Soft Mold Research Articles

Formulation, Characterizations and Antibacterial Activity of some Nanoemulsions Incorporating Monoterpenes

In the current study, we formulated and characterized bio-based oil in water nanoemulsions incorporating monoterpenes; (R)-carvone, cinnamaldehyde, citral, geraniol and pulegone and tested their antimicrobial activity against two plant pathogenic bacteria, Pectobacterium carotovorum sub carotovorum and Ralstonia solanacearum in vitro and in vivo studies. Nanoemulsions (NEs) were prepared by adding dropwise monoterpenes at concentration of 5% in an aqueous solution containing 10% a surfactant (tween 80) with constant stirring and then ultrasonication. NEs were confirmed by dynamic light scattering and transmission electron microscopy. Physical stability and viscosity were, also, investigated. NEs monoterpenes had a poly dispersity index ranged from 0.130 to 0.630 and droplet size in the range of 56.64-176.00 nm. Results revealed that NE -cinnamaldehyde had great antibacterial activity against P. carotovorum and R. solanacearum (MIC = 60 and 100 mg/L, respectively). NE cinnamaldehyde was induced effective defense responses in vivo in potato plant and tubers against two tested bacteria at a rate 1000 and 3000 mg/kg. Higher activities of polyphenoloxidase (PPO), peroxidase (POD) activities and total phenolic content of tubers and leaves were significantly recorded compared to control at all tested times. This was evident from reduced soft and brown rot diseases symptoms of potato spunta cv treated with elicitors subsequently with tested bacteria. These results showed that the PPO, POD and total soluble phenols play a role in instructing resistance to potato soft and brown mold infections. The observed relationship between formulation and activity can lead to the rational design of nanoemulsion based systems for monoterpenes for applications in antimicrobial and agrochemical industries. Amalgamation of such economical treatments might lessen management costs and minimize the environmental pollution.

Surface plasmons superresolution nanolithography technique by using polydimethylsiloxane soft mold based on light coupling

We proposed a novel surface plasmons (SP) nanolithography technique based on light coupling, which adopts the polydimethylsiloxane (PDMS) soft mold to replace the ordinary hard mask. By using the light coupling effect of PDMS mold and the SP resonance effect of silver layer, the nanolithography technique could realize the superresolution lithography with a resolution of 1/10 of exposure wavelength and a high contrast ratio of 0.97. By the numerical simulation, we calculated the electric field distribution, analyzed the influence of the linewidth of PDMS soft mold and the thickness of silver layer on the proposed nanolithography system. The calculated results indicate the physics mechanism that the silver layer acts not only as an amplifier for high-frequency energy, but also as a blocker for the low-frequency energy. The optimal linewidth and silver layer thickness are obtained, which can promote the contrast ratio to 0.99.

Fabrication of high fill-factor microlens array using spatially constrained thermal reflow

In this paper, we introduce a simple method for fabricating high fill-factor microlens array using a novel spatially constrained thermal reflow process. The major difference with the conventional methods is that the proposed thermal reflow is conducted in polydimethylsiloxane (PDMS) solution instead of in the air. During the reflow process, PDMS would serve as a barrier to prevent the merging of adjacent microlenses which is usually a big obstacle of achieving high fill-factor in conventional thermal reflow methods. Moreover, for the microlenses are spatially constrained by the PDMS, the reflow process is very stable and much easier to control. To give a good understanding of the process, theoretical models are also established. Experimental results showed that almost 100% fill-factor and relative PDMS soft mold could be obtained efficiently and easily, and the microlens was good in both shape and surface quality. The proposed method may provide a low-cost and accurate method for fabricating high fill-factor microlens array in a very simple way.

