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1.
Himani Sharma Shailesh N. Sharma Gurmeet Singh Sonnada Math Shivaprasad 《Colloid and polymer science》2007,285(11):1213-1227
In this work, the role of conducting [poly (p-phenylinevinylene) (PPV)] and nonconducting (polystyrene) polymers on the properties
of their respective composites with CdSe quantum dots of varied sizes has been investigated. The emission and structural properties
of polymer–CdSe composites are found to be dependent on the crystallite size and morphology of CdSe nanocrystallites. Smaller
CdSe quantum dots (size, ∼5 nm) ensures efficient charge transfer process across polymer–CdSe interface as evident by almost
complete quenching of photoluminescence (PL) emission as compared to larger CdSe quantum dots (size, ∼7 nm). Presence of residual
trioctylphosphine (TOP)/ tri-n-octylphosphine-oxide (TOPO) species and agglomeration of particles act as a hindrance for quenching of emission and hence
charge transfer for larger CdSe nanocrystallites. Emission studies indicated an increased conjugation length for PPV polymers
in different solvents (toluene, pyridine) and in solid state. Nonconducting polymer polystyrene shows charge transfer across
polymer–CdSe interface as well. However, polystyrene polymer has a shorter chain length, which ensures maximum coverage on
the surface of CdSe nanocrystallites and provides better photostability to CdSe QDs within the polymer matrix as compared
to that for PPV–CdSe nanocomposites. 相似文献
2.
Yuanjing Cui Jiancan Yu Junkuo Gao Zhiyu Wang Guodong Qian 《Journal of Sol-Gel Science and Technology》2009,52(3):362-369
A DCM derivative, namely 4-Dicyanomethylene-2-methyl-6-{[4′-(N-hydroxyethyl-N-methyl)amino]styryl}-4H-pyran (DCMH), has been synthesized and covalently incorporated into the inorganic silica network as pendants via a sol–gel process. Molecular
structures of the resultants are confirmed by elemental analysis, 1H NMR, DSC, TGA, FTIR and UV–Vis spectroscopy. Photoluminescence (PL) spectra shows that the emission of DCMH peaked at 625 nm is almost completely quenched in DMF solution with a concentration of 1 × 10−4 mol/L, however, in hybrid films, the PL intensity enhances obviously with increasing DCMH concentration even at the high loading content of 40 mol%. All the hybrid films exhibit PL emission around 646–650 nm and
the peak position reveal little dependence on the concentration of dye, suggesting they can be used as red emissive materials
in light-emitting diodes. The relationship between fluorescence lifetime and dye concentration is also investigated by time-resolved
PL measurements. 相似文献
3.
The lipid composition of four tissues, musculo-cutaneous, blood, internal organs, and gonads, from the marine worm Urechis unicinctus was studied. It was shown that the principal phospholipids (PL) in the studied tissues were phosphatidylcholine (PC) and
phosphatidylethanolamine (PE). Depending on the tissue type, the fraction of PC was 31.8–42.6%; PE, 16.1–25.7% (of total PL).
Blood contained a high percentage of lyso-PE (20.8%). The fatty-acid (FA) composition of the tissues consisted of C16, C18,
C20, and C22 families with different degrees of unsaturation. Eicosapentaenoic acid (20:5) had the highest percentage in all
tissues at 15.5–26.1%. Tissues with different functions such as musculo-cutaneous and gonads contained the same amounts of
20:5 FA, 26.1% (of total FA). The high content of polyunsaturated FA and, in particular, eicosapentaenoic FA in U. unicinctus confirmed that it was valuable as not only an energy source but also a source of PL and essential FA. 相似文献
4.
Víctor M. Ovando-Medina René D. Peralta Eduardo Mendizábal Hugo Martínez-Gutiérrez Tania E. Lara-Ceniceros Raquel Ledezma-Rodríguez 《Colloid and polymer science》2011,289(7):759-765
Conductive spherical polypyrrole nanoparticles were obtained by polymerization in oil-in-water (o/w) microemulsions using
sodium dodecyl sulfate (SDS) as anionic surfactant, ethanol as co-surfactant, and potassium persulfate (KPS, 0.017 wt.%) as
oxidizing agent. The average particle diameter (Dp) of the nanoparticles was between 38 and 45 nm with narrow particle size
distributions (D
w/D
n < 1.2). Dp increases with the ethanol concentration due to the intercalation between the polar heads of SDS, promoting instability
of the nanoparticles and some coagulation. In this work, low surfactant concentration was used, and the molar ratio of the
oxidizing agent to monomer was 8.5 × 10−3, a value much lower compared with others reported in the literature. Increasing the ethanol concentration in the recipes
enhanced the conductive properties of the polymers due to the high π-conjugation length obtained. 相似文献
5.
