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Understanding the solvent-induced stresses in polymeric materials is of profound importance for drug release and soft robotics. This work presents an alternative method to obtain an analytical solution of solvent-induced stress in an elastic slab using the Moutier theorem under the framework of equilibrium thermodynamics and the elastic solution available in the literature. Using the analytical solution and the temporal evolution of the mass of organic solvents in polymeric slabs, we analyze the spatiotemporal evolution of the solvent-induced stress in the polymeric slabs and reveal the effects of the solvent transport on the stress evolution. The approach presented in this work provides a simple method to solve the decoupling problem involving diffusion and solvent-induced stresses. KEYWORDS elastic slab, Moutier theorem, solvent-induced stress, 1 | INTRODUCTION Solvent transport in glassy polymers has been studied for several decades. In addition to diffusion named Case I transport, Case II and anomalous transport are often observed [...]

Understanding the thermal aging kinetics of animal oils is of vital importance in the storage and applications of animal oils. In this work, we use four different techniques, including UV-Vis spectrometry, viscometry, impedance spectroscopy, and acid–base titration, to study the thermal aging kinetics of tallow, chicken oil, lard, and sheep oil in the temperature range from 120 °C to 180 °C. The evolutions of the UV-Vis absorbance, dynamic viscosity, electric impedance, and acid titration are discussed with the defect kinetics. The evolutions of the color centers, defects for dynamic viscosity, and electric dipoles follow second-order, first-order, and zero-order kinetics, respectively. The temperature dependence of rate constants for the evolutions of the UV-Vis absorbance, dynamic viscosity, electric impedance, and acid titration satisfies the Arrhenius equation with the same activation energy for individual animal oils. The activation energies are ~43.1, ~23.8, ~39.1, and ~37.5 kJ/mol for tallow, chicken oil, lard, and sheep oil, respectively. The thermal aging kinetics of the animal oils are attributed to the oxidation of triglycerides. [ABSTRACT FROM AUTHOR]

Understanding the motion of nanoparticles in liquid is of practical importance for drug delivery and fluid flow in nanofluidic systems. In this work, we use a nanoparticle tracking analyzer to investigate the Brownian motion of polydivinylbenzene (PDVB) nanoparticles in water and a video camera to record the aggregation of PDVB aggregates on the water surface. Using water as the liquid medium precludes the possible complex interaction between the liquid medium and the PDVB nanoparticles, which can possibly alter the random characteristics of the motion of the PDVB nanoparticles. The diffusivity of the PDVB nanoparticles determined from the mean square displacements of the PDVB nanoparticles has the same activation energy as that for the intrinsic viscosity of the corresponding aqueous suspension of the PDVB nanoparticles. The correlation between the diffusivity for the motion of the PDVB nanoparticles in water and the intrinsic viscosity of the corresponding aqueous suspension follows the Stokes–Einstein relation. The capillary effect and the interaction between PDVB aggregates and the liquid media enable the aggregation of the PDVB aggregates on the water surface, which follows the first-order reaction with activation energy larger than that for the random motion of the PDVB nanoparticles in water. [ABSTRACT FROM AUTHOR]

Large area projection sintering (LAPS) promises to be a new method in the field of additive manufacturing. Developed in the Mechanical Engineering Department, University of South Florida, LAPS uses long exposure times over a broad area of powder to fuse into dense, reproducible materials. In contrast, LS, a common powder-based additive manufacturing, uses a focused beam of light scanned quickly over the material. Local regions of concentrated highenergy bursts of light lead to higher peak temperatures and differing cooling dynamics and overall crystallinity. The mechanical properties of laser sintered specimens suffer because of uneven particle fusion. LAPS offers the capacity to fine-tune fusion properties through enhanced thermodynamic control of the heating and cooling profiles for sintering. Further research is required to identify the relationship between LAPS build settings and part properties to enable the fabrication of custom parts with desired properties. This study examines the influence of LAPS sintering parameters on chemical structures, crystallinity, mechanical, and thermal properties of polyamide-12 specimens using powder X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, small-angle X-ray scattering, scanning electron microscopy, and microhardness testing. It was observed that higher crystallinity was imparted to specimens that were sintered for a shorter time and vice versa. KEYWORDS 3D printing, additive manufacturing, crystallinity, large area projection sintering, laser sintering, polyamide-12, powder bed fusion, 1 | INTRODUCTION Developed in the 1970s, additive manufacturing techniques have evolved quickly in the rapid prototyping space as a response to the limitations of traditional manufacturing. [1-4] The time [...]

A novel, high performance ultrasoft polycarbonate Polyurethane polymer was electrospun and tested against its bulk material to investigate changes in its thermal and mechanical properties. A series of fiber membranes was processed via solution electrospinning using a 90:10 ratio of dimethyformamide-ethylacetate. Thermal, mechanical, and structural properties were obtained using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), and tensile testing. TGA revealed that thermal stability of the membranes increased with the concentration of polymer solution used in spinning. DSC showed no variation in glass transition temperatures while the melting point regions varied noticeably with spinning conditions. WAXS profiles in solution casts films and electrospun mats showed the presence of diffraction peaks related to ordered crystal lamellae in the hard segment region at lower concentrations; these intensified after electrospinning. As the concentration of the polymer solution increased, the molecular orientation decreased. Tensile testing showed a significant increase in tensile strength at 18 w/v% fiber membranes. The ability of the polymer membrane characteristics to be tuned by processing conditions is of great interest in applications related to biotechnology, drug delivery, and implantable polymeric systems., INTRODUCTION Electrospinning is a well-established versatile technique that produces fibers with diameter sizes in the micro and nanometer range [1,2]. This methodology employs an electrostatic potential to create nanofibers from [...]

