Thermal Imprint Research Articles

Fabrication of Nanostructured Polycaprolactone (PCL) Film Using a Thermal Imprinting Technique and Assessment of Antibacterial Function for Its Application.

In the use of the medical devices, it is essential to prevent the attachment of bacteria to the device surface or to kill the attached bacteria. To kill bacteria, many researchers have used antibiotics or studied nanostructure-based antibacterial surfaces, which rely on mechanical antibacterial methods. Several polymers are widely used for device fabrication, one of which is polycaprolactone (PCL). PCL is biocompatible, biodegradable, easy to fabricate using 3D printing, relatively inexpensive and its quality is easily controlled; therefore, there are various approaches to its use in bio-applications. In addition, it is an FDA-approved material, so it is often used as an implantable material in the human body. However, PCL has no inherent antibacterial function, so it is necessary to develop antibacterial functions in scaffold or film-based PCL medical devices. In this study, process parameters for nanopillar fabrication were established through a simple thermal imprinting method with PCL. Finally, a PCL film with a flexible and transparent nanopillar structure was produced, and the mechano-bactericidal potential was demonstrated using only one PCL material. PCL with nanopillars showed bactericidal ability against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) bacteria cultured on its surface that resulted in membrane damage and death due to contact with nanopillars. Additionally, bacteriostatic results were shown to inhibit bacterial growth and activity of Staphylococcus aureus (S. aureus) on PCL nanostructured columns. The fabricated nanopillar structure has confirmed that mechanically induced antibacterial function and can be applied to implantable medical devices.

Flexible Electrochemical Platform Coupled with In Situ Prepared Synthetic Receptors for Sensitive Detection of Bisphenol A.

A flexible electrochemical sensor based on the carbon felt (CF) functionalized with Bisphenol A (BPA) synthetic receptors was developed. The artificial Bisphenol A receptors were grafted on the CF by a simple thermal polymerization molecular imprinting process. Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and electrochemical characterizations were used to analyze the receptors. Characterization results demonstrated that the Bisphenol A synthetic receptors successfully formed on the CFs surface. Because the synthetic receptor and the porous CFs were successfully combined, the sensor displayed a better current response once Bisphenol A was identified. The sensor's linear range was determined to be from 0.5 to 8.0 nM and 10.0 to 300.0 nM, with a detection limit of 0.36 nM. Even after being bent and stretched repeatedly, the electrode's performance was unaffected, demonstrating the robustness, adaptability and viability of installing the sensor on flat or curved surfaces for on-site detection. The designed electrochemical sensor has been used successfully to identify Bisphenol A in milk samples with satisfactory results. This work provided a promising platform for the design of implantable, portable and miniaturized sensors.

Influence of Filler Materials on Wettability and Mechanical Properties of Basalt/E-Glass Woven Fabric-Reinforced Composites for Microfluidics.

This paper presents the development of novel hybrid composites in the presence of filler particles and manufactured using a proposed new fabrication technique. The hybrid composites were fabricated using a basalt and E-glass woven fabric-reinforced epoxy resin matrix combined with graphite powder nanoparticles. Six sets of samples were fabricated using the vacuum-assisted free lamination compression molding technique. After the fabrication, wettability, mechanical properties (tensile, flexural and impact properties) and moisture properties were evaluated. Surface morphology and chemical composition of the composite samples were examined using a scanning electron microscope (SEM) and spectroscopy. The obtained results showed that the use of filler materials in hybrid composites improves the properties of hybrid composites. Basalt/E-glass hybrid composites with 10% graphite material exhibited superior mechanical properties over the other composites, with high-quality, improved adhesion and surface morphology. Thus, novel composites with the combination of exceptional properties may be integrated in the design of flexible electronics and microfluidics devices as a structural layer of the system. High flexibility and good surface tension of the designed composites makes them attractive for using the thermal imprint technique for microfluidics channel design.

Development of Finite Element Models of PP, PETG, PVC and SAN Polymers for Thermal Imprint Prediction of High-Aspect-Ratio Microfluidics.

