Dynamic light scattering (DLS) is a technique used to determine the size distribution of small particles in suspension or solutions, based on the analysis of scattered light fluctuations caused by Brownian motion. The method, developed in the 1960s and theoretically grounded by Berne and Pecora in the 1970s, utilizes a monochromatic laser to observe these fluctuations, providing valuable data on particle dynamics through the autocorrelation function. DLS offers insights into the motion and size of particles, where smaller particles exhibit greater intensity fluctuations due to their faster movement.

1. Dynamics light
scattering (DLS)
Key points:
• Introduction
• Brownian motion
• Sample preparation
• Working mechanism
• Auto correlation function
• Stock Einstein equation
• Calculations
• Advantage and disadvantage

2. INTRODUCTION:
• Dynamics light scattering is a technique in physics that can be
used to determine the size of distribution profile of small
particle in suspension or polymers in solution.
• This technique develop in the 1960s for measuring range , in a
suspension or solution
• The first theoretical basis for DLS was established by Berne
and Pecora in 1970s.
• The method is based on the analysis of the fluctuations of
intensity of scattered light, caused by the brownian motion of
the particle .

3. Brownian motion:
• Brownian motion refers to the random
movement of particles suspended in a
fluid(liquid or gas) resulting from collisions
with the molecules of the fluid.
• In the context of DLS Brownian motion
causes the particles in a suspension to move
randomly,leading to fluctuations in intensity
of scattered light.
• The fluctuations In intensity is more wide for
smaller particles as compare to large size
particle,because the thermal energy of small
particles is greater so its move faster then
large particles. Fig. 2 intensity pattern with particle movements
Fig. 1 brownian motion of the particles

4. SAMPLE PREPRATION

5. WORKING MECHENISM
• In this technique we use monochromatic laser light, when
laser light intract with particle then it goes to scattered .
• particle performs brownian motion so that it change own
distance continuously then we got a fluctuation intensity
pattern in motion.
• The intensity pattern change with time.
Diagram for DLS working
DLS Appratus.

6. Auto correlation function
• In DLS we use auto correlation function,the autocorrelation is
a crucial tool for analyzing the motion of particle in a fluid.
• It provide information about size dynamics by examining , how
the intensity of scattered light fluctuated over time.
• The autocorrelation function G(τ) measure the intensity of the
scattered light with a delayed version of itself as a fluction of
time τ.
G(τ) = <I(t) . I(t+τ)>
Here:
<I(t)> = intensity at time t.

7. • for monodisprsion spherical particle , the autocorrelation
function typically decays exponentially.
G(q;τ)=exp⁡
(−Γτ)