168 research outputs found
Pearlnecklacelike chain conformation of hydrophobic polyelectrolyte: a SANS study of partially sulfonated polystyrene in water
The form factor of partially sulfonated polystyrene PSSNa (degree of
sulfonation f =1, 0.72, 0.64 and 0.36), at polymer concentration 0.17M and
0.34M, without or with added salt (0 M, 0.34M, & 0.68M), is measured by Small
Angle Neutron Scattering using the Zero Average Contrast method. The total
scattering function is also measured, allowing extracting the distinct
interchain function and an apparent structure factor. The main result is the
behavior of the form factor which shows contributions of spherical entities as
well as extended chain parts. This is striking for 0.64, while for f = 0.36 the
sphere contribution is more dominant. The conformation does not depend on
polymer concentration. When salt is added, the sphere sizes do not vary, but
the contribution attributed to the stretched parts does vary very much like for
fully sulfonated PSSNa. Discussion of the interchain contribution establishes
that chains are interpenetrated for f= 0.64, and at the overlap limit for
f=0.36. The pearl necklace model appears very suitable. Comparisons are made
with analytical calculation and simulation data. While the roles of Rayleigh
transition, heterogeneous architecture, and strong hydrophobicity of non
sulfonated PS monomers remain to discuss, data give an accurate 3 d image of
the pearl necklace
Hydrophobic Polyelectrolytes in Better Polar Solvent. Structure and Chain Conformation as seen by Saxs and Sans
We demonstrate in this paper the influence of solvent quality on the
structure of the semi-dilute solution of a hydrophobic polyelectrolyte,
partially sulfonated Poly-Styrene Sulfonate. Two solvents are used: (i) one
mixture of water and an organic solvent: THF, which is also slightly polar;
(ii) DMSO, a polar organic solvent. In case (i), it is shown by SAXS study that
the structure - namely the scattering from all chains, characterised by a
maximum ("polyelectrolyte peak"), of the aqueous hydrophobic polyelectrolyte
solutions (PSS) depends on the solvent quality through the added amount of
organic solvent THF. This dependence is more pronounced when the sulfonation
rate is low (more hydrophobic polyelectrolyte). It is proposed that when THF is
added, the chain conformation evolves from the pearl necklace shape already
reported in pure water, towards the conformation in pure water for fully
sulfonated PSS, which is string-like as also reported previously. On the
contrary, for a hydrophilic polyelectrolyte, AMAMPS, no evolution occurs with
added THF in the aqueous solution. In case (ii), it is shown directly by SANS
study that PSS can behave as a classical solvophilic polyelectrolyte when
dissolved in an organic polar solvent such as DMSO: the structure (total
scattering) as well as the form factor (single chain scattering measured by
SANS using the Zero Average Contrast method) of the PSS chains is independent
of the charge content in agreement with Manning condensation, and identical to
the one of a fully charged PSS chain in pure water, which has a classical
polyelectrolyte behaviour in the semi-dilute regime
Nanorods of Well-Defined Length and Monodisperse Cross-Section Obtained from Electrostatic Complexation of Nanoparticles with a Semiflexible Biopolymer
We show by combining small-angle X-ray scattering (SAXS) and
cryo-transmission electron microscopy (cryo-TEM) that anionic silica
nanoparticles (SiNPs) assemble into well-defined 1D cluster when mixed with a
dilute solution of semiflexible chitosan polycation. The nanorods are stable in
excess of SiNPs and composed of 10 SiNPs well-ordered into straight single
strands with length Lrod \approx 184.0 nm and radius Rrod = 9.2 nm = RSiNPs. We
point out that the ratio between the chitosan persistence length and the SiNP
radius, which is here equal to 1, can be the determining condition to obtain
such original objects
Rodlike Complexes of a Polyelectrolyte (Hyaluronan) and a Protein (Lysozyme) observed by SANS
We study by Small Angle Neutron Scattering (SANS) the structure of Hyaluronan
-Lysozyme complexes. Hyaluronan (HA) is a polysaccharide of 9 nm intrinsic
persistence length that bears one negative charge per disaccharide monomer
(Mmol = 401.3 g/mol); two molecular weights, Mw = 6000 and 500 000 Da were
used. The pH was adjusted at 4.7 and 7.4 so that lysozyme has a global charge
of +10 and + 8 respectively. The lysozyme concentration was varied from 3 to 40
