Poly(vinyl alcohol) (PVA) is an important polymer used in a number of applications, such as adhesives, coatings, eye drops, and contact lens solution. Dilute aqueous solutions of PVA and borax are frequently used in “slime” demonstrations to make a low hazard viscous polymeric solution. Typically, these demonstrations use dilute aqueous solutions (e.g., 4 wt/wt %) of PVA with a low average molecular weight (e.g., M<sub>w</sub> = 10,000 – 30,000) in combination with sodium borate (i.e., borax). The borax induces crosslinking between polymer chains, which increases the viscosity of the polymer solution to form a “slime.” Interestingly, use of more concentrated (i.e., 26 wt/wt %) aqueous solutions of higher average molecular weight PVA (i.e., M<sub>w</sub> = 145,000) results in the formation of a rigid hydrogel without the need of a chemical cross linker. Furthermore, exposing the gel to a freeze-thaw cycle increases the mechanical strength of the resulting gel and equips the material with self-healing properties. This presentation describes our efforts to design a teaching lab involving the preparation and analysis of PVA hydrogels with self-healing properties. The lab is amenable to both high school and college teaching laboratories. In this lab students i) prepare a polymeric solution, ii) cast the crude hydrogel into a mold, iii) expose the crude hydrogel to a freeze-thaw cycle, and iv) analyze the self-healing properties of the resulting hydrogel. The presentation will discuss strategies to optimize tensile strength of the “healed” gels along with opportunities to vary the procedure to introduce guided inquiry.

Laboratory experiment in the preparation and analysis of poly(vinyl alcohol) self-healing hydrogels

255th National Meeting (2018)

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