15 research outputs found
Highly Elastic Supramolecular Hydrogels Using Host–Guest Inclusion Complexes with Cyclodextrins
Supramolecular hydrogels, which are
cross-linked via host–guest interactions, show high-performance
physical properties, such as elasticity and toughness. Herein we prepare
a supramolecular hydrogel without chemical cross-linker. The supramolecular
hydrogel was prepared by polymerization of the inclusion complexes
between β-cyclodextrin acrylamide and adamantane acrylamide
monomers. The β-cyclodextrin–adamantane gel (βCD–Ad
gel) shows a high stretching property (990%). The initial strain (0%)
is restored in several minutes for a βCD–Ad gel stretched
to 180% of the initial strain without altering the physical history.
However, chemically cross-linked polyÂ(acrylamide) does not show the
reversible stretching property. These results indicate that host–guest
interaction inside the supramolecular hydrogel plays an important
role in the shape recovery properties
Movable Cross-Linked Polymeric Materials from Bulk Polymerization of Reactive Polyrotaxane Cross-Linker with Acrylate Monomers
Topological cross-linked
polymers attract much attention from their
unique mechanical properties derived from their cross-linking structure.
Here, we have fabricated a polymeric material (Acryl-AcO-PRx) incorporating
topological cross-links into various universal acrylate polymers by
using a modified polyrotaxane as a polymerizable cross-linking agent.
Acryl-AcO-PRx obtained by a simple photocuring technique under bulk
conditions showed a distinctly higher extensibility compared with
the chemical cross-linked polymers. In addition, Acryl-AcO-PRx materials
showed high stress relaxation and deformation hysteresis. These results
indicate that the topologically cross-linked structure composed of
polyrotaxane plays an important role in mechanical properties even
in bulk state
Macroscopic Self-Assembly Based on Molecular Recognition: Effect of Linkage between Aromatics and the Polyacrylamide Gel Scaffold, Amide versus Ester
The
interactions of polyacrylamide- (pAAm-) based gels possessing
cyclodextrin (CD) residues (CD-gels) with pAAm-based gels modified
with aromatic residues through amide and ester linkages (ArA-gels
and ArE-gels, respectively) were investigated to examine the effect
of linkage (i.e., amide and ester) between aromatic residues and the
pAAm gel scaffold. In the present study, benzyl (Bz), 2-naphthylmethyl
(Np), 9-phenanthrylmethyl (Ph), and 1-pyrenylmethyl (Py) residues
were chosen as a series of aromatic residues. αCD-gel did not
interact notably with the ArA-gels and ArE-gels in water. βCD-gel
interacted with the ArA-gels and ArE-gels possessing smaller aromatic
residues (i.e., Bz and Np residues) in water to form gel assemblies.
ÎłCD-gel showed different tendencies of its interactions with
the ArA-gels and with the ArE-gels; ÎłCD-gel interacted with
the ArA-gels carrying larger aromatic residues (i.e., Ph and Py residues),
while ÎłCD-gel formed stable gel assemblies only with NpE-gel
among the ArE-gels examined. This is because ÎłCD residues in
ÎłCD-gel included favorably dimeric aromatic residues in the
ArA-gels and ArE-gels. Reflection fluorescence spectra for the ArA-gels
and ArE-gels possessing fluorescent aromatic residues (i.e., Np, Ph,
and Py residues) in the presence of 10 mM ÎłCD were indicative
of weak selectivities of ÎłCD toward NpE, PhA, and PyA residues.
Such weak selectivities may be largely enhanced in the macroscopic
observation of interaction of CD-gels with the ArA-gels and ArE-gels
presumably because of multivalency
Temperature-Sensitive Macroscopic Assembly Based on Molecular Recognition
The interaction of polyacrylamideÂ(pAAm)-based gel modified
with
benzyl (Bz) moiety (BzÂ(<i>x</i>)-gel, where <i>x</i> denotes the mol % content of Bz moiety) with a pAAm-based gel possessing
cyclodextrin (CD) moieties (αCD-gel, βCD-gel, and γCD-gel)
was investigated at various temperatures to elucidate the effect of
temperature on the formation of macroscopic assembly. The interaction
of BzÂ(<i>x</i>)-gel with CD-gels was stronger at a lower
temperature, consistent with the binding constants for the model system
of pAAm modified with 1 mol % Bz moiety and native CDs. Bz(15)-gel
interacted only with βCD-gel at a higher temperature
Journalists’ orientations toward objectivity and emotionality in the coverage of the nuclear power plant accident and the tsunami-afflicted Tohoku area.
