Carbon/silicon switch

Keywords C/Si bioisosterism, carbon/silicon switch, chirality, o ligands,... 

In a recently published review, silicon chemistry has been demonstrated to be a novel powerful source of chemical diversity in drug design [1]. Sila-substitution of drugs (carbon/silicon switch) is one of the concepts that have been successhilly used for the development of new silicon-based drugs (for recent examples, see Ref. [2]). 

As can be seen from Fig. 2, sila-substitution of rac-Sa (-> rac-Sh) substantially affects the pharmacological profile with respect to serotonin reuptake inhibition. The other (major) structural changes in the molecular shape of rac-5b (-> rac-6, rac-7) also influenced the pharmacological profile with respect to monoamine selectivity rac-1) and/or absolute potency rac-6). These results clearly demonstrate that the carbon/silicon switch strategy is a powerful tool for drug design. 

The use of silicon-containing phenolic polymers with NDS compounds present as the photoactive polarity switch has been investigated. Formaldehyde condensation polymers with m-trimethyl-silylphenol (19) have been prepared. It is necessary to incorporate phenol as a comonomer in order to decrease the hydrophobicity of these resins so that they are soluble in aqueous base. The maximum silicon content obtainable is around 9% due to the acidolysis of the aromatic carbon-silicon bond during the acid-catalyzed polymerization process. Nevertheless, high resolution images with good oxygen etch resistance are obtained when these resins are formulated into resists with NDS derivatives present. 

Like the C NMR chemical shifts for the central carbon of heteroallenes. changing the composition of the allene fragment can have as much of an effect (if not more) on the Si chemical shift as does changing a substituent. Switching the carbon at position 3 to a phosphorus (silaphosphaallene 122) moves the " Si chemical shift downheld to 75.7 ppm, which is the most deshiclded " Si shift fora silaallene to date, even though it has two aryl groups on silicon, which should keep the shift uplield. 

Keyboard switches are integrated composition of insulate silicone rubber and conductive silicone rubber filled with carbon black. They are commonly called rubber contacts, which serve as an electrical contact and a mechanical spring. Contacts made of silicone rubber were developed in response to demands for more compact size, mass production and for lower cost. 

A reduction of the required energy could be reached by the incorporation of conductive fillers such as heat conductive ceramics, carbon black and carbon nanotubes [103-105] as these materials allowed a better heat distribution between the heat source and the shape-memory devices. At the same time the incorporation of particles influenced the mechanical properties increased stiffness and recoverable strain levels could be reached by the incorporation of microscale particles [106, 107], while the usage of nanoscale particles enhanced stiffness and recoverable strain levels even more [108, 109]. When nanoscale particles are used to improve the photothermal effect and to enhance the mechanical properties, the molecular structure of the particles has to be considered. An inconsistent behavior in mechanical properties was observed by the reinforcement of polyesterurethanes with carbon nanotubes or carbon black or silicon carbide of similar size [3, 110]. While carbon black reinforced materials showed limited Ri around 25-30%, in carbon-nanotube reinforced polymers shape-recovery stresses increased and R s of almost 100% could be determined [110]. A synergism between the anisotropic carbon nanotubes and the crystallizing polyurethane switching segments was proposed as a possible... 

The greatest progress has been made in the research of the components that may make up nanoelectronics. Researchers have been able to fabricate molecules that have two states, such that the molecules can be switched on and off . Some of these molecules have shown the functionality of diodes or variable resistors. Scientists have also been able to fabricate silicon nanowires and carbon nanomaterials such as one-dimensional (ID) carbon nanotubes (CNT) or two-dimensional (2D) graphene layers. Both of these technologies can be used as wires or devices, and in some cases both. Nanoimprint lithography, probably the most promising wire fabrication technique, has been used to produce working memories on the nanometer scale. While all of these... 

The conductive polymer is usually composed of dispersed electrically conductive particles such as carbon black or metal in a durable polymer matrix such as silicone rubber. As it is possible to obtain conductivity and elasticity in simple materials, this is useful for high density micro-sized electrical contacts as connector or as key-board switch. However, in spite of the excellent properties, it is difficult to obtain low electrical resistivity. In order to approach this problem, performances of the contacts between the polymer surface and metal were studied from the view point of surface contamination. The electrical conduction mechanism and a method to get low resistivity were also studied. The results show that the surface of the polymers containing carbon black shows contamination resistance properties because of their chemical stability. The conduction mechanism changes with particle content. For large content, electric current flows through particles contacting each other and for small content, the current passes through the gap between particles by Schottky conduction. Thus, as the resistance consists of particle resistance, constriction resistance and gap resistance, the resistance can be controlled by particle material, their content and size. 

The electrical properties of the elastomeric conductive polymer consisting of carbon black particles in silicone rubber for application as an elastomeric connector and switch is described in this paper. Moreover, the chemical corrosion properties of the contact between the polymer and metal surface were examined. 

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