Polydimethylsiloxane Template Research Articles

Pushing the Limits of Capillary Assembly for the Arbitrary Positioning of Sub-50nm Nanocubes in Printable Plasmonic Surfaces.

The fabrication of high quality nanophotonic surfaces for integration in optoelectronic devices remains a challenge because of the complexity and cost of top-down nanofabrication strategies. Combining colloidal synthesis with templated self-assembly emerged as an appealing low-cost solution. However, it still faces several obstacles before integration in devices can become a reality. This is mostly due to the difficulty in assembling small nanoparticles (<50 nm) in complex nanopatterns with a high yield. In this study, a reliable methodology is proposed to fabricate printable nanopatterns with an aspect ratio varying from 1 to 10 and a lateral resolution of 30 nm via nanocube assembly and epitaxy. Investigating templated assembly via capillary forces, a new regime was identified that was used to assemble 30-40 nm nanocubes in a patterned polydimethylsiloxane template with a high yield for both Au and Ag with multiple particles per trap. This new method relies on the generation and control of an accumulation zone at the contact line that is thin as opposed to dense, displaying higher versatility. This is in contrast with conventional wisdom, identifying a dense accumulation zone as a requirement for high-yield assembly. In addition, different formulations are proposed that can be used for the colloidal dispersion, showing that the standard water-surfactant solutions can be replaced by surfactant-free ethanol solutions, with good assembly yield. This allows to minimize the presence of surfactants that can affect electronic properties. Finally, it is shown that the obtained nanocube arrays can be transformed into continuous monocrystalline nanopatterns via nanocube epitaxy at near ambient temperature, and transferred to different substrates via contact printing. This approach opens new doors to the templated assembly of small colloids and could find potential applications in various optoelectronic devices ranging from solar cells to light-emitting diodes anddisplays.

Transdermal Microneedle-Mediated Delivery of Rasagiline Nanoparticles.

In the transdermal drug delivery system, the drug is administered through the skin and attains a systemic effect. It is a drug administration route that includes drug transport to the epidermis and potentially dermal tissue of the skin for locally therapeutic effect, while an exceptionally significant drug division is transported in systemic blood circulation. This study aimed to formulate rasagiline mesylate (RM) as a transdermal microneedle (MN) delivery. The RM is an antiparkinson drug that can be classified as class III with low permeability and subjected to extensive first-pass metabolism. At first, it was formulated as nanoparticles using the chitosan polymer and ion gelation method. Afterward, the prepared nanoparticles were incorporated into a transdermal MN formulated by a polydimethylsiloxane template. The two-step casting process uses two polymer concentrations of polyvinyl alcohol and mixes them with other polymers in a 3:1 ratio (polyvinylpyrrolidone and chitosan) and glycerin as a plasticizer. The selected MN formula was MN4 with a promising shape, no bubbles, fine and well-formed sharp needles that passed the folding endurance test with 130 folding times before broken, drug content of 97±10.02%, and ex vivo permeation. The results showed a significant (P>0.05) permeability enhancement and increase of flux (160%), compared to the transdermal patch. The RS polymeric nanoparticles were successfully prepared and loaded within dissolving MNs of sufficient mechanical strength to penetrate the stratum corneum and enhance the amount permeated through it to induce the systemic effect transdermally.

Ultrasensitive Ionic Liquid Polymer Composites with a Convex and Wrinkled Microstructure and Their Application as Wearable Pressure Sensors.

The development of pressure sensors with high sensitivity and effectiveness that exhibit linearity over a wide pressure range is crucial for wearable devices. In this study, we fabricated a novel ionic liquid (IL)/polymer composite with a convex and randomly wrinkled microstructure in a cost-effective and facile manner using an opaque glass and stretched polydimethylsiloxane template. The fabricated IL/polymer composite was used as the dielectric layer in a capacitive pressure sensor. The sensor exhibited a high linear sensitivity of 56.91 kPa-1 owing to the high interfacial capacitance formed by the electrical double layer of the IL/polymer composite over a relatively wide range (0-80 kPa). We also demonstrated the sensor performance for various applications such as a glove-attached sensor, sensor array, respiration monitoring mask, human pulse, blood pressure measurement, human motion detection, and a wide range of pressure sensing. It would be expected that the proposed pressure sensor has sufficient potential for use in wearable devices.

