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High precision roll-to-roll processes are believed to be one of the most promising technologies for manufacturing flexible and large-area thin film electronics. However, broadband frictional disturbances caused by the guiding ball bearings affect the precision of the processing roller in the roll-to-roll system, severely hampering the quality of the manufactured products. Conventional feedback control techniques encounter difficulties in mitigating the broadband frictional disturbances. This paper presents a novel rotary system for high-precision roll-to-roll manufacturing process. Friction isolator (FI), a robust and cost-effective mechatronics method, is implemented in the system to mitigate the undesirable effects of friction during continuous printing processes. Frequency domain analysis shows that the proposed rotary system with FI achieves significantly improved attenuation of frictional disturbance, compared to the case without it. A rotary FI is designed and optimized to minimize the adverse effects of bearing friction without overly sacrificing the high rigidity of the machine. A precision rotary system is then built using the designed FI prototype. Experiments carried out on the prototype friction-isolated rotary system demonstrate up to 61% reduction in root-mean-square tracking error during constant velocity motion, compared to a conventional roll-to-roll system without FI.

Heterogeneity among particles is an inherent feature that allows nondeterministic prediction of the properties of assembled structures and materials composed of many particles. Here, we report a promising strategy to quantify the heterogeneous and anisotropic interactions between ellipsoid particles using optical laser tweezers. The configuration and separation between two particles at an oil-water interface were optically controlled, and the capillary interaction behaviors were directly observed and measured. As a result, the optimal particle configurations at energetically favorable states were obtained, and the interaction forces between the particles were identified accurately by determining the trap stiffness in the direction of major and minor axes of the particle. Visualization of the capillary field around individual particles confirmed that the capillary interactions were quadrupolar, anisotropic, and heterogeneous. The measurement method presented here can be widely used to quantify interaction fields for various types of anisotropic particles.

In this study, we measured the force of electrostatic interactions between poly(methyl methacrylate) (PMMA) particles dispersed in organic solvent mixtures of cyclohexyl bromide (CHB) and n-decane. Optical laser tweezers were employed to directly measure interactive forces between paired PMMA particles in a CHB medium that contained n-decane in various volume ratios. CHB, having a moderate dielectric constant, provided an environment with a high charge storage capacity. The addition of n-decane lowered the effective refractive index of the medium, which increased the optical trapping efficiency. We also fabricated microscope flow cells with a commonly used UV-curable adhesive and quantified the effects of dissolved adhesive compounds through interactive force measurements and nuclear magnetic resonance analysis. In addition, we studied the impact of CHB dissociation into H+ and Br- ions, which could screen electrostatic interactions.

The efficiency of two prototype catalysis systems using palladium (Pd)-coated microparticles was investigated with regard to the recovery and recyclability of the catalytic particles. One such system was the interface-adsorption method, in which polymer particles coated with Pd nanoparticles strongly and irreversibly attach to the oil-water interface. Due to the irreversible adsorption of the catalytic particles to the interface, particle loss was completely prevented while mixing the aqueous solution and while collecting the products. The other system was based on the magnetic field-associated particle recovery method. The use of polymeric microparticles containing Pd nanoparticles and magnetite nanoparticles accelerated the sedimentation of the particles in the aqueous phase by applying a strong magnetic field, consequently suppressing drainage of the particles from the reactor along the product stream. Upon multiple runs of the catalytic reactions, it was found that conversion does not change significantly, demonstrating the excellent recyclability and performance efficiency in the catalytic processes.

High-precision printing machines are essential for the fabrication of more sophisticated printed electronics. In particular, roll-to-roll printing with flexible substrates and nonideal rolls, which exhibit cylindricity, misalignment, and run-outs, produces nonlinear effects that are hard to manage with conventional control systems. For instance, printing rolls with cylindricity and run-outs cause large perturbations in the printing forces. In this paper, we propose a hybrid printing force control system that provides uniform printing conditions in the regions where printing occurs. The unique parallel arrangement of two force components provides excellent regulation of the printing force; this system also consumes less power. Our experimental results verify that the force control performance of the hybrid force control system is better than that of a conventional system. We also report the results of in situ printing quality tests with a pressure-sensitive film that confirm the effectiveness of the proposed system.

