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

Abstract

Summary: Physical poly(acrylic acid) gels were prepared by micellar copolymerization of hydrophilic monomer acrylic acid with large hydrophobic monomer stearyl methacrylate (C18) in solutions of worm-like anionic surfactant (sodium dodecyl sulfate, SDS) and cationic surfactant (cetyltrimethyl ammonium bromide, CTAB) micelles. Hydrophobe content of the monomer mixtures was 2 mol.% and total monomer concentration in gels was 20 w/v%. Gelation reactions were monitored by rheometry using oscillatory deformation tests. Hydrogel samples were also subjected to uniaxial elongation and compression tests after preparation and swelling. The physical gels with SDS and CTAB showed similar properties as long as they are at the state of preparation, such as insoluble in water and exhibit time-dependent dynamic moduli, high Young's modulus, high fracture stress, high elongation ratios at break. Also self-healing was evidenced by mechanical measurements. Physical gels formed in SDS solution were stable, exhibited high equilibrium swelling ratios and SDS progressively extracted from the network in water. On the other hand, gels with CTAB formed a complex and resulted in shrinkage after gels were immersed in a large excess of water because both electrostatic interactions between the charged components and hydrophobic interactions between the polymer backbone and the alkyl chains of the surfactant are important in driving the self-assembly of molecules to form ordered structures. These structures of the polyelectrolyte surfactant complexes have unusual mechanical properties. Also, the hydrogel samples with CTAB self-healed via heating and surfactant treatment of the damaged areas withstand up to 1.05 MPa stresses and rupture at a stretch of 800%.

Tough and self‐healing hydrophobic association hydrogels with cationic surfactant

“…When the content of LMA and DTAB decreased to 2/3 of the origin content, the tensile stress was increasing by 30 kPa. In other words, HA‐5 hydrogel had superior mechanical behaviors with a fracture stress of 181 kPa and toughness of 2.19 MJ m −3 .HA hydrogels in this paper have higher fracture stress and toughness than that of some references, 17,43,47,54 suggesting that the HA hydrogels had better mechanical strength and toughness.…”

“…The HA hydrogels performed different deformations in the process of stretching, which slowly increased with the cycle times 46 . The n th loading curve was partly overlapped by the (n–1) th loading curve over the whole range of the n th maximum strain 43 . The broken area over Loading‐unloading process consisted of covalent bands and micelles.…”

“…Hydrophobic association (HA) hydrogels were usually synthesized by hydrophilic monomers methacrylate (C 12 ‐C 22 ) and hydrophobic monomer acrylamide or acrylic acid in micellar solution formed by the surfactant and salt 17,32,38–43 . The surfactant system is almost sodium dodecyl sulfate (SDS) and sodium chloride.…”

Hydrogel: Diversity of Structures and Applications in Food Science

“…[187] Besides the inner hydrophobic and external hydrophilic polymer types and concentration, surfactants or emulsifiers that stabilize the structure of micelles also deeply impact the structure and properties (e.g., stress and toughness) of HA-gels. [192,[197][198][199][200][201]…”

Synthesis and Biomedical Applications of Self-healing Hydrogels

“…Hydrophobic interactions occur as a consequence of aggregative hydrophobes in aqueous media. In many cases of self-healing hydrogels based on hydrophobic interactions, the surfactant micelles (Gulyuz and Okay, 2015 ; Liu, Y. et al, 2018 ) or liposomes (Rao et al, 2011 ; Hao et al, 2013 ) are employed as crosslinking points to construct the polymer chains comprising both hydrophilic and hydrophobic monomers. For example, the self-healing hydrogel could form via micellar copolymerization of hydrophobic monomer stearyl methacrylate and hydrophilic monomer acrylamide in the aqueous solution of sodium dodecyl sulfate (SDS) micelles (Tuncaboylu et al, 2011 , 2012a , b ).…”