Self-buckling is an interesting phenomenon that is easily found around us, either in nature or in objects made by human. Palm fronds which initially directed upward when they were short and turned into bending after appreciably longer is an example of the self-buckling phenomenon. We report here that the self-buckling of columns can be treated as a process of second-order phase transition by considering the straight column as "disorder state", the bending column as "order state", and the temperature as the inverse of column length. The "critical temperature" corresponds to the inverse of critical length for buckling, 1/L cr , and the deviation angle made by column free end relative to vertical direction satisfies a scaling relationship with a scaling power of 0.485. Changing of the column geometry from the vertically upward to the bending state can be considered as a transition from disorder state to order state.
We propose a novel method for estimating the elastic modulus of several materials by processing the bending image of cantilever material sheets. The calculated results (tested for five samples) were consistent with data obtained by direct measurement using a tensile strength device. By placing the cantilever sheets in an environment inside of which the temperature could be controlled, we were able to obtain the temperature dependence of elastic modulus. We identified a drastic drop of elastic modulus at a certain temperature and assumed this temperature corresponds to glass transition temperature. We also introduced an equation for describing the elastic modulus around that critical temperature and were able to estimate the glass transition temperature for all tested polymer materials. Surprisingly, the estimated glass transition temperatures conform to data obtained by direct measurement using a DTA device. Since the elastic modulus changes suddenly around the glass transition temperature, the proposed method might be more accurate than measurement using a DTA device where the glass transition temperature corresponds to the location of a weak peak at the DTA curve. This is the first attempt for estimating the glass transition temperature of polymer based on bending of cantilever slender beam, and seems to be the simplest method. The method is very potential for developing new equipment for determining the glass transition temperature of polymeric materials.
Indonesia has great potential of the Solar energy, irradiated by the Sun throughout the years. Cotton textiles antibacterial has been prepared by coating Titania (TiO2) with Polyethylene glycol (PEG) and Polyvinyl alcohol (PVA) as adhesives. The method of depositing cotton using a simple dip coating. Cotton dry for 15 minutes with a halogen lamp, after the deposition process. Then, we do the antibacterial activity test using Plate Count Method. As a result, the coated cotton textiles with Polyvinyl alcohol (PVA), Polyethylene glycol (PEG) has antibacterial properties. Characterization by the Attenuated Total Reflectance (ATR) obtained that Titania (TiO2) surely adhere on the sample. From Attenuated Total Reflectance (ATR) characterization we conclude that Polyvinyl alcohol (PVA) and Polyethylene glycol (PEG) is not affecting the antibacterial ability of Titania (TiO2). But the infusion of Polyvinyl alcohol (PVA) and Polyethylene glycol (PEG) on Cotton increases the stiffness value of Cotton.
Solar cell using TiO2/coffee composite as photon absorbing material has been successfully fabricated. A suspension of TiO2/coffee was dropped on Fluorine Tin Oxide substrate which was previously heated on a hotplate with temperature of 100 °C. The fraction of coffee was varied from 10, 20, 30, 40, and 50 %, compared to the mass of TiO2. PVA-LiOH electrolyte polymer was functionalized as the hole transport medium. The highest efficiency of 0.76 % was achieved with 40% of coffee fraction. The solar cell is promising to be developed in the future due to the easy method and cheap materials used.
We have successfully fabricated solar cell using flexible counter electrode of graphite powder. TiO2 / graphite suspension was simply poured onto heated Fluorine Tin Oxide (FTO) substrate and kept heated at 200°C for 2 hours. PVA.LiOH polymer electrolyte was employed as a positive charge transfer medium. The counter electrode was made of graphite powder which is manually deposited on transparent plastic using tube-shaped metal which its surface covered with tissue of 2 mm thick. Graphite powder was deposited by straight motion of 20 movements for one coating or one layer. The same activity was repeated on the stacked film to increase the conductivity of the film. Resistivity and transmittance measurement of the film was performed by four-point probe method and UV-Vis equipment respectively. The film thickness and 2-D porosity were measured using an electronic microscope and ImageJ software orderly. The film resistivity and transmittance gradually decreased with the increase of coating number and reached the resistivity of 0.35 Ω.cm and transmittance of 5% for 40 times of coating. At the same time, the film thickness was saturated at the 30 times coating and reached the thickness of 9.4 μm. The film 2-D porosity which indicated how well the surface of the film covered the graphite also decreased to reach the film porosity of 18%. The most conductive film (40 times coating) was used as a flexible counter electrode in TiO2/graphite solar cell. The efficiency of this structure was 0.4 %, a reasonable efficiency achievement for a cheap material and easy method used.
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