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We report the design and characterization of a multiphase quadruple shape memory composite capable of switching between 4 programmed shapes, three temporary and one permanent. Our approach combined two previously reported fabrication methods by embedding an electrospun mat of PCL in a miscible blend of epoxy monomers and PMMA as a composite matrix. As epoxy polymerization occurred the matrix underwent phase separation between the epoxy and PMMA materials. This created a multiphase composite with PCL fibers and a two-phase matrix composed of phase-separated epoxy and PMMA. The resulting composite demonstrated three separate thermal transitions and amenability to mechanical programming of three separate temporary shapes in addition to one final, equilibrium shape. In addition, quadruple surface shape memory abilities are successfully demonstrated. The versatility of this approach offers a large degree of design flexibility for multi-shape memory materials.

This article proposes a rapid fabrication method for the production of various molds for the replication of polymer lens arrays. The method involves ultrasonic vibration embossing with a polymer substrate and small steel ball array. Only one embossing step is required in which a concave lens array pattern is directly fabricated onto the polymer substrate. The total processing cycle time is less than 20 s. The polymer substrate with a concave lens array pattern can then be used as a mold for the replication of a polymer lens array through a polydimethylsiloxane casting process. In addition, the diameter and depth of the concave lens array pattern on the surface of the polymer substrate can be changed and controlled by adjusting the processing conditions of the ultrasonic vibration embossing process. Hence, various molds with different concave lens array patterns and thus polymer lens arrays, can be effectively fabricated at very low cost and with high throughput. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Micro-hot embossing is a highly effective process for fabricating micro-devices with microfeatures in polymeric materials. One of the most troublesome problems in precision machinery industry is the time and expense needed to produce a mold for microreplication. Epoxy resin mold has been successfully employed for microreplication using micro-hot embossing. However, the junction of the groove and sprue of the backing plate has serious local stress concentration, leading to the reduction of lifespan of a precision epoxy resin mold during the micro-hot embossing molding. This work presents an effective method for enhancing the lifespan of a precision epoxy resin mold using reduction of local stress concentration. The numerical models were developed for predicting the maximum stress using ANSYS software. The ANSYS simulations have been carried out and the predicted results show good agreement with experimental tests. The junction of the groove and sprue of the backing plate was machined with chamfer to revaluate lifespan of the epoxy resin mold using micro-hot embossing molding. Micro-hot embossing verification test showed that the lifespan of epoxy resin mold with chamfer is about 2.2 times that of the conventional epoxy resin mold.

Generally, the hot embossing cycle time for fabricating microfeatures on the surface of polymer takes no

The two-way shape-memory effect (TWSME) in Nickel–titanium (NiTi) alloys is of interest for applications in aerospace, biomedicine, and microengineering due to its reversible shape recovery. In this study, the authors demonstrate two approaches to obtain switchable surface structures using the TWSME. Samples are structured using two surface geometries by either cold embossing, or pulse electrochemical machining (PECM). After planarization, a change from optically smooth to structured and vice versa is observed. The switch is induced through heating and cooling the sample above and below the phase transformation temperature. The protrusions reflect the pattern applied by the two processes. Both methods are promising for preparation of switchable metallic surfaces on larger areas.

Micro-injection molding or micro-hot embossing is a highly effective process for fabricating micro-devices with microfeatures in polymer. Based on the strong demand on the precision components in the precision machinery industrial, two major concerns are the time and expense required for producing a precision mold for microfabrication. To enhance the competitiveness in the market of micorcomponents, this study presents six approaches for manufacturing precision epoxy resin molds with microfeatures. Evolutions manufacturing processes are described experimentally. Characteristics and applications of micro-featured epoxy resin mold are introduced in detail.

In this study, the authors present a single-step approach for fabricating micrometer structures on metallic hot embossing molds using direct laser interference patterning. Patterns with spatial periods of 1.8 and 2.5 µm are structured on a Ni-mold and used for embossing PET-foils. The influence of the laser parameters on the structure height as function of the spatial period is investigated. A rapid increase in structure height is observed up to a specific laser fluence. Thermal simulations show a linear correlation between the structure height and the amount of molten material. Hot embossing of PET-foils considering the imprint time and temperature is successfully performed. The results show that both the imprint temperature and time do not have any significant influence on the structure height of the imprints.

The natural compound eye is a striking imaging device with a wealth of fascinating optical features such as a wide field of view (FOV), low aberration, and high sensitivity. Dragonflies in particular possess large, sophisticated compound eyes that exhibit high resolving power and information-processing capacity. Here, a large-scale artificial compound eye inspired by the unique designs of natural counterparts is presented. The artificial compound eye is created by a high-efficiency strategy that combines single-pulse femtosecond laser wet etching with thermal embossing. These eyes have a macrobase diameter of 5 mm and ≈30 000 close-packed ommatidia with an average diameter of 24.5 μm. Moreover, the optical properties of the artificial compound eyes are investigated; the results confirm that the eye demonstrates advanced imaging quality, an exceptionally wide FOV of up to 140°, and low aberration.

