Orthogonal printing of uniform nanocomposite monolayer and oriented organic semiconductor crystals for high-performance nano-crystal floating gate memory.

Inkjet printing is of great interest in the preparation of optoelectronic and microelectronic devices due to its low cost, low process temperature, versatile material compatibility, and ability to precisely manufacture multi-layer devices on demand. However, interlayer solvent erosion is a typical problem that limits the printing of organic semiconductor devices with multi-layer structures. In this study, we proposed a solution to address this erosion problem by designing polystyrene-block-poly(4-vinyl pyridine)-grafted Au nanoparticles (Au@PS-b-P4VP NPs). With a colloidal ink containing the Au@PS-b-P4VP NPs, we obtained a uniform monolayer of Au nano-crystal floating gates (NCFGs) embedded in the PS-b-P4VP tunneling dielectric (TD) layer using direct-ink-writing (DIW). Significantly, PS-b-P4VP has high erosion resistance against the semiconductor ink solvent, which enables multi-layer printing. An active layer of semiconductor crystals with high crystallinity and well-orientation was obtained by DIW. Moreover, we developed a strategy to improve the quality of the TD/semiconductor interface by introducing a polystyrene intermediate layer. We show that the NCFG memory devices exhibit a low threshold voltage (<3 V), large memory window (66 V), stable endurance (>100 cycles), and long-term retention (>10 years). This study provides universal guidance for printing functional coatings and multi-layer devices.

Recent Progress in Janus Nano-Objects with Asymmetric Polymer Brushes.

Over the past few decades, Janus materials have drawn much interest owing to the combination of two different functionalities on the opposite sides. Janus nano-objects (JNOs) with asymmetric polymer brushes are one unique material of them, which consist of a polymeric or inorganic core and asymmetric polymer chains coated on the core. Combining the properties of nanomaterials, asymmetric structures and flexible polymer brushes, hairy JNOs have shown great potential in interfacial compatibilization, interfacial catalysis, oil-water separation and drug delivery. This review summarizes recent progress in the preparation strategies of JNOs with asymmetric polymer brushes via self-assembly or grafting strategies, as well as their applications in interfacial engineering, biomedicine and other aspects. Finally, the outlook and challenges of this direction are discussed.

2D superlattices via interfacial self-assembly of polymer-grafted Au nanoparticles.

Nanoparticle (NP) superlattices are periodic arrays of nanoscale building blocks. Because of the collective effect between functional NPs, NP superlattices can exhibit exciting new properties that are distinct from those of individual NPs or corresponding bulk materials. In particular, two-dimensional (2D) NP superlattices have attracted increasing attention due to their emerging applications in micro/opto-electronics, catalysis, sensing, and other fields. Among various preparation methods, evaporation-induced interfacial self-assembly has become the most popular method for preparing 2D NP superlattices because it is a simple, low-cost, and scalable process that can be widely applied to various NPs. Introducing soft ligands, such as polymers, can not only provide convenience in controlling the self-assembly process and tuning superlattice structures but also improve the properties of 2D NP superlattices. This feature article focuses on the methods of evaporation-induced self-assembly of polymer-grafted Au NPs into free-standing 2D NP superlattice films at air/liquid interfaces and 2D NP superlattice coatings on substrates, followed by studies on in situ tracking of the self-assembly evolution process through small-angle X-ray scattering. Their application in nano-floating gate memory devices is also included. Finally, the challenges and perspectives of this direction are discussed.

In Situ Self-Assembly of Nanoscale Particles into Macroscale Ordered Monolayers with Enhanced Memory Performance.

