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Infrared (IR) transmissive polymeric materials for optical elements require a balance between their optical properties, including refractive index (n) and IR transparency, and thermal properties such as glass transition temperature (Tg). Achieving both a high refractive index (n) and IR transparency in polymer materials is a very difficult challenge. In particular, there are significant complexities and considerations to obtaining organic materials that transmit in the long-wave infrared (LWIR) region, because of high optical losses due to the IR absorption of the organic molecules. Our differentiated strategy to extend the frontiers of LWIR transparency is to reduce the IR absorption of the organic moieties. The proposed approach synthesized a sulfur copolymer via the inverse vulcanization of 1,3,5-benzenetrithiol (BTT), which has a relatively simple IR absorption because of its symmetric structure, and elemental sulfur, which is mostly IR inactive. This strategy resulted in approximately 1 mm thick windows with an ultrahigh refractive index (nav > 1.9) and high mid−wave infrared (MWIR) and LWIR transmission, without any significant decline in thermal properties. Furthermore, we demonstrated that our IR transmissive material was sufficiently competitive with widely used optical inorganic and polymeric materials.

The high-temperature plasma process has demonstrated great potential in growing high-quality boron nitride nanotubes (BNNTs) with small diameters (∼5 nm) and few walls (3–4 walls) and led to successful commercialization with a high production rate approaching 20 g/h. However, the process is still accompanied by the production of BN impurities (e.g., a-BN, BN shell, BN flakes) whose physicochemical properties are similar to those of BNNTs. This renders the post-purification process very challenging and thus hampers the development of their practical applications. In this study, we have employed both experimental and numerical approaches for a mechanistic understanding of BN impurity formation in the high-temperature plasma process. This study suggests that the flow structure of the plasma jet (e.g., laminar or turbulent) plays a key role in the formation of BN impurities by dictating the transport phenomena of BNNT seeds (e.g., B droplets), which play an important role in BNNT nucleation. We discussed that the turbulence enhances the radial diffusion of B droplets as well as their interparticle coagulation, which leads to a significant reduction in the population of effective BNNT seeds in the BNNT growth zone (T < 4000 K). This results in the generation of unreacted BN precursors (e.g., B-N-H species) in the BNNT growth zone that eventually self-assemble into BN impurities. Our numerical simulation also suggests that a higher thermal energy input makes the flow more turbulent in the BNNT growth zone due to the elevated velocity difference between the plasma jet and ambient cold gas. This finding provides critical insight into the process design that can suppress the BN impurity formation in the high-temperature plasma process.

We present the excellent and selective activity against human cancer cells and pathogens by double-layer carbon-encapsulated silver nanoparticles ([email protected]) and monolayer carbon-encapsulated silver nanoparticles ([email protected]). [email protected] were synthesized via a modified solvothermal approach, whereas [email protected] were prepared by exfoliation of the outer carbon layer of [email protected] The physicochemical structures and properties of the [email protected] and [email protected] are thoroughly examined; the carbon layer is found to ensure the needful release of Ag+ ions from the core Ag nanoparticles, and improve the biocompatibility and selectivity of NPs to kill the cancer cells. Hence, the [email protected] and [email protected] are substantiated to be beneficial for controlling the overtoxicity caused by unstable bare AgNPs and achieving the targeted actions. The Ag+ ions exhibit their toxic effects against cancer cells or pathogens chiefly through the reactive oxygen species (ROS) generation. The Ag+-ion release and ROS generation of the [email protected] are found greater than those of the [email protected] because of the synergistic effect of the reduced thickness of carbon layer and increased specific surface area. The [email protected] and [email protected] were applied against cancer cells (K562 and Hep3B), normal cells (LO2), and pathogens in vitro. The [email protected] exhibit greater dose- and time-dependent late apoptosis of cancer cells than the [email protected], and reduce the viability of cancer cells more effectively than the [email protected] The crystal violet assay explicitly displays that the as-prepared samples exhibit preferential attack on cancer cells. In the analysis of apoptosis associated proteins, caspase-3 and PARP as markers, the protein expression was visible only for the cancer cells asserting that the prepared [email protected] and [email protected] act selectively, invading only the cancer cells. Moreover, the [email protected] exhibit a larger linear inhibition zone than the [email protected] against both Gram negative and Gram positive pathogenic bacterial stains in bactericidal activity probes.

