R E S E A R C H P A P E R
Optical characterization of CdS nanoparticles embedded
into the comb-type amphiphilic graft copolymer
O¨ zlem A. Kalaycı•O¨ zgu¨r Duygulu• Baki Hazer
Received: 29 June 2012 / Accepted: 5 December 2012 / Published online: 14 December 2012 Ó Springer Science+Business Media Dordrecht 2012
Abstract This study refers to the synthesis and characterization of a novel organic/inorganic hybrid nanocomposite material containing cadmium sulfide (CdS) nanoparticles. For this purpose, a series of poly-propylene (PP)-g-polyethylene glycol (PEG), PP-g-PEG comb-type amphiphilic graft copolymers were synthe-sized. PEGs with Mn = 400, 2000, 3350, and 8000 Da were used and the graft copolymers obtained were coded as PPEG400, PPEG2000, PPEG3350, and PPEG8000. CdS nanoparticles were formed in tetra-hydrofuran solution of PP-g-PEG amphiphilic comb-type copolymer by the reaction between aqueous solutions of Na2S and Cd(CH3COO)2simultaneously. Micelle formation of PPEG2000 comb-type amphi-philic graft copolymer in both solvent/non-solvent (petroleum ether–THF) by transmission electron microscopy (TEM). The optical characteristics, size morphology, phase analysis, and dispersion of CdS nanoparticles embedded in PPEG400, PPEG2000, PPEG3350, and PPEG8000 comb-type amphiphilic
graft copolymer micelles were determined by high resolution TEM (HRTEM), energy dispersive spectroscopy, UV–vis spectroscopy, and fluorescence emission spectroscopy techniques. The aggregate size of PPEG2000-CdS is between 10 and 50 nm; however, in the case of PPEG400-CdS, PPEG3350-CdS, and PPEG8000-CdS samples, it is up to approximately 100 nm. The size of CdS quantum dots in the aggregates for PPEG2000 and PPEG8000 samples was observed as 5 nm by HRTEM analysis, and this result was also supported by UV–vis absorbance spectra and fluorescence emission spectra.
Keywords Quantum dots Cadmium sulfide Comb-type amphiphilic copolymer Micelle HRTEM
Introduction
The semiconductor nanoparticles below 10 nm, which are also named as quantum dots, have recently become technologically important (Kittel1986; Heinglein1989). The quantum dots gain unique electronic, optical, magnetic, and mechanical properties, as the electronic energy states of these materials become discrete. When the size and shape of quantum dots change, the properties related with them also change, compared to their properties observed in the bulk and atomic/ molecular levels (Biju et al.2008). As the particle size of the quantum dots increases, the emission spectrum
O¨ . A. Kalaycı
Department of Physics, Bulent Ecevit University, Zonguldak 67100, Turkey
O¨ . Duygulu
TUBITAK Marmara Research Center, Materials Institute, Gebze, Kocaeli 41470, Turkey
B. Hazer (&)
Department of Chemistry, Bulent Ecevit University, Zonguldak 67100, Turkey
e-mail: [email protected]; [email protected] DOI 10.1007/s11051-012-1355-x
ied by UV–vis absorbance spectrum, photolumines-cence, electroluminesphotolumines-cence, and Raman dispersion (Trindade et al.2001; Alivisatos1996; Pesika et al.2003). A direct band gap material, II–VI semiconductor cadmium sulfide (CdS), can be used in the production of photoelectronic devices. In optical switches, sensors, electroluminescent devices, lasers, and biomedical tags, there are potentially possible applications for lumines-cence of the CdS quantum dots (Tessler et al.2002). In nanometer scale, polymers, colloids, micelles, thin films, and zeolites are used to synthesize the nanocomposite materials containing quantum dots like CdS or metal particles (Pomogailo 2000; Farmer and Patent 2001; Nabok 2005; Tomczak et al. 2009; Tura et al. 2005; Thakur et al.2009; Dong and Hinestroza2009; Hazer et al. 2012a, b; Hazer and Hazer 2011; Nicolais and Carotenuto2005). The synthesis and characterization of the polypropylene (PP)-g-polyethylene glycol (PEG) amphiphilic comb-type copolymers have been recently reported in our study (Balcı et al.2010). The PP-g-PEG amphiphilic comb-type copolymer containing metal nano-particles were also observed in terms of the antibacterial impact (Kalaycı et al.2010) and the in vivo biocompat-ibility (Hazer et al. 2011, 2012a, b). So as to obtain nanoparticles in polymeric matrix, various methods are available such as the chemical reduction, photoreductions, thermal decompositions, and vapor deposition methods. Stabilized colloidal sols or thin film after the evaporation solution can be obtained, depending on the method. The host polymer not only acts as protective polymer to form a dispersing and stabilizing media for the nanoparticles but also acts as functional polymer to affect the material and particle properties directly by surrounding nanoparticles (Mayer2001).
