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Riyad Mahfud_ PhD Thesis.pdf (3.65 MB)

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SYNTHESIS, EVALUATION AND MOLECULAR DYNAMIC SIMULATIONS OF NOVEL ANIONIC POLMERIC SURFACTANTS BASED ON POLYBENZOXAZINES

Mahfud, Riyad Ageli Saleh
http://rave.ohiolink.edu/etdc/view?acc_num=case1390472477

Abstract Details

2014, Doctor of Philosophy, Case Western Reserve University, Chemical Engineering.
Polymeric surfactants attracted considerable attention in recent years for applications such as personal care product and stabilization of emulsions and suspensions. The characteristic properties of polymeric surfactants originate from the formation of aggregates through the association of the hydrophobic alkyl chains in aqueous solution, within a narrow concentration range. The aggregates are called micelles, and the narrow concentration range above which micelles are formed in the solutions is called the critical micelle concentration (cmc),. The characteristics of micelles are easily controlled by changing the solution conditions such as temperature, concentration and ionic strength, and by changing the surfactant properties such as chain length, hydrophobic volume and head group area. In present work, a novel platform of anionic polymeric surfactants, poly(4HBA-oca-Na+), poly(4HBA-dea-Na+), and poly(4HBA-doa-Na+), has been synthesized by polymerizing benzoxazine monomers that are synthesized by reacting an aliphatic amine of variable chain length (C8, C10 and C12), with 4-hydroxybenzoic acid and paraformaldehyde. The structures of the monomers and polymeric surfactants are confirmed by NMR and FTIR. The ring-opening polymerization and thermal behavior of the benzoxazine monomers are studied by DSC and TGA. Size exclusion chromatography (SEC) coupled with Viscotek triple detection technique is used to characterize the molecular weight distribution of polybenzoxazine surfactants. The influence of the structure on the surface activity is investigated by measuring the surface tension of aqueous solutions of the polymeric surfactants using the Wilhelmy plate method. The tensiometry results indicate that the adsorption at the air/water interface is similar for the octylamine, decylamine and dodecylamine-based surfactants. Increasing the alkyl chain length from C8 to C12 does not significantly affect the surface tension at the critical micelle concentration (¿cmc), while the critical micelle concentration (cmc) gradually increases due to increasing hydrophobic effect. The influences of salt addition on the surface tension at the cmc (¿cmc) along with the thermodynamic properties of micellization in aqueous solutions surfactants are studied. Upon salt (NaCl) addition, the cmc initially decreases slightly and remains constant at 3wt% NaCl. For poly(4HBA-oca- Na+), micellization is affected by temperature as the hydrophobic and head group interactions change . As temperature increases the cmc of poly(4HBA-oca- Na+) decreases in the studied temperature range. The synthesis of anionic gemini surfactant based on 4-carboxylphenol benzoxazine dimer, abbreviated as di(4CaP-oca) is described. Molecular dynamics simulations are employed to gain a fundamental understanding of the self-assembly of amphiphilic di(4CaP-oca-Na+); particularly the morphology and dynamics of the aggregates. Starting with a randomly distributed surfactant molecules in water, the mechanism of micelle formation is observed at a molecular level. Simulation results show that this surfactant forms spherical micelles at concentrations higher than the cmc, and the conformation of the di(4CaP-oca-Na+) shows that the spacer is more flexible than the tail. The radial distribution functions (RDF) and the effect of electrostatic interactions between the head groups are investigated. Furthermore, fully atomistic molecular dynamic simulations are performed to address the self-assembly of amphiphilic and comb-like polybenzoxazines (iBnXz) in water, with i=3 (trimer), i=4 (tetramer); i=6 (hexamer), i=8 (octamer), and i=10 (decamer). Spontaneous aggregation of the comb-like polybenzoxazine molecules into a single micelle occurs in the simulations. The simulations show that the molecular size and concentration play important roles in micellar morphology. The micellar morphology is spherical at low concentrations, but undergoes a transition to cylindrical shape as the concentration increases. The transition point depends on the molecular size – both the true size as indicated by molecular weight, as well as an additional effective size dependent on molecular flexibility.
SYED QUTUBUDDIN (Advisor)
DANIEL LACKS (Committee Member)
MOHANN SANKARAN (Committee Member)
HATSUO ISHIDA (Committee Member)
192 p.
Chemical Engineering
Amphiphilic polybenzoxazine; polymeric surfactant; surface tension; critical micelle concentration; molecular dynamics; self-assembly; morphology sphere to cylinder transition

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Citations

  • Mahfud, R. A. S. (2014). SYNTHESIS, EVALUATION AND MOLECULAR DYNAMIC SIMULATIONS OF NOVEL ANIONIC POLMERIC SURFACTANTS BASED ON POLYBENZOXAZINES [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1390472477

    APA Style (7th edition)

  • Mahfud, Riyad. SYNTHESIS, EVALUATION AND MOLECULAR DYNAMIC SIMULATIONS OF NOVEL ANIONIC POLMERIC SURFACTANTS BASED ON POLYBENZOXAZINES. 2014. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1390472477.

    MLA Style (8th edition)

  • Mahfud, Riyad. "SYNTHESIS, EVALUATION AND MOLECULAR DYNAMIC SIMULATIONS OF NOVEL ANIONIC POLMERIC SURFACTANTS BASED ON POLYBENZOXAZINES." Doctoral dissertation, Case Western Reserve University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1390472477

    Chicago Manual of Style (17th edition)

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© 2014, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.
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