Jichun You

Impact of ionic liquid-modified multiwalled carbon nanotubes on the crystallization behavior of poly(vinylidene fluoride).

The impact of pristine multiwalled carbon nanotubes (MWCNTs), an ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], and the ionic liquid-modified MWCNTs (IL-MWCNTs) on the crystallization behavior of melt-crystallized poly(vinylidene fluoride) (PVDF) has been investigated. Pristine MWCNTs accelerate crystallization of PVDF as an efficient nucleation agent, while the formed crystals are mainly nonpolar α crystal form with few polar β crystals. Incorporation of only ionic liquid results in depression of the PVDF melt crystallization rate due to the miscibility of IL with PVDF but leads to a higher content of polar crystals (β and γ forms) than MWCNTs. The ionic liquid and MWCNTs show significant synergetic effects on both the nucleation and the formation of polar crystals for PVDF by melt crystallization. Addition of IL-MWCNTs not only improves the MWCNTs dispersion in PVDF matrix but also increases the overall crystallization rate of PVDF drastically. More important, the melt-crystallized PVDF nanocomposites with IL-MWCNTs show 100% polar polymorphs but no α crystal forms. To the best of our knowledge, this is the first report on the achievements of full polar crystal form in the melt-crystallized PVDF without mechanical deformation or electric field. The IL to MWCNTs ratio and the IL-MWCNTs loading content effects on the crystallization behavior of PVDF in the nanocomposites were also studied. It is considered that the specific interactions between >CF2 with the planar cationic imidazolium ring wrapped on the MWCNTs surface lead to the full zigzag conformations of PVDF; thus, nucleation in polar crystals (β and γ forms) lattice is achieved and full polar crystals are obtained by subsequent crystal growth from the nuclei.

Ionic liquid modified poly(vinylidene fluoride): crystalline structures, miscibility, and physical properties

A room temperature ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], has been used to modify poly(vinylidene fluoride) (PVDF). The crystalline structures, miscibility, and physical properties of PVDF/IL blends were investigated systematically. It was found that the incorporation of IL into the PVDF leads to drastically increased γ crystal forms of PVDF by the interaction between the >CF2 and cationic ions. Moreover, IL is fully miscible with PVDF with the interaction parameter (χ12) of −2.84 calculated by the revised Nishi–Wang equation due to the drastic equilibrium melting temperature depression. Dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS) results indicate that the IL molecules are inserted into the gallery of PVDF lamellae. A small amount of IL induces the appearance of the crystal-amorphous interface relaxation of PVDF, originating from the enrichment of IL distribution near the crystal-amorphous interface. The obtained PVDF/IL blends exhibit excellent mechanical performance with significantly increased ductility and good optical transmittance. In addition, the incorporation of IL into PVDF enhances the electrical conductivity of PVDF films greatly. Therefore, novel PVDF films with high transparency, excellent antistatic properties, and a highly polar crystal form fraction were successfully achieved.

Mechanical and thermal properties of eco-friendly poly(propylene carbonate)/cellulose acetate butyrate blends.

The eco-friendly poly(propylene carbonate) (PPC)/cellulose acetate butyrate (CAB) blends were prepared by melt-blending in a batch mixer for the first time. PPC and CAB were partially miscible because of the drastically shifted glass transition temperatures of both PPC and CAB, which originated from the specific interactions between carbonyl groups and hydroxyl groups. The incorporation of CAB into PPC matrix enhanced not only tensile strength and modulus of PPC dramatically, but also improved heat resistance and thermal stability of PPC significantly. The tensile strength and the modulus of PPC/CAB=50/50 blend are 27.7 MPa and 1.24 GPa, which are 21 times and 28 times higher than those of the unmodified PPC, respectively. Moreover, the elongation at break of PPC/CAB=50/50 blend is as high as 117%. In addition, the obtained blends exhibited good transparency, which is very important for the package materials. The results in this work pave new possibility for the massive application of eco-friendly polymer materials.

