Stress-optical Coefficient Research Articles

Exploring the glass transition region: crowding effect, nonergodicity and thermorheological complexity

Monte Carlo simulations performed on multiple polymer chains have produced accurate relaxation modulus Gs(t) curves which match the experimental G(t) curves of polystyrene reasonably well, over a wide temperature range around the glass transition region. The inter-segmental interactions, defined in terms of ε* (well depth) and σ (monomer size), exert a strong influence on the modulus, the length scale and the relaxation time scale of the system. Judicious selection of these interaction parameters has enabled us to create the whole range of temperature dependence of the thermorheological complexity, from ΔT = 40 °C to ΔT = 0 °C. Near the glass transition temperature, the development of nonergodicity vis-à-vis a crowding effect in the system emerges naturally from the analysis of the G(t) line shapes. The entropic slow mode is well described by the Rouse theory and the energetic fast mode shifts to longer time scales, revealing the generic behavior of the thermorheological complexity. Typical Gs(t) curves, when partitioned into glassy and rubbery components, are shown to obey Inoue-Okamoto-Osaki's modified stress-optical rule, with different stress-optical coefficients for each component. Closer to the glass transition temperature, the distance of the closest monomer shows a considerable increase, suggesting a penetrable resistance to the approach of another monomer. The parameter σ represents the characteristic length scale of the system in the glassy region. The thermorheological complexity incorporates the dynamic length scale of structural relaxation, increasing with the decrease of temperature towards the glass transition point.

Characterizations of the optical and structure properties of rayon acetate fibers due to different thermal conditions

This work throws light on the variations of the optical and structural properties of irregular rayon acetate fibers due to annealing at different temperatures and different times by using two-beam Pluta polarizing interference microscopes. The effect of different annealing temperatures and times were studied on the cross sectional area and optical parameters. The obtained optical parameters were used to calculate the crystallinity, orientation functions and the form birefringence. In addition, stress optical coefficients and thermal stress were obtained. Also different types of polarization; polarizability of monomer unit, the induced polarizability and the permanent dipole moment, activation energy and the shift factor were carried out for thermally treated rayon acetate fibers. The mechanisms of structural variations for annealing rayon acetate fibers were discussed. Illustrations using microinterferogram, graphs and tables are given.

Thermorheological complexity revisited: A simple Monte Carlo simulation scheme to create the near Tg behavior in linear homopolymer melts

Using a coarse-grained multiple chain description for a homopolymer system which includes the inter-segmental interactions (ISI) of the chains, Monte Carlo simulations were performed in order to generate fairly accurate relaxation modulus Gs(t) curves which could be matched with the experimental G(t) curves, over a wide temperature range around the glass transition point (Tg). The ISI, defined in terms of ε* (well-depth) and σ (bead diameter), exert strong influence on the modulus, length scale and relaxation time scale of the system. Judicious combinations of the ISI parameters lead to the creation of the whole range of the temperature dependence (from ΔT = 40 °C to ΔT = 0 °C) of the thermorheological complexity in the system. Near the Tg, the development of nonergodicity in the system emerges from the analysis of the G(t) line shapes. The entropic slow mode is well described by the Rouse theory and the energetic fast mode shifts to longer time scales, revealing the generic behavior of the thermorheological complexity. Typical Gs(t) curves, when partitioned into glassy and rubbery components, could be shown to obey Inoue et al.'s modified stress-optical rule, with different stress-optical coefficients for each. Closer to the Tg, the distance of the closest bead shows a considerable increase, suggesting a penetrable resistance to the approach of another bead. The bead size σ represents the characteristic length scale of the system in the glassy region. The thermorheological complexity thus incorporates the dynamic length scale of the structural relaxation, increasing with the decrease of temperature towards the Tg.

Effect of UV radiation on the optical and some structural properties of irregular rayon acetate fibers

This recent study shed demonstration on how the structural parameters changes due exposure to UV radiation and different wavelengths. So this article throws light on the changes of the optical properties and some structural properties due exposure to UV radiation and different wavelengths on irregular rayon acetate fibers. Pluta polarizing interference microscope is used to study the changes for refractive indices and birefringence with different exposure times at three different intensities on irregular rayon acetate fibers. As the principal optical parameters determined, these give an indication of the isotropic refractive index, stress optical coefficient, stress due to UV radiation, optical configuration parameter, segment anisotropy, the number of molecules per unit volume and polarizability of a monomer unit can be obtained. Also by using different wavelengths are given the spectral dispersions, Cauchy's dispersion constants, the resonant wavelength, the oscillation energy, the dispersion energy, the dielectric constant and the dielectric susceptibility for rayon acetate fibers with different wavelengths at room temperatures. Illustrations are given using graphs and microinterferograms.

