Nikolaos E. Zafeiropoulos

Athens State University, Athens, Alabama, United States

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Publications (51)147.84 Total impact

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    ABSTRACT: The synthesis via anionic polymerization of six linear triblock terpolymers with various sequences of blocks such as PS (polystyrene), PB (polybutadiene), PI (polyisoprene) and PCHD (poly(1,3-cyclohexadiene)) is reported. The synthesis of the terpolymers was accomplished by the use of anionic polymerization with high vacuum techniques and sequential monomer addition. Molecular characterization of the samples was performed via size exclusion chromatography and membrane osmometry to measure polydispersity indices and the number-average molecular weights, respectively. Proton nuclear magnetic resonance spectroscopy was adopted to verify the type of microstructure for the polydienes as well as to calculate the molar composition. Structural characterization was performed via transmission electron microscopy and small angle X-ray scattering and several morphologies were observed including one which has not been reported previously. Real-space self-consistent field theory (SCFT) without a priori knowledge about the symmetry of the periodic structures was used to elucidate the thermodynamics of the synthesized triblock copolymers.
    Polymer 02/2013; 54(5). · 3.77 Impact Factor
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    ABSTRACT: A novel step-wise approach for fabrication of periodic arrays of two different types of nanoparticles (NPs), selectively localized at different block copolymer phases is demonstrated. In the first step, pre-synthesized ≈12 nm silver nanoparticles (AgNPs), stabilized with thiol-terminated polystyrene, are mixed with poly(styrene-block-vinylpyridine) (PS-b-PVP) block copolymer in a common solvent. After film casting and consequent solvent vapor annealing the AgNPs are selectively localized within the PS phase of the block copolymer matrix due to the interaction with PS shell of the nanoparticles. In the second step, ≈2–5 nm gold, platinum, or palladium nanoparticles are directly deposited from their aqueous dispersion on the PVP domains of the self-assembled block copolymer thin films. In such a way, thin films of nanostructured block copolymer with two types of nanoparticles, separated by the two distinct block copolymer phases, are prepared in a step-wise manner. The presented method is very simple and can be applied for various combinations of pre-synthesized nanoparticles where the characteristics of either type of nanoparticles are tuned accordingly in advance, which is more difficult to achieve for in situ synthesized nanoparticles.
    Advanced Functional Materials 01/2013; 23(4):483-490. · 10.44 Impact Factor
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    ABSTRACT: The gradient on block copolymer concentration through film thickness as well as the effects of casting solvents used on the nanostructuring of a thermosetting epoxy coating modified with an epoxidized poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer was studied by means of atomic force microscopy and attenuated total reflectance infrared spectroscopy. Thin coating films based on a commercial epoxy− amine formulation consisting of diglycidyl ether of bisphenol A and a low-temperature fast curing amine were modified with several amounts of epoxidized SBS triblock copolymer. Toluene and a mixture of tetrahydrofuran and N,N-dimethylformamide were used as casting solvents. With epoxidation degrees higher than 45 mol % of polybutadiene block nanostructuring was achieved. Fast curing rate of the epoxy/amine system and the comparatively slow evaporation rate of the casting solvent led to a gradient of morphologies through the film cross section owing to the coalescence of small micelles into larger micellar domains in the case of low block copolymer content. For these reasons, different morphologies were also obtained in the midtransverse section of a film with variable thickness. Finally, pseudolamellar nanostructure at high copolymer contents was achieved as confirmed by parallel and perpendicular cuttings to the air/polymer interface. ■ INTRODUCTION Nanostructured polymers are a unique class of materials that are finding an increasing number of applications. 1 Nanofoamed membranes, 2 nanoreactors, 3 nanotemplates, 4 and nanoporous structures 5 are some of the newest applications of nanostruc-tured materials for microelectronics, nanomaterials synthesis, nanotube fabrication, and antireflection coatings. Thermosetting materials based on epoxy matrices modified with block copoly-mers are being used increasingly in many studies taking advant-age of the capability of generating nanostructured systems as well. 6−9 In addition, the principal limitation of epoxy systems, their poor fracture toughness, can also be improved by the addition of block copolymers to the mixture. 