Phase transitions in octanethiol-capped Ag nanocluster microfilm assemblies

Abstract

We describe phase transitions in microfilm assemblies of octanethiol (OT)-capped 2-4 nm-diameter Ag nanoclusters prepared from solutions with OT/Ag+ ratios of ∼50. Using DSC we observe two melting/crystallization-type reversible phase transitions: one at ∼61°C due to interdigiated unattached octanethiol, and the other at ∼125°C due to the phase comprised of the assembly of OT-capped nanoclusters. Increased thermal fluctuations weaken the inter-chain hydrophobic interactions between interdigitated OT molecules, leading to both phase transitions. The thiolate bond of OT-molecules bound to Ag nanoclusters are more rigid, thereby requiring a higher temperature to increase the flexibility of the ..