Amphiphilic copolymers, including hydrophobic and hydrophilic blocks are known as suitable ‘‘steric stabi-lizator’’ for the nanoparticles. The mutual interaction of polymer blocks and particles in a hybrid structure can affect the dispersion, location and size of the particles (Chiu et al.2005; Oren et al.2009; Kim et al.2006). The amphiphilic copolymers containing PEG as hydrophilic segment especially have specific importance because
solvent environment, the copolymer chains form micelle clusters and they take the form of colloidal distribution (Mayer1998). In the amphiphilic copoly-mers, micelle formation depends on the pair of the solvent/solvent. In the micelle formation, non-soluble block settles down in one micelle core, while the soluble block disperses around the core.
Many studies in literature have presented various ways of obtaining nanoparticles like CdS within polymer matrix (Lemon and Crooks2000; Liu et al.2003; Herron et al. 1990; Jamali et al. 2007; Spanhel et al. 1987; Underhill and Liu2000; Firth et al.2004; Peretz et al. 2011; Ferrer et al. 2009; Yeh et al.2003; Pandey and Pandey2009; Moore and Patel2001). Zhao et al. have studied PS-b-P2VP micelles that involve corona-embed-ded CdS nanoparticles (Zhao and Douglas2002; Zhao et al. 2001). Moffitt et al. (1998) have obtained core-embedded CdS quantum dots within polystyrene-b-poly(cadmium acrylate) (PS-b-PACd) reverse micelles. Petit et al. (1990) have obtained very small CdS nano-particles in reverse micelles by in situ synthesis. Qi et al. (2000) have analyzed high stabilized CdS nanoparticles within PEG block and poly(ethylene imine) double-hydrophilic block copolymers.
In this study, which is one of the studies of our research group, the preparation of a new composite material which stabilizes the CdS quantum dots into the PP-g-PEG comb-type amphiphilic graft copolymers has been reported (Balcı et al.2010; Kalaycı et al.2010; Hazer et al.2011, 2012a,b). The CdS quantum dots into this polymer matrix were studied in view of the micelle formation by high resolution transmission electron microscopy (HRTEM) and its optical behavior by UV–vis spectroscopy and fluorescence emission spectroscopy techniques.
Experimental
Materials
Chlorinated polypropylene (PP-Cl, Mw= 150,000 Da, three repeating units have 1 Cl in average), PEG
Mn= 400, 2000, 3350, 8000 Da and Cd(CH3COO)2 were supplied from Sigma-Aldrich. Tetrahydrofuran was supplied from Sigma-Aldrich and it was purified before being used.