The roll-based high-speed printing process has the two major advantages of high productivity and a simple process over the conventional electronic device manufacturing process. There have been several attempts to commercially apply the roll-based high-speed printing process to various electronic devices. While such attempts have sought to improve the performance of electronic devices, these devices require multi-layered structures to be printed with high overlay accuracy between each layer. Printed patterns always appear to be deformed compared to the designs on the master plate because the printing process is solution based. Given variations in ink transfer volume, the accuracy of the overlay measurement can be degraded by mark deformations. This means that these deformations caused by the printing mechanism should be taken into account. In this paper, we provide the details from a simulation study and experiment carried out using gravure offset printing to investigate the effects of mark deformations on overlay measurement accuracy. We analyzed and optimized the pattern registration algorithms and the type of overlay marks in order to improve the measurement accuracy of the positions of the printed patterns. As a result, the repeatability measuring the positions of the printed patterns can be reduced to 1.0 μm and 2.0 μm in the CD and MD directions in the gravure offset printing process, respectively.

We present analytical calculations of optical forces for drag calibrations via the geometrical optics approximation (GOA) for the case in which a single laser beam is strongly focused on a polystyrene microsphere dispersed in an aqueous phase. When the beam focus is mismatched with the particle center owing to the presence of vertical forces, such as gravity, buoyancy, and the radiation force caused by the laser beam, the trapped particle would be displaced in a radial direction when the lateral drag force is applied. Based on the analytical calculations of optical trapping forces and the force balance upon dragging, we found that the critical laser power at which the beam focus matches the particle center exhibits a power-law relationship with the particle radius a according to the empirical expression log(Pcrit (mW)) = 2.899 log(2a (µm)) - 2.316. We also found an empirical expression for the mechanical equilibrium position of the vertical displacement Δzeq0(Δy=0) as functions of the laser power P and the particle radius, \(\Delta z_{eq}^0 = \frac{{\left[ {{F_{gb}}\left( {pN} \right) - 0.068P\left( {mW} \right)} \right]\left[ {2.7a\left( {\mu m} \right) - 0.252} \right]}}{{P\left( {mW} \right)}}\), where Fgb is the sum of the gravitational and buoyant forces.

The heterogeneous adsorption behaviors of charged colloidal particles to oil-water interfaces were quantitatively and statistically investigated. Using optical laser tweezers, the particles in a sessile water drop formed in an oil phase were laterally translated toward the slope of the oil-water interface and their attachment to the interface was attempted. The adsorption probability was found to logarithmically decrease as the ionic strength decreased and to depend on the holding time during which an optically trapped particle was held at the position closest to the interface. Non-unity of the adsorption probability at particular salt concentrations and the holding time dependence offer an important clue that the particle adsorption to the interface is not deterministic but stochastic. The stochastic adsorption process can be attributed to the surface heterogeneity of colloidal particles that consequently leads to changes in the electrostatic interactions between the particles and the interface. We also demonstrated that the salt dependence on the adsorption properties of the particles, as measured by optical laser tweezers, was consistent with their bulk behaviors with regard to the stability of particle-stabilized emulsions. Furthermore, we revealed the gravity-induced spontaneous adsorption of the particles to the interface under conditions of sufficiently strong ionic strength.

Hypothesis: The charged spherical colloidal particles at the fluid–fluid interface experience considerably strong and long-ranged electrostatic and capillary interactions. The contribution of capillary force becomes more significant as the particle size increases beyond a certain limit. The relative strengths of the two competing interactions between the spherical polystyrene particles at the oil–water interface are quantified depending on their size. Experiments: The studied particles, obtained using the microfluidic method, have diameters of tens to hundreds of micrometers. The scaling behaviors of the commercially available colloidal particles with diameters of ~3 μm are also compared. An optical laser tweezer apparatus is used to directly or indirectly measure the interparticle force. Subsequently, the capillary force that can be attributed to the gravity-induced interface deformation and contact line undulation is calculated and compared with the measured interaction force. Findings: Regardless of the particle diameter (~3–330 μm), the measured force is observed to decay as r−4, where r denotes the center-to-center separation, demonstrating that the dipolar electrostatic interaction is important and that the gravity-induced capillary interaction is negligible. Furthermore, numerical calculations with respect to the undulated meniscus confirm that the magnitude of capillary interaction is significantly smaller than that of the measured electrostatic interaction.

