New Soluble Polyimides with High Optical Transparency and Light Color Containing Pendant Trifluoromethyl and Methyl Groups

A new aromatic diamine containing trifluoromethyl and methyl groups, namely a,a-bis（4-amino-3-methylphetayl）-4-（trifluoromethyl）phenylmethane （1）, was synthesized from 2-methylaniline and 4-（trifluoromethyl）- benzaldehyde. A series of fluorinated polyimides （PIs） were prepared from the diamine with four commercially available aromatic tetracarboxylic dianhydrides using a one-step high-temperature polycondensation procedure. These obtained PIs showed excellent solubility, with the dissolvability at a concentration of 10 wt% in most solvents, and they could afford flexible and strong films. Thin films of these PIs exhibited high optical transparency and light color, with the cutoff wavelength at 324-357 nm and transmittance higher than 74% at 450 nm. Moreover, these Pls possessed eminent thermal stability and good mechanical properties.

Highly Soluble Polyimides Containing Di-tert-butylbenzene and Dimethyl Groups with Good Gas Separation Properties and Optical Transparency

A rigid aromatic diamine monomer containing di-tert-butylbenzene and dimethyl groups,3,3'-dimethyl-4,4'-diaminophenyl-3",5"-di-tert-butyltoluene,was successfully synthesized by a simple coupling reaction using 3,5-di-tert-butylbenzaldehyde and o-toluidine as starting materials.A series of novel polyimides(PI 3a-3c)with large pendant groups were prepared with the obtained diamine monomer and three different commercial aromatic dianhydrides(3,3',4,4'-biphenyltetracarboxylic dianhydride,4,4'-oxydiphthalic anhydride,and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride)by one-step high temperature polycondensation.The prepared polyimides exhibited high solubility and good membrane forming ability:they could be dissolved not only in some high boiling solvents such as DMF,NMP,DMAc,and m-Cresol at room temperature,but also in some low boiling solvents such as CHCl3,CH2Cl2,and THF.Their solubility in most solvents could exceed 10 wt%,and the flexible membranes could be obtained by casting their solutions.The prepared membranes exhibited good gas separation properties.The permeability coefficients of PI 3c for CO2 and O2 were up to 124.6 and 42.8 barrer,respectively,and the selectivity coefficients for CO2/CH4 and O2/N2 were 14.7 and 3.3,respectively.The membranes had light color and good optical transmission.Their optical transmittance at 450 nm wavelength was in the range of 67%-79%,and the cutoff wavelength was in the range of 310-348 nm.They also had good thermal properties with glass transition temperature(Tg)values in the range of 264-302℃.In addition,these membranes possessed good mechanical properties with tensile strength ranging between 77.8-87.4 MPa,initial modulus ranging between 1.69-1.82 GPa,and elongation at break ranging between 4.8%-6.1%.

High Glass Transition and Optical Transparency of Novel Organosoluble Polyamides Containing 4-tert-Butyltoluene Moiety

A series of novel polyamides 3a-3d containing 4-tert-butyltoluene moiety, were prepared using the phosphorylation polycondensation technique. FT-IR and 1↑H NMR techniques were used to investigate the chemical structures of 3a-3d. The results confirmed that they agreed with the proposed structures for 3a-3d completely. The 3a-3d had inherent viscosities ranging from 0.71 to 1.67 dL·g^-1. All the polyamides showed excellent solubility, with the dissolvability at a concentration of 10 wt% in most amide polar solvents. Flexible and tough polyamide films could be prepared by casting from DMAc （N,N-dimethylacetamide） solvent. Their films were nearly colorless and exhibited high optical transparency, with the UV cutoff wavelength in the range of 346-363 nm and transmittance higher than 80% at 450 nm. They also exhibited high glass transition temperatures in the range of 310---343℃ and the onset decomposition temperatures in the range of 435-462 ℃ in nitrogen atmosphere. Meanwhile, these polyamide films possess good mechanical properties with tensile strengths of 76.4-86.1 MPa and elongations at break of 11.2%-27.3%. Due to those properties, these polyamides could be considered as photoelectric and microelectronic materials.