Properties of Ti-doped Al2O3 thin films deposited by simultaneous RF and DC magnetron sputtering

The Ti-doped Al2O3 (Al2O3:Ti) films were prepared by simultaneous RF magnetron sputtering of Al2O3 and DC magnetron sputtering of Ti. The advantage of this method is that the Ti content could be independently controlled. Decreasing the DC power or increasing the ratio of O2 to Ar pressure made the Al2O3:Ti film be more stoichiometric. By decreasing the DC power or increasing the ratio of O2 to Ar pressure, the hydrophilic Al2O3:Ti film exhibited lower surface roughness, higher average visible transmission, higher linear refractive index and lower stress-optical coefficient.

0104 ひも状ミセル水溶液のステップせん断におけるバンディングと流動特性の関係

The shear-banding formation process of wormlike micellar solutions is investigated. The distributions of the flow-induced birefringence and the orientation angle in a concentric cylinder flow cell are evaluated by using a cross-polarizers technique. The birefringence and the angle are almost constant along the radial direction at low shear rate. The high orientation band (H-band) and the SIS state band (SIS-band) are formed when the shear rate exceeds 1s^<-1>. The fluctuations of the birefringence and the angle in the bands are synchronized with stress oscillation at high shear rate. But as for the stress optical coefficient C, only the value of the SIS-band fluctuates significantly.

Stress-induced birefringence for the Er3+: Y2O3 ceramic system

The stress-induced birefringence for erbium doped yttria ceramics were measured at room temperature. An ellipsometer was used to measure the retardation effect of static loading on a set of ceramic equilateral prisms and the stress-optic co-efficients were obtained. The samples measured were equilateral prisms of pure Y2O3, (Er0.1Y0.9)2O3 and (Er0.2Y0.8)2O3. The stress-optic co-efficients were found to be in the range 1.6↔2.5×10−5[nm/cm]/Pa showing no dependence on erbium concentration.

Compositional dependence of the stress-optic response in zinc tellurite glasses

The compositional dependence of the stress-optic coefficient of zinc tellurite glass was studied and correlated with local structure. The stress-optic response was determined by using the Sénarmont method, while local structure was determined by using x-ray absorption fine structure spectroscopy (XAFS) at the zinc K-edge, and Raman spectroscopy. Estimates of bond lengths d and coordination numbers NC were made and the ratio d/NC showed a strong correlation with the stress-optic coefficient, in agreement with the empirical model proposed previously by Zwanziger and co-workers. This finding is significant because both glass constituents, namely ZnO and TeO2, have complex electronic structure and are predicted by the empirical model to be at the threshold between positive and negative stress response; these glasses thus represent a rigorous check of the empirical model.

Compositional control of the photoelastic response of silicate glasses

The stress-induced birefringence (termed photoelastic response) in oxide glasses has important consequences for several applications. In this work, we provide new insights into the structural origins of the photoelastic response of silicate glasses by determining the composition dependence of the stress optic coefficient (C) of forty-nine silicate glasses containing different alkali and alkaline earth oxides. We find that the value of C decreases with increasing modifier-to-silica ratio and increases with alumina-to-silica ratio. The scaling of stress optic coefficient with composition can be predicted based on the average ratio of bond metallicity to cation coordination number in the glass, which varies as a function of composition. This is evidence that the details of the glass network structure need to be considered in order to account accurately for the composition dependence of C, a result that is consistent with a previously proposed empirical model and with topological constraint theory. Our results enable an improved control of the photoelastic response of silicate glasses through compositional design.

Properties of heavily W-doped TiO2 films deposited on Al2O3-deposited glass by simultaneous rf and dc magnetron sputtering

Abstract TiO 2 films were heavily doped with W (TiO 2 :W) by simultaneous rf magnetron sputtering of TiO 2 , and dc magnetron sputtering of W. The advantage of this method is that the W content could be changed in a wide range. The coexistence of TiO 2 , WO 3 and TiWO 5 in the TiO 2 :W film was detected by XPS analysis. Besides, tungsten in TiO 2 :W film on the bare glass may form mixed valence of W 0+ and W 6+ . Electrical conductivity was primarily due to the contribution of oxygen vacancies and W donors (W Ti ). When the film thickness increased, the TiO 2 :W film showed higher carrier concentration and higher mobility. Furthermore, the resistivity and the transmission decreased obviously with film thickness. On comparing with the TiO 2 :W film deposited on the bare glass, the TiO 2 :W film on the Al 2 O 3 -deposited glass exhibited lower surface roughness, lower resistivity, higher optical energy gap, higher optical transmission, and lower stress-optical coefficient.

