Dynamic Light Scattering (DLS)
Introduction:
DLS analysis, or Dynamic Light Scattering, is a method used to determine particle size and distribution in liquids. While SEM and TEM analyses study particle size in a dry state, in various applications such as pharmaceuticals and biology (or any application requiring particle distribution in a liquid), it is essential to study particle behavior in liquids, which necessitates performing DLS analysis.
In fact, all these methods complement each other... In many studies, these analyses are used together to examine particle size and behavior. DLS analysis is the best method for studying the dimensional stability of nanoparticles and their aggregation intensity. Typically, DLS is used to measure particle size distribution ranging from 1 nanometer to 10 micrometers, while SLS is used to measure larger particles, greater than 1 micrometer.
In many studies, all three analyses are used together to examine particle size and behavior. DLS analysis is considered the best method for studying the stability of nanoparticles’ size and aggregation intensity. Generally, DLS is used to measure the particle size distribution ranging from 1 nanometer to 10 micrometers, while SLS is used to measure particles larger than 1 micrometer. DLS analysis is conducted at the Photon Center with the highest quality and the latest interpretations, such as SBL.
Light Scattering:
DLS analysis (Dynamic Light Scattering) is a technique to obtain particle size distribution in liquids, even at very small dimensions down to 1 nanometer. Determining particle size in powdered and colloidal samples is the first step in studying material properties.
There are various methods for studying particle size, but the methods of Dynamic Light Scattering (DLS) and Static Light Scattering (SLS) are two fast and cost-effective ways to study particle size distribution. In both DLS and SLS methods, particle size is determined based on light scattering by these particles.
Generally, the DLS method is used to measure particle size distribution ranging from 1 nanometer to 10 micrometers, while the SLS method measures larger particles over 1 micrometer. Both methods are also capable of studying colloidal samples, so powdered samples must be dispersed in a liquid (usually water or alcohol) before analysis to achieve a uniform colloidal system.
In general, DLS analysis is an effective and essential tool for research and development in various fields, including materials science, pharmaceuticals, and biotechnology.
Mechanism and Principle of Testing:
Dynamic light, also known as Photon Correlation Spectroscopy (PCS), is an advanced technique used to measure particle size in the range of several nanometers to micrometers, as well as to determine surface charges in liquid environments.
In solutions, collisions between particles and small molecules with solvent molecules result in random motion known as Brownian motion, where the movement speed of particles varies based on their size: larger and heavier particles move more slowly.
Particles can scatter a light beam (with a wavelength smaller than the particle size). When a laser beam interacts with moving particles, the scattered light has varying frequencies. The change in the frequency of the incident and scattered light correlates with particle size, enabling the calculation of the average particle size by measuring this frequency change.
The diameter calculated using this method is the hydrodynamic diameter, reflecting the size of a virtual sphere with a permeability coefficient equivalent to the studied particle. The transport coefficient depends on several factors, including particle size, surface structure, concentration, and the type of ions present in the surrounding environment. Generally, the dimensions obtained by this method are larger compared to measurements made using techniques like Transmission Electron Microscopy (TEM).
The relationship between particle size and Brownian motion speed is expressed through the Stokes-Einstein equation:
It is essential to note that Brownian particle motion is influenced by factors other than particle size, such as temperature and liquid viscosity. Therefore, influential parameters during testing must be constant and known to ensure accuracy, as changes in these parameters may lead to measurement errors.
Analysis Capabilities:
1. Measurement of small particles: Capable of measuring particles larger than 1 nanometer.
2. High accuracy: Precise and reliable results.
3. Short testing time: Quick results.
4. Repetitive analysis: Consistent and dependable results.
5. Ease of use: No complex sample preparation required.
6. Small sample size: Capable of measuring very small samples.
Disadvantages of DLS Analysis:
1. Unsuitability for certain solutions: Not suitable for liquids with very low molecular weight or systems with high absorption.
2. Aggregation effects: Results may be affected by particle aggregation.
3. Multi-scattering errors: Errors may arise from scattering from multiple directions.
4. DLS analysis is a vital tool in various fields, including material science, pharmaceuticals, and biotechnology, contributing to a deeper understanding of particle behavior in solutions.
Advantages of DLS and SLS Analysis:
1. Accurate measurement of nanoparticle size distribution according to INSO16247.
2. Advanced result analysis using methods such as NNLS, Pade-Laplace, CONTIN, and Cumulants.
3. Overcoming aggregation effects in results using the SBL computational method.
4. Comprehensive study of particle size and intensity distribution.
5. Accurate analysis of metal particle size distribution.
6. Evaluation of particle size distribution in chemical powders to ensure quality and efficiency.
7. Examination of particle size distribution in ceramics for various industrial applications.
8. Exploring particle size distribution in glass to ensure desired properties.
9. Analyzing particle size distribution in pastes to improve performance and applications.
10. Measuring Zeta potential to understand particle behavior in suspensions.
Interpretation of DLS Results:
DLS analysis is used to measure particle size and distribution in solutions. Results are interpreted through several main aspects:
Particle Size:
Z-Average Value: Represents the average size of particles in the sample, typically given in nanometers or micrometers.
Size Distribution:
Displayed as a graph showing the proportion of particles of a particular size. It can be unimodal (indicating uniform size) or multimodal (indicating the presence of different sizes).
Polydispersity Index (PDI):
PDI Value: Reflects the variability of particle sizes within the sample. Ranges from 0 to 1:
PDI < 0.1: Indicates narrow distribution (homogeneous size).
PDI > 0.3: Indicates wide distribution, possibly due to particle aggregation.
DLS results offer valuable insights into particle characteristics in solutions and are fundamental in fields such as material science, pharmaceuticals, and biotechnology. Obtaining accurate results requires careful monitoring of experimental and environmental parameters.