Positive and Negative TiO2 Micropatterns on Organic Polymer Substrates

Microstructured SiOx/COP Stamps for Patterning TiO2 on Polymer Substrates via Microcontact Printing

Microcontact printing (μCP) techniques have sparked a surge of interests in microfabrication since they help produce arrays on a wide range of target substrates in a facile and efficient manner. Polydimethylsiloxane (PDMS), as a well-established material for stamps, has constraints resulting from its hydrophobicity and softness, and the replication of PDMS stamps usually requires rigid masters or processes using a photoresist. Herein, a novel μCP stamp based on cyclo-olefin polymer (COP) is produced through vacuum ultraviolet (VUV) lithography. 2,4,6,8-Tetramethylcyclotetrasiloxane is selectively deposited at the affinity-patterns on the COP surface, and these patterned siloxane films are converted into SiO_x meanwhile protecting the COP beneath them from the VUV photoetching. By this means, a patterned relief is fabricated on the COP plates, resulting in a hydrophilic SiO_x/COP μCP stamp with punch heights of ∼180 nm. The novelty arises from the simplicity of the master- and photoresist-free microstructuring, and the higher stiffness of SiO_x/COP stamps prevents the deformation during pressing. Finally, an example μCP is given to transfer titania precursor gel and produce TiO₂ micropatterns on flexible polymer substrates. The SiO_x/COP stamps and the μCP of TiO₂ provide simple and cost-effective patterning techniques, which should contribute to the future design and creation of flexible devices.

A Simple Drop-and-Dry Approach to Grass-Like Multifunctional Nanocoating on Flexible Cotton Fabrics Using In Situ-Generated Coating Solution Comprising Titanium-Oxo Clusters and Silver Nanoparticles

Multifunctional nanocoatings have been of central importance in various technological fields, yet their fabrication, especially on flexible substrates, still remains a persistent challenge to date. We herein demonstrate a mild single-step drop-and-dry approach to the in situ growth of hierarchical grass-like nanostructures on flexible cotton fabrics. A precursor solution comprising titanium-oxo clusters [Ti₁₈MnO₃₀(OEt)₂₀(MnPhen)₃] (Phen = 1,10-phenanthroline) and AgNO₃ is employed wherein Ag⁺ cations are in situ-reduced to silver nanoparticles (AgNPs). Drop-casting onto cotton fabrics under mild conditions induces the in situ growth of the heterogeneous grass-like assembly, and each constituent nanofibrous 'grass leaf' incorporates AgNPs both on the surface and embedded in the interior. The hierarchical morphology and heterogeneous composition of these grass-like nanostructures impart the coated cotton fabrics with enhanced antibacterial properties, robust hydrophobicity, and UV-blocking capability, which are features desired in textile materials but lacking in natural cotton.

Micro-Patterning of Magnetron Sputtered Titanium Dioxide Coatings and Their Efficiency for Photocatalytic Applications

Titanium dioxide thin films were deposited onto sola-lime glass substrates by reactive magnetron sputtering. Fine stainless steel mesh sheets with different aperture sizes were applied as masks over glass substrates to allow the deposition of the coatings with micro-patterned structures and, therefore, enhanced surface area. Non-patterned titania films were deposited for comparison purposes. The titanium dioxide films were post-deposition annealed at 873 K for crystallinity development and then extensively analysed by a number of analytical techniques, including scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX), optical and stylus profilometry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-Vis spectroscopy. The photocatalytic activity of non-patterned and micro-patterned titania films was assessed under UV light irradiation by three different methods; namely methylene blue, stearic acid, and oleic acid degradation. The results revealed that the micro-patterned coatings significantly outperformed non-patterned titania in all types of photocatalytic tests, due to their higher values of surface area. Increasing the aperture of the stainless steel mesh resulted in lower photocatalytic activity and lower surface area values, compared to the coatings deposited through a smaller aperture mesh.

Formation of submicron-sized silica patterns on flexible polymer substrates based on vacuum ultraviolet photo-oxidation

Formation of precise and high-resolution silica micropatterns on polymer substrates is of importance in surface structuring for flexible device fabrication of optics, microelectronic, and biotechnology. To achieve that, substrates modified with affinity-patterns serve as a strategy for site-selective deposition. In the present paper, vacuum ultraviolet (VUV) treatment is utilized to achieve spatially-controlled surface functionalization on a cyclo-olefin polymer (COP) substrate. An organosilane, 2,4,6,8-tetramethylcyclotetrasiloxane (TMCTS), preferentially deposits on the functionalized regions. Well-defined patterns of TMCTS are formed with a minimum feature of ∼500 nm. The secondary VUV/(O)-treatment converts TMCTS into SiO _x , meanwhile etches the bare COP surface, forming patterned SiO _x /COP microstructures with an average height of ∼150 nm. The resulting SiO _x patterns retain a good copy of TMCTS patterns, which are also consistent with the patterns of photomask used in polymer affinity-patterning. The high quality SiO _x patterns are of interests in microdevice fabrication, and the hydrophilicity contrast and adjustable heights reveal their potential application as a "stamp" for microcontact printing (μCP) techniques.

