Soap opera : polymer-surfactant interactions on thin film surfaces /

Surfactants are macromolecules with unique properties. They commonly contain a polar head group with a nonpolar hydrocarbon chain. These properties allow surfactants to solubilize greases and other nonpolar molecules. One particular way that this is accomplished is through the formation of micelles. Micelles are formed at the critical micelle concentration (cmc), which varies depending upon the nature of the surfactant and also the media in which the surfactant resides. These micelles can take a variety of shapes, but are generally characterized by surrounding the grease with the nonpolar hydrocarbon chains, exposing only the polarized head groups to the media, usually water. This property of easy solubilization has made surfactants a very attractive industrial agent, They are used most conventionally as industrial cleaning agents and detergents. However, they also have lesser-known applications in conjunction with polymers and other macromolecular mixtures, often creating a system with novel properties, such as increased solubilization and smoother mixture consistency. A recently developed field has investigated the self-assembly of polymers and polyelectrolytes onto thin film surfaces. There are many reasons for studying this process, such as for second harmonic generation purposes and bioassays. In this study, the interaction between the anionic polyelectrolyte poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) and two surfactants of opposite charge, Sodium Dodecyl Sulfate (SDS) and Dodecyl Trimethyl Ammonium Bromide (DTAB), in their assembly onto thin film surfaces was investigated. The kinetics of adsorbance onto the thin films was examined, followed by construction of 10-bilayer films using an alternating layer of the cationic polyelectrolyte poly(ethylenimine) (PEI) to provide the electrostatic means for the PAZO/surfactant combination to assemble onto the thin film. The kinetics of adsorption is being characterized primarily with UV-visible spectroscopy, whereas the ten bilayers are being studied with both UV-visible spectroscopy and ellipsometry. Preliminary results suggest that the rate of adsorbance of various concentrations of SDS below and above the cmc in PAZO is not significantly different from the rate of adsorbance of pure PAZO. However, the amount of adsorbed material decreases as the concentration of SDS dissolved into PAZO increases. This has allowed for less PAZO adsorbance to be detected in the 10-bilayer systems. Preliminary kinetics data suggest longer saturation times for DTAB/PAZO systems, but amount adsorbed may be increased from pure PAZO systems. Further work is being conducted on the kinetics, and more 10 bilayer films remain to be built and characterized. In situ methods of studying the films will also be examined in the future

Surface and Stability Characterization of a Nanoporous ZIF‑8 Thin Film

Zeolitic imidazolate frameworks (ZIFs) have been widely investigated for numerous applications including energy storage, heterogeneous catalysis, and greenhouse gas adsorption. Much of the early work has focused on the bulk properties of microcrystalline ZIFs. Herein, we focus on identifying the nature of the surface of ZIF-8 by studying a supported ZIF-8 nanoparticle film using surface characterization techniques. We have experimentally identified the presence of a zinc-rich surface terminated by carbonates and water/hydroxyl groups (in addition to the expected methylimidazole terminations) using X-ray photoelectron spectroscopy (XPS). The thermal stability of ZIF-8 thin films was also investigated using scanning electron microscopy (SEM) and temperature-programmed reaction spectroscopy (TPRS). We determined the onset of decomposition of ZIF-8 thin films to be approximately 630 K using TPRS in an ultrahigh vacuum (UHV) environment. This work presents the first characterization steps needed to study the evolution of ZIF surfaces in situ using surface characterization techniques. Such techniques are capable of determining reaction products and tracking intermediates and surface evolution in gas adsorption/reaction studies of thin films