The synthesis of PP-g-PEG comb-type amphiphilic graft copolymer
The PP-g-PEG block copolymer synthesis was con-ducted by keeping the PEG ratio at 10 %, as defined in the procedure presented in our previous studies (Balcı et al.2010; Kalaycı et al.2010). A typical endcapping reaction was performed as the following: PEG-2000 (5.0 g, 2.5 mmol) and PP-Cl (1.43 g, 1.0 mmol Cl) were separately dissolved in dry THF (30 mL). NaH in oil (60 wt%) (0.20 g, 5 mmol NaH) was added to the PEG solution and the reaction mixture was stirred at room temperature under argon atmosphere for 3 h. Sodium salt of PEG solution was added to the PP-Cl solution and stirred for half an hour. The reaction mixture was stirred one more day and poured into 500 mL of 1 M HCl. The precipitated polymer was filtered, washed with distilled water, and dried under vacuum at 50°C for a day. For the purification, it was redissolved in chloroform and reprecipitated in 200 mL of methanol, and dried under vacuum overnight at room temperature. The yield was 1.4 g. In order to observe the micelle formation of amphiphilic graft copolymer, pure water was added by continuously stirring the 5 mL THF solution of 0.1 g of the polymer until the turbidity was observed.
The preparation of the PP-g-PEG amphiphilic graft copolymers including CdS nanoparticles
One hundred milligrams of PP-g-PEG was dissolved in 10 mL of THF, and 0.05 mL of 0.2 M Cd(CH3COO)2 aqueous solution was poured on it and the solution was stirred for half an hour. Then, 0.05 mL of 0.3 M Na2S aqueous solution was added to this solution. The yellow color of CdS was observed within 2–3 min. Following this step, the solution was stirred for 1 h, and poured into a Petri dish (diameter, / = 7 cm) by means of film formation via solvent casting. After 1 day, composite polymer film was peeled away from the Petri dish. The composite yellow film was washed with methanol and dried under vacuum at room temperature for a day. The composite polymer was dissolved in 20 mL of toluene. The toluene solution was filtered and used to observe the optical characteristics.
The sample preparation and instrumentation
The solutions were put in ultrasonic bath for 10 min. The TEM sample preparation was done by placing a solution on 200-mesh carbon-coated copper TEM grid (EMS CF200-Cu). The TEM measurements were conducted using JEOL JEM-2100 HRTEM at 200 kV (LaB6 filament) and the elemental analysis were carried on via Oxford Instrument with 6498 energy dispersive spectroscopy (EDS) system. The images were recorded using slow scanning CCD camera (Gatan-694 model) with Gatan Digital Micrograph software. The low magnification TEM imaging, selected area electron diffraction (SAED), HRTEM (atomic lattice imaging and FFT diffractograms), and EDS techniques were used.
The UV–vis absorption spectra of the colloidal solutions of nanoparticle-embedded polymer prepared with the toluene were measured at room temperature using Cary 100 model UV–vis spectrometer. The fluorescence emission spectra measurements were done using Cary Eclipse model Fluorescence Spec-trometer instrument under the 350-nm wavelength at room temperature.
Results and discussion
The examination of micelle formation of PP-g-PEG amphiphilic graft copolymer
In the beginning, PPEG2000 amphiphilic copolymer micelles from the pair of solvent/non-solvent systems (H2O/THF or petroleum ether/THF) were obtained. The hydrophilic side groups interacted with the polar dispersion medium, e.g., H2O/THF, and it was observed that in the micelle formation of PPEG2000, the hydrophobic PP blocks formed the micelle core and the solubilized hydrophilic PEG blocks placed around it (Mayer 1998). In addition, in non-polar solvent medium, e.g., petroleum ether/THF, it was determined that the hydrophilic PEG blocks formed the micelle core that surrounded by the PP shell as seen in Fig.1. Figure 2depicts the CdS nanoparticles embedded in PEG block chains which were suspended as combs in PP blocks. The color of the CdS nanoparticles-embedded PPEG400, PPEG2000, PPEG3350, and PPEG8000 hybrid structure having different PEG chain lengths turned to light yellow, as shown in Fig.3.
Figure4 also shows photographs of the toluene solution of PPEG400, PPEG2000, PPEG3350, and PPEG8000 amphiphilic copolymers containing CdS nanoparticles under ultraviolet light (k = 365 nm). With the size change of CdS nanoparticles, the prepared samples exhibited an interesting color variation (Heinglein 1989; Biju et al.2008; Trindade et al.2001; Alivisatos 1996; Pesika et al.2003; Tamborra et al.2004; Brush 1986).
