Opaque Films Research Articles

Optical Coherent Reflection from a Confined Colloidal Film: Modeling and Experiment.

We study the optical reflectivity of confined colloidal films as a function of the angle of incidence in an internal reflection configuration. Two effective medium models and an extended coherent-scattering model for thin colloidal films are compared against experimental measurements with gold, latex, and titanium dioxide colloids. A derivation of the coherent scattering model for confined colloidal films used in this work is presented in a comprehensive way. The model lies within the framework of the multiple-scattering theory and is valid for any angle of incidence and for colloids of small or large particles compared to the wavelength of light, however, only for small and moderately small particles' volume fraction. Reflectivity versus angle of incidence curves for an opaque colloidal film in an internal reflection configuration show the effects of two critical angles. Within the two critical angles, there is a high sensitivity to the presence of colloidal particles, while the volume of colloidal samples needed is in the microliter range. Upon comparing theory with experiment, no model fitting was done in any case. The experimental setup and its calibration procedure are discussed. The results provide physical insight into applications involving optical properties of colloidal systems.

The effect of plastic film transmittance on heat transfer in a multilayer insulation structure of rectangular air cells for frozen food wrapping

As an alternative to a single-layer structure, a multi-layer structure of rectangular air cells was made of a transparent plastic film that aimed to enhance its thermal resistance. While multiplying layers, the authors observed only a slight growth of thermal resistance instead of the expected proportional increase. The purpose of the article is to investigate this phenomenon by means of a verified mathematical model of heat transfer, which was prepared for a multi-layer structure that respects radiation heat transfer throughout a number of parallel internal films. A model was used to investigate the film transmittance impact.Experimental freezing of a test package filled with Tylose gel showed that the use of insulation made of opaque film does not increase freezing time when compared to a transparent one. Experimental thawing showed that the application of wrap made of transparent film can increase package thawing time by about 1.6–2.2 times, and by about 1.8–3.7 times if the wrap is made of opaque film.

On the Importance of Combined Scratch/Acoustic Emission Test Evaluation: SiC and SiCN Thin Films Case Study

The scratch test, as probably the most widespread technique for assessment of the adhesive/cohesive properties of a film–substrate system, fully depends on reliable evaluation based on assessment of critical loads for systems’ failures. Traditionally used evaluation methods (depth change record and visual observation) may sometimes give misleading conclusions about the failure dynamics, especially in the case of opaque films. Therefore, there is a need for another independent evaluation technique with the potential to complete the existing approaches. The nondestructive method of acoustic emission, which detects the elastic waves emitted during film cracking and delamination, can be regarded as a convenient candidate for such a role even at nano/micro scale. The strength of the combination of microscopic observation of the residual groove and depth change record with the acoustic emission detection system proved to be a robust and reliable approach in analyzing adhesion/cohesion properties of thin films. The dynamics of the gradual damage taking place during the nano/micro scratch test revealed by the combined approach is presented for SiC and SiCN thin films. Comparison of critical load values clearly reflects the higher ability of the AE approach in detecting the initial material failure compared to the visual observation.

بررسی اثر افزودن نانو رس بر خواص فیلم دولایه آگار/ ژلاتین ماهی حاوی نانو ذرات دیاکسید تیتانیوم

