29 research outputs found
Combination of (M)DSC and surface analysis to study the phase behaviour and drug distribution of ternary solid dispersions
Purpose: Miscibility of the different compounds that make up a solid dispersion based formulation play a crucial role in the drug release profile and physical stability of the solid dispersion as it defines the phase behaviour of the dispersion. The standard technique to obtain information on phase behaviour of a sample is (modulated) differential scanning calorimetry ((M)DSC). However, for ternary mixtures (M)DSC alone is not sufficient to characterize their phase behaviour and to gain insight into the distribution of the active pharmaceutical ingredient (API) in a two-phased polymeric matrix.
Methods: MDSC was combined with complementary surface analysis techniques, specifically time-of-flight secondary ion mass spectrometry (ToF-SIMS) and atomic force microscopy (AFM). Three spray-dried model formulations with varying API/PLGA/PVP ratios were analyzed.
Results: The distribution of the API in the ternary solid dispersions depended on formulation parameters. The extent of API surface coverage and therefore the distribution of the API over both polymeric phases differed significantly for the three formulations.
Conclusions: Combining (M)DSC and surface analysis rendered additional insights in the composition of mixed phases in complex systems, like ternary solid dispersions
Tuning the energetics and tailoring the optical properties of silver clusters confined in zeolites
The integration of metal atoms and clusters in well-defined dielectric cavities is a powerful strategy to impart new properties to them that depend on the size and geometry of the confined space as well as on metal-host electrostatic interactions. Here, we unravel the dependence of the electronic properties of metal clusters on space confinement by studying the ionization potential of silver clusters embedded in four different zeolite environments over a range of silver concentrations. Extensive characterization reveals a strong influence of silver loading and host environment on the cluster ionization potential, which is also correlated to the cluster's optical and structural properties. Through fine-tuning of the zeolite host environment, we demonstrate photoluminescence quantum yields approaching unity. This work extends our understanding of structure property relationships of small metal clusters and applies this understanding to develop highly photoluminescent materials with potential applications in optoelectronics and bioimaging
Chitosan–Starch–Keratin composites: Improving thermo-mechanical and degradation properties through chemical modification
The lysozyme test shows an improved in the degradability rate, the weight loss of the films at 21 days is reduced from 73 % for chitosan-starch matrix up to 16 % for the composites with 5wt% of quill; but all films show a biodegradable character depending on keratin type and chemical modification. The outstanding properties related to the addition of treated keratin materials show that these natural composites are a remarkable alternative to potentiat-ing chitosan–starch films with sustainable featuresChitosan–starch polymers are reinforced with different keratin materials obtained from chicken feather. Keratin materials are treated with sodium hydroxide; the modified surfaces are rougher in comparison with untreated surfaces, observed by Scanning Electron Microscopy. The results obtained by Differential Scanning Calorimetry show an increase in the endothermic peak related to water evaporation of the films from 92 °C (matrix) up to 102–114 °C (reinforced composites). Glass transition temperature increases from 126 °C in the polymer matrix up to 170–200 °C for the composites. Additionally, the storage modulus in the composites is enhanced up to 1614 % for the composites with modified ground quill, 2522 % for composites with modified long fiber and 3206 % for the composites with modified short fiber. The lysozyme test shows an improved in the degradability rate, the weight loss of the films at 21 days is reduced from 73 % for chitosan-starch matrix up to 16 % for the composites with 5wt% of quill; but all films show a biodegradable character depending on keratin type and chemical modification. The outstanding properties related to the addition of treated keratin materials show that these natural composites are a remarkable alternative to potentiat-ing chitosan–starch films with sustainable featuresUniversidad Autónoma del Estado de México Tecnológico Nacional de México, Instituto Tecnológico de Querétaro Universidad Nacional Autónoma de México Tecnológico Nacional de México, Instituto Tecnológico de Celaya Universidad Autónoma de Cd. Juáre
Interplay of surface and confinement effects on the molecular relaxation dynamics of nanoconfined poly(methyl methacrylate) chains
The thermally stimulated current (TSC) signatures of the primary (alpha)
transition and its precursor, the Johary-Goldstein (beta) relaxation,
are used to probe effects of nanoconfinement on the dielectric
relaxation dynamics of poly(methyl methacrylate) (PMMA) radically
polymerised in situ 50 Angstrom mean pore size silica-gel.
