Fabrication of polymer antireflective coatings by self-assembly of supramolecular block copolymer

We demonstrated a method of fabricating antireflective coatings based on the self-assembly of supramolecular block copolymer formed by polystyrene terminated with carboxyl (PS-COOH) and poly(methyl methacrylate) terminated with amine (PMMA-NH₂) via hydrogen bonding. Different porous films were generated by selectively removing PS-COOH from the spin-coated films with a selective solvent, cyclohexane, under different conditions. The refractive index of such porous film can be tuned from 1.49 down to 1.26 by controlling the thickness of the porous film. For the porous layer with n ˜ 1.26, the light transmittance of the glass about 97.93% was achieved in the visible range (λ ˜ 574 nm). By varying the solution concentration and exposing time in cyclohexane, inhomogeneous three-layered porous films were generated: top and bottom layers with high porosities and the middle layers with lower porosities, respectively. The light transmittance of the glass coated with this inhomogeneous film was about 98.00% in the near-infrared region corresponding to wavelength between 800 and 1400 nm. The wavelength region of the broadband antireflective films with high transmittance more than 99.00% can be fine tuned to 1200-2000 nm with increasing the film thickness.     

Shell-core-corona aggregates formed from poly(styrene)-poly(4-vinylpyridine) block copolymer induced by added homopolymer via interpolymer hydrogen-bonding

The solution behavior of poly(styrene)-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer with added poly(4,4′-oxydiphenylenepyromellitamic acid) (POAA) homopolymer in DMF is studied by dynamic light scattering (DLS), nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM). It is found that coaggregation takes place when mixing PS-b-P4VP block copolymer and POAA homopolymer in DMF due to the strong interpolymer hydrogen-bonding between POAA chains and P4VP blocks. The coaggregation is a diffusion-controlled process and the complexation-induced aggregates are very stable. NMR measurements demonstrate that the resultant aggregates are much more swollen compared with typical amphiphilic block copolymer core-shell micelles. DLS measurements with Eu³⁺ as a probe combined with TEM observation, are employed to study the structure of the aggregates. Results reveal that the formed aggregates are core-shell spheres with the P4VP/POAA complexes as core and the PS blocks as shell when the weight ratio of POAA to PS-b-P4VP is lower. However, a core-shell-corona structure forms with a thin layer of POAA chains adsorbed on the initial core-shell aggregates with increasing weight content of POAA to 60%. Finally, possible mechanisms of the structural transitions are proposed.     

Fabrication of arrays of silver nanoparticle aggregates by microcontact printing and block copolymer nanoreactors

A combination of microcontact printing and block copolymer nanoreactors succeeded in fabricating arrays of silver nanoparticle aggregates. A complex solution of polystyrene‐block‐poly(4‐vinylpyridine) micelles and silver salt was used as an ink to form thin films or droplets on polydimethylsiloxane stamp protrusions. After these complex aggregates were printed onto silicon substrates under controlled conditions, highly ordered arrays of disklike, dishlike, and dotlike complex aggregates were obtained. A subsequent oxygen reactive ion etching treatment yielded arrays of silver nanoparticle aggregates. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2737–2743, 2006     

pH and salt effects on interpolymer complexation via hydrogen bonding in aqueous solutions

The effect of inorganic salts addition on the complex formation of poly(acrylic acid) with various non‐ionic polymers such as poly(vinyl pyrrolidone), poly(acrylamide), poly(ethylene oxide), pol(vinyl methyl ether), poly(vinyl alcohol), poly(N‐isopropylacrylamide), poly(2‐hydroxyethyl vinyl ether), hydroxypropylcellulose and hydroxyethylcellulose has been studied in aqueous solutions. It was found that, depending on the nature of the polymers and pH medium, addition of inorganic salts could increase or decrease the critical pH values of complexation. A new classification of interpolymer complexes based on critical pH values and ionic strength effects is suggested. Copyright © 2004 Society of Chemical Industry     

Polymerization-induced self-assembly of block copolymer nanoparticles via RAFT non-aqueous dispersion polymerization

There is considerable current interest in polymerization-induced self-assembly (PISA) via reversible addition–fragmentation chain transfer (RAFT) polymerization as a versatile and efficient route to various types of block copolymer nano-objects. Many successful PISA syntheses have been conducted in water using either RAFT aqueous dispersion polymerization or RAFT aqueous emulsion polymerization. In contrast, this review article is focused on the growing number of RAFT PISA formulations developed for non-aqueous media. A wide range of monomers have been utilized for both the stabilizer and core-forming blocks to produce diblock copolymer nanoparticles in either polar or non-polar media (including supercritical CO₂ and ionic liquids) via RAFT dispersion polymerization. Such nanoparticles possess spherical, worm-like or vesicular morphologies, often with controllable size and functionality. Detailed characterization of such sterically stabilized diblock copolymer dispersions provides important insights into the various morphological transformations that can occur both during the PISA synthesis and also on subsequent exposure to a suitable external stimulus (e.g. temperature).     