Sensors for control of water transparency in optical and microwave ranges

In the face of deteriorating environmental conditions in the world,water quality control is an urgent task.It can be solved by creating sensors with high accuracy and low cost,which requires the development of fundamentally new radiophysical methods that take advantage of the optical,microwave and millimeter wavelengths that have a significantly greater sensitivity to low concentrations of pollutants and a lower inertia.The article presents prototypes of measuring cells of the microwave and optical ranges as well as the results of an experimental study of water of various degrees of pollution with their help.The results show that the use of the highly sensitive method of capillary-waveguide resonance makes it possible to detect the presence of micro impurities in water with concentrations up to0.1%and to identify water even from sources of various natural origins.In addition,the use of measurements at several frequencies in the optical range will make it possible to solve the problem of creating water control sensors with high sensitivity to pollution and low cost.It can be concluded that the possibility of complex use of multiwave sensors(optical,infrared and microwave ranges)allows to increase the sensitivity and reliability of water quality assessment.

Effect of Oxygen Concentration and Annealing Theatment on the Optical Properties of the Transparent Conductive CdIn_2O_4 Thin Films

Transparent conductive cadmium indium oxide films (CdIn2O4) were prepared by r.f. reactive sputtering from Cd-In alloy targets under an Ar-O2 atmosphere. Electrical conductivity of the order of 105Ω-1.m-1 and the optical transmission as high as 94% are easily attained by postdeposition annealing treatment. The effects of oxygen concentration in the reactive gas mixture and post-deposition annealing treatment on the optical transmittance as well as optical parameters, such as refractive index (n), extinction coefficient (k), real part (ε') and imaginary part (ε') of the dielectric constant, were studied in the visible and near-infrared region. The highfrequency dielectric constant ε∞ the plasma frequency ωP, and the conduction band effective mass mc of different samples were also investigated

Thin-layer Spectroelectrochemistry of 3,3′,5,5′-Tetramethyl-benzidine on Pt Minigrid Optically Transparent Electrode

The electrooxidation behavior of 3, 3′,5, 5′-tetramethylbenzidine(TMB) was investigated using a platinum minigrid optically transparent thin-layer spectroelectrochemical cell. TMB underwent one two-electron electrooxidation process to yield quinonediimine in the pH range from 2.0 to < 4.0, and two consecutive one-electron electrooxidation processes, gave the mediate product free radical of TMB first, then gave the oxidation product quinonediimine in the pH range from 4.0 to < 7.0. In the pH range from 7.0 to 10.0, the electrooxidation of TMB was also one two-electron electrooxidation process to yield an azo compound. The formal potential E0'and the electron transfer number of the electrooxidation of TMB at pH 2.0 and pH 8.4 were determined by spectroelectrochemical techniques.

Imaging Transparent Objects in a Turbid Medium Using a Femtosecond Optical Kerr Gate

A femtosecond optical Kerr gate time-gated ballistic imaging method is demonstrated to image a transparent object in a turbid medium. The shape features of the object are obtained by time-resolved selection of the ballistic photons with different optical path lengths, the thickness distribution of the object is mapped, and the maximum is less than 3.6%. This time-resolved ballistic imaging has potential applications in studying properties of the liquid core in the near field of the fuel spray.

IN-SITU DISTANCE RESOLVED OPTICALLY TRANSPARENT THIN-LAYER MICROSCOPIC FTIR SPECTROELECTROCEMISTRY.ESTIMATION OF THE ELECTROCHEMICAL CONCENTRATION-DISTANCE PROFILE

An in-situ optically transparent thin-layer microscopic FTIR spectroelectro- chemical cell was constructed.Using this cell,we characterize a concentration-distance profile in the electrochemical diffusion thin-layer by in-situ adjusting the focal point at different distances to the electrode surface.

A NOVEL OPTICALLY TRANSPARENT THIN LAYER ELECTRODE FOR IN SITU IR SPECTROELECTROCHEMISTRY

A novel design of IR OTTLE is shown to have sufficient sensitivity and experi- mental simplicity for obtaining IR spectra of the species generated during electrochemical oxidation-reduction.