The turbid solution was used for TEM analysis to observe the micelle formation of PPEG2000 amphi-philic comb-type graft copolymer. The turbid solution was also obtained by adding water or petroleum ether instead, as shown in Fig.5.
TEM analysis of the micelle formation of CdS nanoparticles embedded in the pp-g-peg amphiphilic graft copolymer
A detailed TEM analysis has been performed on all samples. The low magnification TEM imaging (i.e., Fig.6), EDS (Fig.7), SAED (Fig.8), and HRTEM (atomic lattice imaging and FFT diffractograms) techniques (Figs.9,10,11,12) were used.
The low magnification TEM images illustrate the relatively good size and morphology distribution of the particles in the polymer matrix. The aggregate is observed for all samples. It is seen that the aggregated particle size is the smallest in the PPEG2000-CdS sample. The aggre-gate size of PPEG2000-CdS is between 10 and 50 nm; however, in the case of PPEG8000-CdS, PPEG3350-CdS, and PPEG400-CdS samples, the aggregate size is up to approximately 100 nm (Fig.6).
Figure7shows the representative TEM–EDS spectrum and elemental composition of CdS in PPEG2000 micelle, which confirms the Cd and S coexistence in the micelle. Moreover, Cd to S stoichiometric ratio is found as nearly
Fig. 1 Schematic representation of the micelle formation of PP-g-PEG2000
Fig. 2 Schematic representation of the micelle formation of CdS nanoparticles-embedded PP-g-PEG2000
Fig. 3 Photographsof the toluene solution of PP-g-PEG amphiphilic copolymers containing CdS quantum dots: a PPEG8000-CdS, bPPEG3350-CdS, c PPEG2000-CdS, d PPEG400-CdS
1:1. A relatively small amount of Cl is also observed. C and O elements emerge from the structure of polymer matrix and C, Cu and Si elements are from the TEM grid. Furthermore, the SAED pattern (Fig.8) of CdS embedded PPEG3350-CdS revealed d-spacings of 3.37 A˚ (A), 2.06 A˚ (B), 1.76 A˚ (C) and 1.30 A˚ (D) which corresponded to (111), (220), (311), and (420) lattice planes of cubic CdS phase, respectively.
The quantum dots size around 5 nm was measured for specimens of PPEG2000-CdS and PPEG8000-CdS. The nanoparticles were as mostly spherical.
Figures9 and 10 show HRTEM images and FFT diffractograms of CdS quantum dots in two different regions of PPEG2000-CdS sample. Similarly, Fig. 11 depicts HRTEM images and FFT diffractograms of CdS quantum dots in PPEG8000-CdS sample.
Figures9d,10d, and 11d illustrate FFT grams for CdS quantum dots. In the FFT diffracto-grams, the inner circle spots and the arrows represented d-spacings of 3.37 and 2.06 A˚ , respectively. Similarly, these d-spacings were also measured on the HRTEM atomic lattice images (Figs. 9c,10c, e,11c).