Stephen M. Lipson Ashley J. Cadby Paul A. Lane Diarmuid F. O’Brien Anna Drury Donald D. C. Bradley Werner J. Blau 《Monatshefte für Chemie / Chemical Monthly》2001,132(1):151-158
Summary. We have investigated the effect of film preparation procedures on the photoluminescence efficiency of the luminescent co-polymer
poly-(m-phenylene-co-2,5-dioctoxy-p-phenylenevinylene) (PmPV). The photoluminescence efficiency of PmPV films improved by up to 50% when the solution was degassed by bubbling argon gas through it prior to spin casting in an inert
atmosphere and baking under vacuum. Photoinduced absorption and doping measurements show that this preparation method reduces
polaron photogeneration, which reduces the photoluminescence (PL) yield through exciton quenching and excited state absorption.
It is proposed that this sample preparation method increases interchain separation, reducing the formation of polarons and
non-radiative quenching routes, thus resulting in increased PL efficiency.
Received June 23, 2000. Accepted (revised) August 3, 2000 相似文献
6.
Functional surfaces and especially the control of surface properties depending on external parameters such as light illumination
have gained increasing importance in the last few years. We present the characterization of polymers from the cycloolefin
(co)polymer class (COC/COP) functionalized with an aminosilane as a basis for the further immobilization of compounds. In
a first step, an assay using AlexaFluor?647 fluorescent dye was used to assess surface homogeneity and reproducibility. A
coefficient of variation of less than 15% for dot-to-dot and less than 25% for chip-to-chip could be achieved. The same amino-functionalized
surfaces were then used to immobilize a biotinylated photolabile linker compound, binding AlexaFluor?647-labeled streptavidin.
The linker was photocleaved with high efficiency at λ = 365 nm and P = 0.15 mW/cm2. Fluorescence measurements show that polymers of the COC/COP class can be used as versatile surfaces for the photoinduced
release of compounds immobilized via photolabile linkers. 相似文献
7.
Achille M. Bivigou-Koumba Eckhard Görnitz André Laschewsky Peter Müller-Buschbaum Christine M. Papadakis 《Colloid and polymer science》2010,288(5):499-517
Several series of symmetrical triblock copolymers were synthesized by the reversible addition fragmentation chain transfer
method. They consist of a long block of poly(N-isopropylacrylamide) as hydrophilic, thermoresponsive middle block, which is end-capped by two small strongly hydrophobic
blocks made from five different vinyl polymers. The association of the amphiphilic polymers was studied in dilute and concentrated
aqueous solution. The polymer micelles found at low concentrations form hydrogels at high concentrations, typically above
30–35 wt.%. Hydrogel formation and the thermosensitive rheological behavior were studied exemplarily for copolymers with hydrophobic
blocks of polystyrene, poly(2-ethylhexyl acrylate), and poly(n-octadecyl acrylate). All systems exhibited a cloud point around 30 °C. Heating beyond the cloud point initially favors hydrogel
formation but continued heating results in macroscopic phase separation. The rheological behavior suggests that the copolymers
associate into flower-like micelles, with only a small share of polymers that bridge the micelles and act as physical cross-linkers,
even at high concentrations. 相似文献
8.
Christoph J. Brabec Serdar N. Sariciftci 《Monatshefte für Chemie / Chemical Monthly》2001,132(4):421-431
Summary. Recent developments on photovoltaic elements based on solid state composites of conjugated, semiconducting polymers mixed
with buckminsterfullerene are reviewed. The photoinduced charge transfer from donor-type semiconducting conjugated polymers
onto acceptor-type conjugated polymers or acceptor molecules such as buckminsterfullerene is reversible, ultrafast (within
100 fs) with a quantum efficiency approaching unity, and the charge separated state is metastable (up to ms at 80 K). This
phenomenon of photoinduced electron transfer leads to a number of potentially interesting applications which include, among
others, sensitization of the photoconductivity, reverse saturable absorption (optical limiting), and photovoltaic phenomena.
