Surface-guided self-assembly of silver nanoparticles on edges of heterogeneous surfaces

A general method for the generation of two-dimensional (2D) ordered silver nanoparticles (av 45 nm) ring array has been demonstrated via controllable self-assembly. The selective self-assembly is conducted on the edges of a gold coated polyelectrolyte film. This film is fabricated using the monolayer polystyrene (PS) spheres (av 600 nm) on a substrate as template, followed by depositing a positively charged polyelectrolyte and gold colloids (av 17 nm) via the layer-by-layer (LbL) self-assembly technique, and finally by eliminating the PS monolayer. This gold coated polyelectrolyte film has a regular pattern of sharp edges, and those edges are composed of abundant polyelectrolyte. This heterogeneous surface is easily prepared and universal for site-selective absorption of nanoparticles (silver nanoparticles in this paper, av 45 nm). This surface-guided self-assembly is powerful for fabricating micro/nanostructures on the edges of prepatterns. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the products.     

Fabrication of PDMS/glass microchips by twofold replication of PDMS and its application in genetic analysis

In this paper, we describe a simple method for fabrication of high quality poly(dimethylsiloxane) (PDMS)/glass microchip by twofold replica molding of PDMS. This technique first served to transfer the negative microchannels from the glass template to the PDMS substrate as a master, and then this PDMS master with positive microchannels was used to replicate the PDMS replica with negative microchannels. Finally, the PDMS replica was bound to a glass sheet by UV radiation. The fabricated microchips were successfully applied for the detection of C677T mutation from the human methylenetetrahydrofolate reductase gene.     

Toward Mass Producible Ordered Bulk Heterojunction Organic Photovoltaic Devices

A strategy to fabricate nanostructured poly(3‐hexylthiophene) (P3HT) films for organic photovoltaic (OPV) cells by a direct transfer method from a reusable soft replica mold is presented. The flexible polyfluoropolyether (PFPE) replica mold allows low‐pressure and low‐ temperature process condition for the successful transfer of nanostructured P3HT films onto PEDOT/PSS‐coated ITO substrates. To reduce the fabrication cost of masters in large area, we employed well‐ordered anodic aluminum oxide (AAO) as a template. Also, we provide a method to fabricate reversed nanostructures by exploiting the self‐replication of replica molds. The concept of the transfer method in low temperature with a flexible and reusable replica mold obtained from an AAO template will be a firm foundation for a low‐cost fabrication process of ordered OPVs.     

Interfacial friction of thin PDMS network films

This study focuses on developing dry, surface‐tethered polymeric lubricant coatings capable of significantly decreasing friction and wear of nano‐ and micrometer scale machines. Vinyl‐terminated polydimethylsiloxane chains are spin‐coated with a crosslinking agent and platinum catalyst onto silicon wafers functionalized with a self‐assembling monolayer containing reactive vinyl groups. Lateral force microscopy (LFM) measurements employing a bead probe are used to quantify the coefficient of friction (COF) and adhesion characteristics of the PDMS‐SAM surface tethered networks. The combined polymer network and SAM layer manifest extremely low friction coefficients, μ = 4 × 10^?3, which is nearly one order of magnitude lower than the friction coefficient of the bare silicon substrate. The lowest friction forces are measured using silicon substrates covered with nanometer thick, peroxide crosslinked PDMS networks; though poorly crosslinked, these networks display COFs as much as ten‐times lower than a solitary SAM coating layer. Micrometer thick end‐linked optimal networks also manifest attractive interfacial friction properties, with COFs approximately three times larger than the thinner, imperfect networks. These observations are discussed in terms of the structure of the polymer networks and the role of adhesion forces on interfacial friction. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1773–1787, 2008     

Fabrication of complex multilevel microchannels in PDMS by using three-dimensional photoresist masters

This paper demonstrates a new method of implementing complex microchannels in PDMS, which is simply constructed using three-dimensional photoresist structures as a master mold for the PDMS replica process. The process utilizes UV-insensitive LOR resist as a sacrificial layer to levitate the structural photoresist. In addition, the thickness of photoresist structures can be controlled by multi-step UV exposure. By using these techniques, various three-dimensional photoresist structures were successfully implemented, including the recessed cantilevers, suspended bridges, and the complex plates with micro-pits or micro-villi. We demonstrate that the three-dimensional photoresist structures are applicable to implementing complex multiple microchannels in PDMS by using the PDMS replica method.     