Facile Patterning of Organic Single‐Crystalline Microwire Array for Mode‐Tunable Microlasers and Photodetectors

AbstractThe modulation of organic single‐crystalline micropatterns with ordered alignment and effective output is of great significance to integrated photonic devices as well as optoelectronics. However, it remains an intractable challenge to precisely regulate the crystalline morphology toward specific micropatterns with tunable size, controlled position, and uniform orientation. Here, a combination method with template‐confined self‐assembly and femtosecond laser processing is proposed for the fabrication of large‐scale 1D single‐crystal microwire arrays as high‐quality microlasers and photodetectors. Specifically, the precursor solution of organic semiconductors confined in predefined polydimethylsiloxane template tends to uniaxially crystallize under the guidance of prepatterned linear microchannels, producing highly crystalline and aligned 1D microwire array. Photodetectors based on the 1D microwire array show sensitive and fast responsivity toward 450 nm illumination. Furthermore, the continuous microwire array can be engineered to a series of crystal subunits with tunable lengths through femtosecond laser processing technique. Each microwire subunit can act as a Fabry–Pérot (FP) microcavity resonator for the generation of stable and high‐quality organic laser. This work provides new ideas to obtain highly aligned and size‐controlled microwire arrays based on organic single‐crystalline semiconductors, which contributes to the potential applications in integrated organic lasers and optoelectronics.

Improvement of the comprehensive properties of polymer templates via a novel dry blending method for fabricating OTFT electrodes

Polymer template is widely used in the fabrication of organic thin-film transistor (OTFT) electrodes. However, the mechanical/thermal properties of the polymer template are generally poor owing to their low Young’s modulus (E) and high coefficient of thermal expansion (CTE), resulting in the formation of massive wrinkles and cracks on the OTFT electrodes, as well as the electrodes incomplete transfer, which seriously affects the fabrication of the electrodes. Here, a novel dry blending method is described in which SiO2 nanoparticles are filled into a grooved silicon template, followed by permeation of polydimethylsiloxane (PDMS) into the SiO2 nanoparticle gaps. The SiO2 nanoparticles in the groove are extracted by curing and peeling off PDMS, affording a PDMS/SiO2 composite template with a nanoparticle content of 83.8 wt% and good transparency. The composite template has a Young’s modulus of 16.58 MPa and a CTE of 96 ppm/°C, which constitutes an increase of 91.56 % and a reduction of 69.23 %, respectively, compared with the original PDMS template. Finally, the high performance OTFT electrodes were fabricated using the composite template with good comprehensive properties.

Enhanced performance of superhydrophobic polyvinylidene fluoride membrane with sandpaper texture for highly saline water desalination in air-gap membrane distillation

Here, we report a simple and cost-effective process to fabricate a superhydrophobic Polyvinylidene Fluoride (PVDF) membrane. Four different PVDF membranes were investigated using sandpaper (SP), polydimethylsiloxane (PDMS), stainless steel mesh (SSM), and tempered glass as casting substrate in a non-solvent induced phase separation process. Sandpaper-like texture was replicated on a PVDF membrane using a PDMS template prepared via soft lithography technique. Interestingly, PDMS-based membrane reveals surface with textures depicting the lotus effect. The developed membranes were characterized in terms of their morphology, bulk properties, wetting behavior and MD performance. Among all the membranes developed, PDMS-based textured membrane showed excellent MD performance with high and stable salt rejection at 99.99%, and permeate flux reaching 21 kg m−2 h−1 after a 40-hour test using highly saline water (70 g/L NaCl) in Air-Gap Membrane Distillation (AGMD). Notably, the PVDF membranes developed in this study showed an increase in permeate flux with time due to a decrease in the air gap width as a result of membrane stretching. The textured PVDF membrane that was developed using sandpaper features offers a promising alternative for treating highly saline water in the MD system.

