Theta point of polyacrylamide in aqueous solution and temperature dependence of the molecular dimensions

The molecular weight (M_w) and temperature (T) dependence of the expansion factor and the second virial coefficient of polyacrylamide (PAAm) in dilute solution are investigated. The theoretical predictions of the blob and of the modified Flory's theory are compared with experimental results on polystyrene. We note similar behaviour for these two polymers which cannot certify in the intermediate region if the volume exponent v is higher than the theoretical asymptotic value or not. In addition we give an experimental determination of the theta temperature for PAAm in water θ = ?8°C.     

The temperature dependence of network forces in rubber-like materials

In the simplest model of rubber-like materials only two kinds of forces are assumed: network forces with identical temperature dependence, and liquid forces which. are isotropic. For this simple model the relation between the temperature dependence of the network forces and that of the observed elastic force is calculated. When the elastic equation of the network is of the classical one term type, the well-known equation of Flory, Ciferri and Hoeve is found without using assumptions about the physical meaning of the front factor in the elastic equation. When the elastic equation of the network is of the Mooney-Rivlin type with two terms, the difference between the temperature dependence of the observed forces and of the network forces is found to depend on the ratio of the coefficients in the Mooney-Rivlin equation and on the elongation. The effect of the internal pressure is to add a factor to this term. The conclusion is that detailed knowledge about the network forces is needed in order to establish the value of the correction term for thermal expansion in the equation for the temperature dependence of the elastic force in the material.     

Dissolution of spherical solid particles in a stagnant fluid: An analytical solution

Film theory has often been used to calculate the dissolution rates of solid particles. However, it is only good for the case of low solubility solids due to the assumption of pseudo-steady state. In this study, we propose a more refined model to facilitate the characterization of the dissolution of spherical solid particles in a stagnant fluid. The results indicate that the film theory will overestimate the dissolution time for the case of high solubility, while for low solubility particles, the film theory is quite accurate in predicting the dissolution time.     

Hydrodynamic control of droplets coalescence in microfluidic devices to fabricate two-dimensional anisotropic particles through boundary element method

Multicompartment and patchy particles attract much attention recently due to their great potentials in many fields such as drug delivery systems and photonic crystal materials. The controlled coalescence of droplets might be a promising approach to fabricate such particles since different droplets might be composed of distinct components or might contain diverse functional solutes. Through a two-dimensional boundary element method, we investigate the controlled adhesion of small droplets to specific locations of a main drop via careful flow control at inlets and outlets of a skillfully designed microfluidic device at low Reynolds numbers. This paper presents an original procedure to construct anisotropic particles assisted by microfluidics. By alternating extensional and rotational flow at the central cavity of the micro-device, it is possible to make small droplets adhere to the main drop one by one at expected location and thus fabricate patchy particles with multiple patches at expected angles in two dimensions.     

The temperature and strain-rate dependence of mechanical properties in polyoxymethylene

The computer aided design approach used in current applications of semicrystalline polyoxymethylene (POM) requires high strain-rate mechanical data. The primary aim of this work has been to measure the room temperature modulus and tensile strength of injection molded samples of POM of different molecular weights at cross-head speeds of between 10^?5 ms^?1. We observe no major transition in bulk mechanical behavior in this range of test speeds, the Young's modulus E, in particular, showing little strain rate dependence. This is rationalized on the basis of tensile tests over a range of temperatures, these indicating room temperature to correspond to the plateau in the E(T) curves (T_g for these materials is taken to be ?70°C, and the DSC melting onset occurs at ～ 170°C). The tensile strength increases as ～log(d?/dt) and the behavior is found to be highly nonlinear, strains to fail of the order of 1 being observed even at the highest strain rates, depending on the molecular weight. It is believed that the yield stress of th crystalline regions determines the tensile strength above T_g, the higher degree of crystallinity associated with lower molecular weights resulting in a slightly higher tensile strength. Nevertheless, failure is qualitatively brittle, with no necking and relatively little permanent deformation. This behavior is discussed in terms of morphological investigations of the fractured samples by optical and scanning electron microscopy (SEM). In attempting to relate ultimate failure to the molecular/crystalline structure of the samples, measurements of the critical stress intensity for crack initiation in mode I opening, K_IC, as a function of crystallization temperature T_c have been carried out using compact tension specimens machined from injection molded and compression molded plaques. K_IC increases with molecular weight and decreases with T_c at low test speeds (in spite of an increase in crystallinity with T_c). This is accounted for in terms of a crack shielding model for crack initiation and of molecular rearrangements occurring during crystallization which lead to a decrease in the effective entanglement density with T_c. The implications of this model are then compared with K_IC results over a range of cross-head speeds and temperatures.     

