Surface Memory Effect Research Articles

Super-stable mineralization of arsenic contaminated water using industrialized layered double hydroxides and derivatives

The issue of arsenic contamination, specifically in the form of As(III), is progressively escalating, so presenting a substantial danger to human well-being and security. In this study, commercially industrially produced CaAl-layered double hydroxides (CaAl-LDH) and MgAl-LDH were processed by calcination to produce a series of LDH-based mixed metal oxides (CaAl-x, MgAl-x) at calcination temperatures (x) ranging from 200 to 1000 °C. The resulting CaAl-900 exhibited a remarkable capacity for removing high concentrations of As(III), with a removal capacity of 612.5 mg/g. Besides, MgAl-500 demonstrated effective removal of low levels of As(III) to meet industrial emission standards, specifically below 0.5 mg/L. Furthermore, MgAl-500 was employed to simultaneously stabilize mixed toxic metals (As(III), Pb(II), and Cd(II) ions) in the treatment process of contaminated water, meeting standard levels. The comprehensive analysis of the characterization data indicated that the key determinant for the remarkable capacity of CaAl-900 to remove As(III) was its surface adsorption and memory effect. MgAl-500 also formed complex compounds through formation of As-O-Mg bond. This research showcases the capacity of LDHs produced from the industry for efficient remediation of As(III) ions in water.

Complex characterisation of Cr-doped α-Al 2O3 for DBD applications

Al2O3 samples doped with Cr2O3 up to 10vol.%(12.7wt%) were investigated with respect to their electrical, structural and morphological properties relevant to their use as a dielectric barrier in dielectric barrier discharges (DBDs). The surface properties were analysed using atomic force microscopy and a scanning electron microscope. The structural properties were investigated using x-ray diffraction (XRD) analysis. Regarding electrical properties, we measured the dielectric constant of the material, the discharge ignition voltage in a coplanar configuration in the air as well as in nitrogen, and the working domains (WDs) of atmospheric pressure Townsend discharge (APTD). The charge-trapping properties of the studied samples were measured by an electrostatic voltmeter. There was observed a significant ignition voltage decrease with maximal decrease for sample doped with 1vol.%Cr2O3 . For the samples doped with 10vol.% of Cr2O3 a rapid surface potential decay was observed that is important from the viewpoint of DBDs plasma filamentation due to the so-called surface memory effect. The WDs of the APTD showed variations, and it has been significantly extended for the 5Cr sample up to at least 24 kHz compared to other samples. Thus, the results presented in this paper show the potential of Cr-doped dielectric barriers and point towards future research directions.

Rational design phosphorylation Mg-Fe layered dioxides nanosheets for efficient capture of uranium from wastewater

As the nuclear industry boomed, lots of uranium has entered the water environment and caused great damage to ecological environment. Designing and preparing efficient uranium adsorption materials is essential to solve the problem. Phosphorylated Mg-Fe layered dioxides (P-MF LDOs) nanosheets with a favorable memory effect were prepared by calcination and in-situ phosphorylation for uranium extraction from wastewater (UEW). The unique phosphating method resulted in a uniform distribution of phosphate functional groups in the surface of LDOs, which gave it great ability for capture of uranium. The adsorption capacity of P-MF LDOs was 2.31 times that of pure MF LDOs. According to the Langmuir model, the theoretical extraction capacity of P-MF LDOs was as high as 909.09 mg g−1, which was significantly higher than that of similar sorbents. Additionally, it exhibited excellent anti-interference ability. The results of the adsorption mechanism study revealed that the binding modes included surface complexation, mineralization reaction, dissolution-precipitation, and memory effect. In conclusion, P-MF LDOs represent a type of highly efficient uranium adsorbent with simple preparation and high adsorption capacity for UEW. This study provides new insights into the development of inorganic clay-based uranium adsorbents.