Fig. 4 Photographsof the toluene solution of PP-g-PEG amphiphilic copolymers containing CdS quantum dots under ultraviolet light (k = 365 nm): a PPEG400-CdS, b PPEG3350-CdS, c PPEG2000-CdS, d PPEG8000-CdS
Fig. 5 The micelle TEM images of PP-g-PEG2000: a PP-g-PEG2000 micelles from THF/water system, b PP-g-PEG2000 micelle from THF/petroleum ether system
Therefore, HRTEM images and FFT micrographs exhibited lattice fringes with interplanar distances of 3.37 and 2.06 A˚ which are d-spacings for (111) plane and (220) planes of CdS cubic phase (ICCD pdf
Fig. 6 Low magnifications TEM images of CdS embedded a PPEG2000-CdS, b PPEG8000-CdS, c PPEG400-CdS, and d PPEG3350-CdS sample
Fig. 7 The TEM–EDS spectrum and elemental composition of PPEG2000-CdS micelle with CdS (Cu and Si elements are from the TEM grid)
Fig. 8 SAED pattern of CdS embedded PPEG3350-CdS (A, B, C, D spots represent d-spacings for (111), (220), (311), and (420) lattice planes of cubic CdS phase respectively)
number: 89-0440, space group: 216), respectively. Since other CdS phase (hexagonal (ICCD pdf number: 80-0006, space group: 186) or orthorhombic (ICCD pdf number: 47-1179, space group: 48) lattice spacings were not observed, it can be stated that the particles are mainly cubic CdS phase.
The atomic lattice imaging could be performed on PPEG2000-CdS and PPEG8000-CdS samples. However, HRTEM technique was not successful for PPEG400-CdS and PPEG3350-CdS specimens. Yet, TEM imaging could be achieved (Fig. 12). This can be related to the artifacts of the TEM sample preparation. Since a week has passed between the TEM sample preparation and the solution preparation, it is thought that the PEG chains were destroyed and the stability of the solution was deformed.
The solution characteristics and UV–vis analysis
The UV–vis analysis of the PPEG400-CdS, PPEG2000-CdS, PPEG3350-CdS and PPEG8000-CdS hybrid nanocomposites were conducted in the toluene at room temperature. The absorbance curve is shown in Fig.13. In a semiconductor, the band gap between the valance and conduction band increases with the decreases, in the particle size. If the size of semiconductor nanoparticle is less than Bohr radius, the quantum confined can be considered as a exciton. The excitation of electron from valance band to conduction band depends on the energy that is higher than the band gap. Thus, UV–vis absorbance spectrum is observed in a lower wavelength region. This absorption band exists because of the first optically allowed transition of CdS between the
conduction band and hole state in valance band. As the interaction of excitons of the small size nanocrystals in the aggregates results in the weak and slowly band transition, no observed for the sharp and strong band transition when the UV–vis absorbance spectrum of PPEG8000 sample is analyzed.
The absorbance wavelengths were detected as 460, 480, 462, and 482 nm for the absorbance spectra curve of PPEG400-CdS, PPEG2000-CdS, PPEG3350-CdS, and PPEG8000-CdS, respectively. It was observed that the wavelength value of the CdS bulk shifted from 515 to 460 (482, 480, and 462) nm. This situation is only expected when the particle size is below 10 nm [54].
This result matches with the HRTEM images, as for PPEG2000-CdS and PPEG8000-CdS samples, CdS nanoparticles smaller than 10 nm were detected. The CdS quantum dots were not as single and separate; but, observed as attached to each other in aggregations.
The solution characteristics and fluorescence emission spectra
The emission spectra of the PPEG400-CdS, PPEG2000-CdS, PPEG3350-PPEG2000-CdS, and PPEG8000-CdS samples excited at 350 nm are presented in Fig.14.
Fig. 10 a–c HRTEM images, d FFT diffractogram (of c) and e atomic lattice imaging (processed image of enlarged view of white square in b by filtering and inverse FFT) of CdS quantum dots in CdS-embedded PPEG2000-CdS sample
The broad emission peak for PPEG400-CdS, PPEG-2000-CdS, and PPEG3350-CdS was observed at 625 nm and for PPEG8000 at 640 nm in emission
spectra. In addition, the peaks available in PPEG400-CdS, PPEG2000-PPEG400-CdS, PPEG3350-PPEG400-CdS, and PPEG80-00-CdS were observed at 445, 460, 445, and 417 nm,
Fig. 11 a, b TEM images, c HRTEM image (enlarged view of white square in b and d FFT diffractogram (of c) of CdS-embedded PPEG8000-CdS sample
respectively. The broad peak, observed in emission spectra, is closely related to the size of CdS nanoparticles and surface state. In literature, the broad peak, caused by the surface state, is determined between 530 and 650 nm (Cao et al.2005). The peak in the lower energy region can be caused by the nanoaggregations behaving like big size CdS nanoparticles. The peaks between 420 and 460 nm correspond to the band edge emission of the CdS nanoparticles. From HRTEM images, nanoaggre-gations, having 5-nm size CdS nanocrystals in the hybrid structures have been determined. As a result, the colloidal solution includes both monocrystalline CdS (below 10 nm) and CdS aggregation.
