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Materials Letters 62 (2008) 2088 – 2091 www.elsevier.com/locate/matlet
Temperature anomalies of DEA–CuCl4 and TEA–CoCl2Br2/PMMA nanocomposites M. Piasecki a , P. Bragiel a , S. Tkaczyk a , I.V. Kityk a,⁎, J. Ebothe b , V. Kapustianyk c , M. Partyka c , V. Rudyk c , K. Nouneh d , A.H. Reshak e a
e
Institute of Physics, J.Dlugosz University Czestochowa, Poland b Laboratoire LTME, Universite de Reims, France c Low Temperature Physics Department, Lviv University, Ukraine d Technological Center of Kyoto University, Japan Institute of Physical Biology-South Bohemia University, Institute of System Biology and Ecology-Academy of Sciences – Nove Hrady 37333, Czech Republic Received 18 September 2007; accepted 8 November 2007 Available online 17 November 2007
Abstract Phase transitions were studied for the new synthesized ferroic (NH2(C2H5)2CuCl4 (DEA–CuCl4) and (NH2(C2H5)4CoCl2Br2 (TEA–CoCl2Br2) nanocrystallites (NC) incorporated into polymer matrices. Comparison with the bulk crystals is performed. A giant temperature shift (from 305.1°C to 360.3°C) of onset temperature for TEA–CoCl2Br2 nanoparticles after their incorporation into the PMMA matrix was found and is substantially larger compared to the DEA–CuCl4. The DSC analysis shows that the temperature of phase transition is crucially dependent on the thermocycling and temperature rate. The principal role of the nano-sized effects is shown. © 2007 Elsevier B.V. All rights reserved. Keywords: Ferrolectrics; Phase transitions
The single crystals of diethylammonium tetrachlorcuprtate (NH2(C2H5)2CuCl4 (DEA-CuCl4) (space group P21/n a = 7.36A; b = 15.025A; c = 45.193A) cause substantial interest due to the high sensitivity of the CuCl4 clusters to the surrounding environmental background. It was established that the phase transitions observed at 311–330K are dependent on the local environment of crystallites. We have observed substantial shift of the phase transition temperature for the 10nm DEA–CuCl4 NC in the polymer PMMA matrices compared to the bulk materials. This is related to manifestation of the nano-sized effects in the investigated nanocomposites. The origin of the phenomenon is discussed within a framework of existed nano-confined models. Different regime of cooling-heating cause different features of the phase transitions. Got comparison we will give the same
⁎ Corresponding author. E-mail address:
[email protected] (I.V. Kityk). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.11.024
temperature measurements for the (NH2(C2H5)4CoCl2Br2 (TEA–CoCl2Br2) nanocrystallites (NC) incorporated into PMMA matrices. Following the Figs. 1, 2, 3 and 4 one can see substantial shift of the DSC maxima after incorporation the investigated NC into the PMMA matrix. A giant temperature shift (from 305.1°C to 360.3°C) of onset temperature for the TEA–CoCl2Br2 nanoparticles after their incorporation into the PMMA matrix was found. The observed shift is substantially larger compared to the DEA–CuCl4 composites compare the Fig. 4 and Figs. 1, 2 and 3. The onset temperature for DEA–CuCl4 compound is shifted from 47.2°C for the pure crystallites up to the 53.6°C for the composites. The obtained results unambiguously show that principal role here play the interface borders separating the nanoparticles and the polymers. Because the temperature heating rate is the same these results may indicate on principal role of the nanointerfaces NC-polymer on the observed features of the DSC. It is crucial to emphasize that due to the incorporation of the nanocrystallites into the polymer matrices the
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M. Piasecki et al. / Materials Letters 62 (2008) 2088–2091
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Fig. 1. Temperature dependence of the DSC for bulk DEA–CuCl4: red line — first cycle of the heating–cooling (dotted), blue line — second cycle. Temperature rate 0.3 K/min. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
principal bonds on the borders separating the nanocrystallites and the polymer matrices will be in different external electric field, which leads to the observed temperature shift of the phase transformations [1]. Moreover, the temperature range of the phase transformation is decreased. At lower NC content the
temperature shift is lower which confirms principal role of the chemical bonds in the observed phase transitions. Particular role belongs here to the near-the surface state dipole moments which may change both temperature of the phase transformations as well as the transition dipole moments [2]. One can not exclude
Fig. 2. Temperature dependence of the DSC for 20% DEA–CuCl4/PMMA composites: red line — first cycle heating-cooling (dotted), blue line — second cycle. Temperature rate 0.3 K/min. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 3. Temperature dependence of the DSC for bulk (red line) and 20% NC incorporated into the PMMA matrices (green line). Temperature rate 0.3 K/min. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
that the observed dependences may be also explained by intercrystallite interactions [3], band energy flattering due to strong nano-interface electrostatic potential [4,5]. Additional explanation of the observed effects may be given within a framework of electrete model for the PMMA matrices discovered in the Ref. [6]. Following this model one can assume that the surrounding polymer PMMA matrix is highly polar. So the charge density changes on the borders NC-polymer are
nonlinear with the temperature changes. So we deal with influence of local electrostatic field shifting phase transition's temperature. 1. Conclusions A giant temperature shift (from 305.1°C to 360.3°C) of onset temperature for TEA–CoCl2Br2 NC after their incorporation
Fig. 4. Temperature dependence of the DSC for bulk (red line) and 5%TEA–CoCl2Br2 NC incorporated into the PMMA matrices: (blue line) at temperature rate 10 K/min. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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into the PMMA matrix was found. The results unambiguously show that principal role here play the interface borders separating the NC and the polymers. The observed shift is substantially larger compared to the DEA–CuCl4 composites. Such differences may be caused by higher polarizability of Br ions compared to the Cl ones. Role of interface gradients of electrostatic fields also may be crucial. Acknowledgements For the author Ali Hussain Reshak this work was supported by the institutional research concept of the Institute of Physical Biology, UFB (No. MSM6007665808), and the Institute of System Biology and Ecology, ASCR (No. AVOZ60870520).
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References [1] M. Piasecki, I.V. Kityk, P. Bragiel, K. Ozga, V. Kapustiamyk, B. Sahraoui, Chem Phys. Lett. 433 (2006) 136–139. [2] V. Rudyk, I. Kityk, V. Kapustianyk, K. Ozga, Ferroelectrics V.330 (2006) 19–24. [3] B. Claudet, et al., J. Opt. A: Pure Appl. Opt. 9 (2007) 315–319. [4] I.V. Kityk, Semicond. Sci. Technol. 18 (12) (2003) 1001–1009. [5] I.V. Kityk, M. Makowska-Janusik, E. Gondek, L. Krzeminska, A. Danel, K.J. Plucinski, S. Benet, B. Sahraoui, J. Phys.: Condens. Matter 16 (2004) 231–239. [6] Karol Mazur, J. Phys. D: Appl. Phys. 30 (1997) 1383–1398.
