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METHOD:PUBLISH
BEGIN:VEVENT
DTSTAMP:20260813T182203Z
LAST-MODIFIED:20121116T203436Z
DTSTART:20091019T160000Z
DTEND:20091019T170000Z
UID:event482@bu.edu
URL:http://physics.bu.edu/internal/events/show/482
SUMMARY:Aggregation States and Dynamics of Polymers at Non-solvent Interfac
	es
DESCRIPTION:Featuring Keiji Tanaka\, Kyushu University\, Japan\nHosted by: 
	Ophelia Tsui\n\nPart of the Biophysics/Condensed Matter Seminar Series.\n\n
	Abstract: Interfaces of polymers with "nonsolvents" play an important role 
	in their functional properties such as wettability\, friction with lubrican
	ts\, cell adhesion\, biocompability\, etc.  To design and construct highly 
	functionalized polymers for applications that exploit these characteristics
	\, aggregation states of the polymers at the liquid interfaces must be unde
	rstood as the first benchmark.  However\, this is experimentally difficult 
	because such interfaces are buried.  In this study\, we use neutron reflect
	ivity (NR) and sum-frequency generation (SFG) spectroscopy to study\, respe
	ctively\, the density profile and local conformation of poly(methyl methacr
	ylate) (PMMA) at the interface with air or gaseous nitrogen (N2) and at wat
	er interfaces. \n\nSpecular neutron reflectivity (NR) was applied to a perd
	euterated poly(methyl methacrylate) (dPMMA) film spin-coated on a substrate
	.  The interface of dPMMA with water was diffuse in comparison with the pri
	stine interface with air.  Interestingly\, the dPMMA film was composed of a
	 swollen layer and the interior region\, which also contained water\, in ad
	dition to the diffused layer.  To conserve mass\, the swelling of the film 
	by water is accompanied by an increase in the film thickness.  The change i
	n the film thickness estimated by NR was in excellent accord with the resul
	t of direct observation using atomic force microscopy (AFM).  The modulus o
	f dPMMA in the vicinity of the water interface was also examined on the bas
	is of force-distance curves measured by AFM.  The modulus decreased closer 
	to the outermost region of the film.  The extent to which the modulus decre
	ased in the interfacial region was consistent with the amount of water sorb
	ed into the film.\n\nThe local conformation of PMMA chains at the N2 and wa
	ter interfaces was studied by infrared (IR)-visible SFG spectroscopy.  Alth
	ough SFG spectra in the C-H region for PMMA at the N2 interface have been h
	itherto reported\, the peak assignments are not in accord with one another.
	  Thus\, we first made the accurate assignments of SFG peaks using films\, 
	which had been well annealed at a temperature above the glass transition te
	mperature for a long time\, of three different deuterated PMMAs as well as 
	normal protonated PMMA.  At the N2 interface\, hydrophobic functional group
	s such as  methyl\, ester methyl and methylene groups were present.  Whi
	le the  methyl group was oriented along the direction normal to the inte
	rface\, ester methyl and methylene groups were oriented parallel to the int
	erface.  Quantitative discussion concerning the orientation of the function
	al groups of PMMA at the N2 interface was aided by a model calculation.  On
	ce the PMMA film was contacted with water\, the carbonyl groups of the PMMA
	 side chains were oriented to the water phase to form hydrogen bonds with w
	ater molecules\, resulting in the migration of ester methyl into the intern
	al region of the film.  Concurrently\, the methylene groups became randomly
	 oriented at the water interface and/or in part migrated into the internal 
	region.  Interestingly\, the  methyl groups still existed at the water i
	nterface oriented along the parallel direction.  The outermost region of PM
	MA in water can be consisted of hydrophilic and hydrophobic domains with su
	b-nanometer scale.  Water molecules H-bond to themselves near the hydrophob
	ic domains\, leading to the formation of an ice-like structure of water mol
	ecules.  On the other hand\, water molecules adjacent to the hydrophilic do
	mains H-bond with carbonyl groups.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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