Effect of surfactants on the fluorescence spectra of water-soluble MEHPPV derivatives having grafted polyelectrolyte chains

Poly(2-methoxy-5-[2′-ethylhexyoxy]-1,4-phenylenevinylene) (MEHPPV) derivatives with polyacrylic acid (PAA) chains grafted onto their backbone were found to be water soluble, and they exhibited a dramatic increase in their fluorescence intensity in the presence of a variety of surfactants, even at concentrations far below their critical micelle concentrations (CMC). This increase was accompanied by a blue-shift in the emission maximum. These observations are rationalized based on the postulate that the backbone conformation of the conjugated polymer is modulated upon interaction of the surfactant molecules with the polyelectrolytic tethers, which in turn results in a significant depletion of intra-chain interchromophore interactions that are known to cause red-shifted emission bands with significantly lower emission yields.     

Structural investigation of polystyrene grafted and sulfonated poly(tetrafluoroethylene) membranes

Structural investigation of polystyrene grafted and sulfonated poly(tetrafluoroethylene) (PTFE) membranes prepared by radiation-induced grafting of styrene onto commercial PTFE films and subsequent sulfonation was carried out by differential scanning calorimetry and X-ray diffraction. The effect of the structural changes taking place in the membranes during the preparation procedure (grafting and sulfonation) and the variation of the degree of grafting on melting temperature (T_m), glass transition temperature (T_g), heat of melting (ΔH_m), and degree of crystallinity was studied. The melting temperature (T_m) was found to be independent of the degree of grafting unlike glass transition temperature (T_g), which was found to be a function of the degree of grafting. Moreover, the degree of crystallinity of the membranes was found to decrease with the increase in the degree of grafting. The results of this work suggest that grafting takes place in the entire amorphous region without any significant disruption in the crystalline structure of PTFE film and the decrease in the degree of crystallinity is mainly attributed to the dilution effect.     

Effect of shear history on the steady shear flow behavior of a thermotropic liquid-crystalline polymer

The steady shear stress (σ) and first normal stress difference (N₁) of a thermotropic liquid-crystalline polyester, poly[(phenylsulfonyl)-p-phenylene 1,10-decamethylene-bis(4-oxybenzoate)] (PSHQ10), in both the isotropic and nematic regions were measured as a function of shear rate (γ), using a cone-and-plate rheometer. For the study, PSHQ10 was synthesized via solution polymerization in our laboratory. The PSHQ10 was found to have (a) the weight-average molecular weight of 45,000 relative to polystyrene standards and a polydispersity index of 2, (b) a glass transition temperature of 88°C, (c) a melting point of 115°C, and (d) a nematic-to-isotropic transition temperature of 175°C. For the measurements of σ and N₁ in the nematic region of PSHQ10, its initial conditions for the startup of shear flow was controlled by (a) first heating an as-cast specimen to 190°C, (b) shearing there at γ = 0.085 s^?1 for about 5 min, and then (c) cooling slowly down to a predetermined temperature (130, 140, 150, 160, or 171°C) in the nematic region. For each γ chosen, after start-up of shear flow, we waited for a sufficiently long time until both the shear stress and first normal stress difference leveled off, giving rise to steady-state values of σ and N₁. Emphasis was placed on investigating the effect of shear history on σ and N₁ of PSHQ10 in the nematic region. For this, the following experiments were conducted: (a) a fresh specimen was sheared continuously by increasing the γ stepwise, and (b) a presheared specimen was further sheared continuously by increasing the γ stepwise. We have found that fresh specimens exhibited ‘shear-thinning’ behavior over the entire range of γ (0.008?0.27 s^?1) tested, whereas the presheared specimens exhibited both zero-shear viscosities and shear-thinning behavior. When using fresh specimens, we found that N₁ was positive over the entire range of γ (0.008–0.27 s^?1) tested. However, when using presheared specimens we found that (a) at very low γ, N₁ initially was negative and then became positive as shearing continued, and (b) at higher γ, N₁ was positive over the entire duration of shearing. © 1994 John Wiley & Sons, Inc.     