Chains anisotropy in PDMS networks due to friction on gold surfaces

In this article, we describe an experimental friction study of poly(dimethyl siloxane) (PDMS) networks on metallic substrates such as gold-coated slides, and under different conditions. The friction generates a transfer of a thin layer of PDMS and a preferential orientation of the polymer chains at the interface. However, the characterization of this layer is complicated, given the small amount of matter and the contact with a metallic surface. The polarization-modulation infrared reflexion-absorption spectroscopy (PM-IRRAS), which is an excellent tool for anisotropy and orientation studies, was used to characterize the PDMS transferred layer. Our results showed an induced anisotropy due to the friction, and in which PDMS chains are lying parallel to the gold substrate surface. Our spectroscopic analyzes allowed us to imagine a scheme of PDMS transfer on the gold surface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2348–2353, 2004     

Benchtop micromolding of polystyrene by soft lithography

Polystyrene (PS), a standard material for cell culture consumable labware, was molded into microstructures with high fidelity of replication by an elastomeric polydimethylsiloxane (PDMS) mold. The process was a simple, benchtop method based on soft lithography using readily available materials. The key to successful replica molding by this simple procedure relies on the use of a solvent, for example, gamma-butyrolactone, which dissolves PS without swelling the PDMS mold. PS solution was added to the PDMS mold, and evaporation of the solvent was accomplished by baking the mold on a hotplate. Microstructures with feature sizes as small as 3 μm and aspect ratios as large as 7 were readily molded. Prototypes of microfluidic chips made from PS were prepared by thermal bonding of a microchannel molded in PS with a flat PS substrate. The PS microfluidic chip displayed much lower adsorption and absorption of hydrophobic molecules (e.g. rhodamine B) compared to a comparable chip created from PDMS. The molded PS surface exhibited stable surface properties after plasma oxidation as assessed by contact angle measurement. The molded, oxidized PS surface remained an excellent surface for cell culture based on cell adhesion and proliferation. To demonstrate the application of this process for cell biology research, PS was micromolded into two different microarray formats, microwells and microposts, for segregation and tracking of non-adherent and adherent cells, respectively. The micromolded PS possessed properties that were ideal for biological and bioanalytical needs, thus making it an alternative material to PDMS and suitable for building lab-on-a-chip devices by soft lithography methods.     

水相一步合成锐钛矿型二氧化钛空心球

报道了水相一步直接合成晶体TiO2空心球的方法. 以水溶性的过氧化钛配合物(peroxo-titanium complex, PTC)为前驱体、聚苯乙烯(polystyrene, PS)球为模板, 在水溶液体系中可直接制备得到锐钛矿型纳米TiO2空心球. 与传统的模板法相比, 模板的包覆、去除及TiO2壳层的晶化等步骤在水相中可一步完成. 利用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)及热重分析仪(TGA)对所合成的纳米TiO2空心球进行了表征, 同时推断了可能的反应机理.     

Zeta potentials of PDMS surfaces modified with poly(ethylene glycol) by physisorption

Controlling zeta potential of PDMS surface coated with a layer of PEG is important for electroosmosis and electrophoresis in PDMS made microfluidic chips. Here, zeta potentials of PDMS surfaces modified by simple physisorption of PEG of different concentrations in phosphate buffer solutions, pure water, and PEG solution were reported. Coating PEG on PDMS surfaces was achieved by immersing a PDMS layer into the PEG solution for 10 min and then taking it out and placing it in an oven at 80℃ for 10 h. To avoid damaging the PEG layer on the PDMS surface, an induction current method was employed for zeta potential measurement. Zeta potentials of PEG modified PDMS in electrolyte solutions were measured. The results show that 2.5% PEG can effectively modify PDMS surface with positive zeta potential value in phosphate buffer solutions, pure water and 10% PEG solution. Further increase in PEG solution beyond 5% for surface modification has no obvious effect on zeta potential change.     