Shape- and structure-controlled block copolymer particles have received great attention due to their unusual physical properties, hence achieving structural diversity of the particles is highly des...

Hybrid organic/inorganic systems with modulated nanostructures and well-defined morphologies are of great importance to develop novel nanomaterials with tailored functionalities. Herein, we report ...

Boron nitride (BN) nanofiller-based polymer composites have been considered promising candidates for efficient heat-dissipating packaging materials because of their superior thermal conductivity, mechanical strength, and chemical resistance. However, strong aggregation of the BN nanofillers in the composite matrix as well as the difficulty in the modification of the chemically inert surface prevents their effective use in polymer composites. Herein, we report an effective method by using in situ stabilizers to achieve homogeneous dispersion of boron nitride (BN) nanofillers in an epoxy-based polymeric matrix and demonstrate their use as efficient heat-dissipating materials. Poly(4-vinylpyridine) (P4VP) is designed and added into the epoxy resin to produce in situ stabilizers during preparation of hexagonal BNs (h-BNs) and BN nanotubes (BNNTs) dispersion. In-depth experimental and theoretical studies indicated that the homogeneous distribution of BN nanofillers in epoxy composites achieved by using the in situ stabilizer enhanced the thermal conductivity of the composite by ∼27% at the same concentration of the BN nanofillers. In addition, the thermal conductivity of the h-BN/epoxy composite (∼3.3 W/mK) was dramatically improved by ∼48% (4.9 W/mK) when the homogeneously dispersed BNNTs (∼1.8 vol %) were added. The concept of the proposed in situ stabilizer can be further utilized to prepare the epoxy composites with the homogeneous distribution of BN nanofillers, which is critical for reproducible and position-independent composite properties.

A robust strategy is developed for preparing light-responsive block copolymer (BCP) particles in which shape and color can be actively controlled with high spatial and temporal resolution. The key to achieving light-responsive shape transitions of BCP particles is the design and synthesis of surfactants containing light-active groups (i.e., nitrobenzyl esters and coumarin esters) that modulate the amphiphilicity and interfacial activity of the surfactants in response to light of a specific wavelength. These light-induced changes in surfactant structure modify the surface and wetting properties of BCP particles, affording both shape and morphological transitions of the particles, for example from spheres with an onion-like inner morphology to prolate or oblate ellipsoids with axially stacked nanostructures. In particular, wavelength-selective shape transformation of the BCP particles can be achieved with a mixture of two light-active surfactants that respond to different wavelengths of light (i.e., 254 and 420 nm). Through the use of light-emitting, photoresponsive surfactants, light-induced changes in both color and shape are further demonstrated. Finally, to demonstrate the potential of the light-triggered shape control of BCP particles in patterning features with microscale resolution, the shape-switchable BCP particles are successfully integrated into a patterned, free-standing hydrogel film, which can be used as a portable, high-resolution display.

Research interest in boron nitride nanotubes (BNNTs) has increased after the recent success of large-scale BNNT syntheses using high-temperature-pressure laser ablation or high-temperature plasma methods. Nonetheless, there are limits to the application and commercialization of these materials because of the difficulties associated with their fine structural control. Herein, the growth kinetics of BNNTs were systemically studied for this purpose. The growth pressure of the nitrogen feed gas was varied while the growth temperature remained constant, which was confirmed by black body radiation measurements and calculations based on a heat loss model. Changing from the diffusion-limited regime to the supply-limited regime of growth kinetics based on the optimized BNNT synthesis condition afforded the control of the number of BNNT walls. The total amount of BNNTs possessing single and double walls was over 70%, and the BNNT surface area increased to 278.2 m2/g corresponding to small wall numbers and diameters. Taking advantage of the large surface area and high-temperature durability of the material, BNNTs utilized as a recyclable adsorbent for water purification. The efficiency of the BNNTs for capturing methylene blue particles in water was approximately 94%, even after three repetition cycles, showing the potential of the material for application in the filter industry.

