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.
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Scaling laws to predict humidity-induced swelling and stiffness in hydrogels
From pasta to biological tissues to contact lenses, gel and gel-like materials inherently soften as they swell with water. In dry, low-relative-humidity environments, these materials stiffen as they de-swell with water. Here, we use semi-dilute polymer theory to develop a simple power-law relationship between hydrogel elastic modulus and swelling. From this relationship, we predict hydrogel stiffness or swelling at arbitrary relative humidities. Our close predictions of properties of hydrogels across three different polymer mesh families at varying crosslinking densities and relative humidities demonstrate the validity and generality of our understanding. This predictive capability enables more rapid material discovery and selection for hydrogel applications in varying humidity environments.
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- Award ID(s):
- 2011750
- NSF-PAR ID:
- 10324974
- Date Published:
- Journal Name:
- Soft Matter
- Volume:
- 17
- Issue:
- 43
- ISSN:
- 1744-683X
- Page Range / eLocation ID:
- 9893 to 9900
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1SM01186C