Polymeric microstructures and microchannels are widely used in biomedical devices, optics, microfluidics and fiber optics. The quality, the shape, the spacing and the curvature of microstructure gratings are influenced by different mechanisms and fabrication techniques used. This paper demonstrates a cost-effective way for patterning high-aspect-ratio thermoplastic microstructures using thermal imprint technology and finite element modeling. Polymeric materials polypropylene (PP), polyethylene terephthalate glycol (PETG), polyvinyl chloride (PVC) and styrene-acrylonitrile (SAN) were chosen for the experimental investigations. A finite element model was constructed to define the most suitable parameters (time, heating temperature, pressure, etc.) for the formation of microstructures using the thermal imprint procedure. To confirm the relevance of the finite element model, different types of PP, PETG, PVC and SAN microstructures were fabricated using theoretically defined parameters. Experimental investigations of imprinted microstructures’ morphological and optical properties were performed using scanning electron microscopy, atomic force microscopy and a diffractometer. Obtained results confirmed the relevance of the created finite element model which was applied in the formation of high-aspect-ratio microstructures. Application of this model in thermal imprint would not only reduce the fabrication time, but also would highly increase the surface quality and optical properties of the formed structures.

Evidence for massive methane hydrate destabilization during the penultimate interglacial warming

The stability of widespread methane hydrates in shallow subsurface sediments of the marine continental margins is sensitive to temperature increases experienced by upper intermediate waters. Destabilization of methane hydrates and ensuing release of methane would produce climatic feedbacks amplifying and accelerating global warming. Hence, improved assessment of ongoing intermediate water warming is crucially important, especially that resulting from a weakening of Atlantic meridional overturning circulation (AMOC). Our study provides an independent paleoclimatic perspective by reconstructing the thermal structure and imprint of methane oxidation throughout a water column of 1,300 m. We studied a sediment sequence from the eastern equatorial Atlantic (Gulf of Guinea), a region containing abundant shallow subsurface methane hydrates. We focused on the early part of the penultimate interglacial and present a hitherto undocumented and remarkably large intermediate water warming of 6.8 °C in response to a brief episode of meltwater-induced, modest AMOC weakening centered at 126,000 to 125,000 y ago. The warming of intermediate waters to 14 °C significantly exceeds the stability field of methane hydrates. In conjunction with this warming, our study reveals an anomalously low δ13C spike throughout the entire water column, recorded as primary signatures in single and pooled shells of multitaxa foraminifers. This extremely negative δ13C excursion was almost certainly the result of massive destabilization of methane hydrates. This study documents and connects a sequence of climatic events and climatic feedback processes associated with and triggered by the penultimate climate warming that can serve as a paleoanalog for modern ongoing warming.

In-plane Extended Nano-coulter Counter (XnCC) for the Label-free Electrical Detection of Biological Particles.

We report an in-plane extended nanopore Coulter counter (XnCC) chip fabricated in a thermoplastic via imprinting. The fabrication of the sensor utilized both photolithography and focused ion beam milling to make the microfluidic network and the in-plane pore sensor, respectively, in Si from which UV resin stamps were generated followed by thermal imprinting to produce the final device in the appropriate plastic (cyclic olefin polymer, COP). As an example of the utility of this in-plane extended nanopore sensor, we enumerated SARS-CoV-2 viral particles (VPs) affinity-selected from saliva and extracellular vesicles (EVs) affinity-selected from plasma samples secured from mouse models exposed to different ionizing radiation doses.

