JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Figure 9 shows the typical open-aperture Z-scan results for
the PCBF-NH2 and the MWNT-PCBF, respectively. Unlike
PCBF-NH2, which only displayed weak optical limiting
responses at 532 nm, Z-scan for MWNT-PCBF exhibited a
much broader reduction in transmission at both 532 and
1064 nm, indicating a prominent broadband optical limiting
response. The depth of reduction usually changes along with
the variations of the on-focus intensity. At the same on-focus
intensity, a covalent bonding between MWNTs and PCBF
resulted in the further decrease of the minimal normalized
transmittance from 85.3% for PCBF-NH2 to 49.7% for
MWNT-PCBF at 532 nm. Table 1 summarizes the linear and
NLO coefficients of the samples. The NLO extinction coeffi-
cient of MWNT-PCBF is 43 times that of PCBF-NH2 at
532 nm. This value must contain the effects from light
scattering, nonlinear absorption, and saturated absorption.
However, we currently do not have suitable experimental
setup to quantitatively analyze the contributions of the scat-
tering and nonlinear absorption to optical limiting.
excitation of 375 nm laser, compared with PCBF-NH2, the
photoluminescence of MWNT-PCBF was significantly
quenched probably due to the electron-transfer process from
polymer to 1MWNTs*. Covalent attachment of PCBF onto
MWNTs led to a 0.3 eV red-shift of the N1s XPS peak at
399.7 eV assigning to N in the unreacted NH2 moieties in the
resulting copolymer structure, and an appearance of
new peak at 402 eV corresponding to N bound to the
carbonyl C (i.e., NHAC¼¼O). In contrast to MWNT-COOH, the
D- and G-bands of MWNT-PCBF are shifted to the high wave-
numbers by Dk ¼ 12 and 8 cmꢀ1, respectively. MWNT-PCBF
presents much better optical limiting performance than
PCBF-NH2 at both 532 and 1064 nm. Microplasmas- and/or
microbubbles-induced nonlinear scattering is considered as
the main mechanism for optical limiting.
The authors are grateful for the financial support of the
National Natural Science Foundation of China (20876046),
the Ministry of Education of China (309013), the Funda-
mental Research Funds for the Central Universities, the
Shanghai Municipal Educational Commission for the Shu-
guang fellowship (08GG10), and the Shanghai Eastern
Scholarship.
Figure 10, in which the normalized transmission and the
corresponding scattering were plotted as functions of input
energy density (J cmꢀ2), presents the optical limiting behav-
ior of MWNT-PCBF and PCBF-NH2. It can be clearly seen that
MWNT-PCBF presents much better optical limiting perform-
ance than PCBF-NH2. The MWNT-PCBF manifests the remark-
able broadband optical limiting with the comparable limiting
performance for both 532 and 1064 nm pulses. A lot of
theoretical and experimental results have demonstrated that
the optical limiting responses of CNT suspensions are shown
to be dominated by nonlinear scattering as a result of
thermally induced solvent-bubble formation and sublimation
of the nanotubes, whereas the solubilized CNTs optically
limit through nonlinear absorption mechanism and exhibit
significant solution-concentration-dependent optical limiting
responses.4(a) Therefore, we believed that the thermally
induced nonlinear scattering dominated the optical limiting
for ns pulses at 532 and 1064 nm. As shown in Figure 10,
the big difference for the scattered intensity at 532 and
1064 nm is mainly due to the wavelength dependent
response of the Si photodiode that we used to measure the
scattered light. The response of the Si photodiode at 532 nm
is much larger than that at 1064 nm. Although the nonlinear
scattering dominates the optical limiting observed from the
MWNT-PCBF dispersions, we could not rule out the possible
minor contributions from nonlinear absorption or electronic
absorption.
REFERENCES AND NOTES
1 Tasis, D.; Tagmatarchis, N.; Bianco, A.; Prato, M. Chem Rev
2006, 106, 1106–1136.
2 (a) Bahr, J. L.; Tour, J. M. J Mater Chem 2002, 12, 1952–1958;
(b) Zhang, B.; Chen, Y.; Wang, J.; Blau, W. J.; Zhuang, X. D.;
He, N. Carbon 2010, 48, 1738–1742; (c) Yan, Y.; Zhao, S.; Cui,
J.; Yang, S. J Polym Sci A: Polym Chem 2009, 47, 6135–6144;
(d) Jeon, I. Y.; Tan, L. S.; Baek, J. B. J Polym Sci A: Polym
Chem 2008, 46, 3471–3481; (e) Li, S.; Chen, H.; Bi, W.; Zhou, J.;
Wang, Y.; Li, J.; Cheng, W.; Li, M.; Li, L.; Tang, T. J Polym Sci
A: Polym Chem 2007, 45, 5459–5469; (f) Hong, C. Y.; You, Y.
Z.; Pan, C. Y. J Polym Sci A: Polym Chem 2006, 44, 2419–2427;
(g) Pei, X.; Liu, W.; Hao, J. J Polym Sci A: Polym Chem 2008,
46, 3014–3023; (h) Shanmugharaj, A. M.; Bae, J. H.; Nayak, R.
R.; Ryu, S. H. J Polym Sci A: Polym Chem 2007, 45, 460–470;
(i) Narain, R.; Housni, A.; Lane, L. J Polym Sci A: Polym Chem
2006, 44, 6558–6568.
3 (a) Sano, M.; Kamino, A.; Okamura, J.; Shinkai, S. Langmuir
2001, 17, 5125–5128; (b) Hill, D. E.; Lin, Y.; Rao, A. M.; Allard, L.
F.; Sun, Y. Macromolecules 2002, 35, 9466–9471; (c) Kumar, N.
A.; Kim, S. H.; Cho, B. G.; Lim, K. T.; Jeong, Y. T. Colloid Polym
Sci 2009, 287, 97–102; (d) Baskaran, D.; Sakellariou, G.; Mays,
J. W.; Bratcher, M. S.
J Nanosci Nanotechnol 2007, 7,
1560–1567; (e) Liu, Y. X.; Du, Z. J.; Li, Y.; Zhang, C.; Li, H. Q.
Chin J Chem 2006, 24, 563–568.
CONCLUSIONS
4 (a) Chen, Y.; Lin, Y.; Liu, Y.; Doyle, J.; He, N.; Zhuang, X.; Bai,
J.; Blau, W. J. J Nanosci Nanotechnol 2007, 7, 1268–1283; (b)
Wang, J.; Chen, Y.; Blau, W. J. J Mater Chem 2009, 19,
7425–7443.
Polymer grafting to CNTs produces continuous advances and
novel functional materials with interesting applications due
to their great promise in photonics and optoelectronics. We
designed and synthesized a new soluble conjugated polymer
covalently grafted MWNTs hybrid material, MWNT-PCBF, by
reaction of the surface-bound acryl chloride groups in
MWNT-COCl with PCBF-NH2. The wt % of MWNTs in the
resulting polymer is approximately calculated as 7.3%. Upon
5 (a) Riggs, J. E.; Walker, D. B.; Carroll, D. L.; Sun, Y. P. J Phys
Chem B 2000, 104, 7071–7076; (b) Menna, E.; Scorrano, G.;
Maggini, M.; Cavallaro, M.; Della, N. F.; Battagliarin, M.; Bozio,
R.; Fantinel, F.; Meneghetti, M. Arkivoc 2003, 12, 64–73; (c) Li,
108
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA