1,352 research outputs found
Evidence of Deep Water Penetration in Silica during Stress Corrosion Fracture
We measure the thickness of the heavy water layer trapped under the stress corrosion fracture surface of silica using neutron reflectivity experiments. We show that the penetration depth is 65–85 Å, suggesting the presence of a damaged zone of ~100 Å extending ahead of the crack tip during its propagation. This estimate of the size of the damaged zone is compatible with other recent results
Significant techniques in the processing and interpretation of ERTS-1 data
The discipline oriented investigations underway at the Johnson Space Center (JSC) using ERTS-1 data provide an appropriate framework for the systematic evaluation of the various elements comprising a prototype multispectral data processing and analysis system. In particular such a system may be thought of as the integration of: (1) a preprocessing subsystem; (2) a spectral clustering subsystem, (3) a correlation and classification subsystem; (4) mensuration subsystem; and (5) an information management subsystem. Specific elements of this system are already operational at JSC. It is in the context of this system that technique development and application is being pursued at JSC. Aircraft, ERTS and EREP data will be utilized to refine the subsystem elements for each of the data acquisition systems or system combinations that are optimally suited for a specific Earth Resources application. The techniques reported are those that have been developed to date during the utilization of ERTS-1 data in this processing and analysis system
Submicrometric Films of Surface-Attached Polymer Network with Temperature-Responsive Properties
Temperature-responsive properties of surface-attached
poly(N-isopropylacrylamide) (PNIPAM) network films with well-controlled
chemistry are investigated. The synthesis consists of cross-linking and
grafting preformed ene-reactive polymer chains through thiol--ene click
chemistry. The formation of surface-attached and cross-linked polymer films has
the advantage of being wellcontrolled without any caution of no-oxygen
atmosphere or addition of initiators. PNIPAM hydrogel films with same
cross-link density are synthesized on a wide range of thickness, from
nanometers to micrometers. The swelling-collapse transition with temperature is
studied by using ellipsometry, neutron reflectivity, and atomic force
microscopy as complementary surface-probing techniques. Sharp and high
amplitude temperature-induced phase transition is observed for all
submicrometric PNIPAM hydrogel films. For temperature above LCST,
surface-attached PNIPAM hydrogels collapse similarly but without complete
expulsion of water. For temperature below LCST, the swelling of PNIPAM
hydrogels depends on the film thickness. It is shown that the swelling is
strongly affected by the surface attachment for ultrathin films below 150
nm. For thicker films above 150 nm (to micrometers), surface-attached polymer
networks with the same cross-link density swell equally. The density profile of
the hydrogel films in the direction normal to the substrate is confronted with
in-plane topography of the free surface. It results that the free interface
width is much larger than the roughness of the hydrogel film, suggesting
pendant chains at the free surface.Comment: in Langmuir, American Chemical Society, 2015, LANGMUIR, 31 (42),
pp.11516-1152
Mass Density of Individual Cobalt Nanowires
The mass density of nanowires is determined using in-situ resonance frequency
experiments combined with quasi-static nanotensile tests. Our results reveal a
mass density of 7.36 g/cm3 on average which is below the theoretical density of
bulk cobalt. Also the density of electrodeposited cobalt nanowires is found to
decrease with the aspect ratio. The results are discussed in terms of the
measurement accuracy and the microstructure of the nanowires.Comment: 3 Figure
Universal scattering behavior of co-assembled nanoparticle-polymer clusters
Water-soluble clusters made from 7 nm inorganic nanoparticles have been
investigated by small-angle neutron scattering. The internal structure factor
of the clusters was derived and exhibited a universal behavior as evidenced by
a correlation hole at intermediate wave-vectors. Reverse Monte-Carlo
calculations were performed to adjust the data and provided an accurate
description of the clusters in terms of interparticle distance and volume
fraction. Additional parameters influencing the microstructure were also
investigated, including the nature and thickness of the nanoparticle adlayer.Comment: 5 pages, 4 figures, paper published in Physical Review
The role of electron polarization on nuclear spin diffusion
Dynamic nuclear polarization (DNP) is capable of boosting signals in nuclear
magnetic resonance by orders of magnitude by creating out-of-equilibrium
nuclear spin polarization. The diffusion of nuclear spin polarization in the
vicinity of paramagnetic dopants is a crucial step for DNP and remains yet not
well understood. In this Letter, we show that the polarization of the electron
spin controls the rate of proton spin diffusion in a DNP sample at 1.2 K and 7
T; at increasingly high electron polarization, spin diffusion vanishes. We
rationalize our results using a 2 nucleus - 1 electron model and Lindblad s
Master equation, which generalizes preexisting models in the literature and
qualitatively accounts for the experimental observed spin diffusion dynamics.Comment: Main text: 6 pages, 3 figures Supplement: 9 pages, 4 figure
Small-Angle Neutron Scattering Reveals the Structural Details of Thermosensitive Polymer-Grafted Cellulose Nanocrystal Suspensions.