By use of magnetism and magnetic fluid embossing technology, and in combination with the surface microstructure roughness improvement of seal-film, this paper aimed to reach the purpose of magnetic fluid being driven under the magnetic force of an electromagnetic chuck, where the magnetic particles can be evenly scattered and stacked on the surface of the seal-film in order to uniformly lift and convey the microstructure curved surface magnetic embossing force; thus, creating magnetic pressure in the embossing process of a microstructure curved surface. Moreover, during the process, photocuring technology is integrated with the technical features of soft lithography in order to provide more uniform curved surface embossing and photocuring process technology through the combination of fluid and magnetic force. Copyright © 2015 John Wiley & Sons, Ltd.

Integration of light management solutions relying on biodegradable materials in organic light���emitting devices could assist the development of sustainable light sources or conformable and wearable display technology. Using industrially relevant processing techniques, it is shown that microlens arrays can be seamlessly integrated into flexible and biodegradable cellulose diacetate substrates to facilitate extraction of the trapped substrate modes in light���emitting electrochemical cells. The substrates are patterned for light extraction and optimized for scalable printing processes in a single step by thermally embossing microlenses with polydimethylsiloxane molds on one substrate surface and simultaneous flattening of the other. Furthermore, by implementing the biopolymer substrate with microlens arrays, the total volume fraction of biodegradable materials in the microlense equipped device is 99.94%. The embossed microstructures on the biopolymer substrates are investigated by means of scanning electron microscopy and the angular light extraction profile of the devices is measured and compared to ray tracing simulations. Light���emitting electrochemical cells with integrated microlens array substrates achieve an efficiency enhancement factor of 1.45, exceeding conventional organic light���emitting diodes on glass substrates with laminated microlens arrays (enhancement factor of 1.23).

Many critical issues need to be addressed when microstructured reactors are manufactured in large unit volumes. The most crucial of these are cost, ease of production, and reliability. The lack of breakthrough manufacturing technology to provide high-efficiency, low-cost, high-precision plates is a hindrance to the early market implementation of systems requiring metallic microstructured plates. This contribution focuses on the development and optimization of a combined embossing and bending tool for the quick and continuous manufacture of easily machined plates.

Ultrasonic vibration technology has recently been applied in high-temperature forming processes, such as hot upsetting and hot glass embossing. Experimental research has delineated the effects of ultrasonic vibration on reducing required forces and improving the formability of materials. The purpose of this study was to construct a finite element model of the embossing stage of the ultrasonic vibration-assisted hot glass embossing process. Traditional hot embossing experiments in which the embossing speed and temperature were varied were performed to calculate the viscoelastic dissipation caused by ultrasonic vibration, and this value was then inputted into the simulation. The consistency of the force responses in the experiments and simulation indicated that the proposed model is valid. The findings indicate that the influences of parameters such as the vibration frequency, vibration amplitude, and embossing speed on the ultrasonic vibration-assisted hot glass embossing process must be investigated further.

The tribological properties of lubricated machine elements can be improved by micro lubrication pockets. Depending on the application's tribological system, the pocket dimension needs to be adjusted to achieve an optimum in friction and wear reduction. With respect to production efficiency, a forming operation would be suited to manufacture these pockets. In this work, finite element models were developed to study the steps of the hot micro-coining process: heating, cutting, and coining of micro lubrication pockets. Experiments have been conducted to validate the models and to investigate the emissivity and heat transfer coefficient between tool and specimen by inverse modeling. It was found that the results of the simulations agree well with the experiments as long as the elastic tool deformation is taken into account, which influences the process time. Thus, suitable process parameters and limits have been determined for the coining of hemispherical lubrication pockets in stainless steel AISI 304. An initial forming temperature above 540 °C is recommended to avoid plastic deformation of the die. Complete form filling was achieved at a normalized pressure of three due to the high specimen temperature of 785 °C.

Reactive mesogens (RMs) have found their way into different branches of science and application. They can be processed as standard liquid crystals and can then be polymerised to stabilise their shape and anisotropic properties. Their birefringence is used in optical compensation films while the complex director field is exploited for actuators. However, creating complex shapes while maintaining good alignment is a challenge in these applications. In the present work, the embossing of reactive mesogens is introduced. Embossing is a fast and large-scale method, which allows to form a large variety of structured reactive mesogen devices. To create a polarisation-independent lens, two birefringent Fresnel zone plates (FZPs) are embossed. A lens is formed by assembling the FZPs in a twisted nematic cell and filling the cell with a nematic crystal index matched to the RM. The device can be switched from a non-focusing to a focusing state by applying a small voltage. After characterising the efficiency and beam properties, the method is used to fabricate a switchable multi-level Fresnel zone plate with optical efficiencies beyond 50%. Finally, manufactured polarisation-independent gratings and microlens arrays are presented using the method to illustrate the wide range of applicability.

