Preparation Of Porous Monolith By Concentrated Emulsion Templating

Preparation of porous materials via concentrated emulsion templating method is to polymerize the continuous phase at certain temperature, and then the porous monolith can be obtained when the polymerization completed after cleaning. Comparatively, concentrated emulsion templating method is convenient and inexpensive, more importantly; the pore size and distribution are controllable. In this dissertation, a series of polymer materials with porous structure were prepared. Many factors influenced the stability of the concentrated emulsion and the the morphology of porous monolith were investigated.1. The porous polyacrylamide (PAM) was polymerizated by the template of concentration emulsion, in which cyclohexane is the dispersed phase, acrylamide and poly (ethy glycol) is the continous phase. The density and porosity of PAM can be adjusted by the changing of the content of emulsifier, and the dispersed phase volume fraction. The water absorption of different porosity was studied. The results show that the water absorption of porous PAM is larger than bulk PAM, and increases with the porosity of porous PAM.2. A porous hydrophilic/hydrophobic composite was prepared by concentrated emulsion polymerization, which composed of a porous hudrophobic polystyrene matrix with its cells and intercellular pores partially filled with hydrophilic PAM. The permeation of ther resulted composites was controllable according to the environment humidity. In condition of low humidity, the materials kept open-celled and exhibited a high permeation, whereas at high humidity, the filled PAM was swolled by aqueous vapor and blocked the intercellular pore, the materials became nonpermeated.3. Inverse concentrated emulsions were prepared using aqueous colloidal silica suspension as the hydrophilic dispersed phase and a solution of diglycidyl ether of bisphenol -A (DGEBA), its curing agent polyamide resin, low molecular weight 650, surfactant nonyl phenol polyoxyethylene ether in 4-methyl-2-pentanon as the continuous phase. Without colloidal silica in the aqueous phase and the pre-curing of the continuous phase, the stability of the concentrated emulsion was poor. The colloidal silica tended to accumulated on the surface of the dispersed droplets forming an encapsulation, which strengthened the steric repulsion in the system and thus improved the stability. Pre-curing of the continuous phase provided an increased initial viscosity and enhanced the stability. Lower volume fraction of the dispersed phase can help to maintain stability of the concentrated emulsions.4. A DGEBA porous monolith was prepared via concentrated emulsion templating. The introduction of colloidal silica into the hydrophilic phase strengthened the steric repulsion at the interface and ensured the stability of the concentrated emulsion. A proper pre-curing of the precursors in the continuous phase viscosity, a larger amount of the curing agent accelerated the curing rate. All above factors effectively retarded the rate of phase separation and realized the formation of a porous structure.5. The uniform porous monoliths of glycidyl amino epoxy resin (GAE) were prepared via concentrated emulsion template method. It was found the nonionic surfactant, HLB=8.6, in the aid of colloidal silica were well suited to stabilize such concentrated emulsions. The effect of HLB values of non-ionic emulsifier was taken into account, and the correlation of oil phase, surfactant and colloidal silica was investigated. In addition, a model was built to interpret the stabilization mechanism of concentrated emulsion stabilized by the non-ionic emulsifier in the aid of colloidal silica.6. It was found that a proper pre-cure of the precursors and proper curing agent amount in the continuous phase viscosity can accelerated the curing rate and increased the stability of concentrated emulsion. It was also found when the emulsion concentration was higher than 0.76, the obtained porous monolith possessed high porous with a complex network of channels and interconnected pores.