g/L, at constant HA concentration (10 g/L). At low protein concentration,
samples are monophasic and SANS experiments reveal only fluctuations of
concentration although, at high protein concentration, clusters are observed by
SANS in the dense phase of the diphasic samples. In between, close to the onset
of the phase separation, a distinct original scattering is observed. It is
characteristic of a rod-like shape, which could characterize "single" complexes
involving one or a few polymer chains. For the large molecular weight (500 000)
the rodlike rigid domains extend to much larger length scale than the
persistence length of the HA chain alone in solution and the range of the SANS
investigation. They can be described as a necklace of proteins attached along a
backbone of diameter one or a few HA chains. For the short chains (Mw ~ 6000),
the rod length of the complexes is close to the chain contour length (~ 15 nm)
Foaming properties of protein/pectin electrostatic complexes and foam structure at the nanoscale
The foaming properties, foaming capacity and foam stability, of soluble
complexes of pectin and a globular protein, napin, have been investigated with
a "Foamscan" apparatus. Complementary, we also used SANS with a recent method
consisting in an analogy between the SANS by foams and the neutron reflectivity
of films to measure in situ film thickness of foams. The effect of ionic
strength, of protein concentration and of charge density of the pectin has been
analysed. Whereas the foam stability is improved for samples containing soluble
complexes, no effect has been noticed on the foam film thickness, which is
almost around 315 {\AA} whatever the samples. These results let us specify the
role of each specie in the mixture: free proteins contribute to the foaming
capacity, provided the initial free protein content in the bulk is sufficient
to allow the foam formation, and soluble complexes slow down the drainage by
their presence in the Plateau borders, which finally results in the
stabilisation of foams
Structure Transition in PSS/Lysozyme Complexes: A Chain-Conformation-Driven Process, as Directly Seen by Small Angle Neutron Scattering
Measurements of chain conformation in proteins/polyelectrolytes complexes
(lysozyme and PSSNa) show that the crossover observed between an open structure
-a chain network crosslinked by the proteins, and a globular one - dense
globules of ~ 10 nm aggregated in a fractal way, results from a conformation
modification prior to the transition. Before showing this, we have widened the
parameters range for the observation of the transition. We had shown before
that the two structures can be formed depending on chain length (for a given
[PSS]/[lysozyme] ratio): gel for large chains, globules for short chains. We
show here that the crossover between these two regimes can also be reached as a
function of chains concentration or salinity of the buffer. Since all these
crossover parameters act on chains overlapping concentration c*, we reinforce
the idea of a transition from the dilute to the semi-dilute regime, but c* is
shifted compared to pure PSS solutions. In order to understand this, we have
measured by SANS the conformation of a single chain of PSS in presence of
proteins within the complexes. This is achieved by a specific labeling trick
where we take advantage of the fact that lysozyme and hydrogenated PSS chains
have the same neutron scattering length density. In the gel structure, the PSS
chains keep a wormlike structure as in pure solutions, but their persistence
length is strongly reduced, from 50 {\AA} without proteins to 20 {\AA} in
average with lysozyme. With this value of 20 {\AA}, we calculate new
overlapping thresholds (concentration, mass, ionic strength) in agreement with
observed ones. In a second stage, after the globular structure is formed, the
PSS chains get a third conformation, no longer wormlike, but more collapsed,
within the globules
Spatial structure and composition of polysaccharide-protein complexes from Small Angle Neutron Scattering
We use Small Angle Neutron Scattering (SANS), with an original analysis
method, to obtain both the characteristic sizes and the inner composition of
lysozyme-pectin complexes depending on the charge density. Lysozyme is a
globular protein and pectin a natural anionic semiflexible polysaccharide with
a degree of methylation (DM) 0, 43 and 74. For our experimental conditions
