepare high performance rubber composites for future engineering applications.

Concentric Ring Pattern Formation in a Competing Crystallization and Phase Separation Process

Spherulitic patterns usually form in the single process of crystallization in polymer blends. But when phase separation intervenes under deep quench, the radial growth of the initial spherulitic patterns tends to invert into concentric alternating crystalline-/amorphous-rich ring structures. Within crystalline-rich regions, lateral lamellae orient in the tangential direction rather than in the usual radial direction. We demonstrate the determining factor for this first observed phenomenon is the concentration deviation enhanced phase separation dynamics at the growth interface of crystals.

Fabrication of nanoprotrusion surface structured silica nanofibers for the improvement of the toughening of polypropylene

The toughening of semi-crystalline polymers with inorganic nanofiller is very important in the practical applications of such polymers. In this study, we successfully fabricated the surface attaching silica nanoparticles of silica nanofibers (SiO2@SNFs) from the calcination of electrospun poly(vinyl pyrrolidone)/tetraethyl orthosilicate/silica nanoparticle (PVP/TEOS/SiO2) nanofibers for the toughening of polypropylene (PP). The SiO2@SNFs had a nanoprotrusion structured surface, and the degree of surface nanoprotrusion of the silica nanofibers (SNF) can be adjusted via the incorporated SiO2 nanoparticle content of the SiO2@SNFs. The effects of the SiO2 content of the SiO2@SNFs on the crystallization behavior, relative β-form crystal content, and mechanical properties of PP were investigated with polarized optical microscopy, X-ray diffraction and notched Izod impact test methods. By comparison with SNF, the SiO2@SNFs showed greater improvements in the impact strength and heterogeneous crystal nucleation of PP at the same loading content of filler. The impact strength of PP/SiO2@SNFs at a loading of 2 wt% of SiO2@SNFs with 9 phr (SiO2/TEOS = 9/100) of SiO2 nanoparticles was improved by about 1.9 and 1.4 times that of neat PP and PP/SNFs composite (2 wt% of SNFs), respectively. However, the crystallinity, relative β-form crystal content, and tensile strength of PP/SiO2@SNFs were almost independent of the SiO2 nanoparticle content of the SiO2@SNFs. Our results demonstrated that these nanoprotrusion surface structured silica nanofibers can be used as a novel nanofiller for improving the toughening of PP.

Crystallization-driven surface segregation and surface structures in poly(L-lactide)-block-poly(ethylene glycol) copolymer thick films.

In this work, we used poly(L-lactide)-block-poly(ethylene glycol) (PLLA-b-PEG) copolymer thick films to investigate the effect of crystallization on surface segregation, surface crystal orientation, and morphology by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), reflection optical microscopy (ROM), and two-dimensional grazing incident wide-angle X-ray scattering (2D GIWAXS) methods. ATR-FTIR results indicated that the surface fraction of PLLA block increased from 0.48 to 0.79 when T(c,PLLA) increased from 70 to 110 °C. Polarized ATR-FTIR and 2D GIWAXS results indicated that PLLA crystal lamellae preferentially oriented parallel to the film surface with increasing T(c,PLLA). The surface crystallinity of PLLA was almost independent of T(c,PLLA), while the surface crystallinity of PEG decreased with increasing T(c,PLLA). On the basis of surface crystal orientation and crystallization kinetics, we suggested that the excess of PLLA component at the surface was mainly dominated by a coupling effect of crystallization behavior and surface segregation.

Optimization of mechanical and dielectric properties of poly(urethane–urea)-based dielectric elastomers via the control of microstructure

In this work, we fabricated novel poly(urethane–urea) (PUU)-based dielectric elastomers using a hydroxyl-terminated butadiene–acrylonitrile copolymer (HTBN) as the soft segment and hexamethylene diisocyanate (HDI) and 3,3′-dimethyl-4,4′-diamino dicyclohexyl methane (DMDC) as hard segments. The effect of hard segment (HS) content on the hard domain (HD) structure, morphology, dielectric and mechanical properties was investigated with Fourier transform infrared spectroscopy (FTIR), small/wide angle X-ray scattering (SAXS/WAXS), broadband dielectric spectroscopy and mechanical testing methods. Our results indicated that the hard domain structure units of PUUs such as degree of hydrogen bonding, size and crystallinity played an important role in the dielectric and mechanical properties. The dielectric constant of PUUs was significantly decreased with increasing HS content, whereas the breakdown strength and Youngs modulus of PUUs were significantly increased. The relationship between multi-length scale structure and dielectric constant and breakdown strength properties of PUUEs were discussed. Our results can provide a new insight for optimization of dielectric and mechanical properties of PUU-based dielectric elastomers.