Structure and physical properties of W-doped HfO2 thin films deposited by simultaneous RF and DC magnetron sputtering

The W-doped HfO2 (HfO2:W) films were prepared by simultaneous RF magnetron sputtering of HfO2 and DC magnetron sputtering of W. The advantage of this method is that the W content could be independently controlled. The coexistence of W compounds and HfO2 was observed by XPS. Increasing the ratio of O2 to Ar pressure made the HfO2:W film be more stoichiometric. A control of the presence of HfWO5 is a way to enhance strongly the hydrophilicity of HfO2:W film. By decreasing the W content or increasing the ratio of O2 to Ar pressure, HfO2:W film exhibited lower surface roughness, higher visible transmission, a higher linear refractive index and a lower stress-optical coefficient.

The optical properties of hydrophilic Hf-doped HfO2 nanoceramic films

The Hf-doped HfO 2 (HfO 2 :Hf) nanoceramic films were deposited by simultaneous rf magnetron sputtering of HfO 2 and dc magnetron sputtering of Hf. By doping with Hf, the lowest oxidation state of Hf (Hf 0+ ) presented preferentially and changed the hydrophobicity of HfO 2 film into hydrophilicity. On comparing with the HfO 2 film, the optical transmission of HfO 2 :Hf film was higher and strongly increased with pressure, especially in the ultraviolet region and near infrared region. At higher pressure, HfO 2 :Hf film exhibited better hydrophilicity, higher linear refractive index and lower stress-optical coefficient.

Pockels’ coefficients of alumina in aluminosilicate optical fiber

The photoelastic constants of the alumina component in aluminosilicate optical fibers are evaluated and determined to be p11=−0.237±0.020 and p12=−0.027±0.012, thus confirming that the low and negative pij characteristics of bulk alumina are conserved as part of a binary aluminosilicate glass system in optical fiber form. In order to enumerate these values, the strain- and stress-optic coefficients of two fibers (one with an aluminosilicate core and one with a pure silica core) were measured by applying mechanical tension or twist, respectively, to the fibers and measuring changes to an optical system as a function of the mechanical deformation. In the former, the strain-optic coefficient (eOC) is measured directly by recording changes to the free spectral range of a ring fiber laser. In the latter, the stress-optic coefficient (σOC) is found by measuring the change in polarization angle after linearly polarized light propagates through a segment of twisted test fiber. To the best of our knowledge, this is the first such measurement of its type, i.e., the retrieval of the component photoelastic constants, with their signs, of a multicomponent glass. Binary glass compositions wherein the constituents have opposite signs of the photoelastic constant (such as the aluminosilicates) have the potential to give rise to extremely low values of the Brillouin gain coefficient.

Rheo-Optical Study of Viscoelastic Relaxation Modes in Block Copolymer Micellar Lattice System

Dynamic birefringence and viscoelasticity of a diblock copolymer micellar solution were measured in order to clarify the molecular origin of viscoelastic response of the macrolattice structure formed by micelles. The complex strain-optical ratio changed its sign with angular frequency ω and exhibited very complicated ω dependence, suggesting that the stress emerged/relaxed through several mechanisms. With an assumption of the stress-optical rule for each mechanism, the complex shear modulus was separated into four components corresponding, from high to low ω, to the reorientation of corona chains, reorientation of core chains, deformation of core, and deformation of the micellar lattice. Values of the stress optical coefficients for respective components lent support to these assignments.

Dynamic measurement of stress optical behavior of three amorphous polymers

In the present study, rheo-optical and mechanical properties of three amorphous polymers, i.e., PS (polystyrene), PC(polycarbonate) and COC(cyclo olefin copolymer), widely used for optical products have been investigated. Accurate measurement of stress optical coefficients and elastic modulus data across the glass transition region are essential for predicting optical anisotropy in many injection molded optical products like pickup lenses and waveguide in LCD module since the final products have both flow and thermal history from the melt to glass. To obtain stress optical behavior in wide range of frequency and temperature including rubbery, glassy and glass transition regime, frequency sweep tests with extensional bar and shear sandwich tools were undertaken. As a result, glassy and melt extreme values of stress optical coefficient of PS and PC were evaluated as well as master plots in wide frequency region. The sign change of stress optical coefficient was shown clearly for PS as the frequency increased. On the other hand, the sign of stress optical coefficient over the whole frequency region is always positive for PC. For COC’s of different composition, even though the glass transition temperature can vary, the stress optical coefficient of COC’s with different composition stays almost constant at two extremes.

