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Thesupramolecular assembly of photoactive azobenzenes with passivepolymers via halogen or hydrogen bonding is a cost-effective way todesign materials for various photomechanical applications that convertlight energy directly into macroscopic motion, for instance, in all-opticalsurface patterning and photochemical imaging of plasmonic structures.To elucidate the molecular-level origins of this motion, we show,by coupling dynamic infrared spectroscopy to a photo-orientation setup,that supramolecular bonds above a certain interaction strength thresholdare photostable under vigorous photoisomerization cycling and capableof translating the photo-orientation of azobenzenes into the orientationof nonabsorbing host polymer side chains. A correlation is found betweenazobenzene photoinduced molecular orientation and macroscopic all-opticalsurface patterning efficiency. The improved performance of halogen-bondedsystems in photopatterning applications can be related to the absenceof a plasticizing effect on the polymer matrix, which may enable thematerial to retain an optimal glass transition temperature, in contrastto hydrogen-bonded and nonbonded references. Thus, our results providedesign guidelines in terms of the nature and strength of the supramolecularinteraction and of the degree of azo functionalization needed to optimizethe motion transfer to passive polymers. [ABSTRACT FROM AUTHOR]

A device is investigated that continuouslyand directly convertslight into mechanical energy, using polymers and photodissociation.A polymer brush tethered to a surface is brought into contact witha parallel plate a small distance above it that contains reactionsites where photodissociation of bound polymer and light can occur.Under the appropriate conditions, the collective effect of these polymersis predicted to apply a force parallel to the plates, converting incominglight into mechanical work. Numerical work is carried out to understandthis effect, a three-dimensional Langevin simulation, solution tothe Fokker–Planck equation, and a one-dimensional Monte Carlosimulation. Theoretical analysis of the Fokker–Planck equationis used to study a model where equilibration of the unbound stateoccurs and equilibration to a metastable equilibrium is achieved inthe bound state. It is shown that the work per cycle can be made muchlarger than the thermal energy but at the expense of requiring a greatlydiminished photodissociation rate. Parameters are discussed in orderto optimize mechanical energy conversion. [ABSTRACT FROM AUTHOR]

Background: As the most abundant protein in human tissues, the use of collagen is essential in the fields of biological science and medicine.Objective: The aim of this study is to investigate the mechanical effect of pulsed laser irradiation on collagen tissue.Methods: With various laser parameters such as peak power, pulse width, and repetition rate, the induced stresses on samples were measured and analyzed. Monte Carlo simulation was performed to investigate the effect of laser parameters on the collagen sample.Results: The results indicated that the magnitude of mechanical stress could be controlled by various laser parameters.Conclusions: This study can be used in biostimulation for therapy and mechanoreceptor stimulation for tactile application. [ABSTRACT FROM AUTHOR]

Bilayer photomechanical films are fabricated by depositing one layer of molecular azobenzene chromophores onto flexible low-density polyethylene substrates. The photoinduced bending and unbending behavior of five azobenzene derivatives including azobenzene, 4-hydroxy-azobenzene, 4-((4-hydroxyphenyl)diazenyl)bezoitrile, 4-((4-methoxyph-enyl)diazenyl)phenol, and 4-(phenyldiazenyl)phenol is systematically studied by considering the incident light intensity and the thickness of the coated chromophore layers. Precise control of photoinduced curling of the bilayer film is successfully achieved upon irradiation with two beams of UV light, and the curled films can be recovered by thermal relaxation in the dark. The easily fabricated bilayer films show fast photomechanical response, strong photoinduced stress, and stability similar to crosslinked polymeric films. [ABSTRACT FROM AUTHOR]

The power of electroforming to faithfully capture and replicate metal features down to the atomic scale has been elegantly exploited to consistently produce OLED deposition masks with high yields. Using a unique combination of photolithography and electroforming, we have produced large area, (10-15) µm thick nickel masks with apertures as small as 14 µm. This manufacturing technology is targeted to provide OLED masks for future generations of ultra-high resolution display manufacturing, possibly down to 10 micron aperture sizes. [ABSTRACT FROM AUTHOR]

