Role of Amphiphilic Block Copolymer Composition on Pore Characteristics of Micelle-Templated Mesoporous Cobalt Oxide Films

详细信息    查看全文

• 作者：Siyang Wang ; Pattarasai Tangvijitsakul ; Zhe Qiang ; Sarang M. Bhaway ; Kehua Lin ; Kevin A. Cavicchi ; Mark D. Soucek ; Bryan D. Vogt
• 刊名：Langmuir
• 出版年：2016
• 出版时间：April 26, 2016
• 年：2016
• 卷：32
• 期：16
• 页码：4077-4085
• 全文大小：519K
• 年卷期：0
• ISSN：1520-5827

文摘

Block copolymer templating is a versatile approach for the generation of well-defined porosity in a wide variety of framework chemistries. Here, we systematically investigate how the composition of a poly(methoxy poly[ethylene glycol] methacrylate)-block-poly(butyl acrylate) (PMPEG-PBA) template impacts the pore characteristics of mesoporous cobalt oxide films. Three templates with a constant PMPEG segment length and different hydrophilic block volume fractions of 17%, 51%, and 68% for the PMPEG-PBA are cooperatively assembled with cobalt nitrate hexahydrate and citric acid. Irrespective of template composition, a spherical nanostructure is templated and elliptical mesostructures are obtained on calcination due to uniaxial contraction of the film. The average pore size increases from 11.4 ± 2.8 to 48.5 ± 4.3 nm as the length of the PBA segment increases as determined from AFM. For all three templates examined, a maximum in porosity (∼35% in all cases) and surface area is obtained when the precursor solids contain 35–45 wt % PMPEG-PBA. This invariance suggests that the total polymer content drives the structure through interfacial assembly. The composition for maximizing porosity and surface area with the micelle-templating approach results from a general decrease in porosity with increasing cobalt nitrate hexahydrate content and the increasing mechanical integrity of the framework to resist collapse during template removal/crystallization as the cobalt nitrate hexahydrate content increases. Unlike typical evaporation induced self-assembly with sol–gel chemistry, the hydrophilic/hydrophobic composition of the block copolymer template is not a critical component to the mesostructure developed with micelle-templating using metal nitrate–citric acid as the precursor.