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Ultrathin random copolymer mats with cross-linkable glycidyl methacrylate units, consisting of styrene (S) and 2-vinylpyridine (2VP), are prepared on bare substrates to tune substrate interactions....

Instability, glass transition temperature (Tg), and thermal expansion of polystyrene (PS) films are evaluated with respect to the thickness of a silicon oxide (SiOx) interlayer that mediates favora...

We present a direct approach to fabricating the perfect neutral layer for block copolymer (BCP) self-assembled thin films. An irreversible physisorption of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) itself onto the bottom substrates, though extremely thin, offers such a compositional randomness for the substrates, directing the balanced interfacial interactions toward both blocks of the top-layer PS-b-PMMA. Owing to the neutral property from the skin layers, the chemically identical BCP self-assembles into perpendicular microdomains on the adsorbed layer composed of itself, as identified in symmetric PS-b-PMMA films. Intriguingly, the compositional randomness turns out to be valid when the correlation length (ξ) of the BCP layer adsorbed on the substrates is shorter than equilibrium lamellar spacing (L0) of the BCP. Our strategy provides its versatility applicable to various substrates without any necessity of specific random copolymer brushes or mats, enabling the design of a neutral platform fo...

The structural orientation of an amphiphilic crystalline polymer to a highly ordered microphase-separated lamellar structure on a hydrophobic surface is presented. It is formed by the surface graft polymerization of poly(ethylene glycol)behenyl ether methacrylate onto poly(trimethylsilyl) propyne in the presence of allylamine. In particular, allylamine plays a pivotal role in controlling the crystalline phase, configuration, and permeation properties. The resulting materials are effectively used to improve the CO2 capture property of membranes. Upon the optimization of the reaction conditions, a high CO2 permeability of 501 Barrer and a CO2 /N2 ideal selectivity of 77.2 are obtained, which exceed the Robeson upper bound limit. It is inspiring to surpass the upper bound limit via a simple surface modification method.

We present a compelling evidence for thickness dependence on the order-to-disorder transition (ODT) behavior in cylinder- and lamella-forming polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) films. Such an asymmetric wetting condition that confines the films with selective interactions of the PS/air and P2VP/substrate interfaces generates a parallel orientation of cylindrical and lamellar microdomains. We evaluated thickness-dependent phase transition as a function of interlattice distance (L0) using ex situ grazing incidence small-angle X-ray scattering (GISAXS) and transmission electron microscopy (TEM). Below an onset thickness (t0) above which the ODT temperatures (TODTs) of the films are independent of film thickness, the TODTs of cylinder- and lamella-forming PS-b-P2VP films remarkably increase as the film thickness decreases. Our results confirmed that preferential wetting at the PS/air and P2VP/substrate interfaces in very thin films substantially leads to an ordered state over accessible temperatu...

We propose a simple and quantitative method to evaluate thickness of crosslinked surface layer (tx) for superabsorbent poly(acrylic acid) (PAA) materials using a fluorescent dye of rhodamine B (RhB). The electrostatic attraction between the cationic amine group of dye and the anionic carboxylate group of PAA allows us to measure the fluorescent contrast since the surface-crosslinking causes a significant decrease in concentration of carboxylate group compared to that of inner region. Our method utilizing the distinct adsorption difference of RhB visualizes the crosslinked surface (or shell) layer and successfully demonstrates a direct characterization of tx in a dry state of superabsorbent materials, regardless of irregular particle shape.

We modulated the grafting density (σ) and chain length of polystyrene (PS) brushes on substrates to probe their effect on the glass transition temperature (Tg) in overlaying PS thin films. The Tg of PS films was analyzed as a function of brush thickness (or σRg2), where Rg is the radius of gyration of PS brushes. Our results indicate that PS films below 90 nm exhibit a nonmonotonic dependence of Tg on grafting density with the maximum Tg occurring near the regime of wetting–dewetting transition of the overlaying melt. The maximum Tg was found to be higher than the value of bulk PS system. Computer simulation results suggest that such trends arise as a consequence of the environment of enhanced friction presented by the brush layer and the overlap between the polymer film and the grafted layer.

Fullerene-free all-small-molecule organic photovoltaic cells (SM-OPVs) have attracted considerable attention because of well-defined molecular structures with low batch-to-batch variation. Porphyrin derivatives have recently emerged as one of the promising conjugated building blocks for the small-molecule (SM) donors. Herein, we first report fullerene-free SM-OPVs employing porphyrin-based donors. Three zinc porphyrin (PZn)-based SM donors, which have strong bimodal absorption in the visible region and near-infrared region, are synthesized. Constructing bulk-heterojunction (BHJ) active layers using the PZn donors and a SM acceptor, IDIC, which have complementary absorption, achieved panchromatic photon-to-current-conversion from 400 to 900 nm. The manipulation of side chains in the PZn donors considerably influenced the molecular ordering and nanomorphology of the BHJ active layers. PZn-based fullerene-free SM-OPV devices with promising power conversion efficiency of 6.13% were achieved, which also offers...

