Thermo-induced Changes Research Articles

Thermo-induced changes in the structure of lentil protein isolate (Lens culinaris) to stabilize high internal phase emulsions

This study aims to assess the impact of heat treatment on the emulsifying properties of lentil protein isolate (LPI) dispersion to produce high internal phase emulsions (HIPEs). The heat-treated LPI dispersion was characterized by size, turbidity, solubility, zeta potential, free sulfhydryl group, electrophoresis, differential scanning calorimetry, circular dichroism, Fourier transforms infrared spectroscopy and intrinsic fluorescence. HIPEs were produced with 25% of LPI dispersion (2%, w/w) and soybean oil (75%) using a rotor-stator (15,500 rpm/1 min). HIPEs were evaluated for their droplet size, zeta potential, centrifugal stability, microscopy, appearance, Turbiscan stability, and rheology over 60 days (25 °C). Heat treatment reduced the size of LPI, resulting in increased turbidity, solubility, and exposure of hydrophobic groups. HIPEs produced with heat-treated LPI at 70 °C (HIPE70) and 80 °C (HIPE80) for 20 min exhibited lower droplet sizes, increased stability, reduced oil loss, and a homogeneous appearance compared to HIPE produced with untreated LPI (HIPEc). In addition, HIPE70 and HIPE80 displayed resistance to shear stress, higher apparent viscosity, and increased storage modulus than HIPEc. HIPEs produced with heat-treated LPI were stable, suggesting that the treatment was efficient for improving the functional properties of the protein and the possibility of future research focusing on fat substitutes in food applications.

Thermo-induced changes in the optical linearity and nonlinearity of Dy doped (GeSe2)80(Sb2Se3)20 thin films

Thermo-induced changes in the optical linearity and nonlinearity of Dy doped (GeSe2)80(Sb2Se3)20 thin films

Influence of elevated temperature on electron flows in chloroplasts of barley

The efficiency of electron carriers in thylakoid membranes untreated and exposed to heat 7-day-old barley seedlings was evaluated with PAM fluorescence. Darkness–light transitional states in chloroplasts after heat exposure are studied. Thermoinduced changes in linear and cyclic electron transport chain of chloroplasts are revealed. The activation of NADPH-dependent electron flux after exposure to elevated temperatures is shown. We assumed that ΔрН of thylakoid membranes employed the regulatory role in the distribution of electron flows and the adaptation of the photosynthetic apparatus to stressful effects.

Negative axicon tip micro-cavity with a polymer incorporated optical fiber temperature sensor

A negative axicon micro-cavity polydimethylsiloxane (PDMS) filled Fabry-Perot interferometer (FPI) based sensor for accurate temperature sensing is proposed and demonstrated. The micro-cavity lengths of 130 µm, 160 µm, 240 µm and 260 µm are employed for temperature sensing from 27 °C to 80 °C. The sensing probe responses were measured in terms of wavelength shift resulting from the thermo-induced change in the FP cavity length and in the refractive index of the PDMS filled in the cavity. However, the effect of thermal expansion/contraction of PDMS is found to be more dominating over the change in its refractive index. The highest and least sensitivity of the order of 59 pm/ °C and 24 pm/ °C are observed for 130 µm and 260 µm cavity lengths. The linear relationship between the change in spatial frequency and cavity length with respect to temperature variation are also studied. These miniaturized and stable sensor probes are capable of measuring small change in temperature variation with high accuracy and sensitivity and can be used for remote sensing measurements.

Relationships between lithium and sodium nanoparticles and color centers formation in LiF and NaF crystals with hydroxide and magnesium ions impurities

In this study, we investigated the mutual influence of metal nanoparticles and the color centers in lithium and sodium fluorides based on absorption spectroscopy, infrared spectroscopy, atomic force microscopy, and photoluminescence method. Atomic force images of the fresh cleavage of the γ-irradiated and photo-bleached single crystal of sodium fluoride indicated the photo-induced aggregation of F color centers followed by the formation and integration of sodium nanoparticles. The thermo-induced changes in the photo-bleached samples exhibited the inverse trend, i.e., disintegration of the nanoparticles and restoration of a crystal lattice. In the photo-bleached γ-irradiated lithium fluoride crystals, we detected the luminescence of F3 centers and confirmed that the mechanism of nanoparticle formation was due to aggregation of the color centers.