In situ fabrication of macroscale ordered monolayers of nanoparticles (NPs) on targeted substrates is highly desirable for precision electronic and optical devices, while it remains a great challenge. In this study, a solution is provided to address this challenge by developing a colloidal ink formulation and employing the direct-ink-writing (DIW) technique, where on-demand delivery of ink at a targeted location and directional evaporation with controllable rate are leveraged to precisely guide the deposition of polystyrene-grafted gold NPs (Au@PS NPs) into a macroscale monolayer with an ordered Au NP array embedded in a PS thin film. A 2D steady-state diffusion-controlled evaporation model, which explains the parameter dependence of the experimental results and gives semiquantitative agreement with the experimental evaporation kinetics is proposed. The ordered monolayer is used as both nanocrystal floating gates and the tunneling layer for nonvolatile memory devices. It shows significantly enhanced performance compared with a disordered NP film prepared by spin coating. This approach allows for fine control of NP self-assembly to print macroscaleordered monolayers directly onto substrates, which has great promise for application in broad fields, including microelectronic and photoelectronic devices, sensors, and functional coatings.

How does bilingual experience influence novel word learning? Evidence from comparing L1-L3 and L2-L3 cognate status.

Bilingual experience exerts a complex influence on novel word learning, including the direct effects of transferable prior knowledge and learning skill. However, the facilitation and interference mechanism of such influence has largely been tangled by the similarity of the previously learned word knowledge. The present study compared Chinese-English bilinguals' paired-associate learning of nonwords in logographic and alphabetic writing systems. The logographic nonwords resemble the form and meaning of L1 Chinese words in varying degrees, being cognates, false cognates, or non-cognates of Chinese. The alphabetic nonwords resemble the form and meaning of L2 English words, being cognates, false cognates, or non-cognates of English. The learning sequence of logographic and alphabetic words was cross-balanced. The learning results were measured in production and recognition tasks. As for learning the logographic nonwords, both the recognition and production results showed that cognates were learned significantly faster than the non-cognates, and the false cognates were also learned significantly faster than the non-cognates. This suggests stronger facilitation rather than interference from L1 on novel word learning. As for learning the alphabetic nonwords, both the recognition and production results revealed that cognates were learned significantly faster than the non-cognates, but false cognates showed no advantage over the non-cognates. This indicates that interference from L2 is stronger than that from L1. Taken together, the results provide new evidence for the dissociable facilitation and interference effects of bilingual experience. These results carry potential educational implications in that learning novel words depends on substantial bilingual experience.

Role of Competitive Crystallization Kinetics in the Formation of 2D Platelets with Distinct Coronal Surface Patterns via Seeded Growth.

Low dispersity 2D platelet micelles with controllable surface patterns were prepared by seeded-growth/living crystallization-driven self-assembly (CDSA) of block copolymer/homopolymer (BCP/HP) blends of poly(ferrocenyldimethylsilane)-b-poly(2-vinyl pyridine) (PFS-b-P2VP) and PFS. The precise morphology was found to be dependent on the proportion of the P2VP corona block, which can be efficiently controlled by changing the molar concentration ratio of PFS-b-P2VP/PFS, (cB/cH)t, as well as their relative rates of crystallization, (GB/GH)t. In the case where their molar concentration ratio was comparable to their crystallization rate ratio, platelets with a uniform distribution of P2VP coronal chains were formed. In other cases, as the concentration ratio increased (or decreased) during the living CDSA process, hierarchical structures were formed, including chain-like assemblies consisting of end-to-end linked rectangular platelets and fusiform (tapered) micelles. (GB/GH)t was adjusted by tuning the degree of polymerization of the crystallizable PFS core-forming block and the BCP block ratio and by varying the terminus of the HP or changing the solvent used. Furthermore, the open edge of the platelets remained active for further growth, which permitted control of the morphology and dimensions of the platelets. Interestingly, in cases where the molar concentration ratio was lower than the crystallization rate ratio, growth rings were observed after two or more living CDSA steps. This study on the formation of platelet micelles by living CDSA of BCP/HP blends under kinetic control offers a considerable scope for the design of 2D polymer nanomaterials with controlled shape and surface patterns.

A Versatile 3D-Confined Self-Assembly Strategy for Anisotropic and Ordered Mesoporous Carbon Microparticles.

