2014 NC State Graduate Student Research Symposium

gsrs-2014
L to R: Hammad Cheema, Ya-Ting Su, Abhay Joijode, Alper Gurarslan, Jialong Shen. Not pictured: Nasim Farahbakhsh, Kun Fu, Cassandra Kwon

On March 26th, 2014, the 9th Annual NC State University Graduate Student Research Symposium was held at the McKimmon Center. The Graduate School holds the Symposium each year to “showcase the outstanding quality and diversity of graduate-level research at NC State, in addition to providing students with the opportunity to practice their communication skills with those outside of their discipline.”

Abstracts of participants with Textile Engineering, Chemistry and Science faculty advisors or co-advisors:

Hammad Cheema1, Ahmed El-Shafei1, Ashraful Islam2, Liyuan Han2, Robert Younts3, Bhoj Gautum3, Kenan Gundogdu3
Graduate Programs:  Fiber and Polymer Science, Wilson College of Textiles, North Carolina State University1; Photovoltaic Materials Unit, National Institute for Materials Science (NIMS), Tsukuba, Japan2; Physics Department, North Carolina State University3
Advisor: Ahmed El-Shafei

Carbazole-Based Ancillary Ligands Tethered to Long Alkyl Chains in Amphiphilic Ru (II) Bipyridyl Heteroleptic Complexes for High Efficiency Dye-sensitized Solar Cells
Human society is facing enormous pressure because of rapidly increasing energy demands and depletion of conventional energy resources.  Additionally emissions from burning fossil fuels are contributing to the global warming and affecting the ecosystem of our only home (Earth).  Therefore, alternative, sustainable and green energy sources are vital to fulfill the increasing global energy demands. It is believed that more solar energy strikes the earth surface in one hour than the energy provided by fossil fuels in one year according to current demands. To exploit the solar energy, silicone-based cells have been used widely because of their steady efficiencies. However manufacturing of such cells is expensive and has environmental issues. Dye-sensitized solar cells (DSSCs) have received immense interest from research community owing to their unique features of transparency, flexibility, low cost, independency of incident light angle, simple manufacturing and high power conversion efficiencies year around, including rainy and cloudy weather and diffused light conditions. Here we report two novel amphiphilic Ru (II) bipyridyl heteroleptic complexes HD-14 and HD-15 for applications in DSSCs. We have combined the strong electron donor characteristics of carbazole-based ancillary ligands (AL) and hydrophobic nature of long alkyl chains tethered to the AL to study its effect on charge separation and recombination and dye regeneration by measuring ground and excited states oxidation potentials, incident-photon-to-current conversion efficiency (IPCE), impedance measurements, TCSPC and ultrafast transient absorption measurements, short-circuit photocurrent density (Jsc), and total solar-to-electric conversion efficiency (η). This strategy resulted in highly efficient sensitizers with photocurrent up to 22% greater than N719, and solar-to-power conversion efficiency (η%) of 9.34 for HD-14 and 9.19 for HD-15 against 9.32 of N719, under the same experimental device conditions.

Nasim Farahbakhsh
Graduate Program: Fiber and Polymer Science
Advisors: Dr. Jesse S. Jur, Dr. Richard A. Venditti

Application of Nano-Sized Biofiller from Waste Cotton T-shirts in Thermoplastic Polymer Films
Replacing petroleum-based materials with biodegradable materials that offer low environmental impact and safety risk is of increasing importance in applications that require increased awareness in sustainable materials processing and materials. The purpose of this work is to examine the range of methods to produce uniform microfibrillated cotton from recycled waste cotton T-shirts and evaluate its use as filler in thermoplastic polymers films and fibers. Microfibrillated cotton was prepared by microgrinding mechanical treatment of pulverized cotton, resulting in an aggregated nano-cellulose network with fibril diameters of 10-100 nm and a corresponding crystallinity of 77%. Film composites of low density polyethylene and cotton before and after microfibrilation were fabricated using melt extrusion to show the effect of filler size on mechanical, thermal and morphology of polymer. Compounding microfibrillated cotton with LDPE resulted in well-dispersed nanocomposites with no discoloration after 10 min of melt extrusion at 170°C. The biocomposites produced with microfibillated cotton showed a 21% increase in strength, owing to the higher crystallinity of the nano-sized cotton-derived filler material.

