Size Control and Enhanced Stability of Silver Nanoparticles by Cyclic Poly(ethylene glycol).

Silver nanoparticles (AgNPs) are used in a wide range of applications, and the size control and stability of the nanoparticles are crucial aspects in their applications. In the present study, cyclized poly(ethylene glycol) ( c -PEG) with various molecular weights, along with linear PEG with hydroxy chain ends (HO-PEG-OH) and methoxy chain ends (MeO-PEG-OMe) were applied for the Tollens' synthesis of AgNPs. The particle size was significantly affected by the topology and end groups of PEG. For example, the size determined by TEM was 40 ± 7 nm for HO-PEG 5k -OH, 21 ± 4 nm for c -PEG 5k , and 48 ± 9 nm for MeO-PEG 5k -OMe when the molar ratio of PEG to AgNO 3 ( ω ) was 44. The stability of AgNPs was also drastically improved by cyclization; the relative UV-Vis absorption intensity ( A/A 0 × 100%) at λ max to determine the proportion of persisting AgNPs in an aqueous NaCl solution (37.5 mM) was 58% for HO-PEG 5k -OH, 80% for c -PEG 5k , and 40% for MeO-PEG 5k -OMe, despite the fact that AgNPs with c -PEG 5k were much smaller than those with HO-PEG 5k -OH and MeO-PEG 5k -OMe.