Poly(acrylic acid)/azobenzene microcapsules were obtained through distillation precipitation polymerization and the selective removal of silica templates by hydrofluoric acid etching. The uniform, robust, and monodisperse microcapsules, confirmed by transmission electron microscopy and scanning electron microscopy, had reversible photoisomerization under ultraviolet (UV) and visible light. Under UV irradiation, azobenzene cross-linking sites in the main chain transformed from the trans to cis isomer, which induced the shrinkage of microcapsules. These photomechanical effects of azobenzene moieties were applied to the encapsulation and release of model molecules. After loading with rhodamine B (RhB), the release behaviors were completely distinct. Under steady UV irradiation, the shrinkage adjusted the permeability of the capsule, providing a novel way to encapsulate RhB molecules. Under alternate UV/visible light irradiation, a maximal release amount was reached due to the continual movement of shell networks by cyclic trans-cis photoisomerization. Also, microcapsules had absolute pH responsiveness. The diffusion rate and the final release percentage of RhB both increased with pH. The release behaviors under different irradiation modes and pH values were in excellent agreement with the Baker-Lonsdale model, indicating a diffusion-controlled release behavior. Important applications are expected in the development of photocontrolled encapsulation and release systems as well as in pH-sensitive materials and membranes. [ABSTRACT FROM AUTHOR]

As a polymeric system incorporating rigid molecules within its structure, the liquid-crystal network (LCN) has been envisaged as a novel heterogeneous material. Under the influence of external stimuli, the orientational order of the liquid-crystalline phase becomes dilute and overall anisotropy is hence decreased; the actinic light absorbed by photochromic molecules, for example, induces the geometric isomerization and subsequently yields internal stress within the local network. In this study we investigate light- and temperature-induced spontaneous deformations of the LCN structure via a three-dimensional finite element model that incorporates geometric nonlinearity with a photomechanical constitutive model. We first examine the bending behavior and its nonlinearity and then parametrically study the various behaviors that stem from different origins ranging from the microscale to the macroscale: (i) the geometry of the LCN film, (ii) the macroscopic global order, (iii) the distorted mesogenic orientation due to the Fredericks distortion, and (iv) defect-induced instability. These interrelated behaviors demonstrate both the simulation capability and the necessity of the presenting framework. By employing a nonlinear consideration along with a microscopic shape parameter r the present approach facilitates further understanding of photomechanical physics such as the deconvolution of various stimuli and the deformed shape obtained due to snap-through instability. Furthermore, this study may offer insight into the design of light-sensitive actuation systems by deepening our knowledge and providing an efficient measure. [ABSTRACT FROM AUTHOR]

The extension o f electrophotographic (EP) printing into the additive manufacturing space has been seen as a natural step for this technology; however, the self-insulating nature of the process has prevented the creation of structures beyond a limited number of layers where suiface defects are evident. This paper examines two control strategies for EP-based three-dimensional (EP3D) printing that minimize the suiface defects to obtain the accurate reproduction of the intended 3D geometry. The strategies rely not on material deposition control but rather on progressively compensating layer after layer for irregularities forming on the suiface. This represents an important step toward the development and future commercialization of EP3D printing. [ABSTRACT FROM AUTHOR]

Patterning process control has undergone major evolutions over the last few years. Critical dimension, focus, and overlay control require deep insight into process-variability understanding to be properly apprehended. Process setup is a complex engineering challenge. In the era of mid k1 lithography (>0.6), process windows were quite comfortable with respect to tool capabilities, therefore, some sources of variability were, if not ignored, at least considered as negligible. The low k1 patterning (<0.4) era has broken down this concept. For the most advanced nodes, engineers need to consider such a wide set of information that holistic processing is often mentioned as the way to handle the setup of the process and its variability. The main difficulty is to break down process-variability sources in detail and be aware that what could have been formerly negligible has become a very significant contributor requiring control down to a fraction of a nanometer. The scope of this article is to highlight that today, engineers have to zoom deeper into variability. Even though process tools have greatly improved their capabilities, diminishing process windows require more than tool-intrinsic optimization. Process control and variability compensations are major contributors to success. Some examples will be used to explain how complex the situation is and how interlinked processes are today. [ABSTRACT FROM AUTHOR]

