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Scientific Report
Regarding implementation of the project "Elaboration and characterisation of
functional biopolymers for photonic and electronic applications"
Financial Contract 279/7.10.2011,
January – December 2013
According to the work plan during January-December 2013 were performed activities related to the spectral characterisation of the synthesised biopolymers, nonlinear optical properties of the thin films and electrochemical characterization of the membranes prepared. In this regard were prepared and studied new membranes based on DNA membranes in which has been added glycerin as plasticizer. To increase the conductivity of these membranes they were doped with different chromophores: Blue Nile, Prussian Blue, lithium perchlorate in various concentrations. Hydrophilic / hydrophobic character of these membranes membranes has been studied using the contact angle method. The results showed that the hydrophobicity of the membrane depends on the dopant used, and its concentration (Fig. 1) Fig. 1 Contact angle dependence on dopant type and concentration The obtained membranes were chracterized by UV-Vis spectrometry, FTIR, fluorescence and THG measurements (membranes doped with Disperse Orange 3). In order to determine the conductivity of the membrane was measured their impedance. The ionic conductivity of the DNA biomembrane doped with different molecules was determined using electrochemical impedance spectroscopy (EIS). Electrochemical measurements were performed at free potential and the frequency 1000-100000 Hz with an amplitude of  10mV using PGSTE AUTOLAB 302N with appropriate software. The measurements were carried out also depending on the temperature (20; 30; 40; 50; 60; 70; 80; 90; 100 ° C). The conductivity was calculated using Eq. 1, where - the conductivity is expressed in Scm-1  - membrane thickness, expressed in μm; S is the area of contact between the membrane and the electrode, expressed in cm2, Z - impedance of the membrane, expressed in . Table 1 shows the results for a membrane containing DNA, glycerol and Nile Blue, and in Fig. 2 are given the Arrhenius plots. As it can be seen from Figure 2 all of the DNA membranes doped with Nile Blue present at room temperature conductivity between 10‐9 and 10-8 Scm-1. These values increase with increasing temperature up to about 10-5 Scm-1 at 70 °C. The high conductivity values obtained for temperatures greater than 70 ° C are probably due to the distortion of the DNA. The two chains linked by purine and pyrimidine bases in the double helix structure of the macromolecules of DNA are partially separated as a result of the breaking of hydrogen bonds, thus free molecules of guanine and adenine appear and therefore charge carriers appear due to delocalization of electrons of nucleobase. It is also observed in Figure 2 that the highest conductivity is obtained for the membrane containing 2% Blue Nile. Higher dopant concentrations led to a lower conductivity probably due to the formation of chromophore aggregates on the surface of DNA that have the effect of reducing the number of charge carriers. Table 1 - Example of results obtained for a membrane containing DNA, Glycerine and Nile Blue Figure 2 - Arrhenius plot of conductivity for DNA - Glycerine - Blue Nile membranes Figure 3 shows the effect of glycerol and chromophore on the DNA based membrane conductivity. It may be noted that the addition of glycerin leads to increased conductivity. A concentration of 1% of Nile Blue determine a decrease of the conductivity due to the fact that ionic mobility is low, while a concentration of 1% of lithium perchlorate led to an increase of an order of magnitude conductivity. In the latter case the energy required for the ions migration is lower because the mobile charges are numerous favouring the increasing of the conductivity. Figure 3 - The influence of the glycerol and the nature of dye on the conductivity of DNA membranes (room temperature) Figure 4 shows the conductivity variation with temperature for membranes doped with Prussian Blue (Arrhenius dependencies). It is observed an increasing of the conductivity by two orders of magnitude comparing to the membranes doped Blue Nile. In this case the best results in terms of conductivity have been obtained for membranes with 2% of Prussian Blue. It is observed a similar behaviour of membranes at temperatures above 70 ° C DNA based ionic electrolytes doped with lithium perchlorate present conductivity higher than those obtained for membranes doped with Blue Nile, but lower than those obtained for membranes doped with Prussian Blue. As with the other two cases, the conductivity of the membrane increases with temperature increasing (Fig. 5). It has been observed that in some cases there is a decrease in the conductivity at temperatures above 80 ° C due to evaporation of glycerol used as plasticizers and for increasing the conductivity. Increasing the concentration of lithium perchlorate has a positive effect on the ionic conductivity which can be explained by increasing the number of the mobile ionic species. However, the increase in conductivity is limited by the number of sites of solvation that is sufficient to cause dissolution of the salt. If the number of sites solvation is lower and the salt concentration is high, then ion compounds are formed or the recrystallization occurs, leading to decreased ion mobility. In the case of membranes tested the presence of glycerine causes a higher mobility of ions through a better lithium ion solvation. The addition of greater amounts

of lithium perchlorate causes a decrease in conductivity due to the formation of Figure 4 - Arrhenius dependence for the membranes doped with Prussian Blue Figure 5 - Arrhenius dependence for DNA-based membranes doped with lithium All membranes synthesized were characterized by UV – VIS spectrometry, fluorescence, FTIR, conductivity and contact angle measurements. UV - VIS spectroscopy revealed peaks corresponding to the chromophores colour. Measurements of the fluorescence as expected did not provide conclusive results because of quenching fluorescence (high chromophore concentration due membrane thickness) Conductivity measurements showed that optimum chromophore concentration for Nile Blue and Prussian Blue is 2%, while for the lithium perchlorate a concentration of 1% is considered optimal. The synthesised membranes have hydrophobic character, the highest hydrophobic character showed membranes doped with Prussian Blue. Corroborating the results obtained it can be concluded that it is preferable for electrochromic devices to use the chromophore Prussian Blue. Further research will be performed in order to check the possibility to use these membranes for electrochromic devices such as "Smart Windows". The research results obtained were published in two articles in ISI journals. Also part of the research results were presented at international conferences and workshops in the form of plenary conferences (1), invited conference (2) and oral contributions (5). Project Director, Conf. Habil. Dr. Ing. Ileana Rău

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