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- 저자 : Shima Taheri (검색결과 2 건)
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Shima Taheri,Simon Martin Clark 한국콘크리트학회 2021 International Journal of Concrete Structures and M Vol.15 No.2
Concrete structures undergo internal damage; this usually starts at the atomic level with defects that then grow and form cracks, which can propagate through the material. Here, a method of preparation of poly(methyl methacrylate) (PMMA) nanocapsules adhesive system via miniemulsion polymerization technique is reported, where MMA + DMA (resin + accelerator) and BPO (hardener) components are separately encapsulated by PMMA shells. The crack-healing potential of these nanocapsules was then investigated by embedding them into the mortar matrix. The prepared PMMA core-shell self-healing nanostructures survived the mixing and hardening processes, and the hardened mortar alkaline environment. The stress fields associated with propagating cracks (load‐induced cracking) broke the brittle/weak inert shell of these core-shell structures, resulted in releasing the healing agents to bridge the nascent and early-stage fractures (< 10 μm) in a short time. Long-term healing was achieved through the formation of polymorph calcite crystals in the presence of moisture and CO₂, which improved the durability of mortar by filling the gaps. Formulation design (addition of chemical admixtures) and process parameters (blade design and mixing speed) were found to directly impact the uniform distribution of nanocapsules, the survival rate of nanocapsules, and the overall strength of the hardened concrete. The stepwise approach to formulate and fabricate a novel high-strength self-healing concrete system unlocks unique opportunities to design nanomaterials that safeguard the integrity of concrete structures.
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Shima Taheri Vardanjani,Aliakbar Roosta,Jafar Javanmardi 한국화학공학회 2020 Korean Journal of Chemical Engineering Vol.37 No.12
Natural deep eutectic solvents (NADESs) as green solvents have substantial potential for enhancing the solubility of pharmaceuticals in aqueous solutions. In this work, the solubility of two B vitamins (nicotinic acid and 4aminobenzoic acid) in aqueous solutions of two NADESs was measured at temperatures between 298.15 K and 313.15 K and different concentrations of NADESs. The studied NADESs were prepared by mixing dried choline chloride with urea or malonic acid with molar ratios of 1 : 2 and 1 : 1, respectively. Based on the results, chloride+malonic acid was more effective on the solubility of the pharmaceuticals in aqueous solutions. Furthermore, the DESs increased the aqueous solubility of 4aminobenzoic acid more than that of nicotinic acid. The experimental solubility data were modeled with the van Laar activity model as well as the modified Apelblat equation to correlate the solubility of the pharmaceuticals to the temperature and NADESs concentration. The molar enthalpy of dissolution (hd) and the molar enthalpy of mixing (hmix) of the pharmaceuticals in the aqueous solutions of the NADESs were calculated. These parameters showed that all the dissolution processes were endothermic, while the mixing process as a part of the dissolution process was exothermic.
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