Polyurethane-acrylate-based hydrophobic film: Facile fabrication, characterization, and application

Polyurethane-acrylate (PUA) is a versatile UV-curable polymer with a short curing time at room temperature, whose surface structure can be flexibly modified by applying various micropatterns. In this paper, we propose a facile and cost-effective fabrication method for the continuous production of an optically transparent PUA-based superhydrophobic thin film. Poly(dimethylsiloxane) (PDMS) was employed as a soft mold for the fabrication of PUA films through the roll-to-roll technique. In addition, nanosilica was spray-coated onto the PUA surface to further improve the hydrophobicity. The fabricated PUA thin film showed the highest static water contact angle (WCA) of ∼140°. The high durability of the PUA film was also demonstrated through mechanical impacting tests. Furthermore, only ∼2% of voltage loss was observed in the solar panel covered with the PUA-based superhydrophobic film. These obtained results indicate the feasibility of applying the film as a protective layer in applications requiring a high transparency and a self-cleaning effect.

Fabrication of microlens array with well-defined shape by spatially constrained thermal reflow

We demonstrate a novel method for fabricating a well-defined and large-area microlens array combining digital micro-mirror device (DMD)-based lithography and spatially constrained thermal reflow. Using the flexible processing ability of DMD-based lithography, a micro pillar array is easily prepared on a glass substrate and then the microlens array is formed after a thermal reflow process. Differing from conventional approaches, the proposed thermal reflow process is conducted in polydimethylsiloxane (PDMS) solution instead of in the air. During the process, the partly cured PDMS can effectively prevent the photoresist crawling in the diameter direction, which is very convenient for controlling the precise shape of the microlens. In addition, the photoresist microlens array and PDMS soft mold with a concave cavity array can be achieved in one step. The experimental results showed that the photoresist microlens was good in both shape and surface quality. The presented method may offer great promise for fabricating a high-quality microlens array with different requirements in optical applications.

Direct soft imprint of chalcogenide glasses

The authors explored an approach for nanostructuring of surfaces of chalcogenide glasses by direct soft nanoimprint lithography. The authors produced soft nanoimprint molds with microsized and nanosized relief features using polydimethylsiloxane. To enable the direct replication of the mold pattern on the surface of bulk chalcogenide glasses, the authors engineered a thermal imprint tool that prevents the substrate deformation using a physical confinement. The authors optimized the imprint process parameters to achieve an unprecedented full transfer micropattern onto a bulk chalcogenide glass. Furthermore, the authors explored pattern replication of nanosized structures by thermal imprint. This process paves the way for a facile and cost-effective fabrication of nanostructures on chalcogenide glasses and their numerous applications in optical and photonic devices.

Anodized Aluminum Oxide/Polydimethylsiloxane Hybrid Mold for Roll‐to‐Roll Nanoimprinting

AbstractTwo types (hard and soft) of the molds are widely used in nanoimprint lithography for a high throughput over a large area, and high‐resolution parallel patterning. Although hard molds have proven excellent resolutions and can be used at high temperatures, cracks often occur in the mold in addition to the requirement of high imprinting pressure. On the other hand, though soft molds can operate at lower pressures, they give poor pattern resolution. Here, a novel hybrid mold of anodized aluminum oxide (AAO) template attached to a flexible polydimethylsiloxane (PDMS) plate is introduced. Due to the flexible nature of PDMS, various polymer nanostructures are obtained on flat and curved substrates without crack formation on the AAO mold surface. Furthermore, the hybrid mold is successfully used for roll‐to‐roll imprinting for the fabrication of high density array of various shaped polymeric nanostructures over a large area.

Integrated System of Thermal/Dimensional Analysis for Quality Control of Metallic Melt and Ductile Iron Casting Solidification

The main objective of the present work is to introduce a specific experimental instrument and technique for simultaneously evaluating cooling curves and expansion or contraction of cast metals during solidification. Contraction/expansion analysis illustrates the solidification parameters progression, according to the molten cast iron characteristics, which are dependent on the melting procedure and applied metallurgical treatments, mold media rigidity and thermal behavior [heat transfer parameters]. The first part of the paper summarizes the performance of this two-mold device. Its function is illustrated by representative shrinkage tendency results in ductile cast iron as affected by mold rigidity (green sand and furan resin sand molds) and inoculant type (FeSi-based alloys), published in part previously. The second part of the paper illustrates an application of this equipment adapted for commercial foundry use. It conducts thermal analysis and volume change measurements in a single ceramic cup so that mold media as well as solidification conditions are constants, with cast iron quality as the variable. Experiments compared gray and ductile cast iron solidification patterns. Gray iron castings are characterized by higher undercooling at the beginning and at the end of solidification and lower graphitic expansion. Typically, ductile cast iron exhibits higher graphitic, initial expansion, conducive for shrinkage formation in soft molds.

