Rafal Sliz

High-strength nanocellulose-talc hybrid barrier films.

Hybrid organic-inorganic films mimicking natural nacre-like composite structures were fabricated from cellulose nanofibers obtained from sequential periodate-chlorite oxidation treatment and talc platelets, using a simple vacuum-filtration method. As a pretreatment, commercial talc aggregates were individualized into well-dispersed talc platelets using a wet stirred media mill with high-shear conditions to promote the homogeneity and mechanical characteristics of hybrids. The nanofiber-talc hybrids, which had talc contents from 1 to 50 wt %, were all flexible in bending, and possessed tensile strength and Youngs modulus values up to 211 ± 3 MPa and 12 ± 1 GPa, respectively, the values being remarkably higher than those reported previously for nanofibrillated cellulose-talc films. Because of the lamellar and well-organized structure of hybrids in which the talc platelets were evenly embedded, they possessed a small pore size and good oxygen barrier properties, as indicated by the preliminary results. The talc platelets decreased the moisture adsorption of highly talc-loaded hybrids, although they still exhibited hydrophilic surface characteristics in terms of contact angles.

Porous thin film barrier layers from 2,3-dicarboxylic acid cellulose nanofibrils for membrane structures.

To fabricate a strong hydrophilic barrier layer for ultrafiltration (UF) membranes, 2,3-dicarboxylic acid cellulose nanofibrils with high anionic surface charge density (1.2 mekv/g at pH 7) and a width of 22 ± 4 nm were used. A simple vacuum filtration method combined with a solvent exchange procedure resulted in a porous layer with a thickness of ∼ 0.85 μm. The fabricated membranes reached high rejection efficiencies (74-80%) when aqueous dextrans up to 35-45 kDa were filtrated to evaluate the molecular weight cut-offs (MWCO). A linear correlation between the barrier layer thickness and the flux rate was observed in all tested cases. Further optimization of the barrier layer thickness can lead to an even more effective structure.

Butylamino-functionalized cellulose nanocrystal films: barrier properties and mechanical strength

Cellulose nanocrystals (CNCs), which are strong, rod-like constituents of plant cellulose, are promising materials for green packaging applications as the material is capable of forming tortuous network structures with efficient barriers against outside gases. Here, a two-step procedure based on periodate oxidation followed by reductive amination was used as a pretreatment to modify bleached birch chemical wood pulp. Individualized CNCs were obtained from three different butylamino-functionalized pulps by mechanical homogenization. The fabricated CNCs were utilized to form transparent barrier films with a vacuum filtration method. All the butylamino-functionalized CNC films showed capability to resist oxygen permeability even at high relative humidity (RH 80%), and values as low as 5.9 ± 0.2 cm3 μm per m2 per day per kPa were recorded for pure cellulose based film using tert-butylamino-functionalized CNCs. In addition a barriers against water vapor permeation and dynamic vapor sorption were determined up to relative humidities of 80 and 90%, respectively. For surface characterization of the films time-dependent contact angles and surface roughness were measured. The films had good mechanical characteristics with tensile strength of 105.7 ± 9.7 MPa, strain-to-failure of 6.4 ± 0.6% and a Youngs modulus of 5.8 ± 0.8 GPa.

Characterization of ink-jet printed RGB color filters with spectral domain optical coherence tomography

We present the use of sub-micron resolution optical coherence tomography (SMR SD-OCT) in volumetric characterization of ink- jet printed color filters, aimed for electronic paper display (EPD). The device used in the study is based on supercontinuum light source, Michelson interferometer centered at 600 nm and employs 400-800 nm spectral region. Spectra are acquired at a continuous rate of 140,000 per second. Color filter array of 143 μm x 141 μm sized and 6 rtm deep ink pools was studied. The volumetric OCT reconstruction was done using the experimental SMR SD-OCT device and a commercial SD-OCT imaging system. The ink layer in the pools was estimated to be 2μm thin. The optical profilometer was used for reference measurements.

Disposable optics for microscopy diagnostics

The point-of-care testing (POCT) is having increasing role on modern health care systems due to a possibility to perform tests for patients conveniently and immediately. POCT includes lot of disposable devices because of the environment they are often used. For a disposable system to be reasonably utilized, it needs to be high in quality but low in price. Optics based POCT systems are interesting approach to be developed, and here we describe a low-cost fabrication process for microlens arrays for microscopy. Lens arrays having average lens diameter of 222 μm with 300 μm lens pitch were fabricated. The lenses were characterized to have standard deviation of 0.06 μm in height and 4.61 μm in diameter. The resolution limit of 3.9μm is demonstrated with real images, and the images were compared with ones made with glass and polycarbonate lens arrays. The image quality is at the same level than with the glass lenses and the manufacturing costs are very low, thus making them suitable for POCT applications.

