Browsing by Subject "Static electricity"

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Open Access
Charge dissipation mechanism of low-cost antistatic additive lignin in contact charged polymers
(2019-07) Özel, Mertcan
Contact electrification (C.E.), a phenomenon studied for millennia, develops contact charges on material surfaces, when two materials are contacted and then separated. Accumulation of contact charges and their uncontrolled sudden discharges on dielectric polymers pose major drawbacks in industries i.e. pharmaceutical, (micro)electronics, and space, causing million-dollar losses annually. The overall mechanism of C.E. is unclear until now, however, recent efforts have proven that chemical bond-breakages on polymer surfaces result in mechanoions – which are indeed the contact charges on the surfaces. These studies also showed that removing mechanoradicals (co-formed upon bond-breaking) by molecular radical scavengers destabilizes the mechanoions (charges) and render the doped polymer material antistatic. This method of static charge mitigation has an advantage over the conventional methods (e.g. doping with metals, carbon powder, conductive polymers, or surface humidity enhancers) because it is not based on an increase in surface conductance and smaller doping concentrations are needed to achieve antistatic behavior. However, currently used molecular radical scavenger doping is generally not cost effective method to be upscaled for industrial use. Lignin; however, is a “low-cost” material (the second most abundant polymer on earth, a by-product of paper production) that can act as a radical scavenger. In this thesis work, lignin was extracted from some examples of both hard and softwood. Firstly, it was verified that lignin doping in low concentrations (1 – 5% w/w) reduce the contact charge accumulation on common polymers such as on a crosslinked elastomer polydimethylsiloxane, and on thermoplastics polypropylene, polyethylene, polylactic acid, and polystyrene. Then, the mechanism of the observed charge dissipation was discussed in the light of the results obtained from surface conductance of polymers upon doping, 31P NMR and solid state 13C-NMR spectroscopy, total phenol content, and the reacted number of radicals before and after grinding - which was shown essential to get homogeneous doping- of lignin. The results pointed out a mechanism involving a radical scavenging activity without any change in the surface conductance of the material, similar to that with molecular radicals. The understanding of lignin’s charge dissipation mechanism will be helpful in industrial utilization of lignin as an antistatic additive and in assessment of the limitations of this utilization.
Open Access
Electrostatics of Polymer Translocation Events in Electrolyte Solutions
(American Institute of Physics Inc., 2016) Buyukdagli, S.; Ala-Nissila, T.
We develop an analytical theory that accounts for the image and surface charge interactions between a charged dielectric membrane and a DNA molecule translocating through the membrane. Translocation events through neutral carbon-based membranes are driven by a competition between the repulsive DNA-image-charge interactions and the attractive coupling between the DNA segments on the trans and the cis sides of the membrane. The latter effect is induced by the reduction of the coupling by the dielectric membrane. In strong salt solutions where the repulsive image-charge effects dominate the attractive trans-cis coupling, the DNA molecule encounters a translocation barrier of ∼10 kBT. In dilute electrolytes, the trans-cis coupling takes over image-charge forces and the membrane becomes a metastable attraction point that can trap translocating polymers over long time intervals. This mechanism can be used in translocation experiments in order to control DNA motion by tuning the salt concentration of the solution.
Open Access
Glycosaminoglycan-Mimetic Signals Direct the Osteo/Chondrogenic Differentiation of Mesenchymal Stem Cells in a Three-Dimensional Peptide Nanofiber Extracellular Matrix Mimetic Environment
(American Chemical Society, 2016-02) Arslan, E.; Güler, Mustafa O.; Tekinay, A. B.
Recent efforts in bioactive scaffold development focus strongly on the elucidation of complex cellular responses through the use of synthetic systems. Designing synthetic extracellular matrix (ECM) materials must be based on understanding of cellular behaviors upon interaction with natural and artificial scaffolds. Hence, due to their ability to mimic both the biochemical and mechanical properties of the native tissue environment, supramolecular assemblies of bioactive peptide nanostructures are especially promising for development of bioactive ECM-mimetic scaffolds. In this study, we used glycosaminoglycan (GAG) mimetic peptide nanofiber gel as a three-dimensional (3D) platform to investigate how cell lineage commitment is altered by external factors. We observed that amount of fetal bovine serum (FBS) presented in the cell media had synergistic effects on the ability of GAG-mimetic nanofiber gel to mediate the differentiation of mesenchymal stem cells into osteogenic and chondrogenic lineages. In particular, lower FBS concentration in the culture medium was observed to enhance osteogenic differentiation while higher amount FBS promotes chondrogenic differentiation in tandem with the effects of the GAG-mimetic 3D peptide nanofiber network, even in the absence of externally administered growth factors. We therefore demonstrate that mesenchymal stem cell differentiation can be specifically controlled by the combined influence of growth medium components and a 3D peptide nanofiber environment.
Open Access
Lignin as an antistatic additive for common polymers
(2018-01) Bedük, Tutku
Static electricity is a common phenomenon that can causes million-dollar loses in industries such as polymer, air and space, and drug manufacture due to the detrimental effects of electrostatic discharge of the accumulated charges on surfaces. Doping of the materials, i.e. polymers, with antistatic agents can reduce or prevent these problems. So far, the antistatic additives used were chosen to make the final material/composite conductive to dissipate the surface charges, by either directly doping with conductive materials (e.g. metals or carbon powder), or by doping with additives (e.g. ions) to increase surface humidity. The doped materials usually lose their inherent properties such as the mechanical properties because of the high concentrations of the additive. To provide a more universal solution to this problem and avoid the changes in the material properties after doping, the mechanism of static charge formation, which has been on debate for many years, should be clarified. Recent studies of our group and others have shown that the main mechanism behind the charge formation on electrified (polymer) materials is the bond-breakages on the surfaces of the materials, which lead to mechanoanion, mechanocation, mechanoradical active ends. The former two accounts for the charge on the surfaces and, as we have shown, the latter group (mechanoradicals) stabilizes the charged species. Previously, in our group, it was shown that by removing the mechanoradicals with radical scavenger antioxidants one can destabilize the charges – doping with antioxidants makes materials antistatic. However, the scavenger antioxidants we had used in this example to show the antistatic behavior were far from being practical in use for general polymers -that are produces in millions of tons per year- because of their individual prices. Lignin is the world’s second most abundant polymer. It has antioxidant properties, so it is a good candidate as an antistatic agent for common polymers. In this study we assess the lignin’s antistatic action by doping it into common polymers - elastomers (silicon rubber) and thermoplastics (PE, PP, PVC), and comparing the accumulated net charge on the doped and undoped polymers upon contact electrification. It was shown that the increase in lignin concentration and decrease in particle size of the lignin enhances the antistatic property in the polymers, due to an increase in radical scavenging OH groups, as verified by 31P-NMR analysis. We certify that the antistatic property is because of the radical scavenging action and not by increase in the surface conductivity. By doping polymers with cheap and abundant lignin, we provide a more universal, environment-friendly method for preventing electrostatic charge accumulation on common polymers, which are produced in millions of tons per year.