فیلم دولایه آگار/ژلاتین حاوی نانو ذرات دی‌اکسید تیتانیوم (TiO2) (2 درصد وزنی- وزنی) و نانو رس (با غلظت‌های 3، 5، 10 درصد وزنی- وزنی)، به‌وسیله ترکیب در بستر فیلم ژلاتین به روش قالب‌ریزی و طی 2 مرحله تولید شد و ویژگی‌های ساختاری، فیزیکی، مکانیکی و نوری فیلم تولیدی موردمطالعه قرار گرفت. نتایج نشان داد که اضافه کردن 2 درصد TiO2 به فیلم دولایه باعث کاهش بیش از 15 درصدی نفوذپذیری نسبت به بخار در فیلم‌ دولایه می‌شود. همچنین، نرخ جذب آب و میزان رطوبت با اضافه کردن 2 درصد TiO2 افزایش پیدا کرد. استفاده از نانو ذرات TiO2 به‌طور قابل‌توجهی خاصیت نفوذپذیری فیلم دولایه را در برابر نور UV بهبود بخشید به‌طوری‌که با افزودن 2 درصد وزنی- وزنی TiO2 خاصیت نفوذپذیری نور نسبت به فیلم آگار/ ژلاتین کاهش و کدورت فیلم تولیدی افزایش یافت. از طرفی، نتایج نشان داد که افزودن 3 درصد نانورس (وزنی- وزنی) به فیلم آگار/ ژلاتین حاوی 2 درصد TiO2 (وزنی- وزنی) حلالیت و مقاومت کششی فیلم تولیدی به‌ترتیب از 41/31 درصد و 55/11 مگاپاسکال به 24/33 درصد و 43/18 مگاپاسکال افزایش یافت. افزودن غلظت‌های 5 و 10 درصد (وزنی- وزنی) نانو رس باعث کاهش حلالیت فیلم‌های تولیدی از 41/31 درصد برای فیلم آگار/ ژلاتین شاهد به 09/26 و 49/21 درصد شد. همچنین، افزودن غلظت‌های مختلف نانو رس به فیلم دولایه حاوی 2% TiO2 باعث کاهش معنی‌دار عبور نور، شاخص سفیدی، جذب آب و کدورت در فیلم‌های تولیدی به‌ویژه در غلظت 10% شد. نتایج حاصل نشان داد که استفاده از غلظت 5 درصد نانو رس در فیلم آگار/ ژلاتین حاوی2 درصد TiO2 خواص فیزیکی، مکانیکی و نوری (با در نظر گرفتن کدورت) بهتری در مقایسه با سایر تیمارها داشت.

Elastic Characterization of Transparent and Opaque Films, Multilayers and Acoustic Resonators by Surface Brillouin Scattering: A Review

There is currently a renewed interest in the development of experimental methods to achieve the elastic characterization of thin films, multilayers and acoustic resonators operating in the GHz range of frequencies. The potentialities of surface Brillouin light scattering (surf-BLS) for this aim are reviewed in this paper, addressing the various situations that may occur for the different types of structures. In particular, the experimental methodology and the amount of information that can be obtained depending on the transparency or opacity of the film material, as well as on the ratio between the film thickness and the light wavelength, are discussed. A generalization to the case of multilayered samples is also provided, together with an outlook on the capability of the recently developed micro-focused scanning version of the surf-BLS technique, which opens new opportunities for the imaging of the spatial profile of the acoustic field in acoustic resonators and in artificially patterned metamaterials, such as phononic crystals.

Characterization of edible films based on guar gum and/or maize starch

Edible coatings and films have become new biodegradable conservation alternatives investigated in most food matrices, their application is intended to extend the life of food by increasing its Protection and safety, by mitigating phenomena such as the transfer of gases and water, microbial growth and others, which have an impact on the deterioration of organoleptic and physicochemical characteristics. The composition of these structures varies between proteins, lipids, and polysaccharides with additives that according to their concentration contribute with aspects such as training and functionality. The present project raised a factorial design 33 with percentages of guar gum and cornstarch in ranges of 0.20 to 3.0% w/v; plasticizers such as glycerol and sorbitol from 0.50 to 1.0% v/v; canola oil and polysorbate 80 between 0.10 and 0.30% v/v. With the aim of finding opaque, malleable, tensile resistant, homogeneous and little exudation film for food products. The selected formulations were: guar gum 0.30%, 0.10% glycerol, 0.10% sorbitol, Polysorbate 80 and canola oil 0.20% and guar gum 0.50%, 0.12% glycerol, 0.18% sorbitol, polysorbate 80 and canola oil 0.30%. Films made with guar gum have characteristics of brightness and tensile strength that make them promising formulations for application in food matrices.

Role of Moisture in the Failure of Coatings on Wood

Most wood coating tests are done either in a short term artificial weathering chamber or long term on an outdoor rack/fence. In both cases, the coatings are exposed to both ultraviolet radiation and water. This study is focused on the influence of moisture alone on wood opaque film forming coating failures. As moisture is sorbed into the wood structure, the wood swells in proportion to the volume of water sorbed. As moisture is lost, the wood shrinks in proportion to the volume of the water lost. Moisture in the wood end grain is responsible for coating failure in, for example, window corners and end to end siding. The wood cell wall moisture can be greatly reduced by a process known as acetylation which not only reduces the moisture sorbed in the cell wall but results in high levels of dimensional stability. The reduced moisture uptake along with the stability results in less stress created between the coating wood surface interface improving the performance of the coating and increasing its useful lifetime.

