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Calendar: ALS Calendar
Title: ALS Seminar: Li Yao, "Characterization of 3-D Structures in Functional Nanomaterials Generated by Manipulating and Replicating Block Copolymer Morphologies"
When: 05/22/2013 1:30 PM - 2:30 PM
Description: ALS Special Seminar

"Characterization of 3-D Structures in Functional Nanomaterials Generated by Manipulating and Replicating Block Copolymer Morphologies"
by Li Yao

Wed, May 22, 130pm
2-100B Conference Room

Transmission electron microscopy (TEM) and grazing-incidence small-angle X-ray scattering
(GISAXS) are two of the techniques that were extensively used in my dissertation to characterize the manipulation and replication of 3D nanomaterials. The first section reports the formation of mesoporous silica films with spherical, cylindrical and bicontinuous pores up to 40 nm in diameter through replicating the morphologies of the solid block copolymer (BCP) templates, polystyrene-b-poly(tert-butyl acrylate) (PS-b-PtBA), via phase selective condensation of tetraethylorthosilicate in supercritical CO2. The structural details that were imparted to the
templates prior to precursor infusion were retained in the final mesoporous films with the
structure factors as confirmed by GISAXS and TEM. Next, directed self-assembly was used to
control the orientation of cylindrical domains of PS-b-PtBA templates. Large area aligned
cylindrical mesochannels in silica films were achieved through replication of these oriented
templates in scCO2. The diameters of the channels can be tuned between 5 and 30 nm through
adjusting the molecular weight of the template. The long-range alignment of mesochannels was
confirmed through GISAXS sample stage azimuthal rotation. One potential application of these
materials is in nanofluidics.
In the second part, enantiopure tartaric acid is used as an additive to dramatically improve
ordering in poly(ethylene oxide-block-tert-butyl acrylate) (PEO-b-PtBA) copolymers. TEM,
atomic force microscopy (AFM) and X-ray scattering were used to study the phase behavior and
morphologies within both bulk and thin films. With the addition of a photo acid generator,
photo-induced disorder in PEO-b-PtBA/tartaric acid composite system can be achieved upon UV
exposure to deprotect PtBA block to yield poly(acrylic acid) (PAA), which is phase-miscible
with PEO. Due to the strong interaction of tartaric acid with both blocks, the system undergoes a
disordering transition within seconds during a post-exposure baking step, which can be tracked
by GISAXS to optimize the conditions. Area-selective UV exposure using a photo-mask was
applied with the assistance of trace amounts of base quencher to achieve high resolution,
hierarchical patterns. These sub-micron patterns with ordered and disordered regions were
characterized by AFM. Finally, helical superstructures were observed by TEM in this BCP/chiral
additive system with 3D handedness to be confirmed by TEM tomography

Location: 2-100B