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Crystalline Order (crystalline + order)

Distribution by Scientific Domains

Polymers and Materials Science	88%

Selected Abstracts

Thiophene,Benzothiadiazole Co-Oligomers: Synthesis, Optoelectronic Properties, Electrical Characterization, and Thin-Film Patterning

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2010
Manuela Melucci
Abstract Newly synthesized thiophene (T) and benzothiadiazole (B) co-oligomers of different size, alternation motifs, and alkyl substitution types are reported. Combined spectroscopic data, electrochemical analysis, and theoretical calculations show that the insertion of a single electron-deficient B unit into the aromatic backbone strongly affects the LUMO energy level. The insertion of additional B units has only a minor effect on the electronic properties. Cast films of oligomers with two alternated B rings (B,T,B inner core) display crystalline order. Bottom-contact FETs based on films cast on bare SiO2 show hole-charge mobilities of 1,×,10,3,5,×,10,3,cm2 V,1s,1 and Ion/Ioff ratios of 105,106. Solution-cast films of cyclohexyl-substituted compounds are amorphous and do not show FET behavior. However, the lack of order observed in these films can be overcome by nanorubbing and unconventional wet lithography, which allow for fine control of structural order in thin deposits. [source]

Self-Assembly of a Donor-Acceptor Dyad Across Multiple Length Scales: Functional Architectures for Organic Electronics

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2009
Jeffrey M. Mativetsky
Abstract Molecular dyads based on polycyclic electron donor (D) and electron acceptor (A) units represent suitable building blocks for forming highly ordered, solution-processable, nanosegregated D-A domains for potential use in (opto)electronic applications. A new dyad, based on alkyl substituted hexa- peri -hexabenzocoronene (HBC) and perylene monoimide (PMI) separated by an ethinylene linker, is shown to have a high tendency to self-assemble into ordered supramolecular arrangements at multiple length scales: macroscopic extruded filaments display long-range crystalline order, nanofiber networks are produced by simple spin-coating, and monolayers with a lamellar packing are formed by physisorption at the solution-HOPG interface. Moreover, highly uniform mesoscopic ribbons bearing atomically flat facets and steps with single-molecule heights self-assemble upon solvent-vapor annealing. Electrical measurements of HBC-PMI films and mesoscopic ribbons in a transistor configuration exhibit ambipolar transport with well balanced p- and n-type mobilities. Owing to the increased level of order at the supramolecular level, devices based on ribbons show mobility increases of more than one order of magnitude. [source]

Probing the Anisotropic Field-Effect Mobility of Solution-Deposited Dicyclohexyl-,-quaterthiophene Single Crystals,

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2007

Abstract Measuring the anisotropy of the field-effect mobility provides insight into the correlation between molecular packing and charge transport in organic semiconductor materials. Single-crystal field-effect transistors are ideal tools to study intrinsic charge transport because of their high crystalline order and chemical purity. The anisotropy of the field effect mobility in organic single crystals has previously been studied by lamination of macroscopically large single crystals onto device substrates. Here, a technique is presented that allows probing of the mobility anisotropy even though only small crystals are available. Crystals of a soluble oligothiophene derivative are grown in bromobenzene and drop-cast onto substrates containing arrays of bottom-contact gold electrodes. Mobility anisotropy curves are recorded by measuring numerous single crystal transistor devices. Surprisingly, two mobility maxima occur at azimuths corresponding to both axes of the rectangular cyclohexyl-substituted quaterthiophene (CH4T) in-plane unit cell, in contrast to the expected tensorial behavior of the field effect mobility. [source]

Thermodynamic Model of Structure and Shape in Rigid Polymer-Laden Membranes

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 2-3 2010
Yogesh K. Murugesan
Abstract A mechanical formulation for multi-component rigid-rod-like polymer-laden membranes is integrated with the Gibbs-Duhem equation to describe the role of temperature and adsorption on membrane shape and on the nematic liquid crystal order of the embedded polymer. The rigid-rod polymer model incorporates curvo-philic effects promoting polymer re-orientation along curvature directions and curvo-phobic effects promoting polymer re-orientation away from curvature directions, while the membrane curvature energy is described with the Helfrich formulation. The couplings between thermodynamical variables, polymer liquid crystalline order, and membrane curvature are demonstrated and characterized. The theory provides a road-map to manipulate shape and structure in membranes containing fibers, proteins, and rod-like polymers. [source]

Interfacial Thermodynamics of Polymeric Mesophases

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2004
Alejandro D. Rey
Abstract Summary: A complete mechanical-thermodynamical formulation for multicomponent nematic polymer-isotropic fluid interfaces is derived, validated, and used to derive the structure and shape equations for these soft anisotropic polymer interfaces. The fundamental role of liquid crystalline order and long range effects in coupling bulk and interfacial effects, and in coupling thermodynamical/liquid crystalline order/geometrical variables is demonstrated, discussed, and validated. The Gibbs-Duhem nemato-thermodynamics equation emerges from an interfacial tension ,,=,,(,, ,, Q, ,sQ, k) that depends on temperature (,), chemical potential (,), nematic tensor order parameter Q, surface gradients of Q, and geometry k, and leads to new couplings in these enhanced phase spaces. The role of entropy and adsorption, and long range effects on interfacial shape and structure selection is revealed. For flat interfaces the preferred structure emerges from a competition between energy, entropy, and adsorption. [source]