The regulation of memory effect and its influence on discharge properties of a dielectric barrier discharge driven by bipolar pulse at atmospheric-pressure nitrogen

The regulation of memory effect that the residual charges generated during and after discharge act on the initiation and development of subsequent discharge is explored by adjusting the pulse parameters, which have an influence on the discharge characteristics. The memory effect is quantified by the measurement of ‘wall voltage’ through a series of reference capacitors. The influences of memory effect on the discharge properties corresponding to rising/falling time 50–500 ns, pulse width 0.5–1.5 μs, and frequency 200–600 Hz are analyzed. It is found that the ‘wall voltage’ increases from 1.4 kV to 2.4 kV with rising/falling time from 50 ns to 500 ns, it varies in the range of 0.18 kV with frequency of 200–600 Hz, and 0.17 kV with pulse width of 0.5–1.5 μs. The propagation velocity of wavelike ionization under the negative pulse slows down from 2184 km s−1 to 1026 km s−1 as the rising/falling time increases from 50 ns to 500 ns due to the weakening of the electric field by the surface memory effect. More intense and uniform emission can be achieved through faster rising/falling time and higher frequency based on the volume memory effect, while pulse width has less influence on the emission uniformity. Furthermore, similar laws are obtained for spectral and discharge intensity. Therefore, the memory effect is most effectively regulated by rising/falling time, and the discharge properties are affected by the surface and volume memory effect.

Volume and surface memory effects on evolution of streamer dynamics along gas/solid interface in high-pressure nitrogen under long-term repetitive nanosecond pulses

Evolution of the surface streamer and the discharge mode transition from the corona discharge to the surface flashover were investigated by pulse sequence resolved electrical and optical measurements under long-term repetitive nanosecond pulses (RNP). The test sample was a cylindrical epoxy resin insulator attached with a needle electrode in 0.1–0.4 MPa nitrogen. Under positive RNP, the inception phase of subsequent streamer discharges decreases with increasing the pulse repetition frequency (PRF), and a periodical streamer stagnation phenomenon appears at high gas pressure. Under negative RNP, the surface streamer does not illustrate symbolic decreasing tendencies in light intensity and corona inception phase in gas gap. The dependence of the evolution of surface streamer velocity on PRF is correlated with the repulsive force from surface charges and the accessibility of seed electrons. Statistical characteristics of back discharges under negative RNP are qualitatively explained by the local electric field around the triple junction. The reversal phenomenon of polarity effect of the allowable repetitive working coefficient is probably resulted from the corona stabilization effect, the surface electron detrapping process, and the assistance of background electric field. Principal results qualitatively support that behaviors of surface streamer and flashover are dominated by the electric field distribution, volume and surface memory effects as well as their interactions and bidirectional transformations, which are different from the monotonically facilitative tendency predicted by the metastable-species-dominated memory effect mechanism.

Impact of volume and surface processes on the pre-ionization of dielectric barrier discharges: advanced diagnostics and fluid modeling

The phenomenology and breakdown mechanism of dielectric barrier discharges are strongly determined by volume and surface memory effects. In particular, the pre-ionization provided by residual species in the volume or surface charges on the dielectrics influences the breakdown behavior of filamentary and diffuse discharges. This was investigated by advanced diagnostics such as streak camera imaging, laser photodetachment of negative ions and laser photodesorption of electrons from dielectric surfaces in correlation with 1D fluid modeling. The streak camera images show that an increasing number of residual charges in the volume changes the microdischarge breakdown in air-like gas mixtures from a cathode-directed streamer to a simultaneous propagation of cathode- and anode-directed streamers. In contrast, seed electrons are important for the pre-ionization if the density of residual charges in the volume is low. One source of seed electrons are negative ions, whose density exceeds the electron density during the pre-phase of diffuse helium–oxygen barrier discharges as indicated by the laser photodetachment experiments. Electrons desorbed from the cathodic dielectric have an even larger influence. They induce a transition from the glow-like to the Townsend-like discharge mode in nominally pure helium. Apart from analyzing the importance of the pre-ionization for the breakdown mechanism, the opportunities for manipulating the lateral structure and discharge modes are discussed. For this purpose, the intensity and diameter of a diffuse discharge in helium are controlled by an illuminated semiconducting barrier.

Spatio-temporal characterization of the multiple current pulse regime of diffuse barrier discharges in helium with nitrogen admixtures

This work reports on the spatio-temporal characterization of the multiple current pulse regime of diffuse barrier discharges driven by sine-wave feeding voltage at a frequency of in helium with small nitrogen admixtures. The discharge gap of is bounded by glass plates on both plane electrodes. Priority is given to the lateral discharge inhomogeneities, underlying volume- and surface-memory effects, and the breakdown mechanism. Therefore, relevant processes in the discharge volume and on the dielectric surfaces were investigated by ICCD camera imaging and optical emission spectroscopy in combination with electrical measurements and surface charge diagnostics using the electro-optic Pockels effect of a bismuth silicon oxide crystal. The number of current pulses per half-cycle of the sine-wave voltage rises with increasing nitrogen admixture to helium due to the predominant role of the Penning ionization. Here, the transition from the first glow-like breakdown to the last Townsend-like breakdown is favored by residual species from the former breakdowns which enhance the secondary electron emission during the pre-phase of the later breakdowns. Moreover, the surface charge measurements reveal that the consecutive breakdowns occur alternately at central and peripheral regions on the electrode surface. These spatial inhomogeneities are conserved by the surface charge memory effect as pointed out by the recalculated spatio-temporal development of the gap voltage.

