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Functionality in Electrospun Nanofibrous Membranes Based on Fiber’s Size, Surface Area, and Molecular Orientation

Functionality in Electrospun Nanofibrous Membranes Based on Fiber’s Size, Surface Area, and Molecular Orientation

Abstract: Electrospinning is a versatile method for forming continuous thin fibers based on an electrohydrodynamic process. This method has the following advantages: (i) the ability to produce thin fibers with diameters in the micrometer and nanometer ranges; (ii) one-step forming of the two- or three-dimensional nanofiber network assemblies (nanofibrous membranes); and (iii) applicability for a broad spectrum of molecules, such as synthetic and biological polymers and polymerless sol-gel systems. Electrospun nanofibrous membranes have received significant attention in terms of their practical applications. The major advantages of nanofibers or nanofibrous membranes are the functionalities based on their nanoscaled-size, highly specific surface area, and highly molecular orientation. These functionalities of the nanofibrous membranes can be controlled by their fiber diameter, surface chemistry and topology, and internal structure of the nanofibers. This report focuses on our studies and describes fundamental aspects and applications of electrospun nanofibrous membranes.
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A toolbox for parameter free predictions of solid state properties of monodisperse glassy polymers with frozen in molecular orientation

A toolbox for parameter free predictions of solid state properties of monodisperse glassy polymers with frozen in molecular orientation

temperature. The toolbox predictions also match the experi- mental observation that the effect of molar mass on craze initiation stress is greatest at intermediate draw tempera- tures and smallest at the lowest and highest draw tempera- tures. At the lowest draw temperatures, relaxation times dur- ing melt drawing are very long, and molecular orientation occurs with little to no relaxation (and hence independently of molar mass). At very high temperatures, there is almost complete relaxation during melt drawing, and the oriented polymers craze at a similar stress to isotropic polymers of the same molar mass.
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Influence of Molecular Orientation on the Melting
Behavior of Poly(phenylene sulfide) Fibers

Influence of Molecular Orientation on the Melting Behavior of Poly(phenylene sulfide) Fibers

heating and hence requires higher temperatures for crystal melting. Thus the role of molecular orientation in melting behavior of highly oriented PPS fibers may be two fold: to act as a catalyst for further crystal rearrangement and also to provide resistance to melting of crystals through the presence of highly ordered non-crystalline region. Yamada et al.[19] reported an increase in melting temperature of highly oriented isotactic polypropylene films and attributed this to an increase in amorphous orientation. Through extensive study on melting behavior of isotactic polypropylene fibers, Samuels [12] concluded that the multiple melting endotherms in oriented and restrained fibers are the manifestations of orientation in amorphous regions above a certain minimum value of f am . The increase
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Determining molecular orientation via single molecule SERS in a plasmonic nano gap

Determining molecular orientation via single molecule SERS in a plasmonic nano gap

In this work the optical properties of plasmonic nano-gaps formed between a spherical silver nanoparticle and an extended silver film separated by a gap of width 5 nm (see Figure 1) are systematically investigated for SERS spectroscopy. The results reveal the intimate link between the near-field excitation enhancements and far-field emission enhancements for both the hybridized dipolar and quadrupolar modes of the nano-gaps as a function of the silver particle size. In particular, both finite difference time domain (FDTD) calculations and experimental measurements show that, in those nano-gaps, the SERS signal in the far-field is mainly associated with the hybridized dipolar mode of the nano-gap and strongly affected by the particle size. Finally, using an optimized nano-gap geometry, single molecule Raman sensitivity is demonstrated, enabling to determine the molecular orientation using a convolution of experimental single molecule SERS spectra and Density Functional Theory (DFT) calculations.
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Investigating the molecular orientation of Ir(ppy)3 and Ir(ppy)2(acac) emitter complexes by X ray diffraction

Investigating the molecular orientation of Ir(ppy)3 and Ir(ppy)2(acac) emitter complexes by X ray diffraction

