ISSN 15600904, Polymer Science, Ser. B, 2015, Vol. 57, No. 1, pp. 31–38. © Pleiades Publishing, Ltd., 2015. Original Russian Text © N.N. Volkova, L.M. Bogdanova, L.I. Kuzub, N.N. Dremova, 2015, published in Russian in Vysokomolekulyarnye Soedineniya, Ser. B, 2015, Vol. 57, No. 1, pp. 36–44.
COMPOSITES
Kinetics of the Thermal Degradation of Polycarbonate Films Containing Silver Nanoparticles N. N. Volkova*, L. M. Bogdanova, L. I. Kuzub, and N. N. Dremova Institute of Problems of Chemical Physics, Russian Academy of Sciences, pr. Akademika Semenova 1, Chernogolovka, Moscow oblast, 142432 Russia *email:
[email protected] Received July 11, 2014; Revised Manuscript Received September 30, 2014
Abstract—The kinetic features of thermal degradation of polycarbonate films containing 0.02–0.13 wt % sil ver are investigated. The analysis of surface plasmon resonance spectra shows that the composite films con tain silver nanoparticles with sizes from 10 to 200 nm. The shapes and sizes of particles are determined via scanning electron microscopy. It is shown that the rates of thermal degradation of the nanocomposites are much higher than the rate of degradation of the initial polycarbonate; the highest catalytic activity is exhibited by spherical silver nanoparticles with sizes below than 40 nm, while particles shaped as bipyramids and having sizes of 100–200 nm are less active catalytically. DOI: 10.1134/S1560090415010145
Silver nanoparticles possess unique optical and electrical characteristics [1–3] and are characterized by high bactericidal and catalytic activities [3]. Cata lytic reactions of gases with the participation of silver nanoparticles deposited on a substrate have been stud ied most extensively [4, 5]. The kinetic studies of cat alytic processes involving silver and gold nanoparticles in an organic medium are few in number [6–8].
vent was removed during drying of the films at 120°C for 16 h. The formation of silver nanoparticles was moni tored via measurement of absorption spectra in the visible spectral range. With this aim in view, surface plasmon resonance (SPR) peaks in the wavelength range 200–800 nm were analyzed and maximum absorbance Dmax was determined for each peak. Spec trophotometric measurements were performed with the use of a Cary50 spectrophotometer (Varian). The optimum time for the formation of silver par ticles via the reduction of AgNO3 was estimated from the analysis of kinetic curves of the increase in Dmax [10]. It was found that silver nitrate is fully reduced during evaporation. The concentration of AgNO3 in the solutions was varied from 1.3 × 10–4 to 7.4 × 10–4 mol/L, and the NaBH4toAgNO3 molar ratio was in the range from 1 : 1 to 8 : 1. The resulting films with thicknesses of 40–70 µm contained silver particles with sizes of 10– 200 nm (depending on the reagents concentrations and the formation conditions). The structure of PC composite films was studied with the use of a Zeiss SUPRA 25 scanning electron microscope (SEM). Thermal degradation of the films was investigated in the temperature range 285–400°C under isother mal conditions. The degradation kinetics was moni tored via measurement of the relative decreases in mass, Δm/m0, of the samples with the aid of an ATV 14 automatic electronic thermobalance. The residual pressure in the system was maintained at a level of 0.1 Pa. The initial mass of a sample, m0, was 15–
In this paper, the effect of silver nanoparticles on the thermal stability of polymer composite films was studied. For this purpose, the kinetic features of ther mal degradation of polycarbonate films containing sil ver particles of various shapes and sizes were investi gated. EXPERIMENTAL Composite films based on polycarbonate and silver were prepared via the slow evaporation of the solvent from a solution containing polycarbonate (Mw = 50.7 × 103 and Мn = 20.8 × 103), silver nitrate, and sodium borohydride NaBH4 as a reducing agent. Sil ver nanoparticles formed under these conditions (in situ) were stabilized by the functional groups of the polymer matrix [9, 10]. PC films with thicknesses of 40–70 µm and smooth surfaces were prepared via casting of 3 or 5% PC solu tions in a mixed organic solvent (methylene chloride CH2Cl2–3 vol % acetonitrile CH3CN) on a strongly adjusted horizontal surface of a glass cuvette, and the solvent was evaporated for an hour in a confined vol ume at a temperature of 30–35°C. The residual sol 31
32
VOLKOVA et al.
Table 1. Composition, properties, and kinetic parameters of the thermal degradation of PC composite films Spectral properties of films and sizes of silver particles Sample
[Ag], wt %
Rate constants of thermal degradation, 327°C
wavelength λ, nm
absorbance Dmax
sizes of particles d, nm
k1 × 104, s–1
k2 × 104, s–1
1
0.07
–
–
–
1.18
8.6
2
0.05
418
0.24