Synthesis and Characterization of Novel Schiff Base for Enhanced Dye-Sensitized Solar Cell Photo-Response Mechanism

The efficient photo-response mechanism is one of the key factors in the commercialization of dye-sensitized solar cells in a bid to satisfy renewable energy demands. Progress in green technology has put solar energy on the front burner as a provider of clean and affordable energy for a sustainable society. We report the synthesis of a novel Schiff base with optical transparency in the visible and near IR region of the solar spectrum that can find application in the DSSCs photo-response mechanism. The synthesized crystal exhibited features that could handle some of the shortcomings of dye-sensitized solar cells which include wide band solar spectrum absorption and capability for swift charge transfer within the photoelectrodes. The synthesized Schiff base was characterized using x-ray diffractometer, UV/Visible spectrometer, Frontier transmission infrared spectrometer and conductometer. XRD data revealed the grown crystal to have an average crystallite size of 2.08 nm with average microstrain value of about 269.43. The FT-IR recorded transmission wave ѵ (CO) at 1207.7 cm−1 while dominant wave occurred at ѵ1654.9 and ѵ1592.3 cm−1 relating to ѵ (CN) stretching and ѵ (NH) bending respectively were observed. The IR spectrum revealed the bonding species and a probable molecular structure of 2,6-bis(benzyloxy)pyridine. The UV/Visible spectra convoluted to maximum peak within the near IR region suggesting that 2,6-bis(benzyloxy)pyridine can absorb both the visible and near IR region while its electrical conductivity was determined to be 4.58 µS/cm. The obtained result of the present study revealed promising characteristics of a photosensitizer that can find application in the photo-response mechanism of DSSCs.

Enhancement and Optimization of ATO Nano-crystalline Films Properties by the Addition of Acetylacetone as Modifier in the Sol-gel Process

Sb-doped Sn O2(ATO) thin films have been prepared using the spin coating method by selecting the proper amount of acetylacetone as solution modifier. All ATO powders and films exhibited the cassiterite rutile-like structure in a crystal size below 10 nm under all the experimental conditions and a nonpreviously reported crystal structure was observed at high acetylacetone loads. The acetylacetone molar ratio influenced notably the optical and electrical properties of ATO films. When prepared at an acetylacetone molar ratio of 4, ATO films exhibited optical transparencies above 90% in the visible region and above 40% in the UV region for thicknesses of 100 and 300 nm. Films in a thickness of 100 nm and at an annealing temperature of 650 ℃ accounted for a high transparency of 97% in the visible wavelength. Films prepared at an acetylacetone molar ratio of 4 exhibited an electric resistivity of 1.33×10-3 Ω·cm at an annealing temperature of 650 ℃. The optimal Sb content for ATO films was found to be 8 at%. The relationships among the properties of starting solutions, the experimental parameters, and properties of ATO films are discussed.

SYNTHESIS AND CHARACTERIZATION OF HIGHLY ORGANO-SOLUBLE POLYIMIDES BASED ON ALICYCLIC 1,8-DIMETHYL-BICYCLO[2.2.2]OCT-7- ENE-2,3,5,6-TETRACARBOXYLIC DIANHYDRIDE AND AROMATIC DIAMINES

Organo-soluble alicyclic polyimides (ALPIs) were synthesized from an alicyclic dianhydride, 1,8-dimethyl-bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (DMEA) and several multialkyl-substituted 4,4'-diaminodiphenylmethane compounds, including 3,3'-dimethyl-4,4'-diaminodiphenyt methane (DMDA), 3,31,5,5'-tetramethyl-4,4'-diaminodiphenyl methane (TMDA) and 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane (TEDA). For comparison, the aromatic polyimides (ARPIs) were synthesized from the aromatic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and the same diamines. The ALPIs exhibited better solubility and transparency, but worse thermal stabilities and mechanical properties than those of the ARPIs. And the ALPIs could be dissolved in common organic solvents, such as N-methyl-2-pyrrolidinone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), chloroform, tetrahydrofuran, m-cresol and so on. The ALPI films had an UV-Vis cut-off at 320 nm and a transmittance of higher than 80% in the visible region. In addition, the ALPIs showed thermal decomposition temperatures (T-d) of about 450degreesC, which was nearly 100degreesC lower than that of the ARPIs.

