8 research outputs found
Heat Transfer Organic Materials: Robust Polymer Films with the Outstanding Thermal Conductivity Fabricated by the Photopolymerization of Uniaxially Oriented Reactive Discogens
For the development
of advanced heat transfer organic materials (HTOMs) with excellent
thermal conductivities, triphenylene-based reactive discogens, 2,3,6,7,10,11-hexakis(but-3-enyloxy)triphenylene
(HABET) and 4,4′,4″,4‴,4⁗,4⁗′-(triphenylene-2,3,6,7,10,11-hexaylhexakis(oxy))hexakis(butane-1-thiol)
(THBT), were synthesized as discotic liquid crystal (DLC) monomers
and cross-linkers, respectively. A temperature–composition
phase diagram of HABET-THBT mixtures was first established based on
their thermal and microscopic analyses. From the experimental results,
it was realized that the thermal conductivity of DLC HTOM was strongly
affected by the molecular organizations on a macroscopic length scale.
Macroscopic orientation of self-assembled columns in DLC HTOMs was
effectively achieved under the rotating magnetic fields and successfully
stabilized by the photopolymerization. The DLC HTOM polymer-stabilized
at the LC phase exhibited the remarkable thermal conductivity above
1 W/mK. When the DLC HTOM was macroscopically oriented, the thermal
conductivity was estimated to be 3 W/mK along the in-plane direction
of DLC molecule. The outstanding thermal conductivity of DLC HTOM
should be originated not only from the high content of two-dimensional
aromatic discogens but also from the macroscopically oriented and
self-assembled DLC. The newly developed DLC HTOM with an outstanding
thermal conductivity as well as with an excellent mechanical sustainability
can be applied as directional heat dissipating materials in electronic
and display devices
Photoresponsive Carbohydrate-based Giant Surfactants: Automatic Vertical Alignment of Nematic Liquid Crystal for the Remote-Controllable Optical Device
Photoresponsive carbohydrate-based
giant surfactants (abbreviated
as CELA<i><sub>n</sub></i>D-OH) were specifically designed
and synthesized for the automatic vertical alignment (VA) layer of
nematic (N) liquid crystal (LC), which can be applied for the fabrication
of remote-controllable optical devices. Without the conventional polymer-based
LC alignment process, a perfect VA layer was automatically constructed
by directly adding the 0.1 wt % CELA<sub>1</sub>D-OH in the N-LC media.
The programmed CELA<sub>1</sub>D-OH giant surfactants in the N-LC
media gradually diffused onto the substrates of LC cell and self-assembled
to the expanded monolayer structure, which can provide enough empty
spaces for N-LC molecules to crawl into the empty zones for the construction
of VA layer. On the other hand, the CELA<sub>3</sub>D-OH giant surfactants
forming the condensed monolayer structure on the substrates exhibited
a planar alignment (PA) rather than a VA. Upon tuning the wavelength
of light, the N-LC alignments were reversibly switched between VA
and PA in the remote-controllable LC optical devices. Based on the
experimental results, it was realized that understanding the interactions
between N-LC molecules and amphiphilic giant surfactants is critical
to design the suitable materials for the automatic LC alignment
Hierarchical Striped Walls Constructed by the Photopolymerization of Discotic Reactive Building Blocks in the Anisotropic Liquid Crystal Solvents
A triphenylene-based
reactive mesogenic molecule (abbreviated as
HABET) was newly designed and synthesized as a programmed building
block to construct the striped walls by the photopolymerization in
the anisotropic liquid crystal (LC) solvents. On the basis of thermal,
scattering and microscopic analyses, it was found that HABET formed
three ordered structures: a columnar hexagonal LC phase (Φ<sub>H</sub>), a tilted columnar hexagonal LC phase (Φ<sub>T</sub>) and a highly ordered columnar oblique crystal phase (Φ<sub>OK</sub>). The microscopic molecular orientations in the hierarchical
superstructures were controlled in the anisotropic LC solvents with
the help of surface anchoring forces, while the dimensions of the
striped wall morphologies were determined by the patterned photomasks.
The long axis of self-assembled columns in the striped walls was perpendicular
to the surface alignment direction regardless of the photomask direction.
Additionally, it was realized that the shapes of water drops as well
as the surface water contact angles can be tuned by the hierarchical
superstructures and morphologies of the polymerized HABET networks.