Transition from diffuse to self-organized discharge in a high frequency dielectric barrier discharge

Depending on the operating conditions, different regimes can be obtained in a dielectric barrier discharge (DBD): filamentary, diffuse (also called homogeneous) or self-organized. For a plane-to-plane DBD operated at high frequency (160 kHz) and at atmospheric pressure in helium gas, we show that the addition of a small amount of nitrogen induces a transition from the diffuse regime to a self-organized regime characterized by the appearance of filaments at the exit of the discharge. In this paper, we detail mechanisms that could be responsible of the transition from diffuse mode to this self-organized mode. We point out the critical role of the power supply and the importance of the gas memory effect from one discharge to the following one on the transition to the self-organised mode. The self-organized mode is usually attributed to a surface memory effect. In this work, we show an additional involvement of the gas memory effect on the self-organized mode.

PB25 アゾベンゼンとオリゴエチレンオキシドを側鎖に持つ両親媒性コポリマー薄膜の光濡れ性変化と記憶効果(液晶化学材料,ポスター発表,2015年日本液晶学会討論会)

PB25 アゾベンゼンとオリゴエチレンオキシドを側鎖に持つ両親媒性コポリマー薄膜の光濡れ性変化と記憶効果(液晶化学材料,ポスター発表,2015年日本液晶学会討論会)

Shape Memory of Microscale and Nanoscale Imprinted Patterns on a Supramolecular Polymer Compound.

Surface memory effects for micropattern and nanopattern are demonstrated for shape memory compounds composed of mixtures of the zinc salt of a sulfonated poly(ethylene-co-propylene-co-ethylidene norbornene) ionomer and three different low molar mass fatty acids (FAs): lauric acid (LA), stearic acid (SA), and zinc stearate (ZnSt). This work shows the ability to tune the surface pattern switching temperature (Tc ) by simply varying the FA melting point. The melting point of the FA in the ionomer compound is depressed from that of the pure FA due to strong dipolar interactions between the ionomer and the FAs. Surface pattern memory and recovery are shown for compounds with 20 wt% LA, SA, or ZnSt, where Tc = 50, 80, and 100 °C, respectively. Recovery efficiencies for micropatterns are better than 92% for all three compounds and 73% for a nanopattern for the ionomer/ZnSt compound.

Characterization of a NiTi SMA wire treated by nitrogen plasma based ion implantation (PBII)

NiTi SMA wire with Ni-free surface is desirable as construction materials for a range of biomaterials to actuators associated to shape memory and superelastic properties. In biomaterials a potential problem with NiTi implant devices is the release of Ni in the human body. This work analyzes the effects of nitrogen plasma based ion implantation (PBII) technique in a wire of NiTi with shape memory effect associated to a Ni-free surface. The samples were treated for 60 min at 741 °C, with 16 kV high voltage pulses. Results of the thermo-mechanical properties of the PBII treated samples showed that there is no effect of the PBII treatment on the shape memory effect when compared to NiTi samples with no PBII treatment, which is desirable for applications addressing Ni-free surface and shape memory effect. Although it was noted that the stress-strain test causes cracks perpendicular to the stress direction on the treated surface.

Land surface memory effects on dust emission in a Mongolian temperate grassland

AbstractAeolian processes in temperate grasslands are unique in that the plant growth‐decay cycle, soil moisture/snowpack dynamics, and induced grazing interactively affect seasonal and interannual variations of dust emission. This study uses process‐based ecosystem model DAYCENT and unique saltation flux measurements to (1) identify primary land surface factors that control dust emission with soil moisture and vegetation components (live grasses, standing dead grasses, and litter) in a Mongolian grassland and (2) test the dead‐leaf hypothesis proposed by previous observational studies that correlates plant biomass in summer and dust events the following spring. In general, the DAYCENT model realistically simulates seasonal and interannual variations of the vegetation components and soil moisture that were captured by field observations during 2003–2010. Then, the land surface components are correlated with measured daily saltation flux in the springs of 2008–2009 and the frequency of monthly dusty days during March–June 2002–2010. Results show that dust emission had a similar amplitude of significant correlation with wind speed and a combination of all land surface components, which demonstrates a memory of the preceding year. The memory analysis reveals that vegetation and soil moisture anomalies during spring dust emission are significantly autocorrelated with the preceding year's (autumn) corresponding anomalies, which were controlled by rainfall during a given summer. Most importantly, of the vegetation components, the standing dead grasses had the strongest memory and simultaneous correlation with spring dust emission, suggesting the validity of the dead‐leaf hypothesis.

