From Theory to the Lab

In this chapter, we aim to connect the fundamental and theoretical ideas behind the swelling of gels to the phenomena one can measure and control in a laboratory. We begin with a brief discussion of chemistry to rationalize the fact that a preponderance of materials that swell contains a polymer backbone consisting of either C–C bonds (organic polymers; here, most commonly hydrogels) or Si–O bonds (silicone rubbers). Then, we describe in some detail the underlying silicone chemistry behind the preparation of polydimethylsiloxane (PDMS), the most common silicone rubber, as well as its solubility in a variety of common organic solvents. We then describe the chemical synthesis and properties of a common hydrogel – acrylamide gels. The second portion of this chapter focuses on experimentally characterizing the material properties commonly used in modeling the mechanics of swelling. These include the shear modulus G, the diffusivity D, and the Flory–Huggins χ parameter.