Enhanced Crystallinity of PTFE by Ion Irradiation in a Dense Plasma Focus

PLASMA PROCESSES AND POLYMERS, Issue 2 2007
Mehboob Sadiq
Abstract Nitrogen-ion beam pulses emitted from a low-energy (1.45 kJ) Mather-type plasma focus device are used for the surface modification of PTFE polymer specimens. The specimens, placed at a fixed position, are implanted using different number of pulses. Raman spectroscopy and XRD are employed to probe the structural changes incurred during the ion implantation. Both techniques indicate that the crystalline order in the specimens increases with increasing the irradiation dose. The crystallinity degree of the irradiated specimens, as measured from the XRD data, is found to enhance monotonically from 40% to about 55%. Possible crystallinity enhancement mechanism of irradiated PTFE specimens via chain scission is discussed. [source]

Synthesis and properties of magnetite/poly (aniline-co-8-amino-2-naphthalenesulfonic acid) (SPAN) nanocomposites

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1 2007
Kakarla Raghava Reddy
Abstract Composites were prepared by incorporating magnetite (Fe3O4) nanoparticles into the matrix of a sulfonated polyaniline (SPAN) [poly(aniline-co-8-amino-2-naphthalenesulfonic acid) PANSA] through chemical oxidative polymerization of a mixture of aniline and 8-amino-2-naphthalenesulfonic acid in the presence of magnetite nanoparticles. The composite, magnetite/SPAN(PANSA) was characterized by means of transmission electron microscopy (TEM), X-ray diffraction (XRD), elemental analysis (EA), Fourier transform infrared (FT-IR) spectra, UV-vis spectroscopy, thermogravimetric analysis (TGA), conductivity and magnetic properties measurements. TEM image shows that magnetite nanoparticles were finely distributed into the SPAN matrix. XRD pattern of the nanocomposite reveals the presence of additional crystalline order through the appearance of a sharp peak at ,43° and 71°. Conductivity of the nanocomposite (0.23,S/cm) is much higher than pristine copolymer (1.97,×,10,2,S/cm). The results of FT-IR and UV-visible spectroscopy reveal the presence of molecular level interactions between SO groups in SPAN and magnetite nanoparticles in the composite. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Nature of water molecules in hydrogels based on a liquid crystalline cellulose derivative

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11-12 2003
P. Wojciechowski
Abstract The status and nature of water molecules in hydrogels with a liquid crystalline organization of the polymer network based on a biopolymer were investigated. Liquid crystalline (LC) hydrogels were obtained in situ by the photopolymerization of acrylic acid into the lyotropic liquid crystalline phase of (2-hydroxypropyl)cellulose in a solvent mixture of water and acrylic acid. The photopolymerization of acrylic acid in the lyotropic liquid crystalline phase at room temperature gives a hydrogel in which liquid crystalline order and water are retained. The liquid crystalline hydrogel contains water, which originates from the composition of the lyotropic liquid crystalline phase, and may also contain water after immersion in liquid water. The water molecule characteristics were examined by means of differential scanning calorimetry, dielectric relaxation spectroscopy, and differential scanning calorimetry coupled with thermo-optical measurements. The swelling data were obtained by using a weighing method. The investigations reveal the different nature of the two above-mentioned water types. For the water from the composition of the lyotropic liquid crystalline phase, the phase transitions,typical for the bulk water,were not observed, in contract to the water after swelling of the liquid crystalline hydrogel in the liquid water. The results of the measurements suggest that water, which comes from the composition of the lyotropic liquid crystalline phase, forms,together with a polymer network,a microstructure, stabilized by this water. The water, after swelling of the LC hydrogel in the liquid water, is separated in the pores of the hydrogel and exhibits the phase transitions of the bulk water. Copyright © 2003 John Wiley & Sons, Ltd. [source]

A general approach for determining the diffraction contrast factor of straight-line dislocations

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2009
Jorge Martinez-Garcia
Dislocations alter perfect crystalline order and produce anisotropic broadening of the X-ray diffraction profiles, which is described by the dislocation contrast factor. Owing to the lack of suitable mathematical tools to deal with dislocations in crystals of any symmetry, contrast factors are so far only known for a few slip systems in high-symmetry phases and little detail is given in the literature on the calculation procedure. In the present paper a general approach is presented for the calculation of contrast factors for any dislocation configuration and any lattice symmetry. The new procedure is illustrated with practical examples of hexagonal metals and some low-symmetry mineral phases. [source]