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Quantum-dot-embedded polymeric fiber films with photoluminescence and superhydrophobicity
Materials Letters 99 (2013) 54–56
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Quantum-dot-embedded polymeric fiber films with photoluminescence and superhydrophobicity Lin Zhu, Shengyang Yang, Jing Wang, Cai-Feng Wang n, Li Chen, Su Chen n State Key Laboratory of Materials-Oriented Chemical Engineering and College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 December 2011 Accepted 24 March 2012 Available online 21 February 2013
We report the fabrication of poly(methylmethacrylate) (PMMA)/CdTe composite fiber films with bifunctional photoluminescent and superhydrophobic properties via an electrospinning route. Initially, CdTe quantum dots (QDs) were prepared via an aqueous synthetic approach. Subsequently, the assembly of as-prepared CdTe QDs and dodecylamine at water/chloroform interfaces induced a phase transfer of QDs from the aqueous phase into the chloroform phase. Finally, direct blending of the chloroform solution of QDs with a polymer host PMMA and then electrospinning yielded uniform fibrous films. The as-prepared film is composed of microscale fibers with bead-on-string architecture and submicroscale pore structure, which exhibits superhydrophobicity with a water contact angle of 151.21 and a sliding angle of 3.81. The fluorescence was thoroughly discussed by photoluminescence measurements and confocal microscopy images. This simple and versatile method to achieve bifunctional composite fiber films may find potential applications in diverse fields. & 2013 Elsevier B.V. All rights reserved.
Keywords: Superhydrophobicity Luminescence Semiconductor quantum dot Electrospinning Polymeric composites
1. Introduction Polymer-quantum dot (QD) composites with unique optical properties have attracted great fundamental and practical interests owing to their appealing applications such as in optoelectronic devices [1], nonlinear optical devices [2], and biological fields [3]. Up to now, a variety of elegant strategies have been developed to construct polymer-QD composites with multifunctional properties [4–7]. Among those reported, there are sparse examples on the fabrication of fluorescent materials with self-cleaning properties, and hence efficient pathways are highly needed to achieve such bifunctional materials. It is well known that the surface with a water contact angle (WCA) higher than 1501 and a sliding angle (SA) less than 5–101, referred to as a superhydrophobic surface, is of great promise for self-cleaning purpose [8–10]. We have previously developed a series of superhydrophobic surfaces demonstrating fluorescence by incorporating QDs into polymer films via an assembly process [11,12]. To further extend this interesting regime, we choose a versatile and cost-effective approach, the electrospinning technique [13–15], to prepare polymeric films composed of nanometer-/micrometersized ultrathin fibers. The electrospinning technique has been developed to fabricate superhydrophobic surfaces [16,17], and also some fluorescent QD-embedded polymeric fibers [18]. Thus, it may
n
Corresponding authors. Tel./fax: þ86 25 83172258. E-mail addresses: [email protected] (C.-F. Wang), [email protected] (S. Chen). 0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2012.03.118
direct the formation of fibrous films with multifunctional properties. Herein, we describe the preparation of poly(methylmethacrylate) (PMMA)/CdTe hybrid fiber films simultaneously exhibiting photoluminescence and superhydrophobicity via the electrospinning process.
2. Material and methods Materials: Poly(methylmethacrylate) was prepared via free radical polymerization at 75 1C for 4 h according to a literature method [19]. Cadmium chloride (CdCl2 2.5H2O), N-acetyl-Lcysteine (NAC), tellurium powder (Te), sodium hydroxide (NaOH), sodium borohydride (NaBH4), dodecylamine (DDA) and chloroform (CHCl3) were purchased from standard sources and used as received. Synthesis of water-soluble CdTe QDs: Water-soluble NAC-capped CdTe QDs were synthesized according to our previous work [20]. Typically, the CdTe precursor solution was prepared by the addition of fresh oxygen-free NaHTe solution to a N2-saturated CdCl2 solution at pH¼10.3 in the presence of NAC as a stabilizer. The molar ratio of Cd2þ /NAC/HTe was set as 1:1.5:0.5 ([Cd2 þ ]¼15 mmol/L). Under microwave irradiation (900 W; 95 1C), a series of high-quality negative-ligand-charged CdTe QDs were prepared by controlling microwave irradiation time: 30 min (green), 1 h (yellow) and 3 h (red). To purify the as-synthesized CdTe QDs, the samples were precipitated with absolute ethanol, further isolated by centrifugation, and then redispersed into purified water for use.