In this work, we first report a facile, low-cost and high-throughput method for photolithographical fabrication of microfluidic cloth-based analytical devices (μCADs) by simply using a cotton cloth as a substrate material and employing an inexpensive hydrophobic photoresist laboratory-formulated from commercially available reagents, which allows patterning of reproducible hydrophilic–hydrophobic features in the cloth with well-defined and uniform boundaries. Firstly, we evaluated the wicking properties of cotton cloths by testing the wicking rate in the cloth channel, in combination with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses. It is demonstrated that the wicking properties of the cloth microfluidic channel can be improved by soaking the cloth substrate in 20 wt% NaOH solution and by washing the cloth-based microfluidic patterns with 3 wt% SDS solution. Next, we studied the minimum dimensions achievable for the width of the hydrophobic barriers and hydrophilic channels. The results indicate that the smallest width for a desired hydrophobic barrier is designed to be 100 μm and that for a desired hydrophilic channel is designed to be 500 μm. Finally, the high-throughput μCADs prepared using the developed fabrication technique were demonstrated for colorimetric assays of glucose and protein in artificial urine samples. It has been shown that the photolithographically patterned μCADs have potential for a simple, quantitative colorimetric urine test. The combination of cheap cloth and inexpensive high-throughput photolithography enables the development of new types of low-cost cloth-based microfluidic devices, such as “microzone plates” and “gate arrays”, which provide new methods to perform biochemical assays or control fluid flow. [ABSTRACT FROM AUTHOR]

Attempted cocrystallisation of brominated and iodinated octafluoroazobenzene derivatives with morpholine led to the exhaustive replacement of fluorine substituents that are in ortho-positions to the azobenzene with sterically demanding morpholine groups. The resulting molecules exhibit a highly unusual strained conformation of the azobenzene unit, in which the terminal phenyl rings adopt a mutually nearly completely orthogonal orientation. Substitution of ortho-fluorine groups with N-morpholine fragments provides molecules with active halogen bond donor and acceptor sites that guide the molecular self-assembly in the solid state towards the formation of polymeric halogen-bonded chains. [ABSTRACT FROM AUTHOR]

Photomechanical and photochromic activities are reported for single crystals of a new multiresponsive material, 2,4-di-tert-butyl-6-((e)-((4-((E)-phenyldiazenyl)phenyl)imino)methyl)phenol (Azim-1), with two photoactive groups that can undergo photoisomerization (azo and imine), and an ortho-hydroxy group that is capable of proton transfer. Upon irradiation with UV light, platy and needle-shaped crystals of Azim-1 rapidly bend towards the light source and return to their initial shape as soon as the irradiation is terminated. Upon prolonged exposure to UV light, the crystals change their color from yellow to red. The crystal structure of non-irradiated Azim-1 is reported, and the mechanisms of the photomechanical and photochromic responses are discussed. [ABSTRACT FROM AUTHOR]

Transdermal drug delivery is hindered by the barrier property of the stratum corneum. It limits the route to transport of drugs with a log octanol–water partition coefficient of 1 to 3, molecular weight of less than 500 Da and melting point of less than 200 °C. Active methods such as iontophoresis, electroporation, sonophoresis, magnetophoresis and laser techniques have been investigated for the past decades on their ability, mechanisms and limitations in modifying the skin microenvironment to promote drug diffusion and partition. Microwave, an electromagnetic wave characterized by frequencies range between 300 MHz and 300 GHz, has recently been reported as the potential skin permeation enhancer. Microwave has received a widespread application in food, engineering and medical sectors. Its potential use to facilitate transdermal drug transport is still in its infancy stage of evaluation. This review provides an overview and update on active methods utilizing electrical, magnetic, photomechanical and cavitational waves to overcome the skin barrier for transdermal drug administration with insights into mechanisms and future perspectives of the latest microwave technique described. [ABSTRACT FROM AUTHOR]

Wireless transduction of light into mechanical work manifested as shape-changing surfaces, adaptive structures, or actuators is a topic of considerable recent interest. In the work reported here, the photomechanical responses of a new series of crosslinked azobenzene-functionalized polyimides prepared with increasing backbone rigidity over a range of crosslinker concentrations are examined. The baseline properties of the materials were characterized with X-ray diffraction, thermal analysis, and photomechanical examination including cantilever bending experiments and tensile tests. Increasing the rigidity of the backbone repeat unit reduces the magnitude of the shape change (observed as cantilever deflection) but increases the magnitude of photogenerated stress (in tensile tests). The promise of these materials as wireless actuators was examined in photoinitiated snap-through experiments. [ABSTRACT FROM AUTHOR]

