Ordering Transition of Block Copolymer Thin Films Abraham Arceo, Peter F. Green The University of Te

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Ordering Transition of Block Copolymer Thin
FilmsAbraham Arceo, Peter F. GreenThe
University of Texas at Austin (DMR-0072897)
BULK PHASE DIAGRAM (cN)bulk-ODT10.5

• A-b-B diblock copolymers self-organize into a
  range of geometrical patterns (spheres, lamellae
  etc.) below an order-disorder transition
  temperature, TODT. For bulk symmetric copolymers,
  which form lamellae of spacing L, the transition
  occurs when ?Ngt10.5, where N is the number of
  monomers per chain and ? (1/T) is an energetic
  interaction parameter.
• Finding
• The transition occurs when ?Ngt7.94 for a film
  (hlt2L) of PS-b-PMMA copolymer supported by SiOx,
  corresponding to a decrease of TODT by
  approximately 250 degrees.
• In a solvent environment, supercritical CO2,
  which exhibits a preferential affinity for PMMA,
  the TODT is shifted significantly below the bulk,
  and below that of the supported film in
  air/vacuum.

Lamellar (order)
disorder
Shift of Thin film ODT (cN)film-ODT7.94 (cN)bulk-
ODT10.5
Journal of Physical Chemistry B (LETTER),109,
6958 (2005)
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Broader Impact

• A-b-B diblock copolymers, depending on the
  chemical characteristics of the A and B
  components, are used for a wide range of
  applications, from devices and sensors to
  structural applications. Many of the new
  applications involve thin films. Upon increasing
  temperature, these materials self-organize. Our
  results show that the ordering temperature for
  thin, supported films, can be considerably lower,
  200 degrees, than the bulk ordering temperature
  (enhanced incompatibility between the A/B
  segments).
• Secondly, solvents are often used to process
  block copolymers because they not only plasticize
  the copolymer, but they also make the system
  thermodynamically more compatible. Our results
  reveal that in cases where the solvent exhibits a
  preferential affinity for one component (PMMA in
  this case), that the thin, supported, film may
  become more incompatible than one would
  anticipate. This could have significant
  implications for low temperature processing of
  these systems.