33 research outputs found
Chemical analysis and aqueous solution properties of Charged Amphiphilic Block Copolymers PBA-b-PAA synthesized by MADIX
We have linked the structural and dynamic properties in aqueous solution of
amphiphilic charged diblock copolymers poly(butyl acrylate)-b-poly(acrylic
acid), PBA-b-PAA, synthesized by controlled radical polymerization, with the
physico-chemical characteristics of the samples. Despite product imperfections,
the samples self-assemble in melt and aqueous solutions as predicted by
monodisperse microphase separation theory. However, the PBA core are abnormally
large; the swelling of PBA cores is not due to AA (the Flory parameter
chiPBA/PAA, determined at 0.25, means strong segregation), but to h-PBA
homopolymers (content determined by Liquid Chromatography at the Point of
Exclusion and Adsorption Transition LC-PEAT). Beside the dominant population of
micelles detected by scattering experiments, capillary electrophoresis CE
analysis permitted detection of two other populations, one of h-PAA, and the
other of free PBA-b-PAA chains, that have very short PBA blocks and never
self-assemble. Despite the presence of these free unimers, the self-assembly in
solution was found out of equilibrium: the aggregation state is history
dependant and no unimer exchange between micelles occurs over months
(time-evolution SANS). The high PBA/water interfacial tension, measured at 20
mN/m, prohibits unimer exchange between micelles. PBA-b-PAA solution systems
are neither at thermal equilibrium nor completely frozen systems: internal
fractionation of individual aggregates can occur.Comment: 32 pages, 16 figures and 4 tables submitted to Journal of Interface
and Colloidal Scienc
The mechanism of force transmission at bacterial focal adhesion complexes
Various rod-shaped bacteria mysteriously glide on surfaces in the absence of appendages such as flagella or pili. In the deltaproteobacterium Myxococcus xanthus, a putative gliding motility machinery (the Agl–Glt complex) localizes to so-called focal adhesion sites (FASs) that form stationary contact points with the underlying surface. Here we show that the Agl–Glt machinery contains an inner-membrane motor complex that moves intracellularly along a right-handed helical path; when the machinery becomes stationary at FASs, the motor complex powers a left-handed rotation of the cell around its long axis. At FASs, force transmission requires cyclic interactions between the molecular motor and the adhesion proteins of the outer membrane via a periplasmic interaction platform, which presumably involves contractile activity of motor components and possible interactions with peptidoglycan. Our results provide a molecular model of bacterial gliding motility
Charged diblock copolymers at interfaces: Micelle dissociation upon compression
We use grazing incidence X-ray scattering to study the surface
micellization of charged amphiphilic diblock copolymers poly(styrene-block-acrylic acid) at the air-water interface. Scattering
interference peaks are consistent with the formation of hexagonally packed
micelles. The remarkable increase of inter-micelle distance upon compression
is explained by a dissociation of micelles into a brush. Hence, surface
micelles reorganize, whereas micelles of the same copolymers in solutions
are “frozen”. We show indeed that the energetic cost of unimer extraction
from micelles is much lower for surface than for solution. Finally, a model
combining electrostatic interactions and micelle/brush equilibrium explains
surface pressure vs. area without free parameters
Wetting Behavior of Silicone Oils on Solid Substrates Immersed in Aqueous Electrolyte Solutions
In situ high-energy x-ray reflectivity studies of hydrophobic polyelectrolytes at the solid-liquid interface
Interfacial Activity of Phosphonated-PEG Functionalized Cerium Oxide Nanoparticles
9 pagesInternational audienceIn a recent publication, we have highlighted the potential of phosphonic acid terminated PEG oligomers to functionalize strong UV absorption cerium oxide nanoparticles,1 which yield suspensions that are stable in aqueous or organic solvents and are redispersible in different solvents after freeze-drying. In the present work, we highlight the interfacial activity of the functional ceria nanoparticles and their potential to modify hydrophobic surfaces. We first investigated the phosphonated-PEG amphiphilic oligomers behavior as strong surface active species forming irreversibly adsorbed layers. We then show that the oligomers interfacial properties translate to the functional nanoparticles. In particular, the addition of a small fraction of phosphonated-PEG oligomers with an extra C16 aliphatic chain (stickers) into the formulation enabled the tuning of (i) the nanoparticles adsorption at the air/water, polystyrene/water, oil/water interfaces and (ii) the particle/particle interaction in aqueous solutions. We also found that dense and closely packed two-dimensional monolayers of nanoceria can be formed by spontaneous adsorption or surface compression using a Langmuir trough. A hexagonal organization controlled by reversible and repulsive interaction has been characterized by GISAXS. Mono- or multilayers can also be stably formed or transferred on solid surfaces. Our results are key features in the field of polymer surface modification, solid-stabilized emulsions (Pickering), or supracolloidal assemblies
Interfacial Activity of Phosphonated-PEG Functionalized Cerium Oxide Nanoparticles
In a recent publication, we have highlighted the potential
of phosphonic
acid terminated PEG oligomers to functionalize strong UV absorption
cerium oxide nanoparticles, which yield
suspensions that are stable in aqueous or organic solvents and are
redispersible in different solvents after freeze-drying. In the present
work, we highlight the interfacial activity of the functional ceria
nanoparticles and their potential to modify hydrophobic surfaces.
We first investigated the phosphonated-PEG amphiphilic oligomers behavior
as strong surface active species forming irreversibly adsorbed layers.
We then show that the oligomers interfacial properties translate to
the functional nanoparticles. In particular, the addition of a small
fraction of phosphonated-PEG oligomers with an extra C16 aliphatic
chain (<i>stickers</i>) into the formulation enabled the
tuning of (i) the nanoparticles adsorption at the air/water, polystyrene/water,
oil/water interfaces and (ii) the particle/particle interaction in
aqueous solutions. We also found that dense and closely packed two-dimensional
monolayers of nanoceria can be formed by spontaneous adsorption or
surface compression using a Langmuir trough. A hexagonal organization
controlled by reversible and repulsive interaction has been characterized
by GISAXS. Mono- or multilayers can also be stably formed or transferred
on solid surfaces. Our results are key features in the field of polymer
surface modification, solid-stabilized emulsions (Pickering), or supracolloidal
assemblies