Viewing angle dependent color shift is a fundamental property of all interferometric displays, including Qualcomm's Mirasol™ displays. We present a solution to reduce the color shift using a fiber array fabricated in a polycarbonate film via nano embossing. We discuss FDTD simulation, fabrication, and experimental result.

This study demonstrated a method for manufacturing a micro-featured mold insert of Fresnel lens. The transcription rate of this process is about 92.5%. A plastic Fresnel lens was fabricated using micro-hot embossing process. The transcription rate of the embossed part is about 95.1%. The micro-featured mold insert not only reduces the fabrication cost, but has higher form accuracy as well. In comparison with conventional method for fabricating a pair of mold insert, a cost reduction of 60.4% can be achieved using the hybrid method proposed in this study.

In conventional hot embossing, a thermoplastic polymer undergoes phase transitions in liquid, semi-solid, and solid states through cyclic heating and cooling. This paper, in contrast, describes the development of a constant-temperature embossing process and compares its characteristics against standard hot embossing. The new process utilizes the crystallizing nature of supercooled polymer films to obtain the necessary phase transitions. By softening and crystallizing the supercooled polymer at the same temperature, the embossing and solidification stages can be carried out isothermally without a cooling step. PET, due to its relatively slow crystallizing kinetics, was chosen as a model material for this study. The embossed films with microgroove patterns of different sizes and aspect ratios were characterized for their replication fidelity and accuracy. For supercooled PET films, constant-temperature embossing with high replication quality and acceptable demolding characteristics was achieved in a large processing temperature window between Tg and Tm of PET. A parametric process study involving changes of the embossing temperature and embossing time was conducted, and the results indicated that the optimal process parameters for constant-temperature embossing can be derived from the crystallization kinetics of the polymer. The removal of thermal cycling is a major advantage of constant-temperature embossing over conventional hot embossing and represents an important process characteristic desired in industrial production. POLYM. ENG. SCI., 54:1100–1112, 2014. © 2013 Society of Plastics Engineers

This study proposes a roll-to-roll process-based sub-wavelength grating, which is attached on a light bar to turn the side-lit red/green/blue (620, 520, and 450 nm) incident rays into a uniformly and normally output white light with high illuminance from the light bar's surface. On the basis of the rigorous coupling wave analysis, the relationship between the first-order transmission/reflection efficiency and the pitch of the gratings with different shapes was analyzed. The optimal design can effectively reduce the coupling length and enhance the white color balance for display applications.

Hot-embossing (HE) experiments were conducted on polymethyl methacrylate (PMMA) across its glass transition temperature from 92 to 142°C. The glass transition temperature (Tg) of the PMMA used in this study was ∼ 102°C. The polymer samples were embossed to a depth of 0.8 mm (800 μm). The experiments were carried out at various temperatures for different hold times of 30, 90, and 180 sec during the embossing process. A few additional experiments were conducted at 142°C with cooling of the samples as well. The force required for embossing and the final depth of the embossed features were analyzed. Polymers, including PMMA, show significantly different material behavior around and above Tg. The same was seen in the aforementioned tests; the trends observed for the force as well as the final depth changed considerably around 122°C (Tg + 20). These findings will be used in developing material models for use in simulating the hot-embossing process. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

This article reports a novel infrared (IR)-assisted roll-to-roll embossing method, which enables the replication of microfeatures onto the surfaces of flexible polymer substrates. An IR-assisted roll-to-roll embossing facility was designed and built in our laboratory especially for this study. Metallic rollers bearing micropatterns of two different feature sizes, namely 150 and 20 μm in depth, were employed. The former one was prepared by microelectric discharge machining the roller, whereas the latter was fabricated by electroplating a thin layer of nickel on the surface of the roller, followed by a diamond turning process to create the microstructures. The embossing facility was used to replicate the microstructure onto polyethylene terephthalate and polycarbonate films in the experiments. During roller embossing, the IR radiation shed on the rollers, and the energy was converted into heat to melt the polymer substrates and to replicate the microstructures. The influence of various processing parameters on the replicability of microfeatures was investigated. Under the proper processing conditions, double-sided flexible polymer substrates with microstructures could be successfully fabricated. The proposed method shows great potential for fabrication of micro-optical components due to its simplicity and versatility. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Bulky SiC composites with refined patterns were successfully fabricated from an imprinting lithography process using solid polycarbosilane (PCS) as the ceramic precursor. Structures of the master molds were integrally imprinted to PCS pellets by warm-pressing of nanoimprinter. Total cracking is effectively prevented by precuring of PCS under air condition. The partially cross-linked PCS exhibits a degree of thermoplasticity, which facilitates embossing of master molds onto the PCS pellets with pattern sizes ranging from 50 μm to 300 nm. The embossed samples were pyrolyzed up to 1300°C for polymer-conversion and the prepared patterns can be maintained after the precursor transforms to resultant nanocrystalline SiC composite. Meanwhile, this facile imprinting lithography route is supposed to be capable for the synthesis of SiC patterns with nanosized structures.

