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Nanomaterials, consisting of nanoparticles (NPs) with at least 50% of their external dimensions falling within the range of 1 to 100 nm, exhibit unique chemical and physical properties compared to bulk materials. These properties include enhanced catalytic activity, improved solubility, altered optical behavior due to their high surface area, electronic properties, as well as controlled morphology. Nanomaterials have diverse applications across various scientific disciplines and industries.
With the increasing variety of nanomaterials being synthesized, there is a growing need for precise and reliable characterization techniques.
However, selecting the most appropriate characterization method for studying nanoparticles, especially at low concentrations, remains a challenge.
Several characterization methods have been developed to assess size, distribution, shape, surface charge, and porosity of nanoparticles in different environments. These techniques vary in terms of availability, cost, selectivity, accuracy, simplicity, and their suitability for specific compositions.
| Characterisation Technique | Information Provided | |
|---|---|---|
| Spectroscopic Technique | Ultraviolet-visible spectroscopy (UV-Vis) Infrared (IR) spectroscopy |
Size, aggregation, structure, surface chemistry |
| Chromatographic Technique | Size Exclusion Chromatography (SEC) | Size |
| Calorimetric Techniques | Differential Scanning Calorimetry (DSC) | Structure, stability, conformation |
| Surface Analysis Techniques | Scanning Electron Microscopy (SEM) | Surface, size, shape, morphology, crystallographic composition |
Ultraviolet-Visible Spectroscopy (UV-Vis): UV-Vis spectroscopy is widely used for quantifying compound concentrations, size, and shape of nanomaterials.
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The Beer-Lambert law is applied to measure absorbance, where absorbance (A) is directly proportional to the molar concentration (c) and path length (l) of the sample, as well as the molar absorptivity (ε).
A = log10εcl(I0/I)
UV-Vis works by measuring the attenuation of a light beam as it passes through a sample.
It is useful for analyzing optical characteristics, concentration, agglomeration state, and shape of nanomaterials in suspension. Additionally, it can assess the absorption properties of metallic nanoparticles and the conjugation of biomolecules to nanomedicines. However, it requires nanomaterials to be dissolved in a solvent for analysis, limiting its applicability in some nanotechnology applications.
Infrared (IR) Spectroscopy: Tapping Atomic Force Microscopy-based Infrared Spectroscopy (Tapping AFM-IR) provides high spatial resolution and sensitivity for chemical imaging of nanomaterials. It allows chemical properties to be resolved down to 10 nm. Tapping AFM-IR employs an AFM tip that oscillates at a resonance frequency and occasionally contacts the sample surface. A high-speed IR laser is focused onto the sample at the AFM tip location, causing photothermal expansion due to sample adsorption. This expansion induces a change in cantilever amplitude, enabling high-resolution IR imaging. Tapping AFM-IR broadens the scope of nanoIR applications to various samples, including soft or loose materials.
| Spectroscopic Technique | Principle | Applications |
|---|---|---|
| Ultraviolet-Visible Spectroscopy (UV-Vis) | Beer-Lambert law | Optical characteristics, concentration, agglomeration, shape, absorption properties |
| Infrared (IR) Spectroscopy | Tapping AFM-IR | Chemical imaging, spatial resolution down to 10 nm |
Size Exclusion Chromatography (SEC) or Gel Permeation Chromatography (GPC): SEC/GPC separates polydisperse nanoparticle populations based on their hydrodynamic radius. It utilizes columns packed with porous microparticles of varying pore sizes as the solid phase. Sample molecules in a suitable solvent interact with the column packing, diffusing into and out of pores. Smaller molecules enter pores more easily and are eluted last, while larger molecules elute faster. SEC/GPC can measure molecular weight, molecular weight distribution, size, and structure, with the addition of sodium dodecyl sulfate (SDS) in the mobile phase to prevent irreversible adsorption of NPs onto the stationary phase. It is used in research and industrial settings for producing monodisperse sample populations and nanoparticle purification.
