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Yu, Junchun
Publications (10 of 22) Show all publications
Sundqvist, B., Andersson, O., Gong, C., Liu, B., Tonpheng, B., Yu, J. & Yao, M. (2015). AC impedance of A4C60 fullerides under pressure. New Journal of Physics, 17(2), Article ID 023010.
Open this publication in new window or tab >>AC impedance of A4C60 fullerides under pressure
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2015 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 17, no 2, article id 023010Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2015
Keywords
Fullerides, Li4C60, Na4C60, K4C60, high pressure, conductivity, resistivity, semiconductor, ionic conduction
National Category
Physical Sciences
Research subject
Solid State Physics
Identifiers
urn:nbn:se:umu:diva-99306 (URN)10.1088/1367-2630/17/2/023010 (DOI)000352864600010 ()
Funder
Swedish Research Council, 621-2010-3732
Available from: 2015-02-06 Created: 2015-02-06 Last updated: 2018-06-07Bibliographically approved
Yu, J., Andersson, O. & Johari, G. P. (2015). Effects of nanometer-size Laponite disks on thermal conductivity and specific heat of water and ice, and the gelation time. Colloid and Polymer Science, 293(3), 901-911
Open this publication in new window or tab >>Effects of nanometer-size Laponite disks on thermal conductivity and specific heat of water and ice, and the gelation time
2015 (English)In: Colloid and Polymer Science, ISSN 0303-402X, E-ISSN 1435-1536, Vol. 293, no 3, p. 901-911Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2015
Keywords
laponite, thermal conductivity, heat capacity, gel time
National Category
Physical Chemistry Physical Sciences
Identifiers
urn:nbn:se:umu:diva-101593 (URN)10.1007/s00396-014-3481-8 (DOI)000350367200023 ()
Available from: 2015-04-14 Created: 2015-04-07 Last updated: 2018-06-07Bibliographically approved
Klechikov, A., Yu, J., Thomas, D., Sharifi, T. & Talyzin, A. V. (2015). Structure of graphene oxide membranes in solvents and solutions. Nanoscale, 7(37), 15374-15384
Open this publication in new window or tab >>Structure of graphene oxide membranes in solvents and solutions
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2015 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 7, no 37, p. 15374-15384Article in journal (Refereed) Published
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.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-110218 (URN)10.1039/c5nr04096e (DOI)000361675300045 ()26332400 (PubMedID)
Available from: 2015-10-16 Created: 2015-10-16 Last updated: 2018-06-07Bibliographically approved
Barbero, D., Boulanger, N., Ramstedt, M. & Yu, J. (2014). Carbon nanotube networks: nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading [Letter to the editor]. Advanced Materials, 26(19), 3164
Open this publication in new window or tab >>Carbon nanotube networks: nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading
2014 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 26, no 19, p. 3164-Article in journal, Letter (Refereed) [Artistic work] Published
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.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2014
Keywords
carbon nanotube networks;nano-engineering;charge transport;organic electronic devices;nanoimprinting
National Category
Nano Technology
Identifiers
urn:nbn:se:umu:diva-89133 (URN)10.1002/adma.201470129 (DOI)
Note

Back cover

Available from: 2014-05-22 Created: 2014-05-22 Last updated: 2018-06-07Bibliographically approved
Barbero, D., Boulanger, N., Ramstedt, M. & Yu, J. (2014). Nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading [Letter to the editor]. Advanced Materials, 26(19), 3111-3117
Open this publication in new window or tab >>Nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading
2014 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 26, no 19, p. 3111-3117Article in journal, Letter (Refereed) Published
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.