10−13 Historically, fracture toughness improvement was achieved by epoxy modi-fication with thermoplastics or elastomers. 14,15 However, the worsening of other properties, such as transparency, because of the generated macrophase-separated domains compromises the usefulness of those systems. Thus, recently block copolymers have been used as templates for the generation of nanostructured thermosetting matrices. 12−26 The preparation of these materials can further optimize the final properties, maintaining the transparency of the neat materials. 27−32 Generally, to prepare nanostructured thermosetting materials using block copolymers, at least one of the blocks must be miscible with the matrix and at least one block immiscible. 33−35 However, in the case of styrene−butadiene−styrene (SBS) block copolymer both blocks tend to be immiscible with cured epoxy systems, leading to macrophase-separated material. Thus, in order to promote the compatibility of one of the blocks with the epoxy resin, polybutadiene block must be chemically modified. Serrano et al. 1 reported the synthesis and character-ization of epoxidized styrene−butadiene block copolymers as templates for nanostructured thermosets, following the pro-cedure previously reported by Jian and Hay, 36 by using hydrogen peroxide for the oxidation of the double bound of the butadiene units. Previous work of our group reported the effect of both the extent of epoxidation of polybutadiene blocks and the content of polystyrene phase on the mixture. 37,38 Thus, in general, a transition from spherical micelles to wormlike micelles and then to vesicles occurs with the decrease of the epoxy miscible
    Macromolecules 04/2012; 45(1483-1491). · 5.93 Impact Factor
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    ABSTRACT: Matrix mediated synthesis of nanoparticles was utilized to prepare calcium phosphate nanoparticles with a size of 10 nm. The particles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Nanocomposites of polystyrene and nano-calcium phosphate were prepared by the melt-mixing technique. The composites were characterized by TEM to assess the dispersion of the nanoparticles. SAXS measurements of the composites and the fit with Beaucage model described the fractal dimensions of the particles. Mechanical properties of the composites significantly improved with the addition of nanofillers. Dielectric behavior of the nanocomposites was measured with respect to the filler content, temperature, and frequency. The dielectric constant increases with increase in temperature and decreases with increase in frequencies. Dielectric constant increased with filler content in all frequencies; however, lower frequencies showed marked effect. α-Relaxation of the composites from the dissipation factor of the composites showed higher values for the lower frequencies. Electrical conductivity increased with respect to the filler content and volume resistivity showed the reverse trend. The theoretical prediction of the dielectric constant showed close agreement with the experimental value. POLYM. ENG. SCI. 2011. © 2011 Society of Plastics Engineers
    Polymer Engineering and Science 03/2012; 52(3):689-699. · 1.24 Impact Factor
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    ABSTRACT: In this study, pristine as well as polystyrene (PS) and poly(2-vinylpyridine) (P2VP) functionalized multi-wall carbon nanotubes (MWCNTs) were selectively incorporated in homopolymer binary blends of PS/P2VP and diblock copolymer (BCP) of the PS-b-P4VP type [P4VP: poly(4-vinylpyridine)]. Studies on the blends verified the chemical affinity of PS and P2VP grafted MWCNTs to the corresponding phase. Based on the results obtained from the blend systems, MWCNTs were incorporated in a PS-b-P4VP copolymer matrix with lamellar morphology and large amplitude oscillatory shear (LAOS) experiments were performed to achieve orientation of the BCP lamellae. The PS grafted MWCNTs (MWCNT-g-PS) were selectively sequestered in the PS phase and the P2VP grafted MWCNTs (MWCNT-g-P2VP) in the P4VP phase of the diblock copolymer. Unfunctionalized pristine MWCNTs were localized on the PS phase of the blend system and no special preference was observed towards the diblock copolymer PS domains. Small angle X-ray scattering (SAXS) analysis revealed the orientation of the alternating lamellae formed by the diblock copolymer when studied by LAOS. The localization of PS and P2VP grafted MWCNTs on the corresponding blend and BCP phase was also verified by transmission electron microscopy (TEM) studies.