Single femtosecond laser pulses are employed to ablate an aluminium target in vacuum, and the particle size distribution of the ablated material deposited on a mica substrate is examined with atomic force microscopy (AFM). The recorded AFM images show that these particles have a mean radius of several tens of nanometres. It is also determined that the mean radius of these deposited nanoparticles increases when the laser fluence at the aluminium target increases from 0.44 J/cm 2 to 0.63 J/cm 2 . The mechanism of the laser-induced nanoparticle generation is thought to be photomechanical tensile stress relaxation. Raman spectroscopy measurements confirm that the nanoparticles thus produced have the same structure as the bulk aluminium. [ABSTRACT FROM AUTHOR]

Westudy light-induced deformation of azobenzene elastomers whichcan display liquid-crystalline (LC) order. It is shown that photomechanicalbehavior of azobenzene elastomers is determined by the strength ofthe LC interactions, which is proportional to the density of rodlikeazobenzene chromophores. At weak LC interactions, a uniaxial orderand uniaxial deformation of azobenzene elastomers along the polarizationvector of the light Eis observed. At strong LC interactions,the light is able to induce a phase transition from the uniaxial tothe biaxial state, with two axes being related to the vector Eand to a preferable alignment of the chromophores in theplane perpendicular to E. The phase transition can beof either the first or the second order. Azobenzene elastomers candemonstrate elongation or contraction along the polarization vector E, depending on the orientation distribution of chromophoresaround the main chains of network strands. The results of the theoryare in a qualitative agreement with experiments and computer simulations,which demonstrate biaxial ordering in azo-containing polymers. [ABSTRACT FROM AUTHOR]

Photomechanicaleffects in polymeric materials directly convertinput photonic energy into a macroscopic mechanical output. The photoinitiatedmechanical output of these materials is typically dominated by classicalmechanics, primarily derived from the material stiffness and samplegeometry. Accordingly, large magnitude shape change (e.g., motion)is typically traded for large magnitude force generation. Here, wereport on the systematic preparation and comparison of photomechanicaleffects in a set of isomerically varied linear and cross-linked azobenzene-functionalizedmaterials that demonstrate the critical role of segmental mobility(evident in the magnitude of the β-transition) to assimilatethe typically exclusive properties of large force generation and largeshape change in a single material. [ABSTRACT FROM AUTHOR]

Gears are widely employed in farm machinery transmission units. However, the severe environment imposed to the machine operation generates special problems associated to maintenance, as well as to the expected time life. Machinery which works on field are exposed to excessive dust, moisture, heat, chemicals, uneven mechanical loading and quite frequently the manufacturer recommendations are not adequate or not even available. Based on that, the proposal of new methods for strain and stress distribution analysis on gears under different working conditions is considered necessary. This research paper introduces the application of moiré methods to replace the popular strain gage technique. The proposed method is included in the photomechanical techniques and is considered of easy as well as of low cost application. The moiré family of methods is based on the projection of optical grids onto the object under analysis, generating optical fringes which displace as the object is deformed under mechanical loads. In this research work the tests were carried under different working conditions, as (1) non lubricated clean gears, (2) clean and lubricated, (3) lubricated and contaminated with soil. The comparison of these three situations indicated the influence of soil contamination as well as of the lubrication. The conclusion emphasizes the application of the proposed method to gear transmission design as well as to maintenance. [ABSTRACT FROM AUTHOR]

This paper reports fabrication of 2-DOF vibratory gyroscope using SU-8 based UV-LIGA process. The device structure is designed to be symmetrical in order to match the resonance frequencies of drive and sense mode oscillators and also to minimize their relative temperature dependent drift. The overall arrangement is such that the two vibration modes do not affect each other and therefore, mechanical decoupling is achieved which helps in minimizing bias drift. The design is optimized to be compatible with the UV-LIGA process having 10 μm thick electroformed nickel as structural layer. Photolithography to create 11 μm thick SU-8 molds for electroforming sacrificial copper and structural nickel layer is optimized using multiple exposure technique that ensures near vertical side walls. Since the highly cross-linked SU-8 remaining after development is difficult to remove reliably from high aspect ratio structures without damage or alteration to the electroformed metals, a 2.45 GHz MW plasma etching process is developed with CF/O mixes. The fabricated device is checked for off-plane misalignment between the stationary and movable comb fingers using white light interferometry and it is found to be almost negligible. Also, the prototype device is characterized for amplitude and phase spectral responses using Polytec MSA-500 Micro System Analyzer. The drive and sense mode resonance frequencies are observed at 7.3 and 7.1 kHz respectively against the mode matched designed frequency of 7.5 kHz. [ABSTRACT FROM AUTHOR]