I: Dispersibility of robust alumina particles in non-aqueous solution

This article presents the preparation of well dispersed alumina slurries containing relatively large alumina particles that can withstand accelerated weather conditions. Besides using conventional dispersants such as phosphate esters and menhaden fish oil, dispersants widely used in the surface coatings industries such as Disperbyk 110 and Triton X 100 have also been employed. However, sedimentation tests, sediment density, viscosity and gloss measurements indicate the failure of the anionic dispersants as well as menhaden fish oil to disperse the alumina particles in non-aqueous medium. Instead the binder polyvinyl butyral itself acts as the best dispersant. The well dispersed alumina slurry is stabilized in the presence of a commercially available rheology modifier, Bentone SD2 for a period of 144 h at 60 °C. The rheological behavior of the aged sample was studied under various conditions. Although a rise in viscosity of the suspension was observed when the slurry was exposed to accelerated weather conditions, a lower shear thinning index and higher gloss values indicate a better dispersion state with aging.     

Prediction of the temperature dependence of liquid diffusion coefficients at infinite dilution by a group contribution method

1 INTRODUCTIONSince experimental determination of the mutual liquid diffusion coefficients atinfinite dilution is rather complicated,it is important,therefore,to be able to esti-mate the coefficients under various temperatures from one available coefficient ata certain temperature such as 298K.Empirical equations for this purpose are avail-able in many forms.Typical examples are the Wilke-Chang equation and the Tynequation,given below     

Core–shell PVA/gelatin nanofibrous scaffolds using co‐solvent,aqueous electrospinning: Toward a green approach

Electrospinning (ES) of gelatin often requires cytotoxic organic solvents or acidic environments, which deteriorate cell recognition sites. In this study, aqueous, non‐toxic, co‐solvent ES was performed to obtain core–shell poly(vinyl alcohol) (PVA)/gelatin nanofiber scaffolds. Effects of the core/shell feed rate ratio (FRR) were investigated on a morphological and mechanical basis. PVA:gelatin ratio of 1:4 was the limiting ratio for specific voltage and electrode distance parameters to obtain uniform fibers. Core–shell bead‐free structures were obtained at 8% PVA and gelatin aqueous solutions. A mean diameter of 280 nm was obtained for 1:1 FRR at 15 kV and 15 cm of electrode distance. Crosslinking resulted in slight improvement in tensile strengths and severe decrease in ductility. Fourier transform infrared spectra revealed retention and improvement of stable secondary structures of gelatin after ES. The scaffolds almost degraded more than 60% in 14 days. Based on the results, present scaffolds hold great promise as suitable candidates for biomedical applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46582.     

再议浓浸稀洗法

日常洗衣服是将衣物放入溶有洗涤剂的溶液中洗涤。但衣物上的污垢是不均匀分布的,洗涤剂用量一般以去除重垢为目标,难免过量（一般为2-3‰,高者5‰）。采用浓浸稀洗法,与污垢接触时洗涤剂浓度高、水硬度低,因此洗涤剂用量不多但去污力高。     

An inverse estimation of initial temperature profile in a polymer process

Since one of the most important parameter in polymer processing such as injection stretch blow molding is temperature distribution in the thickness direction, an inverse method has been applied to estimate this profile. This process comprises of four steps. In the first step the preform is injection molded, and in the second and third step it is stretched by a rod to its final length and then inflated and in the last step it is discharged from the mold. In such kind of polymer flows viscous dissipation plays a remarkable role in the evolution of temperature profile. Some theoretical temperature profile has been applied to confirm the validation of the inverse algorithm. Different solution techniques are applied in this article to the inverse problem under consideration, namely: the conjugate gradient and Levenberg–Marquardt method. After the preform is injection molded, which is the first step, it is removed from the mold, which corresponds to time t = 0. At this moment an infrared camera is used to record the surface temperature of the preform with a certain time step. With regard to variation of thermal properties with temperature, the inverse problem becomes nonlinear. These experimental data provided by the infrared camera are then used to estimate the temperature profile at the end of injection process before stretching and inflation took place. POLYM. ENG. SCI., 48:133–140, 2008. © 2007 Society of Plastics Engineers     

Time and temperature dependence of fracture in a unidirectional glass-reinforced epoxy

The results of a study on the time- and temperature-dependent behaviour of unidirectional glass fibre-reinforced epoxy are described and analysed. The fracture parameters examined are the fracture strength, the work of fracture and the apparent fracture toughness. It is shown that the fracture strength decreases with increasing temperature and decreasing loading rate; the work of fracture exhibits a sharp minimum in the vicinity of room temperature, and the fibre pull-out length increases by a factor of 4 at 76K as compared with the room temperature length; the fracture toughness is found to be independent of the crack length and only dependent on the fracture strength; thus its trend with loading rate and temperature follow those of the fracture strength.     

The concentration and temperature dependence of the order parameter and the soft mode of the solid solution of TSCC and TSCB

Experimental investigations of the transition temperature, the order parameter, the soft mode and of the influence of an electric field as well as model calculations show the influence of quantum effects on the ferroelectric behaviour of TSCC_1-xB_x.     

