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Liquid-solid contact electrification is a useful mechanism to harvest wasted micromechanical energy. In this study, we investigate how the surface properties of a solid substrate affect contact electrification efficiency. Substrate surfaces were modified from hydrophilic to hydrophobic by changing the density of self-assembled monolayers (SAMs) on a SiO2 surface. A substrate with a partially-covered SAM exhibited superior performance. The partially-covered SAM substrate is hydrophobic enough to induce quick dewetting of water from the surface and sufficiently electronegative to induce a high charge density on the surface. The quick dewetting results from the aliphatic tail groups of the SAM and -OH groups make the SiO2 surface electronegative; these two competing properties can be simultaneously obtained by optimizing the SAM density. Our findings contribute to the understanding of contact electrification in liquid-solid-type energy-harvesting devices and advance the strategies to maximize the electrification efficiency by optimizing surface geometries and properties.Liquid-solid contact electrification is a useful mechanism to harvest wasted micromechanical energy. In this study, we investigate how the surface properties of a solid substrate affect contact electrification efficiency. Substrate surfaces were modified from hydrophilic to hydrophobic by changing the density of self-assembled monolayers (SAMs) on a SiO2 surface. A substrate with a partially-covered SAM exhibited superior performance. The partially-covered SAM substrate is hydrophobic enough to induce quick dewetting of water from the surface and sufficiently electronegative to induce a high charge density on the surface. The quick dewetting results from the aliphatic tail groups of the SAM and -OH groups make the SiO2 surface electronegative; these two competing properties can be simultaneously obtained by optimizing the SAM density. Our findings contribute to the understanding of contact electrification in liquid-solid-type energy-harvesting devices and advance the strategies to maximize the electrifica...

The electrical manipulation of graphene oxide (GO) alignment in aqueous dispersions is a useful technique with various applications. In particular, the electrical switching of GO particles can be used to devise optical birefringent liquid crystal displays. However, the electric switching of aqueous GO dispersions with a high ionic concentration requires driving voltages with high frequencies (∼10 kHz), which is a challenging limitation. We demonstrate that stable electro-optical switching can be achieved at low frequencies (100 Hz) using GO dispersions in organic solvents instead of water. The hydrodynamic flow of the solvent and the electrophoretic drift of the GO particles are hindered in the GO dispersions in organic solvents with lower dielectric constants. Moreover, the electro-optical performance of these GO dispersions is similar to the aqueous GO dispersions, despite the lower magnitude of the ionization ratio for the GO particle functional groups. These results are crucial for developing a liquid...

In 2001, Dozov predicted that twist-bend nematic phase can be spontaneously formed when K33 2, and this phase has recently been discovered in bimesogens. To verify Dozov's hypothesis, we have measured precisely the temperature dependence of the elastic constants of CB7CB in the entire temperature range of nematic phase and in twist-bend nematic phase close to the transition temperature by combing the Freedericksz threshold methods for a twist nematic and an in-plane switching cells. Anomalous changes in K22 and K33 are observed across the phase transition. The elasticity estimated via extrapolation of the data in the high temperature region of the nematic phase seems to fully satisfy Dozov's hypothesis although the elasticity data in the vicinity of the phase transition exhibit opposite trends. This can be explained by the general nature of a hierarchical system where the macroscopic elasticity is governed mostly by the distortion of a higher level structure.

We devised liquid crystal cell substrates with different surface roughnesses at the molecular scale by controlling the density of two types of trichlorosilanes with different alkyl chain lengths. We investigated surface melting of liquid crystals on these surfaces by observing the anchoring transition (change in the direction of alignment) that usually accompanies surface melting. Surface melting was observed only on substrates that had undulating surface morphologies due to either a low molecular density or interspersed arrangement of the two types of trichlorosilanes. We attributed the surface melting to the influence of molecular-level surface roughness on liquid crystal order parameters near the surface.

We demonstrate a type of nonlinear meta-atom creating a dual-band nonlinear left-handed metamaterial (DNLHM). The DNLHM operates at two distinct left-handed frequency bands where there is an interval of one octave between the two center frequencies. Under the illumination of a high-power signal at the first left-handed frequency band corresponding to fundamental frequency (FF), second-harmonic generation (SHG) is observed at the second left-handed band. This means that our DNLHM supports backward-propagating waves both at FF and second-harmonic (SH) frequency. We also experimentally demonstrate quasi-phase-matching configurations for the backward SHG. This fancy parametric process can significantly transmits the SH generated by an incident FF wave.

