187 research outputs found
Molecular mechanisms driving the microgels behaviour: a Raman spectroscopy and Dynamic Light Scattering study
Responsive microgels based on poly(N-isopropylacrylamide) (PNIPAM) exhibit
peculiar behaviours due to the competition between the hydrophilic and
hydrophobic interactions of the constituent networks. The interpenetration of
poly-acrilic acid (PAAc), a pH-sensitive polymer, within the PNIPAM network, to
form Interpenetrated Polymer Network (IPN) microgels, affects this delicate
balance and the typical Volume-Phase Transition (VPT) leading to complex
behaviours whose molecular nature is still completely unexplored. Here we
investigate the molecular mechanism driving the VPT and its influence on
particle aggregation for PNIPAM/PAAc IPN microgels by the joint use of Dynamic
Light Scattering and Raman Spectroscopy. Our results highlight that PNIPAM
hydrophobicity is enhanced by the interpenetration of PAAc promoting
interparticle interactions, a crossover concentration is found above which
aggregation phenomena become relevant. Moreover we find that, at variance with
PNIPAM, for IPN microgels a double-step molecular mechanisms occurs upon
crossing the VPT, the first involving the coil-to-globule transition typical of
PNIPAM and the latter associated to PAAc steric hindrance.Comment: preprint versio
Study of network composition in interpenetrating polymer networks of poly(N isopropylacrylamide) microgels:the role of poly(acrylic acid)
Hypothesis: The peculiar swelling behaviour of poly(N-isopropylacrylamide)
(PNIPAM)-based responsive microgels provides the possibility to tune both
softness and volume fraction with temperature, making these systems of great
interest for technological applications and theoretical implications. Their
intriguing phase diagram can be even more complex if poly(acrylic acid) (PAAc)
is interpenetrated within PNIPAM network to form Interpenetrating Polymer
Network (IPN) microgels that exhibit an additional pH-sensitivity. The effect
of the PAAc/PNIPAM polymeric ratio on both swelling capability and dynamics is
still matter of investigation. Experiments: Here we investigate the role of
PAAc in the behaviour of IPN microgels across the volume phase transition
through dynamic light scattering (DLS), transmission electron microscopy (TEM)
and electrophoretic measurements as a function of microgel concentration and
pH. Findings: Our results highlight that aggregation is favored at increasing
weight concentration, PAAc content and pH and that a crossover PAAc content
C*_{PAAc} exists above which the ionic charges on the microgel become relevant.
Moreover we show that the softness of IPN microgels can be tuned ad hoc by
changing the PAAc/PNIPAM ratio. These findings provide new insights into the
possibility to control experimentally aggregation properties, charge and
softness of IPN microgels by varying PAAc content.Comment: preprint versio
design and evaluation of electric solutions for public transport
Abstract This study deals with the design and the evaluation of technological solutions for the electrification of public transport in urban areas. A Decision Support System (DSS) developed by ENEA † within the Research program on Electric System (RSE) has been adopted in order to verify the technical feasibility of several electric architectures of single bus lines and compare the investment and management costs, as well as the external costs due to vehicle emissions and noises, of the feasible solutions with respect to the conventional alternatives (Compressed Natural Gas, CNG, and diesel). The DSS has been applied to several bus lines located in the south-west area of the city of Rome, Italy, and covering different types of service: peripheral lines, main lines connecting suburbs with the city center and secondary lines going to the main metro stations. Input data for the DSS derived both by simulation and by open database available from the public transport operator in Rome (ATAC). Results show that a suitable electric architecture can be found for each of these lines with lower or comparable total costs with respect to the traditional alternatives. Finally, a sensitivity analysis has been performed considering several scenarios in terms of discount rate of recharge stations and batteries, battery's duration, price of conventional fuels
Glass and Jamming Rheology in Soft Particles Made of PNIPAM and Polyacrylic Acid
The phase behaviour of soft colloids has attracted great attention due to the large variety of new phenomenologies emerging from their ability to pack at very high volume fractions. Here we report rheological measurements on interpenetrated polymer network microgels composed of poly(N-isopropylacrylamide) (PNIPAM) and polyacrylic acid (PAAc) at fixed PAAc content as a function of weight concentration. We found three different rheological regimes characteristic of three different states: a Newtonian shear-thinning fluid, an attractive glass characterized by a yield stress, and a jamming state. We discuss the possible molecular mechanisms driving the formation of these states
