Application of Small-Angle X-ray Scattering in Nanoparticle Size Distribution

Introduction

Small-Angle X-ray Scattering (SAXS) is a powerful technique used to analyze the size distribution of nanoparticles.

SAXS measures the intensity of X-rays scattered at very small angles (typically 0.1° to 5°) to provide information about the size, shape, and distribution of nanoparticles.

This technique is particularly useful for characterizing nanoparticles in various states, including powders, liquids, and thin films.

SAXS can determine the size distribution of primary particles, which is different from the results obtained by traditional methods like SEM or TEM.

The method is applicable to a wide range of materials, including polymers, proteins, colloids, and nanocomposites.

Principles of SAXS

Definition: SAXS refers to the scattering of X-rays at small angles (2° to 5°) when they interact with a sample.

Scattering Mechanism: The technique relies on the differences in electron density within the sample, causing X-rays to scatter.

Coherent and Incoherent Scattering: coherent scattering occurs in crystalline regions, while incoherent scattering occurs in regions with electron density fluctuations.

Guinier and Porod Laws: These laws describe the scattering intensity in relation to particle size and shape.

Instrumentation: SAXS setups typically include an X-ray source, sample holder, and detector to measure scattered X-rays.

Figure 1: SAXS and WAXS.

Applications in Nanoparticle Research

Nanoparticle Size Distribution: SAXS is widely used to measure the size distribution of nanoparticles.

Catalyst Characterization: Used to measure the size, shape, and concentration of catalyst nanoparticles.

Polymer Research: Helps in understanding the structure and behavior of polymer-based nanocomposites.

Biological Molecules: Used to study the structure of proteins and other biological macromolecules.

Material Science: Characterizes the porosity and surface area of materials like porous carbon and silica.

Figure 2: Parameters that are determined with SAXS instruments.

Sample Requirements

Powder Samples: Require at least 10mg with no visible particles.

Liquid Samples: Concentration of 10mg/mL, volume of 3mL, and no sediment.

Bulk Samples: Optimal thickness ranges from a few micrometers to several tens of micrometers.

Fiber Samples: Should be combed and kept straight.

Special Samples: For GI-SAXS or GI-WAXS, samples are typically prepared on silicon wafers.

Figure 3: Sample and Buffer Preparation for SAXS.

Case Studies

Nanoparticle Size Distribution: SAXS was used to measure the size distribution of nano zirconia particles.

Thin Film Analysis: Analyzed the microstructure of Al2O3/PI hybrid films, determining particle size and interface characteristics.

Alloy Research: Studied phase separation and nanocrystal formation in Al91Gd9 amorphous alloys during annealing.

polymer blends: Investigated the phase structure and molecular orientation in polymer blends.

Porous Materials: Characterized the pore structure and distribution in various porous materials.