Engineering Nanoparticles for Biomedical Applications (eBook)

From Theory to Experiments and Modeling

Sulalit Bandyopadhyay (Herausgeber)

eBook Download: EPUB

2025
804 Seiten
Wiley-VCH (Verlag)
978-3-527-84478-4 (ISBN)

Infos

Practical approach to solution-based synthesis methods and mechanisms from a chemical engineering perspective

Engineering Nanoparticles for Biomedical Applications provides an in-depth, hands-on overview of synthesis and formation mechanisms, characterization, and functionalization of nanoparticles (NPs) using solution-based methods developed from fundamental principles of nucleation and growth. Various experimental synthesis strategies are supported via simulation and modeling. The NPs studied in this book are designed to target an array of biomedical applications.

In this book, readers can practice reverse engineering by first choosing a specific biomedical application, upon which the reader will be exposed to a host of synthesis options. Based on desired properties of NPs, this book can then provide all the relevant information using experimental and modeling approaches for that specific biomedical application.

Sample topics covered in Engineering Nanoparticles for Biomedical Applications include:

• Physico-chemical properties of NPs such as magnetic, plasmonic, and stimuli-sensitivity properties
• Modeling approaches including Density Functional Theory (DFT), Molecular Dynamics (MD), Monte Carlo simulations, and Population Balance Model
• Applications of NPs with emphasis on biomedical applications such as biosensing, diagnostics/imaging, and drug delivery
• Optical, magnetic, stimuli-responsive, and biological properties of multifunctional nanoparticles
• Spherical and anisotropic iron oxide and gold nanoparticles, polymeric nanoparticles and multifunctional nanoparticles

Engineering Nanoparticles for Biomedical Applications is an essential reference on the subject for chemists and engineers at every level of academia and industry.

Sulalit Bandyopadhyay is an Associate Professor in Particle Engineering and Hydrometallurgy in the Department of Chemical Engineering, NTNU. He is Centre Manager for the Particle Engineering Centre and serves as the CTO of a diagnostic company Lybe Scientific A/S. Trained as a chemical engineer, he specializes in the field of colloids, polymers, and nanomaterials with an overall interest in tailoring particles towards specific applications in the field of nanomedicine.

Textauszug

1
Nucleation and Growth of Nanoparticles

Sulalit Bandyopadhyay1 and Seniz Ucar1,2

1Particle Engineering Centre, Department of Chemical Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway
2Middle East Technical University, Department of Metallurgical and Materials Engineering, Üniversiteler, Dumlupınar Bulvarı No: 1, 06800 Ankara, Turkiye

Nanomaterials display properties making them valuable for a broad range of applications ranging from energy production and storage to catalysis, biotechnology, sensing, and so on. Yet, to harness the desired properties effectively, it is essential to produce nanomaterials with precise control over size and shape, as these characteristics directly influence their behavior. Among various synthesis methods, crystallization is a widely utilized bottom-up approach for creating tailored inorganic nanoparticles (NPs). Crystallization refers to the formation of NPs as a result of first-order phase transition processes. During a spontaneous crystallization process, matter transforms from a higher free energy, disordered state into a crystalline state characterized by structural order and lower free energy. The gain in free energy as a result of crystal formation constitutes the thermodynamic driving force for crystallization and marks supersaturation as the first prerequisite and the key parameter controlling crystallization reactions and final particle properties. For crystallization to proceed from vapor, melt, or solution, the medium containing the solute must be supersaturated – an inherently nonequilibrium state that generates the excess free energy necessary to drive the crystallization process.

Crystallization comprises three successive stages: (i) the establishment of supersaturation, (ii) nucleation of particles, and (iii) particle growth. It is important to note that, depending on the reaction conditions, these stages may occur simultaneously within the crystallization medium. However, for the formation of each individual particle, the sequence of events follows the outlined order. Nucleation marks the initial step of particle formation in a supersaturated medium, representing the emergence of a new phase, i.e. phase separation, within the bulk. Following nucleation, growth leads to particle size enlargement, driven by the continued reduction of free energy as supersaturation is consumed. The important particle characteristics of solid phase, size, and shape are determined by the kinetics of nucleation and growth and by how the driving force is distributed between these processes.

The evolution of classical crystallization theory over the past century has provided a robust mathematical framework for predicting nucleation and growth rates. This framework has also enabled control over key crystal properties such as phase, size, uniformity, and morphology by highlighting the two principal factors governing crystallization processes: thermodynamics and kinetics. Thermodynamic factors, which constitute the driving force for nucleation and growth, dictate how material phases behave and crystallize in response to variables such as concentration, temperature, and pressure. In contrast, kinetic factors influence the rates of nucleation and growth, as well as the degree of crystal perfection and uniformity.