Soft roller printing techniques such as rolling mask soft lithography and offset printing are prominent as high-resolution, high-throughput patterning technologies. The overlay accuracy of soft roller printing becomes critical in large-area fabrications since many factors causing overlay errors tend to be proportional to the patterning area. In this study, the mechanism of overlay distortion was investigated in the soft roller printing process using both lab testing and finite element simulations. The overlay distortion is closely related to the deformation of PDMS in soft roller printing and it is key to investigate how PDMS is deformed under various disturbances from equipment and process. Two kinds of major disturbances, 'nip motion error' and 'roundness error', are defined and their effect on the overlay distortion is discussed. The methodology to improve overlay accuracy in the soft roller printing process is also presented and verified. For the nip motion error, the compensation method, in which the nip motion error is modeled based on the previous printed position errors and the modeled error is compensated by the alignment stage, are proposed. It is proven that high compressibility of cushioning can help to relieve the position errors caused by roundness errors by reducing the deformation of PDMS. Finally, printing position errors can be reduced to the level of a few micrometers when the overlay distortion mechanisms investigated in this study are well controlled.

The stochastic interface adsorption behaviors of ellipsoid particles were investigated using optical laser tweezers. The particles were brought close to the oil-water interface, attempting to attach forcefully to the interface. Multiple attempts of the particle attachments statistically quantified the dependence of the adsorption probability on the particle aspect ratio. It was found that the adsorption probability proportionally increased with the aspect ratio because of the decrease in electrostatic interactions between the charged particles and the charged interface for higher aspect ratio particles. In addition, the adsorption holding time required for the interface attachments was found to increase as the aspect ratio decreased. Notably, the probabilistic adsorption behaviors of the ellipsoid particles and the holding time dependence revealed that the particle adsorption to the interface occurred stochastically, not deterministically. We also demonstrated that the adsorption behaviors measured on a single-particle scale were consistent with the gravity-induced spontaneous adsorption properties performed on a large scale with regard to the nondeterministic adsorption behaviors and the aspect ratio dependence on the adsorption probability.

A simple route to fabricate defect-free Ag-nanoparticle-carbon-nanotube composite-based high-resolution mesh flexible transparent conducting electrodes (FTCEs) is explored. In the selective photonic sintering-based patterning process, a highly soft rubber or thin plastic substrate is utilized to achieve close and uniform contact between the composite layer and photomask, with which uniform light irradiation can be obtained with diminished light diffraction. This well-controlled process results in developing a fine and uniform mesh pattern (≈12 μm). The mesh patternability is confirmed to be dependent on heat distribution in the selectively light-irradiated film and the pattern design for FTCE could be adopted for more precise patterns with desired performance. Moreover, using a very thin substrate could allow the mesh to be positioned closer to the strain-free neutral mechanical plane. Due to strong interfacial adhesion between the mesh pattern and substrate, the mesh FTCE could tolerate severe mechanical deformation without performance degradation. It is demonstrated that a transparent heater with fine mesh patterns on thin substrate can maintain stability after 100 repeated washing test cycles in which a variety of stress situations occurring in combination. The presented highly durable FTCE and simple fabrication processes may be widely adoptable for various flexible, large-area, and wearable optoelectronic devices.

Heterogeneous capillary interactions between ellipsoid particles at the oil–water interface were measured via optical laser tweezers. Two trapped particles were aligned in either tip-to-tip (tt) or side-to-side (ss) configurations via the double-trap method and were released from the optical traps, leading to particle–particle attractions due to the capillary forces caused by quadrupolar interface deformation. On the basis of image analysis and calculations of the Stokes drag force, the capillary interactions between two ellipsoid particles with the same aspect ratio (E) were found to vary with the particle pairs that were measured, indicating that the interactions were nondeterministic or heterogeneous. Heterogeneous capillary interactions could be attributed to undulation of the interface meniscus due to chemical and/or geometric particle heterogeneity. The power law exponent for the capillary interaction Ucap ≈ r–β was found to be β ≈ 4 and was independent of the aspect ratio and particle configuration...

Printed electronics is one of the emerging technologies owing to its low cost and productivity. Recently, many researchers tried to adapt printing technology to the fabrication of fine electronic patterns on flexible substrates, including the gate line of thin film transistors. In this study, we fabricated a flexible cliche using the nanoimprint process and used it in reverse offset printing. Then, we analyzed the effect of the surface energy of the imprinted cliche on process parameters, such as printing speed and rolling direction. We showed that the productivity of the process and quality of printed pattern can be considerably enhanced by controlling the surface energy of the cliche. When a flexible cliche is manufactured using a resin with a surface energy considerably different from that of the blanket, the ink can be detached easily and fine patterns can be engraved successfully regardless of the pattern shape.

