Polyacrylonitrile/carbon nanotube composite fibers: reinforcement efficiency and carbonization studies

Polyacrylonitrile (PAN)/carbon nanotube (CNT) composite fibers were made using various processing methods such as conventional solution spinning, gel spinning, and bi-component gel spinning. The detailed characterization exhibited that the smaller and longer CNT will reinforce polymer matrix mostly in tensile strength and modulus, respectively. Gel spinning combined with CNT also showed the promising potential of PAN/CNT composite fiber as precursor fiber of the next generation carbon fiber. High resolution transmission electron microscopy showed the highly ordered PAN crystal layer on the CNT, which attributed to the enhanced physical properties. The subsequent carbonization study revealed that carbonized PAN/CNT fibers have at least 50% higher tensile strength and modulus as compared to those of carbonized PAN fibers. Electrical conductivity of CNT containing carbon fiber was also 50% higher than that of carbonized PAN fiber. In order to have carbon fiber with high tensile strength, the smaller diameter precursor fiber is preferable. Bi-component gel spinning produced 1-2 µm precursor fiber, resulting in ~1 µm carbon fiber. The tensile strength of the carbonized bi-component fiber (islands fibers) is as high as 6 GPa with tensile modulus of ~500 GPa. Further processing optimization may lead to the next generation carbon fiber.Ph.D.Committee Chair: Satish Kumar; Committee Member: Anselm Griffin; Committee Member: Dong Yao; Committee Member: Naresh Thadhani; Committee Member: Samuel Graha

Achieving Both Ultrahigh Electrical Conductivity and Mechanical Modulus of Carbon Films: Templating-Coalescing Behavior of Single-Walled Carbon Nanotube in Polyacrylonitrile

Promoting the feasibility of carbon films as electrode applications requires sufficient performances in view of both electrical and mechanical properties. Herein, carbon films with ultrahigh electrical conductivity and mechanical modulus are prepared by high temperature carbonization of polyacrylonitrile (PAN)/single-walled carbon nanotube (SWNT) nanocomposites. Achieving both performances is ascribed to remarkable graphitic crystallinity, resulting from the sequential templating???coalescing behavior of concentrated SWNT bundles (B-CNTs). While well-dispersed SWNTs (WD-CNTs) facilitate radial templating according to their tubular geometry, flattened B-CNTs sandwiched between carbonized PAN matrices induce vertical templating, where the former and latter produce concentric and planar crystallizations of the graphitic structure, respectively. After carbonization at 2500 ??C with the remaining WD-CNTs as microstructural defects, the flattened B-CNTs coalesce into graphitic crystals by zipping the surrounding matrix, resulting in high crystallinity with the crystal thicknesses of 27.4 and 39.4 nm for the (002) and (10) planes, respectively. For comparison, the graphene oxide (GO) containing carbon films produce a less-ordered graphitic phase owing to irregular templating, despite the geometrical consistency. Consequently, PAN/B-CNT carbon films exhibit exceptional electrical conductivity (40.7 ?? 104 S m???1) and mechanical modulus (38.2 ?? 6.4 GPa). Thus, controlling the templating???coalescing behavior of SWNTs is the key for improving final performances of carbon films

Defect structure evolution of polyacrylonitrile and single wall carbon nanotube nanocomposites: a molecular dynamics simulation approach

In this study, molecular dynamics simulations were performed to understand the defect structure development of polyacrylonitrile-single wall carbon nanotube (PAN-SWNT) nanocomposites. Three different models (control PAN, PAN-SWNT(5,5), and PAN-SWNT(10,10)) with a SWNT concentration of 5 wt% for the nanocomposites were tested to study under large extensional deformation to the strain of 100% to study the corresponding mechanical properties. Upon deformation, the higher stress was observed in both nanocomposite systems as compared to the control PAN, indicating effective reinforcement. The higher Young's (4.76 +/- 0.24 GPa) and bulk (4.19 +/- 0.25 GPa) moduli were observed when the smaller-diameter SWNT(5,5) was used, suggesting that SWNT(5,5) resists stress better. The void structure formation was clearly observed in PAN-SWNT(10,10), while the nanocomposite with smaller diameter SWNT(5,5) did not show the development of such a defect structure. In addition, the voids at the end of SWNT(10,10) became larger in the drawing direction with increasing deformation