Surface Decoration on Polymeric Gate Dielectrics for Flexible Organic Field-Effect Transistors via Hydroxylation and Subsequent Monolayer Self-Assembly

A simple photochemical reaction based on confined photocatalytic oxidation (CPO) treatment and hydrolysis was employed to efficiently convert C-H bonds into C-OH groups on polymeric material surfaces, followed by investigation of monolayer self-assembly decoration on polymeric dielectrics via chemical bonding for the organic field-effect transistors (OFETs) applications. This method is a low temperature process and has negligible etching effect on polymeric dielectric layers. Various types of self-assembled monolayers have been tested and successfully attached onto the hydroxylated polymeric dielectric surfaces through chemical bonding, ensuring the stability of decorated functional films during the subsequent device fabrication consisting of solution processing of the polymer active layer. With the surface decoration of functional groups, both n-type and p-type polymers exhibit enhanced carrier mobilities in the unipolar OFETs. In addition, enhanced and balanced mobilities are obtained in the ambipolar OFETs with the blend of polymer semiconductors. The anchored self-assembled monolayers on the dielectric surfaces dramatically preclude the solvent effect, thus enabling an improvement of carrier mobility up to 2 orders of magnitude. Our study opens a way of targeted modifications of polymeric surfaces and related applications in organic electronics.

The polar side of polyphenylene dendrimers

The site-specific functionalization of poly(phenylene) dendrimers can produce macromolecules with a range of different polarities.

Modification of indium tin oxide with persulfate-based photochemistry toward facile, rapid, and low-temperature interface-mediated multicomponent assembling

The well-controlled material assembly and patterning on indium tin oxide (ITO) coating layer is of great importance for the practical fabrication of a functional device. Nonetheless, the conventional way to achieve this aim is still mainly based on the combination of photolithography with pattern transfer techniques (e.g., wet/dry etching, μCP) due to the lack of one method that is able to directly afford site-selective ITO surface tailoring and subsequent templating for material assembly. Herein, we reported a novel, fast, and efficient photochemical reaction to accurately tailor the surface property of ITO with light-controlled site-selectivity, thus resulting in direct photoresist-free and etching/contact-free lithographic patterning of building blocks, e.g., ZnO, BaTiO3, CdS, lipid membrane, conductive polymers, colloids, and liquid crystals. The entire process reveals new interfacial chemistry suitable for inorganic metal oxide and its important versatile implications for low-cost fabrication of large-area flat and flexible optical/electronic/biorelated devices.

Hydroxylation of organic polymer surface: method and application

It may be hardly believable that inert C-H bonds on a polymeric material surface could be quickly and efficiently transformed into C-OH by a simple and mild way. Thanks to the approaches developed recently, it is now possible to transform surface H atoms of a polymeric substrate into monolayer OH groups by a simple/mild photochemical reaction. Herein the method and application of this small-molecular interfacial chemistry is highlighted. The existence of hydroxyl groups on material surfaces not only determines the physical and chemical properties of materials but also provides effective reaction sites for postsynthetic sequential modification to fulfill the requirements of various applications. However, organic synthetic materials based on petroleum, especially polyolefins comprise mainly C and H atoms and thus present serious surface problems due to low surface energy and inertness in reactivity. These limitations make it challenging to perform postsynthetic surface sequential chemical derivatization toward enhanced functionalities and properties and also cause serious interfacial problems when bonding or integrating polymer substrates with natural or inorganic materials. Polymer surface hydroxylation based on direct conversion of C-H bonds on polymer surfaces is thus of significant importance for academic and practical industrial applications. Although highly active research results have reported on small-molecular C-H bond activation in solution (thus homogeneous), most of them, featuring the use of a variety of transition metals as catalysts, present a slow reaction rate, a low atom economy and an obvious environmental pollution. In sharp contrast to these conventional C-H activation strategies, the present Spotlight describes a universal confined photocatalytic oxidation (CPO) system that is able to directly convert polymer surface C-H bonds to C-OSO3(-) and, subsequently, to C-OH through a simple hydrolysis. Generally speaking, these newly implanted hydroxyl groups preserve their own reactivity toward other complementary compounds, thus creating a novel base with distinct surface properties. Thanks to this functionalized platform, a wide range of organic, inorganic and metal materials have been attached to conventional organic polymer substrates through the rational engineering of surface molecular templates from small functional groups to macromolecules. It is expected that the proposed novel CPO method and its versatile usages in advanced material applications will offer new opportunities for a variety of scientific communities, especially for those working on surface/interface modulation.

