Templated Assembly of pH‐Labile Polymer‐Drug Particles for Intracellular Drug Delivery

The preparation of pH‐labile polymer‐drug particles via mesoporous silica‐templated assembly for anticancer drug delivery into cancer cells is reported. The polymer‐drug conjugate is synthesized via thiol‐maleimide click chemistry using thiolated poly(methacrylic acid) (PMA_SH) and a pH‐labile doxorubicin (Dox) derivative. Drug‐loaded polymer particles that are stable under physiological conditions are obtained through infiltration of the conjugates into mesoporous silica particles, followed by cross‐linking the PMA_SH chains, and subsequent removal of the porous silica templates. The encapsulated Dox is released from the particles through cleavage of the hydrazone bonds between Dox and PMA_SH at endosomal/lysosomal pH. Cell viability assays show that the assembled PMA_SH particles have negligible cytotoxicity to LIM1899 human colorectal cancer cells. In comparison, Dox‐loaded PMA_SH particles cause significant cell death following internalization. The reported particles represent a novel and versatile class of stimuli‐responsive carriers for controlled drug delivery.     

Pseudobilayer Vesicle Formation via Layer‐by‐Layer Assembly of Hydrophobically Modified Polymers on Sacrificial Substrates

A bilayer of a hydrophobically modified polyelectrolyte, octadecyl poly(acrylamide) (PAAm), sandwiched between the layers of a hydrophilic polyelectrolyte, poly(ethyleneimine) (PEI), is prepared by the sequential electrostatic–hydrophobic–electrostatic‐interaction‐driven self‐assembly on planar and colloid substrates. This process results in a PEI/[PAAm]₂/PEI‐multilayer‐coated substrate. The removal of a PAA/PEI/[PAAm]₂/PEI‐multilayer‐coated decomposable colloidal template produces hollow capsules. Irregular hydrophobic domains of the [PAAm]₂ bilayer in the PEI/[PAAm]₂/PEI‐multilayer capsule are infiltrated with a lipid to obtain a uniform, distinct hydrophobic layer, imparting the capsule with a pseudobilayer vesicle structure.     

Surface‐Engineered Nanocontainers for Entrapment of Corrosion Inhibitors

The release properties and reloading ability of polyelectrolyte‐modified halloysite nanotubes, polyelectrolyte‐modified SiO₂ nanoparticles, and polyelectrolyte capsules are studied. Three containers are distinguished by keeping the low‐molecular‐weight corrosion inhibitor benzotriazole in a hollow lumen inside or within the polyelectrolyte matrix and allowing release in either one direction or into all space dimensions. Polyelectrolyte shells, which modify the outer surface of the nanocontainers, are fabricated by using layer‐by‐layer assembly of poly(diallyldimethylammonium chloride)/poly(styrene sulfonate), poly(allylamine hydrochloride)/poly(styrene sulfonate), and poly(allylamine hydrochloride)/poly(methacrylic acid) polyelectrolyte bilayers. All nanocontainers reveal an increase of the benzotriazole release in aqueous solution at alkaline or acidic pH. The highest reloading efficiency (up to 80 %) is observed for halloysite‐based nanocontainers; however, after five reloading cycles the efficiency decreases to 20 %. The application of appropriate nanocontainers depends on the demands required from feedback‐active anticorrosion coatings. For coatings where the immediate release of the inhibitor is necessary, SiO₂‐based or halloysite‐based nanocontainers with a shell consisting of weak polyelectrolytes are preferable. When continuous, gradual release is required, halloysite‐based nanocontainers with a shell consisting of one weak and one or two strong polyelectrolytes are preferable.     

Fabrication of Organized Porphyrin‐Nanotube‐Attached Heat‐Sensitive Polyelectrolyte Capsules

A facile method of connecting fluorescent meso‐tetrakis(4‐sulfonatophenyl)porphine tetranion nanotubes to polyelectrolyte capsules is developed. Heat‐sensitive robust polyelectrolyte capsules consisting of poly(diallyldimethylammonium chloride) and poly(styrene sulfonate) multilayers have been fabricated using the conventional layer‐by‐layer technique. Supramolecular aggregation of porphyrin monomers to nanotubes is induced in the microenvironment of the capsules by sequential addition of salt and acid. Scanning electron microscopy, transmission electron microscopy, and atomic force microscopy images reveal satellite‐like structures consisting of a central capsule core with porphyrin nanotubes emerging radially from the capsule walls. The growth and the distribution of the porphyrin units have been monitored by UV‐vis spectroscopy, fluorescence spectroscopy, and confocal laser scanning microscopy. Changing the temperature alters the dimensions and the arrangement of the nanotubes on the capsule walls. Such an attachment of porphyrin tubes onto robust functional capsules should help in developing an artificial light‐harvesting system.     

