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Hydrogels are soft water-rich materials with physical properties that can be easily tuned by modifying their network structure. For instance, increasing or decreasing the cross-linking density has a profound effect on their water absorption capabilities and mechanical strength. These physical changes are showcased in a new experiment for organic chemistry and polymer science teaching laboratories based on the practical green synthesis and characterization of lactose methacrylate derived hydrogels. Lactose, a disaccharide derived from dairy waste byproducts, is functionalized with photoreactive methacrylate groups using methacrylic anhydride. The resulting mixture is subsequently photoirradiated to generate a cross-linked hydrogel. Structure–property relationships are assessed through comparative studies of three hydrogels of varying compositions. Compression tests and swelling studies in different aqueous environments offer a guided-inquiry experience. Students determine a relationship between cross-linking density and the physical properties of the hydrogels. This experiment highlights the valorization of biomass and multiple green chemistry principles including use of renewable feedstocks, atom economy, energy efficiency, waste prevention, and water as a benign solvent. Learning outcomes for an organic chemistry laboratory course include introduction to disaccharide and cross-linked polymer structures, observable physical change dependency with cross-linking density, and laboratory methods for evaluating water absorption capacities. Objectives aligned with a polymer course are incorporating mechanical compression instrumentation, mechanistic understanding of light-induced free radical polymerizations, and an appreciation for the application of hydrogels to commercial products. Overall, the translation of a current literature publication to an inexpensive and versatile experiment engages students in a modern example of sustainable polymer chemistry. 

Abstract. Nucleation rates involving sulfuric acid and watermeasured in a photolytic flow reactor have decreased considerably over atime period of several years. Results show that the system – flow reactor,gas supplies and lines, flow meters, valves, H2SO4 photo-oxidantsources – has reached a baseline stability that yields nucleationinformation such as cluster free energies. The baseline nucleation rate ispunctuated by temporary bursts that in many instances are linked to cylinderchanges, delineating this source of potential contaminants. Diagnostics wereperformed to better understand the system, including growth studies to assessH2SO4 levels, chemiluminescent NO and NOx detection toassess the HONO source, and deployment of a second particle detector toassess the nanoparticle detection system. The growth of seed particles showstrends consistent with the sizes of nucleated particles and provides ananchor for calculated H2SO4 concentrations. The chemiluminescentdetector revealed that small amounts of NO are present in the HONO source,∼ 10 % of HONO. The second condensation-type particlecounter indicates that the nanoparticle mobility sizing system has a bias atlow sulfuric acid levels. The measured and modeled nucleation ratesrepresent upper limits to nucleation in the binary homogeneous system,H2SO4-H2O, as contaminants might act to enhance nucleationrates and ion-mediated nucleation may contribute. Nonetheless, theexperimental nucleation rates, which have decreased by an order of magnitudeor larger since our first publication, extrapolate to some of the lowest ratesreported in experiments with photolytic H2SO4. Results fromexperiments with varying water content and with ammonia addition are alsopresented and have also decreased by an order of magnitude from our previouswork; revised energetics of clusters in this three-component system arederived which differ from our previous energetics mainly in the five-acid andlarger clusters.