Physicochemical characterization of nanoparticles:
Physicochemical characterization will mostly depend on the nature of Nano Particles. Some of basic tools and instrumentation which are mainly used to characterize NPs are discussed here
* Dynamic light scattering (DLS)--Measures hydrodynamic size, size distribution, and polydispersity.
Dynamic Light Scattering Technology
Particle size in nano range can be measured by calculating the random intensity variation of light scattered from a solution or dispersed suspension. This methodology can be defined as dynamic light scattering (DLS).This technique is also defined as photon correlation spectroscopy (PCS),and In older literature it can be defined as quasi-elastic light scattering (QELS).
Dynamic Light Scattering in analyzing nano particles
DLS is generally used to analyze nanoparticles. The most common examples can be defined as determining protein size,nanogold size, latex size, and also colloid size. The technique is best suitable for submicron particles and can be utilized to determine particle with sizes less than nano scale. In this nanoscale regime for the size measurement (may have difficulties to determine the distinction between a macromolecule and a particle and also another liquid complex fluids phase becomes blurred. Dynamic light scattering is most effective probe of such kind of concentrated solutions.
Particle Size to Particle MotionStokes Einstein:
Small particles in nano range suspension possesa random thermal motion defined n as Brownian motion. This random motion is desgined in the form of equation by the Stokes-Einstein equation. The equation is postulated in the form for particle size analysis equation.
The Stokes-Einstein relation that connects diffusion coefficient measured by dynamic light scattering to particle size.
where
- D is the hydrodynamic diameter
- d is the translational diffusion coefficient (we find this by dynamic light scattering)
- K is Boltzmann's constant
- T is thermodynamic temperature
- u is dynamic viscosity (we know this)
How to Measure Particle Motion I: Dynamic Light Scattering Optical Setup
Dynamic light scattering optical setup is mainly used to measure random motion of the particle.
At the very heart of the laser diffraction technique is the relationship between light and surfaces (which can be freely interchanged with "particle" for our purposes). When light strikes a surface it is either
- Diffracted
- Refracted
- Reflected
- Absorbed
For particles smaller than 20 microns refracted light becomes increasingly important to calculate an accurate particle size. The scattered light is at relatively low intensity and wide angle for these smaller particles
Fig 1:Different features of a Laser Diffraction Analyzer: Optical System
The basic workflow of a laser diffraction particle size analysis can be divided into two parts:
1. Measurement of scattered light angle and intensity
2. Transformation that scattering data into different particle size distribution
Measurement quality is commonly all about the analysis of quality of various components, and a basic design which reflects basic principles. The core technologies are all mature, but as with many things higher quality leads to superior performance. A typical laser diffraction optical system will include:
Static Light Scattering (SLS) is commonly an optical technique WHICH mainly measures the intensity of the scattered light in corresponding of various scattering angle to get relevant information on the scattering source. A typical use is the determination of the weight average molecular weight M_{w} of a macromolecule such as a protein or polymer molecule. Measurement of the scattering intensity at different angles allows calculation of the root mean square radius, also called the radius of gyration R_{g}. By measuring the scattering intensity for one macromolecule at various concentrations, the second virial coefficient A_{2}, can be calculated. A top view of the optical setup for DLS is shown below.
Fig 2: Optical setup for dynamic light scattering (DLS) nanoparticle size analyzer