Synthesis and Applications of Stimuli‐Responsive DNA‐Based Nano‐ and Micro‐Sized Capsules

Stimuli‐responsive, drug‐loaded, DNA‐based nano‐ and micro‐capsules attract scientific interest as signal‐triggered carriers for controlled drug release. The methods to construct the nano‐/micro‐capsules involve i) the layer‐by‐layer deposition of signal‐reconfigurable DNA shells on drug‐loaded microparticles acting as templates, followed by dissolution of the core templates; ii) the assembly of three‐dimensional capsules composed of reconfigurable DNA origami units; and iii) the synthesis of stimuli‐responsive drug‐loaded capsules stabilized by DNA?polymer hydrogels. Triggers to unlock the nano‐/micro‐capsules include enzymes, pH, light, aptamer?ligand complexes, and redox agents. The capsules are loaded with fluorescent polymers, metal nanoparticles, proteins or semiconductor quantum dots as drug models, with anti‐cancer drugs, e.g., doxorubicin, or with antibodies inhibiting cellular networks or enzymes over‐expressed in cancer cells. The mechanisms for unlocking the nano‐/micro‐capsules and releasing the drugs are discussed, and the applications of the stimuli‐responsive nano‐/micro‐capsules as sense‐and‐treat systems are addressed. The scientific challenges and future perspectives of nano‐capsules and micro‐capsules in nanomedicine are highlighted.     

Colorimetric Logic Gates Based on Poly(2‐alkyl‐2‐oxazoline)‐Coated Gold Nanoparticles

A straightforward end‐capping strategy is applied to synthesize xanthate‐functional poly(2‐alkyl‐2‐oxazoline)s (PAOx) that enable gold nanoparticle functionalization by a direct “grafting to” approach with citrate‐stabilized gold nanoparticles (AuNPs). Owing to the presence of remaining citrate groups, the obtained PAOx@AuNPs exhibit dual stabilization by repulsive electrostatic and steric interactions giving access to water soluble molecular AND logic gates, wherein environmental temperature and ionic strength constitute the input signals, and the solution color the output signal. The temperature input value could be tuned by variation of the PAOx polymer composition, from 22 °C for poly(2‐ⁿpropyl‐2‐oxazoline)@AuNPs to 85 °C for poly(2‐ethyl‐2‐oxazoline)@AuNPs. Besides, advancing the fascinating field of molecular logic gates, the present research offers a facile strategy for the synthesis of PAOx@AuNPs of interest in fields spanning nanotechnology and biomedical sciences. In addition, the functionalization of PAOx with xanthate offers straightforward access to thiol‐functional PAOx of high interest in polymer science.     

Temperature‐Switchable Assembly of Supramolecular Virus–Polymer Complexes

Here a method is presented for the temperature‐switchable assembly of viral particles into large hierarchical complexes. Dual‐functional diblock copolymers consisting of poly(diethyleneglycol methyl ether methacry­late) (poly(DEGMA)) and poly((2‐dimethylamino)ethyl methacrylate) (poly(DMAEMA)) blocks self‐assemble electrostatically with cowpea chlorotic mottle virus (CCMV) particles into micrometer‐sized objects as a function of temperature. The poly(DMAEMA) block carries a positive charge, which can interact electrostatically with the negatively charged outer surface of the CCMV capsid. When the solution temperature is increased above 40 °C, to cross the cloud point temperature (T_cp) of the DEGMA block, the polymer chains collapse on the surface of the virus particle, which makes them partially hydrophobic, and consequently causes the formation of large hierarchical assemblies. Disassembly of the virus–polymer complexes can be induced by reducing the solution temperature below the T_cp, which allows the poly(DEGMA) blocks to rehydrate and free virus particles to be released. The assembly process is fully reversible and can sustain several heating–cooling cycles. Importantly, this method relies on reversible supramolecular interactions and therefore avoids the irreversible covalent modification of the particle surface. This study illustrates the potential of temperature‐responsive polymers for controlled binding and releasing of virus particles.     

