- Title
- Experimental and theoretical analysis of polyethyleneimine-silica particle formation
- Creator
- Seyfaee, Ahmad
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2017
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Silica particles are used in many applications from engineering such as catalysis and coatings, to medical sciences such as drug delivery. Although silica sources can be found naturally, they are impure and lack desirable functionalities. To overcome the aforementioned disadvantages, the synthesis of silica particles via liquid phase techniques has become more popular. However, it has been shown that it is more beneficial to use less harsh chemicals such as trimethoxymethylsilane (TMOMS) as the silica precursor and polyethyleneimine (PEI) as the catalyst in a phosphate buffer (PB) solution, to form PEI-silica particles. Compared to the conventional Stöber method, these particles are formed more quickly in a less toxic environment. This method produces hydrophobic particles whose surface charge is positive over a wide range of pH. A positive surface charge and/or hydrophobicity generally enhances the selectivity of the PEI-silica particles, which makes the PEI-silica particles good candidates in targeted separation processes. This thesis focuses on the basics of the formation of PEI-silica particles and their characteristics. Scanning electron microscopy (SEM), dynamic light scattering (DLS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), zeta potential, viscometry and gravimetry measurements, as well as time-lapse photography were used for characterisation. First, a general mechanism for the formation of PEI-silica particles was proposed. Three regions in the formation of silica particles were observed: nucleation, growth and equilibrium. The results showed that when particle synthesis was carried out in phosphate buffer solutions some of the PB molecules were likely to be associated with PEI and formed PEI/PB nuclei. Then, these nuclei grew into small particles called “primary particles”, which then aggregated and formed larger PEI-silica particles. In this work, the extent of each region as well as the final particle size were shown to be a function of TMOMS and PEI concentration. By developing a new semi-empirical equation using mass balance and reaction rate equations, the growth and equilibrium regions of PEI-silica particle formation were successfully modelled. In fact, by assuming the existence of different particle generations the peaks and trough in the DLS data were successfully modelled. Having studied the growth and equilibrium, the nucleation region still needed to be further investigated. In the investigation on the nuclei properties, it was found that when PB was not present, silica gel formed instead of particles at pH 10-11. In addition, when PEI was highly charged (pH below 9) there was no visible reaction suggesting silication did not occur. Finally, the effect of mixing on PEI-silica particles was probed. Three modes of mixing were considered: no mixing, mixing by sonication and mixing by magnetic stirring. The results show that the final particle size and their distribution were affected by the mixing modes and their duration. Furthermore, in general, particles that were made by sonication had the largest size and the particles that were formed in the no mixing mode formed the second largest particles based on the location of silica precursor addition. This thesis is important as it relates the particle characteristics to synthesis conditions, which are especially important when considering silica particle applications that require control of specific interactions, in processes such as separation, catalysis and drug delivery. Overall, the increase in understanding and the determination of the relationship between the particle characteristics and synthesis conditions has opened the possibility of the future optimisation of the particle synthesis process.
- Subject
- polyethyleneimine-silica particle; polyethyleneimine (PEI); silica precursor; trimethoxymethylsilane (TMOMS); thesis by publication; particle formation mechanism; catalyst; semi-emperical modeling; particle synthesis; viscosity of polyethyleneimine solution; scanning electron microscopy (SEM); dynamic light scattering (DLS); polymer
- Identifier
- http://hdl.handle.net/1959.13/1337756
- Identifier
- uon:27896
- Rights
- Copyright 2017 Ahmad Seyfaee
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT01 | Thesis | 17 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 945 KB | Adobe Acrobat PDF | View Details Download |