Direct patterning of methylammonium lead bromide perovskites by thermal imprint

Promising new materials like solution-processable perovskites may provide devices with superior properties, e.g. for opto-electronics. For some applications patterning is required and nanoimprint as a solvent-free, mechanical shaping process has been identified to be particularly favorable for this purpose. The current investigation refers to the organic–inorganic perovskite methylammonium lead bromide (MAPbBr3) and is related to direct imprint under pressure and temperature. Experiments with a single crystal and polycrystalline layers of differing grain size indicate that a large-grained starting layer offers optimum pre-conditions for the replication of micro/nano-structures. The aim of the present study is to develop a physical understanding of the shaping process with this polycrystalline material. To develop such a conception, analogies between the imprint of polycrystalline perovskites and the imprint of thermoplastic polymers are sought, and the consequences resulting from the differences in the microscopic material response are worked out. The main aspect with perovskites is that plastic deformation occurs due to gliding on crystallographic glide planes, similar to the case of metals. With a < 100 > -oriented perovskite layer the imprint pressure activates a (110) < 110 > -type glide system, providing material transport at 45° with respect to the surface normal. The consequences of this preferential direction are investigated by analyzing experiments with partial and complete filling of the cavities of the stamp used for imprint. By considering the geometric correlations during the initial imprint phase the experimental results can be understood. Beyond that, it turns out that under specific conditions the size and the shape of the grains can be controlled by the imprinted pattern. This ‘grain shaping by patterning’ provides unexpected, innovative prospects for the nanoimprint of perovskite layers.

The Namib Turbulence Experiment: Investigating Surface–Atmosphere Heat Transfer in Three Dimensions

Abstract The Namib Turbulence Experiment (NamTEX) was a multinational micrometeorological campaign conducted in the central Namib Desert to investigate three-dimensional surface layer turbulence and the spatiotemporal patterns of heat transfer between the subsurface, surface, and atmosphere. The Namib provides an ideal location for fundamental research that revisits some key assumptions in micrometeorology that are implicitly included in the parameterizations describing energy exchange in weather forecasting and climate models: homogenous flat surfaces, no vegetation, little moisture, and cloud-free skies create a strong and consistent diurnal forcing, resulting in a wide range of atmospheric stabilities. A novel combination of instruments was used to simultaneously measure variables and processes relevant to heat transfer: a 3-km fiber-optic distributed temperature sensor (DTS) was suspended in a pseudo-three-dimensional array within a 300 m × 300 m domain to provide vertical cross sections of air temperature fluctuations. Aerial and ground-based thermal imagers recorded high-resolution surface temperature fluctuations within the domain and revealed the spatial thermal imprint of atmospheric structures responsible for heat exchange. High-resolution soil temperature and moisture profiles together with heat flux plates provided information on near-surface soil dynamics. Turbulent heat exchange was measured with a vertical array of five eddy-covariance point measurements on a 21-m mast, as well as by collocated small- and large-aperture scintillometers. This contribution first details the scientific goals and experimental setup of the NamTEX campaign. Then, using a typical day, we demonstrate (i) the coupling of surface layer, surface, and soil temperatures using high-frequency temperature measurements, (ii) differences in spatial and temporal standard deviations of the horizontal temperature field using spatially distributed measurements, and (iii) horizontal anisotropy of the turbulent temperature field.

Thermal imprint of wide-angle viewing bi-stable cholesteric liquid crystal displays.

A thermal-imprint addressable and electrically erasable bi-stable cholesteric liquid crystal (CLC) display with a wide viewing angle is demonstrated. The proposed device with a multi-domain planar state is realized by filling a negative CLC in a vertical-alignment cell. The thermal-imprint method is introduced to restore the CLC from a reflective state (multi-domain planar state) to a translucent state (focal-conic state) to display images, and an electric field is used to erase the device back to totally reflective mode. This CLC display is bi-stable and does not require a complex driving circuit. Together with the features of a large viewing angle and less color shift, this device shows great potential for update-on-demand applications.

The impact of melt versus mechanical wear on the formation of pseudotachylyte veins in accretionary complexes