Thanks to the use of small-angle neutron scattering (SANS), a detailed structural description of thermosensitive polymer-grafted cellulose nanocrystals (CNCs) was obtained and the behavior of aqueous suspensions of these derivatized biosourced particles upon temperature increase was revealed. Although literature data show that the surface grafting of thermosensitive polymers drastically enhances the colloidal properties of CNCs, direct space microscopic investigation techniques fail in providing sufficient structural information on these objects. In the case of CNCs decorated with temperature-sensitive polyetheramines following a peptide coupling reaction, a qualitative and quantitative analysis of SANS spectra shows that CNCs are homogeneously covered by a shell comprising polymer chains in a Gaussian conformation with a thickness equal to their radius of gyration in solution, thus revealing a mushroom regime. An increase of the temperature above the lower critical solution temperature (LCST) of the polyetheramine results in the formation of finite size bundles whose aggregation number depends on the particle concentration and suspension temperature deviation from the LCST. SANS analysis further reveals local changes at the CNC surface corresponding to a release of water molecules and a related denser polymer shell conformation. Noticeably, data show a full reversibility at all length scales when a sample was cooled down to below the LCST after being heated above it. Overall, the results obtained by SANS allow an in-depth structural investigation of derivatized CNCs, which is of high interest for the design of functional materials comprising these biosourced colloids.Institut Carnot PolyNat (ANR N° 16-CARN-025-01), France
Breaking of the Bancroft rule for multiple emulsions stabilized by a single stimulable polymer
International audienceWe investigated emulsions of water and toluene stabilized by (co)polymers consisting of styrene (S) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) monomer units with different compositions and structures such as a PDMAEMA homopolymer, a P(S-co-DMAEMA) random copolymer and various PS-b-PDMAEMA and PS-b-(S-co-DMAEMA) block copolymers. The model system is used to study the fundamental conditions under which the different kinds of polymer-stabilized emulsions (direct oil in water, inverse water in oil and multiple emulsions) are stabilized or destabilized by pH change (at constant temperature). Polymer properties like chain conformation at the toluene-water interface as probed by SANS and neutron reflectivity at the liquid-liquid interface, the oil-water partitioning of the polymer chains (Bancroft's rule of thumb) as determined by UV spectroscopy and interfacial tensions measured by the rising and spinning drop techniques are determined. Overall, results evidence that the curvature sign, as defined by positive and negative values as the chain segments occupy preferentially the water and toluene sides of the interface respectively, reliably predicts the emulsion kind. In contrast, the Bancroft rule failed at foreseeing the emulsion type. In the region of near zero curvature the crossover from direct to inverse emulsions occurs through the formation of either unstable coexisting direct and inverse emulsions (i) or multiple emulsions (ii). The high compact adsorption of the chains at the interface as shown by low interfacial tension values does not allow to discriminate between both cases. However, the toluene-water partitioning of the polymeric emulsifier is still a key factor driving the formation of (i) or (ii) emulsions. Interestingly, the stabilization of the multiple emulsions can be tuned to a large extent as the toluene-water polymer partitioning can be adjusted using quite a large number of physico-chemical parameters linked to polymer architecture like diblock length ratio or polymer total molar mass, for example. Moreover, we show that monitoring the oil-water partitioning aspect of the emulsion system can also be used to lower the interfacial tension at low pH to values slightly higher than 0.01 mN m-1, irrespective of the curvature sign
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