Characterization of 3D-Printed Moulds for Soft Lithography of Millifluidic Devices.

Increased demand for inexpensive and rapid prototyping methods for micro- and millifluidic lab-on-a-chip (LOC) devices has stimulated considerable interest in alternative cost-effective fabrication techniques. Additive manufacturing (AM)—also called three-dimensional (3D) printing—provides an attractive alternative to conventional fabrication techniques. AM has been used to produce LOC master moulds from which positive replicas are made using soft-lithography and a biocompatible elastomer, poly(dimethylsiloxane) (PDMS). Here we characterize moulds made using two AM methods—stereolithography (SLA) and material-jetting (MJ)—and the positive replicas produced by soft lithography and PDMS moulding. The results showed that SLA, more than MJ, produced finer part resolution and finer tuning of feature geometry. Furthermore, as assessed by zebrafish (Danio rerio) biotoxicity tests, there was no toxicity observed in SLA and MJ moulded PDMS replicas. We conclude that SLA, utilizing commercially available printers and resins, combined with PDMS soft-lithography, is a simple and easily accessible technique that lends its self particularly well to the fabrication of biocompatible millifluidic devices, highly suited to the in-situ analysis of small model organisms.

Soft mold NanoImprint Lithography: a versatile tool for sub-wavelength grating applications

Due to its independency to the substrate used, Soft mold NanoImprint Lithography (S-NIL) is a technique of great interest in particular for the fabrication of optical devices. We demonstrate a mature pathway for the fabrication of optical filters from the conception to the optical characterization. Those filters can be fabricated on large surfaces (up to 6″ diameter wafers) with high conformity on various substrates. Quality of the transfer will be discussed throughout the process and optical performances compared to those obtained with classical techniques. In this paper we fabricated tunable spectral filters with a grating periodicity down to 260 nm and imprint surfaces up to 6″. Physical conformity of the gratings will be discussed in terms of long-range stitching obtained on 6″ Si hard mold, dimensional shrinkage during thermal NanoImprint on Zeonor® soft mold and conformity towards patterned hard mold throughout the process.

Study on imprinting and replica molding of quasi-grey scale soft mold curved surface microstructure mold

The aim of this paper is to fabrication of quasi-greyscale microstructures by curved surface soft magnetic mold. In this paper, a photocuring system is first developed and built independently, then created the magnetic curved surface microstructure soft mold, the magnetic force of the magnetic curved surface via to different heights was obtained after tested and recorded. The experimental results show that, under different surface curvatures and voltage control conditions, will have different quasi-grey scale array microstructures. In addition, this paper conducts research on the imprinting and replica molding of photoresist composite magnetic powder in order to discuss the formability of magnetic photoresist, and finally, the experimental result is combined with the simulation to obtain more accurate prediction and results.

Polymer Periodic Nanostructures on Curved Substrates by UV-Curable Hybrid Soft Nanoimprint Lithography

With rapidly developing nonplanar flexible electronics and photonics devices, high-throughput and low-cost fabrication of polymer periodic nanostructures on curved substrates has become a significant research area. Herein, we report fabrication of different polymer periodic nanostructures directly on cylinder substrate by using hybrid soft nanoimprint lithography (NIL) at room environment. The composite stamp was made up of hybrid soft nanoimprint mold that includes a thin rigid features layer and thick elastomeric poly(dimethylsiloxanes) (PDMS) support layer. Ultraviolet (UV)-curable thiol-ene material has good properties, such as low viscosity, high resolution, rapid reaction rate in benign ambient, and is particularly suitable as nanoimprint resist. Periodic nanopillar arrays, nanoscale hole arrays, and nanograting were fabricated on large-area curved substrate based on this new method. The nanostructures had high resolution and were precisely distributed uniformly onto the curved surfaces.