ORGANO-SOLUBLE FLUORINATED POLYIMIDES DERIVED FROM α,α-BIS(4-AMINO-3,5-DIMETHYLPHENYL)-4'-FLUOROPHENYL METHANE AND VARIOUS AROMATIC DIANHYDRIDES

Organo-soluble fluorinated polyimides were synthesized by the polycondensation of a new aromatic diamine α,α-bis(4-amino-3,5-dimethylphenyl)-4'-fluorophenyl methane with several aromatic dianhydrides.The one-step polymerizationprocedure was conducted at 180℃ in m-cresol,producing the polyimides with inherent viscosities of 0.68-0.76 dL.g^(-1).Thepolyimides could be soluble not only in polar aprotic solvents,such as N-methyl-2-pyrrolidinone,and N,N-dimethylacetamide,but also in common organic solvents,such as chloroform,cyclopentanone,m-cresol and so on.Thepolyimide films show excellent transparency with the UV-Vis cut-off lengths of 310-360 nm and light transmittances ofhigher than 80% in the visible region.In addition,the polyimides exhibit good thermal stability with an initial decompositiontemperature(T_d)higher than 530℃ and have more than 60% of residual weight retentions at 700℃.

Comparative Study of the Performances of Opaque and Transparent Patch Antennas

The performances of two microstrip patch antennas with low visual impact are presented in this paper and compared to an opaque solution. These consist in a copper film deposited on a Borofloat 33 glass substrate through a thin titanium gripping layer. The mesh is obtained by wet chemical etching. Antennas differ by the dimensions in the ground plane mesh pattern. The opaque antenna only consists of a full copper deposit. The transparency work was mainly carried out on the ground plane as it is the largest area available. Specific attention is paid to optical transparency in the visible light spectrum, sheet resistance and electromagnetic performances in the [2.8;3 GHz] bandwidth. They are measured in each case, compared and discussed. Both simulations and measurement results show good performance, especially the antenna with the most transparent ground plane: a high level of optical transparency of almost 73%, coupled with a sheet resistance of less than 0.028 Ohms/sq and a gain of about 3.22 dBi at 2.8 GHz, slightly higher than the gain of the reference opaque antenna of about 2.66 dBi at 2.99 GHz. The opaque reference antenna has a bandwidth of 1.30 GHz while those of the transparent antennas are about 1.60 GHz and 2.10 GHz (S11 < −10 dB). This solution presents a real interest for low cost integrated and discrete antenna solutions in ISM band.

Transparent Thermally Tunable Microwave Absorber Prototype Based on Patterned VO2 Film

Transparent microwave absorbers that exhibit high optical transmittance and microwave absorption capability are ideal,although having a fixed absorption performance limits their applicability.Here,a simple,transparent,and thermally tunable microwave absorber is proposed,based on a patterned vanadium dioxide(VO_(2))film.Numerical calculations and experiments demonstrate that the proposed VO_(2)absorber has a high optical transmittance of 84.9%at 620 nm;its reflection loss at 15.06 GHz can be thermally tuned from–4.257 to–60.179 dB,and near-unity absorption is achieved at 523.750 K.Adjusting only the patterned VO_(2)film duty cycle can change the temperature of near-unity absorption.Our VO_(2)absorber has a simple composition,a high optical transmittance,a thermally tunable microwave absorption performance,a large modulation depth,and an adjustable temperature tuning range,making it promising for application in tunable sensors,thermal emitters,modulators,thermal imaging,bolometers,and photovoltaic devices.

