Task: By establishing the structure-property relation, as chemical engineers, you are expected to propose the formation mechanisms for PSP relations for process-controlled deposition of organic core (MS)-and-shell (CS) nanostructures at low temperatures.
The project work is aimed to establish a comprehensive framework that integrates essential components for discovering reliable approaches to core (MS)-shell (CS) nanoparticle evolution. Process-structure-property relations derived from the above approaches will be used for creation of nanoparticle engineering specifically aimed at multi-scale systems. This will be accomplished through experimental studies and analytical methodologies. Initial results generated from this study will be further expanded to discover the specific low-temperature operational factors for core (MS)-shell (CS) nanostructures.
Eventually, the science will be used to create an engineering platform (NEMPPS) for an in-depth scientific understanding of the nanostructure evolution relationship to targeted integration into process-specific multi-scale systems. The key evolutionary innovation in the project work lies in discovering a scientific platform for using multi-scale process-structure-property relations to enable engineering of currently non-attainable organic nanostructures that are stable in relation to high-process shear conditions when mixed with foreign microscale granular particles, with applications in a wide variety of scientific and industrial processes.
Approach: Develop a thermodynamic hypotheses-driven approach on how to retain core-shell morphologies within the limits of required particle sizes (<20 nm) without altering the PSP relations.
Hypothesis – 1: Rapid expansion of thin liquid film of precursor solution facilitates instant disintegration of aerosol droplets under high vacuum and low pressure conditions.
Problem Statement : High temperature in the spray pyrolysis process instantly evaporates the droplets and also damages the molecular structure. This is because many biomolecules cannot withstand high operating temperatures. In particular, for pharmaceutical and drug related applications, it is essential to obtain both nanosized particles as well as stable biomolecules. Hence, a mechanism must be engineered to facilitate deposition of organic nanostructures in core-shell
Figure 1 . Controlled synthesis of various forms of nanostructures (a) crystalline structure (b) dendrite structure (c) Ring structure (d) Core-and-shell structure [7].
morphologies. Careful choice of operating conditions and parameters generating scientific mechanisms to evolve into an engineering protocol is needed.
How does low temperature facilitate the structural evolution?
Background:
In previous studies, several high temperature methods were used in the synthesis of nanoparticles [1-5]. Due to the sensitivity of many of the organic molecules to high temperature, it is often challenging to retain their biomolecular structure and biocompatibility in the synthesis of organic nanoparticles. Various studies have shown that concentration [1], sono-chemical procedure [2], pH-induced polymerization [3], thermo-electric behavior [4], cross-coupling reactions [5], and density and thermal conductivity [6] are a few factors that govern the nanostructure. However, it not yet clear how stable organic nanostructures can be obtained with MS as core and CS as shell at low operating temperatures. Creating these nanostructures at low-temperature without affecting the overall biomolecular structure is indeed a great challenge.
Central to the hypothesis is that the thin film of the feed solution has to be operated at a very low pressure, in order to break the film and instantly evaporate the aqueous phase. An ultrasonic atomizer facilitates the generation of small droplets. The frequency of the atomizer nozzle can be adjusted to control the spray, thereby generating more finer droplets. A relation between the operating temperature and pressure in the reactor chamber will be assessed for the lowest possible
temperature and pressure at which the particles start to deposit. This is very challenging, as the entire process is rapid and happens in a few seconds. Therefore, the finite time taken by the particles to deposit on the substrate will be studied by facilitating high vacuum inside the chamber. Our previous study [7] on metallic nanoparticles has shown a pattern of widely dispersed particles of various shapes (including core-shell) deposited on the substrate. But these process conditions cannot be applied to organic nanoparticles, as the system was operated at very high temperatures (>1000°C). It is challenging to re-create the same core-shell nanostructure for organic nanoparticles due to low temperature operation (85°C). Synthesis of various nanostructures (Figure 1) obtained by
controlling the process parameters and chemical composition showed that the nanostructural forms can typically be altered by controlling the concentration of the feed solution and temperature of operation. Based on the knowledge gained from my previous studies, the task is to investigate a new set of PSP relations at low temperature (85°C) operation to create core (MS)-shell (CS)
nanoparticles. This task should be accomplished by lowering the operating pressure and increasing the residence time for deposition. The goal is to maximize the time under low pressure conditions to facilitate expansion of aerosol droplet volume. Most importantly, the spherical shape has to be retained as the tempretaure is varied. It was observed during our earlier studies that it was often challenging to retain the spherical shape as the temperature is constantly changing unless the concentration of the precursor solution is varied. A process condition will be discovered at which this structure can be obtained. The second most important factor is to accomplish the desired size of 20nm. But the residence time distribution and the particle dynamics to facilitate the complete evaporation of the acquoeus phase, to accomplish the above conditions, is relatively unknown.
As thermodynamic chemical engineering students, your task is to carefully evaluate the problem by addressing the following questions:
1. Come up with a thermodynamic approach on how to make a solution that can dissolve both MS and CS together? Propose solution thermodynamics and properties studied.
2. Propose s thermodynamic mechanism proposing the dissolution and heat transition behavior of the above mentioned miscible solution.
3. Since the solution has to be processed at low temperatures (less than 45°C), propose a mechanism to operate the aerosol dynamics with specific operating temperature.
4. In order to obtain a binary material of CS and MS, discuss the transition of melting temperature and atomic interaction energy.
5. How do internal energy, pressure and volume of the system (reactor chamber) change with atomic fractions of components A (MS) and B (CS) in liquid phase ?
6. How do internal energy, pressure and volume of the system (reactor chamber) change with atomic fractions of components A (MS) and B (CS) in solid phase ?
7. Propose a mechanism for interaction potential of atomic components as a function of operating temperature.
8. Based on the atomic interaction potential, explain how MS forms as a core and CS as a shell.
9. Identify various technological road blocks when transitioning from metallic to organic structures. How do you overcome them in thermodynamic terms?
10. What is the release in thermal energy from formation of core-shell structure? Compare metallic and organic structures.
11. What is the stored energy associated with the formation of particles?
12. Compare relative thermodynamic stabilities of various structures and suggest a methodology for heat of solution measurements for organic solutions.
References
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[2] Shirazi, F.S.; Akhbari, K. Sonochemical procedures; the main synthetic method for synthesis of coinage metal ion supramolecular polymer nano structures, (2016), Ultrasonics Sonochemistry, 31: 51-61.
[3] Xu, T.; Qi, Y.; Zhao, X. Controlled fabrication of nanostructures by assembling Au nanoparticles on functionalized polymeric spheres, (2016), Colloids and Surfaces A-Physicochemical And Engineering Aspects, 498: 139-145.
[4] Son, W.; Lee, S.H.; Park, H.; Thermoelectric Behavior of Conducting Polymers Hybridized with Inorganic Nanoparticles, (2016), Journal of Electronic Materials, 45(6): 2935-2942.
[5] Song, K.; Liu, P.; Wang, J.; Highly active palladium nanoparticles immobilized on knitting microporous organic polymers as efficient catalysts for Suzuki-Miyaura cross-coupling reaction, (2016), Journal of Porous Materials, 23(3): 725-731.
[6] Zhao, S.; Yang, Z.; Zhou, X.; Fabrication and characterization of in-situ grown carbon nanotubes reinforced SiC/SiC composite, (2016), Ceramics International, 42(7): 9264-9269.
[7] Pingali, K.C., Deng, S.; Rockstraw, D. Direct synthesis of Ru–Ni core-and-shell nanoparticles by spray-pyrolysis: Effects of temperature and precursor constituent ratio. (2008). Powder Technology, 183, 282-289.