Boron nitride (BN) nanofiller-based polymer composites have been considered promising candidates for efficient heat-dissipating packaging materials because of their superior thermal conductivity, mechanical strength, and chemical resistance. However, strong aggregation of the BN nanofillers in the composite matrix as well as the difficulty in the modification of the chemically inert surface prevents their effective use in polymer composites. Herein, we report an effective method by using

Endowing quantum dots (QDs) with robustness and durability have been one of the most important issues in this field, since the major limitations of QDs in practical applications are their thermal and oxidative instabilities. In this work, we propose a facile and effective passivation method to enhance the photochemical stability of QDs using polymeric double shell structures from thiol-terminated poly(methyl methacrylate-b-glycidyl methacrylate) (P(MMA-b-GMA)-SH) block copolymer ligands. To generate a densely cross-linked network, the cross-linking reaction of GMA epoxides in the PGMA block was conducted using a Lewis acid catalyst under an ambient environment to avoid affecting the photophysical properties of the pristine QDs. This provides QDs encapsulated with robust double layers consisting of highly transparent PMMA outer-shell and oxidation-protective cross-linked inner shell. Consequently, the resulting QDs exhibited exceptional tolerance to heat and oxidants when dispersed in organic solvents or QD-nanocomposite films, as demonstrated under various harsh conditions with respect to temperature and oxidant species. The present approach not only provides simple yet effective chemical means to enhance the thermochemical stability of QDs, but also offers a promising platform for the hybridization of QDs with polymeric materials for developing robust light-emitting or light-harvesting devices. A treatment that makes nanoparticles robust and thus more useful for optoelectronics has been developed by researchers in South Korea. Quantum dots are semiconductor particles just a few tens of nanometers in diameter. These tiny dimensions restrict the motion of electrons, which gives the dots properties similar to those of an atom. Specifically, they efficiently absorb and emit spectrally pure light, making them useful for displays, photodetectors and solar cells. However, quantum dots are sensitive to heat, moisture and oxidization. Joona Bang, Korea University, Seoul, and colleagues improved the thermochemical stability of quantum dots by surrounding them with a physical barrier to suppress the creation of surface defects. This protective shell was made using a cross-linkable polymer ligand and was shown to reduce the deleterious effects of exposure to high temperatures and an oxidizing agent. Quantum Dot: Shell cross-linking endows stability: Simple and facile cross-linking chemistry was employed to form the robust network shell on the quantum dot (QD) surface without altering the photoluminescence property of pristine QDs. The resulting shell cross-linked QDs exhibited exceptional tolerance against heat or chemical oxidations. And the exterior brush in QDs can be readily tunable and provide the miscibility with host polymer matrix, resulting in well-defined QD-nanocomposite films. This encapsulation strategy can be generally applicable to many other nanoparticles that are vulnerable to various external stimuli.

Interface engineering of evaporative emulsion droplets containing block copolymers (BCPs) provides an effective route to generate nonspherical particles. Here, we demonstrate the impact of length-controlled nanorods (NRs) on the interfacial properties of BCP emulsions to produce anisotropic BCP particles. A series of lamellae- and cylinder-forming polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) and a series of NRs with different lengths (l) are coassembled, and selective arrangement of the NRs on the P4VP domain at the particle surface enables the production of striped football (prolate) and convex lens-shaped (oblate) particles. In particular, the ratio of the NR length to the size of the NR-hosting domain (l/L), which is varied from 0.07 to 3.60, is the key parameter in determining the location of the NRs in the BCP particles as well as the final particle shape. The oblate particles are generated only in the range of 0.36 ≤ l/L ≤ 0.96, whereas the prolate particles are produced for much wider range of l...

A powerful strategy to enhance the thermal conductivity of liquid crystalline epoxy resin (LCER) by simply replacing the conventional amine cross-linker with a cationic initiator was developed. The cationic initiator linearly wove the epoxy groups tethered on the microscopically aligned liquid crystal mesogens, resulting in freezing of the ordered LC microstructures even after curing. Owing to the reduced phonon scattering during heat transport through the ordered LC structure, a dramatic improvement in the thermal conductivity of neat cation-cured LCER was achieved to give a value ∼141% (i.e., 0.48 W/mK) higher than that of the amorphous amine-cured LCER. In addition, at the same composite volume fraction in the presence of a 2-D boron nitride filler, an approximately 130% higher thermal conductivity (maximum ∼23 W/mK at 60 vol %) was observed. The nanoarchitecture effect of the ordered LCER on the thermal conductivity was then examined by a systematic investigation using differential scanning calorimetry, polarized optical microscopy, X-ray diffraction, and thermal conductivity measurements. The linear polymerization of LCER can therefore be considered a practical strategy to enable the cost-efficient mass production of heat-dissipating materials, due to its high efficiency and simple process without the requirement for complex equipment.

