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CONTENTS
Volume 1, Number 4, December 2012
 

Abstract
Results of isothermal torsional oscillation tests are reported on melts of linear low density polyethylene and isotactic polypropylene. Prior to rheological tests, specimens were annealed at various temperatures ranging from Ta = 180 to 310oC for various amounts of time (from 30 to 120 min). Thermal treatment induced degradation of the melts and caused pronounced decreases in their molecular weights. With reference to the concept of transient networks, constitutive equations are developed for the viscoelastic response of polymer melts. A melt is treated as an equivalent network of strands bridged by junctions (entanglements and physical cross-links). The time-dependent response of the network is modelled as separation of active strands from and merging of dangling strands with temporary nodes. The stress-strain relations involve three adjustable parameters (the instantaneous shear modulus, the average activation energy for detachment of active strands, and the standard deviation of activation energies) that are determined by matching the dependencies of storage and loss moduli on frequency of oscillations. Good agreement is demonstrated between the experimental data and the results of numerical simulation. The study focuses on the effect of molecular weight of polymer melts on the material constants in the constitutive equations.

Key Words
thermal properties; isotactic polypropylene; linear low-density polyethylene; molecular weight; viscoelasticity; thermal degradation

Address
A.D. Drozdov: Department of Chemical Engineering, West Virginia University, WV, USA; A. Al-Mulla: Department of Chemical Engineering, Kuwait University, Safat, Kuwait; R.K. Gupta: Department of Chemical Engineering, West Virginia University, WV, USA

Abstract
Thermoresponsive hydrogels based on N-Isopropylacrylamide (NIPAM) and 2-Hydroxyethylacrylate (HEA) were prepared by free radical polymerization. The hydrogels were characterized by elemental (CHN) analysis, differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA). DSC thermogram showed two endothermic transitions which are due to hydration of water present in different environments. One near 0oC called melting transition of ice and was used to calculate the quantitative determination of the amounts of freezing and non freezing water. The other transition above the ambient temperature was due to the combination of hydrophobic hydration and hydrophilic hydration which changes with the copolymer compositions. Swelling and deswelling studies of the hydrogels were carried out using the aqueous media, salt and urea solutions. The experimental results from swelling studies revealed that copolymers have lower rates of swelling and deswelling than the homopolymer.

Key Words
NIPAM; HEA; DSC; TGA; swelling

Address
Suman Shekhar, M. Mukherjee and Akhil Kumar Sen: Department of Chemical and Polymer Engineering, Birla Institute of Technology, Mesra, Ranchi, Jharkhand, India

Abstract
The present study addresses the problem of quantitative prediction of effective complex relative permittivity of Barium Titanate/Polyvenylidene Fluoride (PVDF) and (Bi0.5Na0.5)0.94Ba0.06TiO3/ Poly(VDF-TrFE) biphasic ceramic-polymer composites. Theoretical results for effective relative permittivity derived from several dielectric mixture equations were fitted to the experimental data taken from the works of Prasad et al. (2010), Wang et al. (2004), Takenaka et al. (1991) and Yamada et al. (1982). The study revealed that out of the different test equations, only a few equations like modified Rother-Lichtenecker equation, Dias-Dasgupta equation or Rao equation for the real part and Bruggeman equation for the imaginary part of complex permittivity well fitted the corresponding experimental results. In the present study, some of the equations were used in their original forms, while some others were modified by choosing suitable shape-dependent parameters in order to get reasonably good agreement with experimental results. Besides, the experimental results have been proposed in the form of a mathematical model using first order exponential growth, which provided excellent fits.

Key Words
ceramic-polymer composite; permittivity; dielectric loss; model fitting

Address
Ansu K. Roy, Z. Ahmad and A. Prasad: University Department of Physics, T. M. Bhagalpur University, Bhagalpur - 812 007, India; K. Prasad: Centre for Applied Physics, Central University of Jharkhand, Brambe, Ranchi 835 205, India