Place, publisher, year, edition, pages
John Wiley & Sons, 2014
Keywords
carbon nanotube networks;nano-engineering;charge transport;organic electronic devices;nanoimprinting
National Category
Nano Technology
Identifiers
urn:nbn:se:umu:diva-89132 (URN)10.1002/adma.201305843 (DOI)000335869100023 ()
Available from: 2014-05-22 Created: 2014-05-22 Last updated: 2018-06-07Bibliographically approved
Boulanger, N., Yu, J. & Barbero, D. (2014). SWNT nano-engineered networks strongly increase charge transport in P3HT [Letter to the editor]. Nanoscale, 6(20), 11633-11636
Open this publication in new window or tab >>SWNT nano-engineered networks strongly increase charge transport in P3HT
2014 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 6, no 20, p. 11633-11636Article in journal, Letter (Refereed) Published
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.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2014
National Category
Nano Technology
Identifiers
urn:nbn:se:umu:diva-89131 (URN)10.1039/C4NR01542H (DOI)000343000800005 ()
Available from: 2014-05-22 Created: 2014-05-22 Last updated: 2018-06-07Bibliographically approved
Yu, J., Sundqvist, B., Tonpheng, B. & Andersson, O. (2014). Thermal conductivity of highly crystallized polyethylene. Polymer, 55(1), 195-200
Open this publication in new window or tab >>Thermal conductivity of highly crystallized polyethylene
2014 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 55, no 1, p. 195-200Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Oxford: Elsevier, 2014
Keywords
Polyethylene, Thermal conductivity, Crystallinity
National Category
Polymer Chemistry Physical Sciences
Identifiers
urn:nbn:se:umu:diva-86333 (URN)10.1016/j.polymer.2013.12.001 (DOI)000330207100025 ()
Available from: 2014-02-25 Created: 2014-02-24 Last updated: 2018-10-03Bibliographically approved
Yu, J., Yao, M., Gröbner, G., Sundqvist, B., Tonpheng, B., Liu, B. & Andersson, O. (2013). Buckminsterfullerene: A Strong, Covalently Bonded, Reinforcing Filler and Reversible Cross-Linker in the Form of Clusters in a Polymer. ACS Macro Letters, 2(6), 511-517
Open this publication in new window or tab >>Buckminsterfullerene: A Strong, Covalently Bonded, Reinforcing Filler and Reversible Cross-Linker in the Form of Clusters in a Polymer
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2013 (English)In: ACS Macro Letters, ISSN 2161-1653, Vol. 2, no 6, p. 511-517Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2013
Keywords
Buckminsterfullerene, C60, filler, cross-linker, cross-linking, polymer, polyisoprene, high pressure, tensile strength, Youngs modulus, vulcanization
National Category
Chemical Sciences Polymer Technologies
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-71668 (URN)10.1021/mz400171e (DOI)000323362900012 ()
Funder
Swedish Research Council, 621-2010-3732
Note

Open Access

Available from: 2013-06-04 Created: 2013-06-04 Last updated: 2018-06-08Bibliographically approved
You, S., Yu, J., Sundqvist, B., Belyaeva, L. A., Avramenko, N. V., Korobov, M. V. & Talyzin, A. V. (2013). Selective Intercalation of Graphite Oxide by Methanol in Water/Methanol Mixtures. The Journal of Physical Chemistry C, 117(4), 1963-1968
Open this publication in new window or tab >>Selective Intercalation of Graphite Oxide by Methanol in Water/Methanol Mixtures
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2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 4, p. 1963-1968Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2013
Keywords
Graphite oxide, intercalation, methanol, water, cooling, low temperature, X-ray diffraction, lattice spacing
National Category
Chemical Sciences
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-67049 (URN)10.1021/jp312756w (DOI)000314492400051 ()
Funder
Swedish Research Council, 621-2010-3732Swedish Research Council, 2012-3654
Note

Open access

Available from: 2013-03-24 Created: 2013-03-12 Last updated: 2018-06-08Bibliographically approved
Yu, J., Tonpheng, B., Gröbner, G. & Andersson, O. (2012). A MWCNT/Polyisoprene Composite Reinforced by an Effective Load Transfer Reflected in the Extent of Polymer Coating. Macromolecules, 45(6), 2841-2849
Open this publication in new window or tab >>A MWCNT/Polyisoprene Composite Reinforced by an Effective Load Transfer Reflected in the Extent of Polymer Coating
2012 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 45, no 6, p. 2841-2849Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2012
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-53160 (URN)10.1021/ma202604d (DOI)000301946600024 ()
Available from: 2012-03-14 Created: 2012-03-14 Last updated: 2018-06-08Bibliographically approved
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