The anisotropic hierarchical superstructures and morphologies concurrently
fabricated during the polymerization in the anisotropic LC medium
can offer a potential pathway for liquid transportation in the microfluidic
devices
Construction of Polymer-Stabilized Automatic MultiDomain Vertical Molecular Alignment Layers with Pretilt Angles by Photopolymerizing Dendritic Monomers under Electric Fields
The synthesized itaconic acid-based
dendritic amphiphile (Ita3C<sub>12</sub>) monomers and the methacryl
polyhedral oligomeric silsesquioxane
(MAPOSS) cross-linkers were directly introduced for the construction
of automatic vertical alignment (auto-VA) layers in the host nematic
liquid crystal (NLC) medium. The auto-VA layer can be stabilized by
irradiating UV light. For the automatic fabrication of a polymer-stabilized
multidomain VA (PS auto-MDVA) layer with a pretilt angle, Ita3C<sub>12</sub> and MAPOSS were photopolymerized under the electric field
by irradiating UV light on the multidomain electrode cell. Mainly
because of the pretilted NLC at zero voltage, the electro-optic properties
of the PS auto-MDVA cell were dramatically improved. From the morphological
observations combined with surface chemical analyses, it was found
that various sizes of protrusions on the solid substrates were automatically
constructed by the two-step mechanisms. We demonstrated the PS auto-MDVA
cell with the enhancement of electro-optic properties as a single-step
process and investigated how the protrusions were automatically developed
during the polymer stabilization
Pyrene-Based Asymmetric Supramolecule: Kinetically Controlled Polymorphic Superstructures by Molecular Self-Assembly
To
understand the kinetically controlled polymorphic superstructures
of asymmetric supramolecules, a pyrene-based asymmetric supramolecule
(abbreviated as Py3M) was newly synthesized by connecting two pyrene
headgroups (Py) to a biphenyl-based dendritic tail (3M) with an isophthalamide
connector. On the basis of thermal,
microscopic, spectroscopic, and scattering results, it was realized
that Py3M exhibited the monotropic phase transition between a stable
crystalline phase (K1) and a metastable crystalline phase (K2). This
monotropic phase transition behavior was mainly originated from the
competitions of intra- and intermolecular interactions (π–π
interactions and hydrogen bonds) as well as from the nanophase separations.
From the two-dimensional (2D) wide-angle X-ray diffraction patterns
and transmission electron microscopy images of the self-assembled
Py3M superstructures, it was found that Py3M formed two synclinically
tilted crystalline superstructures: the 6.75 and 4.4 nm periodicities
of layered structures for K1 and K2 phases, respectively. The stable
K1 phase was predominantly induced by the π–π interactions
between pyrenes, while the intermolecular hydrogen bonds between isophthalamides
were the main driving forces for the formation of the metastable K2
phase. Ultraviolet–visible and photoluminescence experiments
indicated that the photophysical properties of Py3M were directly
related to their molecular packing superstructures
Flexible and Patterned Thin Film Polarizer: Photopolymerization of Perylene-based Lyotropic Chromonic Reactive Mesogens
A perylene-based reactive mesogen
(DAPDI) forming a lyotropic chromonic liquid crystal (LCLC) phase
was newly designed and synthesized for the fabrication of macroscopically
oriented and patterned thin film polarizer (TFP) on the flexible polymer
substrates. The anisotropic optical property and molecular self-assembly
of DAPDI were investigated by the combination of microscopic, scattering
and spectroscopic techniques. The main driving forces of molecular
self-assembly were the face-to-face π–π intermolecular
interaction among aromatic cores and the nanophase separation between
hydrophilic ionic groups and hydrophobic aromatic cores. Degree of
polarization for the macroscopically oriented and photopolymerized
DAPDI TFP was estimated to be 99.81% at the <i><b>λ</b></i><sub>max</sub> = 491 nm. After mechanically shearing the
DAPDI LCLC aqueous solution on the flexible polymer substrates, we
successfully fabricated the patterned DAPDI TFP by etching the unpolymerized
regions selectively blocked by a photomask during the photopolymerization
process. Chemical and mechanical stabilities were confirmed by the
solvent and pencil hardness tests, and its surface morphology was
further investigated by optical microscopy, atomic force microscopy,
and three-dimensional surface nanoprofiler. The flexible and patterned
DAPDI TFP with robust chemical and mechanical stabilities can be a
stepping stone for the advanced flexible optoelectronic devices
Interfacial Engineering for the Synergistic Enhancement of Thermal Conductivity of Discotic Liquid Crystal Composites
To
develop an advanced heat transfer composite, a deeper understanding
of the interfacial correlation between matrix and filler is of paramount
importance. To verify the effect of interfacial correlations on the
thermal conductivity, the conductive fillers such as expanded graphite
(EG) and boron nitride (BN) are introduced in the discotic liquid
crystal (DLC)-based polymeric matrix. The DLC matrix exhibits better
interfacial affinity with EG compared to BN because of the strong
π–π interactions between EG and DLC. Thanks to
its excellent interfacial affinity, the EG-DLC composites show a synergistic
increment in thermal conducting performance
Azobenzene Molecular Machine: Light-Induced Wringing Gel Fabricated from Asymmetric Macrogelator
To develop light-triggered
wringing gels, an asymmetric macrogelator
(1AZ3BP) was newly synthesized by the chemically bridging a photoisomerizable
azobenzene (1AZ) molecular machine and a biphenyl-based (3BP) dendron
with a 1,4-phenylenediformamide connector. 1AZ3BP was self-assembled
into a layered superstructure in the bulk state, but 1AZ3BP formed
a three-dimensional (3D) network organogel in solution. Upon irradiating
UV light onto the 3D network organogel, the solvent of the organogel
was squeezed and the 3D network was converted to the layered morphology.
It was realized that the metastable 3D network organogels were fabricated
mainly due to the nanophase separation in solution. UV isomerization
of 1AZ3BP provided sufficient molecular mobility to form strong hydrogen
bonds for the construction of the stable layered superstructure. The
light-triggered wringing gels can be smartly applied in remote-controlled
generators, liquid storages, and sensors