    Polymer. 01/2012;
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    ABSTRACT: The development of well defined nanostructured thermosets from epoxy/PS-b-P2VP blends are presented in this study. For this purpose an epoxy system constituted by an epoxy resin (Araldite LY556), an anhydride hardener (Aradur 917), and an imidazole accelerator (DY 070) was employed and a block copolymer of PS-b-P2VP, where the block length of poly (2-vinylpyridine) (P2VP) was selected to allow the formation of microphase separated PS block nanodomains. Different ratios of PS-b-P2VP and epoxy system were used to analyze the nanostructuration of the system. Samples were characterized by transmission electron microscopy (TEM), fourier transform infrared, thermogravimetric analysis, and differential scanning calorimetry (DSC). DSC indicated that depletion of T g occurred when concentration of block copolymer increased in the blend. TEM images showed vesicles and well defined cylindrical and lamellar nanostructured thermoset materials which were obtained when the PS-b-P2VP content was higher than 20 wt%.
    Journal of Materials Science. 01/2012;
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    ABSTRACT: A new technique for the modification of lamellar domain sizes in polymeric ionic liquid block copolymers has been proposed. Anion exchange in polymeric ionic liquids opens new ways to modify the sizes of lamella domains without modifying the ratio between the two different blocks of the neat copolymer. This study focuses on the influence of quaternization of poly(2-vinylpyridine) in poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) and the effect of anion exchange in the nanostructured phases for thin films. The resulting materials obtained from the quaternization modification technique of the block copolymers and the anion exchange of the polymeric ionic liquid were characterized with Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR). Furthermore, morphological characterization of the initial block polymer and several polymeric ionic liquid block copolymers has been carried out by atomic force microscopy (AFM) in order to analyze the influence of the anion in the nanostructures of these block copolymers.
    Macromolecules. 01/2011; 44(12-10.1021/ma200213s):4936.
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    ABSTRACT: This study reports on the fabrication of magnetically responsive hollow titania capsules by confining the superparamagnetic Fe(3)O(4) nanoparticles within a hollow and porous titania (TiO(2)) shell. The employed protocol involves precipitation of titania shell on the magnetite (Fe(3)O(4)) encapsulated polystyrene beads followed by the calcination of resulting composite particles at elevated temperature. Scanning electron microscopy and transmission electron microscopy reveal the presence of a thick, complete but irregular titania shell on the magnetic polystyrene beads after the templating process. Electron energy loss mapping image analysis has been employed to investigate the spatial distribution of titania and magnetite phases of magnetic hollow titania capsules (MHTCs). Magnetic characterization indicates that both titania-coated magnetic polystyrene beads (TMPBs) and MHTCs are superparamagnetic in nature with the saturated magnetizations of 5.6 and 8.1 emu/g, respectively. X-ray diffraction (XRD) analysis reveals that titania shell of these capsules is composed of photoactive anatase phase. Nitrogen adsorption-desorption analysis has been employed to estimate the specific surface area and the average pore diameter of the fabricated hollow structures. Photocatalytic activity of the fabricated MHTCs for the photodegradation of rhodamine 6G dye has been demonstrated and compared with that of bulk titania nanoparticles.
    Langmuir 10/2010; 26(22):17649-55. · 4.38 Impact Factor
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    ABSTRACT: We report on the fabrication of three-dimensional colloidal crystal arrays (CCAs) on an underlying substrate via gravity sedimentation of TiO2-coated polystyrene (PS) colloidal particles. The beauty of the described system lies in the fact that obtained CCAs, for the first time, display a photonic band gap in the near-infrared (NIR) region with as much bandwidth (Δλ/λ) as 54−61%. Interestingly, stop band position and bandwidth have been found to be modulated with structural parameters of building blocks such as particle size and thickness of TiO2 shell, etc. Moreover, no significant change in stop band position was observed with the variation in incidence angle of the light. Theoretical calculations from the simulation studies have been found in agreement with the experimental findings.
    The Journal of Physical Chemistry C. 09/2010; 114(39).
