Screen‐printable Electrochromic Polymer Inks and Ion Gel Electrolytes for the Design of Low‐power,Flexible Electrochromic Devices

We have developed electrochromic inks and electrolyte materials to enable mass production of flexible electrochromic displays (ECDs) and other optoelectronic devices by screen printing. Here we present a new screen‐printable ink incorporating electrochromic polymer, poly(3,4‐propylenedioxythiophene)bis(ethylhexyloxy), referred to here as ECP‐Magenta, and antimony‐doped tin oxide (ATO/TiO₂) particles to facilitate electron transport. Their dispersion in a P(VDF‐co‐HFP) binder leads to the formation of a new electrochromic ink that is suitable for screen printing. This strategy opens the door to the preparation of similar electrochromic inks based on other organic or polymeric compounds. This approach is scalable and can applied to different fields. Ion gels (IGs) composed of P(VDF‐co‐HFP) and room temperature ionic liquids (RTILs) are promising solid‐state electrolytes with high ionic conductivity, flexibility, elasticity and eco‐friendliness. The electrochemical features of different ion gels were analyzed as a function of composition and nature of the ionic liquid. Hence, new formulations of IGs were developed, evaluated by Electrochemical Impedance Spectroscopy, Cyclic Voltammetry, before being incorporated into ECDs. The electrochromic performance of ECP‐Magenta ink combined with the RTIL‐based IG was evaluated by terms of spectroelectrochemistry showing that fully flexible ECD operating at voltages below 1 V can be screen‐printed.     

Tuning nanoscopic self‐assembly of diblock copolymer blends on a two‐dimensional interface

Spreading amphiphilic diblock copolymers on a two‐dimensional liquid interface has been observed to produce nanoscale features via self‐assembly. Here, we develop a model that incorporates the effects of polymer entanglement and surface diffusion in polymer blends to quantitatively predict the size of experimentally observed structures. Simulations show that different polymers in the blend cooperate to self‐assemble into nanoscale features of varying sizes. Characteristic nanoscopic dimensions can be tuned by adjusting two easily controllable macroscopic quantities: the blend composition and the initial surface concentration. Theoretical predictions are in agreement with experimentally measured feature dimensions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Inkjet Printing of Polymer Micro‐Arrays and Libraries: Instrumentation,Requirements, and Perspectives

This article reviews commercially available instrumentation for inkjet printing of polymer micro‐arrays for combinatorial materials research, and requirements thereof. These include a print head positioning accuracy better than 10 μm and a minimum drop volume of 100 pL. Commercially available instruments that fulfill these requirements can be divided into two categories, depending on whether they receive ink from a reservoir (dispense mode) or through fluid aspiration (pipette mode). Instruments belonging to the first category are restricted to the preparation of polymer blend micro‐arrays. These consist of a few substances mixed in various ratios. The other instruments can be used for the preparation of both micro‐arrays of large numbers of different pure polymer compounds and polymer blend micro‐arrays. Moreover, ways to mix compounds are discussed.

     

A General One‐Pot Strategy for the Synthesis of High‐Performance Transparent‐Conducting‐Oxide Nanocrystal Inks for All‐Solution‐Processed Devices

For all‐solution‐processed (ASP) devices, transparent conducting oxide (TCO) nanocrystal (NC) inks are anticipated as the next‐generation electrodes to replace both those synthesized by sputtering techniques and those consisting of rare metals, but a universal and one‐pot method to prepare these inks is still lacking. A universal one‐pot strategy is now described; through simply heating a mixture of metal–organic precursors a wide range of TCO NC inks, which can be assembled into high‐performance electrodes for use in ASP optoelectronics, were synthesized. This method can be used for various oxide NC inks with yields as high as 10 g. The formed NCs are of high crystallinity, uniform morphology, monodispersity, and high ink stability and feature effective doping. Therefore, the inks can be readily assembled into films with a surface roughness of 1.6 nm. Typically, a sheet resistance of 110 Ω sq^?1 can be achieved with a transmittance of 88 %, which is the best performance for TCO NC ink‐based electrodes described to date. These electrodes can thus drive a polymer light‐emitting diode (PLED) with a luminance of 2200 cd m^?2 at 100 mA cm^?2.     

