Dynamics and Large Strain Behavior of Self-Healing Hydrogels with and without Surfactants

Abstract

Polyacrylamide hydrogels formed via hydrophobic interactions between stearyl groups in aqueous micellar solution of sodium dodecyl sulfate (SDS) present two faces depending on which state they are. The gels containing SDS micelles exhibit, in addition to the fast mode, a slow relaxation mode in dynamic light scattering (DLS) and timedependent elastic moduli, indicating the temporary nature of the hydrophobic associations having lifetimes of the order of seconds to milliseconds. The gels where SDS had been removed after their preparation behave similar to chemically cross-linked ones with time-independent elastic moduli, a high degree of spatial inhomogeneity, and a single relaxation mode in DLS. Because of this drastic structural change, the physical gels are insoluble in water with a gel fraction close to unity. In surfactant containing gels, a large proportion of physical cross-links dissociate under force, but they do so reversibly, if the force is removed they reform again. The reversible disengagements of the hydrophobic units building the physical cross-links leads to a self-healing efficiency of nearly 100%, while no such healing behavior was observed after extraction of SDS due to the loss of the reversible nature of the cross-linkages.

Functional self-healing materials and their potential applications in biomedical engineering

“…The supramolecular polymer network is formed using hydrophobically modified PAAc with oppositely charged cetyltrimethylammonium (CTA) via hydrophobic and electrostatic interactions. Different from self-healing hydrogels which were formed only through hydrophobic interaction [9], its self-healing behavior still maintained in water due to the electrostatical entrapment of surfactant alkyl chains in the network. Healing efficiency of the hydrogel can be accelerated by heating, treatment of acid, or an addition of surfactant solution.…”

The self‐healing mechanism of an industrial acrylic elastomer

“…12 The self-healing ability of these materials is attributed to the reversible noncovalent interactions in particular such as hydrogen bonding, 6,8,[13][14][15] hydrophobic association, [16][17][18][19][20] ionic bonds, [21][22][23][24] and p-p stacks. 25,26 However, the low mechanical strength has limited the practical application of these materials.…”

Self‐Healing Poly(acrylic acid) Hydrogels: Effect of Surfactant

“…[11,12] Recently, our research group presented a simple strategy for the production of self-healing hydrogels via hydrophobic interaction. [13][14][15][16] Incorporation of hydrophobic sequences within the hydrophilic polymer chains via micellar polymerization generates dynamic hydrophobic associations between the hydrophobic domains of polymer chains and surfactant micelles acting as physical cross-links of the resulting hydrogels. These reversible breakable cross-links are responsible for rapid self-healing.…”