Note: Thermal conductivity measurement of individual poly(ether ketone)/carbon nanotube fibers using a steady-state dc thermal bridge method

Customized engineered fibers are currently being used extensively in the aerospace and automobile industries due to the ability to "design in" specific engineering characteristics. Understanding the thermal conductivity of these new fibers is critical for thermal management and design optimization. In the current investigation, a steady-state dc thermal bridge method (DCTBM) is developed to measure the thermal conductivity of individual poly(ether ketone) (PEK)/carbon nanotube (CNT) fibers. For non-conductive fibers, a thin platinum layer was deposited on the test articles to serve as the heater and temperature sensor. The effect of the platinum layer on the thermal conductivity is presented and discussed. DCTBM is first validated using gold and platinum wires (25 mu m in diameter) over a temperature ranging from room temperature to 400 K with +/- 11% uncertainty, and then applied to PEK/CNT fibers with diverse CNT loadings. At a 28 wt. % CNT loading, the thermal conductivity of fibers at 390 K is over 27 Wm(-1) K-1, which is comparable to some engineering alloys.open6

Multilayered Composites with Modulus Gradient for Enhanced Pressure???Temperature Sensing Performance

Highly sensitive and flexible composite sensors with pressure and temperature sensing abilities are of great importance in human motion monitoring, robotic skins, and automobile seats when checking the boarding status. Several studies have been conducted to improve the temperature-pressure sensitivity; however, they require a complex fabrication process for micro-nanostructures, which are material-dependent. Therefore, there is a need to develop the structural designs to improve the sensing abilities. Herein, we demonstrate a flexible composite with an enhanced pressure and temperature sensing performance. Its structural design consists of a multilayered composite construction with an elastic modulus gradient. Controlled stress concentration and distribution induced by a micropatterned structure between the layers improves its pressure and temperature sensing performance. The proposed composite sensor can monitor a wide range of pressure and temperature stimuli and also has potential applications as an automotive seat sensor for simultaneous human temperature detection and occupant weight sensing

Brain computed tomography angiography in postcardiac arrest patients and neurologic outcome

Objective This study aimed to analyze intracranial vessels using brain computed tomography angiography (CTA) and scoring systems to diagnose brain death and predict poor neurologic outcomes of postcardiac arrest patients. Methods Initial brain CTA images of postcardiac arrest patients were analyzed using scoring systems to determine a lack of opacification and diagnose brain death. The primary outcome was poor neurologic outcome, which was defined as cerebral performance category score 3 to 5. The frequency, sensitivity, specificity, positive predictive value, negative predictive value, and area under receiver operating characteristic curve for the lack of opacification of each vessel and for each scoring system used to predict poor neurologic outcomes were determined. Results Patients with poor neurologic outcomes lacked opacification of the intracranial vessels, most commonly in the vein of Galen, both internal cerebral veins, and the mid cerebral artery (M4). The 7-score results (P=0.04) and 10-score results were significantly different (P=0.04) between outcome groups, with an area under receiver operating characteristic of 0.61 (range, 0.48 to 0.72). The lack of opacification of each intracranial vessel and all scoring systems exhibited high specificity (100%) and positive predictive values (100%) for predicting poor neurologic outcomes. Conclusion Lack of opacification of vessels on brain CTA exhibited high specificity for predicting poor neurologic outcomes of patients after cardiac arrest