  • Macromolecular Chemistry and Physics 08/2010; 211(17):1925 - 1932. · 2.39 Impact Factor
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    ABSTRACT: The present article offers a new approach to create a multifunctional material based on magnetic nanoparticles, which can be dispersed in aqueous and organic media. The preparation of this material was performed by binding covalently polymer chains based on a reactive diblock-copolymer of the polystyrene-SiCl2-poly(2-vinylpyridine) type, with average molecular weight per number (Mn) equal to 14,700 g/mol and a polydispersity index (PDI) less than 1.1, onto the surface of γ-Fe2O3 magnetic nanoparticles. The dichlorosilane moiety of the diblock-copolymer reacted with the OH groups of the magnetic nanoparticles immobilizing the polymer chain onto its surface. This reaction was monitored by FTIR and the polymer grafting density was determined by TGA and BET. Dynamic light scattering revealed that the hydrodynamic diameter of the nanoparticles increased after immobilizing the polymer. Contact angle measurements demonstrated the ability of the hybrid material to interact with organic and aqueous media allowing its dispersion in solvents with different polarities. This property was used to prepare a magnetically active emulsion. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1668–1675, 2010
    Journal of Polymer Science Part B Polymer Physics 06/2010; 48(14):1668 - 1675. · 2.22 Impact Factor
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    ABSTRACT: A novel and versatile approach for the mixing of ZnO nanofillers into a host polymer matrix, poly(ethyl methacrylate) (PEMA), is reported. Firstly, ZnO nanoparticles are deposited onto the surface of polystyrene (PS) colloidal particles in a "raspberry-like" fashion and subsequently obtained PS/ZnO composite particles are mixed into the PEMA matrix in the range of 0.5 to 5 wt.-%. Microscopic analyses reveal a homogenous distribution of PS/ZnO domains into the PEMA matrix even at 5 wt.-% loading level. Thermogravimetric analysis and differential scanning calorimetry results indicate an improvement in thermal stability of PEMA matrix after mixing with PS/ZnO filler particles. A significant enhancement in mechanical properties of PEMA matrix in the presence of PS/ZnO particles has been evidenced by dynamic mechanical analysis and three point bending measurements.
    Macromolecular Rapid Communications 02/2010; 31(4):405-10. · 4.93 Impact Factor
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    ABSTRACT: We investigate in a hybrid material the interactions existing between magnetic nanoparticles of gamma-Fe(2)O(3) and the polymer matrix constituted by core-shell poly(N-isopropylacrylamide-sodium acrylate) microgels. These interactions provoke the shifting of the microgel volume phase transition to higher temperatures when the amount of gamma-Fe(2)O(3) increases. The study was performed using different techniques such as incoherent quasi-elastic neutron scattering (IQNS), infrared spectroscopy (FTIR-ATR), and dynamic light scattering (DLS). Below the low critical solution temperature (LCST) of the polymer, the IQNS data confirm that the presence of inorganic nanoparticles affects the PNIPAM chain motions. Thus, in the swollen state both the mean-square displacement of the polymer segments and the diffusive motion of the polymer chains decrease as the iron oxide content increases. The FTIR-ATR study indicates that the reduction of vibrational and diffusional motions of the polymer chains is due to the formation of hydrogen bonds between the amide groups of the polymer matrix and the OH groups of the magnetic nanoparticles. The creation of this hybrid complex would explain the reduction of the swelling capacity with increasing the iron content in the microgels. Furthermore, this interaction could also explain the shift of the polymer LCST to higher temperatures as due to the extra energy required by the system to break the hydrogen bonds prior to the PNIPAM collapse.