Our measurements reveal that molecular orientation is particularly pronounced for pure films of the emitter molecules and it seems to be an intrinsic property of the material growth during thermal evaporation. The observation that the crystallites and permanent dipoles of both iridium complexes investigated here are oriented in thin evaporated films is particularly significant given that transition dipole moments only show a preferential orientation for Ir(ppy) 2 (acac) but were

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Determination of the ionization energy and the electron affinity of organic molecular crystals from first-principles: dependence on the molecular orientation at the surface

Determination of the ionization energy and the electron affinity of organic molecular crystals from first-principles: dependence on the molecular orientation at the surface

I demonstrate that the ionization energy (IE) and the electron affinity (EA) of organic molecular crystals can be predicted from first-principles. Here, I describe the induced electronic polarization and the electrostatic effects upon crystalline IE and EA. I also demonstrate that the electronic polarization mainly originates from the screened coulomb interaction inside the crystalline bulk phase, and that the electrostatic contribution to IE and EA crucially depends on the orientation of the molecule at the surface. The former is well described by the GW approximation, while the latter is reasonably estimated by the difference in frontier orbital energy between the gas phase and the surface at the level of a generalized gradient approximation to the density functional theory. The present methodology enables to demonstrate the impact of the electrostatic effect upon the energy level of the injected charge at a multi-monolayer surface of an organic semiconductor thin film.
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Viscoelastic Properties of p-n Alkyl Benzoic Acid Mesogens

Viscoelastic Properties of p-n Alkyl Benzoic Acid Mesogens

Abstract: Dynamic rheological behaviour, such as storage modulus (G') and loss modulus (G'') are measured as a function of frequency at different temperatures in nematic region and also studied linear viscoelastic behaviour of p-n alkyl benzoic acid (nBA) mesogens. Different zones are exhibited by the samples, - a plateau zone at low frequencies, a transition zone at high frequencies and a zone entire plateau showing for crossover frequencies and relaxation times. The dependence of the elastic (G′) and loss (G′′) moduli on frequency is strong. The observed crossover points of G′, G′′ in the study of frequency range is indicating that nematic phase of nBA has behaved like both viscoelastic solid and liquid for small deformations (<1% strain). A typical shear thinning behaviour of viscosity has been displayed when the samples are subjected to shearing at a constant temperature. This typical shear thinning has approached slowly moving to Newtonian viscosity at high shear rates showing progressive development of nematic molecular orientation along flow direction on increasing shear rate. Rheological behaviour of the nBA nematic phases is in general consistent like the other reported compounds except the one thermotropic liquid crystals. The higher shear force and lower viscosity ratio is observed in these compounds in which pentyl benzoic acid has high ratio indicating the high molecular orientation may be due to low chain entanglement.
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Orientation of a Diagnostic Ligand Bound to Macroscopically Aligned Amyloid β Fibrils Determined by Solid State NMR

Orientation of a Diagnostic Ligand Bound to Macroscopically Aligned Amyloid β Fibrils Determined by Solid State NMR

With amyloid diseases poised to become a major health burden in countries with ageing populations, diagnostic molecules that aid the detection of amyloid in vitro and in vivo are of considerable clinical value. Understanding how such ligands recognize their amyloid targets would help to design diagnostics that target specific amyloid types associated with a particular disease, but methods to provide comprehensive information are underdeveloped. Here solid-state NMR is used to determine the molecular orientation of the amyloid diagnostic 1-fluoro-2,5-bis[(E)-3- carboxy-4-hydroxystyryl]-benzene (FSB) when bound to fibrils of the Alzheimer’s amyloid- polypeptide aligned on a planar substrate. The 19 F NMR spectrum of the
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Fabrication Parameter Optimization for a Multilayer Photovoltaic Cell Based on the Heterojunction: Zinc(II) Meso Tetrakis(4 Bromophenyl) Porphyrins/Fullerenes

Fabrication Parameter Optimization for a Multilayer Photovoltaic Cell Based on the Heterojunction: Zinc(II) Meso Tetrakis(4 Bromophenyl) Porphyrins/Fullerenes