The response of collagen molecules in acid solution to temperature

The response of collagen molecules in acid solution (0.25, 0.50 and 1.0 mg/mL) to temperature (20–50 °C) was studied by ultra-sensitive differential scanning calorimeter (US-DSC), atomic force microscopy (AFM) and fluorescence spectrophotometer. The enthalpy changes (ΔH) for collagen varied with collagen concentrations, indicating that the aggregation state of collagen molecules was correlated with its thermal effect. Fluorescence measurements of pyrene in collagen solutions, which showed the polarity of the microenvironment in collagen molecules, suggested different behaviors: aggregation (20–32 °C) and disaggregation (38–50 °C), which was manifested by the changes in morphology of collagen fibers as observed by AFM. Furthermore, emission intrinsic fluorescence spectra of collagen at different temperatures showed that the fluorescence intensity of collagen decreased with increasing temperature, and the dynamic response of collagen molecules to temperature was further explored from the corresponding two-dimensional correlation fluorescence spectra.     

The influence of impurity-doping on temperature dependence of dislocation-ribbon width in graphite

By means of an electron microscope, the width of dislocation ribbons in a stress-annealed pyrolytic graphite and doped with iodine chloride (ICl) and bromine was investigated as a function of temperature in the range 100°K to 300°K. The impurity content amounted to 1·1 at % for ICl and 1·6 at % for bromine. Through measurements of the ribbons widths W in steps of 20°K, the average temperature coefficients $\text{1}\text{W}\text{·}\text{dW}\text{?dT}$ were found to be 5 × 10^?4, 3 × 10^?4 and 1 × 10^?4°K^?1, for the original, ICl-doped and bromine-doped material respectively; this shows that the temperature dependence of the ribbon width in graphite is appreciably decreased by the presence of halogen impurities. The phenomenon is quantitatively analyzed in terms of the chemical interaction mechanism between stacking faults and impurities. A discussion of the viscous drag function of impurities for dislocations in relation to the internal friction is included.     

Transition temperature dependence in perovskite ceramics as a function of grain size

Simple effective field arguments assuming an non isotropic layer of thickness L, covering the ferroelectric bulk grain of perovskite ceramics are used to determine an expression for the transition temperature TJL) as a function of grain linear size L. The surface to volume ratio increases as L decreases reducing the value of TJL). Experimental data for BaTiO₃ ceramics as a function of grain size are described reasonably well by the expression of T_c(L) obtained this way.     

Shear-rate dependence of first normal stress difference of poly(isoprene-b-styrene) in solution near the order-disorder transition temperature

Viscoelastic properties of poly(isoprene-b-styrene) in dioctylphthalate under steady shear flow were measured near the order—disorder transition temperature. In ordered states, first normal stress difference N₁ is proportional to shear rate at low region, but becomes proportional to at the high region, similar to the N₁ behaviour of polymer blends undergoing shear-induced homogenization. Because the existence of microdomains was confirmed at the high region by the flow birefringence method, it is concluded that the above N₁ behaviour is not caused by shear-induced homogenization, but is probably caused by the shear-induced alignment of the microdomain structure.     

Comonomer effect: Switching the lower critical solution temperature to upper critical solution temperature in thermo-pH sensitive binary graft copolymers

Hydrophilic biocompatible surfaces can be obtained by grafting stimuli-sensitive polymers onto commercially available medical devices. Thermo and pH-responsive polymers are two of the most studied materials due to their potential application as drug delivery systems. Poly(N-vinylcaprolactam) has a lower critical solution temperature (LCST) near to physiological temperature. However, when it is grafted with pH-sensitive moieties its LCST it is affected undergoing remarkable displacements. We studied the effect of acrylic acid (AAc), 4-vinylpyridine (4VP), and 1-vinylimidazole (Vim) on the LCST of N-vinylcaprolactam (NVCL) grafted onto silicone rubber (SR), and SR-g-NVCL (32.5 °C). The binary graft copolymers were obtained by ionizing grafting radiation using the simultaneous technique; the samples were characterized by Fourier transform infrared attenuated total reflectance (FTIR-ATR), cross-polarization magic angle spinning nuclear magnetic resonance (CP/MAS ¹³C-NMR), and thermogravimetrical analysis (TGA). LCST value was dramatically affected by the comonomer content; even it was observed the switching from LCST to upper critical solution temperature (UCST) for (SR-g-NVCL)-g-AAc and (SR-g-NVCL)-g-4VP samples. The observed behavior is rarely reported for binary graft copolymers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48170.     

The temperature dependence of passivity breakdown on a titanium alloy determined by cyclic noise thermammetry

A new sensitive electrochemical technique is presented which is designed to measure the temperature dependence of the breakdown of passivity of metal surfaces. The method, termed “cyclic noise thermammetry”, consists of scanning the temperature of an electrochemical cell linearly and cyclically between two predefined limits, whilst simultaneously measuring the current flowing from a potentiostatically maintained microelectrode. An example of the new technique is presented, which describes the effect of temperature on the nucleation of corrosion pits on the titanium-based alloy, Ti-6Al-4V, in acidic chloride solution far below the pitting potential. Results are presented over the temperature range 20-50 °C. Events due to breakdown of passivity were detected throughout the entire temperature range. These events are the nucleation of corrosion pits, although they do not propagate into stable pits under the applied experimental conditions. Results show that passivity breaks down over the entire range of temperature, at a frequency that increases with increase in temperature.