Elucidation of Molecular Interactions between Spherical Polymer Brushes Using Sum Frequency Generation Vibrational Spectroscopy

With support from the the Chemical Structure and Dynamics (CSD) program in the Division of Chemistry, Professors Ilya Zharov and John Conboy of the University of Utah, along with their students, are combining their expertise in materials synthesis, characterization, and spectroscopy to investigate the molecular-level interactions between polymer-grafted silica nanoparticles during self-assembly. This process offers a promising pathway to design materials with unique properties and applications.

However, achieving self-assembly remains challenging due to the intricate interactions among the polymer chains. To understand these interactions, the researchers will employ sum-frequency generation (SFG) vibrational spectroscopy, a technique that uses a combination of infrared and visible light to excite polymer vibrations, in order to determine their relative orientations.

This approach provides access to the polymer structure at buried interfaces, a notoriously difficult area to probe. In addition, the team will create polymer nanoparticle films to further study the dynamics of polymer interdigitation. The insights gained from these studies are expected to lead to improved design principles for novel porous materials that can respond to temperature and pH changes.

Furthermore, the project contributes to science education through student mentorship and outreach programs in local schools, inspiring future generations of researchers.

This research aims to elucidate the molecular interactions that govern the self-assembly of polymer-grafted nanoparticles, focusing on the degree of polymer interdigitation and its dependence on polymer structure and environmental conditions, such as solvent polarity, pH and temperature. By systematically varying nanoparticle size, polymer composition, chain length and grafting density, the researchers will investigate how these parameters influence particle-particle interactions and assembly.

Complementary deuterated polymer brushes will be prepared on fused silica substrates to facilitate surface-specific vibrational analysis. The team will utilize sum-frequency generation (SFG) spectroscopy to probe the orientation and conformation of the polymer chains on the nanoparticles, while in situ TEM and Langmuir-Blodgett techniques will provide direct visualization of the self-assembly process.

These studies will generate critical insights into the effects of chain conformation, nanoparticle curvature, and solvent polarity on the self-assembly and formation of porous nanoparticle assemblies. The knowledge gained will have broad implications for nanomaterial design, offering principles for engineering new classes of nanoparticle-based materials with well-defined porosity and which are responsiveness to external stimuli.

This work will also advance the application of SFG spectroscopy for the study of macromolecular and supramolecular chemical interactions, reinforcing its role as a powerful tool for studying complex interfacial phenomena.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.