Wetting Regimes for Residual-Layer-Free Transfer Molding at Micro- and Nanoscales

Transfer molding offers a low-cost approach to large-area fabrication of isolated structures in a variety of materials when recessed features of the open-faced mold are filled without leaving a residual layer on the plateaus of the mold. Considering both macroscale dewetting and microscale capillary flow, a proposed map of wetting regimes for blade meniscus coating provides a guide for achieving discontinuous dewetting at maximum throughput. Dependence of meniscus morphology on the azimuthal orientation of the stamp provides insight into the dominant mechanisms for discontinuous dewetting of one-dimensional (1-D) patterns. Critical meniscus velocity is measured and residual-layer-free filling is demonstrated for 1-D patterned soft molds (stamps) with periods ranging from 140 nm to 6 μm. Transfer of isolated lines, and multilayer woodpile structures were achieved through plasma bonding. These results are relevant to other roll-to-roll compatible processes for scalable production of high-resolution structures across large areas.

Fabrication of engineered particle-doped light diffuser with a soft transparent mold of UV-curable polymer

Engineered particle-doped light diffuser is realized by a simple, low-cost soft lithographic method. A flexible photopolymerizable mold is employed as an intermediate transferring template directly from the developed photoresist texture to fabricate engineered particle-doped light diffuser. The well-designed surface microstructure can directionally scatter the incident light, while the doped ultra-violet curable resin with low concentration of the 2 μm-diameter organosilicone particles can homogenize the scattering light without decreasing transmittance. Experimental results show that the measured transmittance can be as high as 96.9% with little backscattering effect over the whole visible regime. Meanwhile, the haze raises from 30% to 75% with increased dopant concentration from 1 wt% to 7 wt% and thickness of the residual layer from 10 μm to 40 μm remained in the imprinting process. The proposed engineered particle-doped light diffuser can manage scattering angle, luminance uniformity and haze, thus it has the capability of homogenizing light and eliminating striations to create more visually pleasing structured lighting in commercial and residential environments. We anticipate that the approach appears to be a strong candidate for future development because of its scalable nature, environmentally-friendly process and relatively low cost.

Impact of Implant Surface Micropatterns on Epithelial Cell Behavior.

This study investigated the effect of topography on cell behavior by screening polydimethylsiloxane (PDMS) molds with different nanoscale micropatterns to determine the ideal surface characteristics for attachment of human epithelial cells. A soft PDMS mold with regular dot arrays was fabricated based on an aluminum oxide template with ordered nanotube arrays and used as a substrate for cell culture. Cell proliferation, spread, and morphology, as well as features of the extracellular matrix and the actin cytoskeleton were assessed. Cells grown on 100-nm regular dot arrays had the highest proliferation rate and spread, with the longest pseudopodia; they showed robust actin distribution relative to the control group. Three-dimensional PDMS microstructures with 100 nm regular dot arrays were the most effective surface for epithelial cell attachment. These findings can aid in the manufacture of superior materials for use in implants to better integrate into recipient tissue.

Fully-Polymeric pH Sensor Realized by Means of a Single-Step Soft Embossing Technique.

We present here an electrochemical sensor microsystem for the monitoring of pH. The all-polymeric device is comprised of a cyclic olefin copolymer substrate, a 200 nm-thin patterned layer of conductive polymer (PEDOT), and a 70 nm electropolymerized layer of a pH sensitive conductive polymer (polyaniline). The patterning of the fluidic (microfluidic channels) and conductive (wiring and electrodes) functional elements was achieved with a single soft PDMS mold via a single embossing step process. A post-processing treatment with ethylene glycol assured the functional enhancement of the electrodes, as demonstrated via an electrical and electrochemical characterization. A surface modification of the electrodes was carried out, based on voltammetric electropolymerization, to obtain a thin layer of polyaniline. The mechanism for pH sensing is based on the redox reactions of the polyaniline layer caused by protonation. The sensing performance of the microsystem was finally validated by monitoring its potentiometric response upon exposure to a relevant range of pH.

