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BEGIN:VEVENT
DTSTAMP:20260816T124958Z
LAST-MODIFIED:20121116T203436Z
DTSTART:20071012T160000Z
DTEND:20071012T170000Z
UID:event147@bu.edu
URL:http://physics.bu.edu/internal/events/show/147
SUMMARY:"Equilibrium Pathway of Spin-Coated Polymer Films"
DESCRIPTION:Featuring Ophelia Tsui\, Boston University\n\nPart of the Bioph
	ysics/Condensed Matter Seminar Series.\n\nAbstract: Spin-coating is a preva
	lent method for making thin polymer films. In this process\, a drop of dilu
	te polymer solution is added to a substrate whereupon the substrate is spun
	 at 500 – 4000 rpm to spread the solution. Rapid evaporation of the solve
	nt causes the polymer to vitrify into a residue film in seconds. The abrupt
	ness of the process has led many to suggest that polymers in spin-coated fi
	lms are non-equilibrated or metastable\, which may explain some of the more
	 bizarre results\, such as negative thermal expansion and a large residual 
	stress comparable to the polymer’s elastic modulus. There have been some 
	speculations about the physical form of the metastable state\, but none has
	 been verified. Here\, we show that metastability in spin-coated films can 
	arise from their thickness uniformity\, causing the surface profile of the 
	films to deviate from the equilibrium\, comprising thermally excited surfac
	e capillary waves compliant to the equipartition law. As a result\, the equ
	ilibration process of the films encompasses sequential excitations of the c
	apillary wave modes from the short- (fast) to long-wavelength (slow) modes.
	 We anticipate that more detailed models can be constructed upon the ideas 
	presented here to explain the unusual observations in spin-coated polymer f
	ilms. A thorough understanding about the metastability of these films and t
	heir physical behaviors is necessary to predict and control their stability
	 for practical applications.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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