    Langmuir 02/2010; 26(10):7101-6. · 4.38 Impact Factor
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    ABSTRACT: In the present study we report a simple and reproducible method to prepare highly ordered arrays of Fe3O4 superparamagnetic nanoparticles (MNPs) via block copolymer (BCP) self assembly. Pre-synthesized MNPs with a mean diameter of 6.1 nm are selectively segregated within the lamellae or hexagonally packed cylinders composed of PVP blocks in poly(styrene-b-vinylpyridine) (PS-b-PVP) block copolymers without any additional surface modification. The density of the stabilizing shell in the MNPs as well as the position of pyridinenitrogen in the PVP block of the BCPs are found to be crucial for selective incorporation of MNPs into the PVP domains. The obtained results suggest a key importance of a mutual affinity between active blocks and the nanoparticles which should be maximized in order to attain high nanoparticles loadings and long-range structural orders.
    Journal of Materials Chemistry 01/2010; 20(36). · 6.63 Impact Factor
  • Mukesh Agrawal, Smrati Gupta, Andrij Pich, Nikolaos E. Zafeiropoulos, Manfred Stamm
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    ABSTRACT: A facile approach for the fabrication of hierarchically nanostructured hollow spheres composed of mixed metal oxides (ZnO−TiO2) has been demonstrated. The employed protocol involves coating of the functionalized polystyrene (PS) template beads with the successive layers of ZnO and TiO2 nanoparticles, respectively, followed by the calcination of resulting PS/ZnO−TiO2 core shell composite particles at elevated temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been employed to evidence the fabrication of the monodisperse, intact, and closed ZnO−TiO2 hollow spheres. Presence of both ZnO and TiO2 phases in the ceramic shell of resulting hollow spheres has been confirmed by electron energy loss mapping analysis. Phase purity of the ZnO and TiO2 phases of the ceramic shell has been studied by X-ray diffraction analysis. Brunauer−Emmett−Teller (BET) method reveals the specific surface area and the average pore diameter of hollow spheres as 59.63 m2/g and 3 nm, respectively. Photocatalytic properties of the fabricated ZnO−TiO2 hollow spheres has been investigated for the degradation of organic dyes and compared with those of ZnO and TiO2 hollow spheres.
    Chemistry of Materials - CHEM MATER. 11/2009;
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    ABSTRACT: Fabrication of organic-inorganic composite particles with tailored size, shape, and morphology has been attracting great attention from researchers because of their fascinating properties and applications in a variety of potential fields. In this study, we report on the fabrication of PS-In(OH)(3) (polystyrene-indium hydroxide) composite particles by hydrolyzing the In(OC(3)H(7))(3) (indium isopropoxide) salt in the presence of beta-diketone functionalized PS colloidal particles. A systematic investigation of the employed reaction conditions allowed us to tune the morphology, size, and In(OH)(3) content of the PS-In(OH)(3) composite particles. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results illustrate that variation in the employed concentration of the In(OC(3)H(7))(3) salt in reaction media can effectively tune the morphology of resulting composite particles between "core-shell" and "raspberry-like". X-ray diffraction (XRD) analysis confirms the phase purity of In(OH)(3) nanoparticles precipitated on the surface of PS beads. Colloidal stability of the composite particles has been found to be reduced with increasing the deposited amount of In(OH)(3) nanoparticles. Thermogravimetric analysis (TGA) suggests a continuous increase in the deposited amount of In(OH)(3) nanoparticles with increasing concentration of In(OC(3)H(7))(3) salt in reaction media. The resulting PS-In(OH)(3) composite particles are envisioned to be used in a myriad of potential applications including fabrication of optoelectronic devices, absorption/separation supporting material, catalysts, and hydrophobic surfaces.