L. Zhu et al. / Materials Letters 99 (2013) 54–56
55
CdTe CdTe
H2O CHCl3 N
CdTe
N+ N
CdTe
CdTe
CdTe
CdTe
N+
N
N+
CdTe
N+
N+ CdTe
CdTe CdTe
O CdTe
CdTeS
O
OH
N
NH2
NH2
Fig. 1. Schematic representation of the phase transfer of NAC-CdTe QDs from aqueous phase to CHCl3 phase via an interfacial assembly.
1.0
Intensity (a.u.)
0.8
0.6
0.4
0.2
0.0
500
550
600 Wavelength (nm)
650
700
Fig. 3. Normalized PL spectra of PMMA/CdTe QDs composite fibers in the presence of differently sized CdTe QDs: 2.8 nm (green curve, lem ¼ 545 nm), 3.2 nm (yellow curve, lem ¼ 560 nm), and 3.5 nm (red curve, lem ¼605 nm). Inset: fluorescent images of the corresponding samples under irradiation with a 365 nm UV light. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Fig. 2. SEM images of an electrospun PMMA/CdTe fiber film. Insets in panels a and b show the water contact angle and sliding angle of a 5 mL water droplet on the film surface, respectively.
Synthesis of chloroform-soluble CdTe/DDA hybrids: The chloroformsoluble CdTe/DDA hybrids were prepared as follows. First, we used 2 M NAC solution to tune the pH of the as-prepared NAC-capped CdTe QDs solution to about 6.5. And then, 50 mL of this CdTe solution and 50 mL chloroform containing 0.927 g DDA were poured into a 200 mL beaker to form an oil–water interface. After being sealed and maintained at room temperature for a couple of days, the CdTe QDs were slowly transferred from the water phase into the chloroform phase. Finally, the CdTe/DDA hybrids in CHCl3 solution were collected for further experiments. Fabrication of electrospun PMMA/CdTe fiber films: Initially, 0.3 g PMMA was thoroughly dissolved in 9.7 g CdTe/DDA CHCl3 solution to form a homogeneous PMMA/CdTe hybrid solution. Subsequently, the solution was electrospun at constant conditions: a flow rate of 2.25 mL/h, a working distance of 18 cm, and an applied voltage of 20 kV. The electrospun apparatus was equipped with a string, a 20 gauge stainless steel needle, a high-voltage power, and an aluminum foil collector mounted on a steel stand. Typical experiments were carried out at room temperature under 80% humidity. Characterizations: The morphologies of the electrospun fibrous films were characterized by scanning electron microscopy (SEM;
QUANTA 200) at 20.0 kV. Fluorescence microscopy was performed on a laser confocal scanning microscope (Zeiss LSM710) equipped with a high-resolution charge coupled device (CCD) camera, which was connected to a frame grabber and a personal computer for image processing. WCA was measured on a drop shape analysis ¨ system (KRUSS DSA100, Germany) using a 5 mL water droplet at ambient conditions. Photoluminescence (PL) spectra were obtained on a Varian Cary Eclipse spectrophotometer equipped with a Xe lamp at room temperature. The excitation wavelength was set at 350 nm, tube voltage was 600 V, the excitation and emission slits were both 5 nm.