Preparation of soft hydrogel nanoparticles with PNIPAm hair and characterization of their temperature-induced aggregation

There exists a great number of publications concerning the synthesis of core-shell and/or hairy particles by means of controlled/living polymerization. Nevertheless, how to fabricate ultrafine nanosized hairy particles, especially polymeric soft hairy particles, remains a significant challenge. This paper presents a simple self-developed approach consisting of a two-step photoinduced polymerization of cross-linked polyacrylamide (CLPAM) soft hydrogel nanoparticles (5-10 nm in diameter) grafted with poly(N-isopropylacrylamide) (PNIPAm) chains. The architecture of such ultrafine soft water-swollen CLPAM@PNIPAm core/shell nanoparticles (20-35 nm in diameter) demonstrated very specific temperature sensitive behaviors. During heating a fast association process was observed at approximately 33-34 degrees C and the singular hairy particles with 34 nm diameters clustered into aggregates that were approximately 120 nm in diameter. Raising the temperature further, however, led to a decrease in size to about 100 nm at 45 degrees C. This behavior was attributed to the formation of hydrophobic shell layers accompanying the shrinkage of PNIPAm chains with chain polar transformations. With the contraction pressure produced by further shrinkage of the hydrophobic shell layers, the soft fully swollen PAM cores expelled water and diminished in size. During the cooling process, these contracted cores that were trapped in the aggregates gave rise to an early dissociation. The hydrophilic hairy CLPAM@PNIPAm particles are believed to be potentially useful as carriers to specific target regions, e.g., cells for controlled drug delivery and other smart biomaterial applications.

Preparation of polymeric Janus particles by directional UV-induced reactions

Polymeric Janus particles are obtained by UV-induced selective surface grafting polymerizations and coupling reactions, in virtue of the light-absorption of photoreactive materials such as the immobilized photoinitiator and spread photoinitiator solution on the surfaces exposed to UV light and the sheltering of densely arrayed immovable particles from light. Varying the monomers or macromolecules applied in photografting polymerization or coupling reaction, and choosing diverse polymeric particles of various size, bicolor and amphiphilic Janus particles could be successfully achieved. Observations by fluorescence microscope, scanning electron microscope ,and transmission electron microscope confirmed the asymmetrical morphology of the resultant Janus particles.

Photoactivation of alkyl C-H and silanization: a simple and general route to prepare high-density primary amines on inert polymer surfaces for protein immobilization

Surface modification through implanting functional groups has been demonstrated to be extremely important to biomedical applications. The usage of organic polymer phase is often required to achieve satisfactory results. However, organic surfaces usually have poor chemical reactivity toward other reactants and target biomolecules because these surfaces usually only consist of simple alkyl (C-H) and/or alkyl ether (ROR') structures. For the first time, we here report the potential to perform silanization techniques on alkyl polymer surface, which provide a simple, fast, inexpensive, and general method to decorate versatile functional groups at the molecular level. As an example, high-density primary amines could be obtained on a model polymer, polypropylene substrate, through the reaction between amine-capped silane, 3-aminopropyltriethoxysilane (APTES) and hydroxylated polypropylene surface. A model protein, immunoglobulin (IgG), could be effectively immobilized on the surface after transforming amines to aldehydes by the aldehyde-amine condensation reaction between glutaraldehyde (GA) and amines. The routes we report here could directly make use of the benefits from well-developed silane chemistry, and hereby are capable of grafting any functionalities on inert alkyl surfaces via changing the terminal groups in silanes, which should instantly stimulate the development of many realms such as microarrays, immunoassays, biosensors, filtrations, and microseparation.