Mesoporous carbon microparticles (MCMPs) with anisotropic shapes and ordered structures are attractive materials that remain challenging to access. In this study, a facile yet versatile route is developed to prepare anisotropic MCMPs by combining neutral interface-guided 3D confined self-assembly (3D-CSA) of block copolymer (BCP) with a self-templated direct carbonization strategy. This route enables pre-engineering BCP into microparticles with oblate shape and hexagonal packing cylindrical mesostructures, followed by selective crosslinking and decorating of their continuous phase with functional species (such as platinum nanoparticles, Pt NPs) via in situ growth. To realize uniform in situ growth, a "guest exchange" strategy is proposed to make room for functional species and a pre-crosslinking strategy is developed to preserve the structural stability of preformed BCP microparticles during infiltration. Finally, Pt NP-loaded MCMPs are derived from the continuous phase of BCP microparticles through selective self-templated direct carbonization without using any external carbon source. This study introduces an effective concept to obtain functional species-loaded and N-doped MCMPs with oblate shape and almost hexagonal structure (p6mm), which would find important applications in fuel cells, separation, and heterogeneous catalysis.

Structure Regulation of Block Copolymer Assemblies in Emulsion Droplets by Adding a Selective Solvent.

Generally, nanostructured polymer particles are prepared by 3D confined self-assembly (3D-CSA) of block copolymers (BCPs), while micelles are obtained through self-assembly of BCPs in dilute solutions. Herein, a facile yet robust strategy is developed to regulate the assembled structures of BCP, poly(styrene-block-4-vinylpyridine) (PS-b-P4VP), from nanostructured particles to micelles. The assemblies are prepared by an emulsion-solvent diffusion-induced self-assembly route, which is conducted by dialysis. A key feature of this strategy is that a P4VP-selective solvent (e.g., ethanol) is added to the dialysate to tune the interfacial behavior of the droplets and assembled structures of PS-b-P4VP. The authors' results reveal that in the presence of slight ethanol, the surface and internal structural transitions of nanostructured particles are caused by changes in the interfacial selectivity and packing parameter. Interestingly, interfacial instability, which results in the formation of micelles, is observed when the dialysate contains 50 vol% ethanol or more. The reason can be ascribed to the decreased interface tension, which is induced by the increase in ethanol and enhanced solubility of P4VP. This facile strategy provides a new opportunity to bridge the gap between traditional 3D-CSA and solution self-assembly of BCPs, offering a promising route to engineer morphologies and nanostructures of polymeric assemblies.

Halogen-Bond Mediated 3D Confined Assembly of AB Diblock Copolymer and C Homopolymer Blends.

Halogen-bond driven assembly, a world parallel to hydrogen-bond, has emerged as an attractive tool for constructing (macro)molecular arrangement. However, knowledge about halogen-bond mediated confined-assembly in emulsion droplets is limited so far. An I…. N bond mediated confined-assembly pathway to enable order-order phase transitions is reported here. Compared to hydrogen bonds, the distinct features of halogen bonds (e.g., higher directionality, hydrophobicity, favored in polar solvents), offers opportunities to achieve novel nanostructures and materials. Polystyrene-b-poly(4-vinyl pyridine) (PS-b-P4VP) AB diblock copolymer is chosen as halogen acceptor, while an iodotetrafluorophenoxy substituted C-type homopolymer, (poly(3-(2,3,5,6-tetrafluoro-4-iodophenoxy)propyl acrylate), PTFIPA) is designed as halogen donor, synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Formation of halogen bonding donor-acceptor pairs between the PTFIPA homopolymer and the P4VP segments presented in PS-b-P4VP, increase the volume of P4VP domains, in turn inducing an order-to-order morphology transition sequence: changing from spherical → cylindrical → lamellar → inverse cylindrical, by tuning the PTFIPA content and choice of surfactant. Subsequent selective swelling/deswelling of the P4VP domains give rise to further internal morphology transitions, creating tailored mesoporous microparticles, disassembled nanodiscs, and superaggregates. It is believed that these results will stimulate further examinations of halogen bonding interactions in emulsion droplets and many areas of application.