PLLA microalloys versus PLLA nanoalloys: preparation, morphologies, and properties.

Nanostructured polymer blends have attracted significant attention recently. In this paper, the poly(lactic acid) (PLLA)/ethylene-co-acrylic ester-co-glycidyl methacrylate (E-AE-GMA) rubber (80/20) nanoalloys and microalloys were fabricated by melt blending and the structure-property relationships of the prepared alloys were investigated. In the nanoalloys, the rubber domains are homogeneously dispersed in the PLLA matrix with the overall domain size of <100 nm. Such nanoalloys exhibit not only high transparency in the visible region, but also significantly improved ductility and impact strength, compared with neat PLLA. Moreover, the nanodomains in the PLLA matrix enhance the crystallization rate of PLLA drastically. The overall crystallization rate of the PLLA nanoalloy is even higher than that of the PLLA nucleated by talc. In contrast, the PLLA microalloy has a phase structure with the size of the rubber domains being in the micrometer to submicrometer scale. The microalloy is opaque and displays almost the same tensile strength and modulus as the nanoalloy, but much higher impact strength than the nanoalloy.

Crystal orientation behavior and shape-memory performance of poly(vinylidene fluoride)/acrylic copolymer blends.

The crystal orientation behavior and shape-memory performance of miscible poly(vinylidene fluoride) (PVDF)/acrylic copolymer blends in various ratios have been investigated. With the incorporation of amorphous acrylic copolymer into the gallery of PVDF lamellae, the molecular connection (tie molecule concentration) between the neighboring PVDF crystals decreases gradually. For the blends with more than 80 wt % PVDF, most of the PVDF α-crystals are transformed into β-crystals upon deformation, and the molecular chains of the β-crystals are aligned along the stretching direction because tie molecules transfer the loading effectively. For the blends with less than 30 wt % PVDF, almost all of the PVDF crystals are isolated from each other with very few tie molecules. Mechanical deformation induces the perpendicular crystal molecular chain arrangement with no crystal form transitions. For the blends with 40 wt % to 70 wt % PVDF, the c-axis-oriented β-phase and the tilt-oriented α-phase coexist in the uniaxially stretched blends. The shape-memory properties of the blends were also evaluated over the same blend composition range. The maximum shape-memory recovery properties were observed for the blend sample containing 50 wt % PVDF, in which a small amount of tie molecules connect the PVDF crystallites to form a deformable elastic network. This network contributes to the good shape-memory properties of the blend. For the blends with very few tie molecules or high tie molecule concentrations, the deformation induces the slipping of the amorphous molecules or the large fibrillar crystal structure, respectively; thus, these samples exhibit relatively low shape-memory performance.

Novel Cigarlike TiO2 Nanofibers: Fabrication, Improved Mechanical, and Electrochemical Performances

By coupling the self-assembly of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) containing titanium precursors with the electrospinning technique, novel cigarlike nanofibers with an outer-shell and inner-continuous-pore structure and resultant fabrics were fabricated. Different from typical porous metal oxides, the prepared high-surface-area nonwoven fabrics show excellent mechanical properties. Not only are these fabrics self-supporting over a large area, but they can also be cut using scissors, which is important for large-scale applications. Furthermore, as electrode materials in Li-ion batteries, these fabrics exhibit much higher charge/discharge capacity and cycle stability compared with the commercially available nanosized TiO2 (P25). The improved mechanical and electrochemical performances are attributed to the presence of an outer-shell, inner-bicontinuous structures (including continuous TiO2 frame and continuous nanopores) and hierarchical pores from the cigarlike nanofibers.

