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BUILDING BLOCKS AND THEIR EFFECTS ON POLYMER AEROGEL PROPERTIES

Gu, Senlong
http://rave.ohiolink.edu/etdc/view?acc_num=akron1468493203

Abstract Details

2016, Doctor of Philosophy, University of Akron, Polymer Engineering.
We investigated the effects of polymerization conditions, such as temperature, the polarity of the solvents, and microscale confinement during sol-gel transition, on the microstructure and physical properties of the resultant polymer aerogels. This work includes two main parts. (1) Studies of properties and formation mechanism of polybenzoxazine aerogels showing spherical and cylindrical building blocks; (2) Evaluation of properties of the aerogels obtained from the gel precursors synthesized in an oil-in-oil emulsion and a macroporous polymer host, in comparison to the normal aerogel monoliths. In the first part (Chapter III & Chapter IV), p-toluenesulfonic acid (TSA) was used as the catalyst for cationic ring opening polymerization of benzoxazine to produce polybenzoxazine (PBZ) aerogels. The PBZ aerogel building blocks (spheres vs. strands) and pore surface area show strong dependence on the solvent and the gelation temperature. The use of dimethyl sulfoxide (DMSO) and dimethylacetamide (DMA) led to spherical particle networks while fibrillar networks were obtained using N-methyl-2-pyrrolidone (NMP). In order to thoroughly understand the formation of these two types of networks, a combination of dynamic light scattering (DLS) and static light scattering (SLS) was used to monitor the growth of polymer networks during polymerization. The light scattering results revealed that polymer networks formed via nucleation and growth mechanism. In addition, the shape of building blocks was found to be associated with the concentration of the nuclei and the gelation time. In DMSO, a higher concentration of nuclei resulted a fast crowding of the building blocks that constituted the gel network. However, at low concentration of the nuclei and at long gelation times, the spherical building blocks evolved into cylinders by self-assembly and formed a fibrillar network when NMP was used as the solvent. Originally, the differences in the concentration of nuclei were due to the differences in dissociation constant of TSA in DMSO and NMP. In the second part, the preparation and characterization of aerogel microparticles and aerogel foams were presented respectively in Chapter V and Chapter VI. In this regards, polyurea open cell aerogel foams (PUA OCAFs) were created by the sol-gel process inside a macroporous PEO template. The microstructure of PUA OCAFs were found to be a combination of interconnected large pores (pore size ~ 10 µm) and intercellular skins composed of mesoporous aerogel domains. Heterogeneous nucleation and growth was found to play an important role in determining the morphology of OCAFs, which was confirmed by light scattering experiments as described in the first part of this thesis. The unique hierarchical structures of OCAFs offered higher sorption kinetics and air permeability than the regular PUA aerogel monoliths, which are helpful for applications, such as airborne nanoparticles filtration and oil-spill cleanup. PBZ and polyimide (PI) aerogel microparticles were prepared via sol–gel reactions inside micrometer size droplets created in an oil-in-oil emulsion system. The oil-in-oil emulsion system was obtained by dispersing in cyclohexane the droplets of the sols of PBZ or PI prepared in dimethylformamide (DMF). The sol droplets transformed into harder gel microparticles due to sol–gel reactions. The PBZ and PI aerogel microparticles prepared in this manner showed mean diameter 32.7 and 40.0 µm, respectively, mesoporous internal structures, and surface area 55.4 and 512.0 m2/g, respectively. Carbonization of PBZ aerogel microparticles maintained the mesoporous internal structures but yielded narrower pore size distribution.
Sadhan Jana, PhD (Advisor)
Younjin Min, PhD (Committee Chair)
Bryan Vogt, PhD (Committee Member)
Li Jia, PhD (Committee Member)
Jiahua Zhu, PhD (Committee Member)
180 p.
Polymers
Polymer Aerogels, building blocks, polybenzoxazine, polyimide, polyurea, and laser light scattering

Recommended Citations

Citations

  • Gu, S. (2016). BUILDING BLOCKS AND THEIR EFFECTS ON POLYMER AEROGEL PROPERTIES [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1468493203

    APA Style (7th edition)

  • Gu, Senlong. BUILDING BLOCKS AND THEIR EFFECTS ON POLYMER AEROGEL PROPERTIES. 2016. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1468493203.

    MLA Style (8th edition)

  • Gu, Senlong. "BUILDING BLOCKS AND THEIR EFFECTS ON POLYMER AEROGEL PROPERTIES." Doctoral dissertation, University of Akron, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1468493203

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Akron and OhioLINK.
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