Transformable Colloidal Polymer Particles with Ordered Internal Structures.

Based on studies combining experiments and simulations, internally ordered colloidal particles that are able to undergo morphological transformations both in shape and internal structure are presented. The particles are prepared by emulsion solvent evaporation-induced 3D soft confined assembly of di-block copolymer polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP). Control over the solvent selectivity leads to a dramatic change in shape and internal structure for particles. Pupa-like particles of lamellar morphology are obtained when using a non-selective solvent, while patchy particles possessing a plum pudding structure formed when the solvent is selective for PS-block. More interestingly, 3D soft confined annealing drives order-order morphological transformation of the particles. The morphology of reshaped particles can be well controlled by varying the solvent selectivity, annealing time, and interfacial interaction. The experimental results can be explained based on simulations. This study can offer considerable scope for the design of new stimuli-responsive colloidal particles for potential applications in photonic crystal, drug delivery and release, sensor and smart coating, etc.

In Situ Fabrication of Polymeric Microcapsules by Ink-Jet Printing of Emulsions.

Phase separation driven by solvent evaporation of emulsions can be used to create polymeric microcapsules. The combination of emulsion solvent evaporation with ink-jet printing allows the rapid fabrication of polymeric microcapsules at a target location on a surface. The ink is an oil-in-water emulsion containing in the dispersed phase a shell-forming polymer, a core-forming fluid that is a poor solvent for the polymer, and a low-boiling good solvent. After the emulsion is printed onto the substrate, the good solvent evaporates by diffusion through the aqueous phase, and the polymer and the poor solvent phase separate to form microcapsules. The continuous aqueous phase contains polyvinyl alcohol that serves as an emulsifier and a binder of the capsules to the substrate. This method is demonstrated for microcapsules with various shell-forming polymers (polystyrene, poly(methylmethacrylate) and poly(l-lactide)) and core-forming poor solvents (hexadecane and a 4-heptanone/sunflower oil mixture). Cargoes such as fluorescent dyes (Nile Red and tetracyanoquinodimethane) or active ingredients (e.g., the fungicide tebuconazole) can be encapsulated. Uniform microcapsules are obtained by printing emulsions containing monodisperse oil droplets produced in a microfluidic device. We discuss the physical parameters that need to be controlled for the successful fabrication of microcapsules in inkjet printing. The method for rapid, in situ encapsulation could be useful for controlled-release applications such as in agrochemical sprays, fragrances, functional coatings, and topical medicines.

Fabrication of monolayers of uniform polymeric particles by inkjet printing of monodisperse emulsions produced by microfluidics.

Emulsion solvent evaporation is a well-established method for generating microparticles from solutions of polymers in volatile organic solvents dispersed in an aqueous medium. Previous work has shown that this approach can also be used to deposit particles by inkjet printing where the particles are formed during the drying of a liquid ink on a substrate. The particle size distribution, however, was very broad. Here we demonstrate that inkjet printing of oil-in-water emulsions produced by microfluidics can generate micron-sized particles with a narrow size distribution (coefficient of variation <6%) and that these particles can self-assemble into ordered arrays with hexagonal packing. The conditions under which drops can be printed with a minimum of break up and coalescence of the oil droplets in the emulsion are explored. Factors affecting the size of the particles and the morphology of the deposit are described. This study uses polystyrene in dichloromethane as a model system, but the approach can be generalized to the production of structured and functional particles.

Combining Inkjet Printing with Emulsion Solvent Evaporation to Pattern Polymeric Particles.

We demonstrate a concept to produce deposits of polymer in the form of particles by inkjet printing an emulsion in which the discrete phase evaporates preferentially. An oil/water emulsion with polymer contained inside the oil phase is used as ink for printing. Circular deposits of spherical polymer particles with uniform thickness are obtained. The effects of the hydrophobicity of substrates and the physical properties of the oil on the morphology of the deposits are explored. The deposit of aggregated polymeric particles can be transformed into a uniform film by annealing if required. This strategy for the patterning of polymer materials in the form of either particles or a film works for mixtures of polymers and functional cargoes.

