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  • 1
    Online Resource
    Online Resource
    AIP Publishing ; 2013
    In:  The Journal of Chemical Physics Vol. 139, No. 6 ( 2013-08-14)
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 139, No. 6 ( 2013-08-14)
    Abstract: Superhydrophilic graphite surfaces and water-dispersible graphite colloids are obtained by electrochemical exfoliation with hydrophobic graphite electrodes. Such counterintuitive characteristics are caused by partial oxidation and investigated by examining both graphite electrodes and exfoliated particles after electrolysis. The extent of surface oxidation can be explored through contact angle measurement, scanning electron microscope, electrical sheet resistance, x-ray photoelectron spectroscopy, zeta-potential analyzer, thermogravimetric analysis, UV-visible, and Raman spectroscopy. The degree of wettability of the graphite anode can be altered by the electrolytic current and time. The water contact angle declines generally with increasing the electrolytic current or time. After a sufficient time, the graphite anode becomes superhydrophilic and its hydrophobicity can be recovered by peeling with adhesive tape. This consequence reveals that the anodic graphite is oxidized by oxygen bubbles but the oxidation just occurs at the outer layers of the graphite sheet. Moreover, the characteristics of oxidation revealed by UV peak shift, peak ratio between D and G bands, and negative zeta-potential indicate the presence of graphite oxide on the outer shell of the exfoliated colloids. However, thermogravimetric analysis for the extent of decomposition of oxygen functional groups verifies that the amount of oxygen groups is significantly less than that of graphite oxide prepared via Hummer method. The structure of this partially oxidized graphite may consist of a graphite core covered with an oxidized shell. The properties of the exfoliated colloids are also influenced by pH of the electrolytic solution. As pH is increased, the extent of oxidation descends and the thickness of oxidized shell decreases. Those results reveal that the degree of oxidation of exfoliated nanoparticles can be manipulated simply by controlling pH.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2013
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 2
    Online Resource
    Online Resource
    AIP Publishing ; 2011
    In:  The Journal of Chemical Physics Vol. 134, No. 3 ( 2011-01-21)
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 134, No. 3 ( 2011-01-21)
    Abstract: The optoelectronic properties of rod–coil diblock copolymers with π-conjugation are greatly affected by molecular packing, which is closely related to their micellar morphology. Self-assembly of rod–coil block copolymer \documentclass[12pt]{minimal}\begin{document}${\rm B}_{y}{\rm A}_{x}$\end{document}ByAx in a selective solvent for its coil block is studied by using dissipative particle dynamics, where \documentclass[12pt] {minimal}\begin{document}${\rm B}_{y}{\rm A}_{x}$\end{document}ByAx denotes the polymer comprising of y rodlike B beads and x coil-like A beads. The influences of polymer concentration, component compatibility, solvent quality for coil block, rod-block length, and π − π interaction on the resulting aggregate conformations are examined. It was found that distinctly different from coil–coil copolymers, the aggregates of rod–coil copolymers exhibit morphological and structural diversity induced by the intrinsically rigid nature of the rod blocks. In general, the aggregate adopts the overall shape of sphere, cylinder, perforated sheet, or network. The morphology of the rod-block domain within aggregate is even richer and the interesting structures such as porous sphere, spherical spiral, helical bundles, discrete chunks, and nematic cylinder are observed. The short-range order parameter indicates that as rod length is long enough, neighboring rods begin to orient parallel to one another and nematic domains appear. Moreover, in the presence of π − π interactions, the neighboring rods within the B domains become more coherently oriented and smectic domains can thus be formed.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2011
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 3
    Online Resource
    Online Resource
    AIP Publishing ; 2008
    In:  The Journal of Chemical Physics Vol. 129, No. 22 ( 2008-12-14)
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 129, No. 22 ( 2008-12-14)
    Abstract: The self-assembly of star-block copolymer (ByAx)n in a selective solvent for its outer block is studied by using dissipative particle dynamics, where (ByAx)n denotes a n-armed star with each arm comprising of y solvophobic B-segments and x solvophilic A-segments. The effects of arm number, arm length, block length ratio y∕x, solvent quality, and component compatibility on mean aggregation number ⟨p⟩ are examined. Unusual micellization behaviors are observed. The total number of arms in a multimolecular micelle n* is invariant with the arm number but grows with the segment concentration φ, which is different from typical micellization of short-chain surfactants. For a given φ, multimolecular micelles are formed for stars with n & lt;n*(φ) and the mean aggregation number follows ⟨p⟩=n*∕n. As n⩾n*, only unimolecular micelles exist in the solution. According to the n*-φ relation, the critical multimolecular micelle concentration is found to grow linearly with arm number. As solvent quality deteriorates or component compatibility increases, the total arm number within a micelle rises.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2008
