Nanostructured Silicone Materials

Joanna Lewandowska-LaAcucka, Mariusz Kepczynski and Maria Nowakowska  

Faculty of Chemistry, Jagiellonian University, Krakow, Poland 

Nanostructures are objects with at least one dimension in the nanoscale (0.1-100 nm). SiUcones are inert synthetic materials which have found a variety of apphcations, including those in the biomedical area. The aim of this chapter is to present some aspects of the current state of knowledge on silicone nanostructures. In the following sections, we will review the studies on the development of nanostructured materials composed of silicone. The chapter focuses mainly on the structures such as soUd nanoparticles, empty nanocapsules, and ultra-thin polymeric films. The methods of preparation and characterization of these objects are presented. Some aspects concerning the application of the nanostructures are also mentioned. 

Keywords Silicone, nanostructured materials, hollow capsules, sohd particles, ultra-thin films 

SiHcone nanomaterials are gaining increasing attention because of their tunable physical properties [1,2] and associated wide range of applications such as drug delivery, ligand or catalyst supports [3, 4]. For this reason the development 

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Nanostructured silicon built-in an anodic alumina is evident to be a promising material for photovoltaic applications. In view of cheap materials and low cost equipment the investigated films could be used for solar cell fabrication on large area substrates. Thus the fabrication of new nanostructures based on silicon clusters built-in an anodic alumina opens new possibilities for nanotechnology in electronics and photonics. 

Another interesting phenomenon is producing luminescence from electrochemical reactions. This can be achieved by doping crystalline metal oxides and related materials or anodic metal oxide layers (Meulenkamo et al., 1993) or depositing organic molecules onto nanostructured porous materials such silicon (Martin et al., 2006). 

Another remarkable synthetic effort has been made by the preparation of colloidal Q-particles of the technically more relevant IV-IV materials (i.e., silicon and germanium) [20-25]. Silicon nanoparticles, especially, are currently drawing a lot of attention, since it was found by Canham [26] that nanostructured silicon formed under anodic etching of silicon wafers (called porous silicon ) exhibits bright red fluorescence. Due to the indirect nature of the band transition, bulk silicon shows, by contrast, almost no fluorescence and thus cannot be utilized for optoelectronic devices. 

In addition to one-dimensional and two-dimensional silicon anodes, several forms of three-dimensional nanostructured silicon have been explored. For example, silicon nanotubes (Fig. 15.9) were investigated by Cho et al. [21] as an anode material for lithium-ion batteries. Both interior and exterior surfaces of the nanotubes are accessible to the electrolyte and lithium ions. Through carbon coating, a stable solid electrolyte interface (SEI) was generated on the inner and outer surfaces of the silicon nanotubes. These silicon/carbon assemblies showed a reversible capacity as high as 3,247 mAh/g (based on the weight of silicon) and good capacity retention. 

When discussing matrix-free LDI strategies, we should also mention one more related approach that resonated in the specialist literature over the past two decades. In desorption/ ionization on silicon (DIOS), a nanostructured silicon chip is utilized as the SALDI-assisting material [81]. After depositing sample solution on such a chip, the sample is ready for LDI-MS analysis. Furthermore, DIOS chips are compatible with microfluidic and microreactor systems [92, 93]. Thus, DIOS-MS has occasionally been implemented in TRMS-related measurements (see also Chapters 7 and 13). 

Starodub NF, Shulyak LM, Shmyryeva OM, Pylipenko IV, Pylipenko LN, Mel nichenko MM (2009) Nanostructured silicon and its application as the transducer in immune biosensors. In Mikhalovsky SKA (ed) Biodefence advanced materials and methods for health protection, p 87 Springer - Dordrecht, Netherlands... 

One of the most important physical parameters of any material is its thermal conductivity (see handbook chapter Thermal Properties of Porous Silicon ). Bulk crystalline Si, the material that is widely used in today s electronics and sensors, shows moderate thermal conductivity at room temperature (Slack 1964). On the other hand, highly porous Si, which is a complex nanostructured Si material, composed of interconnected nanowires and nanocrystals, shows a much lower thermal conductivity than that of bulk crystalline Si, which depends strongly on its structure and morphology. The voids within the porous Si layer and the low dimensionality of the highly porous Si skeleton serve to inhibit thermal transport within the layer. 

To produce stable nanostructures, the obtained silicone materials should form a densely crosslinked siloxane network. Therefore, the precursor should preferentially possess three reactive functions in its chemical structure (T-unit). Methyltrimethoxysilane (MeSi(OMe)3) can serve as a typical precursor of that kind (see Figure 4.3). The stiffness of the material can be enhanced by increasing the crosslinking density. 

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