Chemomechanical effect

Ordered arrays of carbon nanotubes (CNT) on various substrates [1] seem to be one of the most promising materials of current nanotechnology. Individual tubes in such arrays are bonded by the strong Van der Waals interactions which can be affected significantly by external molecules adsorbed to the inter-nanotubes space. This leads to high value chemomechanical effect of adsorption in CNT array based nanoelectronic structures which can be used in nanosensorics for the development of chemical sensor elements with acoustic pickup [2]. 

For example, in experiments on chromium-nickel steel plasticization by means of anodic polarization within the region of passive state potentials, it obviously prevails over possible manifestations of the barrier effect [53]. A linear dependence of hardness loss on the logarithm current density has been established over all the ranges of active and passive state potentials (Fig. 9.2). This points to the predominant role of chemomechanical effect despite the formation of passive film which is transparent for dislocations. 

The surface electrochemical heterogeneity of a magnesium sample due to the local activating effect of chlorine ions and a friable oxide-based film causes embrittlement caused by microcracking with a much shorter lifetime in NaCl solution than that in buffer solution. However, in the latter medium there is no embrittlement effect and, in contrast, plasticization is observed, i.e. a strong chemomechanical effect is found. The depth of pits in magnesium after corrosion creep is much larger in sodium chloride... 

Based on a local dissolution law, the micromechanical approach is able to discuss the effects of the local heterogeneity of the mechanical affinity on the dissolution process and to predict the evolution of the pore space morphology. Whenever it is possible to describe the latter by a scalar parameter , (22) yields its evolution (t) which captures the chemomechanical coupling in so far as it controls the evolution of the poroelastic coefficients in (13). Nevertheless, the implementation of this modelling requires to be able to determine the microscopic strain state along the fluid-solid interface by appropriate micromechanical techniques. 

Furthermore, chemomechanical coupling (179-183), in which a chemical reaction precedes or is the result of a mechanical (conformational) change, will be a fruitful field of investigation. Dynamic effects on catalysis also remain a topic of intense debate (184-192). Computer simulation will continue to play an increasingly important role in understanding how enzymes achieve their tremendous catalytic power. 

Figure 16 also shows the effect of a chemomechanical contraction of the PVA-PPA membrane on water permeation when 6.5 V DC was applied in alternate on and off cycles [46]. It can be seen that the chemical valve membrane can increase and decrease the water permeability many times on electrical stimulation. Water permeability increased in proportion to the DC current. This makes it possible to use the membrane as a permeation-selective membrane continuously separating solute mixtures with different molecular sizes. This type of electrically activated chemical valve membrane exhibited long-term stability. 

Figure 4.34. Effect of chemomechanical contraction of PEG treated PMAA membranes on albumin (a) and hemoglobin (b) permeation [131] (a) PEG added Af =3000 5x10 molxp albumin added 2.5x10 % solution (b) PEG added = 3000, 5.8x10 molxp solution hemoglobin added 2.5x10 solution. In both cases the transmembrane pressure was 0.2 kg/cm. ...

Figure 21 shows the effect of the chemomechanical contraction of a PMAA membrane on water permeability if small amounts of PEG with various molecular weight are subsequently added to the water . It is seen that the PMAA membrane exhibits a marked increase in water permeation as soon as the membrane is contacted with the PEG solution. Once the PMAA membrane is treated with PEG, the membrane can... 

Fig. 21. Effect of chemomechanical contraction of a PMAA membrane on water permeation Mol wt. of PEG (A) 1000, (B) 2000, (C) 3000, (D) 20,000. PMAA membrane 3.4 cm area, 30 pm thickness. PEG added 5.8 X 10 mol/1, transmembrane pressure 0.2 kg/cm. Vertical arrows indicate the points at which water or PEG solution was added...

Fig. 23a and b. Effect of chemomechanical contraction of PEG treated PMAA membranes on albumin (a) and hemoglobin (b) permeation (a) PEG added mol wt. = 3000, 5.8 x 10" mol/1 solution, albumin (human) added mol wt. = 67,000, 2.5 x 10 % solution, transmembrane pressure 0.2 kg/ cm, A denotes albumin permeation through an untreated PMAA membrane. Insert percent of retention of albumin by the chemomechanical membrane, (b) PEG added mol wt. = 3000, 5.8 X 10 mol/1 solution, hemoglobin (from beef blood) mol wt. = 64,(W0,2.5 x 10 % solution trans-membrane pressure 0.2 kg/cm, A denotes hemoglobin permeation through an untreated PMAA membrane... 

Despite the numerical support, the above model is quite unrealistic in regard to real systems. Actually, most hydrogels used in chemomechanics experiments are polyacids or polybases that sweU/shrink as a function of the pH of the aqueous solution. In this case, the volume dependence cannot be accounted for on the same principles. The volume changes are associated with energetic effects due to the electrostatic interactions between ions attached to the polymer and with entropic effects due to an excess of free ions that exerts an additional osmotic pressure between the gel contents and the surroundings. Although the electrostatic... 

A chemomechanical system can be defined as one that is used to obtain macroscopic mechanical energy caused by microscopic deformation in response to changes in an external environment it is also considered to be a system for obtaining large deformations effectively by using microscopic mechanical energy. Polymer gels can be functional polymers that possess complex system functions similar to those of biomaterials. Thus, they are potentially useful chemomechanical materials and various studies are underway today. Chemomechanical systems actuate by phase transition, oxidation-reduction, chelation, and formation of complexes between polymers. They are classified as follows ... 

Electric field effect-type capacitor, 290, 291 Electric field gradient, 325, 339, 340 Electric field responsive chemomechanical gels, 251... 

The reasons for the choice of the defining words should then also be obvious Electrochemomechanical implies an applied potential which leads to a chemical redox, which in turn leads to a mechanical deformation. Electrochemomechanical in our context is then simply a short form for electrochemomechanical. And Chemomechanical implies we skip the electrical (applied potential) step and effect redox of the CP by direct chemical means. 

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