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# Prashant Mullick <pmullick@scs.uiuc.edu>
# requesting 2 days, at minimum=2 days
# beamline 33ID, Microstructure of Responsive Colloidal Fluids
# instrument 33ID-D SB-USAXS
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# top:/home/www/beamtime-requests/req00589.txt
# UNICAT Member Beam Time Request  #589
# created Mon Apr 19 12:35:22 CDT 2004
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beamline:
	33ID

collaboration:
	Yes

collaborator_Pete:
	ON

contact:
	pmullick@scs.uiuc.edu

days:
	2

description:
	Previous experiments with mixtures of temperature sensitive microgel particles and hard spheres at the APS, ANL have yielded invaluable insights into the clustering of the hard particles in presence of the soft microgel particles, both as a function of temperature as well as increasing concentration of microgels at a fixed hard sphere concentration. 

The hard sphere particles used in this study are Silica particles prepared via the Stober’s synthesis and then coated with hairs of hydrophilic poly(N-isopropylacrylamide) polymer. The soft microgel particles are composed of crosslinked poly(N-isopropylacrylamide) and have a temperature dependent particle size.

Experiments were performed at three different temperatures, 25 oC, 32 oC and 35 oC. At all temperatures, on addition of the soft microgels, the hard particles begin to show signs of clustering. This is evident from the shift in the first peak in the structure factor, S(q) towards higher qD as well as the upturn in S(q) at low qD. 

As the concentration of microgels in the mixture is increased, the upturn in S(q) at low qD gradually disappears. This is also accompanied by the shift of the first peak to lower qD. Both these are indications of the breakage of clusters that might have formed on initial addition of the soft microgels. These observations are contrary to what is expected from typical depletion mixtures (1). 

We propose to conduct further experiments to explore the liquid regime where the growth of the upturn in S(q) is first observed. Experiments will be performed as a function of temperature at the above three temperatures and with increasing microgel concentrations. The hard sphere volume fraction for these measurements will be chosen so as to ensure the samples in the liquid region. 

These measurements will help us further probe the evolution of the structure factor of these mixtures of hard and soft particles. Several studies have shown the link between the microstructure and viscoelasticity of colloidal suspensions. Hence these SB-USAXS experiments will be crucial step in the design of a responsive colloidal fluid.

(1)	Shah, S. A.;  Chen, Y. L.;  Ramakrishnan, S.;  Schweizer, K. S.; Zukoski, C. F. J Phys-Condens Mat 2003, 15, 4751-4778.

equipment_required:
	Temperature bath. 
If this is not available at UNICAT, we can make arrangements to bring our own.

experiment:
	Microstructure of Responsive Colloidal Fluids

foreign_nationals:
	Prashant Mullick

hazards:
	None

instrument:
	other

instrument_other:
	33ID-D SB-USAXS

minimumdays:
	2

name:
	Prashant Mullick

nonmembers:
	

unacceptable_dates:
	Any date in May/June would not be possible.

z34ID_details:
	


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