Fractal Aggregates in Chlorophyll Films
Fractal Aggregates in Chlorophyll Films G.C. Pedro, F.D.S. Gorza, M.S. Sousa, N.C. de Souza, J.R. Silva* Grupo de Materiais Nanoestruturados, Universidade Federal de Mato Grosso, 78600-000, Barra do Garças, MT, Brazil. E-mail: [email protected] Fractal aggregation of chlorophyll (Chl) molecules plays a key role in the efficiency of solar cells and photosynthesis in green plants. To investigate the process of fractal aggregation of Chl in films, we have prepared films by casting technique from aqueous solution of Chl. Optical microscopy analysis shows that film casting present fractal aggregates. In these systems, we investigated the influence of concentration, temperature and applied electric field. The concentrations of 0.50 and 0.12 mg/mL show well defined aggregates. Our results show that temperature affects the form of fractal aggregates in the films. Under applied electric field, the microscopic analysis shows feather-shaped aggregates. Contact angle analysis reveals that the change of surface morphology of the films of Chl at different temperatures is not enough to change its wettability. On the other hand, the variation in morphology imposed by the application of the electric field alters the wettability. Since it has been shown that the solar cell efficiency depends on the morphology of the surfaces and, in turn, the latter depends on the aggregates, the characterization of fractal aggregation of chlorophyll in casting films can be useful to improve the conversion efficiency of these devices.
Keywords: Chlorophyll, Fractal aggregation, Surface morphology, Casting films. Introduction Chlorophyll molecules (Chls) are important because they can act as a natural light-harvesting devices occurring during the photosynthesis [Senthil et al., 2011], and also as component of dye-sensitized solar cells – DSSCs. In this work, we report on investigation of the formation of fractal structures in Chl films prepared by casting technique. Two different concentrations of Chl solution were used and the fractal dimension of the structures was determined by using box count method. The results obtained were discussed on basis of DLA model.
Experimental part Chlorophyll (Chl) was purchased from MP Biomedicals, LLC, and used as receipted. Chl solutions with different concentrations (0.50, 0.12 and 0.03 g/L) have been prepared by dissolving Chl in purified water as a solvent. Thin films were obtained by casting the solutions onto BK7 slices and drying in an air atmosphere at room temperature (23 0C). Surface morphologies of films were examined by using an optical microscope (Nikon, Eclipse Ci/L, USA). The fractal analyzes were performed by the box counting method using the freeware software ImageJ. In this method, the fractal dimension, Df, is determined as the slope of the regression line for log–log plots of the scale r and count N(r), i.e. Df = − lim(log N(r)/log (r)).
Results and discussion In order to examine the possibility of occurrence of fractal structures in Chl films, we have performed a study of dependence of film topography on the concentration. Figure 1 shows images of optical microscopy for Chl films as a function of concentration at room temperature. We can note a well-known fractal form of aggregates, as showed in Figures 1A and 1B.
Figure 1. Optical microscopy images of Chlorophyll films at concentrations of (A) 0.50 g/L and (B) 0.12 g/L. Two selected fractal structures are indicated.
Conclusions We have investigated the formation of fractal structures at two different concentrations in casting films from chlorophyll. The fractal dimension value of the structures was found be Df = 1.55, which is close to that predicted by DLA model.
References [1] Senthil, T.S., Muthukumarasamy, N., Velauthapillai, D., Agilan, S., Thambidurai, M., Balasundaraprabhu, R., 2011. Natural dye (cyanidin 3-O-glucoside) sensitized nanocrystalline TiO2 solar cell fabricated using liquid electrolyte/quasi-solid-state polymer electrolyte, Renewable Energy 36, 2484-2488. Acknowledgement: CAPES, CNPq
Keywords: Chlorophyll, Fractal aggregation, Surface morphology, Casting films. Introduction Chlorophyll molecules (Chls) are important because they can act as a natural light-harvesting devices occurring during the photosynthesis [Senthil et al., 2011], and also as component of dye-sensitized solar cells – DSSCs. In this work, we report on investigation of the formation of fractal structures in Chl films prepared by casting technique. Two different concentrations of Chl solution were used and the fractal dimension of the structures was determined by using box count method. The results obtained were discussed on basis of DLA model.
Experimental part Chlorophyll (Chl) was purchased from MP Biomedicals, LLC, and used as receipted. Chl solutions with different concentrations (0.50, 0.12 and 0.03 g/L) have been prepared by dissolving Chl in purified water as a solvent. Thin films were obtained by casting the solutions onto BK7 slices and drying in an air atmosphere at room temperature (23 0C). Surface morphologies of films were examined by using an optical microscope (Nikon, Eclipse Ci/L, USA). The fractal analyzes were performed by the box counting method using the freeware software ImageJ. In this method, the fractal dimension, Df, is determined as the slope of the regression line for log–log plots of the scale r and count N(r), i.e. Df = − lim(log N(r)/log (r)).
Results and discussion In order to examine the possibility of occurrence of fractal structures in Chl films, we have performed a study of dependence of film topography on the concentration. Figure 1 shows images of optical microscopy for Chl films as a function of concentration at room temperature. We can note a well-known fractal form of aggregates, as showed in Figures 1A and 1B.
Figure 1. Optical microscopy images of Chlorophyll films at concentrations of (A) 0.50 g/L and (B) 0.12 g/L. Two selected fractal structures are indicated.
Conclusions We have investigated the formation of fractal structures at two different concentrations in casting films from chlorophyll. The fractal dimension value of the structures was found be Df = 1.55, which is close to that predicted by DLA model.
References [1] Senthil, T.S., Muthukumarasamy, N., Velauthapillai, D., Agilan, S., Thambidurai, M., Balasundaraprabhu, R., 2011. Natural dye (cyanidin 3-O-glucoside) sensitized nanocrystalline TiO2 solar cell fabricated using liquid electrolyte/quasi-solid-state polymer electrolyte, Renewable Energy 36, 2484-2488. Acknowledgement: CAPES, CNPq