Regenerable ultrafiltration membranes were fabricated via filtration of thermally-stable, highly dispersed boron nitride nanotubes (BNNTs). The highly debundled BNNTs were produced by employing judiciously-chosen poly(4-vinylpyridine) (P4VP) as an efficient steric stabilizer. Density functional theory calculations showed strong adsorption energies of P4VP monomers on top of the BNNTs, illustrating the role of P4VP stabilizers. High performance of the BNNT ultrafiltration membranes with large permeation flux was demonstrated by exclusion of polystyrene and gold nanoparticles (~ 25 nm) with higher than 99% removal efficiency. The BNNT membranes were successfully regenerated and recycled continuously at 450 °C due to their excellent mechanical and thermal properties, demonstrating a stark contrast to the membranes from the carbon nanotubes. Our work indicates that unlike the membranes from carbon nanotubes, BNNT membrane can be a promising candidate for the application in cost efficient industrial ultrafiltration.

BNNTs were functionalized by using a polymer that includes a pyridine group, which can undergo dipole interactions with boron atoms in BNNTs. The functionalized BNNTs were well-dispersed in an alcohol solvent, whereas hexagonal boron nitride impurities precipitated, due presumably to stacked structures. After purification processes, acid was added to a solution that contained functionalized BNNTs to prevent pyridine-boron interactions through stronger acid-base interactions. Thus, the polymer bound to the BNNTs was easily separated, and purified BNNTs could be obtained using a solution process.

The precise self-assembly of block copolymers (BCPs) and inorganic nanoparticles (NPs) under 3D confinement offers microparticles with programmable nanostructures and functionalities. Here, fluorescence-switchable hybrid microspheres are developed by forming doubly alternating arrays of Au NPs and CdSe/ZnS quantum dots (QDs) within polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) BCP domains. These doubly alternating arrays afford controlled nonradiative energy transfer (NRET) between the QDs and Au NPs that is dependent on the layer-to-layer distance. Solvent-selective swelling of the hybrid particles tunes the distance between layers, modulating their NRET behavior and affording switchable fluorescence. The particle fluorescence is "OFF" in water through strong NRET from the QDs to Au NPs, but is "ON" in alcohols due to the increased distance between the Au NP and QD arrays in the swollen P4VP domains. The experimentally observed NRET intensity as a function of interparticle distance shows larger quenching efficiencies than those theoretically predicted due to the enhanced quenching within a 3D-confined system. Finally, the robust and reversible fluorescence switching of the hybrid particles in different solvents is demonstrated, highlighting their potentials for bioimaging, sensing, and diagnostic applications.

We report a simple and robust strategy to prepare pH-responsive biphasic Janus particles composed of polystyrene/poly(2-vinylpyridine) (PS/P2VP) homopolymers that are able to control the reversible formation, breakage, and switching of Pickering emulsions depending on their geometry- and pH-dependent hydrophilic–lipophilic balance. The chemical stability of these PS/P2VP Janus particles was tuned through the incorporation of cross-linkable benzophenone units along the backbone of the homopolymers. By employing these stabilized particles as emulsifiers for toluene and water, a facile transformation of emulsion types (i.e., from toluene-in-water to water-in-toluene emulsions) was achieved by adjusting the pH of the aqueous phase. More importantly, this pH-dependent switching behavior and associated stability of the emulsions could be actively controlled by adjusting the relative size ratio of PS to P2VP. When the PS volume fraction (ϕPS) was between 0.33 and 0.67, a wide range tuning of emulsion phase inclu...

As a promising matrix for developing efficient heat-dissipating materials, liquid crystalline epoxy resins (LCERs) have received much attention for a decade. Here, we present a comprehensive study including the synthesis, fabrication, and characterization of polymer/inorganic composites with a representative LCER, 4,4′-diglycidyloxybiphenyl (BP) epoxy. The thermal conducting properties of composites are systematically investigated by preparing a series of samples with various epoxy resins and alumina fillers. Notably, liquid crystalline BP composites show approximately 30% higher thermal conductivity compared to the composites of commercial epoxy with the same type of filler owing to the highly aligned microstructure of the LCER. In addition, the threshold loading of filler content required to construct an effective thermally conducting path in our system is in the range of 40–50 wt%. Furthermore, the thermal conductivity of BP composites can be controlled by incorporating various fillers differentiated by size and shape. In particular, the highest thermal conductivity among the BP composites with 80 wt% content of alumina is 6.66 W/m·K, which is significantly high for epoxy/alumina composites. The experimental results which agree well with the theory by Agari model reveal that the highly aligned microstructure of the LCER is essential requirement that should be considered to improve thermal conductivity of composites.