No much research has been devoted to the effect of the surface energy of the anode on the structure and mor- phology of the organic films [25,26]. However, the car- rier transport properties of the organic semiconductor comprising π-conjugated molecules strongly depend on the molecular order in the films. So it could be of interest to use an ABL which not only improves the band match- ing at the interface, but also allows some improvement of the order in the absorbing organic layer. Recently, it has been shown that CuI can be used to control the molecular orientation of metal phthalocyanine (MPc) in organic cells based on MPc/C 60 [27-29] Therefore, in the present
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Thermal and Photo Alignment Behavior of Polyethylene Imine Having Methoxy Substituent Azobenzene Side Chain Group

Thermal and Photo Alignment Behavior of Polyethylene Imine Having Methoxy Substituent Azobenzene Side Chain Group

somerization and reached to almost initial level (S = 0.024). Namely the azobenzene molecules aligned ran- domly on the glass substrate. Following non-polarized visible light irradiation again increased the order pa- rameter value from 0.024 to 0.44, indicating the trans- formation of molecular orientation of azobenzene mole- cules from random state to out-of-plane order due to photo-orientation. The efficiency of the induction of ani- sotropy in the polymeric film was higher for the 435 nm non-polarized visible light compared with that of an- nealing because the pre-irradiation with the 365 nm light strongly increased the effectiveness of photoorientation process [15]. Again upon UV irradiation, the azobenzene group aligned randomly on the glass substrate (S = 0.02). It should be noted that after each step of irradiation with the 365 nm UV light the angular-dependent spectra were exactly the same. This indicates a complete erasure of the previously written orientation was achieved. Again, after annealing the out-of-plane order parameter value in- creased from 0.02 to 0.41 and after irradiation of 435 nm non-polarized visible light order parameter value changed from 0.01 to 0.46. In this way, the reversibility of the alignment behavior of azobenzene groups in polyethyl- ene imine could be achieved by changing the conditions such as annealing, UV and non-polarized visible light irradiation. All these results indicated that the optical information in the polymer can be rewritten in the system without any memory effects of previous irradiation or annealing.
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Structure and Orientation of MDBA Self-Assembled Monolayers and Their Interaction with Calcite: A Molecular Dynamics Study

Structure and Orientation of MDBA Self-Assembled Monolayers and Their Interaction with Calcite: A Molecular Dynamics Study

The structures of the para5, meta5, and bimeta5MDBA headgroups are shown in figure 1. The supercell for the simulations was constructed using the cell dimensions of the experimentally measured unit cell of biphenylakanethiol (BP) SAMs with, even5numbered chains, grown on a Au (111) surface 11 . It has been determined 10 that those 'even' BP monomers are close structural analogues of the MDBA monomers, hence their in5plane packing and molecular orientation are expected to be very similar. Our model SAM consists of a supercell periodically repeated in x and y with dimensions x=25.3 Å and y=38 Å, containing 32 MDBA monomers. A vacuum gap of ~65 Å was added in the z5direction, to separate the substrate from the other MDBA layers. Water and/or CaCO 3 was then deposited on the surface.
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Effect Of Orientation On Charge Transport In Molecular Junctions

Effect Of Orientation On Charge Transport In Molecular Junctions

approach with different surface cleavage. We found that the energy difference between HOMO-1(LUMO+1) and HOMO (LUMO) is significantly large indicating no degenerating energy states exist around the band gap. The one of the cause of change in the threshold positions of the HOMO band in these systems is the difference in the relaxation/polarization energies. Since Charge transfer occurs at organic/inorganic interfaces when there is a difference in the ionization energy and the electron affinity of the material, especially at interfaces. Thus we conclude that the molecular orientation and the electronic structure at molecular donor/acceptor interfaces play an important role in the performance of organic optoelectronic devices and contribute to a better understanding of organic Schottky contacts.
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Exploiting orientation selective DEER : determining molecular structure in systems containing Cu(II) centres

