BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Modification of Polymer/Polymer Interfaces Using Block Copolymers 
 and Microgel Particles - Richard J Spontak\, Departments of Chemical &amp\
 ; Biomolecular Engineering and Materials Science &amp\; Engineering\, Nort
 h Carolina State University
DTSTART:20060703T103000Z
DTEND:20060703T113000Z
UID:TALK5137@talks.cam.ac.uk
CONTACT:Edmund Ward
DESCRIPTION:The stability of polymer thin films is critical to the develop
 ment of advanced protective coatings and defect-free multilayer assemblies
 \, in which case the molecular-scale processes responsible for film destab
 ilization must be fully understood. When a thin liquid film contacts a sol
 id substrate\, it can remain stable or\, depending on the nature and magni
 tude of intermolecular forces within the film\, rupture and dewet from the
  substrate. Since film stability governs the function of synthetic coating
 s and numerous biological liquids\, independent efforts have sought to elu
 cidate the dewetting behavior of homopolymer or block copolymer thin films
  on a solid substrate. Dewetting in thin films generally occurs by nucleat
 ion and growth (NG) wherein film rupture proceeds by the formation and gro
 wth of circular holes that ultimately impinge to produce sessile droplets.
  Thin film destabilization may alternatively proceed by spinodal dewetting
  (SD) wherein film thickness fluctuates at the liquid-air interface. The s
 patiotemporal evolution of surface modulations promotes the formation of a
  bicontinuous morphology similar to that observed in liquid mixtures that 
 phase-separate by spinodal decomposition. Instability considerations confi
 rm that the dominant mode of surface fluctuations amplifies with increasin
 g time and occurs at a fast-growing wave vector. The dynamic topology of a
 n unstable thin film on a homogeneous substrate normally occurs when a thi
 n film destabilizes and flows from thin to thick regions. If a substrate i
 s chemically heterogeneous\, a spinodal-like instability can likewise deve
 lop as a consequence of flow from less to more wettable interfacial region
 s. While most efforts have explored thin film stability by varying film th
 ickness\, few studies have reported on the effect of block copolymers as i
 nterfacial modifiers in thin films even though copolymers are conventional
 ly used to compatibilize homopolymers. The dewetting rate of polystyrene (
 PS) from poly(methyl methacrylate) (PMMA) at 180°C\, for instance\, is gr
 eatly reduced by adding a PS-b-PMMA (SM) diblock copolymer to the PS. In t
 his work\, we first demonstrate that the dewetting rate and mechanism of P
 S/SM thin films of constant thickness are both tunable via copolymer conce
 ntration. Atomic force microscopy and transmission electron microtomograph
 y provide complementary information of these dynamically evolving systems 
 and confirm the existence of interfacial copolymer structures. We also exa
 mine the viability of core-shell microgel particles\, which can be envisag
 ed as permanent micelles\, as thin-film stabilizing agents and provide evi
 dence that surface patterning can be achieved using such particles when th
 ey undergo autophobically-driven surface segregation.
LOCATION:T001 [Tower Seminar Room]\, Materials Science and Metallurgy\, De
 partment of
END:VEVENT
END:VCALENDAR