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# Eric Mock <ericmock@uiuc.edu>
# requesting 3 days, at minimum=2 days
# beamline 33ID, Structure and Rheology of Anisotropic Particles
# instrument 33ID-D USAXS
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# top:/home/www/beamtime-requests/req00776.txt
# UNICAT Member Beam Time Request  #776
# created Sun Apr 17 14:34:57 CDT 2005
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apsrun:
	2005-02

beamline:
	33ID

collaboration:
	Yes

collaborator_Pete:
	ON

contact:
	ericmock@uiuc.edu

days:
	3

description:
	Anisotropic colloid particles are encountered in numerous commercial and industrial applications, including coatings, adhesives, impact modifiers, medical diagnostics and photonic crystals.  Controlling the rheology and microstructure of anisotropic colloid suspensions is a major goal of the engineer and chemist.  In particular we are interested in controlling the anisotropy of particle interactions to build novel microstructures to enhance macroscopic properties.

Previously we performed side bounce ultra small angle x-ray scattering (SBUSAXS) experiments on two different morphologies of anisotropic polystyrene nanoparticles, as shown in the SEM micrograph in Figure 1 (figures will be sent via e-mail).  The measured intensities as a function of scattering vector, q, are shown in Figure 2, for the three types of particles in Figure 1 suspended in glycerol at a volume fraction of 0.3.  An important feature of Figure 2 is that the scattering patterns for the three different particles are different indicating that we will be able to the discern differences in anisotropy in Figure 1 (SEM micrographs) in particle form factors.  Therefore, we will characterize anisotropy using standard methods for calculating form factors (Reference 1).

At elevated volume fractions, resuspension of the polystyrene nanoparticles in glycerol is a difficult task.  Consequently, for the previous SBUSAXS experiments, the maximum volume fraction obtained for each type of particle in Figure 1, was only 0.3, thus limiting our ability to study higher volume fractions where we anticipate ordering of the particles will occur.  Furthermore, the emulsion polymerization technique used to synthesize these polystyrene nanoparticles is very sensitive to a variety of experimental parameters.  Because this made it difficult to control the bump sizes on the anisotropic particles, we were only able to synthesize monodisperse nanoparticles of the two different bump sizes in Figure 1.  Also, due to these experimental sensitivities, there were smaller (~50nm) spherical particles, which we had difficulties completely removing from the nanoparticle suspensions.

Since the last set of SBUSAXS experiments on the anisotropic nanoparticles in Figure 1, we have become better at controlling the bump sizes on the anisotropic particles.  Similarly, we have been successful at synthesizing more monodisperse suspensions of the nanoparticles and eliminating the smaller spherical secondary particles.

As a result of our ability to overcome many of the obstacles that limited us in our previous SBUSAXS experiments, we would now like to look at anisotropic nanoparticles with bump sizes between the spheres and the small bump particles in Figure 1, and also nanoparticles with bump sizes between the small bump and large bump particles.  Likewise, we would like to study the scattering from increased volume fractions (0.3-0.5) of these new bump sizes as well as the nanoparticles in Figure 1, in order to study the microstructure of dense suspensions of these anisotropic particles.

The particles will be dispersed in glycerol at different volume fractions (~0.05 to 0.5 in steps of 0.1).  The following are the list of SBUSAXS experiments we plan to perform and the issues we are trying to tackle

1) Dilute solution scattering: Samples with volume fraction~0.01: These set of runs will help us determine the scattering from a single particle and help us set the form factor.

2) Scattering from concentrated suspensions: Once the form factor is obtained, the volume fraction of the five different sets of particles will be increased from dilute to concentrated (~0.5) and the static structure factor measured.  This will allow us to study the microstructure as a function of bump size and particle volume fraction.  After the structure is determined, our goal would be to analyze the scattering pattern with theoretical models: to pick an interaction potential and see if we can extract interaction potential parameters which best describe the thermodynamics of the system.

Reference
1. O. Glatter In Small Angle X-ray Scattering; O. Glatter and O. Kratky, Eds.; Academic Press: New York, 1982.

equipment_required:
	

experiment:
	Structure and Rheology of Anisotropic Particles

foreign_nationals:
	Vijay Gopalakrishnan
Subramanian Ramakrishnan

hazards:
	The polystyrene latex samples should not be ingested, splashed in eyes, etc.  These safety hazards can be eliminated by wearing the appropriate protective equipment (safety glasses, gloves, closed shoes, full length pants, etc.).  There are no other safety hazards associated with the polystyrene latex samples or procedures we plan to carry out in this experiment.

instrument:
	33ID-D USAXS

instrument_other:
	

minimumdays:
	2

name:
	Eric Mock

nonmembers:
	

unacceptable_dates:
	May 23-June 16

z34ID_details:
	


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