A new, easily obtainable silver–pyrrolidone complex that is suitable for printing applications was synthesized by the reaction of silver nitrate and 2-pyrrolidone (Pyl) at room temperature. According to single-crystal X-ray crystallographic studies, the product [Ag(Pyl)2]NO3 crystallizes in the monoclinic space group C2/c (no. 15) [a = 5.358(1) A, b = 15.217(3) A, c = 14.986(3) A, β = 99.296(6)°]. Highly concentrated solutions of the complex can be obtained in an ethanol/water mixture, thereby allowing for the manufacture of thin films by means of dip coating. Subsequent UV irradiation and moderate-temperature treatment yielded compact films of elemental silver with thicknesses of about 100 nm and sheet resistances down to 6.5 Ω. Furthermore, microcontact printing (μcp) and embossing of [Ag(Pyl)2]NO3 were performed, also followed by UV treatment. By means of the photoreduction of the complex and subsequent moderate-thermal treatment, defined structures of elemental silver lines were obtained.

SUMMARY Electromagnetic forming is achieved by a system consisting of an equipment, a tool (coil) and a workpiece. The success of the deformation process depends on the equipment's parameters, the tool characteristics and the properties of the workpiece material. Finite element software FLUX2D was used for electromagnetic parameter simulation in the case of a device with flat spiral coil, used for the following operations: deep drawing, embossing, piercing, blanking etc. The simulations were made with a model previously validated by comparison with values experimentally measured for the discharge current and magnetic induction parameters. Copyright © 2011 John Wiley & Sons, Ltd.

This two-article sequence on rubber-assisted embossing was aimed to understand the basic mechanisms affecting the pattern uniformity and replicability and to determine a process window for achieving uniform patterning and faithful replication. In Part I, the effects of major process and material parameters were identified and studied, and strategies for successful hot embossing with rubber as a pressure medium were proposed. In Part II, the rubber-assisted embossing process was analyzed considering the unique rheological behavior of the materials involved to develop useful predictive capabilities for this new process. Specifically, a finite-strain hyperelastic formulation was used for simulating the isothermal embossing stage, and a generalized Maxwell model was used to study the stress relaxation during the holding stage and to predict the elastic recovery after demolding. The rheological properties obtained in Part I were fitted to the constitutive models and implemented in the simulation procedures. The simulation results agreed with the major findings in the experimental work and provided a more quantitative insight into the process. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

In rubber-assisted hot embossing, a softened thin thermoplastic film is pressurized between a hard mold surface and a rubber pad. The rubber pad, as a soft counter-tool, deforms conformably to the hard mold surface, allowing feature transfer from the hard surface and formation of shell-type structures on the polymer film. This two-article sequence was aimed to understand the basic mechanisms affecting the pattern uniformity and replication in rubber-assisted hot embossing. In Part I, a series of rubber-assisted embossing experiments involving parametric studies of the effects of different processing conditions, as well as material selections, on the pattern thickness uniformity and replicated pattern height were conducted. The difference in film thickness uniformity in different experiments was explained using the mechanical and rheological behavior of the polymer film and the rubber counter-tool under different processing conditions. Based on the experimental results, strategies for determining a feasible process window for achieving uniform shell patterning by rubber-assisted embossing were proposed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

A free-radical-polymerizable SSQ/PEG blend with direct patternability has been proposed as an ideal nonfouling material for nanostructure-based biomedical applications. Cured SSQ/PEG networks show an UV transparency of >90% at 365 nm, high resistance to organic/aqueous solutions, hydrophilicity and Young's moduli of 1.898-2.815 GPa. SSQ/PEG patterns with 25-nm linewidths, 25-nm spacing, and an aspect ratio of 4:1 were directly fabricated on transparent substrates by UV embossing, and cured SSQ/PEG networks with long-term stability under chemical, thermal, and biological stress showed strong resistance to the nonspecific adsorption of biomolecules. These characteristics may offer a new strategy for the development of a number of medical nanodevice applications such as labs-on-a-chip.