Tropical Climate Adaptation via Biomimicry and Surface Functionalization for Electronic Circuitry

Surface functionalization has diverse applications from tropicalization, superhydrophobicity to chemical bonding and biomolecular applications. Tropical climate adaptability is necessary in order to successfully carry out the equipment’s functionality in extreme climate. Temperature gradient can lead to internal damage and humidity also leads to the surface’s degradation, thus lead to circuits’ shortcuts. Hence this research aimed to fabricate and characterize polydimethylsiloxane (PDMS) based biomimicry and surface functionalization for hydrophobic, fungus free and stable layer against tropical climate. Another nanoparticle that needs to be used to optimize the required criteria is polytetrafluoroethylene (PTFE). Varying the ratio of PDMS/PTFE mixture affects the resulting performance. The composite was layered onto taro leaves using soft-lithography technique. Several of the conventional method limitations were addressed such as water contact angle (WCA) and light transmittance. The overall average WCA of a PDMS/PTFE template obtained was between 92° until 108° whereas for a negatively replicated PDMS/PTFE template was between 121° until 131°. The plain PDMS template shows the average transmittance of 62.28% whereas the PDMS/PTFE template shows the average of less than 7.49% transmittance. The negatively replicated leaf PDMS/PTFE template shows the average transmittance percentage of 15.772% and a minimum of less than 2%. The obtained WCA results had proven that the soft-lithography technique is able to increase the surface wettability of equipment.

Superior nanopatterns via adjustable nanoimprint lithography on aluminum oxide in high-K thin films with ultraviolet curable polymer.

The present study substantiate that ultraviolet-nanoimprint lithography (UV-NIL) can be used to transfer a one-dimensional nano-pattern onto a high-k thin film of aluminum oxide mixed with a UV photocuring agent. Polydimethylsiloxane (PDMS) molds fabricated on silicon wafers were made using deep ultraviolet laser interference lithography in order to investigate one-dimension nanopatterns. These imprinted nano-patterns induce geometric deformations in the liquid crystal (LC), creating collective and elastic properties, which act as a guide for homogeneous alignment. The nanoimprint method can process a large area, so it can be processed much easier, faster, and more accurately than the conventional rubbing method. Moreover, the optical properties of the nano-imprinted aluminum oxide (AlO) thin-film are about 1.5p% superior to that of conventional commercialized cells, so it has a high effect on the luminance and color gamut of the display. After pattern imprinting, atomic force microscope (AFM) was performed to confirm the result. We can compared the cycle of AlO mixed with UV photocuring agent PDMS pattern cycle, the period is 776 and 750 nm, the width is 468 and 450 nm, the spacing is 292 and 300 nm, and the height is 40 and 30 nm. The nano-imprinted film appears to replicate the width, amplitude, and spacing of the PDMS template. In addition, X-ray photoelectron spectroscopy was performed to determine the chemical properties of the thin film and it was confirmed that UV irradiation induces oxidation, thus increases the intensity significantly. The binding energies of Al 2p and C–O spectra were situated at 74.27 ± 0.5 eV and 531.78 ± 0.5 eV, respectively.

Controlled growth of organic single-crystal arrays on hydrophobic substrate surface for high-performance transistors

<p indent="0mm">Optoelectronic devices such as organic field-effect transistors (OFETs) and organic light-emitting diodes are expected to achieve low-cost flexible optoelectronic applications, but the low-cost potential depends on the capability of large-area deposition of organic semiconducting single-crystal (OSSC) arrays based on solution methods. However, poor surface-wetting behavior and sophisticated fluid kinetics limit solution deposition of large-scale OSSC arrays. Herein, the wetting-ability and fluid drying dynamics were improved by adding trace surfactants, and the affinity between organic solution and hydrophobic surface was also enhanced. In addition, the groove structures of polydimethylsiloxane templates were used as confined spaces for the nucleation, crystallization, and growth of OSSCs, and finally an OSSC array over large areas was prepared. This strategy has good universality for materials and patterns. OFETs based on the OSSC array show good performance and uniformity. These illustrations will provide more opportunities for integrated applications of organic single-crystal devices.