3. Results and discussion NAC-capped CdTe QDs were initially prepared via an aqueous synthetic strategy. To render them good compatibility with polymeric materials, we further tailored these water-soluble QDs with DDA, as shown in Fig. 1. The assembly of NAC-capped CdTe QDs and DDA occurred at water/chloroform interfaces due to electrostatic interactions between the positively charged amino group of DDA and the negatively charged ligand on the surface of QDs, resulting in a phase transfer of QDs from the aqueous phase into the chloroform phase. Subsequently, an optimal amount of PMMA was introduced
56
L. Zhu et al. / Materials Letters 99 (2013) 54–56
Fig. 4. Laser confocal microscopy images of the electrospun PMMA/CdTe fiber films in the presence of differently sized CdTe QDs: (a) 2.5 nm, (b) 3.2 nm, and (c) 3.6 nm. The excitation wavelength is 405 nm. Scale bar: 50 mm.
into the chloroform solution of CdTe QDs. The resulting PMMA/CdTe composite solution was ultimately electrospun into fibers that were collected on the surface of an aluminum foil mounted on a steel stand to obtain a uniform film. Fig. 2 shows SEM images of the as-prepared PMMA/CdTe electrospun film, demonstrating an obvious fiber structure with the average diameter of ca. 2 mm. A bead-on-string architecture is also observed, which is beneficial to enhance the surface roughness toward good hydrophobicity and stability of the film (Fig. 2a–c) [17]. Interestingly, densely packed submicropores with the diameters of 100–500 nm were formed on the surface of the fibers, as shown in Fig. 2c and d, which may highly improve the hydrophobicity of the film [19,21]. Preliminary studies show that increasing humidity would increase the pore formation, suggesting a ‘‘breath figure’’ mechanism may play a key role in the formation of porous fibers [19,21,22]. During the electrospinning process, the evaporation of chloroform in highly humid conditions can cause a sharp decrease of surrounding temperature and further induce immediate condensation of water vapor onto the polymer. After the condensed water droplets evaporate entirely, the submicroscale porous structures are eventually gained on the surface of the fibers. The surface wettability of the fibrous films was evaluated. As shown in insets in Fig. 2a and b, the WCA of a 5 mL water droplet on the PMMA/CdTe fiber film is 151.21, and the SA is 3.81, revealing the superhydrophobicity of the film. We noted the hydrophobicity of the film is significantly enhanced compared with that of the control film sample obtained by the spin-coating method (72.81). The hierarchical micro-/submicro-structures from the combination of microfibers and submicropores should be the dominant factor to enhance hydrophobicity of the electrospun fiber film. Fig. 3 shows the PL spectra of PMMA/CdTe composite films embedded with differently sized CdTe QDs. In the presence of CdTe QDs with mean sizes of 2.8, 3.2, and 3.5 nm, the fibrous films display size-dependent fluorescence emission at 545, 560 and 605 nm, respectively, corresponding to green, yellow, and red emission as shown in fluorescent images (inset in Fig. 3). Moreover, we measured PL spectra of different positions on the composite nanofiber films, finding no obvious changes in the corresponding PL intensity. This result implies that the CdTe QDs are well dispersed in the as-prepared PMMA/CdTe composite films, which can be further confirmed by laser confocal fluorescence micrographs. As shown in Fig. 4, uniform and strong fluorescence emission is observed through the whole samples, suggesting that the electrospinning process did not cause visible aggregation of QDs with altered optical properties due to the good compatibility between CdTe QDs and polymeric matrices.
4. Conclusion In summary, we have explored an available route to achieve porous PMMA/CdTe QD fiber films exhibiting superhydrophobicity and fluorescence. The phase transfer of CdTe QDs from aqueous phase into the chloroform phase was achieved under the direction of DDA, followed by the addition of PMMA and then electrospinning, resulting in uniform fluorescent films with self-cleaning properties. This relatively simple method presented here contributes a promising way to prepare high-performance QD/polymer composite films with multi-function that might be useful in various applications such as in the optoelectronic field.