A series of rapid and inexpensive methods to produce elastically soft sensors and circuits in minutes using a CO2 laser (10.6 μm wavelength) are introduced. These soft-matter electronics are composed of laser-patterned films of conductive poly(dimethylsiloxane) (cPDMS) and liquid-phase gallium-indium (GaIn) alloy embedded in a thin sheet of soft silicone elastomer. Direct laser patterning eliminates the need for photolithography, replica molding, and customized inkjet or microcontact (μCP) printing, and allows conductive traces of cPDMS and liquid GaIn to be rapidly integrated into a single soft-matter circuit. The versatility of this fabrication method is demonstrated by the production of a variety of electrically functional soft-matter sensors and circuit elements that contain features with >150 μm planar dimensions. It is postulate that in the case of GaIn alloy patterning occurs when the recoil force of the escaping vapor exceeds the liquid's surface tension. This mechanism exploits the unique 'moldability' of liquid GaIn alloy, which forms a surface oxide of Ga2O3 that allows the patterned film to maintain its shape. [ABSTRACT FROM AUTHOR]

Photoinduced color change of naphthalene diimides (NDIs) bearing alkylamine moieties has been observed in the solid state. The color change is attributed to the generation of a NDI radical-anion species, which may be formed through a photoinduced electron-transfer process from the alkylamine moiety to the NDI. The photosensitivity of NDIs is highly dependent on the structures of the alkylamine moieties. Crystallographic analysis, kinetic analysis, UV/Vis/NIR spectroscopic measurements, and analysis of the photoproduct suggested that a radical anion was formed through an irreversible process initiated by proton abstraction between an amine radical cation and the neutral amine moiety. The radical anions formed stacks including mixed-valence stacks and radical-anion stacks, as shown by the broad absorption bands in near-IR spectra. These photosensitive NDIs also showed crystal bending upon photoirradiation, which may be associated with a change in the intermolecular distance of the NDI stacks by the formation of monomeric radical anions, mixed-valence stacks, and radical-anion stacks. [ABSTRACT FROM AUTHOR]

This work demonstrates an innovative microfabricated air-cooling technology that employs an electrohydrodynamic (EHD) corona discharge (i.e., ionic wind pump) for electronics cooling applications. A single, microfabricated ionic wind pump element consists of two parallel collecting electrodes between which a single emitting tip is positioned. A grid structure on the collector electrodes can enhance the overall heat-transfer coefficient and facilitate an IC compatible batch process. The optimized devices studied exhibit an overall device area of 5.4 mm x 3.6 mm, an emitter-to-collector gap of 0.5 mm. and an emitter curvature radius of ~12.5 p.m. The manufacturing process developed for the device uses glass wafers, a single mask-based photolithography process, and a low-cost copper-based electroplating process. Various design configurations were explored and modeled computationally to investigate their influence on the cooling phenomenon. The single devices provide a high heat-transfer coefficient of up to 3200 Wlrrf K and a coefficient of performance (COP) of up to ~47. The COP was obtained by dividing the heat removal enhancement, ΔQ by the power consumed by the ionic wind pump device. A maximum applied voltage of 1.9kV, which is equivalent to approximately 38 mW of power input, is required for operation, which is significantly lower than the power required for the previously reported devices. Furthermore, the microfabricated single device exhibits a flexible and small form factor, no noise generation, high efficiency, large heat removal over a small dimension and at low power, and high reliability (no moving parts); these are characteristics required by the semiconductor industry for next generation thermal management solutions. [ABSTRACT FROM AUTHOR]

PEDOT:PSS is a robust conductive polymer which is promising in future flexible applications. In order to integrate PEDOT:PSS into various devices, we introduce a simple patterning scheme for PEDOT:PSS. By using a silver interlayer, conventional photolithographic processes can be used. High resolution patterns and ITO-free OLEDs are demonstrated. [ABSTRACT FROM AUTHOR]

