Search results for "Colloid"
showing 10 items of 1288 documents
New aspects of scattering and absorbing properties of atmospheric aerosol particles
1972
Abstract Knowledge of the scattering and absorbing processes of the atmospheric aerosol particles in the solar wavelength range is necessary in order to calculate the energy balance of the atmosphere. Both of these depend on the relative humidity of the air. Until now little was known of the behavior of the particles. This paper shows experimental and theoretical results of the real and imaginary part of the refractive index of the aerosol particles at different relative humidities.
Ab initio modeling of excitonic and charge-transfer states in organic semiconductors: the PTB1/PCBM low band gap system.
2013
A detailed quantum chemical simulation of the excitonic and charge-transfer (CT) states of a bulk heterojunction model containing poly(thieno[3,4-b]thiophene benzodithiophene) (PTB1)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is reported. The largest molecular model contains two stacked PTB1 trimer chains interacting with C60 positioned on top of and lateral to the (PTB1)3 stack. The calculations were performed using the algebraic diagrammatic construction method to second order (ADC(2)). One main result of the calculations is that the CT states are located below the bright inter-chain excitonic state, directly accessible via internal conversion processes. The other important aspects…
Arylazopyrazoles for Long-Term Thermal Energy Storage and Optically Triggered Heat Release below 0 °C.
2020
Arylazopyrazole derivatives based on four core structures (4pzMe, 3pzH, 4pzH, and 4pzH-F2) and functionalized with a dodecanoate group were demonstrated to store thermal energy in their metastable Z isomer liquid phase and release the energy by optically triggered crystallization at -30 °C for the first time. Three heat storage-release schemes were discovered involving different activation methods (optical, thermal, or combined) for generating liquid-state Z isomers capable of storing thermal energy. Visible light irradiation induced the selective crystallization of the liquid phase via Z-to-E isomerization, and the latent heat stored in the liquid Z isomers was preserved for longer than 2 …
Photoinduced ultrafast dye-to-semiconductor electron injection from nonthermalized and thermalized donor states.
2001
Electron injection from the transition metal complex Ru(dcbpy)(2)(NCS)(2) (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) into a titanium dioxide nanocrystalline film occurs on the femto- and picosecond time scales. Here we show that the dominating part of the electron transfer proceeds extremely rapidly from the initially populated, vibronically nonthermalized, singlet excited state, prior to electronic and nuclear relaxation of the molecule. The results are especially relevant to the understanding and design of molecular-based photovoltaic devices and artificial photosynthetic assemblies.
Dynamics of Colloidal Hard Spheres in Thin Aqueous Suspension Layers—Particle Tracking by Digital Image Processing and Brownian Dynamics Computer Sim…
1993
Abstract A new experimentally simple technique is introduced for studying dynamical properties of hard sphere colloids in thin aqueous suspension layers by light-microscopy observation supported by computer-aided digital image processing. The thickness of the layers of the colloidal samples confined between two smooth glass plates is accurately adjusted by monodisperse "spacer" spheres which are larger than the diffusing spheres. Tracking of single particles in concentrated phases is accomplished using fluorescence light microscopy where a few dyed particles are mixed with the undyed colloidal spheres of the same size. First results are presented for the self-diffusion coefficient—(i) in ve…
A Multipurpose Instrument To Measure the Vitreous Properties of Charged Colloidal Solids
2001
We present a new high-precision light-scattering setup to study the properties of colloidal solids. It combines static light scattering, dynamic light scattering, and torsional resonance spectroscopy with a flexible and reliable preparational procedure. All three experiments can be performed quasi-simultaneously on the same mechanically undisturbed sample. Thus, unequivocal identification of glassy behavior in a comprehensive characterization dependent on interaction parameters becomes possible. A detailed description of the mechanics is given. We thoroughly tested the new apparatus on dilute colloidal samples and against commercial reference instruments. We performed a first systematic ser…
Measuring the Contact Angle of Individual Colloidal Particles.
1998
The aim of this study was to measure the contact angles of individual colloidal spheres ( solidus in circle 4.4 µm) and compare it to contact angles obtained on similarly prepared planar surfaces. For this purpose the particles were attached to atomic force microscope cantilevers. Then the force between the particle in aqueous medium and an air bubble was measured versus the distance. From the resulting force curves we obtained contact angles and detachment forces of single particles. Contact angles of gold coated silica particles were adjusted between 20 degrees and 100 degrees by self-assembling monolayers from different mixtures of undecanethiols and omega-hydroxy undecanethiols from sol…
Dihydrogen complexes of metalloporphyrins: characterization and catalytic hydrogen oxidation activity
1992
A series of monometallic dihydrogen complexes of the type M(OEP)(L)(H{sub 2}) (M = Ru, Os; L = THF, *Im) was synthesized and characterized by {sup 1}H NMR. The H-H bond length was found to increase when Os was replaced by Ru or when *Im was replaced by THF. The bond distances (as determined by T{sub 1}) range from 0.92 to 1.18 {angstrom}. The first example of a bimetallic bridging dihydrogen complex, Ru{sub 2}(DPB)(*IM){sub 2}(H{sub 2}), was also prepared. The H{sub 2} ligand is simultaneously bound to both Ru-metal centers. High-field {sup 1}H NMR experiments (620 MHz) revealed a -7.37 Hz dipolar splitting of the H{sub 2} ligand for this complex. Analysis of this splitting suggests that th…
Synthesis of rod-shaped gold nanorattles with improved plasmon sensitivity and catalytic activity.
2009
We prepared rod-shaped gold nanorattles solid gold nanorods surrounded by a thin gold shell using a galvanic replacement process starting with silver-coated gold nanorods. These structures are very promising candidates for catalytic applications and optimized plasmon sensors. They combine the advantages of rods (low plasmon resonance frequency, large polarizability, small damping) with the high surface area of hollow structures. The plasmon sensitivity to changes in the dielectric environment is up to 50% higher for gold nanorattles compared to gold nanorods with the same resonance frequency and 6x higher than for plasmons in spherical gold nanoparticles. The catalytic activity measured for…
Quantitative determination of surface area of silica gel particles by near infrared spectroscopy and chemometrics
2008
Abstract Surface areas of silica gel particles have been quantitatively determined by using near infrared spectrometry and chemometrics. Surface areas of six silica gel samples with varying surface area (300–750 m2/g) have been determined by the common Brunauer–Emmett–Teller (BET) method and used in preparing mixtures of silica gel samples with varying surface area in the ranges 300–474 and 500–750 m2/g. The near infrared spectra of the mixtures were measured and the spectral profiles calibrated against the calculated surface area of the mixtures as dependent variable using partial least squares (PLS) technique. The models obtained from the calibrations were then used in predicting the surf…