David and Goliath: How Nano-Sized Effects Can Overcome Bulk Properties
Mark Peterson
Mentor: Sergey Nizkorodov
Deliquescence describes a phase transition of a particle from the solid to liquid state due to the
uptake of water, and is often characterized by abrupt particle growth. The goal of this study is to
measure bulk equilibrium vapor pressure (Pvap) above surfactant enriched saturated solutions and
compare this to DRH values of nanoparticles. To obtain Pvap values, we measured the relative
humidity above mixtures of surfactant enriched salt solutions analogous to the nanoparticle
experiments. The Pvap values above these solutions were carefully measured as a function of mole
fraction NaCl. The addition of surfactant was found to increase the Pvap relative to that of pure NaCl.
Water uptake by surfactant coated nanoparticles was studied in a separate experiment using state-ofthe-art particle mobility methods. The surfactant enriched nanoparticles exhibited a lower DRH
compared to that of pure NaCl. The opposite effect of the surfactant on the DRH in the bulk and in
nanoparticles is a consequence of different structural characteristics of these particles. In bulk
solutions surfactants form separate phases on the surface of NaCl, with weak interaction between the
phases. Contrarily, surfactants prefer to completely envelop the NaCl nanoparticles, forming a soapy
film on its surface. This reduces surface tension and facilitates water uptake by the encapsulated
NaCl, which shows how a small number of surface atoms can drastically alter the behavior of the
entire particle.