Orthogonal Thin Film Photovoltaics on Vertical Nanostructures

Decoupling paths of carrier collection and illumination within photovoltaic devices is one promising approach for improving their efficiency by simultaneously increasing light absorption and carrier collection efficiency. Orthogonal photovoltaic devices are core-shell type structures consisting of thin film photovoltaic stack on vertical nanopillar scaffolds. These types of devices allow charge collection to take place in the radial direction, perpendicular to the path of light in the vertical direction. This approach addresses the inherently high recombination rate of disordered thin films, by allowing semiconductor films with minimal thicknesses to be used in photovoltaic devices, without performance degradation associated with incomplete light absorption. This work considers effects which influence the performance of orthogonal photovoltaic devices. Illumination non-uniformity as light travels across the depth of the pillars, electric field enhancement due to the nanoscale size and shape of the pillars, and series resistance due to the additional surface structure created through the use of pillars are considered. All of these effects influence the operation of orthogonal solar cells and should be considered in the design of vertically nanostructured orthogonal photovoltaics.

Organic solvent wetting properties of UV and plasma treated ZnO nanorods: printed electronics approach

Due to low manufacturing costs, printed organic solar cells are on the short-list of renewable and environmentally- friendly energy production technologies of the future. However, electrode materials and each photoactive layer require different techniques and approaches. Printing technologies have attracted considerable attention for organic electronics due to their potentially high volume and low cost processing. A case in point is the interface between the substrate and solution (ink) drop, which is a particularly critical issue for printing quality. In addition, methods such as UV, oxygen and argon plasma treatments have proven suitable to increasing the hydrophilicity of treated surfaces. Among several methods of measuring the ink-substrate interface, the simplest and most reliable is the contact angle method. In terms of nanoscale device applications, zinc oxide (ZnO) has gained popularity, owing to its physical and chemical properties. In particular, there is a growing interest in exploiting the unique properties that the so-called nanorod structure exhibits for future 1-dimensional opto-electronic devices. Applications, such as photodiodes, thin-film transistors, sensors and photo anodes in photovoltaic cells have already been demonstrated. This paper presents the wettability properties of ZnO nanorods treated with UV illumination, oxygen and argon plasma for various periods of time. Since this work concentrates on solar cell applications, four of the most common solutions used in organic solar cell manufacture were tested: P3HT:PCBM DCB, P3HT:PCBM CHB, PEDOT:PSS and water. The achieved results prove that different treatments change the contact angle differently. Moreover, solvent behaviour varied uniquely with the applied treatment.

Sub-micron resolution high-speed spectral domain optical coherence tomography in quality inspection for printed electronics

We present the use of sub-micron resolution optical coherence tomography (OCT) in quality inspection for printed electronics. The device used in the study is based on a supercontinuum light source, Michelson interferometer and high-speed spectrometer. The spectrometer in the presented spectral-domain optical coherence tomography setup (SD-OCT) is centered at 600 nm and covers a 400 nm wide spectral region ranging from 400 nm to 800 nm. Spectra were acquired at a continuous rate of 140,000 per second. The full width at half maximum of the point spread function obtained from a Parylene C sample was 0:98 m. In addition to Parylene C layers, the applicability of sub-micron SD-OCT in printed electronics was studied using PET and epoxy covered solar cell, a printed RFID antenna and a screen-printed battery electrode. A commercial SD-OCT system was used for reference measurements.

Light Emission Color Conversion of Polyfluorene-Blend OLEDs Induced by Thermal Annealing

This paper investigated the applicability of thermal annealing to be used for the color conversion of organic light-emitting diodes (OLEDs) made of a blend of light-emitting polyfluorenes. Blue-light-emitting polyfluorene poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) was used as the host material and green-light-emitting polyfluorene poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT) as the dopant material. Annealing treatment was conducted at the temperatures of 150 °C and 270 °C, before top contact deposition. Both nonannealed OLEDs and those annealed at 270 °C showed green color emission, implying that emission was taking place via the dopant material F8BT. Instead, the light emission color of the OLEDs annealed at 150 °C was shifted to white upon a rise of a blue spectral component. The origin of the blue light emission was attributed to PFO and indicated considerable phase separation between PFO and F8BT. This paper showed that thermal annealing can be applied to modify the light emission color of polyfluorene-blend OLEDs.

Performance Enhancement of Polymer Electrolyte MEIS Hydrogen Sensor by DC-Biasing

DC-biasing was applied as a method to enhance the performance of a capacitive type gas sensor with a polymer electrolyte layer. The sensor was constructed as a metal-electrolyte-insulator-semiconductor structure with a polymer electrolyte layer deposited on a Si-substrate with SiO2-dielectric layer and aluminum back electrode. The electrolyte was prepared from polyvinyl chloride polymer dissolved in water with adding H3PW12O40 to the mixture making it proton conductive. The device was finalized with a platinum top electrode. The sensor was shown to be sensitive to H2 with detection limit below 100-ppm concentrations in synthetic air at room temperature. The sensor was tested using ac voltages with 250-mV amplitude and frequency from 1 to 100 kHz. In addition, by dc biasing the device with voltages up to 2 V during the capacitive measurements, the response, and sensitivity of the sensor were increased by 70% and 50%, respectively, at the optimal measurement frequency (5 kHz).