Nitrogen-rich plasma-polymerized coatings on PET and PTFE surfaces improve endothelial cell attachment and resistance to shear flow

Low seeding efficiency and poor cell retention under flow-induced shear stress limit the effectiveness of in vitro endothelialization strategies for small-diameter vascular grafts. Primary-amine-rich plasma-polymerized coatings (PPE:N) deposited using low- and atmospheric-pressure plasma discharges on PET and PTFE are evaluated for their ability to improve endothelial cells' kinetics and strength of attachment. PPE:N coatings increase cell adhesion and adhesion rate, spreading, focal adhesion, and resistance to flow-induced shear compared with bare and gelatin-coated PET and PTFE. In particular, about 90% of the cells remain on coated surfaces after 1 h exposure to shear. These coatings, therefore, appear as a promising versatile approach to improve cell seeding strategies for vascular grafts.     

Modeling the phase separation in binary lipid membrane under externally imposed oscillatory shear flow

By adding external velocity terms, the two-dimensional time-dependent Ginzburg-Landau (TDGL) equations are modified. Based on this, the phase separation in binary lipid membrane under externally imposed oscillatory shear flow is numerically modeled employing the Cell Dynamical System (CDS) approach. Considering shear flows with different frequencies and amplitudes, several aspects of such a phase evolving process are studied. Firstly, visualized results are shown via snapshot figures of the membrane shape. And then, the simulated scattering patterns at typical moments are presented. Furthermore, in order to more quantitatively discuss this phase-separation process, the time growth laws of the characteristic domain sizes in both directions parallel and perpendicular to the flow are investigated for each case. Finally, the peculiar rheological properties of such binary lipid membrane system have been discussed, mainly the normal stress difference and the viscoelastic complex shear moduli.     

Effect of shear on human insulin in zinc suspension

Human insulin in zinc suspension was used as a model protein to test the effect of shear on the settling rate of proteins, a possible inference for protein denaturation. The rate of settling was determined directly in a spectropho-tometer. Shear effects are important in retaining the activity of proteins and are present in bubble, foam, and droplet protein fractionation processes. A sim pletest, such as that conducted here, mayeven be useful for monitoring changes in protein structure caused by commercial shipping of the protein. The settling ratefor insulin was continously monitored in theoriginal bottle by spectrophotometric absorbance changes as a function of time. A settling curve was determined following each shear experiment, which included shaking the “worked” insulin solution in a vortex mixer for different lengths of time. It was determined, when comparing long shaking times with short ones, that the initial settling rate was less for the long-term shaking of the insulin samples and greater for the short-term shaking. The secondary effects of light and heat, along with shaking, a pparently did not produce differences from shaking alone.     

Study of a new pervaporation membrane Part I. Preparation and characteristics of the new membrane

A new alcohol dehydration membrane, poly(vinyl alcohol)—chitosan blended composite membrane (PVA-CS) has been prepared. This membrane has high selectivity and promising permeability, especially in separating ethanol—water near the azeotropic region (J_t > 200 g/m² h, _w/e > 500, 70°C). The separating characteristics, which vary with feed composition, operating temperature and the surface structure of the membrane, are determined and the results agree well with the theoretical predictions.

The characteristics of mechanical strength, stability and resistance to water were also determined. The results show that they are considerably enhanced by blending and crosslinking, in comparison with PVA composite membranes.     

A microfluidic generator of dynamic shear stress and biochemical signals based on autonomously oscillatory flow

Biological cells in vivo typically reside in a dynamic flowing microenvironment with extensive biomechanical and biochemical cues varying in time and space. These dynamic biomechanical and biochemical signals together act to regulate cellular behaviors and functions. Microfluidic technology is an important experimental platform for mimicking extracellular flowing microenvironment in vitro. However, most existing microfluidic chips for generating dynamic shear stress and biochemical signals require expensive, large peripheral pumps and external control systems, unsuitable for being placed inside cell incubators to conduct cell biology experiments. This study has developed a microfluidic generator of dynamic shear stress and biochemical signals based on autonomously oscillatory flow. Further, based on the lumped-parameter and distributed-parameter models of multiscale fluid dynamics, the oscillatory flow field and the concentration field of biochemical factors has been simulated at the cell culture region within the designed microfluidic chip. Using the constructed experimental system, the feasibility of the designed microfluidic chip has been validated by simulating biochemical factors with red dye. The simulation results demonstrate that dynamic shear stress and biochemical signals with adjustable period and amplitude can be generated at the cell culture chamber within the microfluidic chip. The amplitudes of dynamic shear stress and biochemical signals is proportional to the pressure difference and inversely proportional to the flow resistance, while their periods are correlated positively with the flow capacity and the flow resistance. The experimental results reveal the feasibility of the designed microfluidic chip. Conclusively, the proposed microfluidic generator based on autonomously oscillatory flow can generate dynamic shear stress and biochemical signals without peripheral pumps and external control systems. In addition to reducing the experimental cost, due to the tiny volume, it is beneficial to be integrated into cell incubators for cell biology experiments. Thus, the proposed microfluidic chip provides a novel experimental platform for cell biology investigations.     