Surface properties and memory effect: Key factors in determining the catalytic efficiency of sulfated zirconia

Three series of zirconia catalysts based on various precursors and grafted with sulfates were synthesized, then calcined at two different temperatures (500 and 600°C) and tested in the n-hexane isomerization. The catalysts based on commercially sulfated zirconium(IV)-hydroxide, and alkoxide prepared at two altered pH values were characterized by means of BET, XRD, SEM, and FTIR methods and relevant procedures. The final catalytic efficiencies were correlated with their physico-chemical properties (surface, textural, structural and morphological ones). It was recognized that the sulfated zirconia catalyst based on commercially sulfated zirconium(IV)-hydroxide and calcined at the lower temperature demonstrated the highest initial activity among all the tested catalysts due to the favorable total acidity, the density of sulfates, the type of acidic active sites, the mesoporous system and nanostructure. Slightly lower but comparable activity of the sulfated zirconia catalyst based on alkoxide and prepared at lower pH is the result of the different memory effect of the starting material and its original properties, and also something different physicochemical features.

Surface memory effect enhanced by atmospheric pressure plasma jet treatment for liquid crystal alignment

In the present work we tried to study Polyimide (PI) film surface memory effect (SME) enhanced by atmospheric pressure plasma jet (APPJ) treatment for liquid crystal (LC) alignment. To evaluate and describe structural changes on the PI film surface, contact angle measurements and Fourier Transformed Infrared (FTIR) Spectroscopy methods were used. After each treatment cycle, the water drop contact angle to the treated surface decreases and FTIR spectra show an increase of CO bonds. When LCs in mesophase are injected into a cell flow alignment occurs, and SME imprints the LC flow alignment pattern onto the surface. Some materials like glass and PI films naturally have SME to some degree; however, in our work we show that treatment by APPJ leads to the enhancement of this effect. Kinetics of the alignment pattern imprinting process was investigated by varying the incubation duration, and at room temperature the minimum required time for the imprinting alignment pattern was found to be 20min. It was shown that the imprinted alignment of LCs on APPJ treated PI films has excellent heat resistance up to 150°C.

Ca-Al Hydrotalcites as Catalysts for Methanolysis and Ethanolysis of Soybean Oil

The use of heterogeneous catalysts in the transesterification reaction of vegetable oils has getting emphasis in recent years, mainly by the alternative of obtaining clean fuel derived from renewable sources. Metal oxide such as MgO or CaO, supported ones like and zeolites are often applied in transesterification process. Among them, hydrotalcite has shown potential as catalysts on this reaction due to their physicochemical properties, such as: thermal stability, porosity, specific surface area, memory effect, basicity, acidity and anion exchange capacity. This work studies the catalytic performance of the calcium and aluminum based hydrotalcite in the transesterification reaction of soybean oil in methanol and ethanol. The hydrotalcite samples treated at 450?C were impregnated with KOH. The efficiency of impregnated and non- impregnated samples was compared and the non-impregnated one showed the best performance. This property was attributed to the higher availability of active sites used in the transesterification process.

Smectic C liquid crystal growth and memory effect through surface orientation by carbon nanotubes

A smectic C liquid crystal texture consisting of well oriented distinct local single crystals was grown using predefined orientation of single wall carbon nanotubes (SWCNTs) adsorbed on a SiOx layer deposited on a ITO treated glass surface. The orientation features of the SWCNTs were analyzed by microtexture analysis and polarized Raman spectroscopy. It was found that the surface memory effect, induced by the SWCNT/SiOx/ITO/glass surface and manifested in the preservation of the smectic C texture in the nematic phase, was many times stronger than memorization promoted by conventional SiOx/ITO/glass and ITO/glass surfaces, usually used for liquid crystal orientations. We observe surface anchoring and memorization strength reinforcement due to trapping of liquid crystal bulk charges by the SWCNTs (surface charge density increase). The SWCNT/SiOx/ITO/glass surface is found to cause a substantial enlargement of the smectic C distinct local single crystals as compared to SiOx/ITO/glass and ITO/glass surfaces. We also discuss the physical nature of the erasure activation energy components contributing to the surface memorization process.