Conclusion
In a water/polar medium, Cd2?ion cores settle down the corona region of micelles by interacting with non-ionic hydrophilic PEG chains. With the addition of Na2S, Cd2?ion cores and S2- interact, and thus CdS nano-particles are obtained. CdS nanonano-particles, settling in the regions that Cd2? ions cores select, are among PEG chains. During this process, PP chains form the core of micelle by aggregating. Controlling the procedure during the transition from Cd2?to CdS in the solvent can change the particle features. It is essential to provide the stability of solution during the transition from
Fig. 13 Solution characteristics and UV–vis spectrum analysis: aPPEG2000-CdS, PPEG8000-CdS; b PPEG400-CdS, PPEG3350-CdS
Fig. 14 Solution characteristic and fluorescence emission spectrum analysis: a PPEG2000-CdS, PPEG8000-CdS; b PPEG 400-CdS, PPEG3350-CdS
Cd2?to CdS and thus goal of this study, that is to obtain colloidal solution stabilized within CdS nanoparticles, has been achieved.
As a result, by means of strong film formation, the PP-g-PEG comb-type amphiphilic copolymers with good mechanical properties stabilized the CdS nanoparticles as successful as they did the metal nanoparticles. The PEG hydrophilic chains form stable bonds with the semiconductor nanoparticles preserving the characteris-tics of these materials. According to the HRTEM images, CdS quantum dots in the polymer micelles were below 10 nm size and this was supported by their optical characterization. The results show that PP-g-PEG amphiphilic comb-type graft copolymer is a fine colloi-dal stabilizer and host for nanosized particle formation. Therefore, the organic–inorganic PP-g-PEG amphiphilic comb-type graft copolymer CdS quantum dot composite material can be regarded as the promising material for the industrial applications because of its strong film forming qualification.
Acknowledgments This work was supported by; both the Bulent Ecevit University Research Fund (#BEU-2012-10-03-13) and TUBITAK (Grant # 211T016).
References
Alivisatos AP (1996) Semiconductor clusters, nanocrystals, and quantum dots. Science 271:5251
Balcı M, Allı A, Hazer B, Gu¨ven O, Cavicchi K, C¸ akmak M (2010) Synthesis and characterization of novel comb-type amphiphilic graft copolymers containing polypropylene and polyethylene glycol. Polym Bull 64:691–705 Biju V, Itoh T, Anas A, Sujith A (2008) Semiconductor quantum
dots and metal nanoparticles: synthesis, optical properties, and biological applications. Anal Bioanal Chem 391:2469–2495 Brush L (1986) Electronic wave functions in semiconductor
clusters: experiment and theory. J Phys Chem 90:2555– 2560
Cao L, Miao Y, Zhang Z, Xie S, Yang G (2005) Exciton interactions in nanocrystal aggregates in reverse micelle. J Chem Phys 123:024702
Chestnoy N, Harris TD, Hull R, Brush LE (1986) Luminescence and photophysics of cadmium sulfide semiconductor clusters: the nature of the emitting electronic state. J Phys Chem 90:3393–3399
Chiu JJ, Kim BJ, Kramer EJ, Pine DJ (2005) Control of nano-particle location in block copolymers. J Am Chem Soc 127:5036
Dong H, Hinestroza JP (2009) Metal nanoparticles on natural cellulose fibers: electrostatic assembly and in situ synthe-sis. ACS Appl Mater Interfaces 1:797–803