A transparent electromagnetic-shielding film based on one-dimensional metal–dielectric periodic structures

In this study, we designed and fabricated optical materials consisting of alternating ITO and Ag layers. This approach is considered to be a promising way to obtain a light-weight, ultrathin and transparent shielding medium, which not only transmits visible light but also inhibits the transmission of microwaves, despite the fact that the total thickness of the Ag film is much larger than the skin depth in the visible range and less than that in the microwave region. Theoretical results suggest that a high dielectric/metal thickness ratio can enhance the broadband and improve the transmittance in the optical range. Accordingly, the central wavelength was found to be red-shifted with increasing dielectric/metal thickness ratio. A physical mechanism behind the controlling transmission of visible light is also proposed. Meanwhile, the electromagnetic shielding effectiveness of the prepared structures was found to exceed 40 dB in the range from 0.1 GHz to 18 GHz, even reaching up to 70 dB at 0.1 GHz, which is far higher than that of a single ITO film of the same thickness.

Reconfigurable intelligent surface with high optical-transparency based on metalmesh

Reconfigurable intelligent surfaces(RISs)have aroused extensive attentions from academic and wireless communication communities due to their abilities to customize the electromagnetic(EM)characteristics of the propagation channels flexibly and rapidly.Recent advances in theoretical innovations and prototype systems have demonstrated the advantages of RISs in terms of low cost,low power consumption,and easy deployment.Meanwhile,the optically transparent RISs are demanded in some application scenarios.In this paper,we propose a 2-bit metalmesh-based RIS with high optical-transparency.By analyzing the surface current distributions on the element,we employ the metalmesh-grid patterns and metalmesh-stripe patterns on the top and ground layers respectively.The metalmesh patterns can help improve the optical transparency of RISs,while maintaining similar microwave characteristics.The RIS can reach the optical transparency of 79%,and the reflection amplitude is greater than3.2 dB within the operating band.Finally,to verify the capability of the proposed RIS in wavefront controls,the far-field scattering patterns of the RIS with different coding sequences are investigated and the simulation results are in good agreement with the theoretical results.

Resonances Characteristics of Parallel Plate Waveguide Cavities

The influence of air gaps on the response of transmission for a transverse-electric mode parallel-plate waveguide（TE-PPWG） with a single cavity and double cavities has been studied experimentally. As the air gap is larger than the resonant wavelength of high order cavity mode in the single deep grooved waveguide, only the fundamental cavity mode can be excited and single resonance can be observed in the transmission spectrum. Based on above observations, a tunable multiband terahertz（THz）notch filter has been proposed and the variation of air gap has turned out to be an effective method to select the band number. Experimental data and simulated results verify this band number tunability. This mechanical control mechanism for electromagnetic induced transparency（EIT） will open a door to design the tunable THz devices.

Hybrid Material of Graphene and Poly(3,4-ethyldioxythiophene)with High Conductivity,Flexibility,and Transparency

A novel hybrid material prepared from graphene and poly(3,4-ethyldioxythiophene)(PEDOT)shows excellent transparency,electrical conductivity,and good flexibility,together with high thermal stability and is easily processed in both water and organic solvents.Conductivities of the order of 0.2 S/cm and light transmittance of greater than 80%in the 4001800 nm wavelength range were observed for fi lms with thickness of tens of nm.Practical applications in a variety of optoelectronic devices are thus expected for this transparent and flexible conducting graphene-based hybrid material。

Optical transparent metamaterial structure for microwave-infrared-compatible camouflage based on indium tin oxide

A visible transparent metamaterial absorber was designed and fabricated with ultrabroadband microwave absorption and low infrared emissivity to meet the increasing demand for multispectral compatible camouflage. The absorber was fabricated with a low-infrared emissive layer at the top, a microwave-absorbing layer in the middle, and a reflective layer at the bottom, which were separated by polymethyl methacrylate plates. The absorber showed an average visible transmittance of 55%, infrared emissivity of ~0.37, and effective microwave absorption bandwidth of 32.1 GHz with a total thickness of 3.0 mm. Furthermore,microwave absorption exhibited wide-angle stability and polarization insensitivity characteristics. The mechanism of microwave attenuation was further explored through effective electromagnetic parameters as well as surface current, electric field, magnetic field, and energy loss density distributions. The experimental results were consistent with those of the simulations and calculations, indicating the potential of the designed metamaterial absorber for future applications in multispectral compatible camouflage.