Biofunctional Polyelectrolyte Multilayers and Microcapsules: Control of Non‐Specific and Bio‐Specific Protein Adsorption

Layers of the polyelectrolytes poly(allylamine hydrochloride) (PAH, polycationic) and poly(styrene sulfonate) (PSS, polyanionic) are consecutively adsorbed on flat silicon oxide surfaces, forming stable, ultrathin multilayer films. Subsequently, a final monolayer of the polycationic copolymer poly(L ‐lysine)‐graft‐poly(ethylene glycol) (PLL‐g‐PEG) is adsorbed onto the PSS‐terminated multilayer in order to impart protein resistance to the surface. The growth of each of the polyelectrolyte layers and the protein resistance of the resulting [PAH/PPS]_n(PLL‐g‐PEG) multilayer (n = 1–4) are followed quantitatively ex situ using X‐ray photoelectron spectroscopy and in situ using real‐time optical‐waveguide lightmode spectroscopy. In a second approach, the same type of [PAH/PSS]_n(PLL‐g‐PEG) multilayer coatings are successfully formed on the surface of colloidal particles in order to produce surface‐functionalized, hollow microcapsules after dissolution of the core materials (melamine formaldehyde (MF) and poly(lactic acid) (PLA; colloid diameters: 1.2–20 μm). Microelectrophoresis and confocal laser scanning microscopy are used to study multilayer formation on the colloids and protein resistance of the final capsule. The quality of the PLL‐g‐PEG layer on the microcapsules depends on both the type of core material and the dissolution protocols used. The greatest protein resistance is achieved using PLA cores and coating the polyelectrolyte microcapsules with PLL‐g‐PEG after dissolution of the cores. Protein adsorption from full serum on [PAH/PPS]_n(PLL‐g‐PEG) multilayers (on both flat substrates and microcapsules) decreases by three orders of magnitude in comparison to the standard [PAH/PPS]_n layer. Finally, biofunctional capsules of the type [PAH/PPS]_n(PLL‐g‐PEG/PEG‐biotin) (top copolymer layer with a fraction of the PEG chains end‐functionalized with biotin) are produced which allow for specific recognition and immobilization of controlled amounts of streptavidin at the surface of the capsules. Biofunctional multilayer films and capsules are believed to have a potential for future applications as novel platforms for biotechnological applications such as biosensors and carriers for targeted drug delivery.     

Diffusion Controlled and Temperature Stable Microcapsule Reaction Compartments for High‐Throughput Microcapsule‐PCR

A novel approach to perform a high number of individual polymerase chain reactions (PCR) in microcapsule reaction compartments, termed “Microcapsule‐PCR” was developed. Temperature stable microcapsules with a selective permeable capsule wall were constructed by matrix‐assisted layer‐by‐layer (LbL) Encapsulation technique. During the PCR, small molecular weight building blocks – nucleotides (dNTPs) were supplied externally and diffuse through the permeable capsule wall into the interior, while the resulted high molecular weight PCR products were accumulated within the microcapsule. Microcapsules (∼110.8 µm average diameter) filled with a PCR reaction mixture were constructed by an emulsion technique having a 2% agarose core and a capsule formed by LbL coating with poly(allylamine‐hydrochloride) and poly(4‐styrene‐sulfonate). An encapsulation efficiency of 47% (measured for primer‐FITC (22 bases)) and 98% PCR efficiency was achieved. Microcapsules formed by eight layers of polyelectrolyte and subjected to PCR cycling (up to 95 °C) demonstrated good temperature stability without any significantly changes in DNA retention yield and microcapsule morphology. A multiplex Microcapsule‐PCR experiment demonstrated that microcapsules are individual compartment and do not exchange templates or primers between microcapsules during PCR cycling.     

Redox‐Responsive and Drug‐Embedded Silica Nanoparticles with Unique Self‐Destruction Features for Efficient Gene/Drug Codelivery

