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  • 1.
    Barbero, David
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Carbon nanotube networks: nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading2014In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 26, no 19, p. 3164-Article in journal (Refereed)
    Abstract [en]

    Arrays of nano-engineered carbon nanotube networks embedded in nanoscale polymer structures enable highly efficient charge transport as demonstrated by D. R. Barbero and co-workers on page 3111. An increase in charge transport by several orders of magnitude is recorded at low nanotube loading compared to traditional random networks in either insulating (polystyrene) or semiconducting (polythiophene) polymers. These novel networks are expected to enhance the performance of next generation hybrid and carbon based photovoltaic devices.

  • 2.
    Barbero, David
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading2014In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 26, no 19, p. 3111-3117Article in journal (Refereed)
    Abstract [en]

    We demonstrate a simple and controllable method to form periodic arrays of highly conductive nano-engineered single wall carbon nanotube networks from solution. These networks increase the conductivity of a polymer composite by as much as eight orders of magnitude compared to a traditional random network. These nano-engineered networks are demonstrated in both polystyrene and polythiophene polymers.

  • 3.
    Boulanger, Nicolas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    SWNT nano-engineered networks strongly increase charge transport in P3HT2014In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 6, no 20, p. 11633-11636Article in journal (Refereed)
    Abstract [en]

    We demonstrate the formation of arrays of 3D nano- sized networks of interconnected single-wall carbon nanotubes (SWNT) with well defined dimensions in a poly-3- hexylthiophene (P3HT) thin film. These novel nanotube nano-networks produce efficient ohmic charge transport, even at very low nanotube loadings and low voltages. An increase in conductivity between one and two orders of magnitude is observed compared to a random network. The formation of these nano-engineered networks is compatible with large area imprinting and roll to roll processes, which makes it highly desirable for opto-electronic and energy conversion applications using carbon nanotubes.

  • 4.
    Klechikov, Alexey
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Thomas, Diana
    Sharifi, Tiva
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr V.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Structure of graphene oxide membranes in solvents and solutions2015In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 7, no 37, p. 15374-15384Article in journal (Refereed)
    Abstract [en]

    The change of distance between individual graphene oxide sheets due to swelling is the key parameter to explain and predict permeation of multilayered graphene oxide (GO) membranes by various solvents and solutions. In situ synchrotron X-ray diffraction study shows that swelling properties of GO membranes are distinctly different compared to precursor graphite oxide powder samples. Intercalation of liquid dioxolane, acetonitrile, acetone, and chloroform into the GO membrane structure occurs with maximum one monolayer insertion (Type I), in contrast with insertion of 2-3 layers of these solvents into the graphite oxide structure. However, the structure of GO membranes expands in liquid DMSO and DMF solvents similarly to precursor graphite oxide (Type II). It can be expected that Type II solvents will permeate GO membranes significantly faster compared to Type I solvents. The membranes are found to be stable in aqueous solutions of acidic and neutral salts, but dissolve slowly in some basic solutions of certain concentrations, e.g. in NaOH, NaHCO3 and LiF. Some larger organic molecules, alkylamines and alkylammonium cations are found to intercalate and expand the lattice of GO membranes significantly, e.g. up to similar to 35 angstrom in octadecylamine/methanol solution. Intercalation of solutes into the GO structure is one of the limiting factors for nano-filtration of certain molecules but it also allows modification of the inter-layer distance of GO membranes and tuning of their permeation properties. For example, GO membranes functionalized with alkylammonium cations are hydrophobized and they swell in non-polar solvents.

  • 5.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People’s Republic of China.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gong, Chen
    State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People’s Republic of China.
    Liu, Bingbing
    State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People’s Republic of China.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics. Faculty of Natural Sciences, National University of Laos (NUOL), Vientiane, Laos.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics. Borås, Sweden.
    Yao, Mingguang
    State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People’s Republic of China.
    AC impedance of A4C60 fullerides under pressure2015In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 17, no 2, article id 023010Article in journal (Refereed)
    Abstract [en]

    Three A4C60 compounds, with A = Li, Na and K, have been studied by impedance spectroscopy between 100 K and 293 K at pressures up to 2 GPa. The results are in very good agreement with earlier DC resistance studies and with data from the literature. For all three materials the measured conductivity can be fitted by a sum of at least two Arrhenius terms. The band gaps derived from the resistance data, 0.3 eV for Na4C60 and 0.5 eV for K4C60, are in excellent agreement with data measured by other methods. For Li4C60, our results disagree with a recent suggestion that the conductivity is dominated by ionic conduction. Although a certain ionic component probably exists we suggest that electronic transport dominates in our samples at and below room temperature because the derived “activation energy” decreases under pressure, the derived “activation volume” is negative, and we observe neither a significant electrode blocking capacitance nor any significant metal transport under DC conditions.