Cellulose nanocrystals obtained from office waste paper and their potential application in PET packing materials

Annually a tremendous amount of office waste paper (OWP) is discarded creating environmental pollution. Therefore, how to make this paper from waste to wealth and use it in new approaches have become a meaningful and challenging work. In this work, OWP being a cellulose rich biomass was employed for the production of cellulose nanocrystals (CNCs) by acid hydrolysis with different acid concentrations but without subjecting OWP to alkali and bleaching treatments. The testing results showed that CNCs prepared using sulfuric acid concentration of 59% with respect to OWP had the highest crystallinity and this concentration was the transition concentration for the production of opaque CNCs film with convoluted nanofibers to transparent one with orientated nanofibers. Besides, CNCs prepared using acid concentration of 65% coated on PET sheet not only had a better water vapor barrier property but also was on a par with the transparency of PET, which was hopeful to be used as coating materials in packaging materials.

Effect of okara dietary fiber on the properties of starch‐based films

This study highlights the potential of okara dietary fiber as reinforcing filler in starch‐based films. Starch‐based films were prepared from corn starch by incorporating 0–15% w/w okara dietary fiber and using glycerol as plasticizer. The rheological properties of film‐forming dispersions were studied. The morphology, thickness, water vapor permeability, opacity, and tensile properties of these films were also investigated. The apparent viscosity of the film‐forming dispersions decreased with increase in okara dietary fiber content. Rough, thick, and opaque films were obtained from the starch‐based films reinforced by okara dietary fiber. The water vapor permeability of starch‐based films was not affected by incorporating 5% w/w fiber and increased with loading 10–15% w/w fiber when compared to the control starch film. The formulation presenting the best mechanical properties contained 10% w/w okara dietary fiber and had a maximal tensile strength of 3.13 MPa.

Dual mode operation, highly selective nanohole array-based plasmonic colour filters

Taking advantage of nanostructured metal films as plasmonic colour filters (PCFs) has been evolved remarkably as an alternative to the conventional technologies of chemical colour filtering. However, most of the proposed PCFs depict a poor colour purity focusing on generating either the additive or subtractive colours. In this paper, we present dual mode operation PCFs employing an opaque aluminium film patterned with sub-wavelength holes. Subtractive colours like cyan, magenta, and yellow are the results of reflection mode of these filters yielding optical efficiencies as high as 70%–80% and full width at half maximum of the stop-bands up to 40–50 nm. The colour selectivity of the transmission mode for the additive colours is also significant due to their enhanced performance through the utilization of a relatively thick aluminium film in contact with a modified dielectric environment. These filters provide a simple design with one-step lithography in addition to compatibility with the conventional CMOS processes. Moreover, they are polarization insensitive due to their symmetric geometry. A complete palette of pure subtractive and additive colours has been realized with potential applications, such as multispectral imaging, CMOS image sensors, displays, and colour printing.

Preparation of photocatalytic TiO 2 -based self-cleaning coatings for painted surface without interlayer

Abstract Photocatalytic TiO 2 provides a promising route to produce self-cleaning coating surfaces, but it often causes decomposition of organic substrates and other coating components. An interlayer is often employed to insulate photocatalytic activity from sensitive substrate layers, complicating the application of these self-cleaning coatings. Herein, photocatalytic TiO 2 -based coatings were prepared based on an aqueous TiO 2 dispersion in a hybrid binder synthesized from tetraethyl orthosilicate and methyl trimethoxy silane via a sol-gel process. Coatings with various levels of nano TiO 2 were prepared and found to be transparent to visible light; i.e., the clear coating could be directly cast on architectural latex coatings without changing its original appearance. The photocatalytic coating system was composed of a TiO 2 -based clear top coat and an opaque latex film underneath. The coatings were evaluated through outdoor exposure studies and accelerated weathering tests. Results of these tests showed that the photocatalytic coatings with a TiO 2 content range of 33–45% exhibited excellent self-cleaning performance, while displaying none of the expected degradation. In fact, this nano TiO 2 -based clear coating actually protected the latex film from UV-induced damage. The increased stability of the organic film may have resulted from reduced UV transmission through the photo-catalyst containing clear coat as well as reduced water permeability. It was demonstrated that the combination of appropriate TiO 2 content and a suitable binder are crucial for the fabrication of robust photocatalytic self-cleaning coatings for painted surfaces without the need for an interlayer.