The development of advanced gene/drug codelivery carriers with stimuli‐responsive release manner for complementary cancer therapy is desirable. In this study, novel disulfide‐bridged and doxorubicin (DOX)‐embedded degradable silica nanoparticles (DS‐DOX) with unique self‐destruction features are synthesized by a facile one‐pot method. In order to realize codelivery of genes and drugs, the surface of DS‐DOX nanoparticles is readily functionalized with the assembled polycation (CD‐PGEA), comprising one β‐cyclodextrin core and two ethanolamine‐functionalized poly(glycidyl methacrylate) arms, to achieve DS‐DOX‐PGEA. The redox‐responsive self‐destruction behavior of DS‐DOX imparts DS‐DOX‐PGEA with a better ability to release anticancer drug DOX, while the low‐toxic hydroxyl‐rich CD‐PGEA brushes can efficiently deliver genes for cancer treatment. Very interestingly, the degradation process of DS‐DOX starts from the outside, while the destruction of the degradable silica (DS) nanoparticles without DOX begins from the center of the nanoparticles. The embedded DOX inside the DS‐DOX nanoparticles can significantly influence the structures and facilitate the cellular uptake and the subsequent gene transfection. The as‐developed DS‐DOX‐PGEA nanostructure with coordinating biodegradability, stimuli‐responsiveness, and controlled release manner might be desirable gene/drug codelivery carriers for clinical cancer treatment.     

Responsive Macroscopic Materials From Self‐Assembled Cross‐Linked SiO2‐PNIPAAm Core/Shell Structures

A way to obtain macroscopic responsive materials from silicon‐oxide polymer core/shell microstructures is presented. The microparticles are composed of a 60 nm SiO₂‐core with a random copolymer corona of the temperature responsive poly‐N‐isopropylacrylamide (PNIPAAm) and the UV‐cross‐linkable 2‐(dimethyl maleinimido)‐N‐ethyl‐acrylamide. The particles shrink upon heating and form a stable gel in both water and tetrahydrofuran (THF) at 3–5 wt% particle content. Cross‐linking the aqueous gel results in shrinkage when the temperature is increased above the lower critical solution temperature and it regains its original size upon cooling. By freeze drying with subsequent UV irradiation, thin stable layers are prepared. Stable fibers are produced by extruding a THF gel into water and subsequent UV irradiation, harnessing the cononsolvency effect of PNIPAAm in water/THF mixtures. The temperature responsiveness translates to the macroscopic materials as both films and fibers show the same collapsing behavior as the microcore/shell particle. The collapse and re‐swelling of the materials is related to the expelling and re‐uptake of water, which is used to incorporate gold nanoparticles into the materials by a simple heating/cooling cycle. This allows for future applications, as various functional particles (antibacterial, fluorescence, catalysis, etc.) can easily be incorporated in these systems.     

Nonfouling Response of Hydrophilic Uncharged Polymers

Polymeric ultrathin films present a possible line of attack against marine biofouling for some applications. A protocol that provides a reliable comparison of the resistance of different polymers to biofouling is described. This is achieved through the use of a common, azide‐terminated adhesion monolayer, to which different nonfouling polymers of various molecular weights, specifically poly(ethylene glycol) (PEG), poly(2‐ethyl‐2‐oxazoline) (PEOXA), poly(vinyl pyrrolidone) (PVP), poly(vinyl alcohol) (PVA), and dextran are covalently bound. These functionalized surfaces are characterized by dynamic contact angle, ellipsometry, and X‐ray photoelectron spectroscopy (XPS). To validate the developed protocol and evaluate performance against a selection of well‐known, marine‐fouling organisms, the nonfouling surfaces are subjected to a comparative biological study by exposure to a complex protein solution (with characterization via ellipsometry and quartz crystal microbalance with dissipation (QCM‐D)), marine bacteria (Cobetia marina and Marinobacter hydrocarbonoclasticus), and zoospores of the green alga Ulva linza. The resulting data are used to draw conclusions on structure‐property relationships. Chemical resistance towards marine fouling can be achieved using the described immobilization method, but is highly dependent on the species tested. Findings show that PVP (55 kDa)‐coated surfaces display consistent resistance towards all tested solutions and organisms and, hence, this polymer could be considered as a potential material for marine‐nonfouling applications.     

Copper‐Assisted Weak Polyelectrolyte Multilayer Formation on Microspheres and Subsequent Film Crosslinking

