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Did you know? Why can lasers see through the tiny world of particles?
In the physics community, dynamic light scattering (DLS) technology has a unique way of revealing the size distribution characteristics of small particles in suspension or polymer solutions. The use of this technology allows scientists to deeply understand and explore the behavior of the microscopic world, especially the dynamic properties of complex fluids. By detecting fluctuations in the intensity of scattered light, DLS provides a way to identify the physical characteristics of particles without directly observing them.
In DLS technology, instantaneous fluctuations are analyzed through the photon autocorrelation function, which allows us to capture the motion information of even extremely small particles and molecules.
Basic principles of DLS technology
The basis of DLS technology is that when light (usually a laser) strikes particles smaller than its wavelength (i.e. smaller than 250 nm), the light undergoes Rayleigh scattering. This causes the intensity of the light wave to fluctuate in time. Each observed photon is scattered by the sample only once, which is called a single scattering event.
In dynamic light scattering, the intensity of scattered light fluctuates over time, resulting from the changing positions of suspended particles due to Brownian motion. They will show a high degree of correlation in short time delays, but as time increases, the correlation will decay. This process can be described by a mathematical model.
"As the time delay increases, the intensity autocorrelation function of the scattered light will decay exponentially, which is related to the movement and diffusion function of the particles."
DLS experimental settings
A typical setup for conducting DLS measurements is to pass a monochromatic light source (such as a laser) through a polarizer and then shine it onto the sample. The scattered light passes through a second polarizer and is collected by a photomultiplier meter (PMT), which projects the result onto a display screen, forming an image called a speckle pattern.
The intensity variation data of these speckle patterns are fed into an autocorrelator for analysis, which allows scientists to observe the movement behavior of the particles. Repeating this process allows us to capture subtle temporal changes, providing detailed information on the instantaneous dynamics of the particles.
Data analysis and application
DLS technology is not limited to materials science, its application scope also extends to biotechnology and chemical engineering. For example, DLS can be used to analyze the size distribution of drug molecules to further understand their behavior in biological systems. Based on the above-mentioned autocorrelation data, different mathematical methods can be used to extract physical information, and the results are widely used in various scientific researches.
“DLS can provide unique insights into the dynamic behavior of even complex polymer solutions, which is particularly important for material design.”
Abstraction process and future prospects
Although DLS technology shows great potential, there are still many challenges to be faced when performing data analysis. For multi-particle systems, good data interpretation is very important, especially when dealing with particles of different sizes. For such complex samples, scientists usually use multi-angle DLS methods to obtain more accurate data.
With the advancement of technology, future DLS instruments will have a more flexible design and be able to automatically select observation angles to achieve higher measurement accuracy. Through these new developments, the applications of DLS will undoubtedly continue to expand to cover a wider range of scientific fields.
In the process of understanding how particles interact and affect their dynamic behavior, DLS technology not only improves our understanding of the microscopic world, but is also an important tool for verifying theories in scientific research. So, as we further explore the world of these extremely small particles, what new wisdom can we gain from them?