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 4
    Online Resource
    Online Resource
    AIP Publishing ; 2006
    In:  The Journal of Chemical Physics Vol. 125, No. 19 ( 2006-11-21)
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 125, No. 19 ( 2006-11-21)
    Abstract: Multicompartment micelles are desirable for advanced applications such as drug delivery. Recently, core-shell-corona (CSC) and segmented-worm (SW) micelles formed by ABC triblock terpolymers with three mutually immiscible blocks are observed in experiments. We have performed dissipative particle dynamics simulations to study the effects of molecular architecture, block length, and solution concentration on the morphologies of ABC triblock terpolymers. The formation of CSC and SW micelles for linear and miktoarm star ABC terpolymers is confirmed in this work. In addition, we predict that different multicompartment micellar morphologies (e.g., incomplete skin-layered micelles and segmented worms) can be formed by linear copolymer with different arrangements of the three blocks.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2006
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 5
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 132, No. 21 ( 2010-06-07)
    Abstract: A combined experimental and simulational investigation is performed to study the surface morphologies of polymer films formed by poly[2,7-(9,9-dihexylfluorene)]-b-poly[N-isopropylacrylamide] (PF-b-PNIPAAm) rod-coil block copolymers, where PF possesses π-π interactions and PNIPAAm is known to exhibit a coil-to-globule phase transition at T=32 °C. Two (PF-b-PNIPAAm) rod-coil block copolymers with different block ratios are synthesized and used to prepare thin films on the quartz glass by physisorption. The surface structures of the thermoresponsive polymer films are found to alter significantly in response to thermostimuli. Small, hemispherical domains of the aggregations of rod-blocks are formed at low temperatures. As the temperature increases, the conformations transform to isolated islands, wormlike structures, or even networklike morphologies depending on the grafting density. These morphological transformations due to temperature variation are consistent with simulation findings. The photophysical properties of PF-b-PNIPAAm films are also found to vary with thermostimuli. The PL spectra reveals that the emission originates from the aggregation of PF blocks and the intensity changes as temperature varies. Our study demonstrates that the surface morphologies and the corresponding photophysical properties of the PF-b-PNIPAAm polymer films can be tuned by thermostimuli.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2010
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 6
    In: Journal of Applied Physics, AIP Publishing, Vol. 114, No. 12 ( 2013-09-28)
    Abstract: We developed a general method based on fluorescence microscopy to characterize the interface dissolution in multi-layer organic light-emitting diodes (OLEDs) by blade coating. A sharp bi-layer edge was created before blade coating, with the bottom layer being insoluble and top layer soluble. After blade coating, fluorescence images showed that the edge of the top layer shifted when the layer dissolved completely, whereas the bottom layer's edge remained in place as a positioning mark. The dissolution depth was determined to be 15–20 nm when the emissive-layer host of 2,6-bis (3-(9H-carbazol-9-yl)phenyl) pyridine (26DCzPPy) was coated on the hole-transport layer of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine(NPB), which was consistent with a sudden drop in efficiency of orange OLEDs with layer thickness below 20 nm. Thus, the layer thickness of OLEDs was optimized to stay more than 20 nm for blade coating. For a two-color white OLED with the structure TCTA/26DCzPPy:PO-01-TB:FIrpic/TPBI, efficiency was 24 cd/A and 8.5 lm/W at 1000 cd/m2. For a three-color white OLED with Os(fptz)2(dhpm) added as the emitter, the efficiency was 12.3 cd/A and 3.7 lm/W at 1000 cd/m2. For a green device with the structure TCTA/26DCzPPy:Ir(mppy)3/TPBI, the efficiency was 41.9 cd/A and 23.4 lm/W at 1000 cd/m2.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2013
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 7
    In: Journal of Applied Physics, AIP Publishing, Vol. 110, No. 9 ( 2011-11-01)