A Customizable DNA and Microsphere-Based, Magnetically Actuated Microswimmer

Locomoting microscale robots—microswimmers—have the potential to impact numerous applications due to their ability to selectively interact with their environment with microscale control. Previous microswimmer designs lack either submicron-level precision over their construction or instantaneous control over their shape. Thus, existing microswimmer designs limit the control afforded over microswimmer interactions with their environment. This work presents a magnetically actuated microswimmer constructed from DNA and microspheres in a hybrid top-down and bottom-up assembly technique that allows for submicron-level precision over microswimmer body construction. Microscale features were fabricated via two-photon polymerization, from which polydimethylsiloxane templates were molded. Templated assembly by selective removal was used to deposit microspheres of select size and composition into the templates. This technique was confirmed to be size-selective within a population of microspheres. To construct the microswimmer, a ferromagnetic microsphere and a nonmagnetic microsphere were deposited into a template, connected with DNA nanotubes in their arrangement, magnetized, and pulled from the template. We demonstrate instantaneous control over shape changes via expansion and contraction of a microswimmer’s body in an external magnetic field. In a rotating magnetic field of constant magnitude, the microswimmer expanded as the two microspheres separated a distance of 4.1± 0.5 micrometers, approximately the distance between microspheres deposited in the template. In an oscillating magnetic field, the same microswimmer contracted and locomoted 58.8± 0.7 micrometers over 126 seconds. [2020-0183]

A novel dry-blending method to reduce the coefficient of thermal expansion of polymer templates for OTFT electrodes

Among the patterning technologies for organic thin-film transistors (OTFTs), the fabrication of OTFT electrodes using polymer templates has attracted much attention. However, deviations in the electrode alignment occur because the coefficient of thermal expansion (CTE) of the polymer template is much higher than the CTE of the dielectric layer. Here, a novel dry-blending method is described in which SiO2 nanoparticles are filled into a grooved silicon template, followed by permeation of polydimethylsiloxane (PDMS) into the SiO2 nanoparticle gaps. The SiO2 nanoparticles in the groove are extracted by curing and peeling off PDMS to prepare a PDMS/SiO2 composite template with a nanoparticle content of 83.8 wt %. The composite template has a CTE of 96 ppm/°C, which is a reduction by 69.23% compared with the original PDMS template. Finally, we achieved the alignment of OTFT electrodes using the composite template.

Customized Kirigami Electrodes for Flexible and Deformable Lithium-Ion Batteries.

Customized deformable lithium-ion batteries (LIBs) have attracted interest in the emerging power systems for flexible and wearable electronics. However, a key challenge for developing these batteries is the fabrication of customized deformable electrodes that exhibit strong mechanical tolerance and robust electrochemical performance during deformation. Here, free-standing customized kirigami electrodes for deformable LIBs are fabricated by an evolutionary printing method with universal viscous electrode inks and a customizable polydimethylsiloxane template. The electrodes comprise lithium iron phosphate or lithium titanium oxide nanoparticles with a conductive carbon nanotubes/poly(vinylidene fluoride) scaffold, which is ideal for electron transfer. The compact microstructure and kirigami pattern endow the electrodes with superior mechanical robustness (over 500 stretch-release cycles) and resistance stability both in unstretched and stretched states. Finite element analysis and corresponding experiment tests reveal ultralow strain inside the materials, showing less than 3% strain even under 100% stretch ratio. With 500-times stretched electrodes, the full-cell LIBs can still deliver a considerable discharge capacity of average 94.5 mA h g-1 at 0.3 C after 100 discharge/charge cycles. The integration of such outstanding mechanical stability, excellent electrochemical performance, and simple printing method with accessible starting materials presents promising opportunities for customizing deformable components for flexible energy storage devices.

Biomimetic Meta‐Structured Electro‐Microfluidics

AbstractFlexible membranes (i.e., paper, cloth, and polydimethylsiloxane (PDMS)) have received extensive attention. The rapid development of flexible microfluidics and electronics and their integration calls for complex substrate structures to allow for multiple functions. Inspired by nature, meta‐structured membranes (MSMs) as substrates for fabricating integrated microfluidics and electronics are presented. These flexible and freestanding MSMs are generated by the self‐assembly of elastic plastic copolymer nanoparticle photonic crystals on micropatterned PDMS templates. The final MSMs constitute with integrated ordered micro‐ and nanostructures and exhibit spontaneous liquid transfer, fluorescence enhancement, and intimate skin contact. MSMs with designed patterns can be fabricated by assembling polymer nanoparticles on patterned molds; complicated and highly integrated electro‐microfluidics are generated on one slice of MSMs by utilizing these patterns as microfluidic channels and electrocircuits. They can be used as chip‐on‐skin sensors for biochemical–physiological hybrid monitoring sensing of the human body and as organ chips for cell culture and metabolite analysis under drug treatment. Their excellent properties show their potential value in cross‐scale sensing and have broad potential applications.