We investigated the electrostatic interactions between particles acting through heterogeneous fluid phases. An oil lens system floating on the surface of water was used to trap particles at different fluid-fluid interfaces. The inner particles are located at the centrosymmetrically curved oil-water interface inside the oil lens while satellite particles are located at the curved air-water interface, separated by a particular distance from the triple phase boundary. The satellite particles are likely to be captured in an energy minimum state due to electrostatic repulsions by the inner particles balanced with the gravity-induced potential energy. As the size of the oil lens decreases upon evaporation, the satellite particles escape from the gravitational confinement at a critical moment. The self-potential values of the inner particles and the satellite particles were calculated by employing an energy balance and the experimentally obtained geometric parameter values. It was found that the self-potential values of the inner particles decrease as oil evaporates over time and that the magnitude of the self-potential of the satellite particles is a hundred times larger than that of the inner particles. These results demonstrate significant effects of the thickness and shape of the nonpolar superphase on the electrostatic interactions between the particles trapped at different fluid-fluid interfaces.

High-linearity wideband transmitter with a high linearity Mixer and RF-PGA is proposed for 802.1af/ah long-range Wi-Fi standards. The transmitter is direct conversion architecture while supporting 1/2/4/6/8/16 MHz signal bandwidth for 802.11af/ah. Implemented in a 40-nm CMOS process with the chip size of 1.0 mm × 1.9 mm, the full transmitter shows a conversion gain range of 31.5 dB with 0.5 dB step and achieves EVM −36.8 dB (802.11 ah) and −37 dB (802.11af) in sub-GHz frequency bands. The measured OIP3 of the transmitter is from 20 dBm to 25 dBm, while consuming 36 mA with the supply voltage of 1.1/2V.

Recently, highly flexible conductive features have been widely demanded for the development of various electronic applications, such as foldable displays, deformable lighting, disposable sensors, and flexible batteries. Herein, we report for the first time a selective photonic sintering-derived, highly reliable patterning approach for creating extremely flexible carbon nanotube (CNT)/silver nanoparticle (Ag NP) composite electrodes that can tolerate severe bending (20 000 cycles at a bending radius of 1 mm). The incorporation of CNTs into a Ag NP film can enhance not only the mechanical stability of electrodes but also the photonic-sintering efficiency when the composite is irradiated by intense pulsed light (IPL). Composite electrodes were patterned on various plastic substrates by a three-step process comprising coating, selective IPL irradiation, and wiping. A composite film selectively exposed to IPL could not be easily wiped from the substrate, because interfusion induced strong adhesion to the underlying polymer substrate. In contrast, a nonirradiated film adhered weakly to the substrate and was easily removed, enabling highly flexible patterned electrodes. The potential of our flexible electrode patterns was clearly demonstrated by fabricating a light-emitting diode circuit and a flexible transparent heater with unimpaired functionality under bending, rolling, and folding.

Simple, low-cost and scalable patterning methods for Cu nanowire (NW)-based flexible transparent conducting electrodes (FTCEs) are essential for the widespread use of Cu NW FTCEs in numerous flexible optoelectronic devices, wearable devices, and electronic skins. In this paper, continuous patterning for Cu NW FTCEs via a combination of selective intense pulsed light (IPL) and roll-to-roll (R2R) wiping process was explored. The development of continuous R2R patterning could be achieved because there was significant difference in adhesion properties between NWs and substrates depending on whether Cu NW coated area was irradiated by IPL or not. Using a custom-built, R2R-based wiping apparatus, it was confirmed that nonirradiated NWs could be clearly removed out without any damage on irradiated NWs strongly adhered to the substrate, resulting in continuous production of low-cost Cu NW FTCE patterns. In addition, the variations in microscale pattern size by varying IPL process parameters/the mask aperture sizes were investigated, and possible factors affecting on developed pattern size were meticulously examined. Finally, the successful implementation of the patterned Cu NW FTCEs into a phosphorescent organic light-emitting diode (PhOLED) and a flexible transparent conductive heater (TCH) were demonstrated, verifying the applicability of the patterned FTCEs. It is believed that our study is the key step toward realizing the practical use of NW FTCEs in various flexible electronic devices.