Photoelastic response of alkaline earth aluminosilicate glasses

Understanding the structural origins of the photoelastic response in oxide glasses is important for discovering new families of zero-stress optic glasses and for developing a predictive physical model. In this Letter, we have investigated the composition dependence of the stress optic coefficient C of 32 sodium aluminosilicate glasses with different types of alkaline earth oxides (MgO, CaO, SrO, and BaO). We find that most of the composition dependence of the stress optic response can be captured by a linear regression model and that the individual contributions from the alkaline earths to C depend on the alkaline earth-oxygen bond metallicity. High bond metallicity is required to allow bonds to be distorted along both the bonding direction and perpendicular to it. These findings are valuable for understanding the photoelastic response of oxide glasses.

The optical properties of Ti-doped TiO2 nanoceramic films deposited by simultaneous rf and dc magnetron sputtering

The Ti-doped TiO2 (TiO2:Ti) nanoceramic films were deposited by simultaneous rf magnetron sputtering of TiO2 and dc magnetron sputtering of Ti. When dc power increased, TiO preferentially formed and the deposited films had lower O/Ti atomic ratio, especially at low substrate temperature. With the decrease of substrate temperature, the TiO2:Ti film had relatively high optical energy gap, therefore the absorption edge showed the blue shift. The nonlinear refractive indices of TiO2:Ti films prepared at different dc powers and substrate temperatures were measured by Moiré deflectometry, and were of the order of 10−8cm2W−1. By decreasing dc power and increasing substrate temperature, TiO2:Ti film exhibited lower surface roughness, higher linear refractive index and lower stress-optical coefficient.

Investigation on residual stress and stress-optical coefficient for flexible electronics by photoelasticity

For flexible electronics in manufacture, the full-field stress measurement is an important issue for the film deposited on the flexible substrate. In this work, the two-dimensional photoelasticity is proposed to measure stress-optical coefficients and an analytical derivation is carried out for investigation on full-field residual stresses under tensional forces. In experimental setup, a polarization beam splitter (PBS) is used to connect with two CCD cameras that are used to capture the intensity of right-hand and left-hand circular polarization separately. It has higher measured speed and better uniformity than a direct rotation method. Stress-optical coefficients can be calculated by extracting the slope from tensional stress versus optical retardation curve. Experimental results show that optical retardations for indium-tin-oxide (ITO)-coated PET (polyethylene terephthalate) substrates can be affected more easily than PET substrates under tensional forces. The difference of stress-optical coefficients between 0° and 90° orientations for PEN (polyethylene naphthalate) substrates is smaller than that for PET substrates. Furthermore, it shows residual stresses for ITO-coated PET substrates in 0° and 90° orientations are different under tensional stress.

Effect of substrate temperature on the properties of TiO2 nanoceramic films

TiO2 nanoceramic films were deposited on glasses by rf magnetron sputtering. This method provides more advantages in controlling the microstructure and composition of the films. TiO preferentially formed and the deposited films tended to become nonstoichiometric by increasing substrate temperature. The morphologies and hydrophilic properties of TiO2 films were significantly affected by the substrate temperature. The nonlinear refractive index of the TiO2 film on the glass substrate measured by Moiré deflectometry was of the order of 10−8cm2W−1. Smaller grain size, higher optical energy gap, visible transmission and linear refractive index, and lower stress-optical coefficient were obtained at lower substrate temperature.

A Transflective Nano-Wire Grid Polarizer Based Fiber-Optic Sensor

A transflective nano-wire grid polarizer is fabricated on a single mode fiber tip by focused ion beam machining. In contrast to conventional absorptive in-line polarizers, the wire grids reflect TE-mode, while transmitting TM-mode light so that no light power is discarded. A reflection contrast of 13.7 dB and a transmission contrast of 4.9 dB are achieved in the 1,550 nm telecom band using a 200-nm wire grid fiber polarizer. With the help of an optic circulator, the polarization states of both the transmissive and reflective lights in the fiber may be monitored simultaneously. A kind of robust fiber optic sensor is thus proposed that could withstand light power variations. To verify the idea, a fiber pressure sensor with the sensitivity of 0.24 rad/N is demonstrated. The corresponding stress-optic coefficient of the fiber is measured. In addition to pressure sensing, this technology could be applied in detecting any polarization state change induced by magnetic fields, electric currents and so on.