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# Subramanian Ramakrishnan <ramakris@scs.uiuc.edu>
# requesting 3 days, at minimum=3 days
# beamline 33ID, Scattering Studies of Block Copolymers and Colloidal Gels
# instrument 33ID-D USAXS
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# top:/home/www/beamtime-requests/req00646.txt
# UNICAT Member Beam Time Request  #646
# created Mon Aug 16 18:37:38 CDT 2004
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beamline:
	33ID

collaboration:
	Yes

collaborator_Pete:
	ON

contact:
	ramakris@scs.uiuc.edu

days:
	3

description:
	1.	Temparature Induced Gelation of Colloidal Suspensions
S. Ramakrishnan and C. F. Zukoski
Extensive rheological measurements in our laboratory have been carried out on suspensions composed of 90 nm diameter, D, silica particles where flow properties can be tuned by changing temperature.  Our aim is to predict flow properties from measured structure factors, S(q). Our preliminary work indicates that in predicting the flow properties of gels, it is the large qD values of S(q) that are important.  This occurs in a region wehre measurements canot be made.  However, we have also demonstrated that if we can fit S(q) for qD<10 uisng analytical models such as the adhesive hard spheres, mechncila properties can be predicted.  Our initial results suggest the curve fitting was extremely sensitive to the low q region of S(q).  In this work we will explore smaller values of qD by working with 45nm diameter particles. 
In our last run at Argonne, we collected data of S(q) for 3 different volume fractions 0.15, 0.2, and 0.25 at different temperatures.  In this trip we plan to go to higher volume fractions: 0.3, 0.35, 0.4 and 0.45.  These provide a complete set of data to fully characterize the system.
The plan is to perform S(q) measurements at a number of volume fractions and decreasing temperatures at each volume fraction.  At each volume fraction, the suspension would go from being a liquid to a gel which has a finite yield stress and elastic modulus.

2.	Scattering from block copolymers and 4 arm stars
S. Ramakrishnan, Robert Lambeth, Jeffrey Moore and C. F. Zukoski
The main goal of the synthetic and characterization work is to determine if by controlling the structure of block co-polymer 4-arm stars we are able to control the structures of the stars as they are placed into poor quality solvents. The ultimate model for these systems is protein folding.  Proteins consist of hydrophobic and hydrophilic residues and it is a unique combination of these residues that gives rise to its structure.
Working with block copolymers and 4 arm stars of Dimethyl acrylamide (DMA) and N-Isopropyl acrylamide (NIPAM) synthesized in our laboratory, we ill explore changes star state and interactions as we change solvent quality by varying temperature.  Poly-NIPAM undergoes a phase transition at 32C and becomes hydrophobic.  As a result the block co-polymer arms of the star are hydrophilic at room temperature, but at elevated temperature consist of regions that are both hydrophobic and hydrophilic parts.  Our aim is to systematically vary the hydrophobic and hydrophilic lengths of the copolymers and to study the structures formed in solution as temperature is varied.   Our scattering studies will be performed as a function of temperature and polymer concentration.

equipment_required:
	Temperature Bath

experiment:
	Scattering Studies of Block Copolymers and Colloidal Gels

foreign_nationals:
	

hazards:
	

instrument:
	33ID-D USAXS

instrument_other:
	

minimumdays:
	3

name:
	Subramanian Ramakrishnan

nonmembers:
	

unacceptable_dates:
	Nov 5 - 13 AIChE meeting

z34ID_details:
	


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