This study develops an improved method for generating aluminum mold inserts used in the replication of polymer-based microfluidic chip. Since molding masters that are suitable for microfluidic chip replication must have features whose dimensions are of the order of tens to hundreds of microns, micro electrical discharge machining is employed herein to fabricate an aluminum mold insert of a microfluidic chip. The width and depth of the aluminum mold insert for the microfluidic chip are 61.50 and 49.61 µm, respectively. The surface roughness values of the microchannel and the sample reservoir in aluminum mold insert for the microfluidic chip are 53.9 and 34.3 nm, respectively. PMMA material is adopted as the molded microfluidic chip that is produced by micro-hot embossing molding. The PMMA material can replicate the microchannel and sample reservoir very well when the aluminum mold insert is used in micro-hot embossing molding. The results indicate that the most important parameter in the replication of molded microfluidic chip is the embossing pressure, which is also the most important parameter in determining the surface roughness of the molded microfluidic chip. Copyright © 2010 John Wiley & Sons, Ltd.

Viscous polymer flow in embossing stage during thermal nanoimprint lithography was investigated. Flow behavior of the thermoplastic polymer was analyzed numerically and experimentally. Fixed grid scheme along with the finite element method was used for numerical analysis. Effects of process parameters such as the temperature, the stamp speed, and the stamp geometry on the filling pattern for single cavity were studied. Also the patterns with several cavities were analyzed to understand the flow behavior between adjacent cavities. Experiments were performed using PMMA sheets to confirm the effects of parameters obtained from numerical analyses. Two different types of geometries were considered and the filled patterns were observed using a scanning electron microscopy. Numerical results exhibited a similar tendency as the experimental observation. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers

Recently, time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) instrumentation has been used to address areas of interest within micro-fluidic devices providing full access to the surface chemistry established at the bottom of micro-channels therein. After careful calibration, information on surface chemistry as obtained by ToF-SIMS or XPS can be interpreted in terms of wettability expressed as contact angles which are then characteristic for the inner walls of micro-channels. Standard contact angle measurement is not applicable in micro-channels. The approach has been demonstrated to be successful with two different micro-fluidic devices hot embossed into high-end quality poly(methyl methacrylate) (PMMA) or Polycarbonate wafers. A pre-selected surface chemistry at micro-channel walls can be established by plasma technologies but ageing and rinsing effects have to be under control. A combination of ToF-SIMS, XPS and contact angle measurement techniques has been demonstrated to provide the required information. Finally, it is shown by ToF-SIMS and XPS analysis that in the production of micro-fluidic parts during practical processing using hot embossing technologies, material originating from cover foils will reside on the polymer wafer's surface. Moreover, residues of releasing agents as silicone oil used during processing can be detected by ToF-SIMS. Both cover foil residues and silicones are issues of trouble shooting in micro-fluidics because they will change contact angles efficiently. Copyright © 2010 John Wiley & Sons, Ltd.

A new pathway for the generation of polymer-based microfluidic devices with tailor-made surface chemistry is described. A simple photochemical process is used to covalently bind polymer molecules to the surfaces of microchannels fabricated by hot embossing. The substrates for the embossing process have the format of a compact disk (CD). CDs from polymethylmethacrylate and polyethylene-co-norbornene were chosen due to their good optical properties. Thin films of polymers containing photoactive benzophenone units were deposited onto the surface of the thus generated devices. These films were subsequently irradiated with UV light leading to the surface-attachment of ultrathin polymer networks. In contrast to their unmodified peers, the obtained, modified microfluidic channels coated with hydrophilic, photoattached layers can be filled in a straightforward manner with water by capillary forces. Channels coated by thin films of poly(ethyloxazoline) show complete resistance to non-specific protein binding. Generation of hydrophobic patches inside the modified microfluidic channels using benzophenone-containing fluoropolymers allowsthegenerationofpassive microfluidic valves to direct fluid motion in these CD-based devices.

Surface forces play a paramount role in most aspects of Nanoimprint Lithography. In particular, subjecting nanoimprinted patterns to moderate heating allows surface tension to smooth out undesirable roughness and defects in the patterns, but this “thermal reflow” treatment can induce structural decay or even collapse of the patterns by capillary instability if this process is not carefully controlled. Adhesion between the mold and polymer film can also cause the imprinted structure to tear or fracture. Fluorinated surfactants (FS) are attractive for reducing mold adhesion, yet the effects of these additives on nanostructure stability during thermal reflow are not well understood. Here we present thermal stability studies of line-space grating patterns created by Thermal Embossing Nanoimprint Lithography (TENIL) on model polystyrene (PS) films with FS additives. As expected by energy considerations, FS segregates to the air interface, where it seems to facilitate mold release. This also reduces the surface energy and thus reduces the driving force for pattern “slumping” (height decay). However, the beneficial effects of the surfactant are counterbalanced by the fact that the FS decreases the effective film viscosity, which accelerates nanopattern leveling. The net effect is that the pattern height decay is strongly a function of FS concentration. This enhanced film fluidity in the presence of FS also makes the pattern more susceptible to an undulatory capillary instability under thermal reflow conditions. Surface phase segregation of FS and PS is also observed in conjunction with both slumping and lateral capillary instabilities, which may be useful for producing chemically patterned surfaces. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2591–2600, 2009