To develop advanced thermally conductive epoxy resins with liquid crystallinity, three novel liquid crystalline epoxies (LCEs) were synthesized via the substitution of phenylcyclohexyl (PCH) mesogenic moieties into the 2,5 positions of diglycidyl terephthalate. Mesomorphic properties of LCEs were evaluated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD). All LCEs exhibited an enantiotropic smectic phase on heating and cooling. Remarkably, the smectic phase with a wide temperature range of 98–145 °C was observed for the eutectic mixtures of a family of stable smectic LCEs. The selection of optimum curing agents, compositions of LCEs and curing agents, and curing conditions were determined based on physical, chemical, and thermal properties of LCEs and curing agents. The thermally cured LCEs at the LC phase exhibited a high thermal conductivity of 0.4 W m−1 K−1.

High-density threading dislocations, the presence of biaxial compressive strain, and heat generation are the major limitations obstructing the performance and reliability of light emitting diodes (LEDs). Herein, we demonstrate a facile epitaxial lateral overgrowth (ELOG) method by incorporating boron nitride nanotubes (BNNTs) on a sapphire substrate by spray coating to resolve the above issues. Atomic force microscopy, X-ray diffraction, micro-Raman, and photoluminescence measurements confirmed the growth of a high quality GaN epilayer on the BNNT-coated sapphire substrate with reduced threading dislocations and compressive strain owing to the ELOG process. GaN LEDs fabricated using this approach showed a significant enhancement in the internal quantum efficiency and electroluminescence intensity compared to conventional LEDs grown on sapphire. Moreover, reduced efficiency droop and surface temperature at high injection currents were achieved due to the excellent thermal stability and conductivity of BNNTs. Based on our findings we infer that the BNNTs would be a promising material for high power devices vulnerable to self-heating problems.

The morphological analysis of the end of boron nitride nanotubes (BNNTs) using high-resolution transmission electron microscopy (HR-TEM) can provide valuable insight into the growth mechanism in high temperature pressure (HTP) laser ablation where the best quality of BNNT materials can be obtained so far. Two growth modes of BNNT coexisting during the synthesis process have been proposed based on HR-TEM observation and length analysis. One is the root growth mode, in which boron nitride (BN) species formed via the surface interaction between surrounding N2 molecules and boron nanodroplets incorporate into the tubular structure. Another mode called open-end growth mode means the prolongation of tube growth from the exposed BN edge surrounding the surface of boron nanodroplets which is constructed by the heterogeneous nucleation of absorbed BN radicals from the gas plume. The statistical data, the proportions of end structures and the length of BNNTs, could be fitted to two growth modes, and the open-end growth mode is found to be especially effective in producing longer nanotubes with a higher growth rate. The scientific understanding of the growth mechanism is believed to provide the control for optimized production of BNNTs.

Surface-engineered, 10 nm-sized graphene quantum dots (GQDs) are shown to be efficient surfactants for producing 3-pentadecyl phenol (PDP)-combined poly(styrene-b-4-vinylpyridine) (PS-b-P4VP(PDP)) particles that feature tunable shapes and internal morphologies. The surface properties of GQDs were modified by grafting different alkyl ligands, such as hexylamine and oleylamine, to generate the surfactant behavior of the GQDs. In stark contrast to the behavior of the unmodified GQDs, hexylamine-grafted GQDs and oleylamine-grafted GQD surfactants were selectively positioned on the PS and P4VP(PDP) domains, respectively, at the surface of the particles. This positioning effectively tuned the interfacial interaction between two different PS/P4VP(PDP) domains of the particles and the surrounding water during emulsification and induced a dramatic morphological transition to convex lens-shaped particles. Precise and systematic control of interfacial activity of GQD surfactants was also demonstrated by varying the ...