Rheology of polystyrene solutions around the coil overlapping concentration: A phenomenological description of stresses in simple shear flow

Linear viscoelasticity behavior is described with the sum of two terms for polystyrene solutions in tricresyl phosphate around the coil overlapping concentration (K. Osaki, T. Inoue, & T. Uematsu, J Polym Sci Part B: Polym Phys 2001, 39, 211). One is a Rouse–Zimm (RZ) term represented by the Zimm theory with arbitrarily chosen values of the hydrodynamic interaction parameter and the longest relaxation time (τ_RZ). The other (the L term) consists of a relaxation mode with a single relaxation time (τ_L > τ_RZ) and a high‐frequency limiting modulus proportional to the square of the concentration. In this study, we describe the viscosity (η) and first normal stress coefficient (Ψ₁) in steady shear with simple formulas. The stress due to the L term is assumed to be given by a Kaye, Bernstein, Kearsley, and Zapas (K‐BKZ) equation with the damping function h(γ) = (1 + 0.2γ²)^?1/2, where γ is the magnitude of shear. Contributions to η and Ψ₁ from the RZ term are derived from the RZ model, in which the relaxation time in steady flow is given by τ_st = τ + (τ_RZ ? τ)/(1 + 0.35τ_RZ γ˙) instead of τ_RZ. Here, γ˙ is the rate of shear, and τ is the τ_RZ value at the infinite dilution limit. η and Ψ₁ at various concentrations for two polystyrene samples (with molecular weights of 2890 and 8420 kg mol^?1) are well described with parameters derived from dynamic viscoelasticity. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1038–1045, 2002     

Review of nonlinear oscillatory shear flow notations and presentations: polymeric liquids

We review notations for, along with ways of presenting, the shear stress responses to large-amplitude oscillatory shear flow (LAOS). We find that the Fourier loss and storage viscosities to be the simplest primal notations for interpreting LAOS. The relative intensities provide the best evidence for oscillatory shear entering the large-amplitude regime. Deviation from linear viscoelastic behaviors can be observed through the distortions of Lissajous loops. We explore these loops in their elastic and viscous projections. The centerpiece of this work is our review table, which summarizes experimental measurements for polymer melts and solutions, targeting 21st century publications. Our review also provides conversion formulae to go from any of many notations to the Fourier loss and storage viscosities. The review table also defines which part of the LAOS measurement field has yet to be ploughed and shines light on which notations have been used, and for which purposes, to interpret nonlinearities.     

Study of a new pervaporation membrane Part 2. Performance test and analysis of the new membrane

The compatibility of poly(vinyl alcohol)—chitosan blends was tested and analyzed by their glass transition temperatures with differential scanning calorimetry with a DSC-7 (Epson). Highest selectivity, promising permeability and good mechanical strength for the dehydration of alcohol—water mixtures were obtained at a 4:1 composition of the blend.

The chemical composition, physical structure and morphology of this blended composite membrane were studied by a variety of surface science techniques, including infrared spectrometry (IR), small-angle X-ray diffraction (SAXRD) and scanning electron microscopy (SEM). The surface investigation is needed for the study of the blended composite membrane, and the results confirm well with the characteristics of the new membrane.     

Blood flow and oxygen transfer rate of an outside blood flow membrane oxygenator

We evaluated effects of the number of tied hollow fibers of an outside blood flow membrane oxygenator with cross-wound hollow fibers on the blood flow pattern and oxygen transfer rate. The number of tied hollow fibers in a bundle was varied from one to six, and the blood flow pattern was observed by X-ray computed tomography. The oxygen transfer rate and blood pressure drop were measured by in vitro experiments using bovine blood. Uniform blood flow patterns were obtained for each number of tied hollow fibers. A decrease in the number of tied hollow fibers caused more effective contact of blood with the tied hollow fibers and oxygen transfer rate was enhanced, demonstrating that single hollow fiber was the most effective. Empirical equations were obtained based on these results and optimum structure parameters of the membrane oxygenator were determined by simulation analysis. Optimum membrane surface area and axial jacket length of the oxygenator were 3.0 m² and 320 mm, respectively, at a hollow fiber outside diameter of 250 μm.     

