The control of the final size depends on the

limitation applied to the coalescence beyond certain nuclearity. For free clusters such as nanocolloids in solution, the coalescence STA-9090 manufacturer may be limited by a polymeric molecule acting as a cluster stabilizer. Stabilization All nanostructured materials possess a huge surface energy due to the large surface area; thus, they are thermodynamically unstable or metastable. Overcoming the large surface energy to prevent the nanostructures from growing is one of the great challenges in the synthesis of nanomaterials [32]. Nanoparticles, exclusively colloidal particles, in a short distance, are attracted to each other by the van der Waals force. If there is no counteracting force, the particles will aggregate and the colloidal system will be destabilized. The stability is achieved when the repulsion forces balance the attraction forces by electrostatic stabilization

and/or steric stabilization. There are several types of colloidal metal stabilizers which depend on the type of metal, KU-57788 cell line method of preparation, and the application of the resultant metallic nanoparticles. For example, polymers having functional groups such as -NH2, -COOH, and -OH have high affinity for metal atoms; however, the use of stabilizers is not desirable for some applications such as catalysis. For example, activities of supported metal nanoparticle catalysts by coordination MAPK inhibitor capture method are higher than those of polyvinyl-pyrrolidone

(PVP)-stabilized metal colloidal catalysts [33, 34]. Due to functional groups namely C = O and N, and long polymer chains, PVP can associate with the metal nanoparticles [35, 36]. The functional groups containing lone pairs of electrons help in the stabilization of metal nanoparticles at their surfaces by covalent interaction, whereas the polymer chain restricts aggregation of metal nanoparticles by steric hindrance. For example, the long chains of PVP stretch out around nickel atom on the surface of the crystal, causing a steric hindrance effect and thus prevent particle growth effectively [37]. Apart from this, PVP is a biocompatible polymer. Hence, nanoparticles synthesized in PVP can be used in biological applications. O-methylated flavonoid There are several reports about using poly(vinyl alcohol) (PVA) as a colloidal stabilizer for the synthesis of metallic nanoparticles by ionizing radiation [38–40]. The PVA chain plays a significant role in avoiding the formation of metal hydroxide clusters by hydrolysis of metal ions, thus preventing them from aggregation. Several active -OH groups in PVA are capable of absorbing metal ions through secondary bonds and steric entrapment [41]. A reaction of metal ions (M+) with PVA that leads to their associations can be expressed as: (12) where R-OH represents a PVA monomer.