4 research outputs found
Emulsion Solvent Evaporation-Induced Self-Assembly of Block Copolymers Containing pH-Sensitive Block
A simple
yet efficient method is developed to manipulate the self-assembly
of pH-sensitive block copolymers (BCPs) confined in emulsion droplets.
Addition of acid induces significant variation in morphological transition
(e.g., structure and surface composition changes) of the polystyrene-<i>block</i>-polyÂ(4-vinylpyridine) (PS-<i>b</i>-P4VP)
assemblies, due to the hydrophobic–hydrophilic transition of
the pH-sensitive P4VP block via protonation. In the case of pH >
p<i>K</i>a<sub>(P4VP)</sub> (p<i>K</i>a <sub>(P4VP)</sub> = 4.8), the BCPs can self-assemble into pupa-like particles because
of the nearly neutral wetting of PS and P4VP blocks at the oil/water
interface. As expected, onion-like particles obtained when pH is slightly
lower than p<i>K</i>a<sub>(P4VP)</sub> (e.g., pH = 3.00),
due to the interfacial affinity to the weakly hydrophilic P4VP block.
Interestingly, when pH was further decreased to ∼2.5, interfacial
instability of the emulsion droplets was observed, and each emulsion
droplet generated nanoscale assemblies including vesicles, worm-like
and/or spherical micelles rather than a nanostructured microparticle.
Furthermore, homopolymer with different molecular weights and addition
ratio are employed to adjust the interactions among copolymer blocks.
By this means, particles with hierarchical structures can be obtained.
Moreover, owing to the kinetically controlled processing, we found
that temperature and stirring speed, which can significantly affect
the kinetics of the evaporation of organic solvent and the formation
of particles, played a key role in the morphology of the assemblies.
We believe that manipulation of the property for the aqueous phase
is a promising strategy to rationally design and fabricate polymeric
assemblies with desirable shapes and internal structures
Dependence of Melt Behavior of Star Polystyrene/POSS Composites on the Molecular Weight of Arm Chains
Rheological
behavior of three-arm and six-arm star polystyrene
(SPS) with a small amount of polyhedral oligosilsesquioxane (POSS)
was studied. Both linear oscillatory frequency sweep and steady state
shear results of SPS/POSS composites showed the reduction of melt
viscosity in the unentangled SPS matrix and the increase of viscosity
in the entangled SPS matrix. In particular, when molecular weight
of the arm (<i>M</i><sub>a</sub>) of SPS was smaller than
the critical molecular weight for entanglement (<i>M</i><sub>c</sub>) of PS, the melt viscosity of SPS/POSS composites with
low content of POSS was lower than that of pure SPS. The abnormal
phenomenon of reduced melt viscosity in SPS/POSS composites was in
coincidence with the melt viscosity behavior of SPS/C<sub>60</sub> composites reported in our previous work (Soft Matter 2013, 9, 6282−6290), although the diameters of two nanoparticles
and their interaction with SPS matrix were different. A possible mechanism
behind the melt viscosity behavior was discussed. Furthermore, the
time–temperature superposition principle (TTS) was applied
in SPS and SPS/POSS composites. The Cox–Merz empirical relationship
was verified to be valid for SPS/POSS composites when the content
of POSS was low (1 wt %)
Responsive Photonic Hydrogel-Based Colorimetric Sensors for Detection of Aldehydes in Aqueous Solution
In
this work, we present a fast and efficient strategy for the
preparation of responsive photonic hydrogels for aldehyde sensing
by combining the self-assembly of monodisperse carbon-encapsulated
Fe<sub>3</sub>O<sub>4</sub> nanoparticles (NPs) and in situ photopolymerization
of polyacrylamide (PAM) hydrogels. The responsive photonic hydrogels
exhibit structural color variation after being treated with formaldehyde
aqueous solution, which can be attributed to the chemical reaction
between the amide groups in the hydrogels and the formaldehyde. We
have also shown that the photonic hydrogels can be used to determine
the concentration of formaldehyde and to differentiate aldehydes through
a facile reflection spectra shift and color change. This study provides
a facile strategy for the visualized determination of aldehyde in
aqueous solution
Nanostructure and Linear Rheological Response of Comb-like Copolymer PSVS‑<i>g</i>‑PE Melts: Influences of Branching Densities and Branching Chain Length
Comb-like
polyÂ(styrene-<i>co</i>-4-(vinylphenyl)-1-butene)-<i>g</i>-polyethylene copolymers (PSVS-<i>g</i>-PE) with
various branching parameters were synthesized to study the influence
of branch chains on morphology (at melt state) and linear rheological
response of the copolymers. The results showed that both the branching
density and branch chain length of PSVS-<i>g</i>-PE copolymers
strongly affected linear rheological behavior of the copolymers, resulting
from the formation of different microphase separation structure in
the melt state. PSVS-<i>g</i>-PE copolymers with low branching
density (2.3–3.5 branch chains per 100 repeating units of the
backbone) showed a microphase-separated structure at the melt state,
and a typical rheological characteristic for network-like structure
was observed. Furthermore, the type of microphase-separated structure
at the melt state strongly influences the applicability of the time–temperature
superposition (TTS) principle. As a result, the TTS failure was observed
in the modulus curves for PSVS52.7-3.5-PE4.9 (poor-order lamellar
structure) and PSVS54.4-2.7-PE10.7 (long tubular structure). In contrast,
the PSVS-<i>g</i>-PE sample with high branching density
(16.6–24.5 branch chains per 100 repeating units of the backbone)
showed homogeneous phase structure and normal rheological behavior,
similar to linear or comb-like homopolymers. The gel-like state appeared
in a limited frequency regime (a plateau regime of tan δ versus
ω) during decreasing the frequency from the high frequency regime
in these comb-like copolymers