Kun Fu1, Yanpeng Li2 and Xiangwu Zhang1
Graduate Programs: Textile Engineering, Chemistry and Science, North Carolina State University1; Materials Science and Engineering, North Carolina State University2
Advisor: Xiangwu Zhang

Unexpected Performance of Carbon Fiber-Sulfur Webs as Cathode for Lithium-Sulfur Batteries
In the pursuit of high battery performance, significant efforts have been placed to explore new types of lithium batteries with high energy density, good safety, and low cost for transportation and stationary energy storage systems. Among various forms of secondary lithium batteries, lithiumsulfur battery shows great potential to substitute traditional lithium-ion battery due to its high theoretical capacity and high energy density, maximizing to 1675 mAh g-1 and 2500 Wh kg-1, respectively. In addition, the low-cost, abundant resource, and non-toxicity factor of sulfur make it economically and environmentally affordable in large-scale lithium-sulfur battery applications. In this work, a novel facile-synthesized carbon nanofiber-sulfur (CNF-S) composite with high sulfur content (> 60%) is designed and it exhibits as a promising binder-free and Al-free electrode with high sulfur loading (> 2.5 mg cm-2) for high-energy density lithium-sulfur batteries. This self-supporting porous CNF web can not only allow the loading large amount of solid sulfur but also help localize polysulfide catholyte inside the cathode electrode. In this work, a facile and fast sulfur loading method was introduced and the composite preparation time can be greatly reduced to ~30 min compared to the several hours in the traditional sulfur impregnation method, and this can significantly simplify the battery processing and configuration. The resultant CNF-S cathode can have high discharge capacity (around 1000 mAh g-1), long term cyclability (over 200 cycles), high sulfur loading (~ 2 mg cm-2) and sulfur content (~65%), offering great potential to get further improvement by optimizing the CNF-S composite structure so as to substitute the conventional sulfur electrode and cell configuration for lithium-sulfur batteries in the near future.

Alper Gurarslan1, 2, Yifei Yu1, Yiling Yu3, Linyou Cao1, 3
Graduate Programs: Materials Science & Engineering, North Carolina State University1, Fiber & Polymer Science, North Carolina State University2, Physics, North Carolina State University3
Advisor: Linyou Cao (work presented was from work with Dr. Cao, also advised by Dr. Alan Tonelli)

Instant Transfer of 2-D MoS2 Films
Molybdenum sulfi de (MoS2) has layered structure where each layer is composed of a plane hexagonal array of molybdenum atoms between two sheets of sulfur atoms. MoS2 monolayers, with a direct bandgap of 1.8 eV, offer an unprecedented prospect of miniaturizing semiconductor science and technology down to a truly atomic scale. Recent studies have indeed demonstrated the promise of 2D MoS2 in fields including field effect transistors, low power switches, optoelectronics, and spintronics. However, device development with 2D MoS2 has been delayed by the lack of capabilities to transfer large-area, uniform, and high-quality MoS2 monolayers. Here we present a transfer method for obtaining high quality and large area monolayer and few-layer MoS2 films on arbitrary substrates.

 Abhay S. Joijode, Gerry J. Antony and Alan E. Tonelli
Graduate Program: Fiber and Polymer Science
Advisor: Alan E. Tonelli

Glass-Transition Temperatures of Nanostructured Amorphous Bulk Polymers and their Blends
Nanostructured amorphous bulk polymer samples were produced by processing them with small molecule hosts. Urea (U) and gammacyclodextrin (γ-CD) were utilized to form crystalline inclusion compounds (ICs) with low and high molecular weight as-received (asr-) poly(vinyl acetate) (PVAc), poly (methyl methacrylate) (PMMA), and their blends as included guests. Upon careful removal of the host crystalline U and γ-CD lattices, nanostructured coalesced (γ-) bulk PVAc, PMMA, and PVAc/PMMA blend samples were obtained, and their glass-transition temperatures, Tgs, measured. In addition, nonstoichiometric (n-s)-IC samples of each were formed with γ-CD as the host. The Tgs of the unthreaded, un-included portions of their chains were observed as a function of their degree of inclusion. In all the cases, these nanostructured PVAc and PMMA samples exhibited Tgs elevated above those of their as-received and solution-cast samples. Based on their comparison, several conclusions were reached concerning how their molecular weights, the organization of chains in their coalesced samples, and the degree of constraint experienced by un-included portions of their chains in (n-s)-γ-CD-IC samples with different stoichiometries affect their chain mobilities and resultant Tgs.

