49 research outputs found
Bending Instability in Electrospinning of Nanofibers
A localized approximation was developed to calculate the bending electric force acting on an electrified polymer jet, which is a key element of the electrospinning process for manufacturing of nanofibers. Using this force, a far reaching analogy between the electrically driven bending instability and the aerodynamically driven instability was established. Continuous, quasi-one-dimensional, partial differential equations were derived and used to predict the growth rate of small electrically driven bending perturbations of a liquid column. A discretized form of these equations, that accounts for solvent evaporation and polymer solidification, was used to calculate the jet paths during the course of nonlinear bending instability leading to formation of large loops and resulting in nanofibers. The results of the calculations are compared to the experimental data acquired in the present work. Agreement of theory and experiment is discussed. (C) 2001 American Institute of Physics
Taylor Cone and Jetting from Liquid Droplets in Electrospinning of Nanofibers
Sessile and pendant droplets of polymer solutions acquire stable shapes when they are electrically charged by applying an electrical potential difference between the droplet and a flat plate, if the potential is not too large. These stable shapes result only from equilibrium of the electric forces and surface tension in the cases of inviscid, Newtonian, and viscoelastic liquids. In liquids with a nonrelaxing elastic force, that force also affects the shapes. It is widely assumed that when the critical potential phi (0*) has been reached and any further increase will destroy the equilibrium, the liquid body acquires a conical shape referred to as the Taylor cone, having a half angle of 49.3 degrees. In the present work we show that the Taylor cone corresponds essentially to a specific self-similar solution, whereas there exist nonself-similar solutions which do not tend toward a Taylor cone. Thus, the Taylor cone does not represent a unique critical shape: there exists another shape, which is not self-similar. The experiments of the present work demonstrate that the observed half angles are much closer to the new shape. In this article a theory of stable shapes of droplets affected by an electric field is proposed and compared with data acquired in our experimental work on electrospinning of nanofibers from polymer solutions and melts. (C) 2001 American Institute of Physics
Nanofiber fabrication in a temperature and humidity controlled environment for improved fibre consistency
To fabricate nanofibers with reproducible characteristics, an important demand for many applications, the effect of controlled atmospheric conditions on resulting electrospun cellulose acetate (CA) nanofibers was evaluated for temperature ranging 17.5 - 35°C and relative humidity ranging 20% - 70%. With the potential application of nanofibers in many industries, especially membrane and filter fabrication, their reproducible production must be established to ensure commercially viability.
Cellulose acetate (CA) solution (0.2 g/ml) in a solvent mixture of acetone/DMF/ethanol (2:2:1) was electrospun into nonwoven fibre mesh with the fibre diameter ranging from 150nm to 1µm.
The resulting nanofibers were observed and analyzed by scanning electron microscopy (SEM), showing a correlation of reducing average fibre diameter with increasing atmospheric temperature. A less pronounced correlation was seen with changes in relative humidity regarding fibre diameter, though it was shown that increased humidity reduced the effect of fibre beading yielding a more consistent, and therefore better quality of fibre fabrication.
Differential scanning calorimetry (DSC) studies observed lower melt enthalpies for finer CA nanofibers in the first heating cycle confirming the results gained from SEM analysis. From the conditions that were explored in this study the temperature and humidity that gave the most suitable fibre mats for a membrane purpose were 25.0°C and 50%RH due to the highest level of fibre diameter uniformity, the lowest level of beading while maintaining a low fibre diameter for increased surface area and increased pore size homogeneity. This study has highlighted the requirement to control the atmospheric conditions during the electrospinning process in order to fabricate reproducible fibre mats
Production of electrospun fast-dissolving drug delivery systems with therapeutic eutectic systems encapsulated in gelatin
Fast-dissolving delivery systems (FDDS) have received increasing attention in
the last years. Oral drug delivery is still the preferred route for the administration of
pharmaceutical ingredients. Nevertheless, some patients, e.g. children or elderly people, have
difficulties in swallowing solid tablets. In this work, gelatin membranes were produced by
electrospinning, containing an encapsulated therapeutic deep-eutectic solvent (THEDES)
composed by choline chloride/mandelic acid, in a 1:2 molar ratio. A gelatin solution (30% w/
v) with 2% (v/v) of THEDES was used to produce electrospun fibers and the experimental
parameters were optimized. Due to the high surface area of polymer fibers, this type of
construct has wide applicability. With no cytotoxicity effect, and showing a fast-dissolving
release profile in PBS, the gelatin fibers with encapsulated THEDES seem to have promising
applications in the development of new drug delivery systems.The research leading to these results has received
funding from Fundação para a Ciência e a Tecnologia
(FCT) through the projects ENIGMA - PTDC/EQU-EPR/
121491/2010 and UID/CTM/50025/2013, LAQVREQUIMTE:
UID/QUI/50006/2013, UCIBIO-REQUIMTE:
UID/Multi/04378/2013 (co-financed by the ERDF under the
PT2020 Partnership Agreement [POCI-01-0145-FEDER-
007728]) and by FEDER through the COMPETE 2020
Programme. Marta Martins is grateful for financial support
from FCT through the grant BIM/PTDC/EQUEPR/121491/
2010/ENIGMA. This research has also received funding from
the European Union Seventh Framework Programme (FP7/
2007-2013) under grant agreement number REGPOTCT2012-316331-POLARIS and from the project BNovel
smart and biomimetic materials for innovative regenerative medicine approaches^ RL1 - ABMR - NORTE-01-0124- FEDER-000016) co-financed by North Portugal Regional
Operational Programme (ON.2 – O Novo Norte), under the
National Strategic Reference Framework (NSRF), through
the European Regional Development Fund (ERDF).info:eu-repo/semantics/publishedVersio
Organic nanofibers embedding stimuli-responsive threaded molecular components
While most of the studies on molecular machines have been performed in
solution, interfacing these supramolecular systems with solid-state
nanostructures and materials is very important in view of their utilization in
sensing components working by chemical and photonic actuation. Host polymeric
materials, and particularly polymer nanofibers, enable the manipulation of the
functional molecules constituting molecular machines, and provide a way to
induce and control the supramolecular organization. Here, we present
electrospun nanocomposites embedding a self-assembling rotaxane-type system
that is responsive to both optical (UV-visible light) and chemical (acid/base)
stimuli. The system includes a molecular axle comprised of a dibenzylammonium
recognition site and two azobenzene end groups, and a dibenzo[24]crown-8
molecular ring. The dethreading and rethreading of the molecular components in
nanofibers induced by exposure to base and acid vapors, as well as the
photoisomerization of the azobenzene end groups, occur in a similar manner to
what observed in solution. Importantly, however, the nanoscale mechanical
function following external chemical stimuli induces a measurable variation of
the macroscopic mechanical properties of nanofibers aligned in arrays, whose
Young's modulus is significantly enhanced upon dethreading of the axles from
the rings. These composite nanosystems show therefore great potential for
application in chemical sensors, photonic actuators and environmentally
responsive materials.Comment: 39 pages, 16 figure