Effect of the sodium dodecyl sulfate/monomer ratio on the network structure of hydrophobic association hydrogels with adjustable mechanical properties

The study of gel-network structure is not as extensive as the study of the application of hydrogels. However, the distribution of the inner structure is crucial for designing hydrogels with tunable mechanical properties to meet certain kinds of demands. In this study, a series of hydrophobic association hydrogels (HA-gels) were synthesized by free-radical micellar copolymerization in a sodium dodecyl sulfate (SDS) surfactant solution. The hydrophobic monomer was palmityl alcohol poly(oxyethylene acrylate) (AEO-AC), which is an ecofriendly alternative to the traditional octyl phenol poly(oxyethylene acrylate). Interestingly, we found that the molar ratio [or ratio point (R)] of SDS to AEO-AC played a key role in tuning the mechanical properties. All series HA-gels denominated a similar down-up-down tendency with increasing R, and the best R is 3. This result was consistent with the microscopic network structure number of the hydrophobic monomer (N-H=21-24), and this indicated that each hydrophobic monomer associated three SDS monomers in its internal networks. The resulting AEO-AC-acrylamide gels exhibited the best mechanical strength (yield maximum broken stress=218 kPa) and the maximum effective crosslink density. Moreover, the relationship between the network structure and the mechanical properties of the HA-gels was investigated with various Rs. Two different interaction effects of distribution between SDS and AEO-AC are discussed in detail. The HA-gels exhibited self-healing properties and maintained their shape in water over 160 days. The results indicate that changing R is an effective method for tuning the mechanical properties of HA-gels as a type of prospective biomedical material. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45196.