(buffer ionic strength I = 2.5 10-2 mol/L and pH between 3 and 7), the
electrostatic charge of lysozyme is always positive (from 8 to 17 depending on
pH). The pectin charge per elementary chain segment is negative and can be
varied from almost zero to one through the change of DM and pH. The weight
molar ratio of lysozyme on pectin monomers is kept constant. The ratio of
negative charge content per volume to positive charge content per volume, -/+,
is varied between 10 and 0.007. On a local scale, for all charged pectins, a
correlation peak appears at 0.2 {\AA}-1 due to proteins clustering inside the
complexes. On a large scale, the complexes appear as formed of spherical
globules with a well defined radius of 10 to 50 nm, containing a few thousands
proteins. The volume fraction Phi of organic matter within the globules derived
from SANS absolute cross-sections is around 0.1. The protein stacking, which
occurs inside the globules, is enhanced when pectin is more charged, due to pH
or DM. The linear charge density of the pectin determines the size of the
globules for pectin chains of comparable molecular weights whether it is
controlled by the pH or the DM. The radius of the globules varies between 10 nm
and 50 nm. In conclusion the structure is driven by electrostatic interactions
and not by hydrophobic interactions. The molecular weight also has a large
influence on the structure of the complexes since long chains tend to form
larger globules. This maybe one reason why DM and pH are not completely
equivalent in our system since DM 0 has a short mass, but this may not be the
only one. For very low pectin charge (-/+ = 0.07), globules do not appear and
the scattering signals a gel-like structure. We did not observe any
beads-on-a-string structure
Adsorption of MultiLamellar tubes with a temperature tunable diameter at the air-water interface: a process driven by the bulk properties
The behavior at the air/water interface of multilamellar tubes made of the
ethanolamine salt of the 12-hydroxy stearic acid as a function of the
temperature has been investigated using Neutron Reflectivity. Those tubes are
known to exhibit a temperature tunable diameter in the bulk. We have observed
multilamellar tubes adsorbed at the air/water interface by specular neutron
reflectivity. Interestingly, at the interface, the adsorbed tubes exhibit the
same behavior than in the bulk upon heating. There is however a peculiar
behavior at around 50\degree for which the increase of the diameter of the
tubes at the interface yields an unfolding of those tubes into a multilamellar
layer. Upon further heating, the tubes re-fold and their diameter re-decrease
after what they melt as observed in the bulk. All structural transitions at the
interface are nevertheless shown to be quasi-completely reversible. This
provides to the system a high interest for its interfacial properties because
the structure at the air/water interface can be tuned easily by the
temperature
Role of the ratio of biopolyelectrolyte persistence length to nanoparticle size in the structural tuning of electrostatic complexes
International audienceAbstract. Aggregation of nanoparticles of given size R induced by addition of a polymer strongly depends on its degree of rigidity. This is shown here on a large variety of silica nanoparticle self-assemblies obtained by electrostatic complexation with carefully selected oppositely charged bio-polyelectrolytes of different rigidity. The effective rigidity is quantified by the total persistence length L T representing the sum of the intrinsic (L p) and electrostatic (L e) polyelectrolyte persistence length, which depends on the screening, i.e., on ionic strength due to counterions and external salt concentrations. We experimentally show for the first time that the ratio L T /R is the main tuning parameter that controls the fractal dimension D f of the nanoparticles self-assemblies, which is determined using small-angle neutron scattering: (i) For L T /R1, L e is strongly increased due to the absence of salt and repulsions between nanoparticles cannot be compensated by the polyelectrolyte wrapping, which allow a spacing between nanoparticles and the formation of one dimensional pearl necklace complexes. (iv) Finally, electrostatic 2 screening, i.e. ionic strength, turned out to be a reliable way of controlling D f and the phase diagram behavior. It finely tunes the short-range interparticle potential, resulting in larger fractal dimensions at higher ionic strength
- …