Acknowledgment This work was supported by the National High Technology Research and Development Program of China (863 Program) (2012AA030313) National Natural Science Foundation of China (21076103, 21006046 and 21176122), the Specialized Research Fund for the Doctoral Program of Higher Education of China (20093221120002), China Postdoctoral Science Foundation (200904501087), and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). References [1] Coe S, Woo WK, Bawendi M, Bulovic V. Nature 2002;420:800–3. [2] Mamedov AA, Belov A, Giersig M, Mamedova NN, Kotov NA. J Am Chem Soc 2001;123:7738–9. [3] Bruchez M, Moronne M, Gin P, Weiss S, Alivisatos AP. Science 1998;281:2013–6. [4] Zhang H, Cui ZC, Wang Y, Zhai K, Ji XL, Lv CL, et al. Adv Mater 2003;15:777–80. [5] Lu XF, Zhao YY, Wang C. Adv Mater 2005;17:2485–8. [6] Kotov NA, De´ka´ny I, Fendler JH. J Phys Chem 1995;99:13065–9. [7] Yang SY, Wang CF, Chen S. J Am Chem Soc 2011;133:8412–5. [8] Barthlott W, Neinhuis C. Planta 1997;202:1–8. [9] Hozumi A, Kim B, McCarthy TJ. Langmuir 2009;25:6834–40. [10] Sun TL, Feng L, Gao XF, Jiang L. Acc Chem Res 2005;38:644–52. [11] Hou LR, Wang CF, Chen L, Chen S. J Mater Chem 2010;20:3863–8. [12] Yang SY, Wang LF, Wang CF, Chen L, Chen S. Langmuir 2010;26:18454–8. [13] Doshi J, Srinivasan G, Reneker DH. Polym News 1995;20:206–13. [14] Wang SG, Li YX, Wang YZ, Yang QB, Wei W. Mater Lett 2007;61:4674–8. [15] Li D, Xia YN. Adv Mater 2004;16:1151–70. [16] Acatay K, Simsek E, Ow-Yang C, Menceloglu YZ. Angew Chem Int Ed 2004;43:5210–3. [17] Wang LF, Yang SY, Wang J, Wang CF, Chen L. Mater Lett 2011;65:869–72. [18] Li MJ, Zhang JH, Zhang H, Liu YF, Wang ChL X, et al. Adv Funct Mater 2007;17:3650–6. [19] Wang J, Wang CF, Shen HX, Chen S. Chem Commun 2010;46:7376–8. [20] Guo X, Wang CF, Fang Y, Chen L, Chen S. J Mater Chem 2011;21:1124–9. [21] Wang J, Shen HX, Wang CF, Chen S. J Mater Chem 2012;22:4089–96. [22] Megelski S, Stephen JS, Chase DB, Rabolt JF. Macromolecules 2002;35:8456–66.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Quantum-dot-embedded polymeric fiber films with photoluminescence and superhydrophobicity Lin Zhu, Shengyang Yang, Jing Wang, Cai-Feng Wang n, Li Chen, Su Chen n State Key Laboratory of Materials-Oriented Chemical Engineering and College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 December 2011 Accepted 24 March 2012 Available online 21 February 2013
We report the fabrication of poly(methylmethacrylate) (PMMA)/CdTe composite fiber films with bifunctional photoluminescent and superhydrophobic properties via an electrospinning route. Initially, CdTe quantum dots (QDs) were prepared via an aqueous synthetic approach. Subsequently, the assembly of as-prepared CdTe QDs and dodecylamine at water/chloroform interfaces induced a phase transfer of QDs from the aqueous phase into the chloroform phase. Finally, direct blending of the chloroform solution of QDs with a polymer host PMMA and then electrospinning yielded uniform fibrous films. The as-prepared film is composed of microscale fibers with bead-on-string architecture and submicroscale pore structure, which exhibits superhydrophobicity with a water contact angle of 151.21 and a sliding angle of 3.81. The fluorescence was thoroughly discussed by photoluminescence measurements and confocal microscopy images. This simple and versatile method to achieve bifunctional composite fiber films may find potential applications in diverse fields. & 2013 Elsevier B.V. All rights reserved.