Ultraviolet-assisted three-dimensional (3D) printing (UV-3DP) was used to manufacture photopolymer-based microdevices with 3D self-supported and freeform features. The UV-3DP technique consists of the robotized deposition of extruded filaments, which are rapidly photopolymerized under UV illumination during the deposition process. This paper systematically studies the processing parameters of the UV-3DP technique using two photo-curable polymers and their associated nanocomposite materials. The main processing parameters including materials' rheological behavior, deposition speed and extrusion pressure, and UV illumination conditions were thoroughly investigated. A processing map was then defined in order to help choosing the proper parameters for the UV-3DP of microstructures with various geometries. Compared to self-supported features, the accurate fabrication of 3D freeform structures was found to take place in a narrower processing region since a higher rigidity of the extruded filament was required for structural stability. Finally, various 3D self-supported and freeform microstructures with high potential in micro electromechanical systems, micro-systems and organic electronics were fabricated to show the capability of the technique. [ABSTRACT FROM AUTHOR]

As near-infrared spectroscopy (NIRS) broadens its application area to different age and disease groups, motion artifacts in the NIRS signal due to subject movement is becoming an important challenge. Motion artifacts generally produce signal fluctuations that are larger than physiological NIRS signals, thus it is crucial to correct for them before obtaining an estimate of stimulus evoked hemodynamic responses. There are various methods for correction such as principle component analysis (PCA), wavelet-based filtering and spline interpolation. Here, we introduce a new approach to motion artifact correction, targeted principle component analysis (tPCA), which incorporates a PCA filter only on the segments of data identified as motion artifacts. It is expected that this will overcome the issues of filtering desired signals that plagues standard PCA filtering of entire data sets. We compared the new approach with the most effective motion artifact correction algorithms on a set of data acquired simultaneously with a collodion-fixed probe (low motion artifact content) and a standard Velcro probe (high motion artifact content). Our results show that tPCA gives statistically better results in recovering hemodynamic response function (HRF) as compared to wavelet-based filtering and spline interpolation for the Velcro probe. It results in a significant reduction in mean-squared error (MSE) and significant enhancement in Pearson's correlation coefficient to the true HRF. The collodion-fixed fiber probe with no motion correction performed better than the Velcro probe corrected for motion artifacts in terms of MSE and Pearson's correlation coefficient. Thus, if the experimental study permits, the use of a collodion-fixed fiber probe may be desirable. If the use of a collodion-fixed probe is not feasible, then we suggest the use of tPCA in the processing of motion artifact contaminated data. [ABSTRACT FROM AUTHOR]

Precise evaluation of the electrostatic potential distributions of and around samples with multiple charges using electron holography has long been a problem due to unknown perturbation of the reference wave. Here, we report the first practical application of split-illumination electron holography (SIEH) to tackle this problem. This method enables the use of a non-perturbed reference wave distant from the sample. SIEH revealed the electrostatic potential distributions at interfaces of the charged particles used for development in electrophotography and should lead to dramatic improvements in electrophotography. [ABSTRACT FROM AUTHOR]

The optical diffraction limit has stood for a long time in the way of achieving higher optical resolution in far-field imaging, photolithography, and optical data storage. We present here a simple and original concept for broadband far-field imaging in the visible and ultraviolet range that beats this limit. A finite-sized ultrathin metallic slab is used to encode subwavelength details of the broadband field radiated by an object. This field excites a set of surface plasmon modes on the finite-sized slab that radiates in the far field. A numerical time reversal imaging process is applied to reconstruct the image of the object with a resolution smaller than λ/6 for a gold slab and λ/8 for a silver slab. With these structures, the highest spatial frequencies are no longer limited by the pitch of the array of the subwavelength resonators as in classical metalenses. We show that the resolution depends mainly on the intrinsic properties of the metal but can be slightly controlled by the geometry design of the slab. Thanks to advances in the control of light in space and time, this concept would provide a promising alternative for high-resolution imaging techniques in the visible and ultraviolet range. [ABSTRACT FROM AUTHOR]

Micro-scale pentacene organic field effect transistors (OFETs) were fabricated on a flexible poly(ethylene terephthalate) (PET) substrate. By applying a highly fluorinated developing solvents and its compatible photoresist materials, it has become possible to make the micro-scale patterning for organic devices using standard photolithography without damaging the underlying polymer layers. The flexible pentacene OFETs with 3 μm-sized channel length exhibited stable electrical characteristics under bent configurations and under a large number of repetitive bending cycles. Furthermore, we demonstrated micro-scale organic complementary inverters on a flexible PET substrate using p-type pentacene and n-type copper hexadecafluorophthalocyanine materials. [ABSTRACT FROM AUTHOR]

