78 research outputs found
Effect of Volume and Temperature on the Global and Segmental Dynamics in Polypropylene Glycol and 1,4-polyisoprene
Published dielectric relaxation measurements on polypropylene glycol and
1,4-polyisoprene are analyzed to determine the relative effect that thermal
energy and volume have on the temperature dependence of the normal mode
relaxation times, and compare this to their effect on the temperature
dependence of the local segmental relaxation times. We find that for both
polymers at temperatures well above Tg, both relaxation modes are governed more
by thermal energy than by volume, although the latter's contribution is not
negligible. Such a result is consistent with an assumption underlying models
for polymer viscoelasticity, such as the Rouse and tube models, that the
friction coefficient governing motions over large length scales can be
identified with the local segmental friction coefficient. We also show that
relaxation data for both the segmental and the normal mode superimpose, when
expressed as a function of the product of the temperature and the volume, the
latter raised to a power. This scaling form arises from an inverse power form
for the intermolecular potential. The value of the exponent on the volume for
these two polymers indicates a relatively "soft" potential.Comment: 15 pages, 3 figure
Dielectric relaxation and anhydrous proton conduction in [C2H5NH3][Na0.5Fe0.5(HCOO)3] metal-organic frameworks
Metal–organic frameworks (MOFs), in which metal clusters are coupled by organic moieties, exhibit inherent porosity and crystallinity. Although these systems have been examined for vast potential applications, the elementary proton conduction in anhydrous MOFs still remains elusive. One of the approaches to deal with this problem is the utilization of protic organic molecules, to be accommodated in the porous framework. In this work we report the temperature-dependent crystal structure and proton
conduction in [C2H5NH3][Na0.5Fe0.5(HCOO)3] metal–organic frameworks using X-ray diffraction and broadband dielectric spectroscopic techniques. The detailed analysis of the crystal structure reveals disorder of the terminal ethylene groups in the polar phase (space group Pn). The structural phase transition from Pn to P21/n at T ≈ 363 K involves the distortion of the metal formate framework and ordering of EtA+ cations due to the reduction of the cell volume. The dielectric data have been presented in the
dynamic window of permittivity formalism to understand the ferroelectric phase transition. The relaxation times have been estimated from the Kramers–Kronig transformation of the dielectric permittivity. A Grotthuss type mechanism of the proton conduction is possible at low temperatures with the activation energy of 0.23 eV. This type of experimental observation is expected to provide new prospective on the fundamental aspect of elementary proton transfer in anhydrous MOFs
Data-driven modeling of the bicalutamide dissolution from powder systems
Low solubility of active pharmaceutical compounds (APIs) remains an
important challenge in dosage form development process. In the manuscript, empirical
models were developed and analyzed in order to predict dissolution of bicalutamide (BCL)
from solid dispersion with various carriers. BCL was chosen as an example of a poor watersoluble
API. Two separate datasets were created: one from literature data and another based
on in-house experimental data. Computational experiments were conducted using artificial
intelligence tools based on machine learning (AI/ML) with a plethora of techniques including
artificial neural networks, decision trees, rule-based systems, and evolutionary computations.