Exploiting orientation selective DEER : determining molecular structure in systems containing Cu(II) centres

centres of a homodimer of AGAO provided an accurate distance distribution measurement. However, in this case of a single molecular orientation the DEER data provided only a broad range of possible orientations all of which satisfactorily described the experimental DEER data. This uncertainty in the orientation of the two copper centres is due to the intrinsic limitations resulting from the spin Hamiltonian symmetry, and also the uncertainty in orientating the g-matrix, which is required to compute the DEER orientation selectivity. However, the orientation-selective DEER data can still be exploited to limit the relative orientations of the two paramagnetic centres to a reasonably small range. In cases where the g-tensor orientation is not known it could be deter- mined experimentally through a detailed analysis of orientation- selective ENDOR and/or HYSCORE data in conjunction with the structure of the paramagnetic centre if it is known. 60
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Optical Characterization of Anisotropic Interfaces

Optical Characterization of Anisotropic Interfaces

In Chapter 2, we have summarized the main experimental procedures and setups used in this thesis. We first report on the development of polarization modulation spectroscopy developed in our laboratory to investigate dynamically the orientation of molecules that undergo specific molecular orientation when irradiated by a polarized light. The setup has been modified to measure the molecular orientation of azobenzene-containing glass thin films dynamically with in-situ irradiation of the samples. The fundamental principles of plasmonics are then explained by considering the complex dielectric function of metals. The modeling of the electric field in the vicinity of the metal nanostructures organized in arrays provides essential information regarding the localization of the EM field and to define its relationship with the incident polarization of the incoming light. We provide here the basis of Finite-Difference Time-Domain calculations used in this study. Last, a brief introduction of second-order nonlinear optical processes is provided with a focus on second harmonic generation technique developed and used in this thesis. In Chapter 3, we report on the photoinduced vibrational linear dichroism in azobenzene- containing molecular glasses. We focus on the use of the polarization modulation technique to access dynamically the rate constants associated with the dynamics of each vibrational modes of a series of azobenzene-containing glasses. This work has been published in Langmuir 29 and was performed within a multidisciplinary environment involving Western University and Université de Nantes (France). In this project, I was in charge of the development of the experimental setup, its calibration and the data treatment of the collected data. The first author (Dr. Kristen Snell) was in charge of the chemical synthesis of an original series of triphenylamine compounds substituted with azobenzene core.
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Exploiting orientation-selective DEER: Determining molecular structure in systems containing Cu(II) centres

Exploiting orientation-selective DEER: Determining molecular structure in systems containing Cu(II) centres

centres of a homodimer of AGAO provided an accurate distance distribution measurement. However, in this case of a single molecular orientation the DEER data provided only a broad range of possible orientations all of which satisfactorily described the experimental DEER data. This uncertainty in the orientation of the two copper centres is due to the intrinsic limitations resulting from the spin Hamiltonian symmetry, and also the uncertainty in orientating the g-matrix, which is required to compute the DEER orientation selectivity. However, the orientation-selective DEER data can still be exploited to limit the relative orientations of the two paramagnetic centres to a reasonably small range. In cases where the g-tensor orientation is not known it could be deter- mined experimentally through a detailed analysis of orientation- selective ENDOR and/or HYSCORE data in conjunction with the structure of the paramagnetic centre if it is known. 60
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Investigation and Control of "Sphere-Like" Buckminsterfullerene C60 and "Disk-Like" Copper(II) Phthalocyanine.

Investigation and Control of "Sphere-Like" Buckminsterfullerene C60 and "Disk-Like" Copper(II) Phthalocyanine.

The probability of a free electron(hole) encountering a free hole(electron) and recombining is directly related to the density of free charge carriers in the active layer. Since you do not want to decrease the rate free charges are being created, the only beneficial way to reduce the density of free charge carriers is to extract the charges as quickly as possible. To extract charges more rapidly, either the path length to the electrodes must decrease or the transport velocity must increase. Reducing the path length to the electrodes is not practical since it would require reducing the active layer thickness resulting in less light absorption. The transport velocity is determined by the charge carrier mobility of the material and the strength of the electric field. The charge carrier mobility is determined primarily by the intrinsic properties of the organic semiconducting material chosen as well as the morphology within that material. Due to increased orbital overlap, charge transport between molecules is fastest in the Pi-Pi stacking direction. The presence of grain boundaries and/or molecular disorder within the material induces trap sites and/or band bending which can greatly inhibits charge transfer.
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Spatial mapping of flow induced molecular alignment in a noncrystalline biopolymer fluid using double quantum filtered (DQF) 23Na MRI

