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- Capillary conductivity (1)
- CdS shell (1)
- CdSe (1)
- Ensemble measurements (1)
- Fluorescence (1)
- Insulation material (1)
- Mechanism (1)
- Nuclear magnetic resonance (1)
- Photophysics (1)
- Pore-size distribution (1)
Organisationseinheit der BAM
The fluorescence quantum yield (QY) of CdSe dot/CdS rod (DR) nanoparticle ensembles is dependent on the Shell growth and excitation wavelength. We analyze the origin of this dependency by comparing the optical properties of DR ensembles to the results obtained in single-particle experiments. On the Ensemble level, we find that the QY of DRs with shell lengths shorter than 40 nm exhibits no dependence on the excitation wavelength, whereas for DRs with shell lengths longer than 50 nm, the QY significantly decreases for excitation above the CdS band gap. Upon excitation in the CdSe core, the ensemble QY, the fluorescence wavelength, and the fluorescence blinking behavior of individual particles are only dependent on the radial CdS shell thickness and not on the CDs shell length. If the photogenerated excitons can reach the CdSe core region, the fluorescence properties will be dependent only on the surface passivation in close vicinity to the CdSe core. The change in QY upon excitation above the band gap of CdS for longer DRs cannot be explained by nonradiative particles because the ratio of emitting DRs is found to be independent of the DR length. We propose a model after which the decrease in QY for longer CdS shells is due to an increasing fraction of nonradiative exciton recombination within the elongated shell. This is supported by an effective-mass-approximation-based calculation, which suggests an optimum length of DRs of about 40 nm, to combine the benefit of high CdS absorption cross section with a high fluorescence QY.
Autoignition temperature (AIT) round robin tests were conducted by seven laboratories on eight polymeric materials. A statistical analysis was conducted that focused on investigating data variability both within and between test methods. With some exceptions, the methods ranked the materials consistently and as expected from their chemical makeup. There was no consistent difference between AIT values determined at 6.9 and 10.3 MPa. BAM and ASTM G72 consistently provided lower, more conservative AITs at both 6.9 and 10.3 MPa. Within an estimated accuracy obtained from all methods from this round robin, data from the following methods appeared to be more accurate than the rest: NF E 29763/88 and Parr Bomb at 6.9 MPa; automated ASTM G72 at 10.3 MPa. The following methods provided lower within-method variability than the average for all methods: BS 3N 100 and ASTM G72 at 6.9 and 10.3 MPa; Parr Bomb at 6.9 MPa. At 6.9 MPa the BAM method provided data with greater within-method variability than the average for all methods. For most materials, the automated ASTM G72 method at 10.3 MPa provided data with greater within-method variability than the average for all methods. Two data points for this method, Zytel? and Teflon? FEP, exceeded critical . At 6.9 MPa, the largest within-method variability resulted from NF E 29763/88 on Zytel, the only data that exceeded critical . Two extreme results were caused by significant effects of method-specific test parameters: BAM on Zytel at 6.9 MPa and BS 3N 100 on Viton? at 10.3 MPa. Statistically these results had a probability of less than 5 percent of occurring by chance.
Capillary active interior insulation materials are an important approach to minimize energy losses of historical buildings. A key factor for their performance is a high liquid conductivity, which enables redistribution of liquid moisture within the material. We set up an experiment to investigate the development of moisture profiles within two different interior insulation materials, calcium-silicate (CaSi) and expanded perlite (EP), under constant boundary conditions. The moisture profiles were determined by two different methods: simple destructive sample slicing with subsequent thermogravimetric drying as well as non-destructive NMR measurements with high spatial resolution. The moisture profiles obtained from both methods show good agreement, when compared at the low spatial resolution of sample slicing, which demonstrates the reliability of this method. Moreover, the measured T2-relaxation-time distributions across the sample depth were measured, which may give further insight into the saturation degree of the different pore sizes. In order to explain differences in the moisture profiles between CaSi and EP, we determined their pore-size distribution with different methods: conversion of the NMR T2 relaxationtime distribution at full saturation, mercury intrusion porosimetry and indirect determination from pressure plate measurements. CaSi shows a unimodal distribution at small pore diameters, while in EP, a bi-modal or wider distribution was found. We assume that the smaller pore diameters of CaSi lead to a higher capillary conductivity, which causes a more distributed moisture profile in comparison with that of EP.