A thermally tunable narrowband selector based on a chiral nematic containing a binary thermosensitive chiral dopant mixture

ABSTRACTWe employed a thermosensitive chiral dopant (CD), characterized by its thermoinduced change in helical twisting power (HTP) in terms of the handedness and strength, to shift the Bragg reflection band of a CLC. A thermally tunable photonic bandgap (PBG) device was demonstrated using a one-dimensional asymmetric photonic crystal (PC) infiltrated with the CLC as a defect layer. With a temperature controller to shift the PBG of the CLC, two narrow transmission bands can be tuned in the spectrum dominated by the asymmetric PC structure. This optical device can find applications as a tunable narrowband wavelength selector or an intensity controller.

Selective etching of spin-coated and thermally evaporated As30S45Se25 thin films

Chalcogenide glasses are intensively studied materials due to their interesting optical properties such as high values of refractive index, wide transparency in IR, photosensitivity, etc. We report on the comparison of photo and thermo-induced changes in optical properties and chemical resistance of thermally evaporated and spin-coated As30S45Se25 thin films. Significantly different trends of photo-induced changes in chemical resistance in both types of thin films such as negative etching of thermally evaporated thin films and positive etching of spin-coated thin films were observed. The structural changes responsible for the observed phenomena were investigated as well.

Engineering Thermoswitchable Lithographic Hybrid Gold Nanorods as Plasmonic Devices for Sensing and Active Plasmonics Applications

In this article, we aim to investigate the sensitivity of regular arrays of hybrid plasmonic nanostructures to variations in properties of the local environment (temperature, refractive index, polymer thickness), in the context of sensing and active plasmonic applications. A proper description and characterization of such hybrid systems is indeed essential in order to provide designed criteria for efficient stimuli-responsive devices. As an ideal model, we introduce a novel kind of hybrid plasmonic core–shell system made of lithographic gold nanorods (GNRs), coated by a thermosensitive polymer shell based on poly(N-isopropylacrylamide) (pNIPAM). The grafting of the polymer on the GNRs results from a multistep but simple approach in order to confine the pNIPAM brushes on the GNRs and to control the thickness of the polymer coating. We show that the optical response of the plasmonic hybrid structures (GNR@pNIPAM) is strongly modified upon a variation of the external temperature, due to a physical change of the conformation of the polymer coating. These thermo-induced changes of the optical properties can be optimized by changing the aspect ratio of the GNRs and the polymer thickness to obtain very efficient optical reporters of the polymer state in a controlled and reversible manner. This work could provide an important step toward the use of GNR@pNIPAM structures for applications spanning from opto-mechanical modulators to nanoscale adhesion and molecular sensing.

Synthesis, structure and optical properties of thin films from GeS2–In2S3 system deposited by thermal co-evaporation

This paper deals with the properties of the glasses and thin films from multi-component chalcogenide prepared by co-evaporation technique. The thin chalcogenide layers from GeS2–In2S3 system were deposited by thermal co-evaporation of GeS2 and In2S3. Using X-ray microanalysis it was found that the film compositions are closed to the expected ones. X-ray diffraction analysis shows that the thin films deposited by co-evaporation are amorphous. The refractive index, n and the optical band gap, Egopt were calculated from the transmittance and reflectance spectra. The thin film's structure was investigated by infrared spectroscopy. It was found that the photo-induced optical changes decrease with increase of indium content while significant thermo-induced changes in the optical properties and structure were observed at 14at.% indium. The infrared spectra demonstrated high transmittance of the thin films in the range 4000–500cm−1. The far-infrared spectra indicated that the indium participates in the glass network of the layers from Ge–S–In system in four coordinated InS4/2− tetrahedral and six-coordinated InS6/23− octahedral units. The changes in infrared spectra after annealing of the thin films evidence an increase of population of ethane-like S3Ge–GeS3 units and/or structural or phase change of indium contain units.

Photo- and Thermo-Induced Changes in Optical Constants and Structure of Thin Films from GeSe2-GeTe-ZnTe System