Potential analysis of a new removable insulation system

In this paper, the potential of a facade element with switchable U-value and g-value is investigated. This new switchable facade element consists of a series of air-filled cavities separated by opaque films, that can be rolled up or down between two fixed layers, thus switching the thermal and optical properties from a thermally insulating state to a conducting state. A first prototype has been built and measured in the insulating state and the properties of the facade element have been optimized using a theoretical analysis at the facade level. The U-value can be switched from a value of 0.35Wm−2K−1 in the insulating state to a value of 2.7Wm−2K−1 in the conducting state. Building energy simulations using EnergyPlus showed that the sum of the heating and cooling demands could be reduced by about 30% with the switchable insulation used as a window application or in front of an opaque massive wall. Even better performance could be achieved by reducing the frame or edge losses. The influence of the thermal mass, and finally the influence of orientation on the overall performance are also investigated and were found to be non-negligible.

Characterization of citrus pectin films integrated with clove bud essential oil: Physical, thermal, barrier, antioxidant and antibacterial properties

The increasing demand for bio-based materials to be used in food packaging has stimulated the development of novel, environmentally-friendly edible films. Antimicrobial films were developed by incorporating different levels of clove bud essential oil (0.5%, 1.0%, and 1.5%) into the citrus pectin in order to modify the functional properties of the films. Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry analysis (DSC) and X-ray diffraction (XRD) were performed, together with the determination of physical, optical, mechanical, antioxidant and antimicrobial properties of pectin emulsified films. The inclusion of oil significantly enhanced the water barrier properties of the films. Addition of oil leads to more opaque films with relatively heterogeneous microstructure, resulting in an increase in film opacity. The composite films were more resistant to breakage and more flexible than the control films. Differential scanning calorimetry (DSC) demonstrated that films incorporating CEO exhibited improved heat stability with slightly higher degradation temperature, compared with control films. The inhibitory effect of pectin films with CEO was also evaluated on three common foodborne bacteria. These results revealed that clove oil has a good potential to be incorporated into citrus pectin to make antimicrobial edible films or coatings for various food applications.

Thermal characterization of metal phthalocyanine layers using photothermal radiometry and scanning thermal microscopy methods

The metal phthalocyanines (MePc) were thermally investigated using photothermal radiometry (PTR) and scanning thermal microscopy (SThM). Copper phthalocyanine and lead phthalocyanine layers with different thicknesses were deposited on Si (111) wafer and on glass substrates by physical vapor deposition in a high vacuum. SThM measurements allowed the determination of local thermal conductivity (κ) of studied MePcs. This method did not require any preliminary sample preparation. The influence of the substrate thermal properties on SThM thermal signal was taken into account for estimating the true value of κ for the organic layer. For PTR investigations MePcs were coated with an opaque aluminum film. Photothermal measurements enabled determination of the in-depth κ. To complement thermal investigations of MePc layers, quantitative analysis of surface morphology properties was performed by an atomic force microscopy. The results of thermal investigations were explained on the base of different surface morphologies of examined organic layers.

Optical and structural properties of biodegradable whey protein isolate nanocomposite films for active packaging

ABSTRACTFilms of whey protein isolate/sodium montmorillonite/citric acid nanocomposites were developed by casting. The objective of this study was to evaluate the effect of the sodium montmorillonite clay (MMT) and citric acid (CA) content on the water vapor barrier, optical, morphological and structural properties of whey protein isolate (WPI) films. The interaction between MMT (3 g/100 g of WPI) and CA (5 g/100 g of WPI) showed lower water vapor permeability (WVP). The addition of CA and MMT caused small alterations in the optical properties without affecting appearance, in more opaque films, in relation to the WPI. The scanning electron microscopy (SEM) showed possible dispersion results for films with 1% MMT, and 5 and 10% CA. Infrared Spectroscopic peaks (FTIR) showed interaction between CA, MMT and WPI.

Interfaces with fractional optical constants and linear reflectance versus angle of incidence for incident unpolarized or circularly polarized light.