<p>Journalists’ orientations toward objectivity and emotionality in the coverage of the nuclear power plant accident and the tsunami-afflicted Tohoku area.</p
Supramolecular Materials Cross-Linked by Host–Guest Inclusion Complexes: The Effect of Side Chain Molecules on Mechanical Properties
Functional
polymeric materials constructed by noncovalent bonds
have attracted considerable attention due to their beneficial stretching
and self-healing properties. We chose host–guest interactions
using cyclodextrins (CDs) as host molecules to realize supramolecular
materials with stretching and self-healing properties. Notably, an
inclusion complex of a CD and a guest molecule functions as a reversible
bond in a material. Herein, we studied the relationship between the
mechanical properties of the materials and host–guest interactions
based on the association constants of CDs with guest molecules and
molecular structures of the guest molecules. A chemically cross-linked
polyÂ(acrylamide) gel showed high rupture stress, although the rupture
strain was noticeably low. However, the host–guest hydrogels
(CDAAmMe-R hydrogels) exhibited a higher rupture stress and strain
of approximately 1000%. These rupture stress and strain values were
related to the association constants of the CDs with guest units on
the polymer side chain and the structure of the guest molecules. In
particular, the αCDAAmMe-Dod hydrogel with a dodecyl group with
a long, rod-like structure showed better rupture stress and strain
(1250%). The βCDAAmMe-AdAAm hydrogel with a spherical adamantyl
acrylamide (AdAAm) group showed better self-healing properties. To
realize a practical self-healing process under dry conditions, a polyÂ(methyl
triethylene glycol acrylate) xerogels with βCDAAmMe and AdAAm
(βCDAAmMe-AdAAm TEGA xerogel) was prepared. The βCDAAmMe-AdAAm
TEGA xerogel exhibited self-healing properties, regaining 61% of its
initial material strength at 100 °C
A Photoresponsive Polymeric Actuator Topologically Cross-Linked by Movable Units Based on a [2]Rotaxane
A photoresponsive
polymeric material, in which [2]Ârotaxane units
with α-cyclodextrin threading onto an azobenzene derivative
is used as a topological cross-link for the main chains of the polymeric
material in aqueous media, was achieved. [2]ÂRotaxane structures were
found to act as movable links in the polymer network, and the mechanical
properties of the material were enhanced to show a rupture strain
of 2800%. The materials were reversibly deformed by irradiation with
UV or visible light in aqueous media, which caused photoisomerization
of the azobenzene moiety and changed the structure of the [2]Ârotaxane
linker, leading to deformation of the polymer network. Surprisingly,
the dry materials, which had been uniaxially extended in air, showed
a faster response than the hydrogel. The orientation of the polymeric
network in the materials enables the efficient response. This dry
material (5.6 mg) performed 5.6 ÎĽJ of mechanical work within
10 s, which is approximately 50 times higher than that achieved in
our previous work
Coding categories and prevalence in TV program contents (percentage).
<p>Coding categories and prevalence in TV program contents (percentage).</p
pH- and Sugar-Responsive Gel Assemblies Based on Boronate–Catechol Interactions
The interaction between polyÂ(acrylamide)
gels carrying phenylboronic
acid (PB gel) and catechol moieties (CAT gel) respectively is investigated.
The PB gel forms an assembly with the CAT gel on a macroscopic scale
in basic aqueous media. The adhesion strength is estimated by stress–strain
measurements. The assembly and disassembly of the gels are reversibly
switched by varying the pH of the medium. The adhesion strength is
tunable by competitive monosaccharide molecules in accordance with
the association constant with PB moieties
Coding categories and prevalence in newspaper contents (percentage).
<p>Coding categories and prevalence in newspaper contents (percentage).</p