  • 6.
    Tonpheng, Bounphanh
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Britt M
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tensile strength and young's modulus of polyisoprene/single-wall carbon nanotube composites increased by high pressure cross-linking2010In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 43, no 18, p. 7680-7688Article in journal (Refereed)
    Abstract [en]

    High-viscosity liquid cis-1,4 polyisoprene (PI), with up to 20 wt % single-wall carbon nanotubes (SWCNTs), has been cross-linked by high pressure and high temperature (HP&HT) treatment at 513 K and pressures in the range 0.5 to 1.5 GPa to yield densified network polymer composites. A composite with 5 wt % SWCNTs showed 2.2 times higher tensile strength σUTSUTS = 17 MPa), 2.3 times higher Young’s modulus E (E = 220 MPa) and longer extension at break than pure PI. The improvement is attributed to SWCNT reinforcement and improved SWCNT−PI interfacial contact as a result of the HP&HT cross-linking process, and reduced brittleness despite a higher measured cross-link density than that of pure PI. The latter may originate from an effect similar to crazing, i.e., bridging of microcracks by polymer fibrils. We surmise that the higher cross-link densities of the composites are due mainly to physical cross-links/constraints caused by the SWCNT−PI interaction, which also reflects the improved interfacial contact, and that the CNTs promote material flow by disrupting an otherwise chemically cross-linked network. We also deduce that the PI density increase at HP&HT cross-linking is augmented by the presence of CNTs.

  • 7.
    Tonpheng, Bounphanh
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Effects of cross-links, pressure and temperature on the thermal properties and glass transition behaviour of polybutadiene2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 33, p. 15047-15054Article in journal (Refereed)
    Abstract [en]

    The thermal conductivity κ, heat capacity per unit volume ρcp and glass transition behaviour under pressure have been established for medium and high vinyl content polybutadiene PB with molecular weights 2600 and 100 000 and their highly cross-linked (ebonite) states obtained purely by high-pressure high-temperature treatments. Cross-linking eliminates the glass transitions and increases κ by as much as 50% at 295 K and 1 atm, and decreases ρcp to a limiting level close to that of the glassy state of PB, which is reached before the ultimate cross-link density is achieved. The pressure and temperature behaviours of κ are strongly changed by cross-links, which increases the effect of temperature but decreases the effect of pressure. We attribute these changes to a cross-linked induced permanent densification and consequential increase of phonon velocity simultaneously as conduction along polymer chains is disrupted. The glass transition temperatures for a time scale of 1 s are described to within 0.5 K by: Tg(p) = 202.5 (1 + 2.94 p)0.286 and Tg(p) = 272.3 (1 + 2.57 p)0.233 (p in GPa and T in K) up to 1 GPa, for PB2600 and PB100000, respectively, and can be estimated for medium and high vinyl content PBs with molecular weights in between by a constant, pressure independent, shift in temperature.

  • 8.
    Tonpheng, Bounphanh
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Polyisoprene  single-wall carbon nanotube composites synthesized under high pressure2008In: High Pressure Research,  vol 28, No 4, 2008, p. 287-290Conference paper (Refereed)
    Abstract [en]

    The mechanical and thermal properties of high-pressure-synthesized composites of polyisoprene (PI) and single-walled carbon nanotubes (SWCNTs) (1 wt%) have been measured using a tensile tester and the transient hot-wire method. PI–SWCNT composites were prepared by ultrasonic mixing in toluene to obtain good dispersion of the nanotubes within the polymer matrix, which was verified by atomic force microscopy. The mixtures were dried for several days under dynamic vacuum and subsequently treated at a high pressure (0.5 GPa) and temperature (513 K) to improve the SWCNT–polymer interaction. As a result of the high-pressure treatment, PI becomes crosslinked, yielding an elastomeric PI–SWCNT composite. Preliminary results show that the tensile strength and Young’s modulus of the composite are 2.8 and five times higher, respectively, than those of pure high-pressure-treated PI, and that the thermal conductivity increased 30% by adding 1 wt% SWCNTs.