Molecular engineering of conjugated polymers for solar cells and field‐effect transistors: Side‐chain versus main‐chain electron acceptors

Two model polymers, containing fluorene as an electron‐donating moiety and benzothiadiazole (BT) as an electron‐accepting moiety, have been synthesized by Suzuki coupling reaction. Both polymers are composed of the same chemical composition, but the BT acceptor can be either at a side‐chain (i.e., S‐polymer) or along the polymer main chain (i.e., M‐polymer). Their optical, electrochemical, and photovoltaic properties, together with the field‐effect transistor (FET) characteristics, have been investigated experimentally and theoretically. The FET carrier mobilities were estimated to be 5.20 × 10^?5 and 3.12 × 10^?4 cm² V^?1 s^?1 for the S‐polymer and M‐polymer, respectively. Furthermore, polymeric solar cells (PSCs) with the ITO/PEDOT:PSS/S‐polymer or M‐polymer:PC₇₁BM(1:4)/Al structure were constructed and demonstrated to show a power conversion efficiency of 0.82 and 1.24% for the S‐polymer and M‐polymer, respectively. The observed superior device performances for the M‐polymer in both FET and PSCs are attributable to its relatively low band‐gap and close molecular packing for efficient solar light harvesting and charge transport. This study provides important insights into the design of ideal structure–property relationships for conjugate polymers in FETs and PSCs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

In Situ Synchrotron Radiation X‐Ray Microspectroscopy of Polymer Microcontainers

Direct, real‐time analytical techniques that provide high‐resolution information on the chemical composition and submicrometer structure of various polymer micro‐ and nanoparticles are in high demand in a range of life science disciplines. Synchrotron‐based scanning transmission X‐ray microspectroscopy (STXM) combines both local‐spot chemical information (assessed via near‐edge X‐ray absorption fine structure spectroscopy) and imaging with resolution of several tens of nanometers, and thus can yield new insights into the nanoscale properties of these materials. Furthermore, this method allows in situ examination of soft‐matter samples in aqueous/gaseous environments and under external stimuli, such as temperature, pressure, ultrasound, and light irradiation. This Minireview highlights some recent progress in the application of the STXM technique to study the temperature‐dependent behavior of polymer core–shell microcapsules and to characterize the physicochemical properties of the supporting shells of gas‐filled microbubbles in their natural hydrated state.     

Photopolymerization with microscale resolution: Influence of the physico‐chemical and photonic parameters

This article is aimed at demonstrating that physicochemical parameters can be used to control the spatial extent (length, width, and shape) of polymer objects in view of micro‐ and nano‐fabrication applications. In particular, we showed that oxygen quenching and internal filter effects could be turned to advantage to modulate the response of the material by controlling the threshold energy of polymerization and/or the shape of the light into the photopolymerizable medium. The experimental configuration used in this study is based on light‐induced polymerization at the extremity of an optical fiber that produces polymer micro‐objects after development. Spectroscopic approaches and polymerization threshold measurements were performed to quantitatively evaluate the influence of the physicochemical parameters on the micropatterning of photopolymerizable material. Interestingly, fluorescence that is usually regarded as a process competing with photopolymerization reaction, was used for controlling the fabrication process. By this means, it was possible to better understand the impact of a nonhomogeneous irradiation on photopolymerization process and thus, to tune the shape and the size of the final polymer objects. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3783–3794, 2008     

Fabricating Super‐Hydrophobic Lotus‐Leaf‐Like Surfaces through Soft‐Lithographic Imprinting

Summary: A soft‐lithographic imprinting approach to fabricate super‐hydrophobic surfaces has been developed in this work. In this process, fresh lotus leaves were used as masters and PDMS stamps were prepared by replica molding against the lotus‐leaf surfaces. By using the stamps and an epoxy‐based azo polymer solution as “ink”, the mimicked lotus‐leaf surfaces made of the polymer were fabricated by pressing the featured faces of the stamps against “inked” substrates and drying under a proper condition after peeling off the stamps. The lotus‐leaf‐like surfaces show super‐hydrophobic characteristics with the water contact angle higher than 150° and contact angle hysteresis less than 3°.