Bulk- and surface-modified combinable PDMS capillary sensor array as an easy-to-use sensing device with enhanced sensitivity to elevated concentrations of multiple serum sample components

To enhance sensitivity and facilitate easy sample introduction into a combinable poly(dimethylsiloxane) (PDMS) capillary (CPC) sensor array, PDMS was modified in bulk and on its surface to prepare "black" PDMS coated with a silver layer and self-assembled monolayer (SAM). India ink, a traditional Japanese black ink, was added to the PDMS pre-polymer for bulk modification. The surface was modified by a silver mirror reaction followed by SAM formation using cysteine. These modifications enhanced the fluorescence signals by reflecting them from the surface and reducing background interference. A decrease in the water contact angle led to enhanced sensitivity and easy sample introduction. Furthermore, a CPC sensor array for multiplex detection of serum sample components was prepared that could quantify the analytes glucose, potassium, and alkaline phosphatase (ALP). When serum samples were introduced by capillary action, the CPC sensor array showed fluorescence responses for each analyte and successfully identified the components with elevated concentrations in the serum samples.     

LAYER-BY-LAYER ASSEMBLY OF NANOZEOLITE BASED ON POLYMERIC MICROSPHERE: ZEOLITE COATED SPHERE AND HOLLOW ZEOLITE SPHERE

ABSTRACT

Zeolite β, silicalite-1, ZSM-5, and TS-1 coated spheres have been prepared successfully through layer-by-layer assembly of nanozeolite/polymer multilayers on polystyrene (PS) microspheres, and hollow zeolite spheres have been obtained by removal of the core by calcination. In the adsorption process of nanozeolites onto the polyelectrolyte-modified template spheres, it has been found that zeta potential of the zeolite colloidal solution that determines the electrostatic interaction has important effects on the zeolite adsorption procedure. The charge on the original sphere template is not necessary, because proper polyelectrolyte modification could change the surface property of the template and make it suitable for layer-by-layer adsorption. The influences of zeolite type and/or size (40–120 nm), the number of zeolite/poly(diallyl-dimethyl-ammonium) layer pairs, and the template sphere size (0.53–10.3 µm) on the preparation of the hollow zeolite spheres were also discussed.     

Influence of chemistry and topology effects on superhydrophobic CF(4)-plasma-treated poly(dimethylsiloxane) (PDMS)

Superhydrophobic surfaces are gaining considerable interest in a lot of different applications, and nonetheless, precise control over the wettability properties of such surfaces is still a challenge due to difficulties when controlling the effects independently induced on superhydrophobicity by the chemical and topological surface characteristics. We have fabricated engineered superhydrophobic surfaces onto poly(dimethylsiloxane) (PDMS) substrates by means of suitable CF4-plasma treatments. These treatments allowed the modification of both the morphological properties of the PDMS surface, due to a preferential etching of certain components of its macromolecules, and the chemical ones, by the deposition of a fluorinated layer. Chemical effects were separated from topological ones by performing a double replica molding process of the CF4-plasma-treated surfaces. This allowed us to obtain positive copies of the structured surfaces without the overlaying fluorinated coating affecting the surface chemistry. Such replicated surfaces showed a decrease of the contact angle if compared to the treated ones and therefore evidenced chemistry's weight in superhydrophobicity effects. In particular, we found that, for highly dense columnar-like PDMS microstructures, the effect of the plasma-deposited fluorinated layer covering surfaces produces an enhancement of the contact angle of about 20 degrees .     

ICP刻蚀硅模板用于PDMS规则超疏水表面的制作

在ICP(inductively coupled plasma)刻蚀后的硅模板上复制聚二甲基硅氧烷(PDMS),经剥离得到含有一定尺寸的规则微柱阵列疏水表面.实验表明,当微柱高度较小时,微柱高度和边长对接触角有正影响,而间距则呈负影响;但如微柱高度较大,则高度对接触角的影响趋小,而边长呈负影响.间距对接触角的影响表现复杂.微柱间距6μm,边长14μm和高14μm微柱阵列的PDMS表面,静态接触角最大,约151°.     

