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Topics Covered
Background
Design and Setup of the S3-MICROcaliX
Measurements and Results
Summary
Background
Scanning calorimetry (DSC) has been combined with small-angle X-ray scattering
(SAXS) and was incorporated into the laboratory S3-Micro SWAX-camera system.
It is based a on a brilliant, point-focussing laboratory X-ray microsource/optics
and equipped with a fast and reliable 1D dual-detector system for simultaneous
SAXS and WAXS measurements. Simultaneous DSC/SWAXS provides real-time information
on the nanostructural events during enthalpic transitions, a topic essential
e.g. in food-, drug- and pharma-analytics.
In the following application note we present the results of DSC/SWAX measurements
of dry silver-behenate powder performed with the S3-MICROcaliX
in a heating-scan. This dry powder exhibits a lamellar lattice spacing of 58.4
Å (at room temperature) which is frequently used for angular scale calibration
in SAXS.
Design and Setup of the S3-MICROcaliX
S3-MICROcaliX in the laboratory: The Microcalorimeter sample-stage
is integrated into the SWAXS-camera
(S3-MICRO) which is equipped with two independent linear 1D-PSD detectors
for simultaneous SAXS and WAXS measuremnts, respectively. Dimensions approximately:
80 x 15 x 40 cm.
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Figure 1. The MICROcaliX system from Hecus.
Detail of the microcalorimeter sample stage: Capacity: 20 µl in 1.5 mm
quartz-capillaries. Max. heating-rate: 5°C/min. Max. temperature-range:
-30 to 200°C. Dimensions of the block: 4.5 x 6.5 x 22 cm.
Measurements and Results
Heating scan of dry Ag-Behenate (CH3-(CH2)20-COOAg)
powder (30 mg) from 20° to 200°C at a constant scan-rate of 1.5°C/min
and an exposure time of 1min/SAXS pattern (1.5°C/frame). The SAXS-intensity
contour-plot (A) shows the last 60 frames (T from 110° to 200°C). The
corresponding signals of the microcalorimter are displayed on the right showing
the (endothermic) heat-flow signal (red), and temperatures T (black=furnace
T, blue=sample T). The five detected nanostructural transitions seen by SAXS
and calorimetry are indicated by the arrows. Beyond 200°C the sample decomposes.
To the left: (B, C) SAXS and WAXS spectra of all frames (T from 20° to 200°C)
are shown.
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Figure 2. DSC-SAXS of Silver-behenate powder
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Figure 3. DSC-SAXS/WAXS of Silver-behenate powder
Summary
The lamellar lattice (long range order, 58.4 A) of Silver-behenate undergoes
several (endothermic) structural transitions before thermal decomposition (>200°).
Upon heating between 120°C and 200°C 4 different lattice structures
are observed in SAXS with lattice-spacings always smaller than the previous
one. The short range (lateral) order (~ 4 A) is lost immediately after the first
transition at 130°C as it can be clearly seen in the WAXS-spectrum.
Authors - M.Kriechbaum, P.Herrnegger, S.Bodner and P.Laggner
Source - Hecus
For more information on this source, please visit Hecus.