We investigated the geometric and chemical factors of nonspherical Janus particles (i.e., Janus ellipsoids) with regard to the pinning and unpinning behaviors of the Janus boundary at the oil-water interface using attachment energy numerical calculations. The geometric factors were characterized by aspect ratio (AR) and location of the Janus boundary (alpha) separating the polar and apolar regions of the particle. The chemical factor indicated the supplementary wettability (beta) of the two sides of the particle with identical deviations of apolarity and polarity from neutral wetting. These two factors competed with each other to determine particle configurations at the interface. In general, the critical value of beta (beta(c)) required to preserve the pinned configuration was inversely proportional to the values of alpha and AR. From the numerical calculations, the empirical relationship of the parameter values of Janus ellipsoids was found; that is, lambda = Delta beta(c)/Delta alpha approximate to 0.61AR - 1.61. Particularly for the Janus ellipsoids with AR > 1, the beta(c) value is consistent with the boundary between the tilted only and the tilted equilibrium/upright metastable region in their configuration phase diagram. We believe that this work performed at the single particle level offers a fundamental understanding of the manipulation of interparticle interactions and control of the rheological properties of particle-laden interfaces when particles are used as solid surfactants.

In printed electronics technology, the overlay accuracy of printed patterns is a very important issue when applying printing technology to the production of electric devices. In order to achieve accurate positioning of the printed patterns, this study proposes a novel precision reverse offset printing system. Furthermore, the study evaluates the effects of synchronization and printing force on position errors of the printed patterns, and presents methods of controlling synchronization and printing force so as to eliminate positional errors caused by the above-mentioned reasons. Finally, the printing position repeatability of 0.40 μm and 0.32 μm (x and y direction, respectively) at a sigma level is obtained over the dimension of 100 mm under repeated printing tests with identical printing conditions.

We propose a method to fabricate a supercapacitor for smart textiles using silver (Ag) nanoparticle (NP) ink, simple spray patterning systems, and intense pulsed light (IPL) sintering systems. The Ag NP current collectors provided as high conductivity as the metal current collectors. The spray patterning technique is useful for fabricating supercapacitors because it is simple, fast, and cheap. IPL systems reduced the sintering temperature of Ag NPs and prevented thermal damage to the textiles during the Ag NP sintering process. The two-dimensional (2D) all-solid state fabric supercapacitor with an interdigitated configuration, developed here, exhibited a specific capacitance of 25.7 F/g and an energy density of 1.5 Wh/kg at a power density of 64.3 W/kg. These results support the utility of our proposed method in the development of energy textiles.

A devised tip–tilt guide mechanism (TTGM) for the fast steering of a large-scale mirror is presented. The TTGM uses a parallel structure with four struts, in which a double right-circular notch and a leaf spring are serially connected via a nondeformable rectangular linkage in aid of an axial flexure at the center of the payload. The benefits provided by the TTGM include pure rotation in the desired directions, an adaptable mechanism for a large and heavy mirror, and an adjustable virtual pivot of the moving body allowed by the configuration design. Closed-form stiffness equations of the individual flexure hinges are derived, and the equations of motion of the TTGM are mathematically formulated to predict the behaviors of the mechanism. To validate the performance of the TTGM, a design is presented and optimization of the geometric parameters of the TTGM is carried out. The model prediction accuracy for the resonant frequency relative to experimental results is found to be satisfactory, with errors of less than 11.4%. It is proven that the devised TTGM is an appropriate structure as a two-axis guide mechanism in three-dimensional space for the 160-mm diameter mirror with an angular travel range of 1 mrad.

In roll-offset printing (patterning) technology with a PDMS blanket as a transfer medium, one of the major reliability issues is the occurrence of swelling, which involves absorption of the ink solvent in the printing blanket with repeated printing. This study developed a method to resolve blanket swelling in gravure offset roll printing and performed experiments for performance verification. The physical phenomena of mass and heat transfer were applied to fabricate a device based on convection drying. The proposed device managed to effectively control blanket swelling through drying by blowing air and additional temperature control. The experiments verified that printing quality (in particular the variation of the width of printed patterns) was maintained over 500 continuous printing.