Combining the functionality of nanoparticles (NPs) with the processability of polymers offers great promise for designing novel materials. In particular, NPs with tailored surface properties can effectively modify the interface between two distinct fluids and/or different polymer matrices which allows them to function as efficient surfactants. The efficiency of NP surfactants is strongly affected by their size and shape, which influences their adsorption energy to the interface, and the entropic contribution to the system. In this review, the assembly of size- and shape-controlled inorganic NPs at the interface of block copolymers (BCPs) and polymer blends has been focused. First, we discuss the design of size- and shape-controlled NP surfactants and we review the examples of NP surfactant-driven BCPs and polymer blend morphologies. In addition, we review the recent investigations of the morphological transition of BCP emulsion particles induced by NP surfactants. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 228–237

Block copolymer/nanoparticle (BCP/NP) composites have attracted much attention due to their easiness of fabricating nanoscopic hierarchical structures, and significantly enhanced chemical and physical properties of the nanocomposites. Most of the focus in co-assembly of BCPs and NPs has been placed on the controlled alignment of NPs, “passively,” in the BCP domain. However, NPs with carefully designed interfacial properties “actively” direct self-assembled structure of BCP in a nonconventional route. Herein, we review recent investigations of the self-assembly of BCP domains in thin films via the addition of structure-directing organic and inorganic NPs. Understanding the phase behavior of BCP/NP co-assembly along with the theoretical description can shed a light on the far-reaching potentials to creating nonconventional nanostructures rarely obtained via traditional fabrication tools. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015

Monodisperse colloidal particles of polystyrene-b-polybutadiene (PS-b-PB) block copolymers (BCPs) were successfully prepared, in which uniform emulsions containing BCPs were first generated by cross-flow membrane emulsification using tubular Shirasu porous glass (SPG) membrane, and then unique internal nanostructures were developed by controlled evaporation of solvent inside emulsion. The diameter of those BCP particles could be controlled from 200 nm to 5 μm by tuning the pore diameter of the membrane. With symmetric BCPs, onion-like nanostructures inside particles were formed. Coiled cylinders in the BCP particles were also developed by adding homopolymers, in which the assembled BCP structure is strongly dependent on the particle size, demonstrating the importance of our membrane method in generating monodisperse BCP particles. Further investigation of process parameters showed that for a given pore diameter, the operation pressure (P) and surfactant concentration were critical parameters for narrow si...

A performance and economic analysis of a commercial-scale coal-fired power plant with a post-combus- tion CO2 capture process in South Korea was performed. Based on the KoSol Process for CO2 Capture (KPCC) devel- oped by the Korea Electric Power Company Research Institute, a power plant cost model coupled with a performance model was developed to evaluate the levelized cost of electricity and the cost of CO2 avoided for power plants with CCS. A techno-economic evaluation result, based on the general guideline suggested by the IEA task force group and key performance data of the pilot-scale CO2 capture test results showed that at the base case, the LCOE of a commer- cial-scale USC power plant with CCS in South Korea will increase from 47 USD/tCO2 (without CCS) to 68 USD/tCO2 (with CCS), and the cost of CO2 avoided was calculated as 33 USD/tCO2. Comparing this with various studies in other literature showed that the cost of CO2 avoided for power plants in South Korea was much lower than that of the OECD average, which was mainly due to the relatively low capital expenditure (CAPEX) and operating expenditure (OPEX) of a power plant with/without CCS.

High internal phase emulsions have been widely used as templates for various porous materials, but special strategies are required to form, in particular, particle-covered ones that have been more difficult to obtain. Here, we report a versatile strategy to produce a stable high internal phase Pickering emulsion by exploiting a depletion interaction between an emulsion droplet and a particle using water-soluble polymers as a depletant. This attractive interaction facilitating the adsorption of particles onto the droplet interface and simultaneously suppressing desorption once adsorbed. This technique can be universally applied to nearly any kind of particle to stabilize an interface with the help of various non- or weakly adsorbing polymers as a depletant, which can be solidified to provide porous materials for many applications., The fabrication of emulsion droplets stabilized by solid particles adsorbed on the interface is restricted to delicate interfacial conditions. Here, Kim et al. show a general approach to prepare them using the depletion interaction, modified by soluble polymers, between particles and emulsions.

