The effect of poly(acrylic acid) on temperature-dependent behaviors and structural evolution of poloxamer 407

Understanding temperature-dependent behaviors and structural evolution plays an essential role in the development of thermosensitive hydrogels. In this work, thermosensitive hydrogels composed of poly(acrylic acid) (PAA) and poloxamer 407 (PX) were investigated. The effect of PAA on the thermosensitive micellization, gelation and structural evolution of 20% PX (20PX) was studied by means of differential scanning calorimetry (DSC), rheology and small angle X-ray scattering. In addition, the structural and amplitude-dependent rheological characteristics of mixtures of 20PX and various concentrations of PAA (PAA/PX) gels at body temperature were also examined. The DSC thermograms of the PAA/PX mixtures revealed overlapping double endothermic peaks, reflecting the micellization of PX micelles with attached PAA and pure PX micelles. The formation of PX micelles with attached PAA increased when PAA concentration was increased. The intermicellar packing of PX micelles might be interfered by the attached PAA; the presence of PAA modulated the gelation temperature. All thermosensitive systems showed disorder-to-order structural evolution upon heating. Although the micelles in the plain 20PX gel arranged into a face-centered cubic (FCC) geometry, a body-centered cubic (BCC) phase emerged in the PAA/PX mixtures and became predominant with increasing PAA concentration. The presence of PAA chains tailored the ordered structure of the gels and favored the BCC arrangement.The rheological and ordered structural properties of the PAA/PX gels at body temperature can be modulated by varying the concentration of PAA. (c) 2021 Society of Chemical Industry

Automated summary

Understanding temperature-dependent behaviors and structural evolution is crucial for the development of thermosensitive hydrogels. In this study, the effect of PAA concentration on the thermosensitive micellization, gelation, and structural evolution of PAA/PX gels was investigated. The presence of PAA influenced the intermicellar packing and modulated the gelation temperature, leading to a transition from a face-centered cubic (FCC) to a body-centered cubic (BCC) phase with increasing PAA concentration. The rheological and ordered structural properties of the PAA/PX gels at body temperature can be modulated by varying the concentration of PAA.