Spatial mapping of flow induced molecular alignment in a noncrystalline biopolymer fluid using double quantum filtered (DQF) 23Na MRI

To probe the formation of fl ow-induced microstructure in fl uids, one needs to detect and to characterize short-range molecular order. 1 Contemporary methods that are suited the most for this purpose are small-angle X-ray scattering (SAXS) or small neutron scattering (SANS). Although these methods have been successfully applied to probe short-range molecular order in situ, 4 X-ray transparency of micro fl uidic devices is required (SAXS methods), or speci fi c fl uid manipulation is needed to incorporate tracer particles (SANS methods). Rheo- optical methods necessitate optical transparency of fl uids.
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Self assembled growth of MnSi~1 7 nanowires with a single orientation and a large aspect ratio on Si(110) surfaces

Self assembled growth of MnSi~1 7 nanowires with a single orientation and a large aspect ratio on Si(110) surfaces

also be grown on the Si substrates with reactive epitaxy method at temperatures above approximately 500°C [20-22]. The growth mechanism of the NWs was con- sidered to be anisotropic lattice mismatch between the silicide and the Si substrates. The growth direction of the NWs is confined along Si<110>, resulting in the NWs orienting with the long axis along one direction (Si 1 ½ 10 ), two orthogonal directions (Si 01 ½ 1 and [011]), and three directions (Si 01 ½ 1 , 01 ½ 1 , and 1 ½ 10 ) on the Si(110), (001), and (111) surfaces, respectively. However, for scientific investigation as well as device applications, it would be highly expected to grow NWs with a single orientation because the NWs grown in this mode would never cross and have larger length. Parallel NW arrays can be used as nanomechanical devices [23], and using parallel NWs, the anisotropic electronic structure of silicide NWs can be investigated by angle-resolved photoelectron spectroscopy [11]. On the other hand, the Si(110) surface is currently
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Sub tomogram averaging of COPII assemblies reveals how coat organization dictates membrane shape

Sub tomogram averaging of COPII assemblies reveals how coat organization dictates membrane shape

cryo-EM density (Supplementary Figure 6b). This orientation is compatible with models proposing that amphipathic helices embed shallowly into lipid bilayers, creating a wedge to induce and/or sense membrane curvature 17 . Membrane curvature likely derives from Sar1 amphipathic helix insertion, as well as inter- action with the membrane-proximal surface of Sec23–Sec24. Sec24 in particular appears to extensively contact the membrane through a largely basic surface that encompasses its Zn finger domain (Supplementary Figure 6d–e). Formation of ordered arrays of inner coat thus leads to many Sar1 helices inserting parallel to each other (Fig. 3c) and to the inner surface of Sec23–Sec24 to adopt a cylindrical profile, reinforcing local membrane curvature and favoring tubes. This might in turn be sensed by additional Sar1 and Sec23–Sec24 subunits, which are efficiently recruited to the site of budding to further promote tubulation.
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Studies on Optical and Molecular Orientations of Nano Molecular Self assembly of Nematic Dimmer and Cholesteric Materials

Studies on Optical and Molecular Orientations of Nano Molecular Self assembly of Nematic Dimmer and Cholesteric Materials

Studies on Optical and Molecular Orientations of Nano Molecular Self-assembly of Nematic Dimmer and Cholesteric Materials Abstract: We report the results of our studies on optical and thermal properties of binary mixtures of nematic dimmer and cholesteric compounds, namely, cholestery lnonanoate (CN) and 1,7-bis-4-(4′-cyanobiphenyl) heptane (CB7CB).Different concentrations of the nematic dimmer show a very interesting spherulitic texture of cholesteric, induced chiral smectic and reentrantsmectic-A phase, sequentially when the specimen is cooled from its isotropic melt at different temperatures. The temperature variations of helical pitch and optical textures have also been discussed. Nano-aggregated size of the molecules has been confirmed by X-ray studies.
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