#
# top.uni.aps.anl.gov:/home/www/beamtime-requests/req00233.txt
# UNICAT Member Beam Time Request  #233

# created Mon Dec 03 12:55:26 CST 2001
#
beamline:
	33ID

collaboration:
	Yes

collaborator+Pete:
	on

contact:
	syedshah@uiuc.edu

days:
	3

description:
	APS Proposal for Beamtime
	Brief Description of Experiment
	
	Formation of gels is often desired for a number of applications widely used in the coatings, food and pharmaceutical industries.  The addition of non-adsorbing polymer to a stable suspension of particles is a useful way of inducing attractions via the depletion mechanism.  Depending on the strength and the range of these attractions, systems often undergo non-equilibrium phase transitions like gel transitions.  The strength and range of the depletion attraction is proportional to the polymer concentration and radius of gyration respectively.  The structure of these flocculated suspensions is inherently linked to the rheological properties of these systems.  
	
	In our study we intend to systematically alter both the strength and range of the attractions and investigate the effects of these parameters on the suspension microstructure as we traverse across the gel transition boundary.  Experiments will be conducted both in the one-phase fluid region (before gelation) and well into the gel phase.  We intend to use the USAXS technique to probe subtle changes in the suspension structure factor as the gel boundary is traversed.  Knowledge of these effects on the flow properties of the system will help establish links between the suspension microstructure and mechanics.  These studies will be compared to model predictions of the suspension microstructure to elucidate the origin of gel transitions.
	
	Previous data gathered at the APS facility have shown excellent qualitative agreement with model predictions.  However, we hope to be able to use the pin-hole collimated USAXS setup to avoid desmearing issues which could ultimately lead to better quantitative agreement.

equipment+required:
	

experiment:
	USAXS Studies of Depletion Flocculated Gels

foreign+nationals:
	Syed Ali Shah (Approved for access to APS facility)

hazards:
	The only hazardous materials used will be toluene as a solvent for dispersing our silica particles.
	The samples will be transported to the facility in accordance with DOT regulations.  Sample quanities will be below
	30 ml and will be packaged in APS approved glass bottles.

minimumdays:
	3

name:
	Syed Ali Shah

nonmembers:
	

unacceptable+dates:
	March 16th -March 25th 2002


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