On Polymer Nanocomposites - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 224

An orderly arrangement of interacting nanocrystals in a long-range potential
minimum leads to formation of periodic structures. Because of the well-developed
interface, an important role in such systems belongs to adsorption processes, which
are determined by the structure of the nanocrystal surface. In a polymer medium,
nanocrystals are surrounded by an adsorption layer consisting of polymer, which may
change the electronic properties of the nanocrystals. The structure of the adsorption
layer has an effect on the processes of self-organization of solid-phase particles, as
well as on the size, shape, and optical properties of resulting aggregates. According
to data obtained for metallic [1] and semiconducting [2] clusters, aggregation and ad-
sorption in three-phase systems with nanocrystals have an effect on the optical proper-
ties of the whole system. In this context, it is important to reveal the structural features
of systems containing nanocrystals, characterizing aggregation and adsorption pro-
cesses in these systems, which will make it possible to establish a correlation between
the structural and the optical properties of functional nanocomposite systems.
Silicon nanoclusters embedded in various transparent media are a new interesting
object for physico-chemical investigation. For example, for particles smaller than 4
nm in size, quantum size effects become signi¿ cant. It makes possible to control the
luminescence and absorption characteristics of materials based on such particles us-
ing of these effects [3, 4]. For nanoparticles about 10 nm in size or larger (containing
~10 4 Si atoms), the absorption characteristics in the UV and visible ranges are deter-
mined in many respects by properties typical of massive crystalline or amorphous
silicon samples. These characteristics depend on a number of factors: the presence of
structural defects and impurities, the phase state, and so on [5, 6]. For effective practi-
cal application and creation on a basis nc-Si the new polymeric materials possessing
useful properties: sun protection ¿ lms [7] and the coverings [8] photoluminescent and
electroluminescent composites [9, 10], stable to light dye [11], embedding of these
nanosized particles in polymeric matrixes becomes an important synthetic problem.
The method of manufacture of silicon nanoparticles in the form of a powder by
plasma chemical deposition, which was used in this study, makes possible to vary the
chemical composition of their surface layers. As a result, another possibility of con-
trolling their spectral characteristics arises, which is absent in conventional methods
of manufacture of nc-Si in solid matrices (for example, in Į-SiO 2 ) by implantation
of charged silicon particles [5] or radio frequency deposition of silicon [2]. Polymer
composites based on silicon nanopowders are a new object for comprehensive spec-
tral investigation. At the same time, detailed spectral analysis has been performed for
silicon nanopowder prepared by laser induced decomposition of gaseous SiH 4 (see,
for example, [6, 12]. It is of interest to consider the possibility of designing new ef-
fective UV protectors based on polymer containing silicon nanoparticles [13]. An ad-
vantage of this nanocomposite in comparison with other known UV protectors is its
environmental safety, that is, ability to hinder the formation of biologically harmful
compounds during UV-induced degradation of components of commercial materials.
In addition, changing the size distribution of nanoparticles and their concentration in
a polymer and correspondingly modifying the state of their surface, one can deliber-
ately change the spectral characteristics of nanocomposite as a whole. In this case, it is
necessary to minimize the transmission in the wavelength range below 400 nm (which