Scott Kaiser

Self-assembled monolayers (SAMs) can be terminated with various functional groups, which are often acido-basic groups (acid, amine, sulfonate etc...) bearing either a positive or negative net charge. The degree of ionization of the surface controls potential electrostatic interaction with charged species in solution. Nondestructive and simple ways of characterizing the surface charge of a SAM, in solution, is thus important. We propose an electro-analytical study of surface ionization based on the analysis of the voltammetric response of adsorbed redox species. Charged iron complexes are electrostatically adsorbed onto an ionized SAM and the width of the voltammetric peaks of the adsorbed redox couple is then analyzed with an electrostatic model accounting for potential drop within the SAM ¹ as well as electrostatic interactions between adsorbates and ionized terminal groups. We will present two mirror situations (positive redox couple onto a negative SAM and vice versa) to show the versatility of our approach. ¹ Smith, C. P.; White, H. S. Theory of the Interfacial Potential Distribution and Reversible Voltammetric Response of Electrodes Coated with Electroactive Molecular Films. Anal. Chem. 1992 , 64 , 2398– 2405, DOI: 10.1021/ac00044a017

Polyethylene (PE) is an intensely utilized polymer, which has consequently led to it becoming a common environmental contaminant. PE and other plastic waste are known to be highly persistent in surface waters; however, chemical and physical changes do take place over time, dependent mostly on highly variable natural conditions, such as oxygen (O₂) availability. Gamma radiation was used to generate reactive oxygen species, namely hydroxyl radicals, in initially aerated aqueous solutions to simulate the natural weathering of microplastics in waters where there are fluctuations and often depletions in dissolved O₂. The headspace of the irradiated PE-containing solutions was probed for the formation of degradation products using solid-phase microextraction (SPME) fibers in combination with gas chromatography mass spectrometry (GCMS). The major species detected were n-dodecane, with trace levels of tridecane, 2-dodecanone, and hexadecane, which were believed to be predominately adsorbed in the PE microplastics in excess of their aqueous solubility limits. Surface characterization by Raman spectroscopy and light and dark field microscopy indicated no change in the chemical composition of the irradiated PE microplastics under low O₂ to anaerobic conditions. However, morphological changes were observed, indicating radical combination reactions.