Electrowetting (EW) of an electrolyte droplet containing zinc or silica particles was investigated for durability and degradation of devices. Two types of experimental geometries exist, an upward droplet standing on a substrate and a downward droplet hanging under a substrate. Different gravitational effects of droplets for the two geometries shift the contact angle of the EW dynamics. Added zinc and silica particles significantly accelerated the degradation in the EW switching with increased driving time, which may result from the surface damage due to the collision between the particles and surface. The degradation was significantly influenced by many factors such as the particle dispersity, droplet direction, particle concentration, and viscosity of dispersions. Interestingly, the device with a downward droplet degraded much less than that with the upward droplet. Our findings will be highly useful in designing durable microfluidic and EW devices.

The present work describes the development of polybenzoxazine (PBZ) nanocomposite with high dielectric constant using varying weight percentages of (0.5, 1.0, and 1.5 wt. %) benzoxazine functionalized MWCNT (CNT-BS) and benzoxazine through thermal ring opening polymerization. The dielectric constants are increased with increasing weight percentages of incorporation of CNT-BS, whereas dielectric losses are in the reverse trend. Data from Cyclic Voltammogram and impedance studies confirm the conducting behavior of CNT-BS/PBZ nanocomposites. The increase in the weight ratio of CNT-BS enhances the values of Tg and thermal stability. The uniform distribution of functionalized CNT-BS was ascertained from transmission electron microscope.

The electromagnetic behaviors of the metamaterial can be artificially controlled by changing the effective permittivity of the nearby background medium. Utilizing this fantastic feature, an ultrathin and frequency-tunable polarization rotation device, which can achieve 90° polarization rotation for a linearly polarized incident wave, is constructed via the combination of a composite chiral metamaterial and two auxiliary dielectric slabs. It shows that the operating frequency of the resulting 90°-polarization rotation device can be continuously and reversibly tuned in a wide frequency range by mechanical means. The experimentally measured results are in agreement with the numerical values.

We experimentally demonstrate the trapped rainbow in tapered left-handed heterostructures (LHHs) at visible frequencies. The employed left-handed metamaterials (LHMs) are isotropic with the size of hundreds of square millimeter. Specifically, the LHMs sample at visible frequencies has a broad spectral range and low loss, making it an intrinsic optical response for the LHHs. It is found that the frequency components of the wave packet separate at positions with different guide thicknesses only if the inclination of tapered LHHs is greater than zero and smaller than the critical value.

We report a peculiar enhancement in the accumulation capacitance Cacc in the capacitance-voltage (C-V) characteristics of metal-insulator-semiconductor capacitors consisting of poly(4-vinylphenol) (PVP) and pentacene. Cacc at low frequency C-V was five times larger than the PVP dielectric capacitance CPVP. Cacc decreased as the frequency was increased and returned to the level of CPVP at 1 MHz. The origin of the capacitance enhancement appears to be associated with water molecules adsorbed into the PVP dielectric film when considering the correlation with the concentration of PVP polymer in which OH phenol is known to absorb water molecules.

PUBLISHED, Antiphase relaxation process of antiferroelectric phase is investigated in binary mixtures of antiferroelectric and ferroelectric liquid crystalline compounds. It is found that the frequency of the antiphase mode ranges from 2 to 4 MHz, being one of the fastest collective processes reported so far. This can be exploited in a photonic switch with a submicrosecond response time. However, the frequency of the antiphase mode decreases by the mixing ratio of the ferroelectric compound. The decrease in the frequency is shown to be due to a reduction in the elastic constant in between the adjacent layers., The authors thank SFI for funding 02/IN.1/I.031 and RFP06/ENE039 and Mitsubishi Gas Chemical, Co., Japan for donating their valuable compounds.

The authors observe the sign reversals in the dielectric anisotropy as functions of temperature and of frequency in SmA* phase, for the first time. The sign reversal in the dielectric anisotropy with frequency arises from the molecular relaxation process (fluctuations around the short axis), the same mechanism as for the dual frequency nematics. On the contrary, the sign reversal with temperature is due to the soft mode, which is a dominant collective relaxation process in SmA* phase and increases ϵ⊥′ sharply with decreasing temperature as the soft mode becomes more dominant close to the SmCA* to SmA* transition temperature. We find that the alignment of the cell can be controlled by applying fields of appropriate frequencies at certain temperatures. This method is so effective that we can obtain a homeotropic aligned cell that had previously been planarily aligned by applying an external alternating electric field.

We propose a method to implement low voltage operation of pentacene thin film transistors (TFTs). Ultrathin Al2O3 was used as a gate dielectric and was directly grown on a preexisting Al gate by an oxygen plasma process. Thus, an extra patterning process for the gate dielectric is not necessary, and the overall fabrication process is thereby simplified. The organic TFTs operated at low voltage, producing 1.5μA at VGS=−2V and VDS=−1.5V, with a threshold voltage of −1.18±0.027V, a mobility of 0.12±0.015cm2∕Vs, and an on/off current ratio of 8.76±5.3×103.