Fabrication and Measurement of Microtip Electrode Array Integrated With Self-Aligned Hemispherical Cell Trapping PDMS Template

This paper presents a novel microtip electrode array integrated with a self-aligned cell trapping polydimethylsiloxane (PDMS) template. Cells can be captured in the hemispherical PDMS template using the ultrasonic assembly technique, and their electrochemical responses can be measured using the microtip electrode positioned at the center of the template. The hemispherical PDMS template can be integrated with the microtip electrode through a sequential process of copper electroplating in a spherical form at the tip end, PDMS coating, and etching of PDMS and electroplated copper, in which an additional photolithography process is not required. The fabricated microtip electrode array integrated with the PDMS template was examined using cyclic voltammetry measurements and applied to the measurements of oxygen reduction current from the photosynthetic reaction of captured chlorella cells in the PDMS template.

SERS amplification by ultra-dense plasmonic arrays on self-organized PDMS templates

High density gold nanostructures are grown by thermal deposition on flat and nanostructured polymeric templates by exploiting the extraordinarily low wettability of Au on polydimethylsiloxane (PDMS). Undulated PDMS templates are fabricated by replica molding process (REM) on “masters” prepared by defocused Ion Beam Sputtering (IBS). Closely packed and laterally disconnected Au nanostructures are grown at grazing incidence on the PDMS replica templates exploiting the shadowing instability. The peculiar nanocluster morphology determines a Localized Surface Plasmon Resonances (LSPR) which is tunable in the visible range by varying light polarization and metal dose. All samples exhibit a strong increase of the Surface Enhanced Raman Scattering (SERS) intensity with amplification factors exceeding 103.

Facile preparation of superhydrophobic PDMS with patternable and controllable water adhesion characteristics

Control of water adhesion is important for superhydrophobic surfaces in various applications. In this work, we present a facile approach to prepare superhydrophobic polydimethylsiloxane (PDMS) with patternable and controllable water adhesion capabilities. Surface grafting of N-isopropylacrylamide was primarily exploited to regulate the PDMS template morphologies, either by tuning the ultraviolet irradiation duration or adopting repeated grafting process. The surface topologies of as-prepared PDMS templates can be flexibly constructed with roughness degrees ranging widely from 1.5 to 738.7 nm. Followed with covering of carbonyl iron particles (CIP) on the template surface, the duplicated PDMS substrate can thus recur the surface topology incorporated with CIP onto the upper surface, leading to the feasibility to regulate diverse water adhesion capabilities. Owing to the synergistic effect by the surface roughness and CIP incorporation, the water adhesion capabilities of the PDMS substrates can be flexibly tuned ranging from droplet pinning to excellent water repellency. The presented strategies were further developed to create PDMS substrates with patterned water adhesion for controllable micro-droplet transportation or rapidly programmable droplet localizations. We believe that the environmentally friendly method can offer as a convenient yet cost-effective tool for future microfluidic devices, biochemical analysis, etc.

Optical properties of a biomimetically prepared hierarchical structured polydimethyl siloxane template for potential application in anti-reflection and photovoltaic encapsulation

This paper describes optical studies on a polydimethyl siloxane (PDMS) surface biomimicked from rose petals. The textured PDMS membrane showed hierarchical nanostructures and significantly improved optical transmittance (96%; 400–1400 nm), and also indicated good superhydrophobic and self-cleaning properties. The average optical reflectance obtained was as low as 3% within a broad wavelength range of 400–1400 nm. Furthermore, an optical degradation analysis in the ambient atmosphere under varying weather conditions (46–4 °C) for a period of 12 months indicated a slow rate of decline in the optical properties of the hierarchical structured PDMS surface with negligible moisture permeation.