Keywords: Superhydrophobicity Luminescence Semiconductor quantum dot Electrospinning Polymeric composites
1. Introduction Polymer-quantum dot (QD) composites with unique optical properties have attracted great fundamental and practical interests owing to their appealing applications such as in optoelectronic devices [1], nonlinear optical devices [2], and biological fields [3]. Up to now, a variety of elegant strategies have been developed to construct polymer-QD composites with multifunctional properties [4–7]. Among those reported, there are sparse examples on the fabrication of fluorescent materials with self-cleaning properties, and hence efficient pathways are highly needed to achieve such bifunctional materials. It is well known that the surface with a water contact angle (WCA) higher than 1501 and a sliding angle (SA) less than 5–101, referred to as a superhydrophobic surface, is of great promise for self-cleaning purpose [8–10]. We have previously developed a series of superhydrophobic surfaces demonstrating fluorescence by incorporating QDs into polymer films via an assembly process [11,12]. To further extend this interesting regime, we choose a versatile and cost-effective approach, the electrospinning technique [13–15], to prepare polymeric films composed of nanometer-/micrometersized ultrathin fibers. The electrospinning technique has been developed to fabricate superhydrophobic surfaces [16,17], and also some fluorescent QD-embedded polymeric fibers [18]. Thus, it may
n
Corresponding authors. Tel./fax: þ86 25 83172258. E-mail addresses: [email protected] (C.-F. Wang), [email protected] (S. Chen). 0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2012.03.118
direct the formation of fibrous films with multifunctional properties. Herein, we describe the preparation of poly(methylmethacrylate) (PMMA)/CdTe hybrid fiber films simultaneously exhibiting photoluminescence and superhydrophobicity via the electrospinning process.
2. Material and methods Materials: Poly(methylmethacrylate) was prepared via free radical polymerization at 75 1C for 4 h according to a literature method [19]. Cadmium chloride (CdCl2 2.5H2O), N-acetyl-Lcysteine (NAC), tellurium powder (Te), sodium hydroxide (NaOH), sodium borohydride (NaBH4), dodecylamine (DDA) and chloroform (CHCl3) were purchased from standard sources and used as received. Synthesis of water-soluble CdTe QDs: Water-soluble NAC-capped CdTe QDs were synthesized according to our previous work [20]. Typically, the CdTe precursor solution was prepared by the addition of fresh oxygen-free NaHTe solution to a N2-saturated CdCl2 solution at pH¼10.3 in the presence of NAC as a stabilizer. The molar ratio of Cd2þ /NAC/HTe was set as 1:1.5:0.5 ([Cd2 þ ]¼15 mmol/L). Under microwave irradiation (900 W; 95 1C), a series of high-quality negative-ligand-charged CdTe QDs were prepared by controlling microwave irradiation time: 30 min (green), 1 h (yellow) and 3 h (red). To purify the as-synthesized CdTe QDs, the samples were precipitated with absolute ethanol, further isolated by centrifugation, and then redispersed into purified water for use.
L. Zhu et al. / Materials Letters 99 (2013) 54–56
55
CdTe CdTe
H2O CHCl3 N
CdTe
N+ N
CdTe
CdTe
CdTe
CdTe
N+
N
N+
CdTe
N+
N+ CdTe
CdTe CdTe
O CdTe
CdTeS
O
OH
N
NH2
NH2
Fig. 1. Schematic representation of the phase transfer of NAC-CdTe QDs from aqueous phase to CHCl3 phase via an interfacial assembly.
1.0
Intensity (a.u.)
0.8
0.6
0.4
0.2
0.0
500
550
600 Wavelength (nm)
650
700
Fig. 3. Normalized PL spectra of PMMA/CdTe QDs composite fibers in the presence of differently sized CdTe QDs: 2.8 nm (green curve, lem ¼ 545 nm), 3.2 nm (yellow curve, lem ¼ 560 nm), and 3.5 nm (red curve, lem ¼605 nm). Inset: fluorescent images of the corresponding samples under irradiation with a 365 nm UV light. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Fig. 2. SEM images of an electrospun PMMA/CdTe fiber film. Insets in panels a and b show the water contact angle and sliding angle of a 5 mL water droplet on the film surface, respectively.