Isothermal acetone absorption in UV-irradiated polycarbonate (PC) was investigated at temperatures from -23 to +25[degrees]C. The crystalline fraction of PC increased with UV dose. The anomalous transport data were analyzed based on Harmon's model which includes contributions from Case I transport characterized by the diffusion coefficient, D, and Case II transport characterized the velocity, v. Diffusion coefficients were monitored by both mass uptake using the model (D and v), and movement of the sharp front ([D.sub.f]). Plots of log of D, v, and equilibrium swelling ratio (ESR) versus 1/T exhibited similar features. That is, plots were linear and superimposable for all doses at the higher temperatures, and exhibited a transition temperature and then a linear region that varied with dose. The values of D, [D.sub.f], and v increased with increasing dose, whereas the ESR decreased with dose. The direction of Case II transport was opposite to that of Case I diffusion during which time, sorbed solvent was expelled from the samples. Results are discussed in terms of a solvent-induced change in lattice structure at the lower temperatures and in terms of UV radiation effects on the PC matrix that enhance solvent crystallization. POLYM. ENG. SCI., 58:1174-1183, 2018., INTRODUCTION Photodegradation of polycarbonate (PC) has been studied extensively for several decades, documenting scission and cross-linking reactions, changes in mechanical properties, and the evolution of degradation products [1-4]. It is [...]

Vegetable oils provide lipids and nutrition and provide foods with a desirable flavor, color, and crispy texture when used to prepare fried foods. However, the oil quality is degraded at elevated temperatures, and thus must be examined frequently because of the damage to human health. In this study, sunflower, soybean, olive, and canola oils were examined, and their properties were measured periodically at different elevated temperatures. The unsaturated triglyceride in oils reacted with the environmental oxygen or water vapor significantly changes in optical absorbance, viscosity, electrical impedance, and acid value. We used defect kinetics to analyze the evolution of these oil properties at elevated temperatures. The optical absorbance, viscosity, and electrical impedance follow the second-order, first-order, and zeroth-order kinetics, respectively. The rate constants of the above kinetics satisfy the Arrhenius equation. Olive oil has the lowest rate of color center and dynamic viscosity among the four oils, with the smallest pre-exponential factor and the largest activation energy, respectively. The rate constants of acid reaction also satisfy the Arrhenius equation. The activation energies of the polar compound and acid reaction are almost the same, respectively, implying that the rate constant is controlled by a pre-exponential factor if four oils are compared. Olive oil has the largest rate constant of acid reaction among the four oils, with the lowest pre-exponential factor. [ABSTRACT FROM AUTHOR]

The effect of biaxial-residual-compressive surface stress on the surface modulation of solid films is analyzed. The results show that the biaxial compressive stress can create surface modulation with the orientation being 45° (135°) to the principal directions of the stresses. Using uniaxial tension, a complementary set of nonsymmetrical polymer ripple gratings is formed on the fracture surface of a polymer film that is sandwiched between two relatively glass slides. The effect of geometrical shape and boundary confinement is examined on the surface modulation. The orientation of the polymer ripple gratings is found to be 45 to the longitudinal direction of the films for long-rectangular polymer thin films in accord with the analysis. POLYM. ENG. SCI., 53:1454-1462, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION Polymer materials have been extensively applied to the technique of micropatterning and nanopatterning. A compliant thin film deposited on a relatively rigid substrate may experience residual stress, which results [...]

Tensile testing of polycarbonate (PC) with and without gamma-ray irradiation at elevated temperatures was investigated. Two deformation mechanisms, the shear bands at low temperatures and the craze formation at high temperatures accompanied with force oscillation, were responsible for the deformation. The tensile force oscillation was observed during the tensile testing in air, but not in water or oil. This difference is attributed to the periodic variation in the elastic modulus of PC, caused by local temperature change during the deformation process. Note that air is a poor medium for heat conduction, whereas water and oil are good conductors. In addition to the test environment, the effect of the crosshead speed on the force oscillation was also investigated. The oscillation was preferably observed at lower crosshead speeds within the testing range, and was more pronounced for the irradiated specimens. POLYM. ENG. SCI., 53:589-596, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION The use of engineering plastic materials is an important innovation in human history, and polycarbonate (PC) is one of such significant materials. PC can be manufactured into different shapes [...]

Annihilation kinetics of color center in polycarbonate (PC), irradiated with gamma ray at elevated temperatures, was investigated. The transmission loss in the PC was monitored in the ultraviolet and visible wavelength range. The transmittance decreased with increasing gamma-ray dose. The loss was attributed to the presence of annealable and permanent color centers. The absorbance in situ data were detected at the wavelength of 450 nm and found in good agreement with the theoretical model in which the annealable color center followed a first-order kinetic process. The rate constant satisfies the Arrhenius equation, with the activation energy of the color centers decreasing with increase of the gamma-ray dose. The results were compared with the early findings reported in the literature. POLYM. ENG. SCI., 52:2391-2395, 2012. © 2012 Society of Plastics Engineers, INTRODUCTION Polycarbonate (PC) is a high performance engineering thermoplastic, which has found broad applications in many industrial fields due to its high toughness, high impact strength, excellent optical clarity, heat [...]