339 research outputs found
Polymer nanofibers as novel light-emitting sources and lasing material
Polymer micro- and nano-fibers, made of organic light-emitting materials with
optical gain, show interesting lasing properties. Fibers with diameters from
few tens of nm to few microns can be fabricated by electrospinning, a method
based on electrostatic fields applied to a polymer solution. The morphology and
emission properties of these fibers, composed of optically inert polymers
embedding laser dyes, are characterized by scanning electron and fluorescence
microscopy, and lasing is observed under optical pumping for fluences of the
order of 10^2 microJ cm^-2. In addition, light-emitting fibers can be
electrospun by conjugated polymers, their blends, and other active organics,
and can be exploited in a range of photonic and electronic devices. In
particular, waveguiding of light is observed and characterized, showing optical
loss coefficient in the range of 10^2-10^3 cm^-1. The reduced size of these
novel laser systems, combined with the possibility of achieving wavelength
tunability through transistor or other electrode-based architectures embedding
non-linear molecular layers, and with their peculiar mechanical robustness,
open interesting perspectives for realizing miniaturized laser sources to
integrate on-chip optical sensors and photonic circuits.Comment: 7 pages, 3 figures, 27 references. Invited contribution. Copyright
(2013) Society of Photo Optical Instrumentation Engineers. One print or
electronic copy may be made for personal use only. Systematic reproduction
and distribution, duplication of any material in this paper for a fee or for
commercial purposes, or modification of the content of the paper are
prohibite
Effect of finite terms on the truncation error of Mie series
The finite sum of the squares of the Mie coefficients is very useful for
addressing problems of classical light scattering. An approximate formula
available in the literature, and still in use today, has been developed to
determine a priori the number of the most significant terms needed to evaluate
the scattering cross section. Here we obtain an improved formula, which
includes the number of terms needed for determining the scattering cross
section within a prescribed relative error. This is accomplished using extended
precision computation, for a wide range of commonly used size parameters and
indexes of refraction. The revised formula for the finite number of terms can
be a promising and valuable approach for efficient modeling light scattering
phenomena.Comment: 3 pages, 3 figure
Effects of Nanoparticles on the Dynamic Morphology of Electrified Jets
We investigate the effects of nanoparticles on the onset of varicose and
whipping instabilities in the dynamics of electrified jets. In particular, we
show that the non-linear interplay between the mass of the nanoparticles and
electrostatic instabilities, gives rise to qualitative changes of the dynamic
morphology of the jet, which in turn, drastically affect the final deposition
pattern in electrospinning experiments. It is also shown that even a tiny
amount of excess mass, of the order of a few percent, may more than double the
radius of the electrospun fiber, with substantial implications for the design
of experiments involving electrified jets as well as spun organic fibers.Comment: 8 pages, 7 figures, 1 tabl
Non-linear Langevin model for the early-stage dynamics of electrospinning jets
We present a non-linear Langevin model to investigate the early-stage
dynamics of electrified polymer jets in electrospinning experiments. In
particular, we study the effects of air drag force on the uniaxial elongation
of the charged jet, right after ejection from the nozzle. Numerical simulations
show that the elongation of the jet filament close to the injection point is
significantly affected by the non-linear drag exerted by the surrounding air.
These result provide useful insights for the optimal design of current and
future electrospinning experiments.Comment: 11 pages, 6 figures, 1 table. arXiv admin note: text overlap with
arXiv:1503.0469
Computational homogenization of fibrous piezoelectric materials
Flexible piezoelectric devices made of polymeric materials are widely used
for micro- and nano-electro-mechanical systems. In particular, numerous recent
applications concern energy harvesting. Due to the importance of computational
modeling to understand the influence that microscale geometry and constitutive
variables exert on the macroscopic behavior, a numerical approach is developed
here for multiscale and multiphysics modeling of thin piezoelectric sheets made
of aligned arrays of polymeric nanofibers, manufactured by electrospinning. At
the microscale, the representative volume element consists in piezoelectric
polymeric nanofibers, assumed to feature a piezoelastic behavior and subjected
to electromechanical contact constraints. The latter are incorporated into the
virtual work equations by formulating suitable electric, mechanical and
coupling potentials and the constraints are enforced by using the penalty
method. From the solution of the micro-scale boundary value problem, a suitable
scale transition procedure leads to identifying the performance of a
macroscopic thin piezoelectric shell element.Comment: 22 pages, 13 figure
A multiscale-multiphysics strategy for numerical modeling of thin piezoelectric sheets
Flexible piezoelectric devices made of polymeric materials are widely used
for micro- and nano-electro-mechanical systems. In particular, numerous recent
applications concern energy harvesting. Due to the importance of computational
modeling to understand the influence that microscale geometry and constitutive
variables exert on the macroscopic behavior, a numerical approach is developed
here for multiscale and multiphysics modeling of piezoelectric materials made
of aligned arrays of polymeric nanofibers. At the microscale, the
representative volume element consists in piezoelectric polymeric nanofibers,
assumed to feature a linear piezoelastic constitutive behavior and subjected to
electromechanical contact constraints using the penalty method. To avoid the
drawbacks associated with the non-smooth discretization of the master surface,
a contact smoothing approach based on B\'ezier patches is extended to the
multiphysics framework providing an improved continuity of the
parameterization. The contact element contributions to the virtual work
equations are included through suitable electric, mechanical and coupling
potentials. From the solution of the micro-scale boundary value problem, a
suitable scale transition procedure leads to the formulation of a macroscopic
thin piezoelectric shell element.Comment: 11 pages, 6 pages, 21 reference
Different regimes of the uniaxial elongation of electrically charged viscoelastic jets due to dissipative air drag
We investigate the effects of dissipative air drag on the dynamics of
electrified jets in the initial stage of the electrospinning process. The main
idea is to use a Brownian noise to model air drag effects on the uniaxial
elongation of the jets. The developed numerical model is used to probe the
dynamics of electrified polymer jets at different conditions of air drag force,
showing that the dynamics of the charged jet is strongly biased by the presence
of air drag forces. This study provides prospective beneficial implications for
improving forthcoming electrospinning experiments.Comment: 12 pages, 6 figure
Effects of non-linear rheology on the electrospinning process: a model study
We develop an analytical bead-spring model to investigate the role of
non-linear rheology on the dynamics of electrified jets in the early stage of
the electrospinning process. Qualitative arguments, parameter studies as well
as numerical simulations, show that the elongation of the charged jet filament
is significantly reduced in the presence of a non-zero yield stress. This may
have beneficial implications for the optimal design of future electrospinning
experiments
JETSPIN: a specific-purpose open-source software for simulations of nanofiber electrospinning
We present the open-source computer program JETSPIN, specifically designed to
simulate the electrospinning process of nanofibers. Its capabilities are shown
with proper reference to the underlying model, as well as a description of the
relevant input variables and associated test-case simulations. The various
interactions included in the electrospinning model implemented in JETSPIN are
discussed in detail. The code is designed to exploit different computational
architectures, from single to parallel processor workstations. This paper
provides an overview of JETSPIN, focusing primarily on its structure, parallel
implementations, functionality, performance, and availability.Comment: 22 pages, 11 figures. arXiv admin note: substantial text overlap with
arXiv:1507.0701
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