We examined the condition of preparation of thin films from GeSe2-GeTe-ZnTe system by thermal evaporation and changes in their optical properties after exposure to light and thermal annealing. The results for composition analysis of thin films showed absence of Zn independently of the composition of the bulk glass. By X-ray diffraction (XRD) analysis it was found that a reduction of ZnTe in ZnSe in bulk materials takes of place during the film deposition. A residual from ZnSe was observed in the boat after thin film deposition. Optical constants (refractive index, n and absorption coefficient, α) and thickness, d as well as the optical band gap, E g , depending of the content of Te in ternary Ge-Se-Te system are determined from specrophotometric measurements in the spectral range 400-2500 nm applying the Swanepoel's envelope method and Tauc's procedure. With the increase of Te content in the layers the absorption edge is shifted to the longer wavelengths, refractive index increases while the optical band gap decreases from 2.02 eV for GeSe 2 to 1.26 eV for Ge 34 Se 42 Te 24 . The values of the refractive index decrease after annealing of all composition and E g increase, respectively. Thin films with composition of Ge 27 Se 47 Te 9 Zn 17 and Ge 28 Se 49 Te 10 Zn 13 were prepared by co-evaporation of (GeSe 2 ) 78 (GeTe) 22 and Zn from a boat and a crucible and their optical properties, surface morphology and structure were investigated. The existence of a correlation between the optical band gap and the copostion of thin films from the system studied was demonstrated.

Optical properties of normal and thermally coagulated chicken liver tissue measured ex-vivo with diffuse reflectance

The purpose of the present study is to determine the optical properties of normal and thermally coagulated chicken liver at 720, 740, 770, 810, 825 and 840 nm wavelengths of laser irradiation. So, we were able to evaluate these optical properties (absorption and scattering coefficients) with ex-vivo study using Kubelka Munk Model (KMM) from the radial dependence of the diffuse reflectance with femtosecond pulsed laser in near IR region. These coefficients were significantly increased with coagulation. The penetration depths of the diffused light have been reported to a maximum value of 8.12 ± 0.36 mm in normal liver and 2.49 ± 0.17 mm in coagulated liver at 840 nm showing increasing behavior towards IR region. The Monte Carlo simulation was used to check the theoretical validation of measured optical properties of the tissue that showed a good match with our experimental results. We believe that these differences in optical properties will be helpful for the understanding arid optimal use of laser applications in medicine and differential diagnosis of tissues by using different optical methods. Especially for the investigation of biological tissue for photodynamic therapy (PDT), the knowledge of the specific optical properties and their thermo-induced changes is important.

Interdependence of optical parameter changes in Ge–As–S films

The presence or absence of correlation between irreversible and reversible photo- and thermoinduced changes of optical band gap ( E g ) and refractive index ( n) is analyzed in films (∼700 nm thick) from compositions of the Ge 2S 3–AsS 3 glassy system. We have shown that the large irreversible photoinduced changes of E g and n agree qualitatively with the Moss relation ( n o 4 E g =const). Moreover, the thermoinduced changes of E g also correlate with that of n. However, this relation is not fulfilled in some cases when annealing is performed on the virgin films illuminated in vacuum. The irreversible changes of E g after illumination in vacuum are smaller than that after illumination in air, where photooxidation could have an influence. It is found that the component with increased E g , which is related to photooxidation, does not govern changes in n responsible for Moss relation. In the annealed films from some compositions the photodarkening fully disappears with increase in the illumination time. The Moss relation is not observed in some stages of this photoinduced process. The quantitative deviations from Moss relation are discussed based on formulas where thickness changes, which usually show no one-to-one correspondence with Δ E g , are taken into account.

Photo- and Thermoinduced Changes of the Optical Absorption in Bi<SUB>12</SUB>SiO<SUB>20</SUB> Crystals

Photo- and Thermoinduced Changes of the Optical Absorption in Bi<SUB>12</SUB>SiO<SUB>20</SUB> Crystals

Function of plastoquinone in heat stress reactions of plants

The effect of high temperature treatment (40 °C, 3 h, illumination at 100 μmol m − 2 s − 1 ) on the photosynthetic electron flow in barley seedlings of different age was investigated. Thermoinduced inhibition of the liner electron flow due to partial impairment of the water oxidizing complex (WOC) and the increase in the extent of Q A − reoxidation by Tyr z ox in thylakoids isolated from 4-day-old leaves was shown by measurements of oxygen evolution using benzoquinone or potassium ferricyanide as electron acceptors, as well as by following Q A − reoxidation kinetics in the absence and presence of exogenous electron acceptors, DCBQ and DMBQ. Using HPLC analysis, an increase in the oxidation of the photoactive plastoquinone pool in young leaves under heating was shown. In older, 11-day-old leaves, heat treatment limited both photosynthetic electron flow and oxygen evolution. The same effects of heat shock on oxygen evolution caused an inhibition of electron flow on the donor side of PSII only. However, a rise in the proportion of PSII with Q A − reoxidized through recombination with the S 2/S 3 state of the WOC was observed. The addition of exogenous electron acceptors (DCBQ and DMBQ) and a donor (DPC) showed that the thermoinduced decrease in the electron transport rate was caused by an impediment of electron flow from Q A − to acceptor pool. The decrease in size of the photoactive PQ-pool and a change in the proportions of oxidized and reduced PQ in older leaves under heat treatment were shown. It was suggested that a thermoinduced change of the redox state of the PQ-pool and a redistribution of plastoquinone molecules between photoactive and non-photoactive pools are the mechanisms which reflect and regulate the response of the photosynthetic apparatus under heat stress conditions.

