Construction of Continuous Porous Organogels, Hydrogels, and Bicontinuous Organo/Hydro Hybrid Gels from Bicontinuous Microemulsions

Abstract

A new class of unique soft gels was produced by gelations of bicontinuous microemulsions (BME). Three alternative composite gel systems, namely BME organogel, hydrogel and an organo/hydro hybrid gel, prepared by hydrogelation and/or organogelation of BME solutions were proposed. These gels were self-supported, and aqueous and oil microphases bicontinuously coexisted and were immobilized in the gels. Even in "one side only" gelation products such as the BME organogel and the BME hydrogel, alternate solvent phases without gelator were also macroscopically immobilized. Microscopic structures of the gels were confirmed by CLSM and SEM observation. The BME organogels or hydrogels and BME hybrid gels showed continuous porous structures and double network structures, respectively. Mesostructures of the gels significantly depended on gelation conditions. It was found that the hierarchical structure of the BME gels was regulated by competition among three synergetic rate factors: immobilization of the BME structure by gelation, mesoscopic phase separation by gelation, and the time-dependent transformation of a solution/ solution structure toward a thermodynamic structure in an equilibrium state.

Mesostructured Polymer Materials Based on Bicontinuous Microemulsions

“…The BME organogels were produced by "rapid" (d and h) and "slow" (e and i) cooling. 27 The structures of BME gels are influenced by the kinetics of the gelation process, rather than by thermodynamic control of the original BME solution structure; this is similar to the case of condensed gels prepared by BME polymerization. Kinetic control of the physical gelation process to produce BME organogels was achieved relatively simply by control of the rate of cooling from the "sol state" to the "gel state".…”

Continuous Porous Poly(N-isopropylacrylamide) Gels Prepared from a Bicontinuous Microemulsion

“…A number of methods for the mesoscale structural control of swollen soft gels, 1 including porous, 28 composite, 3,9 and bicontinuous 35,10a,10b gels, have been proposed and investigated both as soft materials and self-assembly. Among a variety of unique soft gels such as double-network gels, 2 nanocomposite gels, 9 aqua materials, 11 topological gels, 12 hostguest polymer gels, 13 and stimuli-responsive (intelligent) gels 1,10,12a,1315 have seen particular focus because of their potential as polymer materials for actuators 1,13c,14,16 and drug-release systems.…”

“…17 To form the BME phase, the concentrations of salt and 2-butanol in the system were adjusted (Table S1) 17 according to previous studies. 3 The volumes of separated saline and oil phases in the three-phase solution were equalized to provide a BME sample solution that consisted of equal volumes of saline and toluene on a microscopic scale. The BME solution with NIPAM/MBAAM required a relatively lower salt concentration than the BME solution without monomers, because the monomers existed in the saline phase and decreased the hydrophilicity of the surfactant system.…”

“…17 The solution instantly became white and lost its transparency, indicating an increase in emulsion thickness caused by polymerization-induced phase separation. 3 The sample tube was typically allowed to stand for 30 min at 25°C, after which the formed NIPAM gels were immersed in water for 1 day to remove remaining NaCl, SDS, 2-butanol, and monomers. Figure 1 shows typical photographs of the homogeneous and BME gels.…”

Composite Polymer Materials Consisting of Nanofilms Formed by Click Reaction between Polymers at an Oil–Water Interface

“…When the O/W solution containing the polymers and Cu catalyst was shaken and heated slightly to accelerate the crosslinking reaction before formation of a thin film at the O/W interface and macroscopic separation of the solution, it was found that O/W composite soft gels formed, 20 as shown in Figure 1c. Figures 1d and 1e show typical SEM images of soft gel samples after freeze drying.…”