Synthesis of chloroform-soluble CdTe/DDA hybrids: The chloroformsoluble CdTe/DDA hybrids were prepared as follows. First, we used 2 M NAC solution to tune the pH of the as-prepared NAC-capped CdTe QDs solution to about 6.5. And then, 50 mL of this CdTe solution and 50 mL chloroform containing 0.927 g DDA were poured into a 200 mL beaker to form an oil–water interface. After being sealed and maintained at room temperature for a couple of days, the CdTe QDs were slowly transferred from the water phase into the chloroform phase. Finally, the CdTe/DDA hybrids in CHCl3 solution were collected for further experiments. Fabrication of electrospun PMMA/CdTe fiber films: Initially, 0.3 g PMMA was thoroughly dissolved in 9.7 g CdTe/DDA CHCl3 solution to form a homogeneous PMMA/CdTe hybrid solution. Subsequently, the solution was electrospun at constant conditions: a flow rate of 2.25 mL/h, a working distance of 18 cm, and an applied voltage of 20 kV. The electrospun apparatus was equipped with a string, a 20 gauge stainless steel needle, a high-voltage power, and an aluminum foil collector mounted on a steel stand. Typical experiments were carried out at room temperature under 80% humidity. Characterizations: The morphologies of the electrospun fibrous films were characterized by scanning electron microscopy (SEM;
QUANTA 200) at 20.0 kV. Fluorescence microscopy was performed on a laser confocal scanning microscope (Zeiss LSM710) equipped with a high-resolution charge coupled device (CCD) camera, which was connected to a frame grabber and a personal computer for image processing. WCA was measured on a drop shape analysis ¨ system (KRUSS DSA100, Germany) using a 5 mL water droplet at ambient conditions. Photoluminescence (PL) spectra were obtained on a Varian Cary Eclipse spectrophotometer equipped with a Xe lamp at room temperature. The excitation wavelength was set at 350 nm, tube voltage was 600 V, the excitation and emission slits were both 5 nm.
3. Results and discussion NAC-capped CdTe QDs were initially prepared via an aqueous synthetic strategy. To render them good compatibility with polymeric materials, we further tailored these water-soluble QDs with DDA, as shown in Fig. 1. The assembly of NAC-capped CdTe QDs and DDA occurred at water/chloroform interfaces due to electrostatic interactions between the positively charged amino group of DDA and the negatively charged ligand on the surface of QDs, resulting in a phase transfer of QDs from the aqueous phase into the chloroform phase. Subsequently, an optimal amount of PMMA was introduced
56
L. Zhu et al. / Materials Letters 99 (2013) 54–56
Fig. 4. Laser confocal microscopy images of the electrospun PMMA/CdTe fiber films in the presence of differently sized CdTe QDs: (a) 2.5 nm, (b) 3.2 nm, and (c) 3.6 nm. The excitation wavelength is 405 nm. Scale bar: 50 mm.
into the chloroform solution of CdTe QDs. The resulting PMMA/CdTe composite solution was ultimately electrospun into fibers that were collected on the surface of an aluminum foil mounted on a steel stand to obtain a uniform film. Fig. 2 shows SEM images of the as-prepared PMMA/CdTe electrospun film, demonstrating an obvious fiber structure with the average diameter of ca. 2 mm. A bead-on-string architecture is also observed, which is beneficial to enhance the surface roughness toward good hydrophobicity and stability of the film (Fig. 2a–c) [17]. Interestingly, densely packed submicropores with the diameters of 100–500 nm were formed on the surface of the fibers, as shown in Fig. 2c and d, which may highly improve the hydrophobicity of the film [19,21]. Preliminary studies show that increasing humidity would increase the pore formation, suggesting a ‘‘breath figure’’ mechanism may play a key role in the formation of porous fibers [19,21,22]. During the electrospinning process, the evaporation of chloroform in highly humid conditions can cause a sharp decrease of surrounding temperature and further induce immediate condensation of water vapor onto the polymer. After the condensed water droplets evaporate entirely, the submicroscale porous structures are eventually gained on the surface of the fibers. The surface wettability of the fibrous films was evaluated. As shown in insets in Fig. 2a and b, the WCA of a 5 mL water droplet on the PMMA/CdTe fiber film is 151.21, and the SA is 3.81, revealing the superhydrophobicity of the film. We noted the hydrophobicity of the film is significantly enhanced compared with that of the control film sample obtained by the spin-coating method (72.81). The hierarchical micro-/submicro-structures from the combination of microfibers and submicropores should be the dominant factor to enhance hydrophobicity of the electrospun fiber film. Fig. 3 shows the PL spectra of PMMA/CdTe composite films embedded with differently sized CdTe QDs. In the presence of CdTe QDs with mean sizes of 2.8, 3.2, and 3.5 nm, the fibrous films display size-dependent fluorescence emission at 545, 560 and 605 nm, respectively, corresponding to green, yellow, and red emission as shown in fluorescent images (inset in Fig. 3). Moreover, we measured PL spectra of different positions on the composite nanofiber films, finding no obvious changes in the corresponding PL intensity. This result implies that the CdTe QDs are well dispersed in the as-prepared PMMA/CdTe composite films, which can be further confirmed by laser confocal fluorescence micrographs. As shown in Fig. 4, uniform and strong fluorescence emission is observed through the whole samples, suggesting that the electrospinning process did not cause visible aggregation of QDs with altered optical properties due to the good compatibility between CdTe QDs and polymeric matrices.