  • 9.
    Tonpheng, Bounphanh
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Thermal conductivity, heat capacity, and cross-linking of polyisoprene/single-wall carbon nanotube composites under high pressure2009In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 42, no 23, p. 9295-9301Article in journal (Refereed)
    Abstract [en]

    Polyisoprene (PI)/single-wall carbon nanotube (SWCNT) composites and pure PI have been cross-linked by high-pressure treatment to yield densified elastomeric states. Simultaneously, the SWCNT and cross-linked-induced changes of the thermal conductivity, heat capacity per unit volume, and glass transition were investigated by in situ measurements. The thermal conductivity of both the elastomeric and liquid PI improves ≈120% by the addition of 5 wt % SWCNT filler. The SWCNT filler (5 wt %) increases the glass-transition temperature of liquid PI by ≈7 K and that of the elastomeric state by as much as 12 K, which is due to a filler-induced increase in the cross-link density. Moreover, the 5 wt% filler yields a heat capacity decrease by ≈30% in both the glassy and liquid/elastomeric states, which indicates that SWCNTs cause a remarkably large reduction of both the vibrational and configurational heat capacity of PI. Finally, the consequences of high-pressure densification and the possibilities this provides to help elucidating the nature of the heat conduction in polymer/carbon nanotube composites are discussed.

  • 10.
    You, Shujie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Luzan, Serhiy
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr V
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Phase transitions in graphite oxide solvates at temperatures near ambient2012In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 3, no 7, p. 812-817Article in journal (Refereed)
    Abstract [en]

    It is demonstrated that solvent-saturated graphite oxide can be considered to be solid solvate, and two phases with distinctly different solvent composition are found near room temperature. Phase transitions between these two solvated phases were observed using synchrotron powder X-ray diffraction and DSC for methanol, ethanol, acetone, and dimethylformamide (DMF) solvents. Solvate A, formed at room temperature, undergoes a reversible phase transition into expanded Solvate L at temperatures slightly below ambient due to insertion of one monolayer of solvent molecules between the GO planes. The phase transition is reversible upon heating, whereas the low-temperature expanded phase L can be quenched to room temperature for ethanol and DMF solvates.

  • 11.
    You, Shujie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Belyaeva, L. A.
    Avramenko, Natalya V.
    Korobov, Mikhail V.
    Talyzin, Alexandr V.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Selective Intercalation of Graphite Oxide by Methanol in Water/Methanol Mixtures2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 4, p. 1963-1968Article in journal (Refereed)
    Abstract [en]

    Graphite oxide is selectively intercalated by methanol when exposed to liquid water/methanol mixtures with methanol fraction in the range 20-100%. Insertion of water into the GO structure occurs only when the content of water in the mixture with methanol is increased up to 90%. This conclusion is confirmed by both ambient temperature XRD data and specific temperature variations of the GO structure due to insertion/deinsertion of an additional methanol monolayer observed upon cooling/heating. The composition of GO-methanol solvate phases was determined for both low temperature and ambient temperature phases. Understanding of graphite oxide structural properties in binary water/methanol mixtures is important for the unusual permeation properties of graphene oxide membranes for water and alcohols. It is suggested that graphite oxide prepared by Brodie's method can be used for purification of water using selective extraction of methanol from water/alcohol mixtures.

  • 12.
    You, Shujie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Solvation of graphite oxide in water-methanol binary polar solvents2012In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 249, no 12, p. 2568-2571Article in journal (Refereed)
    Abstract [en]

    The phase transition between two solvated phases was studied by DSC for graphite oxide (GO) powders immersed in water–methanol mixtures of various compositions. GO forms solid solvates with two different compositions when immersed in methanol. Reversible phase transition between two solvate states due to insertion/desertion of methanol monolayer occurs upon temperature variations. The temperature point and the enthalpy (DH) of the phase transition are maximal for pure methanol and decrease linearly with increase of water fraction up to 30%.

     

  • 13.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Studies of novel phases and states produced by means of high pressure: Polymer and polymer based carbon nanocomposites2011Doctoral thesis, comprehensive summary (Other academic)
  • 14.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johari, G P
    Effects of nanometer-size Laponite disks on thermal conductivity and specific heat of water and ice, and the gelation time2015In: Colloid and Polymer Science, ISSN 0303-402X, E-ISSN 1435-1536, Vol. 293, no 3, p. 901-911Article in journal (Refereed)
    Abstract [en]

    We report the thermal conductivity, kappa, and the specific heat, C-p, of dispersion of 0.95-nm-thick, 25-nm-diameter disks of Laponite in water and in ice, as well as the thermal effects during gelation of several compositions, and the temperature dependence of the gelation time. The kappa values of its 5.0 wt% sol and gel states at T>273 K are similar to 3 % larger than those of pure water. In the frozen state of water, kappa is lower than that of hexagonal ice and the difference increases on cooling. kappa of the sol and gel calculated from Maxwell's mixture model agrees with the measured kappa. During the course of homogenization and formation of the gel state, kappa and C-p do not change significantly. The time for gel formation, t(gel), decreases rapidly when the sol is aged at high temperatures. The change occurs almost according to the relation, log(10)(t(gel)) proportional to 1/T. The accelerated formation of the Laponite gel at high T is distinguished from that of organic, mostly protein gels which form more rapidly at low T. The gels are not thermo-reversible. We consider the consequences of our findings for the current understanding of the phonon propagation and electrostatic interactions between H2O molecules and Laponite disks.

