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A simple energy conversion system—particularly, the conversion of mechanical energy into electrical energy by using shaker flashlights—has recently been presented.1 This system uses hand generators, consisting of a magnet in a tube with a coil wrapped around it, and acts as an ac source when the magnet passes back and forth through the coil. Additionally, this system includes an LED, a capacitor, a switch, and a full-wave bridge rectifier. We were inspired by this work to design a simpler demonstrator made for teaching energy conversion concepts to science students using piezoelectric material.2,3

Cellulose membrane (SE) was prepared by culturing Acetobacter xylinum in a media with sucrose as a carbon source and was used as a supporting membrane in this study. Pore size of the supporting membrane was studied by means of molecular weight cut off (MWCO) and SEM micrographs. For making cellulose/chitosan composite membrane SE/CH, chitosan solution was used as a coating polymer and applied by a casting method.This resulted in a smaller hydraulic permeability coefficient (Lp) from 6.7 × 10–11 m3 N–1 s–1 in membrane SE to 1.94 × 10–12 m3 N–1 s–1 in the composite membrane SE/CH. Using PEG of several molecular weights as feed solution, the MWCO of the SE membrane was 200 kDa while that of the SE/CH membrane was 6 kDa. The former rejected 1 g L–1 BSA by 80%. With pH between 3 and 8, the composite membrane SE/CH rejected NaCl and NaHCO3 by 50%, independent of the pH level. However, when using a divalent salt solution of MgSO4 the rejection was increased up to 85%, with an optimum at pH 6–7 and a permeate flux of 5.0 L m–2h–1 at pressures of 0.5 MPa.

This work presents the fabrication of the polymer matrix in which the dispersing agent has been added, leading to the changes in the overall properties of the polymer. Polyvinylidene fluoride (PVDF) polymer was selected owing to its attractive properties in various applications such as actuator, sensor, and more recently energy harvesting applications [1]. I. MATERIAL PREPARATIONThe commercial PVDF powder was dissolved into Nmethyl-2-pyrrolidone (NMP) to obtain a PVDF solution. A non-ionic surfactant of polyethylene glycol dodecyl ether (Brij-30) was added into the solution. The morphology of PVDF without and with different quantities of the Brij-30 was investigated by the scanning electron microscope (SEM). The PVDF became more porous with increasing the surfactant content. The FT-IR was used to ascribe the C=C, C-H and C-F stretching vibrations which are the characteristics of the alpha phase of the PVDF. For the PVDF/Brij-30, a new peak appeared at about 3436 cm -1 and the peaks of C=C, C-H and C-F were shifted to some higher wave number and, the percentage of transmittance of fine structure, located at about 700-1700 cm -1 , increased. This was because the crystallinity of the modified PVDF analysed by the DSC method was reduced. The enhancement of an electrical conductivity of the PVDF with Brij-30 was also observed and this was related to the reduction of the crystallinity of the polymer.Further investigation was made by mixing the copper filler into the modified PVDF matrix to obtain the composite. The Brij-30 surfactant leads to an increasing content of the filler from 0.01% to 60% without any agglomerations of the filler but isolated particles and tiny clusters. The crystallinity of the modified PVDF was further reduced after adding the copper filler. Fig. 1. SEM image of PVDF with 0.05%Brij-30. II.RESULTS AND DISCUSSIONWhen compared to the as-prepared PVDF, the composite has much higher the volume conductivity and the relative permittivity measured at 1 kHz was at a maximum value when the content of the copper filler reached 60%. This was due to a uniform distribution of the copper filler in the modified PVDF matrix, leading to an increase in electrical conductivity and permittivity.The investigations confirm that the modified PVDF including its composites are suitable for MEM applications and some problems related to the piezoceramic deposited on silicon are no longer existed. However, the composites with high content of the filler which is highly conductive are promising for a certain application differed from the low-content-filler composites. The applications of the materials [2] have been addressed in future