SEM images of lotus‐leaf‐like papillary structures on the imprinted surface.     

Nanoimprint Lithography‐Directed Self‐Assembly of Bimetallic Iron–M (M=Palladium,Platinum) Complexes for Magnetic Patterning

Self‐assembly of d⁸ metal polypyridine systems is a well‐established approach for the creation of 1D organometallic assemblies but there are still challenges for the large‐scale construction of nanostructured patterns from these building blocks. We describe herein the use of high‐throughput nanoimprint lithography (NIL) to direct the self‐assembly of the bimetallic complexes [4′‐ferrocenyl‐(2,2′:6′,2′′‐terpyridine)M(OAc)]⁺(OAc)^? (M=Pd or Pt; OAc=acetate). Uniform nanorods are fabricated from the molecular self‐organization and evidenced by morphological characterization. More importantly, when top‐down NIL is coupled with the bottom‐up self‐assembly of the organometallic building blocks, regular arrays of nanorods can be accessed and the patterns can be controlled by changing the lithographic stamp, where the mold imposes a confinement effect on the nanorod growth. In addition, patterns consisting of the products formed after pyrolysis are studied. The resulting arrays of ferromagnetic FeM alloy nanorods suggest promising potential for the scalable production of ordered magnetic arrays and fabrication of magnetic bit‐patterned media.     

Metal–Organic‐Framework‐Templated Polyelectrolyte Nanocapsules for the Encapsulation and Delivery of Small‐Molecule–Polymer Conjugates

Herein, we report a strategy for exploiting nanoscale metal–organic frameworks (nano‐MOFs) as templates for the layer‐by‐layer (LbL) assembly of polyelectrolytes. Because small‐molecule drugs or imaging agents cannot be efficiently encapsulated by polyelectrolyte nanocapsules, we investigated two promising and biocompatible polymers (comb‐shaped polyethylene glycol (PEG) and hyperbranched polyglycerol‐based PEG) for the conjugation of model drugs and imaging agents, which were then encapsulated inside the nano‐MOF‐templated nanocapsules. Furthermore, we also systemically explored the release kinetics of the encapsulated conjugates, and examined how the encapsulation and/or release processes could be controlled by varying the composition and architecture of the polymers. We envision that our nano‐MOFs‐templated nanocapsules, through combining with small‐molecule–polymer conjugates, will represent a new type of delivery system that could open up new opportunities for biomedical applications.     

Functional micropatterned surfaces prepared by simultaneous UV‐lithography and surface segregation of fluorinated copolymers

A new procedure focused on the design and preparation of structured and functional polymer surfaces by combination of two approaches acting simultaneously is developed. The elaboration of micrometer size patterned surfaces by UV‐light lithography is reported where, in addition, the surface chemical composition can be controlled by surface segregation of a fluorinated copolymer incorporated in the photopolymerizable mixture. As evidenced by contact angle and XPS measurements, the surface composition can be modified depending on such factors as with the environmental conditions or the concentration of copolymer in the blend. Moreover, the functionality of the copolymer is enhanced by the surface pattern created. As a consequence, the wettability of the films can be modified depending on the pattern and composition of the blend. By using this methodology, functional adaptive sensitive surfaces with a well‐defined topography will be obtained in one single step and without the use of tedious and time‐consuming multistep procedures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Invisible Security Ink Based on Water‐Soluble Graphitic Carbon Nitride Quantum Dots