Cassandra Kwon
Graduate Program: Textile Technology Management
Advisors: Kristin Thoney-Barletta and William Oxenham

Characterizing the Relationship of Tensile Properties and Pressure Profi les of Compression Bandages and Fabrics
Compression therapy is the cornerstone treatment for venous and lymphatic disorders and is commonly administered through medical compression hosiery, pneumatic pumps, and compression bandages. Research has shown compression therapy to be the most effective technique in alleviating symptoms associated with venous disorders, such as painful swelling and skin ulcerations, but is also implemented in sports therapy and preventing edema that may affect pregnant women and stationary travelers. While the medical community agrees on compression therapy’s efficacy, there is no approved testing standard in the US, with manufacturers adopting standards from Europe. There are various devices used for measuring the pressure applied by a compression textile, and these work either indirectly by gathering force measurements or directly, by observing the pressure profi le as it is worn on a patient or leg form. These methods are often associated with compression hosiery and not bandages. This study explored implementing a newly developed indirect testing technique in order to characterize the relationship between tensile properties and pressure profiles for commonly used bandage wrap systems and hosiery samples. Two separate direct testing techniques were also performed – the first using participants’ legs to measure interface pressure with the PicoPress Compression Measuring System and the second test used a set of specially designed tubes with a sensor foot built into the surface known as the CRIM Pressure System. Pressure data was collected from all three testing techniques using three different circumferences and analyzed to show the correlation between each measuring system. While the indirect testing approach indicated good correlation between rigidity and pressure profiles, a comparison of the extrapolated data with direct PicoPress pressure readings indicated that some bandage and hosiery samples had good correlation, but others did not. PicoPress and CRIM Pressure System values showed a better correlation between readings, but still varied for some sampling.

 Jialong Shen
Graduate Program: Fiber and Polymer Science
Advisor: Dr. Alan E. Tonelli

Evaluating the Relative Importance of Three Structural Factors Commonly Suggested to Contribute to the Softening/glass Transition Temperatures of Polymers
Glass-transition temperatures (Tgs) are temperatures at which polymer materials soften and therefore are critical to their processing, use, and behaviors. However, the molecular structural bases for the wide range of glass-transition temperatures (several hundred K) observed for chemically distinct polymers are largely unknown. Three factors are often cited as being pivotal in the literature: 1.The inherent conformational flexibilities of their individual chain backbones; 2.The sizes or steric bulk of their side-chains; and 3.The interactions (steric, dipolar, hydrogen64 bonding, van der Waals, etc.) between polymer chains. But because these three factors are usually structurally interdependent, it can be difficult to evaluate their relative importance to the Tgs of chemically different polymers. Our approach to this problem is synthesizing and comparing the Tgs of structurally analogous copolymer pairs which differ in only a single structural or conformational factor. With the irregularity introduced by the inherent expected randomness of step-growth copolymerization, the crystallinities of copolymers can be significantly reduced to near or wholly amorphous, leaving their Tgs unaffected by crystallinity. A nylon tetrapolymer with very little discernible crystallinity and a Tg ~ 47 °C was produced by melt transamidation from Nylon 6, 66, 610, and 11. While the melt polymerization of 66 and 610 salts with various ratios did not yield amorphous copolyamides. Addition of α,ω- aminoundecanoic acid as the third component largely impeded the crystallization during the subsequent cooling scan from its melt, and manifested a cold crystallization upon heating which is a sign of their diminishing crystallizability.  Amorphous linear aliphatic polyesters were made by following a recent report on copolymerization of succinic acid with ethylene glycol and 1,3-propanediol. Corresponding polyamide-34, though not amorphous, showed a Tg over 240K higher than polytrimethylenesuccinate, which indicated Tgs are highly sensitive to factor 3, the interactions between polymer chains; i.e., dipolar vs. H-bonding in this case.
Keywords: Polymer, Glass-transition temperature, Amorphous, Polyester, Polyamide

Ya-Ting Su
Graduate Program: Fiber and Polymer Science
Advisors: Dr. Russell Gorga and Dr. Melissa Pasquinelli

A Systematic Investigation of the Factors that Trigger Thermal Degradation During the Processing of Industrially-Relevant Polymers
During the formation of polymer products, thermal degradation has been an issue, which is also affected by the presence of oxygen and other impurities as well as the processing conditions. Thermal degradation not only impacts the physical and mechanical properties of the products, but also often leads to the failure of production lines. An understanding of the molecular mechanisms that underlie thermal degradation can thus lead to the production of polymer materials with enhanced properties and can minimize waste during production. The goal of this work is to utilize both experiments and simulations to investigate the effects on polymer thermal degradation of its processing conditions (residence time, temperature, pressure) and the local environment (the presence of oxygen, water, additives, crystal domains, or impurities). We studied two model systems, polypropylene (PP) and polyethylene (PE). From both simulations and experiments, the processing conditions including temperature and the residence time during the melt processing phase of extrusion were identified to be critical factors. Both PP and PE were observed to have has their own mechanisms for thermal degradation. Other interesting observations from both the simulations and the experiments will also be discussed.

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