Rheological Characterization of Polymer-based Nanocomposites with Different Nanoscale Dispersions

Polyamide 6 - clay nanocomposites with different nanoscale dispersions were prepared by melt compounding via twin-screw extrusion and their internal structures were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The rheological behaviour of these nanocomposites in shear and extensional flow were investigated using an Advanced Rheometric Expansion System and an Elongational Melts Rheometer in connection with the analysis by XRD and TEM. Nanocomposites with fully exfoliated structure and with poorly dispersed structure showed very different rheological behaviour. In general, addition of clay increased the viscosity and the storage modulus of nanocompo-sites, but different rheological behaviours were observed depending upon the degree of clay dispersion in the polymer matrix. In shear flow, only the exfoliated nanocomposite showed solid-like plateau behaviour in storage modulus and strong shear-thinning behaviour in shear viscosity. In extensional flow, only fully exfoliated nanocomposites showed strain-hardening behaviour, which is caused by the inter-action between nanoparticles as well as between polymer molecules and nano-particles.This study was partially supported by the Korea Science and Engineering Foundation (KOSEF) through the Applied Rheology Center (ARC) and by the Ministry of Science and Technology through the National Research Laboratory (NRL). The authors are grateful for the support

Ultraviolet nanoimprinted polymer nanostructure for organic light emitting diode application

Light extraction efficiency of a conventional organic light emitting diode (OLED) remains limited to approximately 20% as most of the emission is trapped in the waveguide and glass modes. An etchless simple method was developed to fabricate two-dimensional nanostructures on glass substrate directly by using ultraviolet (UV) curable polymer resin and UV nanoimprint lithography in order to improve output coupling efficiency of OLEDs. The enhancement of the light extraction was predicted by the three-dimensional finite difference time domain method. OLEDs integrated on nanoimprinted substrates enhanced electroluminance intensity by up to 50% compared to the conventional device

Lightweight polyester composites

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1984.Vita.Includes bibliographical references.by Jae Ryoun Youn.Ph.D

Effect of Bending Rigidity on the Capstan Equation

A tensioned fiber or yam in contact with a circular body is analyzed. In the model, a fiber is considered as a linear elastic and inextensible beam. An exact mathematical model is derived and the analytical solution is obtained. Both the beam-body contact and two noncontact regions are analyzed. From the equilibrium equation of force and bending moment, the derived model has three compatible ordinary differential equations, and one algebraic equation from the Euler beam theory with four unknown parameters. From the solutions, the relationship between incoming and outgoing tension is obtained, and we call this the modified capstan equation. The results show the correction connecting the capstan equation and its applications. For example, in a typical case, the capstan equation underestimates the effect of bending rigidity, which renders the only physically possible situation of tension in a real capstan to be the equilibrium of inclined tension. Moreover, the sensitivity of the tension ratio on the variation of the inclined angle is extensive. For instance, the difference in the tension ratio between the classical and modified results may be the maximum 71 % value for a mere 100 variation of the inclined angle direction. Also, it is directly applicable to fiber contact with a body whose surface has a noncircular convex profile. Several further topics are suggested for discussion

Sustainable solar energy harvesting using phase change material (PCM) embedded pyroelectric system

This work proposes a smart control of pyroelectric energy harvesting, based on the form-stable phase change material (PCM) composites utilizing polyethylene glycol (PEG) and 1-tetradecanol (1-TD). Solar light transmitted into a pyroelectric system made of window glass and indium tin oxide (ITO) pyro-electrode can provoke thermoelectric energy conversion by the change of temperature difference. The transparent pyro-electrode allows the transmitted solar light to reach the other side of the window glass. The PCM composite placed at the side can reduce the temperature fluctuation to control the change of temperature difference during the light-on/-off process. Since pyroelectric harvesting effects depends on the intensity of sunlight, different solar irradiations (10, 15, and 20 mW/cm2) were applied to the energy harvesting system in this study. The pyro-electrode could generate stable and continuous electrical energy by the combination of PCM composites. In addition, the underlying physics behind the system are theoretically modeled by utilizing the finite element method (FEM).N