Versatile control of cylindrical nanostructures formed by supramolecular assembly of end-functionalized polymer blends is demonstrated not only in their orientation over large areas but also in their surface chemical functionalities. Two binary blends consisting of supramolecular analogues of diblock copolymers with complementary end-sulfonated and aminated groups are investigated, viz., mono-end-functionalized polymers of (i) one-end-sulfonated polystyrene (SPS) and one-end-aminated poly(butadiene) (APBD) and (ii) one end-aminated polystyrene (APS) and one end-sulfonated poly(butadiene) (SPBD). The orientation of the cylinders with respect to the substrate surface depends on the solvent annealing time; either hexagonally ordered vertical cylinders or in-plane ones are readily obtained by controlling the solvent annealing time. Selective chemical etching of one of the polymers provides four different chemically modified nanostructures, viz., hexagonally ordered cylindrical holes and cylindrical posts with either sulfonate or amine surface functional groups. Additional supramolecular assembly is successfully achieved by solution coating either polymers or organic dyes that complementarily interact with the functional groups on the nanostructures. Furthermore, the supramolecularly assembled nanostructures are controlled by confining them to topographically pre-patterned Si substrates with pattern geometries of various shapes and sizes to produce globally ordered vertical or in-plane cylinders with chemical functionalities on their surfaces.

We modulated the grafting density (σ) of a random copolymer brush of poly(styrene-r-methyl methacrylate) on substrates to probe its effect on the formation of perpendicularly aligned lamellae of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA). Supported by coarse-grained simulation results, we hypothesized that an increase in σ will allow us to systematically tune the block copolymer interfacial interactions with the substrates from being preferential to one of the blocks to being neutral toward both blocks and will thereby facilitate enhanced regimes of perpendicularly aligned lamellae. We verified such a hypothesis by using a simple grafting-to approach to modify the substrates and characterized the thickness window for perpendicular lamellae as a function of brush thickness (or σ) on the grafted substrates using scanning force microscopy (SFM) images and grazing incidence small-angle X-ray scattering (GISAXS) measurements. The experimental results validated our hypothesis and suggested that the σ o...

We investigated the orientation of gyroid structures in thin films of high-molecular-weight (HMW) polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) upon a solvent vapor annealing (SVA) process with tetrahydrofuran nonselective to the PS and PMMA blocks. During the SVA process, the swollen PS-b-PMMA films produced the gyroid structures that were developed through a cylindrical morphology from a poorly ordered structure. The interfacial interactions exerted by the substrates significantly influenced the orientation of cylinders, like the parallel and perpendicular orientations on the selective and neutral substrates, respectively, while the solvent vapor generated perpendicular cylinders at the surface. In the final formation of gyroid structures, we identified the two distinct [211] and [111] planes on the surface throughout the interior of the films, which were directed from cylinders on the selective and neutral substrates, respectively. To provide the insight of the molecular mechanisms taking place d...

A Ka-band push-push voltage-controlled oscillator (VCO) using a parasitic capacitance cancelling technique is presented. To enhance the oscillation frequency ( f osc ) and the tuning range (TR), the parasitic capacitance of the VCO is cancelled with negative capacitance (NC). To realise NC, a negative impedance circuit (NIC) is analysed and designed. Because of self-resonance frequency, NC is realised using an open-circuit stable NIC. For further enhancement of the f osc , the VCO is developed in a push-push operation. The proposed VCO is fabricated in a commercial 0.15 μm GaAs pHEMT process. It shows 12.4% of the TR at 31.6 GHz with 11 dBm output power. With the NIC, the centre frequency of the VCO increases from 20.1 to 31.6 GHz and the TR increases from 5.7 to 12.4% compared with a VCO without the NIC.

Room-temperature ionic liquids (RTILs) containing bis-imidazolium salts were explored to control their optical properties of them in an organic device. The neat bis-imidazolium salts showed ionic conductivity of 3.5 × 10−4 S/cm at room-temperature and the electrochemical window was exhibited within ±2.5 V in a two electrode cell. The bis-imidazolium salts were transparent yellow and showed fluorescence upon excitation with light in the range of 360 to 500 nm. A two electrode organic ionic liquid cell was fabricated using a mixture of PEO200BIm-TFSI and electroactive molecules to control the emission property of the ionic liquid by electrochemical methods. The first example of the ionic liquid containing electro-fluorescence switch was explored with an electroactive benzyl viologen (BzV) blend of bis-imidazolium ionic liquid.