Using Dynamic Covalent Chemistry To Drive Morphological Transitions: Controlled Release of Encapsulated Nanoparticles from Block Copolymer Vesicles.

Dynamic covalent chemistry is exploited to drive morphological order-order transitions to achieve the controlled release of a model payload (e.g., silica nanoparticles) encapsulated within block copolymer vesicles. More specifically, poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer vesicles were prepared via aqueous polymerization-induced self-assembly in either the presence or absence of silica nanoparticles. Addition of 3-aminophenylboronic acid (APBA) to such vesicles results in specific binding of this reagent to some of the pendent cis-diol groups on the hydrophilic PGMA chains to form phenylboronate ester bonds in mildly alkaline aqueous solution (pH ∼ 10). This leads to a subtle increase in the effective volume fraction of this stabilizer block, which in turn causes a reduction in the packing parameter and hence induces a vesicle-to-worm (or vesicle-to-sphere) morphological transition. The evolution in copolymer morphology (and the associated sol-gel transitions) was monitored using dynamic light scattering, transmission electron microscopy, oscillatory rheology, and small-angle X-ray scattering. In contrast to the literature, in situ release of encapsulated silica nanoparticles is achieved via vesicle dissociation at room temperature; moreover, the rate of release can be fine-tuned by varying the solution pH and/or the APBA concentration. Furthermore, this strategy also works (i) for relatively thick-walled vesicles that do not normally exhibit stimulus-responsive behavior and (ii) in the presence of added salt. This novel molecular recognition strategy to trigger morphological transitions via dynamic covalent chemistry offers considerable scope for the design of new stimulus-responsive copolymer vesicles (and hydrogels) for targeted delivery and controlled release of cargoes. In particular, the conditions used in this new approach are relevant to liquid laundry formulations, whereby enzymes require protection to prevent their deactivation by bleach.

Using Host-Guest Chemistry to Tune the Kinetics of Morphological Transitions Undertaken by Block Copolymer Vesicles.

Host-guest chemistry is exploited to tune the rate at which block copolymer vesicles undergo morphological transitions. More specifically, a concentrated aqueous dispersion of poly(glycerol monomethacrylate-co-glycidyl methacrylate)-poly(2-hydroxypropyl methacrylate) [P(GMA-co-GlyMA)-PHPMA] diblock copolymer vesicles was prepared via polymerization-induced self-assembly (PISA). The epoxy groups in the GlyMA residues were ring-opened using a primary amine-functionalized ß-cyclodextrin (NH2-ß-CD) in order to prepare ß-CD-decorated vesicles. Addition of azobenzene-methoxypoly(ethylene glycol) (azo-mPEG) to such vesicles results in specific binding of this water-soluble macromolecular reagent to the ß-CD groups on the hydrophilic P(GMA-co-GlyMA) stabilizer chains. Such host-guest chemistry induces a morphological transition from vesicles to worms and/or spheres. Furthermore, the rate of this morphological transition can be tuned by UV/visible-light irradiation and/or guest molecule competition. This novel molecular recognition strategy offers considerable scope for the design of new stimulus-responsive diblock copolymer vesicles for targeted delivery and controlled release of cargoes.

Stimulus-responsive block copolymer nano-objects and hydrogels via dynamic covalent chemistry.

Herein we demonstrate that dynamic covalent chemistry can be used to induce reversible morphological transitions in block copolymer nano-objects and hydrogels. Poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer nano-objects (vesicles or worms) were prepared via polymerization-induced self-assembly. Addition of 4-carboxyphenylboronic acid (CPBA) leads to the formation of phenylboronate ester bonds with the 1,2-diol pendent groups on the hydrophilic PGMA stabilizer chains; such binding causes a subtle reduction in the packing parameter, which in turn induces either vesicle-to-worm or worm-to-sphere transitions. Moreover, CPBA binding is pH-dependent, so reversible transitions can be achieved by switching the solution pH, with relatively high copolymer concentrations leading to associated (de)gelation. This distinguishes these new physical hydrogels from the covalently cross-linked gels prepared using dynamic covalent chemistry reported in the literature.

