Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 Experime ntal Design on Nano Calcite Production Murat Molva 1 and Ekrem Özdemir 1 * 1 -Izmir, Turkey Abstract- Based on the carbonation route, nano calcite crystals were produced by Ca(OH) 2 – CO 2 - H 2 O system in the presence of different organic solvents (methanol, ethanol, hexane, toluene and benzene). A three factor – two level (2 3 ) full factorial methodology was studied to understand the combined and interaction effects of Ca(OH) 2 amount, organic solvent / water ratio, and the stirring rate on the precipitation time. Regression model equations were derived as functions of the main three factors to predict the reaction times for the intermediate, lower or upper values of the factor levels. Effects of these factors on shape were also determined by X-ray diffraction and scanning electron microscopy. At room temperature, some organic solvents, such as hexane, toluene and benzene can not exhibit amphiphilic property since they are not miscible in water. However, these organic solvents can exhibit amphiphilic property to some extent under vigorous stirring. Thus, generally, molecular structural framework and solvating degree of additive may affect the initial formation of crystallization by blocking of growth site and confining the reaction solutions with organized media and can lead to high localized accumulation of ionic charge with high spatial density, thereby determining the size, shape, and organization of the crystal forms. Therefore, it can be speculated that the amphiphilic property of organic solvent plays an important role in determining both polymorph and morphology of CaCO 3 [1,2]. Various unusual crystal morphologies, such as dendrite-shaped, flower-like, wheatgrass-like, needle-like, whiskers, doubletaper-like, cubical, spherical etc. can be obtained depending on the experimental conditions [1,3]. pH and conductivity curves were obtained by CO2 injection in the presence of various organic additives (methanol, ethanol, hexane, toluene and benzene) / water mixtures and Ca(OH) 2 . Methanol and ethanol were miscible in water. On the other hand, hexane, toluene and benzene were immiscible in water but they were used above their solubility limits. Therefore, mixtures of water and solvents were formed in order to obtain attraction with the Ca(OH) 2 powders. Ca(OH) 2 in mixtures was both below the solubility limit (20 mM ) and above the solubility limit (40 mM). The main intention of the usage of those additives was to modify the precipitate morphologies and create a database for the precipitation time with different additives. The experimental design and optimization study reports the effects of Ca(OH) 2 amount in slurry, additives (methanol, ethanol, hexane, toluene, benzene) and stirring rate on precipitation time. A 2 3 full factorial methodology with three factors involving two levels of each variable (40 runs with 1 replicates, totally 40 experiments) were carried out to determine the significant parameters and the interaction effects. Factors and their levels for screening design of experiments are given in Table 1. Tables 2 give the contributions for the effects of three main factors and their interaction effects. Sign (+) refers to positive effects of factors on the response (precipitation time), and sign (-) represents the negative effects of factors on the precipitation time. If a factor represented by a (+) sign, this factor increase the precipitation time, if it is represented by a (-) sign, it decreases the precipitation time. For examp le, hexane and toluene increase the precipitation time individually. Factor C (stirring rate) has negative effects on precipitation time for all sets. A striking example can be given to understand the interaction effect: when the methanol and benzene concentrations were increased, the precipitation time decreased, however, when Ca(OH) 2 amount was increased together with methanol and hexane, the precipitation time was seen to decrease. Further details will be discussed during the presentation. Table 1. Factors and their levels for screening design of experiments Low High Response Factors A - Ca(OH) 2 20 mM 40 mM B - Additives Ethanol Methanol Hexane Toluene Benzene 5 % 20 % C- Stirring 400 rpm 800 rpm Precipitation time (minutes) Table 2. Sign of standardized effects of the main factors and their interactions. (A: Ca(OH)2 B: Additive C: Stirring Rate) 0T*Corresponding Author: ekremozdemir@iyte.edu.tr Main Interactions SET Additive A B C AB AC BC ABC 1 Methanol + + - - - + - 2 Ethanol + + - + + - - 3 Hexane - - - + - + - 4 Toluene + - - + - - + 5 Benzene + + - - - - - [1] Lei, M., Li, P. G., Sun, Z. B. and Tang, W. H. (2006) Effects of organic additives on the morphology of calcium carbonate particles in the presence of CTAB. Materials Letters 60, 1261-1264 [2] Dickinson, S. R. and McGrath, K. M. (2004) Aqueous precipitation of calcium carbonate modified by hydroxyl-containing compounds. Crystal Growth & Design 4, 1411-1418 [3] Carmona, J. G., Morales, J. G., and Clemente, R. R. (2003). "Rhombohedral-scalenohedral calcite transition produced by adjusting the solution electrical conductivity in the system Ca(OH) 2 -CO 2 -H 2 O." Journal of Colloid and Interface Science, 261(2), 434-44 6th Nanoscience and Nanotechnology Conference, zmir, 2010 300
