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# Benjamin Anderson <banders3@uiuc.edu>
# requesting 2 days, at minimum=1 days
# beamline 33ID, Microstructure of Silica Nanoparticles in Low MW PEG
# instrument 33ID-D USAXS
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# top:/home/www/beamtime-requests/req00937.txt
# UNICAT Member Beam Time Request  #937
# created Sat Mar 11 02:41:18 CST 2006
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apsrun:
	2006-02

beamline:
	33ID

collaboration:
	Yes

contact:
	banders3@uiuc.edu

days:
	2

description:
	Filled polymers are an important class of materials where particulate matter is dispersed in a polymer matrix to improve strength and durability over the neat polymer. Such materials find application in carbon filled rubber, nanocomposites, and coatings.  The development of systematic studies aimed at understanding the microscopic physio-chemical effects that manifest themselves in macroscopic material properties has been difficult. Relaxation times are long for high molecular weight polymers; therefore, filled polymers are intractable to an equilibrium suspension. To circumvent this issue, we propose investigating silica nanoparticle dispersions in low molecular weight solvents of increasing molecular weight.

We employ dispersions of monodisperse Stober silica nanoparticles in polyethylene glycol (PEG) 400-20000 MW as a model system to investigate particle/polymer mixtures.  We have found 50 nm silica to form stable liquids in low MW PEG opening the possibility of probing equilibrium suspension properties. From previous SBUSAXS experiments performed at APS on particle dispersions in PEG400-6000, we have linked the stability of these suspensions to the absorption of polymer chains to the particle surface. This polymer layer increases the excluded volume of the particles and provides steric stabilization giving the appearance of hard spheres. The thickness of the polymer layer appears to saturate at a MW of 6000. We also found that obtaining a good dispersion depends on the method of sample preparation. In order to complete this study, we request additional beam time. Our experiments can be summarized as follows:
1) We want to conduct scattering studies of more concentrated suspensions in PEG400-6000, particle volume fraction of 0.3 to 0.5.
2) We want to investigate particle structure in higher MW PEG of 12000 and 20000.
Particle structure will be analyzed through the calculation of interparticle structure factors.

equipment_required:
	Use of a constant temperatrue water bath and the vaccum pump

experiment:
	Microstructure of Silica Nanoparticles in Low MW PEG

foreign_nationals:
	

hazards:
	No hazards associated with this experiment.

instrument:
	33ID-D USAXS

instrument_other:
	

minimumdays:
	1

name:
	Benjamin Anderson

nonmembers:
	

submit:
	Submit

unacceptable_dates:
	07/15/06 to 08/15/06

z34ID_details:
	


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