Janus nanodisc of diblock copolymers.

Janus nanodiscs of diblock copolymers are prepared by stepwise disassembly of PS-b-P4VP disc-stacked particles. The Janus nanodiscs are uniform in thickness and regular in contour. By preferential growth of functional materials at the positively charged P4VP side, the composition, microstructure, and performance of the Janus nanodiscs are tunable.

Assembly of Polymer-Tethered Gold Nanoparticles under Cylindrical Confinement.

The assembly of polystyrene (PS)-tethered gold nanoparticles (Au@PS NPs) in anodic aluminum oxide (AAO) cylindrical nanopores was investigated. This cylindrical confined assembly strategy allows us to generate novel assemblies (e.g., linear chain, zigzag, two-NP layer, three-NP layer, and hexagonally packed NP structures) by manipulating the AAO membrane pore size and molecular weight of PS ligands. Moreover, the optical property of the hybrid assemblies can be tuned through varying the interparticle distances and assembly structures. This work provides a guideline for confined assembly of functional NPs and lays groundwork for fabricating well-ordered hybrid nanostructures for optical, electronic, biosensing, and data storage devices.

Multifunctional biodegradable polymer nanoparticles with uniform sizes: generation and in vitro anti-melanoma activity.

We present a simple, yet versatile strategy for the fabrication of uniform biodegradable polymer nanoparticles (NPs) with controllable sizes by a hand-driven membrane-extrusion emulsification approach. The size and size distribution of the NPs can be easily tuned by varying the experimental parameters, including initial polymer concentration, surfactant concentration, number of extrusion passes, membrane pore size, and polymer molecular weight. Moreover, hydrophobic drugs (e.g., paclitaxel (PTX)) and inorganic NPs (e.g., quantum dots (QDs) and magnetic NPs (MNPs)) can be effectively and simultaneously encapsulated into the polymer NPs to form the multifunctional hybrid NPs through this facile route. These PTX-loaded NPs exhibit high encapsulation efficiency and drug loading density as well as excellent drug sustained release performance. As a proof of concept, the A875 cell (melanoma cell line) experiment in vitro, including cellular uptake analysis by fluorescence microscope, cytotoxicity analysis of NPs, and magnetic resonance imaging (MRI) studies, indicates that the PTX-loaded hybrid NPs produced by this technique could be potentially applied as a multifunctional delivery system for drug delivery, bio-imaging, and tumor therapy, including malignant melanoma therapy.

Multiresponsive hydrogel photonic crystal microparticles with inverse-opal structure.

Hydrogel photonic crystal microparticles (HPCMs) with inverse-opal structure are generated through a combination of microfluidic and templating technique. Temperature and pH responsive HPCMs have firstly been prepared by copolymerizing functional monomers, for example, N-isopropylacrylamide (NIPAm) and methacrylic acid (MAA). HPCMs not only show tunable color variation almost covering the entire wavelength of visible light (above 150 nm of stop-band shift) by simply tailoring temperature or pH value of the solution, but also display rapid response (less than 1 min) due to the small volume and well-ordered porous structure. Importantly, the temperature sensing window of the HPCMs can be enlarged by controlling the transition temperature of the hydrogel matrix, and the HPCMs also exhibit good reversibility and reproducibility for pH response. Moreover, functional species or particles (such as azobenzene derivative or magnetic nanoparticles) can be further introduced into the hydrogel matrix by using post-treatment process. These functionalized HPCMs can respond to the UV/visible light without significantly influencing the temperature and pH response, and thus, multiresponsive capability within one single particle can be realized. The presence of magnetic nanoparticles may facilitate secondary assembly, which has potential applications in advanced optical devices.