- Post Doctoral
MIT Unit Affiliation:
- Chemical Engineering
Post Doc Sponsor / Advisor:
Date PhD Completed:
Top 3 Areas of Expertise:
Expected End Date of Post Doctoral Position:
1. Modeling and experiments of solid formation and clogging in flow reactors
2. Deterministic model development to describe the kinetics of growth and nucleation of II-VI semiconductor nanocrystals
In the present thesis the formation of chemical and physical gels is deepened. Chemical gels are constituted by polymeric macromolecules of large enough sizes to become insoluble. Such chains are formed in the presence of a multi-functional monomer (crosslinker) which causes the linking of chains, leading to a significant increase in the molecular weight. Once a critical size of the chain is reached, a new phase, termed gel, precipitates out of the reactive mixture. Such new phase can be visualized as a single, highly crosslinked macromolecule spanning the entire reaction locus. The formation of physical gels instead is mediated by the aggregation of pre-formed colloidal particles which build up macro-aggregates spanning throughout their vessel.
In the first part of the thesis, free-radical crosslinking copolymerization, which typically leads to the formation of chemical gels, has been studied employing different modelling approaches. Initially, a statistical/kinetic model has been employed to estimate the kinetic parameters for the industrially relevant copolymerization of acrylamide and N’N’-methylene- bisacrylamide, allowing to describe their gel properties such as their swelling and crosslinking density. Successively, a deterministic model has been developed to clarify the role of multiple active sites (multiradicals) in crosslinking copolymerization. Based on the methyl- methacrylate/ethylene-glycol dimethacrylate system, a new quantitative criterion was proposed to decide whether or not such multiple active sites should be accounted for. The latter two models were then compared with a Kinetic Monte Carlo and another deterministic model, in order to clarify their strength and weaknesses and provide guidelines for their application.
In the second part of the thesis, the shear-stability of Inverse Latexes, i.e. polymer particles suspended in an oil phase, has been investigated experimentally by means of a rheometer. In these conditions the Inverse Latexes undergo gelation as a result of irreversible shear-induced particle aggregation, characterized by a significant increase in viscosity: a physical gel is formed. The experimental studies allowed identifying the key parameters affecting the shear-stability of Inverse Latexes both during as well as after the polymerization. It turned out that a competition between aggregation and coalescence regulates the gelation process. Finally, a deterministic model accounting for both aggregation and coalescence of such particles has been developed in order to provide a tool for quantifying their role.
Top 5 Awards and honors (name of award, date received):
5 Recent Papers:
Lazzari, S. et al (2017), “Modeling of the formation kinetics and size distribution evolution of II-VI Quantum Dots”, Reaction Chemistry & Engineering, in press
Lazzari, S. et al (2017), “Growth and Aggregation Regulate Clusters Structural Properties and Gel Time”, The Journal of Physical Chemistry B 121 (11), 2511-2524
Lazzari, S., et al. (2016), "Fractal-like structures in colloid science", Advances in colloid and interface science, 235, Pages 1–13
Lazzari, S., et al. (2015), "Interplay between aggregation and coalescence of polymeric particles: experimental and modeling insights", Langmuir, 31, (34), 9296-9305
Lazzari S., et al. (2014), "Modeling the pH-dependent PLA oligomer degradation kinetics", Polymer Degradation and Stability 110, 80-90