Development of particles that change shape in response to external stimuli has been a long-thought goal for producing bioinspired, smart materials. Herein, the temperature-driven transformation of the shape and morphology of polymer particles composed of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block copolymers (BCPs) and temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) surfactants is reported. PNIPAM acts as a temperature-responsive surfactant with two important roles. First, PNIPAM stabilizes oil-in-water droplets as a P4VP-selective surfactant, creating a nearly neutral interface between the PS and P4VP domains together with cetyltrimethylammonium bromide, a PS-selective surfactant, to form anisotropic PS-b-P4VP particles (i.e., convex lenses and ellipsoids). More importantly, the temperature-directed positioning of PNIPAM depending on its solubility determines the overall particle shape. Ellipsoidal particles are produced above the critical temperature, whereas convex lens-shaped particles are obtained below the critical temperature. Interestingly, given that the temperature at which particle shape change occurs depends solely on the lower critical solution temperature (LCST) of the polymer surfactants, facile tuning of the transition temperature is realized by employing other PNIPAM derivatives with different LCSTs. Furthermore, reversible transformations between different shapes of PS-b-P4VP particles are successfully demonstrated using a solvent-adsorption annealing with chloroform, suggesting great promise of these particles for sensing, smart coating, and drug delivery applications.

The tuning of interfacial properties at selective and desired locations on the particles is of great importance to create the novel structured particles by breaking the symmetry of their surface property. Herein, a dramatic transition of both the external shape and internal morphology of the particles of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) was induced by precise positioning of size-controlled Au nanoparticle surfactants (Au NPs). The size-dependent assembly of the Au NPs was localized preferentially at the interface between the P4VP domain at the particle surface and the surrounding water, which generated a balanced interfacial interaction between two different PS/P4VP domains of the BCP particles and water, producing unique convex lens-shaped BCP particles. In addition, the neutralized interfacial interaction, in combination with the directionality of the solvent-induced ordering of the BCP domains from the interface of the particle/water, generated defect-free, vertically ordered porous channels within the particles. The mechanism for the formation of these novel nanostructures was investigated systemically by varying the size and the volume fraction of the Au NPs. Furthermore, these convex lens-shaped particles with highly ordered channels can be used as a microlens, in which the light can be concentrated toward the focal point with enhanced near-field signals. And, these particles can possess additional optical properties such as unique distribution of light scattering as a result of the well-ordered Au cylinders that filled into the channels, which hold great promise for use in optical, biological-sensing, and imaging applications.

We herein report a new facile strategy to ellipsoidal block copolymer nanoparticles that exhibit a pH-triggered anistropic swelling profile. In a first step, elongated particles with an axially stacked lamellae structure are selectively prepared by utilizing functional surfactants to control the phase separation of symmetric polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) in dispersed droplets. In a second step, the dynamic shape change is realized by cross-linking the P2VP domains, thereby connecting glassy PS discs with pH-sensitive hydrogel actuators.

Shape, size, and orientation of fillers within polymer matrix are important factors for realizing various composite functionalities. Here, we describe an industrially scalable approach to preparing composites bearing highly aligned model hexagonal boron nitride filler (hBN) by simple melt-pressing. This outcome is achieved by using a malleable but thermal stiffening polymer matrix. The matrix maintains or even increases its stiffness during processing at elevated temperatures, producing the composites with highly aligned hBN and consequently a high thermal conductivity (28 W/mK). Furthermore, the composite bearing aligned hBN exhibits a 62% reduction in oxygen permeation with only 2.7 vol% of hBN. Since the matrix can be chemically depolymerized with an aid of acid, it is also possible to recover the hBN from the composite without physical/chemical denaturation of the filler, thus the recovered filler can be re-used in the future.

The confined self-assembly of block copolymers (BCPs) can be used to generate hierarchically structured composite microspheres. In this study, microspheres of gold-cored BCP (Au-BCP) spheres were first produced from an evaporative toluene-in-water-emulsion in which polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) BCPs incorporated with Au precursors (AuCl4–) were dissolved in toluene. Interestingly, the addition of cetyltrimethylammonium bromide (CTAB) into the microspheres resulted in the selective extraction of Au precursors within the Au-BCP spheres near the surface of the microsphere because of the strong electrostatic attraction between the CTAB and Au precursors. Therefore, regular-patterned porous nanostructures on the surface of Au-BCP microspheres were formed, of which the size could be varied by controlling the molecular weight of the PS-b-P4VP polymers. In addition, the depth of the pores could be modulated independently by tuning the amounts of Au precursors that were incorporated into the Au-B...