Hot embossing and nanoimprinting processes are being widely practiced in industry. Fast and reliable production of micro/nanofeatured patterns on large-area polymer films is of a great importance. In this study, a novel roll-to-roll thermal imprinting process was developed, capable of providing a mold-heating rate of 125°C/s with sufficient temperature control to produce large-area patterns continuously at a rapid production rate. With this new process, selected micro/nano patterns were produced on a polyethylene terephthalate film at a production rate exceeding 1 m/min. The roller mold temperature played a profound role in affecting the replication quality. To achieve good feature transfer properties, an elevated roller mold temperature approaching the melting temperature of the polymer was found to be critical. Microcavity filling time calculation further revealed that the elevated roller mold temperature is also necessary for achieving a rapid film feed rate as desired in the continuous roll-to-roll process. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 28:246–256, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20167

This article reviews a novel method to produce microembossed features with an aspect ratio of three and negligible flash on polymer surfaces. An embossing technique that utilizes localized heating (ultrasonic energy) was used with polystyrene and polypropylene substrates. It was demonstrated that when foamed substrates were used, the amount of flash produced was negligible compared to nonfoamed substrates, which has been a significant unresolved problem with embossing using localized heating. The depth of microembossed features as a function of heating times and amplitudes of ultrasonic embossing is detailed in this article, along with a characterization of complex embossed geometries. It was seen that embossing depth was generally proportional to heating time and amplitude until the maximum feature depth was achieved. Although this article deals with embossing of microfeatures for lab-on-a-CD applications, it is envisioned that it is also suitable for lab-on-a-chip applications. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

In this study, master of the microlens arrays is fabricated using micro dispensing technology, and then electroforming technology is employed to replicate the Ni mold insert of the microlens arrays. Finally, micro hot embossing is performed to replicate the molded microlens arrays from the Ni mold insert. The resin material is used as the dispensing material, which is dropped on a glass substrate. The resin is exposed to a 380 W halogen light. It becomes convex under surface tension on the glass substrate. A master for the microlens arrays is then obtained. A 150-nm-thick copper layer is sputtered on the master as an electrically conducting layer. The electroforming method replicates the Ni mold insert from the master of the microlens arrays. Finally, micro hot embossing is adopted to replicate the molded microlens arrays. The micro hot embossing experiment employs optical films of polymethylmethacrylate (PMMA) and polycarbonate (PC). The processing parameters of micro hot embossing are processing temperature, embossing pressure, embossing time, and de-molding temperature. Taguchi's method is applied to optimize the processing parameters of micro hot embossing for molded microlens arrays. An optical microscope and a surface profiler are utilized to measure the surface profile of the master, the Ni mold insert and the molded microlens arrays. AFM is employed to measure the surface roughness of the master, the Ni mold insert and the molded microlens arrays. The sag height and focal length are determined to elucidate the optical characteristics of the molded microlens arrays. Copyright © 2009 John & Sons, Ltd.

The fabrication of three-dimensional (3D) architectures withnanoscale dimensions is still an evolving research area ofnanotechnology. Various methodologies including conven-tional and unconventional fabrications, such as photolitho-graphy, scanning beam lithography, molding, embossing, andimprinting, have been developed in the past decade.

The hot embossing process has so far been developed mainly for replication of surface structures on thermoplastic substrates. Because of the lack of a through-thickness action, fabrication of discrete microparts such as microgears is considered difficult. In this study, embossing molds having multiple microcavities were used in a through-thickness embossing process with a rubber-assisted ejection mechanism. Microparts made of HDPE and ABS with each part weighing approximately 1 and 1.4 mg, respectively, were produced. When in the mold, embossed microparts were intermittently connected to each other through thin residual films of a thickness approximately 20 μm. The residual films were detached from the microparts during a rubber-assisted ejection stage. Because no resin delivery paths, e.g., runners and gates, are needed for microcavities on the multicavity embossing mold, this micropart fabrication process could replace micro injection molding in many applications. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

For the investigation of the effect of 3-dimensional structures upon cell attachment and growth, polymeric micropyramids with dimensions comparable to the size of cells were fabricated. Moulds for the hot embossing of the polymers were manufactured in silicon by photolithography and wet chemical etching. For an accurate casting the moulds need very smooth surfaces, which were achieved by using KOH/IPA for crystallographic etching. A PTFE-like layer was deposited by a RIE process from C 4 F 8 plasma to form an anti-sticking layer on the mould surfaces to result in an easy release of the embossed substrates. Preparation methods and embossing parameters were established and optimised to emboss pyramidal structures with different base lengths and distances from 1 μm to 40 μm into PMMA. The imprinted polymeric micro-structures were characterised with profilometry and SEM. First cell culture experiments were performed using neuronal and epithelial cell types on the micropyramidal surfaces to investigate their influence upon the cell-surface interactions. While both cell types attached nicely on either plane or microstructured PMMA surfaces, especially the neurite outgrowth was influenced by the pyramidal structures. The effect of the pyramidal design upon cell development might be of potential interest for the use in cell culture and tissue engineering.

