whereas the particles generated inside the film are larger (~30–50 nm). In the case
of X-ray irradiation, the nucleation of NPs is similarly controlled by the formation
and transport of radiolysis products in the IPEC film and in the external
water–alcohol medium. However, in this case, some other regimes of reduction
come into play, being determined by specific features of the energy transfer from
X-ray radiation to the substance [81, 132, 133]. The structure of the material
depends on the nature of the reduced metal ions and their initial content in the
sample. The unique ability of the IPEC matrices to stabilize NPs allows one to
obtain information about peculiarities of their formation at different stages of X-ray
irradiation (Fig. 20c–e) [115, 133]. A study of nanostructures obtained in IPECs
{PAA-PEI} under the radiation–chemical reduction of Cu
2+ using X-ray irradiation
demonstrated that the NPs are selectively formed in the subsurface layer of the
IPEC films. The observed effect is due to favorable conditions for reduction of
metal ions in the surface region because of the effective diffusion of radiolysis
products from the outer water–alcohol medium and transport of Cu
2+ through the
IPEC matrix to the ligand vacancies near the interface boundary. The specific
feature of the interaction of X-rays with matter at the physical stage results in
significant heterogeneity of energy absorption and increases the rate of formation of
reducing radiolysis products near the surface of the IPEC films. The reduction of
Cu
2+ is a slow, two-stage process [121]. The duration of the reduction of Cu
2+ and
the formation of metal clusters provides an almost complete localization of NPs
near the surfaces of the samples. In contrast to the formation of copper nanoclusters,
single-stage radiation-induced chemical reduction of Ag
þ to silver atoms proceeds
with a relatively high rate [122]. In this case, the efficient formation of NPs of
10–30 nm in size occurs not only at the surface of the IPEC film but also inside the
IPEC film (Fig. 20f) [115].
Generation and transport of radiolysis products and the migration of metal ions
across the polymer matrix control the formation of NPs in the irradiated IPEC films
[115]. When irradiation is performed in a water–alcohol medium, metal clusters
form via local processes, which proceed with participation of active species having
high reduction potentials. Here, growth of NPs is provided by interfacial processes,
in which the stable radiolysis products take part.
The ratio between the rates of NP nucleation and growth is determined by the
dose rate and by the mechanisms of reduction of metal ions and formation of metal
nanoclusters. The character of the formation of NPs is strongly controlled by the
mechanisms of energy transfer from the ionizing radiation to the substance that
determine the spatial distribution of radiolysis products. Variations in radiation
parameters provide the different regimes for reduction on the surface of the IPEC
film and inside the IPEC film. They make it possible to prepare composites both
with NPs that are uniformly distributed throughout the polymer matrix and with a
regular spatial distribution of NPs across the film thickness, including their localization in the subsurface layers.
Microdifractograms show a size effect on the packing of metal atoms in the
prepared NPs. In the case of ultrasmall NPs with a mean size of 2–3 nm, the wide
reflexes correspond to the interplane distances of ca. 1.20 A ˚ and 2.00 A ˚ for copper
212
D.V. Pergushov et al.
of X-ray irradiation, the nucleation of NPs is similarly controlled by the formation
and transport of radiolysis products in the IPEC film and in the external
water–alcohol medium. However, in this case, some other regimes of reduction
come into play, being determined by specific features of the energy transfer from
X-ray radiation to the substance [81, 132, 133]. The structure of the material
depends on the nature of the reduced metal ions and their initial content in the
sample. The unique ability of the IPEC matrices to stabilize NPs allows one to
obtain information about peculiarities of their formation at different stages of X-ray
irradiation (Fig. 20c–e) [115, 133]. A study of nanostructures obtained in IPECs
{PAA-PEI} under the radiation–chemical reduction of Cu
2+ using X-ray irradiation
demonstrated that the NPs are selectively formed in the subsurface layer of the
IPEC films. The observed effect is due to favorable conditions for reduction of
metal ions in the surface region because of the effective diffusion of radiolysis
products from the outer water–alcohol medium and transport of Cu
2+ through the
IPEC matrix to the ligand vacancies near the interface boundary. The specific
feature of the interaction of X-rays with matter at the physical stage results in
significant heterogeneity of energy absorption and increases the rate of formation of
reducing radiolysis products near the surface of the IPEC films. The reduction of
Cu
2+ is a slow, two-stage process [121]. The duration of the reduction of Cu
2+ and
the formation of metal clusters provides an almost complete localization of NPs
near the surfaces of the samples. In contrast to the formation of copper nanoclusters,
single-stage radiation-induced chemical reduction of Ag
þ to silver atoms proceeds
with a relatively high rate [122]. In this case, the efficient formation of NPs of
10–30 nm in size occurs not only at the surface of the IPEC film but also inside the
IPEC film (Fig. 20f) [115].
Generation and transport of radiolysis products and the migration of metal ions
across the polymer matrix control the formation of NPs in the irradiated IPEC films
[115]. When irradiation is performed in a water–alcohol medium, metal clusters
form via local processes, which proceed with participation of active species having
high reduction potentials. Here, growth of NPs is provided by interfacial processes,
in which the stable radiolysis products take part.
The ratio between the rates of NP nucleation and growth is determined by the
dose rate and by the mechanisms of reduction of metal ions and formation of metal
nanoclusters. The character of the formation of NPs is strongly controlled by the
mechanisms of energy transfer from the ionizing radiation to the substance that
determine the spatial distribution of radiolysis products. Variations in radiation
parameters provide the different regimes for reduction on the surface of the IPEC
film and inside the IPEC film. They make it possible to prepare composites both
with NPs that are uniformly distributed throughout the polymer matrix and with a
regular spatial distribution of NPs across the film thickness, including their localization in the subsurface layers.
Microdifractograms show a size effect on the packing of metal atoms in the
prepared NPs. In the case of ultrasmall NPs with a mean size of 2–3 nm, the wide
reflexes correspond to the interplane distances of ca. 1.20 A ˚ and 2.00 A ˚ for copper
212
D.V. Pergushov et al.