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Terence's Project Page - RISE Summer 2006 |
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Intern: Terence Choy, Chemistry,
Columbia University
Mentor: Karen Sohn
Faculty Supervisor: Ed Kramer
Department: Materials |
SPHERICAL AND CYLINDRICAL PHASE TRANSITIONS IN DIBLOCK AND TRIBLOCK COPOLYMERS
Block copolymers composed of immiscible monomer units are known to phase
separate into chemically distinct domains on the order of 10 to 100 nm. This
property has been the interest of much research in the past 35 years for
applications in nanolithography and electronics manufacturing. Therefore,
understanding the kinetics of pattern formation and producing ordered domains
is highly desirable.
A commercial blend of poly(styrene-b-ethylene-r-butylene) (SEB) diblock and
poly(styrene-b-ethylene-r-butylene-b-styrene) (SEBS) triblock exhibits an
order-order transition (OOT) between hexagonally packed cylinders and body-
centered cubic spheres at ~140° C before crossing into the disordered phase at
~200° C.
In thin films, however, the film thickness and annealing time also affect the
expressed morphology. Curiously, the spherical morphology has been observed
below the OOT at low film thicknesses and short annealing times in the blend.
The project aims to derive the kinetics that govern the morphologies of the
block copolymers. To simplify the system, the two components of the blend were
fractionally precipitated and purified. Films of SEB diblock and SEBS triblock
were annealed under various conditions, and then characterized by surface force
microscopy (SFM). This affords valuable knowledge for future projects seeking to
obtain long range ordering on templated substrates.
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