  In this work, the particle size distribution measured using the dynamic light
scattering (DLS) technique is compared with that obtained from the static light
scattering (SLS) technique or provided by the supplier measured using the
Transmission Electron Microscopy (TEM) technique for dilute
Poly($N$-isopropylacrylamide) microgel and standard polystyrene latex samples
in dispersion respectively. The results show that the narrow particle size
distribution that can be measured accurately using the SLS technique is not
suited to the determination by the DLS technique and the particle size
distribution obtained from the DLS technique is different from the value
provided by the supplier. With the assistance of the simulated data of the
normalized time auto-correlation function of the scattered light intensity
$g^{(2)}(\tau)$, the effects of the particle size distribution on the
nonexponentiality of $g^{(2)}(\tau)$ measured at a scattering angle of
30$^\mathrm o$ are investigated. The analysis reveals that the influences of
the particle size distribution are small on the nonexponentiality of
$g^{(2)}(\tau)$ and very large on the initial slope of the logarithm of
$g^{(2)}(\tau)$. The values of the apparent hydrodynamic radius are also
largely influenced by the particle size distribution and the difference between
the distributions of the apparent hydrodynamic radius and hydrodynamic radius
of particles is determined by the method of cumulants.