Nanoconfinement leads to a broadened and low-temperature-shifted beta
band (peaking at T-beta, with DeltaT(beta) = T-beta(conf). -
T-beta(bulk) = -15 degreesC for a heating rate of 5 deg/min), signifying
the occurrence of faster relaxing moieties compared to the bulk-like
PMMA film. Furthermore, both TSCs and differential scanning calorimetry
(DSC) estimate a rise of the glass transition temperature for the
confined phase (DeltaT(alpha) proportional to DeltaT(g)(DSC) = + 13
degreesC) and an increased width for the corresponding transition
signals, relative to the signals in the bulk. Simple free-volume and
entropy models seem inadequate to provide a collective description of
the above perturbations. The observation of a spatial heterogeneity
regarding the relaxation dynamics is discussed in terms of the presence
of a motional gradient, with less mobile segments near the interface and
more mobile segments in the core, and the interplay of adsorption (e.g.,
strong physical interactions that slow down molecular mobilities) and
confinement effects (e.g., lower entanglements concentration and local
density fluctuations that provide regions of increased free space). The
results suggest that in the case of high-molecular-weight polymers
confined in small-pore systems, adsorption effects have considerable
bearing on the glass transition phenomenon whereas confinement primarily
influences side-chains’ rotational mobilities. The confinement effect is
expected to dominate over adsorption for PMMA phases occluded in higher
pore sizes and silanised walls
Dielectric and thermal characterization of electroactive sol gel polymer composites
The dielectric characterization of silica gel-poly (methyl
methacrylate)-organic dye composites has identified three relaxation
mechanisms which give rise to partially overlapping thermocurrent bands
in the range 10-320K of the Thermally Stimulated Depolarization Currents
(TSDCs) spectra: a relatively low intensity relaxation band maximized at
around 130K, a broad band around 225Y and intense signals above 275K.
Spectral results show that these relaxations are mainly bulk rather
electrode interfacial effects, and are discussed in terms of intrinsic
dipolar (e.g. rotations of H2O molecules and conformational motions of
the polymer side chain segments), Maxwell-Wagner-Sillars interfacial
polarizations, and other types of compositional/structural defects.
Differential Scanning Calorimetry (DSC) analysis of PMMA/Sol-gel
composites has shown that the impregnated polymer’s transition
temperature increases by about 15 degrees, compared to bulk PMMA. The
effect is attributed to hydrogen bonding between the pore surface
silanols and the polymer side chains, based on additional Raman and NMR
measurements
Polarizing-field orientation and thermal treatment effects on the dielectric behavior of fluorapatite
A thermally stimulated depolarization currents (TSDC) study in natural
fluorapatite single crystals has established different relaxation
mechanisms for two polarization orientations (E-p parallel and
perpendicular to the crystallographic c axis), which are discussed in
relation to the defect chemistry and the specific columnar structure in
apatite. The intensities of the thermostimulated current signals between
the two poling field orientations demonstrate a difference of at least
one order of magnitude, with the higher one recorded for the electric
field parallel to the c axis. The TSDC thermogram appearing with the
electric field parallel to c axis, in the 10-320 K range, consists of a
broad and complex band (HT), with a maximum around 300 K. The relative
intensity of associated current signals is indicative of extensive
dipole-like ionic motions along c axis with a distribution in their
activation energies ranging between 0.14 and 0.85 eV. The microdomain
structure of fluorapatite along c axis permits the formation of charge
layers at the interfaces. After annealing, the induced changes of size
and/or shape of the interfaces could explain the observed changes of
band intensity and location. With the electric field perpendicular to c
axis, the spectrum consists of at least five well-defined relaxation
bands, the high temperature ones (HT1, HT2, HT3) decreasing after
heating at 673-873 K. The most dramatic change was recorded for an
intermediate LT2 single-relaxation band located around 185 K, with a
high activation energy of 1.06 eV, which manifested a significant growth
after annealing. Rietvelt analysis of the x-ray diffraction patterns of
the original and annealed apatite powders, indicates change in the unit
cell parameters of the hexagonal structure (i.e., a increases from
9.3921 to 9.3940 Angstrom after annealing), which can be related to the
establishment of a new equilibrium distribution of the abundant
trivalent rare-earth (Ce, La, Nd, Pr,...) impurity ions. The origin of
the TSDC bands is discussed and tentative correlations are suggested, in
terms of substitute aliovalent ions-vacancy dipoles. The thermal
response of the high temperature relaxation bands in the case of E-p
perpendicular to c axis, is characteristic of dipole clustering
phenomena - although an explanation based on localized changes in the
structural environment of the pertinent dipoles/ions cannot be
disregarded. (C) 1999 American Institute of Physics.
[S00218979(99)10001- X]