1.1 Classical Nucleation Theory

Classical nucleation theory (CNT), originally developed in the nineteenth century, explains nucleation as a dynamic and stochastic process where monomeric units – whether ions, atoms, or molecules – continuously coalesce and dissociate until they reach a critical size. At this critical size, a stable cluster, or nucleus, forms within the bulk, leading to phase separation. According to CNT, the thermodynamic basis for nucleation lies in the reduction of the system's free energy through the formation of a solid phase, with supersaturation serving as a prerequisite for spontaneous crystallization. This theory enables the derivation of a mathematical expression to quantify supersaturation, based on the chemical potential difference between the metastable (high free energy) and stable (low free energy) states of the system.

The chemical potential difference, Δμ, between the two states of a system can be expressed as:

(1.1)

The chemical potential at any state, μ, is a function of the standard potential (μ0), temperature (T), and activity of the solute (α):

(1.2)

where kB is the Boltzmann constant. Combining these two equations, the thermodynamic driving force for spontaneous crystallization is found (Equation (1.3)), where α is the activity in an arbitrary state and α* is the activity of the same solute at equilibrium.

(1.3)

Supersaturation (S) is then defined as the ratio between the activities of the solute at two states and gives a measure of the thermodynamic potential of a system to form precipitates (Equation (1.4)):

(1.4)

The activity of a solute can be determined by considering all the reactions involving the solute within a reaction medium, which requires knowledge of the respective equilibrium constants. However, calculating activity may not be feasible in multicomponent, complex systems. In such cases, solute concentration is often used as a substitute for activity, with the understanding that deviations will arise in nonideal solutions. These deviations are quantified by the activity coefficient, which accounts for the difference between the actual and ideal behavior of the solution.

Once a metastable system is achieved, i.e. supersaturation is established, nucleation can occur. Supersaturation provides the thermodynamic driving force necessary for nucleus formation. However, the phase separation of the nucleus within the bulk requires the creation of a surface, which incurs an energy cost. The overall Gibbs free energy change, ΔG, resulting from these two processes – the free energy change associated with the phase transformation, which scales with the volume of a nucleus (ΔGV), and the free energy change associated with surface formation, which scales with the surface area (ΔGS) – defines a critical size at which a stable nucleus can form in the system (Figure 1.1). When the total Gibbs free energy change is expressed as a function of the radius of a nucleus, assuming it is spherical, the critical size represents the thermodynamic energy barrier, or activation energy (ΔGcrit or ΔG*), required for nucleation.

(1.5)

ΔGυ represents the chemical potential difference that induces the phase transformation and scales with supersaturation, where kB is the Boltzmann constant, νm is unit volume, and γ is the surface free energy of the nucleus-bulk interface.

(1.6)

Combining Equations (1.5) and (1.6), and taking the first derivative of ΔG with respect to r, gives us the expression for ΔG*:

(1.7)

Figure 1.1 Schematic plot of total free energy change (ΔG ) as a function of radius of nucleus (r), as a sum of two energy contributors, and the corresponding activation energy barrier (ΔGcrit).

Source: [1] / The Royal Society of Chemistry.

Using the activation energy barrier for nucleation, an Arrhenius-type equation can be used to express nucleation rate, J:

(1.8)

The expression for the activation energy barrier highlights the key parameters that influence the energy requirement for nucleation and, consequently, the nucleation rate. These parameters include interfacial energy, temperature, and supersaturation. Additionally, the rate expression underscores the role of kinetic factors. As will be discussed later in this chapter, the ability to control the nucleation rate during crystallization is crucial for regulating particle size and size distribution.

The nucleation rate defines the number of nuclei that form per unit volume per unit time and is challenging to measure directly. In practice, induction time, tind, is used as an indirect measurement of nucleation rate, which is defined as the time interval between the formation of an appreciable amount of the solid phase and the establishment of supersaturation. Induction time is dependent on the sensitivity of the measuring method that is used to detect solid phase formation and thus cannot be considered as an intrinsic property of a crystallization system. Yet, induction time measurements are useful for the comparison of nucleation rates in similar experimental setups.

1.2 Phase Stability and Phase Transformations

For a given set of experimental conditions, such as composition and temperature, the solid phase with the lowest free energy is considered thermodynamically the most stable. All other phases that might exist under the same conditions are metastable in comparison. According to classical crystallization theory, the most stable phase forms from a supersaturated medium. However, this doesn't mean the system will directly transform into that stable phase. Instead, intermediate, metastable phases can emerge and persist in the system for significant periods.

When a solution is...

Produkt-Details

• Erscheint lt. Verlag: 2.12.2025
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Chemie
• Schlagworte: nanoparticles characterization • nanoparticles engineering • nanoparticles formation mechanisms • nanoparticles functionalization • nanoparticles mechanisms • nanoparticles modeling • nanoparticles properties • synthesis nanoparticles
• ISBN-10: 3-527-84478-3 / 3527844783
• ISBN-13: 978-3-527-84478-4 / 9783527844784