Orientation Control of Block Copolymer Thin Films Placed on Ordered Nanoparticle Monolayers

We investigate orientation and lateral ordering of poly­(styrene-<i>block</i>-methyl methacrylate) (PS-<i>b</i>-PMMA) diblock copolymer (diBCP) thin films placed on ordered nanoparticle (NP) monolayers. The densely packed NP monolayers were prepared on silicon substrates with the Langmuir–Blodgett (LB) deposition technique. The perpendicular domain orientation of BCP thin films is obtained on the ordered NP monolayers due to the nanoscale regular roughness which exerts the elastic deformation on the BCP nanodomains and suppresses the substrate-induced parallel orientation. The effect of BCP film thickness as well as the NP size on the orientation of BCP nanodomains was systematically investigated. We also demonstrate the defect-tolerant ordering of the perpendicular orientation of BCP thin films on the NP-vacant sites

Amine-Reactive Poly(pentafluorophenyl acrylate) Brush Platforms for Cleaner Protein Purification

Reactive pentafluorophenyl acrylate (PFPA) polymer brushes grafted on silica particles were prepared using surface-initiated reversible addition and fragmentation chain transfer polymerization. The polymer brush was successfully immobilized with antibody, then used for protein separation. The immunoprecipitated proteins showed successful enrichment of target protein, with reduced nonspecific background and less contamination from eluted antibodies. To further improve protein recovery, the hydrophobic poly­(PFPA) brush was modified with hydrophilic poly­(ethylene glycol) (PEG). The partially PEG-substituted poly­(PFPA) brush showed better dispersion in aqueous solution, leading to improved antibody immobilization efficiency. By optimizing both the brush molecular weight and the degree of PEG substitution, an optimal balance between surface hydrophilicity and number of available PFP units was found, leading to efficient target protein purification. This study shows that poly­(PFPA) platform offers a versatile approach to prepare biomolecule-activated surfaces with tunable surface property, which has potential applications in protein separation and other areas

Molecular Weight Dependence on the Disintegration of Spin-Assisted Weak Polyelectrolyte Multilayer Films

We present the effect of molecular weight (MW) of polyelectrolytes (PEs) on the disintegration behavior of weak PE multilayer films consisting of linear poly­(ethylene imine) (LPEI) and poly­(methacrylic acid) (PMAA). The multilayer films prepared by the spin-assisted layer-by-layer deposition have well-ordered internal structures and also show the linear thickness growth behavior regardless of MWs of PMAA. The well-defined weak PE multilayer films were subject to disintegration into bulk solution when the electrostatic interactions between LPEI and PMAA layers were reduced by treatment at pH 2. However, we demonstrated the change in the disintegration mode and kinetics (i.e., from burst erosion to controlled surface erosion) as a function of MW of PMAA based on neutron reflectivity and quartz crystal microbalance with dissipation, revealing the correlation between the structural changes and the viscoelastic responses of the weak PE films upon pH treatment. Also, the unique swelling behavior as well as the significant increase in dissipation energy was monitored before the complete disintegration of the multilayer films containing high MW PMAA, which is believed to originate from their slow rearrangement kinetics within the film. We believe that the results shown in this study provide chain-level understanding as to the MW-dependence on pH-triggered disintegration mechanism of weak PE multilayer films

Controlled Release from Model Blend Multilayer Films Containing Mixtures of Strong and Weak Polyelectrolytes

We have designed the controlled release platforms based on polyelectrolyte (PE) blend multilayer films to investigate the release mode and kinetics at the nanoscale level. The model blend multilayer films are composed of positively charged layers with weak polyelectrolytes (PEs) (linear poly­(ethylenimine), LPEI) and negatively charged blend layers with mixtures of strong (poly­(sodium 4-styrenesulfonic acid), PSS) and weak (poly­(methacrylic acid), PMAA) PEs. The blend multilayer films ([LPEI/PSS:PMAA]_<i>n</i>) with well-defined internal structure were prepared by the spin-assisted layer-by-layer (LbL) deposition method. Release properties of the multilayer films were systematically studied as a function of blend ratio by neutron reflectivity (NR), ellipsometer, AFM, FT-IR spectroscopy, and quartz crystal microbalance with dissipation (QCM-D). Since PSS strong PEs serve as robust skeletons within the multilayer films independent of external pH variation, the burst disruption of pure weak PE multilayer films was dramatically suppressed, and the release kinetics could be accurately controlled by simply changing the PSS content within the blend films. These release properties of blend multilayer films form the basis for designing the controlled release of target active materials from surfaces

Colloidal Random Terpolymers: Controlling Reactivity Ratios of Colloidal Comonomers via Metal Tipping

We report on a versatile synthetic method of preparing colloidal copolymers and terpolymers composed of dipolar Au@Co core–shell nanoparticles (NPs) in the backbone, along with semiconductor CdSe@CdS nanorod (NR), or tetrapod (TP) side chain groups. A seven-step colloidal total synthesis enabled the synthesis of well-defined colloidal comonomers composed of a dipolar Au@CoNP attached to a single CdSe@CdS NR, or TP, where magnetic dipolar associations between Au@CoNP units promoted the formation of colloidal co- or terpolymers. The key step in this synthesis was the ability to photodeposit a single AuNP tip onto CdSe@CdS NR or TP that enables selective seeding of a dipolar CoNP onto the AuNP seed. We show that the variation of the AuNP size directly controlled the size and dipolar character of the CoNP tip, where the size modulation of the Au and Au@CoNP tips is analogous to control of comonomer reactivity ratios in classical copolymerization processes

High-Power Genuine Ultraviolet Light-Emitting Diodes Based On Colloidal Nanocrystal Quantum Dots