Abstract: Disperse red 1 azobenzene (DR1) doped poly(methyl methacrylate) (PMMA) optical fiber has been shown to have a fast photomechanical response upon 633nm laser irradiation originating in photo-isomerization of the dopants between the cis and trans forms. In this work, laser light of 355nm wavelength is used to investigate the trans to cis isomerization process, which should result in length contraction. A three-point-contact optically actuated beam-controlling mount is made of dye doped polymer fiber segments and metal-coated microscope coverslips to measure the photomechanical response. The length change of the fiber is determined from a quadrant photodetector reading upon beam deflection. The fiber is observed to elongate upon UV irradiation. We find that for DR1 dye in PMMA polymer, the dominant mechanism of the photomechanical effect is photo-thermally stimulated isomerization rather than direct photoisomerization. [Copyright &y& Elsevier]

Separation and characterization of wear debris from ferrograph images are demanded for on-line analysis. However, particle overlapping issue associated with wear debris chains has markedly limited this technique due to the difficulty in effectively segmenting individual particles from the chains. To solve this bottleneck problem, studies were conducted in this paper to establish a practical method for wear debris separation for on-line analysis. Two conventional watershed approaches were attempted. Accordingly, distance-based transformation had a problem with oversegmentation, which led to overcounting of wear debris. Another method, by integrating the ultimate corrosion and condition expansion (UCCE), introduced boundary-offset errors that unavoidably affected the boundary identification between particles, while varying the corrosion scales and adopting a low-pass filtering method improved the UCCE with satisfactory results. Finally, together with a termination criterion, an automatic identification process was applied with real on-line wear debris images sampled from a mineral scraper gearbox. With the satisfactory separation result, several parameters for characterization were extracted and some statistics were constructed to obtain an overall evaluation of existing particles. The proposed method shows a promising prospect in on-line wear monitoring with deep insight into wear mechanism. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrated fabrication of photo-mechanical materials alternatively-including azobenzene-side-chained acrylate polymer, PMAz6Ac, and polyvinyl alcohol, PVA, without cross-linking. The multi-bilayered (PMAz6Ac/PVA) n films were obtained by alternative spin-coating methods of PVA and PMAz6Ac solutions on glass substrates. After thermal treatment, the azobenzene groups as mesogen were self-organized and were induced out-of-plane orientation. After UV irradiation (λ=375nm), the self-standing films obtained by peeling off was bent to an opposite side of the light source, and the bended film reverted toward the initial position by following visible light irradiation (λ>420nm). Their optical properties of the PMAz6Ac layers indicated that change of molecular orientation, out-of-plane orientation and disordered random, of azobenzene groups in the PMAz6Ac layers closely related with the photo-mechanical behaviors. [Copyright &y& Elsevier]

Abstract: A three-dimensional (3D) graphene incorporated electrochemical sensor was constructed for sensitive enzyme based phenol detection. To form the 3D graphene structure, polydimethylsiloxane (PDMS) micropillars were fabricated in the microchannel by using a conventional photolithography and the surface was modified with 3-aminopropyltriethoxysilane. Then, the negatively charged graphene oxide sheets were electrostatically adsorbed on the PDMS micropillar surface, and reduced in the hydrazine vapor. The resultant 3D graphene film provides a conductive working electrode as well as an enzyme-mediated sensor with a large surface area. After bonded with an electrode patterned glass wafer, the 3D graphene based electrochemical sensor was produced. Using the 3D graphene as a working electrode, an excellent electron transfer property was demonstrated by cyclic voltammetry measurement in an electrolyte solution containing 1mM K3Fe(CN)6 and 0.1M KCl. To utilize the 3D graphene as an enzyme sensor, tyrosinase enzymes were immobilized on the surface of the graphene micropillar, and the target phenol was injected in the microchannel. The enzyme catalytic reaction process was monitored by amperometric responses and the limit of detection for phenol was obtained as 50nM, thereby suggesting that the 3D graphene micropillar structure enhances the enzyme biosensing capability not only by increasing the surface area for enzyme immobilization, but also by the superlative graphene conductivity property. [Copyright &y& Elsevier]

