Spatially Heterogeneous Water Dynamics Templated by Self-Assembled Materials

We report, for the first time, observations of spatially heterogeneous water dynamics in self-assembled materials by a new spatially resolved infrared (IR) pump vibrational sum frequency generation (VSFG) probe microscope. Using this new technique, we studied water bounded by host-guest self-assembled sheets comprised of sodium dodecyl sulfate (SDS) and β-cyclodextrin (β-CD). We found that there are strong hydrogen-bond interactions between β-CD and nearby water, which not only template nearby water networks to adopt the chirality of β-CD, but also allow perturbations to the water network by optically exciting β-CD. More interestingly, the dynamics associated with the intermolecular interaction are heterogeneous among domains, while remaining uniform within domains. This surprising result indicates that the dynamics of water near to self-assembled materials can be templated uniformly across micron domains. The advancement in adding spatial resolution to ultrafast molecular vibrational spectroscopy opens a new way to measure micron-size local molecular structure ordering and relaxation dynamics in self-assembled systems, which are key components in purification materials, biological systems, and hydro-responsive materials for micro-optics and electronics.