  • 15.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gröbner, Gerhard
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Microstructure, nucleation and thermal properties of high-pressure crystallized MWCNT/nylon-6 composites2011In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 52, no 24, p. 5521-5527Article in journal (Refereed)
    Abstract [en]

    Multi-wall carbon nanotube (MWCNT)/nylon-6 composites made by in-situ polymerization and subsequently modified by treatment at 1.0 GPa (or 1.7 GPa) and 530 K have been studied by WAXD, DSC and NMR. The pressure treatment gives an amorphous to crystalline transformation where the crystallinity increases from ∼31% to as much as ∼58% concurrently as the nylon-6 crystals increase in size and attain a preferred orientation relative to the applied pressure. A composite of 2.1 wt% purified MWCNT in nylon-6 shows significantly higher melting temperature than neat nylon-6 after identical pressure treatments. The improved thermal stability of the composite is attributed to crystal growth in the presence of reinforcing MWCNTs. The NMR spectrum of a pressure treated composite is similar to that of nylon-6 single crystals, which suggests a reduction of crystal boundaries after treatment, but there is no indication of covalent bonds between the nylon-6 chains and the MWCNTs.

  • 16.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Thermal conductivity of highly crystallized polyethylene2014In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 55, no 1, p. 195-200Article in journal (Refereed)
    Abstract [en]

    We report thermal conductivity (kappa) of low-density, high-density and ultra-high density polyethylene (PE) with different crystallinity and microstructures. PE was crystallized under high-pressure and high-temperature conditions which produce extended chain crystals. By applying a two-phase model, we estimate kappa of 100% crystallized PE as a function of pressure and temperature. The increased crystallinity and lamellar thickness (fold length) reduce the thermal resistance, which is reflected not only in the absolute value of kappa but also in more pronounced pressure and temperature dependencies approaching those of polycrystalline low-molecular weight materials. The results suggest that it is crucial to increase the lamellar thickness to significantly improve kappa of PE with randomly oriented lamellae.

  • 17.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High-pressure-induced microstructural evolution and enhancement of thermal properties of nylon-62010In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 43, no 24, p. 10512-10520Article in journal (Refereed)
    Abstract [en]

    The transition behavior and thermal properties of nylon-6 at elevated pressure, p, have been established by in-situ thermal conductivity, κ, and heat capacity measurements. The glass transition temperature, Tg, of virgin nylon-6 is described well by the empirical equation Tg(p) = 319.60(1 + 1.90 p)0.24 (p in GPa and Tg in K). Moreover, isobaric heating in the 1−1.2 GPa range causes a cold-crystallization transition near 500 K. As a result, κ increased 15% whereas the heat capacity per unit volume decreased 7% slowly with time during 4 h annealing at 530 K. The transformation is associated with a significantly increased crystallinity, from 35% to 55−60%, and a pressure-induced preferred orientation and increased size for the lamellae of monoclinic α crystalline structure. This state has 8−10 K higher melting temperature and better formic acid resistance than that of virgin nylon-6. However, the results show no indication of cross-linking, as reported for similarly treated nylon-1010 and nylon-11, but instead chain scissoring.

  • 18.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Thermal conductivity and heat capacity of a nylon-6/multi-wall carbon nanotube composite under pressure2010In: AIP Conference Proceedings / [ed] A. D'Amore, Domenico Acierino and Luigi Grassia, American Institute of Physics , 2010, Vol. 1255, no 1, p. 145-147Conference paper (Refereed)
    Abstract [en]

    The thermal conductivity, κ, of nylon-6 increased 22% whereas the heat capacity per unit volume, ρcp, decreased 10% by adding 2.1 wt% Multi-Wall Carbon Nanotubes MWCNTs. Simultaneously, the glass transition temperature, Tg, which was detected as a weak sigmoidal increase in ρcp and a decrease in dκ/dT, increased 11 K. These results show that the MWCNTs-nylon-6 interaction restricts the segmental mobility of nylon-6 and decreases cp of nylon-6.