The formation of weak polyelectrolyte films on planar and spherical supports has recently evoked major interest, as such coatings allow novel material properties to be tunable by pH and salt adjustment of the polyelectrolyte deposition conditions. We report on the build up of multilayers of the weak polyelectrolytes poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) on submicrometer‐sized polystyrene (PS) and silica colloid spheres (～ 500 nm) with the aid of copper ion templating. The copper ions complex to the carboxylate groups of PAA, facilitating the formation of PAA/PAH multilayers on the particles. Regular growth of the layers on the colloid spheres with each polyelectrolyte deposition step was confirmed by microelectrophoresis, single‐particle light scattering (SPLS), and transmission electron microscopy (TEM), with an average bilayer thickness of ～ 3 nm. The polyelectrolyte multilayer‐coated particles formed stable colloidal dispersions, with ζ‐potentials ranging from 30 mV (PAH outer layer) and –50 mV (PAA outer layer). Complementary quartz‐crystal microbalance and UV‐vis spectrophotometry studies on PAA/PAH multilayers formed on planar supports were performed to examine the film formation and the role of copper ion binding to the layers. PAA/PAH multilayers formed on colloid particles were also chemically crosslinked by using the activator 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC). The degree of film crosslinking could be readily controlled by varying the concentration of EDC employed. Following solvent decomposition of the template particles coated with crosslinked PAA/PAH multilayers, intact hollow polymer capsules were obtained. These capsules were found to be impenetrable to polystyrene.     

Facile Photo‐Crosslinking of Azide‐Containing Hole‐Transporting Polymers for Highly Efficient,Solution‐Processed,Multilayer Organic Light Emitting Devices

A novel framework of azide containing photo‐crosslinkable, conducting copolymer, that is, poly(azido‐styrene)‐random‐poly(triphenylamine) (X‐PTPA), is reported as a hole‐transporting material for efficient solution‐processed, multi‐layer, organic light emitting diodes (OLEDs). A facile and energy‐efficient crosslinking process is demonstrated with UV irradiation (254 nm, 2 mW/cm²) at a short exposure time (5 min). By careful design of X‐PTPA, in which 5 mol% of the photo‐crosslinkable poly(azido‐styrene) is copolymerized with hole‐transporting poly(triphenylamine) (X‐PTPA‐5), the adverse effect of the crosslinking of azide moieties is prevented to maximize the performances of X‐PTPA‐5. Since the photo‐crosslinking chemistry of azide molecules does not involve any photo‐initiators, superior hole‐transporting ability is achieved, producing efficient devices. To evaluate the performances of X‐PTPA‐5 as a hole‐transporting/electron‐blocking layer, Ir(ppy)₃‐based, solution‐processable OLEDs are fabricated. The results show high EQE (11.8%), luminous efficiency (43.7 cd/A), and power efficiency (10.4 lm/W), which represent about twofold enhancement over the control device without X‐PTPA‐5 film. Furthermore, micro‐patterned OLEDs with the photo‐crosslinkable X‐PTPA‐5 can be fabricated through standard photolithography. The versatility of this approach is also demonstrated by introducing the same azide moiety into other hole‐transporting materials such as poly(carbazole) (X‐PBC).     

pH‐Responsive Nanoporous Silica Colloidal Membranes

Free‐standing colloidal membranes (nanofrits) with varied thickness and nanopore size are fabricated and modified with pH‐responsive poly(2‐(dimethylamino)ethyl methacrylate) brushes. The polymer‐modified nanofrits demonstrate excellent gating behavior for molecular diffusion: in the presence of acid, the diffusion rate of positively charged species significantly decreases. Increasing the polymer length and membrane thickness and decreasing the nanopore size leads to the complete acid‐controlled gating of the membranes.     

Confinement of Thermoresponsive Hydrogels in Nanostructured Porous Silicon Dioxide Templates

A thermoresponsive hydrogel, poly(N‐isopropylacrylamide) (poly(NIPAM)), is synthesized in situ within an oxidized porous Si template, and the nanocomposite material is characterized. Infiltration of the hydrogel into the interconnecting nanoscale pores of the porous SiO₂ host is confirmed by scanning electron microscopy. The optical reflectivity spectrum of the nanocomposite hybrid displays Fabry–Pérot fringes characteristic of thin film interference, enabling direct, real‐time observation of the volume phase transition of the confined poly(NIPAM) hydrogel. Reversible optical reflectivity changes are observed to correlate with the temperature‐dependent volume phase transition of the hydrogel, providing a new means of studying nanoscale confinement of responsive hydrogels. The confined hydrogel displays a swelling and shrinking response to changes in temperature that is significantly faster than that of the bulk hydrogel. The porosity and pore size of the SiO₂ template, which are precisely controlled by the electrochemical synthesis parameters, strongly influence the extent and rate of changes in the reflectivity spectrum of the nanocomposite. The observed optical response is ascribed to changes in both the mechanical and the dielectric properties of the nanocomposite.     