Stimuli‐responsive photoluminescent (PL) materials have been widely used as fluorescent ink for data security applications. However, traditional fluorescent inks are limited in maintaining the secrecy of information because the inks are usually visible by naked eyes either under ambient light or UV‐light illumination. Here, we introduced metal‐free water‐soluble graphitic carbon nitride quantum dots (g‐CNQDs) as invisible security ink for information coding, encryption, and decryption. The information written by the g‐CNQDs is invisible in ambient light and UV light, but it can be readable by a fluorescence microplate reader. Moreover, the information can be encrypted and decrypted by using oxalic acid and sodium bicarbonate as encryption reagent and decryption reagent, respectively. Our findings provide new opportunities for high‐level information coding and protection by using water‐soluble g‐CNQDs as invisible security ink.     

Transfer of Two‐Dimensional Oligonucleotide Patterns onto Stereocontrolled Plasmonic Nanostructures through DNA‐Origami‐Based Nanoimprinting Lithography

The precise functionalization of self‐assembled nanostructures with spatial and stereocontrol is a major objective of nanotechnology and holds great promise for many applications. Herein, the nanoscale addressability of DNA origami was exploited to develop a precise copy‐machine‐like platform that can transfer two‐dimensional oligonucleotide patterns onto the surface of gold nanoparticles (AuNPs) through a deliberately designed toehold‐initiated DNA displacement reaction. This strategy of DNA‐origami‐based nanoimprinting lithography (DONIL) demonstrates high precision in controlling the valence and valence angles of AuNPs. These DNA‐decorated AuNPs act as precursors in the construction of discrete AuNP clusters with desired chirality.     

Microphase Separation of Block Copolymer Thin Films

Today, high‐ordered micro‐ and nano‐patterned surfaces are widely used in many areas, such as in the preparation of super‐thin dielectric films, photonic crystals, antireflective films, super‐non‐wetting surfaces, bio‐compatible surfaces and microelectric devices. Considering the critical fabrication conditions and the irreducible high cost of the photolithography technique in patterning nano‐scale structures (<100 nm), the development of other micro‐ and nano‐patterning techniques that can be used to fabricate long‐range ordered features – especially nanoscale arrays – is a promising subject in surface science. In contrast to the traditional photolithography patterning technique, block copolymers can spontaneously phase separate into arrays of periodic patterns with length‐scales of 10–50 nm, which provides an efficient pathway to pattern nanoscale features. Today, preparing long‐range ordered arrays by block copolymer microphase separation is one of the most promising techniques for the fabrication of nanoscale arrays, not only being a simple process but also having a lower cost than traditional methods. In this feature article, we first summarize the many techniques developed to induce ordering in the microphase separation of the block copolymer thin films. Then, evolution, order–order transitions and reversible switching microdomains are considered, since they are very important in the ordered engineering of microphase separation of the block copolymer thin films. Finally, the outlook of this research area will be given.

     

Materials for the preparation of polymer pen lithography tip arrays and a comparison of their printing properties

Polymer Pen Lithography (PPL) uses an array of polymeric tips, typically composed of poly(dimethyl siloxane), to transfer ink onto a surface and create patterns of soft molecules with micrometer to nanometer feature dimensions. In this study, tip arrays were fabricated from poly(methyl methacrylate), poly([methyl methacrylate]‐co‐[butyl methacrylate]), and poly(3‐mercaptopropylmethylsiloxane), and used to pattern 1‐mercaptohexadecanoic acid onto Au surfaces to determine the fidelity of pattern transfer by PPL as a function of the mechanical properties of the materials. It was found that the dependence between the applied force and feature edge length correlates directly to the mechanical properties of each of the polymers used to fabricate the tip arrays, where stiffer polymers have a reduced dependence between the applied force and feature size. This study demonstrates that PPL tip arrays can be composed of a wide variety of materials whose choice is determined by the desired printing application. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

A Photo‐annealing Approach for Building Functional Polymer Layers on Paper

A straightforward photo‐annealing approach was developed for building functional polymer layers on paper. Conducting polyaniline with the ability for photothermal conversion can be readily annealed by near‐infrared light. The annealed polymers become both insulating and hydrophobic. Selective photo‐annealing produces a functional layer with patterned conductive arrays. This material exhibits real‐time response to ammonium gas. Complete photo‐annealing preserves the porous structure but changes the wettability of the polyaniline‐nanofiber film.     

