Conversion into mechanical work

Soluble, stimuli-responsive polymers in aqueous solutions can be precipitated at specific environmental conditions. Even if such systems can not be used for chemical energy conversion into mechanical work, it can be useful as temperature of pH indicators, or as on-off light transmission switches. Of peculiar interest are... 

Entropy A measure of the unavailability of the thermal energy within a system for conversion into mechanical work All energy transformations (i.e. chemical to chemical, chemical to thermal) increase entropy. 

Electricity is produced by the conversion of heat energy (produced in a boiler and transmitted as steam) into mechanical work by use of a turbine, which is connected to an electrical generator (turbine generator). 

Wind is the motion of air masses caused by the different thermal conditions that occur over the earth s surface as a result of the transmission of solar radiation. Wind energy is defined as the kinetic energy of the wind converted into mechanical work. This mechanical work can be used to drive an electrical generator for the production of electricity. A machine that performs this conversion is called a wind turbine generator (WTG) and a group of these, including the auxiliary equipment, constitute a WF. 

Its numerical value is independent of the manner in which the heat is produced by work. It is the same for the boring of metals for the friction of solid or of liquid bodies against one another, etc. Conversely, if we convert heat into mechanical work, the ratio of the work done to the heat which has disappeared is again equal to J under all circumstances. 

It seems possible to amplify the photostimulated conformational changes in solution at the molecular level into shape changes of polymer gels or solids at the visible macro level. The first proposal to use the structural changes at the molecular level for direct conversion of photon energy into mechanical work has been made by Merian (13.) in 1966. Since then, many materials, most of which contained azobenzene chromophores, have been reported to show photostimulated deformation(JM). Till now, however, the reported deformations were limited to less than 10%. In addition, Matejka et. al. have pointed out that in many cases photo-heating effect instead of photochemical reaction plays a dominant role in the deformation(15,16). 

Hill, T.L. and Kirschner, M.W. (1982). Subunit treadmiUing of microtubules or actin in the presence of cellular barriers possible conversion of chemical free energy into mechanical work. Proc. Natl. Acad. Sci. U.S.A. 79, 490- 94. 

These results of 18 years ago, demonstrating the capacity of de wovo-designed model protein-based machines for the conversion of chemical energy into mechanical work, remain unex-... 

Figure 5.20. Experimental results that demonstrate the same form of hydrophobicity dependence as shown in Figure 5.19. (A) Conversion of electrical into chemical energy when the model protein contains both redox couple and protonatable chemical couple. (Adapted with permission from Urry. ) (B) Hydrophobicity dependence for the conversion of chemical energy into mechanical work when the model protein contains a protonatable function...

The isothermal conversion of chemical energy into mechanical work is the base of motility of all living organisms, and it is manifested of all levels of structural organisation, namely 1) molecular motility, which is based on the conformational changes of the proteins macromolecules 2) intracelular movements (flagellar or ciliar), contraction of muscular fibres, heart beats, plants movement and 3) movement of pluricellular organisms (locomotion). 

At the cellular level, the striated fiber is characterised by a high structural self-organisation as well as of its components. Consequently, striated fiber constitutes a suitable contractile model for the analysis of its technical potential, regarding the conversion of chemical energy into mechanical work. Its investigation is usually done by common methods used in polymer science, such as optical and electronic microscopy, X-ray diffraction these ones are often used in combination with those typical to immunochemistry and enzymology fields [3]. 

The order-disorder transitions are responsive for the conversion of chemical energy into mechanical work in the case of protein based networks. It was established that modifying the temperature and to certain values of pH, the conformational transitions from a-helix to elastic spiral takes place. Figure 4.17 [99, 100]. 

Do we have any possibility to build conversion systems capable of directly transforming chemical energy into mechanical work The answer is yes . 

The concept of systems transforming chemical energy directly into mechanical work has been investigated for many years. Such systems would be much more efficient in terms of fuel consumption than conventional thermal engines which first convert chemical energy into heat or electricity and then the latter into mechanical work. A one-step conversion is also expected to produce less waste products and work noiselessly. 

J. H. van t Hoff already showed the possibility of conversion of a certain amount of chemical free energy into mechanical work. He also suggested a system of osmotic cells with pistons which converts free energy directly to work. Of course van t Hoff s theoretical osmotic engine had no similarity with the processes taking place in living muscles, where the motility is generated not by a difference of osmotic pressure, but by a pertinent assembly system of macromolecular compounds (proteins), which contracts and expands as the consequence of a chemical reaction. 

For certain types of recM tion it is possible to obtain a direct conversion of chemical energy into electricity and thereby into mechanical work. Processes of heat transfer are thereby avoided and the conversion factor, I be heat engine does not come into the picture. This can be achieved whenever the reaction has an ionic mechanism and can be set up as a galvanic cell. The electrodes act in much the same manner as the semi-permeable membranes of the equilibrium box. That is to say, the reagents can be added to the system, and the recK tion products withdrawn, under reversible conditions. The two great prcu tical advantages of this method of operation are as follows ... 

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