Whether seismic rupture propagates over large distances to generate mega-earthquakes or is rapidly aborted mainly depends on the slip processes within the fault core, including particularly frictional melting or intense grain-size reduction and amorphization. The record of seismic slip in exhumed fault zones consists in many instances in Black Faults Rocks, dark and glass-like-filled aphanitic veins that have been interpreted as resulting from the quenching of frictional melts, i.e. pseudotachylytes. Such interpretation has nevertheless been questioned as similar macro to nano-microstructures have been observed either on intensely comminuted natural fault rocks or on slow creep experiments conducted on crustal rocks, where melting is absent. Here, we report a new dataset of Raman Spectroscopy of Carbonaceous Material analyses, aimed at discriminating the slip weakening processes operating in the fault core during slip. Using high spatial resolution profiles on natural Black Fault Rocks from exhumed accretionary complexes and an experimentally calibrated modelling of Raman intensity ratio evolution with temperature, we assessed different scenarios of temperature evolution during fault slip. None of them is able to account for the distribution of Raman signal, so that in the three studied Black Fault Rocks interpreted so far as natural pseudotachylytes, Raman Spectroscopy of Carbonaceous Material rather reflects the effect of intense and localized strain during fault slip. Furthermore, the absence of thermal imprint on Raman signal puts upper bounds on the temperature reached within the fault zone. If one cannot rule out the occurrence of high and short-lived temperature increase due to friction, the latter was not high enough as to melt the large quartz fraction of the fault zone rocks.

Chain movements of a molecularly flat PMMA substrate surface prepared by thermal imprinting with mica and isolated PMMA chains deposited on the PMMA substrate observed by AFM around the bulk Tg

Chain movements of a molecularly flat PMMA substrate surface prepared by thermal imprinting with mica and isolated PMMA chains deposited on the PMMA substrate observed by AFM around the bulk Tg

Development of robust amphiphobic hierarchical structure on polymer substrate by thermal imprinting and sputter etching

Amphiphobic surfaces are found in many natural organisms for protection from external contamination because they can repel both water and oil. The development of an amphiphobic surface is based on the construction of hierarchical structures and chemical modification. In this study, thermal imprinting and sputter etching were conducted to create a micropillar array and nano-protrusions to form a hierarchical structure. Different hierarchical structures were developed by using different nickel stamps and upon varying the etching time. These structures were modified using an environment-friendly drysurf (G993G3, Harves) solution through a spraying method. The surface presented high repellency toward various liquid droplets with surface tensions ranging from 72 to 22 mN m −1 , with contact angles of 158° for water and 120° for hexadecane. The surface showed good self-cleaning performance without any traces of water droplets or glass bead particles. In addition, various tests including sand abrasion , bending, and immersion tests were conducted to evaluate the mechanical and chemical robustness of the hierarchical structure, which exhibited good performance. Hierarchical structures with these excellent properties are expected to be widely applied in surface waterproofing, antifouling, and self-cleaning treatments. • Micropillars with appropriate size are required to create hierarchical structure. • Net-like nanoprotrusions are fabricated on micropillars by sputter etching. • Hierarchical micro/nanostructure shows better amphiphobicity than micropillars. • The amphiphobic surface presents good chemical stability and mechanical robustness. • The amphiphobic surface can be applied as antifouling and self-cleaning materials.

ICMCTF 2021 – Preface

Amphiphobic surfaces are found in many natural organisms for protection from external contamination because they can repel both water and oil. The development of an amphiphobic surface is based on the construction of hierarchical structures and chemical modification. In this study, thermal imprinting and sputter etching were conducted to create a micropillar array and nano-protrusions to form a hierarchical structure. Different hierarchical structures were developed by using different nickel stamps and upon varying the etching time. These structures were modified using an environment-friendly drysurf (G993G3, Harves) solution through a spraying method. The surface presented high repellency toward various liquid droplets with surface tensions ranging from 72 to 22 mN m−1, with contact angles of 158° for water and 120° for hexadecane. The surface showed good self-cleaning performance without any traces of water droplets or glass bead particles. In addition, various tests including sand abrasion, bending, and immersion tests were conducted to evaluate the mechanical and chemical robustness of the hierarchical structure, which exhibited good performance. Hierarchical structures with these excellent properties are expected to be widely applied in surface waterproofing, antifouling, and self-cleaning treatments.