“Raft” Formation by Two‐Dimensional Self‐Assembly of Block Copolymer Rod Micelles in Aqueous Solution

Block copolymers can form a broad range of self‐assembled aggregates. In solution, planar assemblies usually form closed structures such as vesicles; thus, free‐standing sheet formation can be challenging. While most polymer single crystals are planar, their growth usually occurs by uptake of individual chains. Here we report a novel lamella formation mechanism: core‐crystalline spherical micelles link up to form rods in solution, which then associate to yield planar arrays. For the system of poly(ethylene oxide)‐block‐polycaprolactone in water, co‐assembly with homopolycaprolactone can induce a series of morphological changes that yield either rods or lamellae. The underlying lamella formation mechanism was elucidated by electron microscopy, while light scattering was used to probe the kinetics. The hierarchical growth of lamellae from one‐dimensional rod subunits, which had been formed from spherical assemblies, is novel and controllable in terms of product size and aspect ratio.     

Water‐mediated transport in ion‐containing polymers

Water‐mediated ion conduction enables high conductivity in hydrated polymer membranes commonly used in electrochemical devices. Understanding the coupling of the absorbed water with the polymer matrix and the dynamics of water inside the polymer network across the full range of length scales in the membrane is important for unraveling the structure–property relationships in these materials. By considering the water behavior in ion‐containing polymers, next‐generation fuel cell membranes are being designed that exceed the conductivity of the state‐of‐the‐art materials and have optimized conductivity and permeability that may be useful in other types of devices such as redox flow batteries. Water–polymer associations can be exploited to tune the transport and mechanical property tradeoffs in these polymers. Measurements of water motion provide important criteria for assessing the factors that control the performance of these types of materials. This review article discusses current understanding of water behavior in ion‐containing polymers and the relationship between water motion and ion and molecular transport. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Light‐Triggered Release of Trapped Charges in Molecular Assemblies

We demonstrate the mediation of charge transport and release in thin films and devices by shifting the redox properties of layers of metal complexes by light. The nanoscale surface arrangement of both photo‐ and electrochemically‐active components is essential for the function of the thin films. Layers of well‐defined ruthenium complexes on indium‐tin‐oxide electrodes provide electron‐transport channels that allow the electrochemical addressing of layers of isostructural cobalt complexes. These cobalt complexes are electrochemically inactive when assembled directly on transparent metal‐oxide electrodes. The interlayer of ruthenium complexes on such electrodes allows irreversible oxidation of the cobalt complexes. However, shifting the redox properties of the ruthenium complexes by excitation with light opens up an electron‐transport channel to reduce the cobalt complexes; hence releasing the trapped positive charges.     

Liquid‐crystalline and light‐emitting polyacetylenes

Rigid polymer backbones have often been considered to be detrimental to the packing of mesogenic pendants, and polyacetylenes have generally been regarded as unpromising materials for light‐emitting applications. Our group, however, has succeeded in creating a series of liquid‐crystalline polyacetylenes with rigid backbones and a variety of light‐emitting polyacetylenes with luminescent chromophores. Here we demonstrate that the rigid polyacetylene skeleton can play a constructive role in guiding the alignments of mesogenic pendants and prove that polyacetylenes can be highly emissive with photoluminescence quantum yields of up to 98% and electroluminescence performances comparable or superior to those of the best blue‐light‐emitting polymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2607–2629, 2003