Recent studies on the realization of photovoltaic elements with 3% power conversion efficiency are reported.
Received December 19, 2000. Accepted December 22, 2000 相似文献
9.
The synthesis and evaluation of a molecularly imprinted polymer (MIP) used as a selective solid-phase extraction sorbent and
coupled to high-performance liquid chromatography (HPLC) for the efficient determination of sulfamerazine (SMR) in pond water
and three fishes are reported. The polymer was prepared using SMR as the template molecule, methacrylic acid as the functional
monomer and ethylene glycol dimethacrylate as the crosslinking monomer in the presence of tetrahydrofuran as the solvent.
The SMR-imprinted polymers and nonimprinted polymers were characterized by FT-IR and static adsorption experiments. The prepared
SMR-imprinted material showed a high adsorption capacity, significant selectivity and good site accessibility. The maximum
static adsorption capacities of the SMR-imprinted and nonimprinted materials for SMR were 108.8 and 79.6 mg g−1, respectively. The relative selectivity factor of this SMR-imprinted material was 1.6. Several parameters influencing the
solid-phase extraction process were optimized. Finally, the SMR-imprinted polymers were used as the sorbent in solid-phase
extraction to determine SMR in pond water and three fishes with satisfactory recovery. The average recoveries of the MIP-SPE
method were 94.0% in ultrapure water and 95.8% in pond water. Relative standard deviations ranging from 0.3% to 5.2% in MIP
were acquired. The results for the SMR concentrations in crucian, carp and wuchang fish were 66.0, 127.1 and 51.5 ng g−1, respectively. The RSDs (n = 5) were 3.51%, 0.53% and 5.08%, respectively. The limit of detection (LOD) for SMR was 1 ng g−1 and the limit of quantitation (LOQ) was 3.5 ng g−1. 相似文献
10.
Variations in average fiber length and fiber length distribution both in the longitudinal and horizontal directions of a first-thinning
Scots pine (Pinus sylvestris) stem and between six stems of similar age (26–30 years) and height (10.7–12.8 m) were studied. As a general trend, fiber
length increased from the pith (0.8–1.3 mm) to the outer part of the stem (1.9–2.9 mm) maximizing at the relative stem height
of 20–40%. Variations in fiber length between stems were smaller than those within a stem. The average fiber length of different
stems of the same age (28 years) or diameter at breast height (11 cm) depended typically on wood growth rate. Finally, kraft
cooking experiments on different parts of the stem (i.e., butt and top as well as inner and outer parts of the stem) indicated
clear differences in their pulp properties. It was concluded that due to the acceptable properties of these pulps, first-thinning
wood material as such or after the suitable fractionation may offer a potential source of fiber for a variety of different
purposes. 相似文献
11.
The preparation of CdSe nanospheres (ns-CdSe) and their application as electron acceptor in conjugated polymer photovoltaic
devices are reported. ns-CdSe with diameters of 5 nm were prepared through an organometallic method. The transmission electron
microscopy (TEM), ultraviolet-visible (UV-Vis) absorption and photoluminescence (PL) spectra indicate that the CdSe nanocrystals
(NCs) are monodispersed nanospheres with the first exciton absorption peak at around 625 nm and the emission peak at around
652 nm. The PL spectra of the ns-CdSe/polymer composite films show that the PL of the conjugated polymers is effectively quenched
upon the addition of ns-CdSe. Photovoltaic devices were fabricated from the composites of ns-CdSe and poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene]
(MEH-PPV) or poly(3-hexylthiophene) (P3HT). Under AM1.5 illumination (100 mW/cm2), the short circuit current (I
SC), open circuit voltage (V
OC), fill factor (FF) and energy conversion efficiency (η) reached 1.56 mA/cm2, 0.75 V, 34.5% and 0.40%, respectively for device from the ns-CdSe/MEH-PPV (15: 1 by weight) and 1.93 mA/cm2, 0.65 V, 38.4% and 0.48%, respectively for device from the ns-CdSe/P3HT (10: 1 by weight).