| Chromatographic Technique | Principle | Parameters |
|---|---|---|
| Size Exclusion Chromatography (SEC) / Gel Permeation Chromatography (GPC) | Porous column packing with varying pore sizes | Size (1 to 200 nm), Size distribution (Population based) |
High-Performance Liquid Chromatography (HPLC): HPLC separates components in a mixture using a liquid mobile phase and solid column stationary phase. It provides excellent resolution due to high pressures, small column particle sizes, and increased surface area for interactions. HPLC is used to fractionate nanoparticles by size and is widely employed in life sciences, food sciences, pharmaceutical research, and environmental research. It is also used for quantification, separation of actives in nanosystems, and studying drug encapsulation efficiency, release kinetics, and conjugation percentages.
| Chromatographic Technique | Principle | Applications |
|---|---|---|
| High-Performance Liquid Chromatography (HPLC) | Liquid mobile phase, solid column stationary phase | Fractionation by size, quantification, separation of actives in nanosystems, drug encapsulation efficiency |
Differential Scanning Calorimetry (DSC): DSC is a thermal analysis technique that measures temperature and heat flow associated with material transitions over time. It compares the energy required to match the sample's temperature to that of a reference. DSC is used to determine glass transition and melting temperatures, assess nanomaterial structure, stability, conformation, and drug incorporation in nanoparticles.
| Calorimetric Technique | Principle | Parameters |
|---|---|---|
| Differential Scanning Calorimetry (DSC) | Comparison of energy required to match sample and reference temperatures | Glass transition temperature (Tg), Melting temperature, Structure, Stability, Conformation |
Scanning Electron Microscopy (SEM): SEM is employed to analyze nanomaterial surface morphology. It uses high-energy electron beams scanned across a specimen in a vacuum chamber, with emitted signals recorded by detectors. SEM provides quick and simple nanoparticle size and shape characterization, although nonconductive samples may require metallic coating. SEM can distinguish materials by atomic number through backscattered electron (BSE) imaging and assess surface composition via elastically backscattered electrons or x-ray emission, making it valuable for various applications.
Cathodoluminescence principles applied to SEM can evaluate electrical conductivity, insulating properties, and surface defects in nanomaterials.
| Surface Analysis Technique | Principle | Parameters |
|---|---|---|
| Scanning Electron Microscopy (SEM) | High-energy electron beams and detectors | Surface, size, shape, morphology, crystallographic composition |
Results from the various characterization techniques have provided valuable insights into the properties and characteristics of nanomaterials. UV-Vis spectroscopy revealed information about the optical properties, size, and concentration of nanomaterials in suspension. Tapping AFM-IR demonstrated the high spatial resolution and chemical imaging capabilities for nanomaterials down to 10 nm.
Size Exclusion Chromatography (SEC) or Gel Permeation Chromatography (GPC) proved effective in separating nanoparticles based on their hydrodynamic radius, providing information on size distribution. High-Performance Liquid Chromatography (HPLC) allowed for the fractionation of nanoparticles by size and the quantification of their concentrations.
Differential Scanning Calorimetry (DSC) revealed valuable data about the structural and thermal properties of nanomaterials, including glass transition and melting temperatures. SEM provided detailed surface morphology and composition information for nanomaterials, aiding in their characterization and understanding.
In conclusion, the characterization of nanomaterials is essential for understanding their unique properties and optimizing their applications in various fields. Spectroscopic, chromatographic, calorimetric, and surface analysis techniques play vital roles in assessing the size, distribution, structure, stability, and surface properties of nanoparticles.
Each technique has its strengths and limitations, and the choice of method should be based on the specific properties of the nanomaterials and the information required. Combining multiple characterization techniques can provide a comprehensive understanding of nanomaterials, allowing for better control and utilization of their properties.
Overall, the development of precise and reliable characterization techniques is crucial for advancing nanotechnology and harnessing the potential of nanomaterials in science and industry.
Nanoparticle Characterization Laboratory Report. (2024, Jan 17). Retrieved from https://studymoose.com/document/nanoparticle-characterization-laboratory-report
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