Thin-film ultraviolet (UV) light-emitting diodes (LEDs) with emission wavelengths below 400 nm are emerging as promising light sources for various purposes, from our daily lives to industrial applications. However, current thin-film UV-emitting devices radiate not only UV light but also visible light. Here, we introduce genuine UV-emitting colloidal nanocrystal quantum dot (NQD) LEDs (QLEDs) using precisely controlled NQDs consisting of a 2.5-nm-sized CdZnS ternary core and a ZnS shell. The effective core size is further reduced during the shell growth via the atomic diffusion of interior Cd atoms to the exterior ZnS shell, compensating for the photoluminescence red shift. This design enables us to develop CdZnS@ZnS UV QLEDs with pure UV emission and minimal parasitic peaks. The irradiance is as high as 2.0–13.9 mW cm^–2 at the peak wavelengths of 377–390 nm, several orders of magnitude higher than that of other thin-film UV LEDs

Copolymerization of Polythiophene and Sulfur To Improve the Electrochemical Performance in Lithium–Sulfur Batteries

We first report on the copolymerization of sulfur and allyl-terminated poly­(3-hexylthiophene-2,5-diyl) (P3HT) derived by Grignard metathesis polymerization. This copolymerization is enabled by the conversion of sulfur radicals formed by thermolytic cleavage of S₈ rings with allyl end-group. The formation of a C–S bond in the copolymer is characterized by a variety of methods, including NMR spectroscopy, size exclusion chromatography, and near-edge X-ray absorption fine spectroscopy. The <b>S-P3HT</b> copolymer is applied as an additive to sulfur as cathode material in lithium–sulfur batteries and compared to the use of a simple mixture of sulfur and P3HT, in which sulfur and P3HT were not covalently linked. While P3HT is incompatible with elementary sulfur, the new <b>S-P3HT</b> copolymer can be well dispersed in sulfur, at least on the sub-micrometer level. Sulfur batteries containing the <b>S-P3HT</b> copolymer exhibit an enhanced battery performance with respect to the cycling performance at 0.5C (799 mAh g^–1 after 100 cycles for <b>S-P3HT</b> copolymer versus only 544 mAh g^–1 for the simple mixture) and the C-rate performance. This is attributed to the attractive interaction between polysulfides and P3HT hindering the dissolution of polysulfides and the charge transfer (proven by electrochemical impedance spectroscopy) due to the homogeneous incorporation of P3HT into sulfur by covalently linking sulfur and P3HT

Template-Free Uniform-Sized Hollow Hydrogel Capsules with Controlled Shell Permeation and Optical Responsiveness

This study has established a robust and straightforward method for the fabrication of uniform poly­(vinylamine) hydrogel capsules without using templates that combines the dispersion polymerization and the sequential hydrolysis/cross-linking. The particle sizes are determined by the degree of cross-linking as well as by the cross-linking reaction time, while the shell thickness is independent of these variables. Diffusion-limited reactions occur at the periphery of the particles, leading to the formation of hydrogel shells with a constant thickness. The treatment of the surfaces of hollow hydrogel capsules with oppositely charged biopolymers limits the permeability through the shell of species even with low molecular weights less than 400 g/mol. Furthermore, we demonstrated that the hydrogel shell phase decorated with Au nanoparticles can be optically ruptured by exposure to laser pulse, a feature that has potential uses in optically responsive drug delivery

In Situ Fibril Formation of κ‑Casein by External Stimuli within Multilayer Thin Films

We have developed the in situ fibrillation of κ-casein, employed as amyloid precursor, within multilayer films consisting of κ-casein and poly­(acrylic acid) (PAA) prepared by the layer-by-layer (LbL) deposition. The fibrillation of κ-casein within the multilayered films is strongly dependent on the extent of intermolecular interactions between κ-casein and PAA. When films constructed initially at pH 3 were heat treated at the same pH, κ-casein did not transform into fibrils. However, when the films were subjected to heat treatment at pH 5, κ-casein was transformed into fibrils within multilayer films due to weakened intermolecular interactions between κ-casein and PAA. We also noted that the multilayer film was swollen at pH 5 by the charge imbalance within the film, which we believe gives enough mobility for κ-caseins to form fibrils with adjacent κ-caseins within the multilayer. The fibrils were found to be uniformly distributed across the entire film thickness, and the aspect ratio as well as the number density of fibrils increased as a function of incubation time. The present study reveals a strategy to realize in situ nanocomposites within LbL multilayer films simply by triggering the formation of protein fibrils by controlling the intermolecular interactions between amyloid precursors and polyelectrolytes (PEs)

Highly Efficient Cadmium-Free Quantum Dot Light-Emitting Diodes Enabled by the Direct Formation of Excitons within InP@ZnSeS Quantum Dots

We demonstrate bright, efficient, and environmentally benign InP quantum dot (QD)-based light-emitting diodes (QLEDs) through the direct charge carrier injection into QDs and the efficient radiative exciton recombination within QDs. The direct exciton formation within QDs is facilitated by an adoption of a solution-processed, thin conjugated polyelectrolyte layer, which reduces the electron injection barrier between cathode and QDs <i>via</i> vacuum level shift and promotes the charge carrier balance within QDs. The efficient radiative recombination of these excitons is enabled in structurally engineered InP@ZnSeS heterostructured QDs, in which excitons in the InP domain are effectively passivated by thick ZnSeS composition-gradient shells. The resulting QLEDs record 3.46% of external quantum efficiency and 3900 cd m^–2 of maximum brightness, which represent 10-fold increase in device efficiency and 5-fold increase in brightness compared with previous reports. We believe that such a comprehensive scheme in designing device architecture and the structural formulation of QDs provides a reasonable guideline for practical realization of environmentally benign, high-performance QLEDs in the future