4. Conclusion In summary, we have explored an available route to achieve porous PMMA/CdTe QD fiber films exhibiting superhydrophobicity and fluorescence. The phase transfer of CdTe QDs from aqueous phase into the chloroform phase was achieved under the direction of DDA, followed by the addition of PMMA and then electrospinning, resulting in uniform fluorescent films with self-cleaning properties. This relatively simple method presented here contributes a promising way to prepare high-performance QD/polymer composite films with multi-function that might be useful in various applications such as in the optoelectronic field.
Acknowledgment This work was supported by the National High Technology Research and Development Program of China (863 Program) (2012AA030313) National Natural Science Foundation of China (21076103, 21006046 and 21176122), the Specialized Research Fund for the Doctoral Program of Higher Education of China (20093221120002), China Postdoctoral Science Foundation (200904501087), and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). References [1] Coe S, Woo WK, Bawendi M, Bulovic V. Nature 2002;420:800–3. [2] Mamedov AA, Belov A, Giersig M, Mamedova NN, Kotov NA. J Am Chem Soc 2001;123:7738–9. [3] Bruchez M, Moronne M, Gin P, Weiss S, Alivisatos AP. Science 1998;281:2013–6. [4] Zhang H, Cui ZC, Wang Y, Zhai K, Ji XL, Lv CL, et al. Adv Mater 2003;15:777–80. [5] Lu XF, Zhao YY, Wang C. Adv Mater 2005;17:2485–8. [6] Kotov NA, De´ka´ny I, Fendler JH. J Phys Chem 1995;99:13065–9. [7] Yang SY, Wang CF, Chen S. J Am Chem Soc 2011;133:8412–5. [8] Barthlott W, Neinhuis C. Planta 1997;202:1–8. [9] Hozumi A, Kim B, McCarthy TJ. Langmuir 2009;25:6834–40. [10] Sun TL, Feng L, Gao XF, Jiang L. Acc Chem Res 2005;38:644–52. [11] Hou LR, Wang CF, Chen L, Chen S. J Mater Chem 2010;20:3863–8. [12] Yang SY, Wang LF, Wang CF, Chen L, Chen S. Langmuir 2010;26:18454–8. [13] Doshi J, Srinivasan G, Reneker DH. Polym News 1995;20:206–13. [14] Wang SG, Li YX, Wang YZ, Yang QB, Wei W. Mater Lett 2007;61:4674–8. [15] Li D, Xia YN. Adv Mater 2004;16:1151–70. [16] Acatay K, Simsek E, Ow-Yang C, Menceloglu YZ. Angew Chem Int Ed 2004;43:5210–3. [17] Wang LF, Yang SY, Wang J, Wang CF, Chen L. Mater Lett 2011;65:869–72. [18] Li MJ, Zhang JH, Zhang H, Liu YF, Wang ChL X, et al. Adv Funct Mater 2007;17:3650–6. [19] Wang J, Wang CF, Shen HX, Chen S. Chem Commun 2010;46:7376–8. [20] Guo X, Wang CF, Fang Y, Chen L, Chen S. J Mater Chem 2011;21:1124–9. [21] Wang J, Shen HX, Wang CF, Chen S. J Mater Chem 2012;22:4089–96. [22] Megelski S, Stephen JS, Chase DB, Rabolt JF. Macromolecules 2002;35:8456–66.