Thermally induced wavelength tunability of microcavity solid-state dye lasers

Wavelength tunability of a microcavity solid-state dye laser is modeled and demonstrated by simulations making use of the finite element method. We investigate the application of two phenomena, thermoelastic expansion of the microcavity material and thermo-induced change of the refractive index, to tune the microcavity mode frequencies by a variation of the effective optical path. An optimized size of the laser microcavity is defined depending on the operation wavelength bandwidth and the glass transition temperature of the gain material.

Determination of the optimal wavelength for temperature independent detection of commercial gasoline with a polymer cladding optical fiber

An influence of temperature variations on transmission of a polymer cladding silica core (PCS) optical fiber was investigated in a wide spectral range covering the first (1710nm) and the second (1170nm) vibrational overtone bands of gasoline absorption. Thermo-induced changes of the fiber background transmittance have strong dependence on wavelength. A narrow wavelength band around 1214nm was found to be almost free from the thermal effects while maintaining sufficient sensitivity for gasoline detection.

Thermo-induced changes in EPR spectra of metal-free oligo- and polyphthalocyanines

Conjugated polymers (CP) are promising materials for various electronic, optical and magnetic applications, but clear understanding of their electron structure is not still achieved. Electron paramagnetic resonance (EPR) studies can give valuable information about electron states in polymers. We present a study of metal-free oligomeric (OPc) and polymeric (PPc) phthalocyanines by the EPR technique in the temperature interval from 300 to 500 K. Both of air-exposed and vacuum-processed samples have been investigated. The g-value, the intensity, the width and the shape of EPR signals observed in OPC and PPc at room temperature are typical of conjugated polymers. However, we found specificities of the EPR thermal behavior that was dependent on the oligomer molecular weight and sample's treatment. There was a certain temperature T 1 above which the EPR signal becomes time-dependent that reflects in a growing of the EPR signal intensity. We detected also another characteristic temperature T 2 ( T 2 > T 1) above which the irreversible increasing of the EPR linewidth was observed. After vacuumization of OPc and PPc samples, the temperatures T 1 and T 2 shift to the higher values. The low-molecular OPc were characterized by the lesser value of T 2 in comparison with OPc of higher molecular masses and polymer samples. The computer analysis showed that the specific shape of the EPR line and its thermo-induced evolution can be explained by the coexistence of both localized and delocalized EPR-active centers.

Photo- and thermo-induced bandgap and volume changes in Ge-based chalcogenide films

Irreversible and reversible changes induced by illumination and/or annealing of thin Ge–As–S films are studied. Attention is paid to the volume (thickness) changes and their correlation with changes in the bandgap. The revealed dependences are compared to that obtained for obliquely deposited As(Ge)–S films, and substantial differences are found.

Photostructural transformations in amorphous chalkogenide nanolayered films produced by thermal vapour deposition

Photo- and thermoinduced changes of As2S3 \\SexTe1−x (0.1 < x < 0.5) multilayer structures were investigated by optical and electrical methods as well as by low angle X-ray diffraction (LAXD). It was shown that samples with total thicknesses up to 0.7–0.8 μm of 4–20 nm thick alternating layers with good periodicity, may be prepared by cyclic thermal vapour deposition. The structure of this multilayer may be changed by thermal treatment or illumination with focused laser beam due to the interdiffusion. The corresponding photoinduced changes of optical parameters (absorption, refraction) are useful for optical reading.

Photoinduced changes of mechanical stress in amorphous Ge-As-S(Se) film/Si substrate systems

Thin amorphous Ge-As-S(Se) films were deposited on Si substrates. After deposition, a mechanical stress arises in the film due to the difference in lattice parameters. Photo- and thermo-structural changes were induced in the films by band-gap illumination or heat treatment. These structural changes cause the stress to change its value and/or sign. That is why the stress was used as a tool to investigate the photo- and thermo-induced changes. The investigation includes also a study of the compositional dependence of the stress in the chalcogenide film/Si substrate systems. Some infrared spectra have been measured in order to analyze the possible nature of the induced changes.