3D whispering-gallery-mode microlasers by direct laser writing and subsequent soft nanoimprint lithography.

We demonstrate the realization of 3D whispering-gallery-mode (WGM) microlasers by direct laser writing (DLW) and their replication by nanoimprint lithography using a soft mold technique ("soft NIL"). The combination of DLW as a method for rapid prototyping and soft NIL offers a fast track towards large scale fabrication of 3D passive and active optical components applicable to a wide variety of materials. A performance analysis shows that surface-scattering-limited Q-factors of replicated resonators as high as 1×105 at 635nm can be achieved with this process combination. Lasing in the replicated WGM resonators is demonstrated by the incorporation of laser dyes in the target material. Low lasing thresholds in the order of 15 kW/cm2 are obtained under ns-pulsed excitation.

3D multiscale controlled micropatterning of lead-free piezoelectric electroceramics via Epoxy Gel Casting and lift-off

We report on the fabrication of multiscale three-dimensional (3D) micropatterning of 0.5Ba(Zr0.2Ti0.8)O3−0.5(Ba0.7Ca0.3)TiO3 (BZT−BCT) electroceramic material using soft lithographic PDMS moulds. The ceramic microcomponents were successfully consolidated by Epoxy Gel Casting from stable aqueous suspension of BZT-BCT material. A successful aqueous processing of electroceramic material was employed with surface protection of powder particles against hydrolysis as considerably an important parameter to achieve high solid loading suspension with pseudoplastic behaviour suitable for casting in micro scale moulds. The process to obtain micro sized pattern of material was divided in two steps: (i) production of high quality SU-8 master moulds and the respective negative replicas in PDMS (soft mould) by photolithography and soft mould replication, respectively; (ii) casting the soft moulds by stable high solid loading BZT-BCT suspensions in presence of gelation agents followed by de-moulding, drying and sintering. The resulting green micropattern structures show interesting features, including complex structures with a periodic variations through their length and, multiscale array of hexagonal shaped pillars of different aspect ratios (AR) (max AR≈8 with approx ∼320μm of height and side length ∼40μm) with smooth side wall features along height. The green pillar arrays were further sintered to show the suitability of aqueous processing of material and proposed casting method.

Wafer‐Scale Highly Ordered Anodic Aluminum Oxide by Soft Nanoimprinting Lithography for Optoelectronics Light Management

The porous anodic aluminum oxide (AAO) membranes have been intensively studied as nanoscale templates for material fabrication. However, the preparation of large‐area highly ordered AAO remains a challenge. In this work, the large‐area soft polydimethylsiloxane mold is employed to transfer the nanopatterns onto Al foil substrates by UV nanoimprinting lithography. It is found that the anodizing behaviors are closely related to the electric field profiles, which can be defined by the morphologies of nanoindentations. The first‐step anodization carried out on the chemical etched patterns leads to some sub‐pores randomly distributed in the main channels. After removal of the as‐formed oxide layer, the stepwise second anodization produces highly ordered inverted nanocone AAO structure. In order to explore the potential application as high‐performance light management nanostructure, electromagnetic simulations are performed on thin‐film perovskite (CH3NH3PbI3) photodetectors using the inverted nanocone AAOs as a substrate. The results indicate that the nanotextured substrate delivers a much higher absorption property than the flat counterpart, demonstrating a promising application for high‐performance optoelectronic devices.

Periodic upright nanopyramid fabricated by ultraviolet curable nanoimprint lithography for thin film solar cells

In this work, a periodic upright nanopyramid structure was developed for light harvesting applications suitable for thin film solar cells. The periodic inverted nanopyramid structure was fabricated on Si substrate by laser interference lithography (LIL) and subsequent pattern transfer by combined reactive ion etching and KOH wet etching. The silicon substrate was used as a master mould in the replication process utilising ultraviolet curable nanoimprint lithography (UV-NIL) process. The inverted nanopyramid patterns were transferred onto OrmoStamp resist layer to form upright pyramids on glass substrates by UV-NIL. The replicated periodic upright nanopyramid structures can be used as light trapping structures in thin film solar cells and as soft mould in the 3D imprint process.