1,949 research outputs found
An effective long-range attraction between protein molecules in solutions studied by small angle neutron scattering
Small angle neutron scattering intensity distributions taken from cytochrome
C and lysozyme protein solutions show a rising intensity at very small wave
vector, Q, which can be interpreted in terms of the presence of a weak
long-range attraction between protein molecules. This interaction has a range
several times that of the diameter of the protein molecule, much greater than
the range of the screened electrostatic repulsion. We show evidence that this
long-range attraction is closely related to the type of anion present and ion
concentration in the solution
The Origin of Tunneling Anisotropic Magnetoresistance in Break Junctions
First-principles calculations of electron tunneling transport in Ni and Co
break junctions reveal strong dependence of the conductance on the
magnetization direction, an effect known as tunneling anisotropic
magnetoresistance (TAMR). The origin of this phenomenon stems from resonant
states localized in the electrodes near the junction break. The energy and
broadening of these states is strongly affected by the magnetization
orientation due to spin-orbit coupling, causing TAMR to be sensitive to bias
voltage on a scale of a few mV. Our results bear a resemblance to recent
experimental data and suggest that TAMR driven by resonant states is a general
phenomenon typical for magnetic broken contacts and other experimental
geometries where a magnetic tip is used to probe electron transport.Comment: 4 pages, 3 figure
Alternative pathways of dewetting for a thin two-layer film of soft matter
We consider two stacked ultra-thin layers of different liquids on a solid
substrate. Using long-wave theory, we derive coupled evolution equations for
the free liquid-liquid and liquid-gas interfaces. Linear and non-linear
analyses show that depending on the long-range van-der-Waals forces and the
ratio of the layer thicknesses, the system follows different pathways of
dewetting. The instability may be driven by varicose or zigzag modes and leads
to film rupture either at the liquid-gas interface or at the substrate
Direct Observation of the Dynamics of Latex Particles Confined inside Thinning Water-Air Films
The dynamics of micrometer-size polystyrene latex particles confined in thinning foam films was
investigated by microscopic interferometric observation. The behavior of the entrapped particles depends
on the mobility of the film surfaces, the particle concentration, hydrophobicity, and rate of film formation.
When the films were stabilized by sodium dodecyl sulfate, no entrapment of particles between the surfaces
was possible. When protein was used as a stabilizer, a limited number of particles were caught inside
the film area due to the decreased mobility of the interfaces. In this case, extraordinary long-ranged (>100
ĂŚm) capillary attraction leads to two-dimensional (2D) particle aggregation. A major change occurs when
the microspheres are partially hydrophobized by the presence of cationic surfactant. After the foam films
are opened and closed a few times, a layer of particles simultaneously adsorbed to the two interfaces is
formed, which sterically inhibits any further film opening and thinning. The particles within this layer
show an excellent 2D hexagonal ordering. The experimental data are relevant to the dynamics of defects
in coating films, Pickering emulsions, and particle assembly into 2D arrays
Gel transitions in colloidal suspensions
The idealized mode coupling theory (MCT) is applied to colloidal systems
interacting via short-range attractive interactions of Yukawa form. At low
temperatures MCT predicts a slowing down of the local dynamics and ergodicity
breaking transitions. The nonergodicity transitions share many features with
the colloidal gel transition, and are proposed to be the source of gelation in
colloidal systems. Previous calculations of the phase diagram are complemented
with additional data for shorter ranges of the attractive interaction, showing
that the path of the nonergodicity transition line is then unimpeded by the
gas-liquid critical curve at low temperatures. Particular attention is given to
the critical nonergodicity parameters, motivated by recent experimental
measurements. An asymptotic model is developed, valid for dilute systems of
spheres interacting via strong short-range attractions, and is shown to capture
all aspects of the low temperature MCT nonergodicity transitions.Comment: 12 pages, LaTeX, 5 eps figures, uses ioplppt.sty, to appear in J.
Phys.: Condens. Matte
Direct measurements of the effects of salt and surfactant on interaction forces between colloidal particles at water-oil interfaces
The forces between colloidal particles at a decane-water interface, in the
presence of low concentrations of a monovalent salt (NaCl) and of the
surfactant sodium dodecylsulfate (SDS) in the aqueous subphase, have been
studied using laser tweezers. In the absence of electrolyte and surfactant,
particle interactions exhibit a long-range repulsion, yet the variation of the
interaction for different particle pairs is found to be considerable. Averaging
over several particle pairs was hence found to be necessary to obtain reliable
assessment of the effects of salt and surfactant. It has previously been
suggested that the repulsion is consistent with electrostatic interactions
between a small number of dissociated charges in the oil phase, leading to a
decay with distance to the power -4 and an absence of any effect of electrolyte
concentration. However, the present work demonstrates that increasing the
electrolyte concentration does yield, on average, a reduction of the magnitude
of the interaction force with electrolyte concentration. This implies that
charges on the water side also contribute significantly to the electrostatic
interactions. An increase in the concentration of SDS leads to a similar
decrease of the interaction force. Moreover the repulsion at fixed SDS
concentrations decreases over longer times. Finally, measurements of three-body
interactions provide insight into the anisotropic nature of the interactions.
The unique time-dependent and anisotropic interactions between particles at the
oil-water interface allow tailoring of the aggregation kinetics and structure
of the suspension structure.Comment: Submitted to Langmui
An environmentally benign antimicrobial nanoparticle based on a silver-infused lignin core
Silver nanoparticles have antibacterial properties, but their use has been a cause for concern because they persist in the environment. Here, we show that lignin nanoparticles infused with silver ions and coated with a cationic polyelectrolyte layer form a biodegradable and green alternative to silver nanoparticles. The polyelectrolyte layer promotes the adhesion of the particles to bacterial cell membranes and, together with silver ions, can kill a broad spectrum of bacteria, including Escherichia coli, Pseudomonas aeruginosa and quaternary-amine-resistant Ralstonia sp. Ion depletion studies have shown that the bioactivity of these nanoparticles is time-limited because of the desorption of silver ions. High-throughput bioactivity screening did not reveal increased toxicity of the particles when compared to an equivalent mass of metallic silver nanoparticles or silver nitrate solution. Our results demonstrate that the application of green chemistry principles may allow the synthesis of nanoparticles with biodegradable cores that have higher antimicrobial activity and smaller environmental impact than metallic silver nanoparticles
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