Erciyes AT, Erim M, Hazer B, Yag˘cı Y (1992) Synthesis of polyacrylamide flocculants with PEG segments by redox polymerization. Angew Macromol Chem 200:163–171 Farmer SC, Patent TE (2001) Photoluminescent polymer/quantum
dot composite nanoparticles. Chem Mater 13:3920–3926 Ferrer JC, Castillo SA, Alonso JL, Fernandez de Avila S,
Mallavia R (2009) Synthesis and characterization of CdS nanocrystals stabilized in polyvinyl alcohol–sodium poly-phosphate. Mater Lett 63:638–640
Firth AV, Haggata SW, Khanna PK, Williams SJ, Allen JW, Magennis SW, Samuel IDW, Cole-Hamilton DJ (2004) Production and luminescent properties of CdSe and CdS nanoparticle–polymer composites. J Lumin 109:163–172 Hazer B (1995) Grafting on polybutadiene with macro or
ma-cromonomer initiator containing poly(ethylene glycol) units. Macromol Chem Phys 196:1945–1952
Hazer B (2010) Amphiphilic poly(3-hydroxy alkanoate)s: potential candidates for medical applications. Int J Polym Sci, Article Number: 423460. doi:10.1155/2010/423460
Hazer DB, Hazer B (2011) The effect of gold clusters on the autoxidation of poly(3-hydroxy 10-undecenoate-co-3-hydroxy octanoate) and tissue response evaluation. J Polym Res 18: 251–262
Hazer DB, Hazer B, Dinc¸er N (2011) Soft tissue response to the presence of polypropylene-g-poly(ethylene glycol) comb-type graft copolymers containing gold nanoparticles. J Biomed Biotechnol. doi:10.1155/2011/956169
Hazer DB, Kilicay E, Hazer B (2012a) Poly(3-hydroxyalkano-ate)s: diversification and biomedical applications. A state of the art review. Mater Sci Eng C 32:637–647
Hazer DB, Mut M, Dinc¸er N, Sarıbas¸ Z, Hazer B, O¨ zgen T (2012b) The efficacy of silver-embedded polypropylene-grafted polyethylene glycol-coated ventricular catheters on prevention of shunt catheter infection in rats. Childs Nerve Syst. doi:10.1007/s00381-012-1729-5
Heinglein A (1989) Small-particle research: physicochemical properties of extremely small colloidal metal and semi-conductor particles. Chem Rev 89:1861–1873
Herron N, Wang Y, Eckert YH (1990) Synthesis and charac-terization of surface-capped, size-quantized CdS clusters. Chemical control of cluster size. J Am Chem Soc 112: 1322–1326
Jamali S, Iranizad ES, Shayesteh SF (2007) Synthesis, optical and structural characterization of CdS nanoparticles. Int J Nanosci Nanotechnol 3(1):53–62
Kalaycı O¨ A, Co¨mert FB, Hazer B, Atalay T, Cavicchi K, C¸ak-mak M (2010) Synthesis, characterization, and antibacterial activity of metal nanoparticles embedded into amphiphilic comb-type graft copolymers. Polym Bull 65:215–226 Kim BJ, Bang J, Hawker CJ, Kramer EJ (2006) Effect chain
density on the location of polymer-modified gold nano-particles in a block copolymer template. Macromolecules 39:4108–4114
Kittel C (1986) Introduction to solid state physics. Wiley, New York
Kumbhakar P, Singh D, Tiwary CS, Mitra AK (2008) Chemical synthesis and visible photoluminescence emission from monodispersed ZnO nanoparticles. Chalcogenide Lett 5:387–394
amphiphilic polymers. Mater Sci Eng C 6:155
Mayer ABR (2001) Colloidal metal nanoparticles dispersed in amphiphilic polymers. Polym Adv Technol 12:96–106 Moffitt M, Vali H, Eisenberg A (1998) Spherical assemblies of