A hyperelastic–viscoplastic constitutive model for amorphous polymers was used in finite element simulations of micro-hot embossing across the glass transition. The model was selected for its ability to capture finite strain temperature and rate dependence over a wide range of temperatures, including across the glass transition. The simulations focused on the glass transition temperature regime, and particularly probed the effects of time and temperature during cooling and mold release. The results show that strong temperature sensitivity of the material across the glass transition leads to a wide range of required embossing force and springback. The interplay between changes in material properties upon cooling and stress relaxation can lead to significant increases in embossing force during the cooling stage, especially when high cooling rates are employed. The effects of thermal expansion also complicate the problem during rapid cooling. Nonlinear material behavior is shown to affect results in parametric hot embossing studies. Careful tailoring of embossing temperature, cooling rate, and demolding temperature is critical in acceptable feature replication. The best results are found for moderate cooling rates, which allow adequate time for stress relaxation in the material prior to mold release. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

The microfluidic chip has been used as an example to discuss different mold insert materials by micro hot-embossing molding. For the mold insert, this study uses the SU-8 photoresist to coat on the silicon wafer, then uses UV light to expose the pattern on the surface of SU-8 photoresist, and coat the seed layer on the SU-8 structure using thermal evaporation. The micro electroforming technology has been combined to fabricate the mold inserts (Ni, Ni-Co) followed by replicating the microstructure from the metal mold insert by micro-hot embossing molding. Different processing parameters (Embossing temperature, embossing pressure, embossing time, and demolding temperature) for the properties of COP film of microfluidic chip have been discussed. The results show that the most important parameter is the embossing temperature for replication properties of molded microfluidic chip. The demolding temperature is the most important parameter for surface roughness of the molded microfluidic chip. The Ni-Co mold insert is the most suitable mold material for molded microfluidic chip by microhot embossing molding. The bonding temperature is the most important factor for the bonding strength of sealed microfluidic chip by tensile bonding test. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers

A low cost zinc oxide embossing technique is reported as a method of fabricating structures relevant to a variety of applications. A zinc based sol–gel material was prepared from zinc acetate [Zn(C2H3O2)2], monoethanolamine [H2NC2H4OH] and isopropanol. The sol–gel was cast into a polydimethylsiloxane (PDMS) mould a track design, placed in contact with the substrate and dried under vacuum at 70 °C for 3 hours. The formed track pattern was further densified to provide a stable conductor film that retained the embossed shape. An optimum Zn sol–gel content of 0.6 M was identified. The embossed films had a transparency of greater than 83% in the visible region. The optical bandgap energy was evaluated to be 3.306 eV. The influence of ZnO sol–gel film synthesis and embossing parameters on the microstructure, morphology and optical transparency of fabricated structures is described. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Summary We use near-field optical microscopy to investigate the early state formation of photo-induced topographical structures on the free surface of azobenzene-containing polymers. The near-field technique is employed to monitor in real time the mass migration during the embossing of the surface of 50/50 copolymer films of polymethacrylate and polymethacrylate containing 3-methyl-4′-pentyloxy-azobenzene units. The dynamic of surface relief formation induced by light have been investigated as a function of the sample temperature. Furthermore, a formula derived from Navier–Stokes equations for classical laminar flow has been used to fit the mass displacement data during the embossing process. Excellent agreements between the experimental data and the fitting formula have been found for all the temperature considered.

Micropatterning technology[1–3] has been a major driving force behind the development of organic microelectronic devices. There have been significant efforts devoted to exploring this technology for the fabrication of conducting polymer (CP)-based devices in particular, because CPs[4–6] exhibit the unique advantages of tunable conductance, chemical specificity, flexible modification, and low fabrication cost. In general, most of the existing micropatterning approaches,[1–3] for example, the embossing method,[7] imprint lithography,[8] capillary molding,[9, 10] and microcontact printing,[11, 12] require the use of prefabricated solid molds or templates to determine the features and dimensions of the micropatterns. These molds and templates are normally fabricated by lithographic means, so their embedded features are very much fixed and it is unlikely that they would be reprogrammed for different micropattern features.

