DOI: 10.1007/s00339-005-3283-4 Appl. Phys. A 81, 835–838 (2005) Materials Science & Processing Applied Physics A p. sreekumari nair 1, ∗ t. radhakrishnan 1, ∗∗ n. revaprasadu 1 g.a. kolawole 1 a.s. luyt 2 v. djokovi ´ c 2,3, ✉ Structure and properties of PbS–polyacrylamide nanocomposites 1 Department of Chemistry, University of Zululand, Private Bag X1001, Kwa Dlangezwa, 3886, South Africa 2 Department of Chemistry, University of the Free State (Qwaqwa Campus), Private Bag X13, Phuthatidjhaba, 9866, South Africa 3 Institut of Nuclear Sciences ‘Vinˇ ca’, P.O. Box 522, 11001 Belgrade, Serbia and Montenegro Received: 12 April 2005/Accepted: 20 April 2005 Published online: 7 June 2005 • © Springer-Verlag 2005 ABSTRACT A synthetic procedure for the incorporation of PbS nanoparticles in a polyacrylamide (PAM) matrix is introduced. The method is based on the simultaneous polymerization of the monomer and thermal decomposition of the dithiooxamide– lead complex. X-ray diffraction analysis revealed that the PbS nanoparticles have a sphalerite crystal structure (galena). A transmission electron micrograph showed spherical particles, with an average diameter of about 3 nm, well dispersed in the polymer matrix. Although a sharp edge was not observed, the optical absorption of the PAM–PbS nanocomposite is shifted to- wards lower wavelengths compared to the bulk PbS. It was also found that, despite a low concentration of the inorganic phase, the nanoparticles significantly affect the thermal properties of the matrix. PACS 82.35.Np; 81.07.-b 1 Introduction Semiconductor–polymer nanocomposites are cur- rently the subject of intensive investigation because of their potential application as high-technology materials [1–21]. Due to the large number of surface atoms and/or three- dimensional confinement of electrons, nanometric semicon- ductor particles exhibit novel properties that are different from the corresponding bulk solids. Because the degree of con- finement depends on the nanoparticle dimensions, theory and experiments have shown that optical, electrical, magnetic, and other properties are tunable by changing their sizes and shapes. Polymers are also good hosts for nanostructured ma- terials, since they are easily processable and show good long- term stability. PbS is a narrow-gap semiconductor (0.41 eV at room tem- perature) used in a variety of applications such as IR de- tectors [22], photography [23], and Pb +2 ion-selective sen- sors [24]. However, its band gap is very sensitive to finite size ✉ Fax: +381-11-344-0100, E-mail: djokovic@vin.bg.ac.yu ∗ Present address: Department of Chemistry, Lash-Miller Chemical Lab- oratories, University of Toronto, Ontario, M5S 3H6, Canada ∗∗ Present address: Department of Chemistry, University of Toronto at Mississauga, Mississauga, Ontario, L5L 1C6, Canada effects, increasing to 5 eV when the diameter of the particles falls in the nanometer scale [25, 26]. The resulting changes in optical properties can be successfully exploited by in- corporation of the PbS nanoparticles into a polymer matrix. For example, it has been shown [4] that nanocomposites of polyaniline and PbS can operate as photovoltaic cells. Struc- tural and/or optical properties of PbS nanoparticles in other host polymers have also been investigated [2–12]. In the present study we introduce a novel procedure for the synthesis of PbS nanoparticles in a polyacrylamide (PAM) matrix. The method is based on the polymerization of the monomer in the presence of a Pb complex. A precursor complex was chosen to undergo thermal decomposition at the polymerization temperature, forming nanostructured PbS. The obtained PbS nanoparticles in the matrix are further in- vestigated by spectroscopic and structural techniques. On the other hand, it is well known that, because of their high surface-to-bulk ratio, even small concentrations of nanopar- ticles can significantly affect the properties of the host poly- mer. In our previous investigations we observed strong ef- fects of HgS [21] and silver [27] nanoparticles on polystyr- ene (PS) and polyvinyl alcohol (PVA), respectively. Most of the studies of polyacrylamide nanocomposites (different nanofillers) [3, 10, 13, 28–32] and PbS nanocomposites (dif- ferent matrices) [2–11] did not take into account this aspect of material behavior. Hence, in these investigations, the effects of nanoparticles on the thermal properties of the matrix will also be considered. 2 Experimental 2.1 Synthesis of PbS in PAM The procedure for the preparation of PAM–PbS nanocomposites is based on the simultaneous polymerization of acrylamide and the thermal decomposition of a single- source precursor complex giving PbS nanoparticles. To an aqueous solution of acrylamide (2g in 100 ml of water) was added 75 mg lead acetate, followed by 30 mg azobi- sisobutyronitrile (AIBN). The solution was well stirred and heated to 60 ◦ C. As the polymerization reaction began, 25 mg dithiooxamide was added and the heating continued. The lead–dithiooxamide complex formed and decomposed to give PbS. The formation of PbS was indicated by the appearance of a wine red color in the reaction mixture. Ethanol was added