Room temperature synthesized rutile TiO(2) nanoparticles induced by laser ablation in liquid and their photocatalytic activity

TiO(2) nanoparticles were prepared by one-step pulsed laser ablation of a titanium target immersed in a poly-(vinylpyrrolidone) solution at room temperature. The products were systematically characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy and x-ray photoelectron spectroscopy (XPS). The results indicated that the rutile TiO(2) nanocrystalline particles were one-step synthesized at room temperature and the mean size in diameter is about 50 nm with a narrow size distribution. A probable formation process was proposed on the basis of the microstructure and the instantaneous plasma plume induced by the laser. Photocatalytic activity was monitored by degradation of a methylene blue solution. The as-prepared rutile TiO(2) nanoparticles demonstrate a good photocatalytic performance. This work shows that pulsed laser ablation in liquid media is a good method to synthesize some nanosized materials which are difficult to produce by other conventional methods.

The pursuit of a scalable nanofabrication platform for use in material and life science applications

In this Account, we describe the use of perfluoropolyether (PFPE)-based materials that are able to accurately mold and replicate micro- and nanosized features using traditional techniques such as embossing as well as new techniques that we developed to exploit the exceptional surface characteristics of fluorinated substrates. Because of the unique partial wetting and nonwetting characteristics of PFPEs, we were able to go beyond the usual molding and imprint lithography approaches and have created a technique called PRINT (Particle [or Pattern] Replication In Nonwetting Templates). PRINT is a distinctive "top-down" fabrication technique capable of generating isolated particles, arrays of particles, and arrays of patterned features for a plethora of applications in both nanomedicine and materials science. A particular strength of the PRINT technology is the high-resolution molding of well-defined particles with precise control over size, shape, deformability, and surface chemistry. The level of replication obtained showcases some of the unique characteristics of PFPE molding materials. In particular, these materials arise from very low surface energy precursors with positive spreading coefficients, can be photocured at ambient temperature, and are minimally adhesive, nonswelling, and conformable. These distinctive features enable the molding of materials with unique attributes and nanometer resolution that have unprecedented scientific and technological value. For example, in nanomedicine, the use of PFPE materials with the PRINT technique allows us to design particles in which we can tailor key therapeutic parameters such as bioavailability, biodistribution, target-specific cell penetration, and controlled cargo release. Similarly, in materials science, we can fabricate optical films and lens arrays, replicate complex, naturally occurring objects such as adenovirus particles, and create 2D patterned arrays of inorganic oxides.

Positive and negative ZnO micropatterning on functionalized polymer surfaces

Patterned ZnO deposition on substrates has received increasing attention because of its great potential in photocatalysis, energy conversion, and electro-optical techniques. Chemical solution growth is especially promising for organic substrates due to its very mild reaction conditions. Here this method is used on functionality-patterned polymer surfaces in order to fabricate positive and negative ZnO micropatterns. A ZnO film made of arrayed rods, typically 500-750 nm in diameter and 2.5 microm in length, is selectively obtained on sulfated and hydroxylated regions of biaxially oriented poly(propylene), giving rise to positive patterns. For reactive polyesters such as poly(ethylene terephthalate), the ZnO rods selectively remain on the unmodified original regions, creating negative patterns. Unlike complex photolithography procedures, the irradiation and patterning processes do not require the use of positive or negative photoresists, and possible damage from acidic solutions on the underlying substrate during the chemical etching process is avoided. The process thus proves to be a simple, creditable, and low-cost method, which could be easily applied on a variety of inert and reactive polymer surfaces.

The Patterning of Sub-500 nm Inorganic Oxide Structures

Elastomeric perfluoropolyether molds are applied to pattern arrays of sub-500 nm inorganic oxide features. This versatile soft-lithography technique can be used to pattern a wide range of materials; in this work inorganic oxides including TiO2 , SnO2 , ZnO, ITO, and BaTiO3 are patterned on a variety of substrates with different aspect ratios. An example of TiO2 posts is shown in the figure.

In vitro formation of capillary networks using optical lithographic techniques

Tissue engineering approaches have been developed for vascular grafts, but success has been limited to arterial replacements of large-caliber vessels. We have developed an innovative technique to transplant engineered capillary networks by printing techniques. Endothelial cells were cultured on a patterned substrate, in which network patterns were generated by prior optical lithography. Subsequently, the patterned cells were transferred to extracellular matrix and tissue at which point they changed their morphologies and formed tubular structures. Microinjection of dye showed that the micrometer-scale tubular structure had in vitro flow potential. When capillary-like networks engineered on amnion membranes were transplanted into mice, we found blood cells inside of the lumen of the transplanted capillary-like structure. This is the first report of the in vitro formation of capillary networks using cell transfer technique, and this novel technique may open the way for development of rapid and effective blood perfusion systems in regenerative medicine.