    Langmuir 09/2009; 26(1):526-32. · 4.38 Impact Factor
  • Konrad Schneider, N.E. Zafeiropoulos, Manfred Stamm
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    ABSTRACT: Journal article
    Advanced Engineering Materials 06/2009; · 1.61 Impact Factor
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    ABSTRACT: The effect of annealing on the miscibility and phase behavior of Sorona {poly(trimethylene terephthalate), PTT} and bisphenol A polycarbonate (PC) blends was examined. These blends exhibited heterogeneous phase-separated morphology and two well-spaced glass transition temperatures (Tgs) indicating immiscibility. The Sorona/PC blends were thermally annealed at 260 degrees C for different times to induce various extents of transreactions between the two polymers. After annealing at high temperature the original two Tgs of blends were found to merge into one single Tg, exhibiting a homogeneous morphology. It is interesting to note that upon extended annealing the original semicrystalline morphology transformed into an amorphous nature. This is attributed to chemical transreactions between the PTT and PC chain segments as evidenced with FTIR, DSC, DMA, 1H NMR, and WAXS measurements. A new characteristic aryl C-O-C vibration band present at 1070 cm(-1) in the FTIR spectra of the annealed blends indicated the formation of an aromatic polyester structure due to the transreactions between PTT and PC. The sequence structures of the produced copolyesters were determined by a NMR triad analysis, which showed that the randomness increased with time of heating. WAXS analysis confirmed that the PTT/PC blends completely lost their crystallinity when annealed at 260 degrees C for a period of 120 min or longer, indicating the formation of fully random copolyesters. A random copolymer formed as a result of the transreactions between PTT and PC serves as a compatibilizer at the beginning, and upon extended annealing this became the main species of the system which is finally transformed to a homogeneous and amorphous phase.
    The Journal of Physical Chemistry B 03/2009; 113(6):1569-78. · 3.61 Impact Factor
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    ABSTRACT: Nanocomposites based on organically modified montmorillonites (OMMTs) and sodium montmorillonite (CLO-Na+) with poly(styrene-b-butadiene-b-styrene) (SBS) diblock copolymer have been investigated. Solution blending of OMMT suspension in toluene with SBS and subsequent static casting and annealing resulted in transparent films. Final samples were processed by compression molding. The intercalation spacing in the nanocomposites, microphase separation of the SBS, and the degree of dispersion of nanocomposites were investigated by X-ray diffraction (Wide and small-angle X-ray scattering), transmission optical microscopy (TOM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The increase of basal spacing of OMMT in the nanocomposites suggested the intercalation of SBS. The lamellar structure perfection was extensively affected by both OMMT. AFM images and TOM micrographs only showed well dispersed but not exfoliated nanocomposites. On the other hand, TEM showed inserted tactoids into both blocks depending on the surfactant used (stained samples) and the dispersion of those tactoids (unstained samples). Fourier transform infrared spectroscopy indicated only the presence of the OMMT into the SBS. Deviations of the decomposition pathway of pristine SBS with addition of the OMMT were found by thermogravimetric analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
    Journal of Applied Polymer Science 09/2008; 110(6):3624 - 3637. · 1.40 Impact Factor
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    ABSTRACT: In the present study, we report a method for preparing a fluorescent thermosensitive hybrid material based on monodisperse, thermosensitive poly( N-isopropyl acrylamide) (PNIPAM) microgels covered with CdTe nanocrystals of 3.2 nm diameter. The CdTe nanocrystals were covalently immobilized on the surface of PNIPAM microgels. The chemical environment around the CdTe nanocrystals was modified by changing the temperature and inducing the microgel volume-phase transition. This change provoked a steep variation in the nanocrystal photoluminescence (PL) intensity in such a way that when the temperature was under the low critical solution temperature (LCST) of the polymer (36 degrees C) the PL of the nanocrystals was strongly quenched, whereas above the LCST the PL intensity was restored.
    Langmuir 09/2008; 24(17):9820-4. · 4.38 Impact Factor

Publication Stats

543 Citations
147.84 Total Impact Points

Institutions

  • 2013
    • Athens State University
      Athens, Alabama, United States
  • 2010–2013
    • University of Ioannina
      • Department of Materials Science and Engineering
      Yannina, Epirus, Greece
    • Technische Universität Dresden
      Dresden, Saxony, Germany
  • 2012
    • Mahatma Gandhi University
      • School of Chemical Sciences
      Kottayam, Kerala, India
  • 2003–2010
    • Leibniz Institute of Polymer Research Dresden
      • Max Bergmann Center for Biomaterials
      Dresden, Saxony, Germany
    • University of Surrey
      Guilford, England, United Kingdom
  • 2001–2007
    • Imperial College London
      • Department of Materials
      London, ENG, United Kingdom