For unpolarized or circularly polarized light incident at a dielectric-conductor interface, the intensity reflectance Ru(ϕ) can be made an essentially linear function of the angle of incidence ϕ over a significant range of ϕ at specific values of the normal-incidence intensity reflectance R0 (≈1/3) and the associated normal-incidence reflection phase shift δ0 (≈40°). This places the complex refractive index n-jk of the interface in the domain of fractional optical constants. As demonstrated by specific examples, this is realizable in external reflection at vacuum-metal interfaces in the UV, and in internal reflection in the IR at interfaces between a transparent high-index substrate and an optically opaque thin film of the proper n and k. Fractional optical constants are also achievable for light reflection in air at planar surfaces of appropriately designed, nanostructured, metamaterial substrates.

Poly(l-lactide-b-butylene succinate-b-l-lactide) triblock copolymer: A multi-functional additive for PLA/PBS blend with a key performance on film clarity

Blending of poly(butylene succinate) (PBS) with poly(lactic acid) (PLA) is an effective way to fine tune PLA brittleness. However, the immiscibility between these two polymers leads to product defects in terms of strength and clarity. The present work proposes a simple triblock copolymer, i.e. poly(l-lactide-b-butylene succinate-b-l-lactide) (PLLA-b-PBS-b-PLLA), as a multi-functional additive, i.e. compatibilizer, plasticizer, and nucleating agent for improving the PLA/PBS blend. Based on a critical content of PLA/PBS (at 80/20 wt%) which gives the opaque film, an addition of PLLA-b-PBS-b-PLLA induces drastic changes in crystallization behavior and mechanical properties. The ratio between PLLA and PBS block length, and the amount are the factors to fine tune the PLA/PBS blend. The PLLA40-b-PBS28-b-PLLA40 at 3 phr is an optimal condition to tune the blends with the decreases in glass transition temperature (Tg) (from ∼50 °C to ∼20 °C) as well as an increase in the elongation at break (for two-fold). At that time, the rapid co-crystallization of PBS and PLA in the blend as seen from the small and homogeneously dispersed spherulite results in a key performance to enhance the clarity of the blend film. The present work demonstrates how the block copolymer of PLA and PBS performs its multi-function for miscibility, toughness, and clarity of PLA/PBS blends.

An electric field sensor based on reflected light intensity modulation from electro-optical media

An optical sensor of an alternating electric field is described. The sensing element is a crystal quartz plate which reflects incident light by its front surface. Reflected light intensity is modulated by the tested electric field by means of changing the refractive index of the plate. Modulation of the reflection coefficient of the quartz by the tested electric field occurs due to the electro-optic effect. It is noted that the main advantage of the sensor working on the modulation of the reflected light is the ability to use opaque electro-optical media and thin films.

Ultra-broadband Tunable Resonant Light Trapping in a Two-dimensional Randomly Microstructured Plasmonic-photonic Absorber

Recently, techniques involving random patterns have made it possible to control the light trapping of microstructures over broad spectral and angular ranges, which provides a powerful approach for photon management in energy efficiency technologies. Here, we demonstrate a simple method to create a wideband near-unity light absorber by introducing a dense and random pattern of metal-capped monodispersed dielectric microspheres onto an opaque metal film; the absorber works due to the excitation of multiple optical and plasmonic resonant modes. To further expand the absorption bandwidth, two different-sized metal-capped dielectric microspheres were integrated into a densely packed monolayer on a metal back-reflector. This proposed ultra-broadband plasmonic-photonic super absorber demonstrates desirable optical trapping in dielectric region and slight dispersion over a large incident angle range. Without any effort to strictly control the spatial arrangement of the resonant elements, our absorber, which is based on a simple self-assembly process, has the critical merits of high reproducibility and scalability and represents a viable strategy for efficient energy technologies.

Setup for high-temperature surface Brillouin light scattering: Application to opaque thin films and coatings

A setup combining surface Brillouin light scattering with a high-temperature chamber has been developed. The temperature of the sample is controlled with a Bühler HDK chamber for optical measurements (maximum temperature of 1600 °C), in controlled atmospheres or high vacuum (10-6 mbar). This setup allows the study of sound velocity of surface acoustic waves and of the elastic constants of opaque thin films and coatings in situ as a function of temperature from surface Brillouin light scattering, by analyzing the backscattered light from the sample at a fixed angle of incidence. In this paper, we will demonstrate the applications of this setup for metallic glass thin films devitrification study and evaluation of high temperature elastic properties of hard nitride coatings. This kind of study using surface acoustic waves is rare, in contrast to those made on transparent bulk materials.