Microscale features and surface chemical functionality patterned by electron beam lithography: a novel route to poly(dimethylsiloxane) (PDMS) stamp fabrication

Poly(dimethylsiloxane) (PDMS) has become a ubiquitous material for microcontact printing, yet there are few methods available to pattern a completed PDMS stamp in a single step. It is shown here that electron beam lithography (EBL) is effective in writing patterns directly onto cured PDMS stamps, thus overcoming the need for multiple patterning steps. Not only does this method allow the modification of an existing lithographic pattern, but new 3D features such as cones, pits, and channels can also be fabricated. EBL can also be used to fabricate PDMS masks for photolithography whereby 1:1 pattern transfer into a photoresist is achieved. Additionally, direct EBL writing of surface chemical features has been achieved using a PDMS stamp coated with a self-assembled monolayer. An electrostatic mechanism appears to be operative in the EBL patterning process, as supported by calculations, thermogravimetric analysis, time-of-flight secondary ion mass spectroscopy, optical and atomic force microscopy, and chemical functionalization assays.     

In situ GISAXS investigation of gold sputtering onto a polymer template

Microphase-separation structures in mixed diblock-triblock copolymer thin films are used for the incorporation of gold atoms inside the polymer matrix via sputtering of gold. Polystyrene (PS) spheres are arranged in a liquidlike type with a well defined nearest neighbor distance inside a polyisoprene matrix acting as a template for directing the gold atoms. Sputtering conditions are selected with a very low sputtering rate to avoid clustering in the atmosphere so that gold reaches the polymer surface in its atomic state. Due to the mobility of the gold atoms and the selective interaction with the PS parts of the microphase separation structure, gold is accumulated inside the polymer film in the PS spheres, as probed in situ with grazing incidence small-angle X-ray scattering (GISAXS). Nominally 4.3 A of gold is deposited, which by diffusion is spread out vertically over a thickness of 280 nm. UV-vis spectroscopy reveals a small blue shift for the gold sputtered polymer film. Atomic force microscopy proves the absence of gold clusters on the film surface. For low sputtering rate, GISAXS proves good sensitivity for gold migration inside the polymer film and opens new possibilities for studying polymer-metal interaction.     

Accessible and Cost-Effective Method of PDMS Microdevices Fabrication Using a Reusable Photopolymer Mold

This work describes a novel and cost-effective method of polydimethylsiloxane (PDMS) microchips fabrication by using a printing plate photopolymer called Flexcel as a master mold (Fmold). This method has demonstrated the ability to generate multiple devices from a single master, reaching a minimum channel size of 25 μm, structures height ranging from 53 to 1500 μm and achieving dimensions of 1270 × 2062 mm², which are larger than those obtained by the known techniques to date. Scanning electron microscopy, atomic force microscopy, and profilometry techniques have been employed to characterize the Fmold and PDMS replicas. The results showed high replication fidelity of Fmold to the PDMS replica. Furthermore, it was proved the reusability of the Fmold. In our study, up to 50 PDMS replicas have been fabricated without apparent degradation of the mold. The feasibility of the resulting PDMS replica was effectively demonstrated using a microfluidic device for enhanced oil recovery analysis. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1433–1442     

Synthesis of nanostructured films from template electrodeposition technique

In this report, the use of a simple and versatile technique of templated electrodeposition through colloidal templates to produce nanostructured films of Pt and Au with regular submicron spherical holes arranged in a hexagonal close-packed structure is described. The templates were produced by self assembly of a monodispersed suspension of polystyrene spheres on gold substrates using capillary forces. The self assembly process was modified through the chemical modification of the gold substrate with cysteamine thiol. Films of Pt and Au were prepared by electrochemical deposition through the template. The electrochemical deposition charge and the current time curve were used to control the film height with a precision of approximately 10 nm. The colour of the nanostructured films changed as the film thickness was changed. On the other hand, high surface area of the nanostructured Pt film on top of the gold substrate was calculated using electrochemical cyclic voltammogram. About 55 roughness factor was obtained. SAXS measurements showed strong scattering at low angles indicating the presence of a well-ordered mesostructure.     