Polymer‐Modified Mesoporous Silica Thin Films for Redox‐Mediated Selective Membrane Gating

Controlling structure and function to switch ionic transport through synthetic membranes is a major challenge in the fabrication of functional nanodevices. Here we describe the combination of mesoporous silica thin films as structural unit, functionalized with two different redox‐responsive ferrocene‐containing polymers, polyvinylferrocene (PVFc) and poly(2‐(methacryloyloxy)ethyl ferrocenecarboxylate) (PFcMA), by using either a grafting to, or a grafting from approach. Both mesoporous film functionalization strategies are investigated in terms of polymer effect on ionic permselectivity. A significantly different ionic permselective behavior can be observed. This is attributed to different polymer location within the mesoporous film, depending on the functionalization strategies used. Additionally, the influence of chemical oxidation on the ionic permselective behavior is studied by cyclic voltammetry showing a redox‐controlled membrane gating as function of polymer location and the pH value. This study is a first step of combining redox‐responsive ferrocene‐containing polymers and mesoporous membranes, and thus towards redox‐controlled ionic transport through nanopores.     

Microgel‐Based Stimuli‐Responsive Capsules

In this paper, a preparation of stimuli‐responsive capsules based on aqueous microgels is described. Microgel particles act as stabilizers for oil‐in‐water emulsion and organize themselves on the surface of chloroform droplets containing the biodegradable polymer poly(4‐hydroxybutyrate‐co‐4‐hydroxyvalerate) (PHBV). After chloroform evaporation, composite capsules consisting of a thin PHBV wall with integrated microgels are obtained. Due to the presence of microgels acting as sensitive building blocks, the capsules respond to different stimuli (temperature, solvent concentration). Preliminary results indicate that the capsule dimensions and morphology can be tuned by microgel and PHBV concentration in water and chloroform, respectively.     

Enhancing the Performance of Solid‐State Dye‐Sensitized Solar Cells Using a Mesoporous Interfacial Titania Layer with a Bragg Stack

High efficiency dye‐sensitized solar cells (DSSCs) are fabricated with a heterostructured photoanode that consists of a 500‐nm‐thick organized mesoporous TiO₂ (om‐TiO₂) interfacial layer (IF layer), a 7 or 10‐μm thick nanocrystalline TiO₂ layer (NC layer), and a 2‐μm‐thick mesoporous Bragg stack (meso‐BS layer) as the bottom, middle and top layers, respectively. An om‐TiO₂ layer with a high porosity, transmittance, and interconnectivity is prepared via a sol‐gel process, in which a poly(vinyl chloride)‐g‐poly(oxyethylene methacrylate) (PVC‐g‐POEM) graft copolymer is used as a structure‐directing agent. The meso‐BS layer with large pores is prepared via alternating deposition of om‐TiO₂ and colloidal SiO₂ (col‐SiO₂) layers. Structure and optical properties (refractive index) of the om‐TiO₂ and meso‐BS layers are studied and the morphology of the heterostructured photoanode is characterized. DSSCs fabricated with the heterostructured IF/NC/BS photoanode and combined with a polymerized ionic liquid (PIL) exhibit an energy conversion efficiencies of 6.6% at 100 mW/cm², one of the highest reported for solid‐state DSSCs and much larger than cells prepared with only a IF/NC layer (6.0%) or a NC layer (4.5%). Improvements in energy conversion efficiency are attributed to the combination of improved light harvesting, decreased resistance at the electrode/electrolyte interface, and excellent electrolyte infiltration.     

Controlled Topology of Block Copolymer Gate Insulators by Selective Etching of Cylindrical Microdomains in Pentacene Organic Thin Film Transistors

We investigate the effect of surface topology of a block copolymer/neutral surface/SiO₂ trilayered gate insulator on the properties of pentacene organic thin film transistor (OTFT) by the controlled etching of self assembled poly(styrene‐b‐methyl methacrylate) (PS‐b‐PMMA) block copolymer. The rms roughness of the uppermost block copolymer film directly in contact with pentacenes was systematically controlled from 0.27 nm to approximately 12.5 nm by the selective etching of cylindrical PMMA microdomains hexagonally packed and aligned perpendicular to SiO₂ layer with 20 and 38 nm of diameter and periodicity, respectively. Both mobility and On/Off ratio were significantly reduced by more than 3 orders of magnitudes with the film roughness in OTFTs having 60 nm thick pentacene active layer. The poor device performance observed with the etched thin film of block copolymer dielectric is attributed to a defective pentacene active layer and the mixed crystalline structure consisting of thin film and bulk phase arising from the massive nucleation of pentacene preferentially at the edge of each cylindrical etched hole.