A Facile in Situ and UV Printing Process for Bioinspired Self-Cleaning Surfaces.

A facile in situ and UV printing process was demonstrated to create self-cleaning synthetic replica of natural petals and leaves. The process relied on the spontaneous migration of a fluorinated acrylate surfactant (PFUA) within a low-shrinkage acrylated hyperbranched polymer (HBP) and its chemical immobilization at the polymer-air interface. Dilute concentrations of 1 wt. % PFUA saturated the polymer-air interface within 30 min, leading to a ten-fold increase of fluorine concentration at the surface compared with the initial bulk concentration and a water contact angle (WCA) of 108°. A 200 ms flash of UV light was used to chemically crosslink the PFUA at the HBP surface prior to UV printing with a polydimethylsiloxane (PDMS) negative template of red and yellow rose petals and lotus leaves. This flash immobilization hindered the reverse migration of PFUA within the bulk HBP upon contacting the PDMS template, and enabled to produce texturized surfaces with WCA well above 108°. The synthetic red rose petal was hydrophobic (WCA of 125°) and exhibited the adhesive petal effect. It was not superhydrophobic due to insufficient concentration of fluorine at its surface, a result of the very large increase of the surface of the printed texture. The synthetic yellow rose petal was quasi-superhydrophobic (WCA of 143°, roll-off angle of 10°) and its self-cleaning ability was not good also due to lack of fluorine. The synthetic lotus leaf did not accurately replicate the intricate nanotubular crystal structures of the plant. In spite of this, the fluorine concentration at the surface was high enough and the leaf was superhydrophobic (WCA of 151°, roll-off angle below 5°) and also featured self-cleaning properties.

Surface‐Grafted Nanogel Arrays Direct Cell Adhesion and Motility

It has long been appreciated that material chemistry and topology profoundly affect cell adhesion and migration. Here, aqueous poly(N‐isopropyl acrylamide) nanogels are designed, synthesized and printed in form of colloidal arrays on glass substrates using wrinkled polydimethylsiloxane templates. Using low‐temperature plasma treatment, nanogels are chemically grafted onto glass supports thus leading to highly stable nanogel layers in cell culture media. Liquid cell atomic force microscopy investigations show that surface‐grafted nanogels retain their swelling behavior in aqueous media and that extracellular matrix protein coating do not alter their stability and topography. It is demonstrated that surface‐grafted nanogels could serve as novel substrates for the analysis of cell adhesion and migration. Nanogels influence size, speed, and dynamics of focal adhesions and cell motility forcing cells to move along highly directional trajectories. Moreover, modulation of nanogel state or spacing serves as an effective tool for regulation of cell motility. It is suggested that nanogel arrays deposited on solid surfaces could be used to provide a precise and tunable system to understand and control cell migration. Additionally, such nanogel arrays will contribute to the development of implantable systems aimed at supporting and enhancing cell migration during, for instance, wound healing and tissue regeneration.

Microstructured Hydrogel Templates for the Formation of Conductive Gold Nanowire Arrays.

Microstructured hydrogel allows for a new template-guided method to obtain conductive nanowire arrays on a large scale. To generate the template, an imprinting process is used in order to synthesize the hydrogel directly into the grooves of wrinkled polydimethylsiloxane (PDMS). The resulting poly(N-vinylimidazole)-based hydrogel is defined by the PDMS stamp in pattern and size. Subsequently, tetrachloroaurate(III) ions from aqueous solution are coordinated within the humps of the N-vinylimidazole-containing polymer template and reduced by air plasma. After reduction and development of the gold, to achieve conductive wires, the extension perpendicular to the long axis (width) of the gold strings is considerably reduced compared to the dimension of the parental hydrogel wrinkles (from ≈1 μm down to 200-300 nm). At the same time, the wire-to-wire distance and the overall length of the wires is preserved. The PDMS templates and hydrogel structures are analyzed with scanning force microscopy (SFM) and the gold structures via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy. The conductivity measurements of the gold nanowires are performed in situ in the SEM, showing highly conductive gold leads. Hence, this method can be regarded as a facile nonlithographic top-down approach from micrometer-sized structures to nanometer-sized features.