Assessment of Allergic Rhinitis Websites in Korea

Objectives. The internet has become an important source of medical information and a great amount of information related to allergic rhinitis (AR) is available on the internet. However, the quality of this information is still a matter of debate. Therefore, this study was conducted to assess the AR-related information on Korean websites. Methods. The key word "allergic rhinitis" was entered into 4 popular search engines, and this led to identifying 40 websites. After being categorized according to authorship, the informational value of these websites was evaluated using 4 different assessment tools such as the Journal of the American Medical Association (JAMA) benchmarks, the DISCERN questionnaire, the Allergic Rhinitis and its Impact on Asthma (ARIA) 2008 Update and the Health On the Net (HON) code. Results. The 40 websites containing AR-related information were categorized according to their authorship as Western physician: 20, Oriental physician: 14, commercial: 1, and others: 5. The mean citation frequencies of the JAMA benchmarks and the ARIA 2008 Update concepts was 1.23 out of 4 and 4.33 out of 8, respectively, while the mean DISCERN score was 1.92 out of 5. When the websites were evaluated based on the type of authorship, the mean citation frequencies of the AMA 2008 Update concepts were Western physician: 5.35, Oriental physician: 2.64. Additionally, three websites authored by Western physicians and 13 authored by Oriental physicians contained unreliable information. Among these 16 websites, only 3 websites met the requirements for the HON code "Justification". Conclusion. AR-related information available on Korean websites is of variable quality and not all of the information provided is justifiable. Thus, performing surveillance of the medical information on these websites is necessary. Furthermore, common criteria that can be used to evaluate the websites created by both Western and Oriental physicians are also needed.Bousquet J, 2008, ALLERGY, V63, P8*HLTH NET FDN, 2006, HLTH NET COD COND VESILVA LVE, 2005, BRAZILIAN J OTHORHIN, V71, P590Park HW, 2004, J KOREAN MED SCI, V19, P364Winker MA, 2000, JAMA-J AM MED ASSOC, V283, P1600Charnock D, 1999, J EPIDEMIOL COMMUN H, V53, P105Silberg WM, 1997, JAMA-J AM MED ASSOC, V277, P1244

Solid-State Spun Fibers from 1 mm Long Carbon Nanotube Forests Synthesized by Water-Assisted Chemical Vapor Deposition

In this work, we report continuous carbon nanotube fibers dry-drawn directly from water-assisted CVD grown forests with millimeter scale length. As-drawn nanotube fibers exist as aerogel and can be transformed into more compact fibers through twisting or densification with a volatile liquid. Nanotube fibers are characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman microscopy and wide-angle X-ray diffraction (WAXD). Mechanical behavior and electrical conductivity of the post-treated nanotube fibers are investigated

Early Compliance and Efficacy of Sublingual Immunotherapy in Patients with Allergic Rhinitis for House Dust Mites