semiconductor nanoparticles in water-soluble block copolymer aggregates. Chem Mater 10:1021–1028 Moore DE, Patel K (2001) Q-CdS photoluminescence activation
on Zn?2and Cd?2salt introduction. Langmuir 17:2541– 2544
Nabok A (2005) Organic inorganic nanostructures. Artech House Inc., Boston
Nicolais L, Carotenuto G (2005) Metal polymer nanocompos-ites. Wiley, Hoboken
Oren R, Liang Z, Barnard SJ, Warren SC, Wiesner U, Huck WTS (2009) Organization of nanoparticles in polymer brushes. J Am Chem Soc 131:1670–1671
Pandey S, Pandey AC (2009) Optical properties of hybrid composites based on highly luminescent CdS and ZnS nanocrystals in different polymer matrices. Transport and optical properties of nanomaterials. AIP Conf Proc 1147:216–222
Peretz S, Anghel DF, Theodor E, Stanciu G, Stoian C, Zgherea G, Florea-Spiroiu M (2011) Improving the properties of CdS nanoparticles by adding polymers. Part Sci Technol 29:229–241
Pesika NS, Stebe KJ, Searson PC (2003) Determination of the particle size distribution of quantum nanocrystals from absorbance spectra. Adv Mater 15:1289–1291
Petit C, Lixon P, Pileni MP (1990) Synthesis of cadmium sulfide in situ in reverse micelles. 2. Influence of the interface on the growth of the particles. J Phys Chem 94:1598–1603 Pomogailo AD (2000) Hybrid polymer–inorganic
nanocom-posites. Russ Chem Rev 69:53–80
Qi L, Collfen H, Antonietti M (2000) Synthesis and character-ization of CdS nanoparticles stabilized by double-hydro-philic block copolymers. Nano Lett 1(2):61–65
Spanhel L, Haase M, Weller H, Henglein A (1987) Photo-chemistry of colloidal semiconductors. 20. Surface
polymer. Nanotechnology 15:240–244
Tang H, Yan M, Zhang H, Xia M, Yang D (2005) Preparation and characterization of water soluble CdS nanocrystals by surface modification of ethylene diamine. Mater Lett 59:1024–1027
Tessler N, Medvedev V, Kazes M, Kan SH, Banin U (2002) Efficient near-infrared polymer nanocrystal light-emitting diodes. Science 295:1506
Thakur P, Joshi SS, Kapoor S, Mukherjee T (2009) Fluores-cence behavior of cysteine-mediated Ag@CdS nanocol-loids. Langmuir 25:6377–6384
Tomczak N, Janczewski D, Han M, Vansco GJ (2009) Designer polymer-quantum dot architectures. Prog Polym Sci 34: 393–430
Trindade T, O’Brien P, Pickett NL (2001) Nanocrystalline semiconductors: synthesis, properties and perspectives. Chem Mater 13:3843–3858
Tura C, Coombs N, Dag O (2005) One-pot synthesis of CdS nanoparticles in the channels of mesostructured silica films and monoliths. Chem Mater 17:573–579
Underhill RS, Liu G (2000) Triblock nanospheres and their use as templates for inorganic nanoparticle preparation. Chem Mater 12:2082
Wang J, Blau W (2009) Inorganic and hybrid nanostructures for optical limiting. Pure Appl Opt 11:024001
Yeh SW, Wei KH, Sun YS, Jeng US, Liang KS (2003) Mor-phological transformation of PS-b-PEO diblock copolymer by selectively dispersed colloidal CdS quantum dots. Macromolecules 36:7903–7907
Yıldız U, Hazer B, Tauer K (2012) Tailoring polymer archi-tectures with macromonomer azo initiators. Polym Chem 3:1107–1118
Zhao H, Douglas EP (2002) Preparation of corona-embedded CdS nanoparticles. Chem Mater 14:1418–1423
Zhao H, Douglas EP, Benjamin SH, Schanze KS (2001) Preparation of CdS nanoparticles in salt induced block copolymer micelles. Langmuir 17:8428–8433