Structure and dynamics of concentration fluctuations in a polymer blend solution under shear flow

The technique of small-angle light scattering (SALS) has been employed to investigate the time-dependent behavior of a single-phase, semidilute solution of polystyrene and polybutadiene in dioctyl phthalate under shear flow. Concentration fluctuations in the polymer blend solution are found to grow with time in the direction of flow, and their orientation angles evolve from 45° from the flow direction toward 0°, with the steady-state value being dependent on shear rate. SALS patterns are simulated using a modified Cahn-Hilliard-Cook model, with an additional collective restoring force to account for polymer elasticity. Predictions from this modified model for the orientation angles of the concentration fluctuations are in excellent agreement with the experimental results. Our model also predicts that the quiescent structure factor has a Gaussian form and that the steady-state orientation of the scattering patterns is dependent on shear rate. These predictions are also in good agreement with our experimental observations. © 1994 John Wiley & Sons, Inc.     

Fabrication of a thin palladium membrane supported in a porous ceramic substrate by chemical vapor deposition

A thin, gas-tight palladium (Pd) membrane was prepared by the counter-diffusion chemical vapor deposition (CVD) process employing palladium chloride (PdCl₂) vapor and H₂ as Pd precursors. A disk-shaped, two-layer porous ceramic membrane consisting of a fine-pore γ-Al₂O₃ top layer and a coarse-pore -Al₂O₃ substrate was used as Pd membrane support. A 0.5–1 μm thick metallic membrane was deposited in the γ-Al₂O₃ top layer very close to its surface, as verified by XRD and SEM with a backscattered electron detector. The most important parameters that affected the CVD process were reaction temperature, reactants concentrations and top layer quality. Deposition of Pd in the γ-Al₂O₃ top layer resulted in a 100- to 1000-fold reduction in He permeance of the porous substrate. The H₂ permeation flux of these membranes was in the range 0.5–1.0 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 350–450°C. The H₂ permeation data suggest that surface reaction steps are rate-limiting for H₂ transport through such thin membranes in the temperature range studied.     

Elimination of non-uniform, extra-device flow effects in membrane adsorbers

Commercial use of membrane adsorbers in the biotechnology industry is increasing. Here the system time lag created by membrane adsorber peripherals and the membrane adsorber flow distribution headers has been modeled using an anion exchange membrane and bovine serum albumin (BSA). The system time lag was modeled as a zero order and first order time lag. The zero and first order time lags have been removed from the breakthrough curve. The method used does not involve fitting a mathematical expression to the breakthrough curve. Further no assumptions are made regarding the shape of the breakthrough curve in the absence of the time lag. The method has been used to calculate the Langmuir isotherm parameters.The membrane capacity was found to be twice as large as the capacity determined after removal of the time lag. The Langmuir constant was five times as large for the system without accounting for the time lag. Errors in fitting isotherm parameters can significantly impact frontal analysis and membrane adsorber scale-up. The Langmuir isotherm calculated under dynamic conditions with the system time lag removed, was in agreement with the static adsorption isotherm.     

Design of a modified three-rail shear test for shear fatigue of composites

There are various ways of determining the static in-plane shear properties of a fibre-reinforced composite. One of them is the standard three-rail shear test, as described in “ASTM D 4255/D 4255M The standard test method for in-plane shear properties of polymer matrix composite materials by the rail shear method”. This setup, however, requires drilling holes through the specimen. In this study, a new design based on friction and geometrical gripping, without the need of drilling holes through the composite specimen is presented. Quasi-static tests have been performed to assess the symmetry of the setup and the occurrence of buckling. Then, fatigue tests were done to assess the behaviour of the grips under fatigue loading conditions, yielding excellent results; the specimen fails under shear loading conditions in the loaded area. The material used to validate this setup was a carbon fabric-reinforced polyphenylene sulphide.

During fatigue, this material shows an increase in permanent deformation and a decrease in shear stiffness until a certain point in time, after which a drastic increase in deformation and temperature, higher than the softening temperature of the matrix occurs. Furthermore, the maximum value of the shear stress for fatigue with R=0 has a large influence on the fatigue lifetime.