Poster Session, Tuesday, June 15 Theme A1 - B702 Investigation of nucleation and growth mechanism during formation of poly(azure A) Emrah Kalyoncu, Kader Dacı, brahim Hakkı Kaplan, Ezgi Topçu, Murat Alanyalıolu* Department of Chemistry, Sciences Faculty, Atatürk University, Erzurum 25240, Turkey Abstract—Nucleation and growth mechanism during formation of poly(AA) films on gold substrates was intestigated. Repeated potential cycling by using cyclic voltammetry and potential controlled electrolysis techniques have been performed to synthesize poly(AA) thin films on gold working electrodes in the solution containing 0.1 mM AA and 0.1 M phosphate solution (pH:6.2). Chronoamperometry, STM (Scanning Tunneling Microscopy), AFM (Atomic Force Microscopy), and UV-vis. absorption spectroscopy techniques were applied for the characterization of prepared polymeric films. Dye polymer films show excellent catalytic and photoelectrochemical properties and have been applied for batteries and electrodes, electrochromic devices, light emitting diodes, and immobilizitaion of enzymes [1,2]. Dye polymer films must have a well-ordered surface to be used in these technological applications. Electropolymerization is one of the simple and useful method to obtain dye polymer films. In the electropolymerization process, deposition of polymeric dye film on the electrode surface is achieved by constant or cycled potential oxidation of a dye-containing solution. Azure A is a derivative of phenothiazine dye material (Figure 1). for progressive case. Growth of nuclei is slow for instantaneous nucleation and fast for progressive nucleation [7,8]. According to Li and Albery [9], two possible mechanisms are possible for polymer films: Progressive twodimensional layer-by-layer nucleation and instantaneous threedimensional nucleation and growth. In this study, chronoamperometry data (Figure 2) that is obtained during potential controlled electrolysis has been compared with theoretical data to determine the nucleation and growth mechanism of poly(AA). . Figure 1. Chemical structure of azure A The redox behaviour of dyes has been under study for nearly 65 years [3-7]. Chen et al. [6] prepared poly(AA) films in different pH’s and found that the optimum pH of the electrolysis solution is 6.0. It is known that the film growth of polymeric films of dyes is related to the upper potential limit besides pH value of the solution [4,5]. In this study, we have investigated nucleation and growth mechanism during the formation of poly(AA) films on gold substrates. Repeated potential cycling by using cyclic voltammetry and potential controlled electrolysis techniques have been performed to synthesize the thin films of poly(AA) on gold working electrodes. In all cases, an Ag/AgCl (3M NaCl) electrode served as reference electrode, and a Pt wire electrode was used as counter electrode. In the solution containing 0.1 mM AA and 0.1 M phosphate solution (pH:6.2), the potential of working electrode was kept at different upper potential limit of 0,90, 0.95, and 1.00 V. We have investigated nucleation and growth mechanism of poly(AA) film by using chronoamperometry technique. Nucleation and growth term can be described as either instantaneous or progressive. The current densities for these two cases are 2 J ins = at exp( −bt) for the instantaneous case and 2 3 = ct exp( −dt) J prog Figure 2. Experimental current-time transients for different electrooxidation potential values. The non-faradaic charging currents in the absense of AA have been subtracted from these data STM (Scanning Tunneling Microscopy), and AFM (Atomic Force Microscopy) techniques was applied to investigate poly(AA) film surface structure. We have also studied the optical properties of the prepared polymeric films by using UV-vis. absorption spectroscopy. This work was partially supported by Atatürk University under Project No. BAP-2009/245. * Corresponding author: malanya@atauni.edu.tr [1] K. Naoi, H. Sakai, S. Ogano, J. Power Sources 20, 237 (1987) [2] G. Yu, J. Gao, J. C. Hummelen, F. Wudl, A. J. Heeger, Science 270, 1789 (1995) [3] R. Brdicka, Z. Elektrochem. 48, 278 (1942) [4] A. A. Karyakin, A. K. Strakhova, E. E. Karyakina, S. D. Varfolomeyev, A. K. Yatsimirsky, Bioelectrochem. Bioenergetics 32, 35 (1993) [5] J. Liu, S. Mu, Synthetic Metals 107, 159 (1999) [6] C. Chen, S. Mu J. Appl. Polym. Sci. 88, 1218 (2003) [7] M. Alanyalioglu, M. Arik, J. Appl. Polym. Sci. 111, 94 (2009) [8] A. Bewick, M. Fleiscmann, H. R. Thirsk, H. R. Trans Faraday Soc. 58, 2200 (1962) [9] F. Li, W. Albery, J. Electrochim Acta 37, 393 (1992) 6th Nanoscience and Nanotechnology Conference, zmir, 2010 301
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