Solvent annealing assisted self-assembly of hydrogen-bonded interpolymer complexes of AB block copolymer/C homopolymer in thin film

A simple process of solvent annealing has been shown to produce ordered self-assembly structures of poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP)/poly(4,4′-oxydiphenylenepyromellitamic acid) (POAA) block copolymer/homopolymer blends in thin film, where POAA chains selectively interact with P4VP blocks by strong interpolymer hydrogen-bonding. By simply exposing the thin film to benzene/NMP (0.97/0.03, in volume) vapor mixture, ordered microphase-separated structures with PS spherical microdomains distributed within P4VP/POAA complexes matrix were obtained. The formation of the microphase-separated structures could be attributed to the substantial mobility of PS blocks and P4VP/POAA complexes and enhanced repulsion between them under the benzene/NMP mixture vapor. When the volume ratio of benzene to NMP increased to 0.98/0.02, the increasing benzene in the mixture vapor induced the adhesive collision of spherical microphase-separated structures to form long “pearl necklaces”. With increasing volume ratio of benzene to NMP to 0.99/0.01, an ordered “pearl necklace” array oriented parallel to the film surface formed. The self-assembly structures were studied by FTIR spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Finally, possible mechanism of self-assembly and formation of microphase morphology was proposed.     

Large-scale parallel arrays of silicon nanowires via block copolymer directed self-assembly

Extending the resolution and spatial proximity of lithographic patterning below critical dimensions of 20 nm remains a key challenge with very-large-scale integration, especially if the persistent scaling of silicon electronic devices is sustained. One approach, which relies upon the directed self-assembly of block copolymers by chemical-epitaxy, is capable of achieving high density 1?:?1 patterning with critical dimensions approaching 5 nm. Herein, we outline an integration-favourable strategy for fabricating high areal density arrays of aligned silicon nanowires by directed self-assembly of a PS-b-PMMA block copolymer nanopatterns with a L(0) (pitch) of 42 nm, on chemically pre-patterned surfaces. Parallel arrays (5 × 10(6) wires per cm) of uni-directional and isolated silicon nanowires on insulator substrates with critical dimension ranging from 15 to 19 nm were fabricated by using precision plasma etch processes; with each stage monitored by electron microscopy. This step-by-step approach provides detailed information on interfacial oxide formation at the device silicon layer, the polystyrene profile during plasma etching, final critical dimension uniformity and line edge roughness variation nanowire during processing. The resulting silicon-nanowire array devices exhibit Schottky-type behaviour and a clear field-effect. The measured values for resistivity and specific contact resistance were ((2.6 ± 1.2) × 10(5)Ωcm) and ((240 ± 80) Ωcm(2)) respectively. These values are typical for intrinsic (un-doped) silicon when contacted by high work function metal albeit counterintuitive as the resistivity of the starting wafer (～10 Ωcm) is 4 orders of magnitude lower. In essence, the nanowires are so small and consist of so few atoms, that statistically, at the original doping level each nanowire contains less than a single dopant atom and consequently exhibits the electrical behaviour of the un-doped host material. Moreover this indicates that the processing successfully avoided unintentional doping. Therefore our approach permits tuning of the device steps to contact the nanowires functionality through careful selection of the initial bulk starting material and/or by means of post processing steps e.g. thermal annealing of metal contacts to produce high performance devices. We envision that such a controllable process, combined with the precision patterning of the aligned block copolymer nanopatterns, could prolong the scaling of nanoelectronics and potentially enable the fabrication of dense, parallel arrays of multi-gate field effect transistors.     

One step fabrication and characterization of platinum nanopore electrode ensembles formed via amphiphilic block copolymer self-assembly

A novel one-step approach to Pt nanopore electrode ensembles (NEEs) has been developed using an amphiphilic block copolymer [polystyrene-block-poly (acrylic acid)] self-assembly. This procedure is simple and fast, and requires only conventional, inexpensive electrochemical instrumentation. Electrochemical methods are used to characterize the Pt nanopore electrode ensembles prepared using this new procedure. And the capacitance and voltammetric characteristics for the NEEs have been examined. At lower scan rates, it remains the features of a single nanoelectrode, while at high scan rates the nanoelectrodes act independently. This is an important feature for vivo sensing and other electroanalytical applications.     

