Sponge-like Heterogeneous Gels: Hierarchical Structures in Poly(N-isopropylacrylamide) Chemical Gels As Observed by Combined Scattering and Confocal Microscopy Method

Internal structures of the opaque poly(N-isopropylacrylamide) gel obtained at the preparation temperature (TP) higher than 24.5 °C was found to have hierarchical structures by means of a combined small-angle-scattering (CSAS) method of small-angle light scattering (SALS), ultra-small-angle neutron scattering (USANS), and small-angle neutron scattering (SANS) with an aid of laser scanning confocal microscopy (LSCM). The combined CSAS and LSCM studies revealed that a global structure of the gels had a sponge-like two-phase structure. The polymer-rich phase of the sponge was filled with microgels having highly cross-linked network (“tight network”) chains that are interconnected by loosely cross-linked network (“loose network”) chains swollen with water, while the other phase of the sponge was mostly composed of water. These two phases were cocontinuous in three-dimensional space, hence, forming macroscopic gels. The SALS and USANS studies clarified that the sponge had a characteristic spacing of ≈12 μm and ...