#
# top.uni.aps.anl.gov:/home/www/beamtime-requests/req00234.txt
# UNICAT Member Beam Time Request  #234

# created Mon Dec 03 13:21:00 CST 2001
#
beamline:
	33ID

collaboration:
	Yes

collaborator+Pete:
	on

contact:
	pmullick@scs.uiuc.edu

days:
	3

description:
	Stimuli-responsive particles have received increasing attention in various applications like bio-separation, drug delivery systems and in suspension rheology modifiers. Controlling the stimuli-response of these systems requires an understanding of the underlying links between pair interactions and the resulting phase behavior. Current emphasis is on preparation of thermo-sensitive monodispersed microgel particles of poly n-isopropylacrylamide. Thermo-sensitive microgel particles undergo volume phase transitions and size changes with small changes in temperature. Dynamic light scattering studies indicate that the particle diameter ranges from 300 nm to 150 nm as the temperature increases 20 oC to 32 oC. This size change can be used as a precise control of volume fraction for a fixed number density of polymer. Transitions from fluids with well-defined zero shear rate viscosities to suspensions with well-defined zero frequency elasticities accompany the onset of iridescence suggesting an order-disorder transition. Furthermore, these microgel particles can be used as non-adsorbing depletants in a stable colloidal suspension to induce depletion attractions.  Controlled manipulation of the microgel size can induce a variety of thermo-reversible phase transitions.  Changes in the suspension structure factor over these transitions will be investigated using USAXS. This will help elucidate the link between the microstructure and rheology of these thermo-sensitive microgel suspensions. Previous USAXS measurements performed at the Advanced Photon Source indicate the presence of a high degree of ordering and a sharp peak in the structure factor. 
	
	Samples will include varying concentrations of microgel particles in water ranging from dilute solutions to concentrated samples that show a high degree of ordering. Controlled temperature variation from 25 oC to 40 oC will be performed. The particles collapse as the temperature is increased above 32 oC. The changes in structure factor will be investigated over this transition.

equipment+required:
	

experiment:
	USAXS studies of soft temperature sensitive microgel particle suspensions

foreign+nationals:
	Prashant Mullick (pre-approved for access to APS facility)

hazards:
	No known hazardous materials are involved in this study. The samples will be transported in accordance with DOT regulations. Sample quantities will be below 30 ml and will be packaged in APS approved glass bottles.

minimumdays:
	3

name:
	Prashant Mullick

nonmembers:
	

unacceptable+dates:
	January 23rd to January 26th 2002
	March 16th - March 25th 2002


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