Nine-fold density multiplication of hcp lattice pattern by directed self-assembly of block copolymer

Block copolymer assembly directed by electron beam (EB) lithography enhances both resolution and throughput of the EB-generated patterns and provides a feasible path to fabricating master molds of nanometer scale patterns over macroscopic areas. In our previous paper [27], we demonstrated that the self-assembly process can interpolate points in between the EB-generated pattern, thus attaining four-fold density multiplication. Here, we report a nine-fold feature density multiplication can be attained by the directed block copolymer assembly. The equilibrium formation of perpendicular cylindrical domains in registration with the pre-patterned surface is confined within a narrow thickness range once all other parameters are fixed as found in a four-fold feature density multiplication. The tolerance of the lattice mismatch between chemical pattern and d spacing of domains for nine-fold feature density multiplication is smaller than that for four-fold feature density multiplication. We also found that the critical dimension formed by the block copolymer domains is independent of that defined by the EB pre-patterned features.     

嵌段共聚物薄膜自组装热退火技术进展

大分子自组装能使嵌段共聚物薄膜中微相结构进行自发地有序排列,形成高度图案化的微观形貌,继而赋予薄膜特殊的物理与化学功能。热退火诱导技术是制备嵌段共聚物自组装薄膜的一种主要手段,具有操作简单和实验条件易于控制的优点。综述了多种新型热退火诱导技术以及制备高取向、低缺陷密度自组装薄膜的方法,并对多种新型技术的特点进行了总结。     

Selective self-assembly of surface-functionalized carbon nanotubes in block copolymer template

Microphase-separated styrene-butadiene-styrene (SBS) triblock copolymer was utilized as a template for the selective self-assembly of polystyrene (PS)-functionalized carbon nanotubes (CNTs) in the PS phase. It was also found that PS-functionalized CNTs could be accommodated in the PS phase of SBS regardless of the molecular weight of the PS ligand. This is different from the case for assembling nanoparticles or nanorods with a block copolymer, in which the ligand should be shorter than the corresponding block such that the nanoparticles or nanorods can be incorporated into that block. This phenomenon is explained based on the different chain morphologies of the ligands functionalizing the CNTs, nanoparticles and nanorods.     

嵌段共聚物薄膜自组装热退火技术进展

大分子自组装能使嵌段共聚物薄膜中微相结构进行自发地有序排列,形成高度图案化的微观形貌,继而赋予薄膜特殊的物理与化学功能。热退火诱导技术是制备嵌段共聚物自组装薄膜的一种主要手段,具有操作简单和实验条件易于控制的优点。综述了多种新型热退火诱导技术以及制备高取向、低缺陷密度自组装薄膜的方法,并对多种新型技术的特点进行了总结。     

羟化含氟嵌段共聚物的合成及其自组装行为研究

用α-溴代丙酸乙酯（EPN—B）／氯化亚铜（CuCl）／联二吡啶（bpy）作为催化引发体系,环己酮为溶剂,进行甲基丙烯酸2,2,2-三氟乙酯（TFEMA）的原子转移自由基聚合（ATRP）,得到单分散PTFEMA—X预聚体。并以此预聚体为大分子引发剂引发甲基丙烯酸-β-羟乙酯聚合,得到分子质量可控、分子质量分布窄的聚甲基丙烯酸2,2,2-三氟乙酯-b-聚甲基丙烯酸-β-羟乙酯嵌段共聚物,用FTIR、^1H—NMR、GPC等对产物的结构与性能进行了表征。同时利用动态激光光散射（DLS）对嵌段共聚物的自组装行为进行了研究。     

Encapsulation of phenylacetic acid in block copolymer nanoparticles during polymerization induced self-assembly

Polymerization induced self-assembly (PISA) is an in situ method for producing block copolymer nanoparticles. Performing PISA in the presence of a pharmaceutical drug causes the nanoparticles to encapsulate the drug. While this approach is straightforward, the effects of drug loading and block copolymer composition remain unclear. Here, we investigate encapsulation of the drug phenylacetic acid (PA) in poly(glycerol monomethacrylate)-block-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) nanoparticles during PISA. Nanoparticle morphology is characterized by electron microscopy and light scattering, while encapsulation efficiency ($p$) is quantified using nuclear magnetic resonance diffusometry. Increasing the PA loading shifts the nanoparticle morphology from spherical micelles $\to$ cylindrical micelles $\to$ vesicles. At a 32 mg/ml PA loading, $p$ maximizes at ~80%. Increasing the PHPMA degree of polymerization minimally impacts $p$. The invariance of $p$ toward core block length suggests that PA binds to the nanoparticle corona, highlighting the importance of the hydrophilic block for drug encapsulation during PISA.     