The latter resulting in classical mathematical equations provided models characterized by the
lowest prediction error. In-house data turned out to be more homogeneous, as well as
formulations were more extensively characterized than literature-based data. Thus, in-house
data resulted in better models than literature-based data set. Among the other covariates, the
best model uses for prediction of BCL dissolution profile the transmittance from IR spectrum
at 1260 cm−1 wavenumber. Ab initio modeling–based in silico simulations were conducted to
reveal potential BCL–excipients interaction. All crucial variables were selected automatically
by AI/ML tools and resulted in reasonably simple and yet predictive models suitable for
application in Quality by Design (QbD) approaches. Presented data-driven model
development using AI/ML could be useful in various problems in the field of pharmaceutical
technology, resulting in both predictive and investigational tools revealing new knowledge
Glass transition of an epoxy resin induced by temperature, pressure and chemical conversion: a configurational entropy rationale
A comparative study is reported on the dynamics of a glass-forming epoxy
resin when the glass transition is approached through different paths: cooling,
compression, and polymerization. In particular, the influence of temperature,
pressure and chemical conversion on the dynamics has been investigated by
dielectric spectroscopy. Deep similarities are found in dynamic properties. A
unified reading of our experimental results for the structural relaxation time
is given in the framework of the Adam-Gibbs theory. The quantitative agreement
with the experimental data is remarkable, joined with physical values of the
fitting parameters. In particular, the fitting function of the isothermal
tau(P) data gives a well reasonable prediction for the molar thermal expansion
of the neat system, and the fitting function of the isobaric-isothermal tau(C)
data under step- polymerization conforms to the prediction of diverging tau at
complete conversion of the system.Comment: 16 pages, 8 figures, from the talk given at the 4th International
Discussion Meeting on Relaxations in Complex Systems (IDMRCS), Hersonissos,
Helaklion, Crete (Greece), 17-23 June 200
Revealing fast proton transport in condensed matter by means of density scaling concept
Herein, we investigate the charge transport and structural dynamics in
the supercooled and glassy state of protic ionic material with an efficient interionic
Grotthuss mechanism. We found that superprotonic properties of studied acebutolol
hydrochloride (ACB-HCl) depend on thermodynamic conditions with the most
favorable regions being close to the glass-transition temperature (Tg) and glasstransition
pressure (Pg). To quantify the contribution of fast proton hopping to overall
charge transport over a broad T−P space, we employed the density scaling concept,
one of the most important experimental findings in the field of condensed matter
physics. We found that isothermal and isobaric dc-conductivity (σdc) and dynamic
light scattering (τα) data of ACB-HCl plotted as a function of (TVγ)−1 satisfy the
thermodynamic scaling criterion with the ratio γσ/γα appearing as a new measure of
fast charge transport in protic ionic glass-formers in the T−P plane. Such a universal
factor becomes an alternative to the well-known Walden rule being limited to ambient
pressure conditions
Invariance of the Local Segmental Relaxation Dispersion in Polycyclohexylmethacrylate / Poly-alpha-Methylstyrene Blends
Dielectric spectroscopy was carried out on polycyclohexylmethacrylate (PCHMA)
and its blend with poly-alpha-methylstyrene (PaMS) as a function of temperature
and pressure. When measured at conditions whereby the local segmental
relaxation time for the PCHMA was constant, the dispersion in the loss spectra
had a fixed shape; that is, the relaxation time determines the breadth of the
relaxation time distribution, independently of T and P. This result is known
for neat materials and could be observed for the blend herein due to the
nonpolar character of the PaMS and the degree of thermodynamic miscibility of
the blend.Comment: 13 pages 5 figure
Post-tracheostomy complications: respiratory failure caused by authologic foreign body – case report
Tracheostomy is performed frequently as a palliative treatment in patients with end-stage
respiratory failure (RF). However, in patients requiring prolonged mechanical ventilation it may be difficult to recognize and can often lead to life-threatening RF. We present two cases of acute-on-chronic respiratory failure (ACRF) occurring in patients who had undergone tracheostomy [one with percutaneous dilatational
tracheostomy (PDT) and the second with surgical tracheostomy (ST)]. The first case was admitted due to
ACRF several months after previous successful decannulation and the second case after failure of several
attempts of weaning from tracheal cannula. In both cases, noninvasive mechanical ventilation assisted flexible
bronchoscopy (NIV-FB) was able to identify and solve the tracheal stenosis secondary to stiff bananashaped
whitish foreign bodies. Histology sampling and genetic testing confirmed autologous foreign body
formation—tracheal cartilage calcification. NIV-FB was found to be safe and effective in both diagnosis
and treatment of the tracheal stenosis. Life-threatening RF connected with tracheal stenosis may be caused
by rupture of tracheal cartilage ossification in patients with a history of ST and PDT. Bronchofiberoscopy
performed with NIV will be a useful procedure to evaluate and treat the respiratory tract in patients with RF
with suspected tracheal stenosis
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