Abstract
This article describes the synthesis of a novel N-substituted pyrrole monomer containing an azobenzene group. The 2-[N-ethyl-N-[4-[(4-nitrophenyl) azo]-phenyl] amino] ethyl-3-chloropropionate (RedII) compound was synthesized via reaction of 4-nitro-4\'-[N-ethyl-N-(2-hydroxyethyl)-amino] azobenzene (RedI) and 3-chloropropionic acid. RedII was reacted with the potassium salt of pyrrole then 2-[N-ethyl-N-[4-[(nitro phenyl) azo] phenyl] amino] ethyl-N-pyrrolyl propionate (Py-RedII) was prepared. Chemical polymerization of Py-RedII and copolymerization of Py-RedII with pyrrole carried out using FeCl3. Poly (2-[N-ethyl-N-[4-[(nitro phenyl) azo] phenyl] amino] ethyl-N-pyrrolyl propionate) (PPy-RedII) was characterized by UV, IR, 1HNMR, 13CNMR spectroscopies. Electropolymerization of Py-RedII and electroco-polymerization of Py-RedII and pyrrole were studied using conventional three electrodes system, Ag/AgCl reference electrode, platinum counter electrode and GC disk working electrode. Scanning electron microscopy (SEM), thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) were used for thermal and rheological studies. The TGA curve of PPy-RedII demonstrated a high thermal stability up to 200

Key Words
azo polymers; conductivity; liquid crystals polymers; polypyrroles

Address
Seyed Hossein Hosseini: Department of Chemistry, Faculty of Science, Islamic Azad University, Islamshahr branch, Tehran-Iran

Abstract
Infections are caused due to the infiltration of tissue or organ space by infectious bacterial agents, among which Staphylococcus aureus bacteria are clinically most relevant. While current treatment modalities are in general quite effective, several bacterial strains exhibit high resistance to them, leading to complications and additional surgeries, thereby increasing the patient morbidity rates. Titanium dioxide is a celebrated photoactive material and has been utilized extensively in antibacterial functions, making it a leading infection mitigating agent. In view of the property amelioration in materials via nanofication, free-standing titania nanofibers (pure and nominally doped) and nanocoatings (on Ti and Ti6Al4V implants) were fabricated and evaluated to assess their efficacy to mitigate the viability and growth of S. aureus upon brief (30 s) activation by a portable hand-held infrared laser. In order to gauge the effect of exposure and its correlation with the antibacterial activities, both isolated (only titania substrate) and simultaneous (substrate submerged in the bacterial suspension) activations were performed. The bactericidal efficacy of the IR-activated TiO2 nanocoatings was also tested against E. coli biofilms. Toxicity study was conducted to assess any potential harm to the tissue cells in the presence of photoactivated materials. These investigations showed that the photoactivated titania nanofibers caused greater than 97% bacterial necrosis of S. aureus. In the case of titania-coated Ti-implant surrogates, the bactericidal efficacy exceeded 90% in the case of pre-activation and was 100% in the case of simultaneous-activation. In addition to their high bactericidal efficacy against S. aureus, the benignity of titania nanofibers and nanocoatings towards tissue cells during in-vivo exposure was also demonstrated, making them safe for use in implant devices.

Key Words
titanium dioxide; doped-titanium dioxide; titanium implant; nanofibers; nanotubes; staphylococcus aureus; photoactivation; infra red laser; infection mitigation; electron microscopy; confocal microscopy

Address
Abdul-Majeed Azad: Chemical Engineering Department, The University of Toledo, USA; Asem Aboelzahab: Bioengineering Department, The University of Toledo, 5051 Nitschke Hall,
2801 W. Bancroft St., Toledo, OH 43606-3390, USA; Vijay Goel: Bioengineering Department, The University of Toledo, 5051 Nitschke Hall, 2801 W. Bancroft St., Toledo, OH 43606-3390, USA; Department of Orthopedic Surgery, The University of Toledo, Toledo, Ohio 435606-3390, USA

Abstract
To reveal localized plastic deformation zones in a tough pitch copper, the etching characteristics of a copper sample have been examined. The etching was carried out on a sample surface using an etchant consisting of 25 ml nitric acid solution and 75 ml water. To clarify the plastic deformation zone, the sample deformed plastically was heated to between 250oC and 300oC before the etching process. This is due to a change of the microstructure and crystal orientation in the plastic deformation zone producing recrystallized small grains. In this case, the plastically deformed zone is severely etched, whereas the undeformed zone is only slightly etched. Identification of the details of the deformation zone from the etching is further discussed.

Key Words
etching technique; tough pitch copper; plastic deformation; microstructure

Address
Mitsuhiro Okayasu, Shuhei Takeuchi and Tetsuro Shiraishi: Department of Materials Science and Engineering, Ehime University, 3 Bunkyo-cho, Matsuyama, Ehime, 790-8577, Japan; Tatsuya Taki and Satoshi Takasu: Department of Machine Intelligence and Systems Engineering, Akita Prefectural University, 84-4 Aza Ebinokuchi, Tsuchiya, Yurihonjo-city, Akita, 015-0055, Japan


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