Fabrication of chemical patterns from graphoepitaxially assembled block copolymer films by molecular transfer printing

Fabrication of chemical patterns by electron beam lithography or extreme ultraviolet interference lithography is either low-throughput or prohibitively expensive to practice at sub-50 nm feature dimension. Here we report a new high-throughput approach that combines the advantages of both graphoepitaxy and molecular transfer printing (MTP) to fabricating chemical patterns at low cost for directed assembly of block copolymers. In this new approach, a cylinder-forming block copolymer ternary blend film is directed to assemble on a topographic HSQ substrate with sub-L_o, where L_o is the natural period of the block copolymer, relief structures to increase the feature density by a factor of ∼20, the surface domain pattern is replicated using MTP to create 1:1 chemical pattern, and then a lamellae-forming block copolymer is directed to assemble on the chemical pattern to realize high-aspect ratio Manhattan type nanostructures. This combined strategy allows us to fabricate chemical patterns with feature dimension below the resolution limit of current lithographic tools.     

Fabrication of porous carbon micropillars using a block copolymer as porogen

A technique to fabricate porous carbon micropillars using a block copolymer, F127, as porogen is described. In this process, negative tone photoresist (i.e. SU-8) mixed with F127 was photopatterned and carbonized under inert atmosphere. The thermal behavior of the photoresist precursor (F127 + SU-8) during carbonization process was characterized using differential scanning calorimetry and thermogravimetric analysis. Texture analysis on the carbon surface showed a mesoporous feature distribution. Electrochemical characterization based on the reaction of redox couple was utilized to study the change in the effective surface area (A_eff) of the porous carbon electrodes with different weight percentages of F127 in SU-8. These results indicated that porous carbon thin film electrodes derived from 10% F127 mixed in SU-8 had an A_eff 185% compared to the conventional photoresist derived carbon electrode. This fabrication approach can be employed to produce reproducible high aspect ratio carbon microelectrodes with different shapes for various electrochemical devices.     

Fabrication of nanostructure via self-assembly of nanowires within the AAO template

The novel nanostructures are fabricated by the spatial chemical modification of nanowires within the anodic aluminum oxide (AAO) template. To make the nanowires better dispersion in the aqueous solution, the copper is first deposited to fill the dendrite structure at the bottom of template. During the process of self-assembly, the dithiol compound was used as the connector between the nanowires and nanoparticles by a self-assembly method. The nanostructures of the nano cigars and structure which is containing particles junction are characterized by transmission electron microscopy (TEM). These kinds of novel nanostructure will be the building blocks for nanoelectronic and nanophotonic devices.      

When emulsification meets self-assembly: The role of emulsification in directing block copolymer assembly

Emulsification is used to generate spherical particles or droplets of immiscible liquids, while block copolymer self-assembly yields a wide variety of nanostructures. The combination of these two methodologies can yield a variety of structures that would not be otherwise observed. The emulsification/solvent evaporation process provides a powerful means to direct block copolymer assembly. Various factors arising from the emulsification can direct the block copolymer assembly, such as confinement effects, interfacial tension, as well as other conditions. In this review, various emulsification techniques are discussed, such as oil-in-water emulsions, double emulsions, as well as the use of microfluidic devices. While emulsification-induced self-assembly may be used to control internal morphologies as well as overall shapes of particles, it also lends a convenient method for controlling surface structures. Examples of exotic structures that may be obtained through the use of these techniques will be described. Also, ways in which morphologies may be controlled using these methods will be discussed.     

Large-size bamboo-shape nanotube from self-assembly of poly(ferrocenyldimethylsilane-b-dimethylsiloxane) block copolymer

One kind of large-size bamboo-shape nanotube from self-assembly of poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFS-b-PDMS) block copolymer was obtained. It was found that firstly, PFS-b-PDMS formed sphere micelles and pearl-like cluster at room temperature, and then bamboo-shape nanotube formed when the solution was aged about 3 days. The formation mechanism of bamboo-shape nanotube was also discussed.     

High yield preparation of all-organic raspberry-like particles by heterocoagulation via hydrogen bonding interaction

We describe here a straightforward strategy towards the high yield preparation of raspberry-like all-organic particles. Poly(acrylic acid)-b-poly(butyl acrylate) core–shell nanoparticles (D ∼ 80 nm) and larger poly(ethylene oxide)-b-poly(butyl acrylate) core–shell (D ∼ 230 nm), synthesized by RAFT emulsion polymerization, were mixed at high solids content (23 wt%) at room temperature without any particular precaution (no dropwise addition, no pH adjustment). Raspberry-like particles constituted of one central PEO-b-PBA particle surrounded by about thirty PAA-b-PBA particles were successfully obtained, with no coagulum formation. The heteroaggregation process is probably driven by the hydrogen-bond interactions between the PAA and the PEO shells of the particles. The raspberry-like particles were characterized using electron microscopy (TEM and cryo-TEM), dynamic light scattering (DLS), chromatography (HDC) and calorimetry (ITC), demonstrating the selectivity of the process.