Nanoimprint lithography (NIL) is a patterning technique that has emerged as one of the most promising technologies for high-throughput nanoscale replication. Several applications in electronics, photonics, magnetic devices, and the biological field have been developed using this simple, low-cost, and high-resolution technique. In the biological field, DNA, proteins, and guides for molecular motors have been patterned; nanowire arrays have been fabricated for electronic applications; new magnetic devices, such as patterned magnetic media and high density quantized magnetic discs, have been engineered; and wire grid polarizers, lightemitting diodes, and diffractive optical elements have been developed for photonics. The success of NIL as a next generation lithographic technique strongly depends on the research for new materials that are better suited as the nanoimprint resist. Because imprint lithography makes a conformal replica of surface relief patterns by mechanical embossing, the resist materials used in imprinting should be deformed easily under an applied pressure. The most commonly used materials in the original NIL scheme are thermal plastic polymers, which become viscous fluids when heated above their glass transition temperatures (Tg). However the viscosity of the heated polymers is typically high and thus the imprinting process requires significant pressure. In addition, these thermal plastic resists normally have a high tendency to stick to the mold because of non-optimized chemistry and orientation of the polymer backbone structures, which seriously affects the fidelity and quality of the pattern definition. Furthermore they do not offer the necessary etch resistance. Therefore, a nanoimprint resist system with combined mold-release and etch-resistance properties that allows fast and precise nanopatterning is highly desirable. Thermally curable monomers are very attractive materials for nanoimprint applications because they present in the liquid state, making it possible for them to be imprinted in a short period of time under low pressure and temperature, in sharp contrast to thermal plastic polymers. As one of these materials, poly(dimethylsiloxane) (PDMS) has previously been used by several research groups for micropatterning, mainly in the context of soft lithography, and has found numerous applications in fields as diverse as microelectrochemical systems (MEMS), biotechnology, photonics, and nanoelectronics. In addition to its well known transparency to UV and visible light along with its good biocompatibility, it has a low surface energy (18–21 mN m) that allows easy mold release without causing any structural damage to the imprinted structures; moreover, it posses a high resistance to oxygen plasma because of a higher silicon content. However, the PDMS material made from commercial Sylgard 184 as precursor is not suitable for nanoimprint applications because of two significant drawbacks. Firstly, its curing typically requires hours, which is impractical as a resist material for NIL. Secondly, the cured material has a low modulus of ca. 2 MPa, which not only makes the imprinted pattern prone to lateral collapsing when replicating submicrometer patterns, but more importantly, it makes it impossible to replicate features less than hundreds of nanometers. The latter point can be understood by considering the radius of curvature of a cured PDMS with a modulus E and surface energy (c), which is r = c/E. Well-defined and sharp-corner structures required for nanometer scale lithography can not be satisfied with a large radius of curvature. As an illustration, an attempt was made to replicate a grating pattern with a 350 nm line width and spacing by using the Sylgard 184 formulation. As shown in the atomic force microscopy (AFM) images (Figure 1), not only are all the lines rounded at the top, but massive collapsing can be seen everywhere in the sample. As an improvement, a higher modulus (ca. 8 MPa) poly(dimethylsiloxane) (hard-PDMS) was developed by Schmid and Michel to achieve the patterning of 80 nm diameter posts with an aspect ratio 1.25 (depth/width) for soft lithography. Unfortunately, the imprinting cycle (heating–cooling time) for this hard-PDMS remained very long (about 2 h). Following the same strategy, C O M M U N IC A TI O N

In this paper, we have developed novel pixel design of advanced fringe field switching (AFFS) mode with high transmittance and high reflectance for superior sunlight readability. These properties are achieved by high aperture pixel design and by reflective areas of metal embossing pattern on the gate area as well as data bus line with BM-less of color filter on the data bus line. We also achieved low surface reflectance with anti-reflective (AR) polarizer and high transmittance with DBEF polarizer. In this paper, we will show panel characteristics of 10.4-inch XGA tablet with improved indoor and outdoor images.

A new embossing method based on sacrificial templates and fast surface heating was developed, in which the de-embossing step was avoided to prevent deformation or damage of polymer microstructures. The microstructures of interest have a high feature density, high aspect ratio, and/or undercuts. Soft lithography was used to prepare a water-soluble mold, using polyvinylpyrrolidone (PVP) in the hot embossing process. Arrays of microchannels and microgrids with an aspect ratio greater than five were replicated on poly(DL-lactide-co-glycolide) (PLGA). In conjunction with localized surface heating of the polymer surface by a laser/IR system, this technique was able to micromold high temperature polymers such as poly(methyl methacrylate) (PMMA) with high aspect ratios. POLYM. ENG. SCI., 47:830–840, 2007. © 2007 Society of Plastics Engineers