3 Structural Peculiarities and Properties of Silver-Containing Polymer. . .
53
where - is a constant related to a shape of the crystallites (K = 0.9 if their shape is
unknown) and β is the angular half-width (width at a half-height) of the singlet of a
discrete diffraction maximum, showed that the average L value is 17.5 nm (for the
calculation, singlet diffraction maxima at 2θ m = 18.7 ◦ and 30.8 ◦ were applied).
However, the X-ray pattern of the pectin sample in the form of a film prepared
from a 5% aqueous solution displays only contours of the groups of diffraction
maxima with basic intensities that are present on the X-ray pattern of the pectin
powder (Fig. 3.1, curves 3, 4). This circumstance indicates a low rate of pectin
crystallization, as well as the relaxation character of the structurization processes in
the polymers.
IPEC formed from pectin and P4VP is characterized by short-range ordering
during translation of fragments of oppositely charged polyelectrolyte macromolecular chains in a space. This fact is confirmed by the appearance of diffuse
diffraction maximum at 2θ m ∼ 21.2 ◦ on the X-ray profile of the IPEC sample
(see Fig. 3.1, curve 2). The average value for the period of short-range ordering
of macromolecular chains’ fragments of oppositely charged polyelectrolytes in
the IPEC (the average Bragg distance between chains of the polyanion and the
polycation) is equal to 4.2 Å.
The following fact should be taken into consideration: in the IPEC profile
obtained for equimolar quantity of pectin and P4VP, the angular location of the
secondary (rated by intensity) diffraction maximum is shifted from 10.6
◦ to 11.8
◦
comparing with P4VP (Fig. 3.1, curves 1, 2), while the average Bragg distance (d)
between P4VP’s main macrochains (as part of IPEC) is falling down from 8.3 Å to
7.5 Å.
Once the pectin–Ag + –P4VP IMC is formed, the diffraction pattern changes.
This is confirmed by the appearance of a low-intense diffuse diffraction maximum at 2θ m ∼ 11.0 ◦ (Fig. 3.2, curve 2) in the presence of a low-intensity
amorphous halo, which, unlike that for the IPEC, has an angular position at
2θ m ∼ 21.4 ◦ . According to [18], this diffraction maximum characterizes the existence of interpolyelectrolyte–metal complexes between the ions (Ag + ) and ligands.
Taking into account the angular position of this diffraction peak on the X-ray
diffractogram of the IMC, average Bragg distance d between the macromolecular
chains of polyelectrolytes coordinated with Ag + ions is found to be 8.0 Å.
Chemical reduction of the Ag + ions in the IMC by sodium borohydride results
in formation of a nanocomposite based on the IPEC and Ag. In the nanocomposite’s
profile (Fig. 3.2, curve 3), one can see that the low-intense diffraction maximum at
2θ m ∼ 11.0 ◦ , which is typical of the above interpolyelectrolyte–metal complexes,
is absent, unlike two intensity diffraction peaks appeared at 2θ m ∼ 37.8 ◦ and
43.6 ◦ , corresponding to the crystallographic plan of the face-centered cubic lattice
of silver with (111) and (200) indexes, respectively, thus confirming presence of
metallic silver in the polymeric system. Moreover, diffraction maximum intensity at
2θ m ≈ 20.8 Ñ , characterizing structure of IPEC “pectin–P4VP,” is enhanced.
Effective size L of Ag nanoparticle crystallites in the IPEC proved to be 4.0 nm
(for the calculation, diffraction maxima at 2θ m = 37.8 ◦ and 43.6 ◦ were used,
curve 3).
53
where - is a constant related to a shape of the crystallites (K = 0.9 if their shape is
unknown) and β is the angular half-width (width at a half-height) of the singlet of a
discrete diffraction maximum, showed that the average L value is 17.5 nm (for the
calculation, singlet diffraction maxima at 2θ m = 18.7 ◦ and 30.8 ◦ were applied).
However, the X-ray pattern of the pectin sample in the form of a film prepared
from a 5% aqueous solution displays only contours of the groups of diffraction
maxima with basic intensities that are present on the X-ray pattern of the pectin
powder (Fig. 3.1, curves 3, 4). This circumstance indicates a low rate of pectin
crystallization, as well as the relaxation character of the structurization processes in
the polymers.
IPEC formed from pectin and P4VP is characterized by short-range ordering
during translation of fragments of oppositely charged polyelectrolyte macromolecular chains in a space. This fact is confirmed by the appearance of diffuse
diffraction maximum at 2θ m ∼ 21.2 ◦ on the X-ray profile of the IPEC sample
(see Fig. 3.1, curve 2). The average value for the period of short-range ordering
of macromolecular chains’ fragments of oppositely charged polyelectrolytes in
the IPEC (the average Bragg distance between chains of the polyanion and the
polycation) is equal to 4.2 Å.
The following fact should be taken into consideration: in the IPEC profile
obtained for equimolar quantity of pectin and P4VP, the angular location of the
secondary (rated by intensity) diffraction maximum is shifted from 10.6
◦ to 11.8
◦
comparing with P4VP (Fig. 3.1, curves 1, 2), while the average Bragg distance (d)
between P4VP’s main macrochains (as part of IPEC) is falling down from 8.3 Å to
7.5 Å.
Once the pectin–Ag + –P4VP IMC is formed, the diffraction pattern changes.
This is confirmed by the appearance of a low-intense diffuse diffraction maximum at 2θ m ∼ 11.0 ◦ (Fig. 3.2, curve 2) in the presence of a low-intensity
amorphous halo, which, unlike that for the IPEC, has an angular position at
2θ m ∼ 21.4 ◦ . According to [18], this diffraction maximum characterizes the existence of interpolyelectrolyte–metal complexes between the ions (Ag + ) and ligands.
Taking into account the angular position of this diffraction peak on the X-ray
diffractogram of the IMC, average Bragg distance d between the macromolecular
chains of polyelectrolytes coordinated with Ag + ions is found to be 8.0 Å.
Chemical reduction of the Ag + ions in the IMC by sodium borohydride results
in formation of a nanocomposite based on the IPEC and Ag. In the nanocomposite’s
profile (Fig. 3.2, curve 3), one can see that the low-intense diffraction maximum at
2θ m ∼ 11.0 ◦ , which is typical of the above interpolyelectrolyte–metal complexes,
is absent, unlike two intensity diffraction peaks appeared at 2θ m ∼ 37.8 ◦ and
43.6 ◦ , corresponding to the crystallographic plan of the face-centered cubic lattice
of silver with (111) and (200) indexes, respectively, thus confirming presence of
metallic silver in the polymeric system. Moreover, diffraction maximum intensity at
2θ m ≈ 20.8 Ñ , characterizing structure of IPEC “pectin–P4VP,” is enhanced.
Effective size L of Ag nanoparticle crystallites in the IPEC proved to be 4.0 nm
(for the calculation, diffraction maxima at 2θ m = 37.8 ◦ and 43.6 ◦ were used,
curve 3).