__________
Translated from Chemical Journal of Chinese Universities, 2007, 28(3): 596–599 [译自: 高等学校化学学报] 相似文献
12.
Summary. Silicon oxide or metal oxide clusters or small particles with polymerizable organic groups covalently bonded to their surface
can be copolymerized with organic monomers by various polymerization techniques. Whereas the preparation and properties of
the polymers reinforced by R
8Si8O12 have already been well investigated, analogous materials with incorporated transition metal oxide clusters are only beginning
to show their potential as an interesting new class of inorganic-organic hybrid polymers. In the second part of the article,
approaches are reviewed in which the inorganic building block serves as an initiator for polymerization reactions. This results
in materials in which the organic polymer is grafted from an inorganic core. Most work has been done with surface-modified
silica particles. Free radical polymerizations and atom transfer radical polymerizations with macroinitiators are summarized.
The latter method results in polymeric particles in which an inorganic core is surrounded by an organic polymer shell. A new
approach is the use of polyfunctional inorganic molecules or molecular clusters as initiators.
Received July 28, 2000. Accepted August 7, 2000 相似文献
13.
The surfactant effect on the lower critical solution temperature (LCST) of thermosensitive poly(organophosphazenes) with
methoxy-poly(ethylene glycol) and amino acid esters as side groups was examined in terms of molecular interactions between
the polyphosphazenes and surfactants including various anionic, cationic, and nonionic surfactants in aqueous solution. Most
of the anionic and cationic surfactants increased the LCST of the polymers: the LCST increased more sharply with increasing
length and hydrophobicity of the hydrophobic part of the surfactant molecule. The ΔLCSTs (T
0.03M − T
0M), the change in the LCST by addition of 0 and 0.03 M sodium dodecyl sulfate (SDS), were found to be 7.0 and 14.5 °C for the
polymers bearing ethyl esters of glycine and aspartic acid, respectively. The LCST increase of poly(organophosphazene) having
a more hydrophobic aspartic acid ethyl ester was 2 times larger compared with that of the polymer having glycine ethyl ester
as a side group. The binding behavior of SDS to the polymer bearing glycine ethyl ester as a hydrophobic group was explained
from the results of titration of the polymer solutions containing SDS with tetrapropylammonium bromide. Graphic models for
the molecular interactions of polymer/surfactant and polymer/surfactant/salt in aqueous solutions were proposed.
Received: 17 February 2000/Accepted: 25 April 2000 相似文献
14.
M. Saeed Butt Zareen Akhter M. Zafar-uz-Zaman Humaira Masood Siddiqi 《Colloid and polymer science》2008,286(12):1455-1461
The diamine, 4-aminophenyloxy-N-4-[(4-amiophenyloxy)benzylidene]aniline, was prepared via the nucleophilic substitution reaction and was polymerized with
different dianhydrides either by one-step solution polymerization reaction or two-step procedure. The latter includes ring-opening
polyaddition to give poly(amic acid), followed by cyclodehydration to polyimides. The inherent viscosity ranges from 0.61–0.79 dl/g.
Some of the polymers were soluble in most of the organic solvents such as DMSO, DMF, DMAc, NMP, and m-cresol even at room temperature. The degradation temperature of the resultant polymers falls in the ranges from 240–500 °C
in nitrogen with only 10% weight loss. Specific heat capacity at 200 °C ranges from 1.0929–2.6275 J g−1 k−1. The temperature at which the maximum degradation of the polymer occurs ranges from 600–630 °C. The glass transition temperature
(Tg) values of the polyimides ranged from 185 to 272 °C. The activation energy and enthalpy of the polyimides ranged from
47.5–55.0 kJ/mole and 45.7–53.0 kJ/mole and the moisture absorption in the range of 0.23–0.72%. 相似文献
15.