Fabrication of superhydrophobic surface with hierarchical structure by thermal imprinting and spraying

Superhydrophobic surfaces have recently attracted considerable attention in industry owing to their high water repellency and self-cleaning property. Many studies on the development of superhydrophobic surfaces have been reported, but the issues of the poor durability and difficulty in forming the desired hierarchical structures remain. Herein, a superhydrophobic surface with a hierarchical micro/nanostructure and good durability was developed on a poly(methyl methacrylate, PMMA) substrate. The micro-scale pillar array was first fabricated on PMMA by thermal imprinting. 1 H,1 H,2 H,2 H-perfluorooctyltriethoxysilane (PFOTES) was used to chemically modify silicon dioxide (SiO2) nanoparticles before developing nanostructure on the micro-scale pillar array. Subsequently, a nanocomposite suspension composed of polyvinylidene fluoride (PVDF) and PFOTES-SiO2 nanoparticles was sprayed on the pillar surface, forming the desired micro/nano hierarchical structure. The effect of the SiO2 nanoparticle size on the surface hydrophobicity was studied in detail. The good superhydrophobicity of the hierarchical surface, with a high contact angle of 163° and low sliding angle of 7°, was related to its high Brunauer-Emmett-Teller specific surface area of 42.43 m2 g−1 and pore volume of 0.35 cm3 g−1. The contaminants on the surface were cleaned easily as the water droplet rolled off, showing good self-cleaning performance. Owing to the binder of PVDF, the nanocomposite coating showed good adhesion to the PMMA substrate. The developed superhydrophobic surface is expected to be widely applied in self-cleaning, anti-fouling, and waterproof fields.

One-step fabrication of high refractive index inorganic nanostructures

Direct printing of spin-on functional films is probably the most efficient method to develop low-cost novel photonic nanodevices, such as diffraction gratings, planar waveguides, nano- lasers, and antireflective coatings. For these applications high refractive index transparent materials are demanded; however, this class of materials generally requires inorganic oxides, well known for their hardness, typical of ceramic materials, and so incompatible with a soft character of printable resins. Herein, inorganic high refractive index TiO2 micro- and nano- structures, with unusual depth up to 600 nm and aspect ratio larger than 5, are obtained by combining thermal nanoimprint lithography (NIL) with UV curing. To achieve printed patterns, a hybrid organic-inorganic spin-on film is deposited at low-temperature by sol–gel processing. Two distinct bottom-up synthetic approaches are used, called in situ and ex situ, using titanium isopropoxide (90%) or TiO2 anatase nanoparticles (70%), respectively, and adding a silica sol modified by organic moieties. The two syntheses were optimized to obtain, after patterning by thermal imprint, amorphous or crystalline titania crack-free micro- and nano- patterns for in situ and ex situ, respectively. The further UV irradiation converts imprinted films to totally inorganic patterns, through the titania photocatalytic effect, allowing refractive indexes up to 1.82 at 632 nm to be achieved. This novel strategy of combining thermal imprint with UV exposure allows inorganic deep patterns to be fabricated without a calcination step, which is generally needed for inorganic resists processing. Eventually, a thermal treatment only at 300 °C can be applied to achieve a final refractive index of 2 at 632 nm.Direct printing of spin-on TiO2 high refractive index (1.82 @632 nm) transparent films, with depth up to 600 nm, aspect ratio larger than 5 and without lateral shrinkage are obtained combining thermal Nanoimprint Lithography (NIL) with UV curing.

Ultrafast Thermal Imprinting of Plasmonic Hotspots.

Plasmonic photochemistry is driven by a rich collection of near-field, hot charge carrier, energy transfer, and thermal effects, most often accomplished by continuous wave illumination. Heat generation is usually considered undesirable, because noble metal nanoparticles heat up isotropically, losing the extreme energy confinement of the optical resonance. Here it is demonstrated through optical and heat-transfer modelling that the judicious choice of nanoreactor geometry and material enables the direct thermal imprint of plasmonic optical absorption hotspots onto the lattice with high fidelity. Transition metal nitrides (TMNs, e.g., TiN/HfN) embody the ideal material requirements, where ultrafast electron-phonon coupling prevents fast electronic heat dissipation and low thermal conductivity prolongs the heat confinement. The extreme energy confinement leads to unprecedented peak temperatures and internal heat gradients (>10 K nm-1 ) that cannot be achieved using noble metals or any current heating method. TMN nanoreactors consequently yield up to ten thousand times more product in pulsed photothermal chemical conversion compared with noble metals (Ag, Au, Cu). These findings open up a completely unexplored realm of nano-photochemistry, where adjacent reaction centers experience substantially different temperatures for hundreds of picoseconds, long enough for bond breaking to occur.