Testing for state dependence in binary panel data with individual covariates
We propose a test for state dependence in binary panel data under the dynamic logit model with individual covariates. For this aim, we rely on a quadratic exponential model in which the association between the response variables is accounted for in a different way with respect to more standard formulations. The level of association is measured by a single parameter that may be estimated by a conditional maximum likelihood approach. Under the dynamic logit model, the conditional estimator of this parameter converges to zero when the hypothesis of absence of state dependence is true. This allows us to implement a Wald test for this hypothesis which may be very simply performed and attains the nominal significance level under any structure of the individual covariates. Through an extensive
simulation study, we find that our test has good finite sample properties and it is more robust to the presence of (autocorrelated) covariates in the model specification in comparison with other existing testing procedures for state dependence. The test is illustrated by an application based on data coming from the Panel Study of Income Dynamics
Microglia-derived microvesicles affect microglia phenotype in glioma
Extracellular-released vesicles (EVs), such as microvesicles (MV) and exosomes (Exo)
provide a new type of inter-cellular communication, directly transferring a ready to use
box of information, consisting of proteins, lipids and nucleic acids. In the nervous
system, EVs participate to neuron-glial cross-talk, a bidirectional communication
important to preserve brain homeostasis and, when dysfunctional, involved in several
CNS diseases. We investigated whether microglia-derived EVs could be used to transfer
a protective phenotype to dysfunctional microglia in the context of a brain tumor.
When MV, isolated from microglia stimulated with LPS/IFNg were brain injected in
glioma-bearing mice, we observed a phenotype switch of tumor associated myeloid
cells (TAMs) and a reduction of tumor size. Our findings indicate that the MV cargo,
which contains upregulated transcripts for several inflammation-related genes, can
transfer information in the brain of glioma bearing mice modifying microglial gene
expression, reducing neuronal death and glioma invasion, thus promoting the recovery
of brain homeostasis
Local structure of temperature and pH-sensitive colloidal microgels
The temperature dependence of the local intra-particle structure of colloidal microgel particles, composed of interpenetrated polymer networks, has been investigated by small-angle neutron scattering at different pH and concentrations, in the range (299÷315) K, where a volume phase transition from a swollen to a shrunken state takes place. Data are well described by a theoretical model that takes into account the presence of both interpenetrated polymer networks and cross-linkers. Two different behaviors are found across the volume phase transition. At neutral pH and T 307 K, a sharp change of the local structure from a water rich open inhomogeneous interpenetrated polymer network to a homogeneous porous solid-like structure after expelling water is observed. Differently, at acidic pH, the local structure changes almost continuously. These findings demonstrate that a fine control of the pH of the system allows to tune the sharpness of the volume-phase transition
Confocal fluorescence microscopy and confocal raman microspectroscopy of X-ray irradiated LIF crystals
Radiation-induced color centers locally produced in lithium fluoride (LiF) are successfully used for radiation detectors. LiF detectors for extreme ultraviolet radiation, soft and hard X-rays, based on photoluminescence from aggregate electronic defects, are currently under development for imaging applications with laboratory radiation sources, as well as large-scale facilities. Among the peculiarities of LiF-based detectors, noteworthy ones are their very high intrinsic spatial resolution across a large field of view, wide dynamic range, and versatility. LiF crystals irradiated with a monochromatic 8 keV X-ray beam at KIT synchrotron light source (Karlsruhe, Germany) and with the broadband white beam spectrum of the synchrotron bending magnet have been investigated by optical spectroscopy, laser scanning confocal microscopy in fluorescence mode, and confocal Raman micro-spectroscopy. The 3D reconstruction of the distributions of the color centers induced by the X-rays has been performed with both confocal techniques. The combination of the LiF crystal capability to register volumetric X-ray mapping with the optical sectioning operations of the confocal techniques has allowed performing 3D reconstructions of the X-ray colored volumes and it could provide advanced tools for 3D X-ray detection
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