Objectives. Sublingual immunotherapy (SLIT) has recently received much attention around the world as a treatment for allergic rhinitis. This study aimed to investigate the efficacy and adverse effects of SLIT in Korean patients with allergic rhinitis caused by house dust mites. The treatment compliance and the patient satisfaction with SLIT were also assessed. Methods. The patients who were sensitized to Dermatophagoides pteronyssinus and Dermatophagoides farinae and who started SLIT between November 2007 and July 2008 were included in this study. The symptom questionnaires, which included items on rhinorrhea, sneezing, nasal obstruction, itchy nose, olfactory disturbance, eye discomfort and sleep disturbance, were obtained before and 6 months after SLIT. The patient satisfaction and the adverse effects were also investigated. Results. One hundred forty-two patients started SLIT and 98 of them continued SLIT for 6 months or more. Ninety-two of the 98 patients completed the questionnaires. The duration of receiving SLIT was 9.8 months on average (range, 6 to 13 months). All the symptoms of allergic rhinitis were improved with SLIT. Forty-five percent of the patients were satisfied for SLIT, while 12% were unsatisfied. The incidence of adverse effects was 12% during maintenance therapy, although it was 48% during the up-dosing phase. The drop-out rate of SLIT was 31.0%. Conclusion. The subjective symptoms were improved with SLIT in Korean patients with allergic rhinitis for house dust mites. Yet the drop out rate was high despite of the symptomatic improvement.Roder E, 2008, CLIN EXP ALLERGY, V38, P1659, DOI 10.1111/j.1365-2222.2008.03060.xEsch RE, 2008, CURR OPIN OTOLARYNGO, V16, P260Frew AJ, 2008, NEW ENGL J MED, V358, P2259BOUSQUET J, 2008, ALLERGY S, V86, P8Eifan AO, 2007, ALLERGY, V62, P567, DOI 10.1111/j.1398-9995.2006.01301.xDunsky EH, 2006, ALLERGY, V61, P1235, DOI 10.1111/j.1398-9995.2006.01137.xAntico A, 2006, ALLERGY, V61, P1236, DOI 10.1111/j.1398-9995.2006.01155.xDahl R, 2006, J ALLERGY CLIN IMMUN, V118, P434, DOI 10.1016/j.jaci.2006.05.003Durham SR, 2006, J ALLERGY CLIN IMMUN, V117, P802, DOI 10.1016/j.jaci.2005.12.1358Passlacqua G, 2006, J ALLERGY CLIN IMMUN, V117, P946, DOI 10.1016/j.jaci.2005.12.1312Canonica GW, 2006, ALLERGY, V61, P20PASSALACQUA G, 2006, INFLAMM ALLERGY DRUG, V5, P43RIENZO VD, 2005, CLIN EXP ALLERGY, V35, P560KIM DY, 2004, KOREAN J OTOLARYNGOL, V47, P132WILSON DR, 2003, COCHRANE DB SYST REV, P2893NUHOGLU Y, 2003, J INVESTIG ALLERGOL, V17, P375Lombardi C, 2001, ALLERGY, V56, P989Guez S, 2000, ALLERGY, V55, P369, DOI 10.1034/j.1398-9995.2000.00413.xPurello-D`Ambrosio F, 1999, ALLERGY, V54, P968Pradalier A, 1999, ALLERGY, V54, P819Durham SR, 1996, J ALLERGY CLIN IMMUN, V97, P1356CASANOVAS M, 1994, J INVEST ALLERG CLIN, V4, P305

Molecular characterization and genogrouping of VP1 of aquatic birnavirus GC1 isolated from rockfish Sebastes schlegeli in Korea

The cDNA nucleotide sequence of genome segment B encoding the VP1 protein was determined for the aquatic birnavirus GC1 isolated from the rockfish Sebastes schlegeli in Korea. The VP1 protein of GC1 contains a 2,538 bp open reading frame, which encodes a protein comprising 846 amino acid residues that has a predicted MW of 94 kDa. The sequence contains 6 potential Asn-X-Ser/Thr motifs. Eight potential Ser phosphorylation sites and 1 potential Tyr phophorylation site were also identified. GC1 contains the Leu-Lys-Asn (LKN) motif instead of the typical Gly-Asp-Asp (GDD) motif found in other aquatic birnaviruses. We also identified the GLPYIGKT motif, the putative GTP-binding site at amino acid position 248. In total, the VP1 regions of 22 birnavirus strains were compared for analyzing the genetic relationship among the family Birnaviridae. Based on the deduced amino acid sequences, GC1 was observed to be more closely related to the infectious pancreatic necrosis virus (IPNV) from the USA, Japan, and Korea than the IPNV from Europe. Further, aquatic birnaviruses containing GC1 and IPNV have genogroups that are distinct from those in the genus Avibirnaviruses and Entomo-birnaviruses. The birnavirusstrains were clustered into 5 genogroups based on their amino acid sequences. The marine aquatic birnaviruses (MABVs) containing GC1 were included in the MABV genogroup; the IPNV strains isolated from Korea, Japan, and the USA were included in genogroup 1 and the IPNV strains isolated primarily from Europe were included in genogroup 2. Avibirnaviruses and entomobirnaviruses were included in genogroup 3 and 4, respectively