Simple and Versatile Protocol for Preparing Self-Healing Poly(vinyl alcohol) Hydrogels

As the role of polymers in undergraduate chemistry curricula continues to expand, opportunities will emerge for adopting experiments involving smart materials (i.e., materials that change properties in response to external stimuli). Slime demonstrations are routinely carried out with poly(vinyl alcohol) (i.e., PVA) hydrogels because the polymer is inexpensive and nontoxic, and the resulting material has interesting physical properties. This report describes an activity where PVA is processed into an autonomous self-healing smart material. Specifically, students prepare rigid PVA hydrogels using a simple freeze/thaw protocol. The resulting material is cut, and the severed edges are pressed together to initiate autonomous self-healing. Healing is observed by measuring sufficiently high (i.e., >40 kPa) uniaxial tensile strengths at the repaired surface. Preparing the hydrogel does not require chemical additives beyond commercially available PVA (i.e., M-w similar to 145,000 g mol(-1)) and water. Additionally, the tensile strength can be determined using a spring force gauge and a ruler. The simplicity of the procedure, use of low-cost materials, and ties to green chemistry make the activity suitable for use in high school or introductory college chemistry settings. Furthermore, procedural variation and more rigorous analysis make the activity versatile by allowing the protocol to be used in second- or third-year chemistry courses (e.g., organic and physical chemistry). Overall, the activity provides a straightforward approach to introducing students to modern topics in polymer chemistry and materials science.