  • 19.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gröbner, Gerhard
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    A MWCNT/Polyisoprene Composite Reinforced by an Effective Load Transfer Reflected in the Extent of Polymer Coating2012In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 45, no 6, p. 2841-2849Article in journal (Refereed)
    Abstract [en]

    Tensile and microstructural properties of multiwall carbon nanotube (MWCNT)/polyisoprene (PI) composites have been investigated after cross-linking achieved purely by simultaneous high-pressure high-temperature treatment. The method enables gradual increase of the cross-link density without interference of vulcanization chemicals, and the results suggest a link between an interfacial PI layer wrapped/coated on the MWCNTs and reinforcement in carbon nanotube (CNT)/PI composites. The interfacial layer, which is augmented by high-pressure treatment, was detected indirectly in swelling experiments and also reflected in results of atomic force microscopy. The results imply more efficient load transfer and mechanical reinforcement by CNTs with improved interfacial layer and that changes in the layer can be probed by swelling measurements.

  • 20.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gröbner, Gerhard
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Microstructural and property changes in high pressure treated carbon nanotube/polybutadiene composites2011In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 21, no 35, p. 13672-13682Article in journal (Refereed)
    Abstract [en]

    In a comprehensive investigation of carbon nanotube (CNT) filled liquid and solid polybutadienes of molecular weights 2600 and 100000, respectively, we report results of thermal conductivity (κ), glass transition temperature (Tg), interfacial interaction and microstructure before and after simultaneous high-pressure and high-temperature (HP&HT) treatment. The HP&HT treatment changed polybutadiene from a liquid or solid to a highly cross-linked, ebonite-like, state. Concurrently, the microstructure changed from randomly dispersed CNTs to a web-like structure of coated and/or wrapped CNTs, with a permanent shift in their D*-band by as much as 16 cm−1. Moreover, κ of the recovered state of a 2.9 wt% –COOH functionalized multi-wall carbon nanotube (MWCNT) composite increased by 34% predominantly due to an irreversible densification and a consequentially increased phonon velocity. Results prior to treatment show that single-wall carbon nanotube (SWCNT) fillers promote κ better (17%/wt%) than –SH functionalized MWCNT fillers (8%/wt%), which is accounted for by their higher aspect ratio, whereas their about twice as high κ appears to be unimportant. The SWCNTs also raise Tg slightly more than MWCNTs and, in particular, under the most densified conditions and for the high molecular weight polybutadiene, which may be due to more favorable conditions for coating/wrapping.

  • 21.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gröbner, Gerhard
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Thermal properties and transition studies of multi-wall carbon nanotube/nylon-6 composites2011In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 49, no 14, p. 4858-4866Article in journal (Refereed)
    Abstract [en]

    Transition behavior and thermal properties of a multi-wall carbon nanotube (MWCNT)/nylon-6 composite (P-composite) made by in situ polymerization and subsequently structurally modified by high-pressure–high-temperature treatment have been established. The thermal conductivity (κ) of nylon-6 improved 27% by the addition of 2.1 wt.% MWCNT filler simultaneously as the heat capacity per unit volume decreased 22% compared with that of nylon-6 at 1 atm and 298 K. Moreover, the MWCNT filler raises the glass transition temperature (Tg) of nylon-6, but the pressure dependence of Tg remains unchanged. A model for κ indicates that the interfacial thermal resistance between the MWCNT filler and the nylon-6 matrix decreases 20% up to 1 GPa and most significantly above 0.8 GPa. P-composite was structurally modified by a sluggish cold-crystallization transition at 1.0 GPa, 530 K, which further increased κ by as much as 37% as the crystallinity of nylon-6 improved from 31% to 58% with a preferred crystal orientation and increased crystal size.

  • 22.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yao, Mingguang
    Gröbner, Gerhard
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Liu, Bingbing
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Buckminsterfullerene: A Strong, Covalently Bonded, Reinforcing Filler and Reversible Cross-Linker in the Form of Clusters in a Polymer2013In: ACS Macro Letters, ISSN 2161-1653, Vol. 2, no 6, p. 511-517Article in journal (Refereed)
    Abstract [en]

    A Buckminsterfullerene/polyisoprene (C60/PI) composite was synthesized at high-temperature, high-pressure (HP&HT) conditions. The composite has significantly improved tensile strength and Young’s modulus, by up to 49% and 88% per wt % C60, respectively, which is much higher than for corresponding composites with carbon nanotube (CNT) fillers. The reinforcing action of C60 fillers is different from that of CNTs as C60 becomes covalently bonded to PI chains, and C60 clusters in PI form C60–C60 covalent bonds. The latter are reversible and break by heating at 1 bar, which suggests improved recyclability of the material and indicates that carbon nanostructures can be used as strong reversible cross-linkers (“vulcanizers”) in elastomers.

1 - 22 of 22
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