What are the developments in dynamic light scattering this year?

The basic principle of measuring nanoparticles by dynamic light scattering method is the Brownian motion of basic nanoparticles.A variety of measurement methods have been developed, among which photon correlation spectroscopy (PCS) has been the most widely used. The vast majority of nanoparticle measurement instruments on the market today are based on photon correlation Spectroscopic technology, so that the past literature often equated dynamic light scattering with photon correlation spectroscopy.

(1) Visible dynamic light scattering method

The method was proposed by Dr. Carr of NanoSight, UK. Its basic principle is that nanoparticles suspended in a liquid will scatter under laser irradiation because the refractive index of the particles is different from that of the liquid, forming a light beam. particle. Continuously shoot Brownian motion images of light particles, record the trajectory of the particles, and then analyze these motions After processing the trajectory, the particle size can be obtained by the Stocks-Einstein formula. This method is due to the Brownian motion trajectory of each particle is tracked and processed mathematically, so it can be obtained higher than the existing PCS method .Much finer granularity resolution.

For agglomerated particles, the shape of the scattered light particles is different from that of a single particle, which is easy to distinguish. therefore,This method can be used to measure easily agglomerated particles and mixed particles of different substances more effectively.

When the microscope is used, the field of view and depth of field are determined, that is to say, the measurement volume is determined, so record The number of all particles in the volume is measured, and the concentration of particles can also be obtained.

Because this method can directly observe the Brownian motion of nanoparticles, this method is called "visual dynamic Light Scattering Method".

(2) Electrophoretic induced grating dynamic light scattering method

This method was proposed by Shimadzu Corporation of Japan in 2009. Its basic principle is that the suspension of nanoparticles is placed alternately.On the electrode sheet, the concentration will change with the alternation of electrode polarity. When the electrode is charged, the nanoparticles.It will move towards the positive electrode under the action of an electric field, forming a high-concentration area, producing a grating effect, and then changing the electrode

Polarity, the nanoparticles will diffuse in the opposite direction, and the induced grating will gradually disappear. Diffusion of large particles Slower, while smaller particles diffuse faster. If a laser beam passes through the induced grating to produce.The scattered light is received by the photodetector, and according to the measured change process of the scattered light, the Stock-Einstein formula is used to the particle size distribution of the particles can be obtained.

What is measured in this method is the scattered light of the induced grating formed by the nanoparticles, not the scattered light of the nanoparticles,Therefore, this method has a high signal-to-noise ratio and good repeatability. At the same time, a small amount of larger impurities mixed in the sample ,Particles are not sensitive. Can be used for high concentration nanoparticles measurement. It is reported that the lower limit of measurement of this method can reach 0.5nm.

(3) Backward dynamic light scattering method

When applying traditional photon correlation spectroscopy, in order to avoid multiple scattering (Multiple Scattering), the sample ,The concentration of the sample is strictly limited, and the absorbance of the sample at the working wavelength should not exceed 0.04 when the sample is collected at 90°.Within this limit, conventional photon correlation spectroscopy samples are extremely low in concentration and clear in appearance. Actual.In general, the volume concentration of most colloidal products is above 5%, and the appearance is turbid.

It is not convenient to use and may break the stability of bad colloids; on the other hand, the particle size analysis of traditional photon correlation spectroscopy is easily affected by external contamination. Therefore, the backward dynamic light scattering technique that can be used for particle size analysis of high-concentration nano-colloidal particles should be applied and born.

The solution to increase the measurement concentration is to ensure that the scattering volume is small enough to reduce the multiple scattered light in the signal light.The proportion in . In addition, the transmitter and receiver are placed on the same side of the sample, that is, the backscattered light signal is measured, And by properly controlling the size of the scattering area, a more ideal effect of suppressing multiple scattering can be obtained. According to reports

The VASCO Particle Size Analyzer from Cordouan Technologies uses this protocol to measure concentration by volume increased to 40%.

Another improvement to backscattered light measurement is shown in Figure  The light from the laser passes through a 2+1 optocoupler into a single-mode fiber