39,956 research outputs found
Modulated 3D cross-correlation light scattering: improving turbid sample characterization
Accurate characterization using static light scattering (SLS) and dynamic
light scattering (DLS) methods mandates the measurement and analysis of
singly-scattered light. In turbid samples, the suppression of multiple
scattering is therefore required to obtain meaningful results. One powerful
technique for achieving this, known as 3D cross-correlation, uses two
simultaneous light scattering experiments performed at the same scattering
vector on the same sample volume in order to extract only the single scattering
information common to both. Here we present a significant improvement to this
method in which the two scattering experiments are temporally separated by
modulating the incident laser beams and gating the detector outputs at
frequencies exceeding the timescale of the system dynamics. This robust
modulation scheme eliminates cross-talk between the two beam- detector pairs
and leads to a four-fold improvement in the cross-correlation intercept. We
measure the dynamic and angular-dependent scattering intensity of turbid
colloidal suspensions and exploit the improved signal quality of the modulated
3D cross-correlation DLS and SLS techniques.Comment: Review of Scientific Instruments, accepted for publicatio
Investigating Static and Dynamic Light Scattering
A new size, static radii , can be measured accurately using Static
Light Scattering (SLS) technique when the Rayleigh-Gans-Debye approximation is
valid for dilute homogenous spherical particles in dispersion. The method
proposed in this work not only can measures the particle size distribution and
average molar mass accurately but also enables us to explore Dynamic Light
Scattering (DLS) technique further. Detailed investigation of the normalized
time auto-correlation function of the scattered light intensity
shows that the measurements of DLS can be expected accurately and the static
and hydrodynamic radii of nanoparticles are different. Only at some special
conditions, the Z-average hydrodynamic radius can be measured accurately at a
given scattering angle. The fact that the values of average hydrodynamic radius
measured at different scattering angles are consistent or the values of
polydispersity index are small does not mean the particle size distribution is
narrow or monodisperse.Comment: 8 figures, discussing the questions about the accurate size
measurements of particles obtained using Dynamic Light Scattering technique
and the particle sizes obtained using Static Light Scattering techniqu
Characterizing Nanoparticle Size by Dynamic Light Scattering Technique (DLS)
The Dynamic Light Scattering Technique was used to determine the size, shape and diffusion coefficient of nanoparticle. The intensity auto correlation functions of light scattered by particles in a solution were measured by using a photomultiplier tube and analyzed to get the relaxation rates for decay of intensity correlations, which correspond to the diffusion constants pertaining to the motion of the particle. In the case of nanorods there are two types of motion - translational and rotational. By dis-entangling the relaxation rates, corresponding to these two types of motion, the shape and size of nanoparticle could be characterized. These experiments, though limited in scope, demonstrate the promise of dynamical light scattering as an inexpensive and convenient technique for characterizing regular shaped nano-particles in a fluid medium
Self-diffusion and Cooperative Diffusion in Semidilute Polymer Solutions as measured by Fluorescence Correlation Spectroscopy
We present a comprehensive investigation of polymer diffusion in the
semidilute regime by fluorescence correlation spectroscopy (FCS) and dynamic
light scattering (DLS). Using single-labeled polystyrene chains, FCS leads to
the self-diffusion coefficient while DLS gives the cooperative diffusion
coefficient for exactly the same molecular weights and concentrations. Using
FCS we observe a new fast mode in the semidilute entangled concentration regime
beyond the slower mode which is due to self-diffusion. Comparison of FCS data
with data obtained by DLS on the same polymers shows that the second mode
observed in FCS is identical to the cooperative diffusion coefficient measured
with DLS. An in-depth analysis and a comparison with current theoretical models
demonstrates that the new cooperative mode observed in FCS is due to the
effective long-range interaction of the chains through the transient
entanglement network
Apparatus for simultaneous DLS-SANS investigations of dynamics and structure in soft matter
Dynamic Light Scattering (DLS) and Small-Angle Neutron Scattering (SANS) are
two key tools with which to probe the dynamic and static structure factor,
respectively, in soft matter. Usually DLS and SANS measurements are performed
separately, in different laboratories, on different samples and at different
times. However, this methodology has particular disadvantages for a large
variety of soft materials which exhibit high sensitivity to small changes in
fundamental parameters such as waiting times, concentration, pH, ionic
strength, etc. Here we report on a new portable DLS-SANS apparatus that allows
one to simultaneously measure both the microscopic dynamics (through DLS) and
the static structure (through SANS) on the same sample. The apparatus has been
constructed as a collaboration between two laboratories, each an expert in one
of the scattering methods, and was commissioned on the \textit{LOQ} and
\textit{ZOOM} SANS instruments at the ISIS Pulsed Neutron \& Muon Source, U.K
Measurement of Dynamic Light Scattering Intensity in Gels
In the scientific literature little attention has been given to the use of
dynamic light scattering (DLS) as a tool for extracting the thermodynamic
information contained in the absolute intensity of light scattered by gels. In
this article we show that DLS yields reliable measurements of the intensity of
light scattered by the thermodynamic fluctuations, not only in aqueous polymer
solutions, but also in hydrogels. In hydrogels, light scattered by osmotic
fluctuations is heterodyned by that from static or slowly varying
inhomogeneities. The two components are separable owing to their different time
scales, giving good experimental agreement with macroscopic measurements of the
osmotic pressure. DLS measurements in gels are, however, tributary to
depolarised light scattering from the network as well as to multiple light
scattering. The paper examines these effects, as well as the instrumental
corrections required to determine the osmotic modulus. For guest polymers
trapped in a hydrogel the measured intensity, extrapolated to zero
concentration, is identical to that found by static light scattering from the
same polymers in solution. The gel environment modifies the second and third
virial coefficients, providing a means of evaluating the interaction between
the polymers and the gel
Charactrisation of particle assemblies by 3D cross correlation light scattering and diffusing wave spectroscopy
To characterize the structural and dynamic properties of soft materials and small particles, information on the relevant mesoscopic length scales is required. Such information is often obtained from traditional static and dynamic light scattering (SLS/DLS) experiments in the single scattering regime. In many dense systems, however, these powerful techniques frequently fail due to strong multiple scattering of light. Here I will discuss some experimental innovations that have emerged over the last decade. New methods such as 3D static and dynamic light scattering (3D LS) as well as diffusing wave spectroscopy (DWS) can cover a much extended range of experimental parameters ranging from dilute polymer solutions, colloidal suspensions to extremely opaque viscoelastic emulsions
Softening of the stiffness of bottlebrush polymers by mutual interaction
We study bottlebrush macromolecules in a good solvent by small-angle neutron
scattering (SANS), static light scattering (SLS), and dynamic light scattering
(DLS). These polymers consist of a linear backbone to which long side chains
are chemically grafted. The backbone contains about 1600 monomer units (weight
average) and every second monomer unit carries side-chains with ca. 60 monomer
units. The SLS- and SANS data extrapolated to infinite dilution lead to the
form factor of the polymer that can be described in terms of a worm-like chain
with a contour length of 380 nm and a persistence length of 17.5 nm. An
analysis of the DLS data confirm these model parameters. The scattering
intensities taken at finite concentration can be modeled using the polymer
reference interaction site model. It reveals a softening of the bottlebrush
polymers caused by their mutual interaction. We demonstrate that the
persistence decreases from 17.5 nm down to 5 nm upon increasing the
concentration from dilute solution to the highest concentration 40.59 g/l under
consideration. The observed softening of the chains is comparable to the
theoretically predicted decrease of the electrostatic persistence length of
linear polyelectrolyte chains at finite concentrations.Comment: 4 pages, 4 figure
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