A Simple Method for Fabricating Patterned Curvilinear Microstructures in Poly(dimethylsiloxane) by Selective Wetting

The fabrication of patterned microstructures in poly(dimethylsiloxane) (PDMS) is a prerequisite for soft lithography. Herein, curvilinear surface relief microstructures in PDMS are fabricated through a simple three‐stage approach combining microcontact printing (μCP), selective surface wetting/dewetting and replica molding (REM). First, using an original PDMS stamp (first‐generation stamp) with linear relief features, a chemical pattern on gold substrate is generated by μCP using hexadecanethiol (HDT) as an ink. Then, by a dip‐coating process, an ordered polyethylene glycol (PEG) polymer‐dot array forms on the HDT‐patterned gold substrate. Finally, based on a REM process, the PEG‐dot array on gold substrate is used to fabricate a second‐generation PDMS stamp with microcavity array, and the second‐generation PDMS stamp is used to generate third‐generation PDMS stamp with microbump array. These fabricated new‐generation stamps are utilized in μCP and in micromolding in capillaries (MIMIC), allowing the generation of surface micropatterns which cannot be obtained using the original PDMS stamp. The method will be useful in producing new‐generation PDMS stamps, especially for those who want to use soft lithography in their studies but have no access to the microfabrication facilities.     

Surface enhanced raman scattering of aromatic thiols adsorbed on nanostructured gold surfaces

In this paper we describe the use of a simple and versatile technique of templated electrodeposition through polystyrene sphere templates to produce nanostructured films of gold with regular submicron spherical holes arranged in a hexagonal close-packed structure. The templates were produced by self assembly of a monodispersed suspension of polystyrene spheres on gold substrates using capillary forces. The self assembly process was modified through the chemical modification of the gold substrate with cysteamine thiol. Films of gold were prepared by electrochemical deposition through the template. The electrochemical deposition charge and the current time curve were used to control the film height with a precision of approximately 10 nm. The colour of the nanostructured films changed as the film thickness was changed. Surface enhanced Raman Scattering spectra were recorded and used to identify very low concentrations of aromatic thiol molecules, 4-Nitrobenzenethiol (4-NBT) and 4-Aminobenzenethiol (4-ABT), adsorbed on the surface of the nanostructured gold substrates.      

Design of experiment for optimization of plasma-polymerized octafluorocyclobutane coating on very high aspect ratio silicon molds

As-fabricated deep reactive ion etched (DRIE) silicon mold with very high aspect ratio (>10) feature patterns is unsuitable for poly(dimethylsiloxane) (PDMS) replication because of the strong interaction between the Si surface and the replica and the corrugated mold sidewalls. The silicon mold can be conveniently passivated via plasma polymerization of octafluorocyclobutane (C4F8), which is also employed in the DRIE process itself, to enable the mold to be used repeatedly. To optimize the passivation conditions, we have undertaken a Box-Behnken experimental design on the basis of three passivation process parameters (plasma power, C4F8 flow rate, and deposition time). The measured responses were fluorinated film thickness, demolding status/success, demolding force, and fluorine/carbon ratio on the fifth replica surface. The optimal passivation process conditions were predicted to be an input power of 195 W, a C4F8 flow rate of 57 sccm, and a deposition time of 364 s; these were verified experimentally to have high accuracy. Demolding success requires medium-deposited film thickness (66-91 nm), and the thickness of the deposited films correlated strongly with deposition time. At moderate to high ranges, increased plasma power or gas flow rate promoted polymerization over reactive etching of the film. It was also found that small quantities of the fluorinated surface were transferred from the Si mold to the PDMS at each replication, entailing progressive wear of the fluorinated layer.