Prediction of Effective Thermal Conductivities of Fibre Reinforced Composites using a Thermal-Electrical Analogy

Anapproach for predicting the effective thermal conductivities of fibre rein forced composites has been developed. based on a thermal-electrical analogy. In the boxelization method, the unit cell of the laminate composites is divided into a number of volume elements, and the material properties considering the local variations of fibre orientation have been given to each element. By constructing a series-parallel thermal resistance network, the thermal conductivities of a fibre reinforced composite in both in-plane and out-of-plane directions have been predicted. The reported thermal conductivities of a graphite/epoxy composite of a balanced plain weave laminate were used for the comparison with the predicted values of the model, and good agreement was found.This study was supported by the Ministry of Science and Technology in Korea through the National Research Laboratory at Seoul National University. The authors are greateful for the support

Effects of surface modification on rheological and mechanical properties of CNT/epoxy composites

Despite superior properties of carbon nanotubes (CNTs), physical properties of the CNT/epoxy composites are not improved significantly because interfacial bonding between the CNTs and the polymer matrix is weak. CNTs were treated by an acidic solution to remove impurities and modified subsequently by amine treatment or plasma oxidation to improve interfacial bonding and dispersion of nanotubes in the epoxy matrix. The functional groups on the surface of treated CNTs were investigated by X-ray photoelectron spectroscopy. The surface modified CNTs were embedded in the epoxy resin by ultra-sonication and the cured nanotube containing composites were characterized by field emission scanning electron microscopy. Rheological properties of nanotube containing epoxy resin and mechanical properties of the modified CNT/epoxy composites were improved because the modification of CNTs improved dispersion and interaction between the CNT and the epoxy resin.This study was partially supported by the Applied Rheology Center (ARC) and by the National Research Laboratory (NRL). The authors are grateful for the support

Carbon Nanotube Embedded Nanostructure for Biometrics

Low electric energy loss is a very important problem to minimize the decay of transferred energy intensity due to impedance mismatch. This issue has been dealt with by adding an impedance matching layer at the interface between two media. A strategy was proposed to improve the charge transfer from the human body to a biometric device by using an impedance matching nanostructure. Nanocomposite pattern arrays were fabricated with shape memory polymer and carbon nanotubes. The shape recovery ability of the nanopatterns enhanced durability and sustainability of the structure. It was found that the composite nanopatterns improved the current transfer by two times compared with the nonpatterned composite sample. The underlying mechanism of the enhanced charge transport was understood by carrying out a numerical simulation. We anticipate that this study can provide a new pathway for developing advanced biometric devices with high sensitivity to biological information

Prediction and Measurement of Residual Stresses in Injection Molded Parts

Residual stresses were predicted by a flow analysis in the mold cavity and residual stress distribution in the injection molded product was measured. Flow field was analyzed by the hybrid FEM/FDM method, using the Hele Shaw approximation. The Modified Cross model was used to determine the dependence of the viscosity on the temperature and the shear rate. The specific volume of the polymer melt which varies with the pressure and temperature fields was calculated by the Tait's state equation. Flow analysis results such as pressure, temperature, and the location of the liquid-solid interface were used as the input of the stress analysis. In order to calculate more accurate gap-wise temperature field, a coordinate transformation technique was used. The residual stress distribution in the gap-wise direction was predicted in two cases, the free quenching and the constrained quenching, under the assumption that the shrinkage of the injection molded product occurs within the mold cavity and that the solid polymer is elastic. Effects of the initial flow rate, packing pressure, and mold temperature on the residual stress distribution was discussed. Experimental results were also obtained by the layer removal method for molded polypropylene.This study was supported by research grants from the Korea Science and Engineering Foundation (KOSEF) through the Applied Rheology Center (ARC), an official KOSEF-created engineering research center (ERC) at Korea University, Seoul, Korea. The authors are grateful for the support