Imprinted polymers are now being increasingly considered for active biomedical uses such as drug delivery. In this work, the
use of molecularly imprinted polymers (MIPs) in designing new drug delivery devices was studied. Imprinted polymers were prepared
from methacrylic acid (functional monomer), ethylene glycol dimethacrylate (cross-linker), and bromhexine (as a drug template)
using bulk polymerization method. The influence of the template/functional monomer proportion and pH on the achievement of
MIPs with pore cavities with a high enough affinity for the drug was investigated. The polymeric devices were further characterized
by FT-IR, thermogravimetric analysis, scanning electron microscopy, and binding experiments. The imprinted polymers showed
a higher affinity for bromhexine and a slower release rate than the non-imprinted polymers. The controlled release of bromhexine
from the prepared imprinted polymers was investigated through in vitro dissolution tests by measuring absorbance at λ
max of 310 nm by HPLC-UV. The dissolution media employed were hydrochloric acid at the pH level of 3.0 and phosphate buffers,
at pH levels of 6.0 and 8.0, maintained at 37.0 and 25.0 ± 0.5 °C. Results from the analyses showed the ability of MIP polymers
to control the release of bromhexine In all cases The imprinted polymers showed a higher affinity for bromhexine and a slower
release rate than the non-imprinted polymers. At the pH level of 3.0 and at the temperature of 25 °C, slower release of bromhexine
imprinted polymer occurred. 相似文献
16.
Magdalena Staszewska Monika Dzieciuch Joanna Lewandowska Mariusz Kepczynski Szczepan Zapotoczny Marcin Oszajca Anna Łatkiewicz Maria Nowakowska 《Journal of Sol-Gel Science and Technology》2011,59(2):276-282
In this article, we report on the formation of well-defined highly emissive silica-covered porphyrin microstructures in base-catalyzed
sol–gel processes. The microstructures were obtained by self-assembly of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (mTHPP)
at room temperature. Tetraethoxysilane (TEOS) was used as a silica precursor. The hybrid mTHPP- silica particles were characterized
by means of reflectance UV–Vis and microscopy techniques including atomic force microscopy, scanning electron microscopy (SEM)
and confocal fluorescence microscopy (CM). The SEM and TEM observations revealed that depending on the porphyrin concentration
used in the synthesis, the shape of the hybrid mTHPP-silica particles has changed from ribbon-like (c
mTHPP = 2.09 mM) to rhombus-like structures (c
mTHPP = 4.35 mM). The ribbons were straight-edged, uniform in width (1.2–1.8 μm) and height (350–400 nm), and variable in length
(40–100 μm). The rhombs were 1–3.7 μm in height, 7–25 μm in length, and 3.5–15 μm in width, and the ratio of length to width
was uniform and equal to ca. 1.8–2. UV–Vis absorption spectra indicated that the J-aggregates and H-aggregates formed in the
systems with lower and higher porphyrin content, respectively. Formation of different type of porphyrin aggregates in both
systems resulted in different emission spectra, as it was shown with CM. 相似文献
17.
Joseph D. Menczel 《Journal of Thermal Analysis and Calorimetry》2011,106(1):7-24
The first experimental evidence of the existence of the rigid amorphous fraction (RAF) was reported by Menczel and Wunderlich
for several semicrystalline polymers. It was observed that the hysteresis peak at the glass transition was absent when these
polymers were heated much faster than they had previously been cooled. In the glass transition behavior of poly(ethylene terephthalate)
(PET), the hysteresis peak gradually disappeared as the crystallinity increased. At the same time, it was noted that the ΔC
p of higher crystallinity PET samples was much smaller than could be expected on the basis of the crystallinity calculated
from the heat of fusion. It was also observed that this behavior was not unique to PET only, but is characteristic of most
semicrystalline polymers: the sum of the crystallinity calculated from the heat of fusion and the amorphous content calculated
from the ΔC
p at the glass transition is much less than 100% (a typical difference is ~20–30%). This 20–30% difference was attributed to
the existence of the “RAF”. The presence of the RAF also affected the unfreezing behavior of the “mobile (or traditional)
amorphous fraction.” As a consequence, the phenomenon of the enthalpy relaxation diminished with increasing rigid amorphous
content. It was suggested that the disappearance of the enthalpy relaxation was caused by the disappearance or drastic decrease
of the time dependence of the glass transition. To check the validity of this suggestion, the glass transition had to be also
measured on cooling in order to overlay it on the DSC curves measured on heating. However, before this overlaying work could
be accomplished, the exact temperatures on cooling had to be determined since the temperature of the DSC instruments that
time could not be calibrated on cooling using the usual low molecular weight standards due to the common phenomenon of supercooling.