Optical properties of dimeric liquid crystals doped with single-walled carbon nanotubes

Well oriented distinct local single crystals were grown in smectic C liquid crystal (LC) (heptyloxybenzoic acid – 7OBA) using predefined orientation of the single-walled carbon nanotubes (SWCNT). The SWCNT/SiOx/ITO/glass surface is found to cause a substantial enlargement of the smectic C distinct local single crystals and to reinforce both surface memory effect and surface anchoring. We synthesized and examined a set of nanocomposites, built of LC with hydrogen-bonded in dimers molecules (7OBA) and SWCNT. We found that the surface orientation strength and the interaction of the dimeric molecules with the carbon nanotubes play a decisive role for the type (symmetry), thermal stability and chirality of the LC states induced in the nanocomposites. As a result, a set of phase transitions and new phases (chiral smectic C, reentrant nematic, reentrant chiral nematic and a unique low-temperature chiral biaxial fluid smectic phase CG) not typical for pristine 7OBA were found.

Memory effect in composites of liquid crystal and silica aerosil

Aerosil silica nanoparticles dispersed in a liquid crystal (LC) possess the interesting property of keeping memory of an electric- or magnetic-field-induced orientation. Two types of memory have been identified: thermally erasable memory arising from the pinning of defect lines versus a "permanent" memory where the orientation persists even after thermal cycling the samples up to the isotropic phase. To address the source of the latter type of memory, solid-state nuclear magnetic resonance spectroscopy and conventional x-ray diffraction (XRD) were first combined to characterize the LC orientational order as a function of multiple in-field temperature cycles. Microbeam XRD was then performed on aligned gels of different concentrations to gain knowledge of the structural properties at the origin of the memory effect. No detectable anisotropy of the gel or significant breaking of silica strands with heating ruled out the formation of an anisotropic silica network as the source of the permanent memory as previously proposed. Instead, support for a role of the surface memory effect, well known for planar substrates, in stabilizing the permanent memory was deduced from "training" of the composites, that is, optimizing the orientational order through the thermal in-field cycling. The ability to train the composites is inversely proportional to the strength of the random-field disorder. The portion of thermally erasable memory also decreases as the silica density increases. We propose that the permanent memory originates from the surface memory effect operating at points of intersection in the silica network. These areas, where the LC is strongly confined with conflicted surface interactions, are trained to achieve an optimized orientation and subsequently act as sites from which the LC orientational order regrows after zero-field thermal cycling up to the isotropic phase.

Cooperative Ordering at Liquid Crystal Interfaces and Its Role in Orientational Memory

Orientational memory in interfacial liquid crystal films occurs when cells heated above the isotropic transition temperature return to their initial ordered texture upon cooling. First observed over 80 years ago, the origins of orientational memory, which is sometimes called the surface memory effect, remain poorly understood. In this study, films of the thermotropic liquid crystal 4'-octyl-4-cyanobiphenyl on graphite were studied by scanning tunneling and polarizing optical microscopy. Strong orientational memory was observed despite relatively weak molecule-surface interactions of the kind previously thought to be responsible for this effect. By preparing cells in a uniformly oriented initial reference state and separately measuring bulk and surface order parameters as systems were thermally disordered, cooperative interactions were found to play an important role, leading to the recovery of long-range order that neither the bulk nor surface layers alone retained. When the surface and bulk layers were partially decoupled using a magnetic field, orientational memory in the surface layer almost disappeared. The findings provide a new interpretation of the origins of orientational memory in liquid crystal films and underscore the potentially important role of cooperativity in bulk <--> interfacial liquid crystal interactions.

Dynamics of surface memory effect in liquid crystal alignment on reconfigurable microwrinkles

Microwrinkles generated by thin film buckling on elastic substrates serve as reconfigurable microgrooves that can align nematic liquid crystals (NLCs). Through rapid switching of the groove direction to generate controlled perturbation in surface-induced NLC alignment, we studied the dynamical behavior of the surface memory effect. Combined with annealing that resets the alignment memory, the time-dependent response to groove switching indicates that substantial memory develops in a few seconds after contact between the surface and the nematic phase.