ABSTRACT This article presents an optomechanical actuator, which is driven by infra red (IR) radiation. The actuator is a nanocomposite-containing graphene platelets embedded in poly(styrene- b-isoprene- b-styrene) (SIS) matrix. 0.1 mm thick free-standing nanocomposite films are fabricated by a simple process of solvent casting. We demonstrate that graphene/SIS nanocomposite contracts on irradiation with IR radiation under strained conditions, whereas expansion behavior was exhibited by them when no prestrain is applied. A maximum photomechanical stress of 28.34 kPa and strain upto 3.1% was obtained for these nanocomposite actuators. We have also studied the mechanical characteristics and thermal degradation of these nanocomposite actuators. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3902-3908, 2013 [ABSTRACT FROM AUTHOR]

Materials, exhibiting light induced strain, are of great interest for future generation wireless remote control photo-actuators. Herein, we demonstrate the light triggered actuation in thermally reduced graphene oxide (TRGO)–Polydimethylsiloxane (PDMS) nanocomposite with much larger photomechanical stress and strain. The photomechanical stress for TRGO–PDMS nanocomposite is more than 100% that of carbon nano tube (CNT)–PDMS nanocomposites. Results show that 1 wt.% of TRGO–PDMS nanocomposite at 46% prestrain exhibits a photomechanical stress of 133.44 kPa and a strain of 7.17%, which is much greater than that reported for graphene–nanoplatelet-PDMS nanocomposite photoactuators. [ABSTRACT FROM PUBLISHER]

Mesa structural n-type nanocrystalline (NC) FeSi2/p-type Si heterojunctions were fabricated by a liftoff technique combined with photolithography in order to improve the diode performance, particularly to reduce the parasitic capacitance. Their current-voltage characteristics were experimentally studied in the dark and under illumination using a 1.31 μm laser at room temperature. Their junction capacitance density and leakage current density were evidently reduced as compared with those of the normal structural diodes. The mesa diode exhibits a good rectifying action with a rectification ratio of approximately three orders of magnitude at bias voltages of ±1 V. The photodetection was clearly observed owing to the suppression in the dark current. The estimated detectivity is 2.0 × 109 cm√Hz/W at zero bias, which is an order of magnitude larger than that of the normal structural diodes. This should be because the formation of interface states is reduced accompanied by the interface area reduction. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Photomechanical effects in polymeric materials and composites transduce light into mechanical work. The ability to control the intensity, polarization, placement, and duration of light irradiation is a distinctive and potentially useful tool to tailor the location, magnitude, and directionality of photogenerated mechanical work. Unfortunately, the work generated from photoresponsive materials is often slow and yields very small power densities, which diminish their potential use in applications. Here, we investigate photo-initiated snap-through in bistable arches formed from samples composed of azobenzene-functionalized polymers (both amorphous polyimides and liquid crystal polymer networks) and report orders-of-magnitude enhancement in actuation rates (approaching 102 mm/s) and powers (as much as 1 kW/m3). The contactiess, ultra-fast actuation is observed at irradiation intensities <<100 mW/cm2. Due to the bistability and symmetry of the snap-through, reversible and bidirectional actuation is demonstrated. A model is developed to elucidate the underlying mechanics of the snap-through, specifically focusing on isolating the role of sample geometry, mechanical properties of the materials, and photomechanical strain. Using light to trigger contactless, ultrafast actuation in an otherwise passive structure is a potentially versatile tool to use in mechanical design at the micro-, meso-, and millimeter scales as actuators, as well as switches that can be triggered from large standoff distances, impulse generators for microvehicles, microfluidic valves and mixers in laboratory-on-chip devices, and adaptive optical elements. [ABSTRACT FROM AUTHOR]

In this review, we highlight the properties, functions and applications of stimuli-responsive hydrogel patterns in bioanalytical applications. Stimuli-responsive hydrogel patterns can be realized by well-established micro- and nanofabrication technologies such as photolithography and micromolding, and are currently adopted as active components for manipulation of flow and biosamples in microchannel and microarray systems. We overview the properties of stimuli-responsive hydrogel materials and their fabrication methods along with some representative examples in microfluidics and microarrays. [ABSTRACT FROM AUTHOR]

Highlights: [•] We developed a cylinder mold with hybrid-layered patterns. [•] A precise cutting was combined with 3-D photolithography using a flexible mask. [•] The imprint speed was improved by changing a press-force control method. [•] We succeeded in continuous imprinting on a POF at a feeding speed of 20m/min. [Copyright &y& Elsevier]