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# William Smith <wesmith@uiuc.edu>
# requesting 4 days, at minimum=3 days
# beamline 33ID, "Structure of mixtures of thermoresponsive microgels and hard sphere colloids via USAXS"
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# top:/home/www/beamtime-requests/req00301.txt
# UNICAT Member Beam Time Request  #301
# created Wed Oct 30 15:06:05 CST 2002
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beamline:
	33ID

collaboration:
	Yes

collaborator+Pete:
	on

contact:
	wesmith@uiuc.edu

days:
	4

description:
	Stimuli-responsive particles have potential applications in various areas like separation of bio-molecules, drug delivery and rheological property modifiers. Controlling particle size is key to these applications. In the case of temperature sensitive microgels, because the gel particles are composed of cross-linked polymer chains, the particle size is a function of temperature and solvent chemical potential. Previous experiments at the 33ID beamline at the UNICAT facility at the APS have shown that the particle size of these microgel particles is dependent on the number density of the particles as well as temperature. Increasing the number density leads to an increase in osmotic pressure which cause the particle to deswell.
	
	In this study we propose to study the effect of this deswelling transition on the structure factor of a mixture of the microgel particles with hard core colloidal particles. The polymeric microgel particles in such a mixture are expected to behave as depletants that have a tunable particle size. The microgel particles are non-adsorbing onto the hard core particles and thus are capable of inducing depletion attractions between the particles. The strength and range of these depletion attractions will depend on the concentration and size of these microgel particles. Thus by tuning the size of the microgel particles, one can tune the range of the depletion attractions between the hard core particles leading to a rich variety of colloidal phase behavior. 
	
	The system that will be studied will include Stober silica coated with poly(N-isopropylacrylamide) (polyNIPAM) and microgel particles composed of polyNIPAM. The solvent in all samples will be DI water. We hope to use the USAXS technique to probe the changes in the structure factor of the colloidal suspension of the silica particles with increasing concentration of polyNIPAM microgel particles at different temperatures.  
	
	In an associated study, anisotropic particle interactions will be investigated by using a model system involving colloidal fractal aggregates. The scattering data obtained will be used to gain insight into the thermodynamics and structural information due to the colloid-colloid interactions. The system will be studied as a function of function of concentration across phase boundaries. Also of interest will be the effect of changing electrostatic repulsions on both the structure and the thermodynamics. 
	The system that will be studied will include fumed silica in water, THF and ethanol as solvents.

equipment+required:
	Wet Chemistry Lab.

experiment:
	Structure of mixtures of thermoresponsive microgels and hard sphere colloids via USAXS

foreign+nationals:
	Prashant Mullick

hazards:
	None

minimumdays:
	3

name:
	William Smith

nonmembers:
	

unacceptable+dates:
	


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