Relevance of processing parameters for grain growth of metal halide perovskites with nanoimprint

The quality and the stability of devices prepared from polycrystalline layers of organic–inorganic perovskites highly depend on the grain sizes prevailing. Tuning of the grain size is either done during layer preparation or in a post-processing step. Our investigation refers to thermal imprint as the post-processing step to induce grain growth in perovskite layers, offering the additional benefit of providing a flat surface for multi-layer devices. The material studied is MAPbBr3; we investigate grain growth at a pressure of 100 bar and temperatures of up to 150 °C, a temperature range where the pressurized stamp is beneficial to avoid thermal degradation. Grain coarsening develops in a self-similar way, featuring a log-normal grain size distribution; categories like ‘normal’ or ‘secondary’ growth are less applicable as the layers feature a preferential orientation already before imprint-induced grain growth. The experiments are simulated with a capillary-based growth law; the respective parameters are determined experimentally, with an activation energy of Q ≈ 0.3 eV. It turns out that with imprint as well the main parameter relevant to grain growth is temperature; to induce grain growth in MAPbBr3 within a reasonable processing time a temperature of 120 °C and beyond is advised. An analysis of the mechanical situation during imprint indicates a dominance of thermal stress. The minimization of elastic energy and surface energy together favours the development of grains with (100)-orientation in MaPbBr3 layers. Furthermore, the experiments indicate that the purity of the materials used for layer preparation is a major factor to achieve large grains; however, a diligent and always similar preparation of the layer is equally important as it defines the pureness of the resulting perovskite layer, intimately connected with its capability to grow. The results are not only of interest to assess the potential of a layer with respect to grain growth when specific temperatures and times are chosen; they also help to rate the long-term stability of a layer under temperature loading, e.g. during the operation of a device.

Effect of temperature on the SU‐8 photoresist filling behavior during thermal nanoimprinting

AbstractSU‐8 photoresist is an ideal thermal‐imprinting polymer, which has been widely used in micro‐nano devices in recent years. However, the research on the filling behavior of SU‐8 photoresist during thermal nanoimprinting is not complete. In this paper, the stress relaxation curves and shear stress/rate flow curves were measured to analyze the temperature dependent rheological properties of SU‐8 photoresist. The filling behavior of SU‐8 photoresist was discussed based on thermal imprinting results at various temperatures. High‐precision nanochannels were fabricated with replication error of 2.8% at optimized thermal imprinting temperature of 85°C and duration of 10 min, which paves the way for high‐precision fabrication of SU‐8‐based micro‐nanofluidic chips.

Fault analysis for wastewater treatment plant equipment using thermography

Infrared thermography is a very effective non-destructive control method for detecting and locating defects. It is a technique that allows to obtain, with the help of an equipment called thermal imaging camera, the image or thermal imprint of a targeted area in the field of infrared radiation. Infrared thermography deals with the acquisition and analysis of thermal information obtained using non-contact infrared scanning equipment.

Laser-assisted thermal imprinting of glass guided mode resonant (GMR) optical filter

Laser-assisted thermal imprinting of glass nanostructures is demonstrated. Compare to the existing thermal imprinting, this method significantly reduced the contact imprinting time. The quality of the replicated glass nanostructures revealed by field emission scanning electron microscope ( SEM) and atomic force microscope ( AFM) exhibited a very smooth surface finish that closely matched the profile of the silicon mold. As proof-of-concept, the utility of laser-assisted, imprinted glass nanostructures as guided-mode resonant (GMR ) optical filter was evaluated. The peak spectral values obtained were satisfactory; which yielded an average FWHM and PWV of 4.6 nm and 691.39 nm respectively.