Therefore, a temperature calibration method needed to be developed for cooling DSC experiments utilizing high purity liquid
crystals using the isotropic → nematic, the isotropic → cholesteric, and other liquid crystal → liquid crystal transitions.
After the cooling calibration was accomplished, the cooling glass transition experiments indicated that the glass transition
in semicrystalline polymers is not completely time independent, because its width depends on the ramp rate. However, it was
shown that the time dependence is drastically reduced, and the midpoint of the glass transition seems to be constant which
can explain the absence of the enthalpy relaxation. The work presented here has led to a number of studies showing the universality
of the rigid amorphous phase for semicrystalline polymers as well as an ASTM standard for DSC cooling calibration. 相似文献
18.
Yukiko Enomoto-Rogers Hiroshi Kamitakahara Kunihiro Nakayama Toshiyuki Takano Fumiaki Nakatsubo 《Cellulose (London, England)》2009,16(3):519-530
Model experiments for synthesis of a comb-shaped copolymer with cellulose side-chains were performed with cellobiose derivatives.
A novel cellobiose monomer, N-(15-methacryloyloxypentadecanoyl)-2,3,6-tri-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-β-d-glucopyranosylamine (2) was prepared from heptaacetylcellobiosyl- amine. Homopolymerization of cellobiose monomer 2 and copolymerization of monomer 2 with methyl methacrylate (MMA) were performed using 2,2′-azobis(isobutyronitrile) (AIBN) as an initiator to obtain homopolymers
3-i (i = 1–4) and copolymers 3-i (i = 5–7), poly(methyl methacrylate)-graft-(heptaacetylcellobiosylamine-C15). The size exclusion chromatography—multi-angle laser light scattering (SEC-MALS) measurements
revealed that comb-shaped homopolymers 3-i (i = 1–4) had more compact structures compared to copolymers 3-i (i = 5–7) at the same elution volume. Selective deacetylation of polymers 3-i (i = 1–7) gave novel cellobiose polymers 4-i (i = 1–7), poly(methyl methacrylate)-graft-(cellobiosylamine-C15). The amide linkages between cellobiose moiety and long-chain alkyl group, and the ester linkages between
PMMA main-chain and long-chain alkyl group remained after deprotection.
The differential scanning calorimetry (DSC) measurements revealed that the T
gs of the polymers 4-i (i = 1, 5, 6, 7) increased with increasing cellobiose composition in the polymers. It was indicated that cellobiose moieties
of polymers 4-i (i = 1, 5, 6, 7) reduced the mobility of PMMA main-chain. 相似文献
19.
Eri Yoshida 《Colloid and polymer science》2010,288(8):901-905
The effects of the structure of initiators and photo-acid generators on the nitroxide-mediated photo-living radical polymerization
of methyl methacrylate were explored. The bulk polymerization was performed at room temperature using nine different initiators
in the presence of (4-tert-butylphenyl)diphenylsulfonium triflate as the photo-acid generator. 2,2′-Azobisisobutyronitrile, 2,2′-azobis(2,4-dimethylvaleronitrile),
dimethyl 2,2′-azobis(2-methylpropionate), and 2,2′-azobis(N-butyl-2-methylpropionamide) produced the polymers with a molecular weight distribution (MWD) around 1.6, while the racemic-
and meso-(2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) provided a 1.4 MWD. 2,2′-Azobis(2-methylbutyronitrile), 1,1′-azobis(cyclohexane-1-carbonitrile),
and 1-(cyano-1-methylethoxy)-4-methoxy-2,2,6,6-tetramethylpiperidine produced a broad MWD over 4.0. The structure of the photo-acid
generator also had an influence on the molecular weight control. The photo-acid generator of sulfonium salts supporting the
alkyl, methoxy, phenoxy, methylthio, and tert-butoxycarbonylmethoxy groups, coupled with halogens with the exception of the iodide had no effect on the MWD. On the other
hand, the salts containing the iodide, phenylthio, and naphthyl groups produced polymers with broad MWDs and with uncontrolled
high molecular weights. 相似文献