#
# arev:/usr/local/unicat/unireq/beamreq/req00117.txt
# UNICAT Member Beam Time Request  #117

# created Mon Jun 19 17:40:24 CDT 2000
#

collaboration:
	Yes

collaborator+Pete:
	on

days:
	2

description:
	Structure of Silica Suspensions with Depletion Interactions.
	C.F. Zukoski
	Depletion interactions occur when polymers are mixed with suspensions
	of particles.  When the polymers cannot penetrate between two closely
	spaced particles there is an imbalance of osmotic pressure and the 
	particles experience a net attraction.  These interactions are well 
	understood in the limit where the polymer radius of gyration, Rg,  is 
	much smaller than the radius of the particle, R. The physics 
	controlling the interactions changes dramatically and is poorly 
	understood in the limit where the polymer is larger than the particle.
	Poorly explores areas include changes in microstructure as polymer 
	concentration and the solvent quality for the polymer are altered.
	As the polymer approaches the point where, in the absence of
	particles, the polymer solution will undergo a phase transition into
	polymer rich and polymer poor phases, the extent of the depletion
	interaction expands dramatically giving rise to large depletion 
	attractions. In this study we will characterize the microstructure 
	of 100 nm hard sphere colloids in the presence of polymers.  The 
	solvents are chosen are toluene and cyclohexane which are a good 
	solvent and in a theta solvent for polystyrene, respectively.  We will
	investigate the effects of particle volume fraction and polymer 
	concentration on particle structure factors.  The particles to be 
	investigated are monodisperse silica particles coated with an 
	octadecyl silica layer.  When suspended in toluene or cyclohexane, 
	these particles interact as hard spheres.  The polymer to be used in 
	monodisperse polystyrene with molecular weights of 30,000 to 2 million
	 giving a ratio of Rg/R of 0.4 to 1.3.  Our goal is to characterize 
	microstructures for comparison with recently developed theoretical 
	descriptions for depletion interactions in the nanoparticle limit 
	(i.e., where Rg>R).
	

equipment+required:
	Possibly liquid cell sample heater
	USAX liquid cell

experiment:
	Structure of Silica Suspensions with Depletion Interactions.

foreign+nationals:
	Subramanian Ramakrishnan
	Amit Kulkarni
	Prashant Mullick

hazards:
	The materials to be used are 100 nm silica partiles, polystyrene, 
	toluene and cyclohexane.  Small quanitiies will be used. 

name:
	Charles F. Zukoski

new+request:
	on

nonmembers:
	

station:
	33ID-D

unacceptable+dates:
	Aug 8-20



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