Crystallization-Modulated Nanoporous Polymeric Materials with Hierarchical Patterned Surfaces and 3D Interpenetrated Internal Channels

Poly(oxymethylene)/poly(L-lactic acid) (POM/PLLA) blends are typical melt-miscible binary systems. During isothermal crystallization at various temperatures, in the presence of amorphous PLLA chains, POM crystallizes into banded spherulites with different band spaces, which forms a continuous crystalline phase and serves as a sturdy frame in the final porous materials. On the other hand, the amorphous PLLA chains are simultaneously expelled out from POM crystal lamellae to generate the other continuous phase during the crystallization of POM. Consequently, the interpenetration of the POM lamellae and the amorphous PLLA phase construct a cocontinuous phase structure. All the PLLA constituents are fully included in the interlamellar or interfibrillar of POM crystals. Thus, nanoporous POM materials with hierarchical patterned surface and 3D interpenetrated internal channels have been successfully obtained by extracting the amorphous PLLA phase. It is further found that the POM crystal morphologies in the blends are much dependent on the crystallization conditions. Therefore, the hierarchical patterned structure and the size of internal channels (pore size) can be modulated by adjusting the crystallization conditions.

Solvent annealing induced phase separation and dewetting in PMMA/SAN blend films: composition dependence

The competition between “dewetting” and “phase separation” behaviors in polymer blend films attracts significant attention. The simultaneous phase separation and dewetting in PMMA/SAN [poly(methyl methacrylate) and poly(styrene-ran-acrylonitrile)] blend ultrathin films upon solvent annealing have been observed in our previous work. The composition dependence of phase behaviors in the same system has been investigated using atomic force microscopy and grazing incidence small-angle X-ray scattering. Both phase separation and dewetting were observed across the entire composition range investigated. The evolution of film structures during solvent annealing was dependent on the blend composition. Solvent annealing led to complex structures, in which the upper (small spots, bicontinuous structures or large continuous droplet) and lower (mimic-film) parts were composed of phase-separated SAN- and PMMA-rich phases, respectively. With increasing blend SAN weight fraction, the diameter of the lower PMMA-rich mimic-film decreased. The upper SAN-rich phase structure transformed depending on the SAN content; to small spots ( 50% SAN content), on top of the PMMA mimic-film.

Ionic liquid induced supramolecular self-assembly of poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) thin films with enhanced conductivity and tunable nanoporosity

AbstractWe present a facile strategy, for the first time as the best of our known, to prepare high conducting poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT:PSS) film with a novel nanoporous morphology directly from a commercial PEDOT:PSS dispersion. Both conducting properties and surface morphology of PEDOT:PSS film can be systematically tunable by simply controlling addition of an ionic liquid, 1,3-dihydroxy-2-methylimidazolium bis(trifluoromethylsulfonyl)-imide (DHIL). The electrical conductivity increases from 0.07 for pristine PEDOT:PSS to 55 S cm−1 after addition of 2 wt% DHIL, with no necessary of any further heat treatment, which is around 800 times increase in the electrical conductivity. On the other hand, the discrete compact PEDOT:PSS film is gradually transformed into the nanoporous film with addition of DHIL. It is considered that such size-tunable porous PEDOT:PSS films with high surface area as well as high conductivity combining solution-processibility show great potential in applications that require high interfacial area, such as flexible electronic components, nextgeneration catalytic, and separation supports.

Reactive bonding mediated high mass loading of individualized single-walled carbon nanotubes in an elastomeric polymer

A reactive chemical bonding strategy was developed for the incorporation of a high mass loading of individual single-wall carbon nanotubes (SWCNTs) into an elastomeric matrix using a reactive ionic liquid as a linker. This method simultaneously prevented the agglomeration of SWCNTs and caused strong interfacial bonding, while the electronic properties of the SWCNTs remained intact. As a result, the high conductivity of the carbon nanotubes (CNTs) and the flexibility of the elastomeric matrix were retained, producing optimum electrical and mechanical properties. A composite material with a loading of 20 wt% SWCNTs was fabricated with excellent mechanical properties and a high conductivity (9500 S m(-1)). The method could be used to form transparent thin conductive films that could tolerate over 800 bend cycles at a bending angle of 180° while maintaining a constant sheet resistance.