    Abstract: A continuous roll-to-roll compatible blade-coating method for multi-layers of general organic semiconductors is developed. Dissolution of the underlying film during coating is prevented by simultaneously applying heating from the bottom and gentle hot wind from the top. The solvent is immediately expelled and reflow inhibited. This method succeeds for polymers and small molecules. Uniformity is within 10% for 5 cm by 5 cm area with a mean value of tens of nanometers for both organic light-emitting diode (OLED) and solar cell structure with little material waste. For phosphorescent OLED 25 cd/A is achieved for green, 15 cd/A for orange, and 8 cd/A for blue. For fluorescent OLED 4.3 cd/A is achieved for blue, 9 cd/A for orange, and 6.9 cd/A for white. For OLED with 2 cm by 3 cm active area, the luminance variation is within 10%. Power conversion efficiency of 4.1% is achieved for polymer solar cell, similar to spin coating using the same materials. Very-low-cost and high-throughput fabrication of efficient organic devices is realized by the continuous blade-only method.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2011
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 8
    In: Applied Physics Letters, AIP Publishing, Vol. 120, No. 19 ( 2022-05-09)
    Abstract: Manipulation of the spin-wave coherent length is highly desirable to overcome intrinsic damping and to improve functionalities of magnonics materials and devices. In this work, based on angle-resolved propagating spin-wave spectroscopy and micro-focused Brillouin light scattering, we report a giant anisotropy of spin wave propagation in a 20 nm-thick La0.67Sr0.33MnO3 film grown on a NdGaO3 substrate. Vanishing of such anisotropic features in reference experiments where the La0.67Sr0.33MnO3 film is grown on SrTiO3 suggests that the anisotropic spin-wave propagation might be originated from different lattice mismatches of the LSMO film with these two substrates. Interestingly, the decay length and the relaxation time of spin waves are found to be largest when the wavevector is along the [110] crystalline orientation, which is neither at easy nor hard axis related to the in-plane uniaxial magnetic anisotropy. This suggests the possibility of individual control of the magnetic anisotropy and spin-wave anisotropy via strain engineering. Our discovery may enrich the material systems for anisotropic spin wave behavior and promote strain engineering and optimization of versatile magnonic devices.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    RVK:
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 9
    Online Resource
    Online Resource
    AIP Publishing ; 2017
    In:  AIP Advances Vol. 7, No. 11 ( 2017-11-01)
    In: AIP Advances, AIP Publishing, Vol. 7, No. 11 ( 2017-11-01)
    Abstract: A high voltage pulse generator is presented to drive Pockels cell. The Pockels cell behaves like a capacitor which slows the rise/fall time of the pulse and restrains the repetition rate of the generator. To drive the Pockels cell applied in quantum communication system, it requires about 1 MHz repetition rate with the rise/fall time of the pulse less than 50 ns, adjustable amplitude up to 800 V and an adjustable duration. With the assistance of self-designed transformers, the circuits is simplified that a pair of high current radio frequency (RF) MOSFET drivers are employed to switch the power MOSFETs at a high speed, and the power MOSFETs shape the final output pulse with the requirements. From the tests, the generator can produce 800 V square pulses continously at 1 MHz rate with 46 ns in risetime and 31 ns in falltime when driving a 51 pF capacitive load. And the generator is now used to drive Pockels cell for encoding the polarization of photons.
    Type of Medium: Online Resource
    ISSN: 2158-3226
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2017
    detail.hit.zdb_id: 2583909-3
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  • 10
    In: Biomicrofluidics, AIP Publishing, Vol. 8, No. 5 ( 2014-09-01)
    Abstract: We developed a microfluidic device to culture cellular spheroids of controlled sizes and suitable for live cell imaging by selective plane illumination microscopy (SPIM). We cocultured human umbilical vein endothelial cells (HUVECs) within the spheroids formed by hepatocellular carcinoma cells, and studied the distributions of the HUVECs over time. We observed that the migration of HUVECs depended on the size of spheroids. In the spheroids of ∼200 μm diameters, HUVECs migrated outwards to the edges within 48 h; while in the spheroids of ∼250 μm diameters, there was no outward migration of the HUVECs up to 72 h. In addition, we studied the effects of pro-angiogenic factors, namely, vascular endothelial growth factor (VEGF) and fibroblast growth factor (β-FGF), on the migration of HUVECs in the carcinoma cell spheroid. The outward migration of HUVECs in 200 μm spheroids was hindered by the treatment with VEGF and β-FGF. Moreover, some of the HUVECs formed hollow lumen within 72 h under VEGF and β-FGF treatment. The combination of SPIM and microfluidic devices gives high resolution in both spatial and temporal domains. The observation of HUVECs in spheroids provides us insight on tumor vascularization, an ideal disease model for drug screening and fundamental studies.
    Type of Medium: Online Resource
    ISSN: 1932-1058
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2014
    detail.hit.zdb_id: 2265444-6
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