Critical fluctuations in liquid-liquid extraction organic phases controlled by extractant and diluent molecular structure.

Extractant aggregation in liquid-liquid extraction organic phases impacts extraction energetics and is related to the deleterious efficiency-limiting liquid-liquid phase transition known as third phase formation. Using small angle X-ray scattering, we find that structural heterogeneities across a wide range of compositions in binary mixtures of malonamide extractants and alkane diluents are well described by Ornstein-Zernike scattering. This suggests that structure in these simplified organic phases originates from the critical point associated with the liquid-liquid phase transition.

Phase diagrams and microstructures of aqueous short alkyl chain polyethylene glycol ether carboxylate and carboxylic acid triblock surfactant solutions.

Hypothesis: The surfactant CEOCHCOOH (Akypo LF2) and its salts have a small hydrophobic and a significantly longer hydrophilic part. As a consequence, there must be a significant steric constraint, once these surfactant molecules form micelles. In addition, the partially charged headgroups should bring some additional fine-tuning via electrostatic interactions to this "essentially non-ionic" surfactant.

Structure of supported DPPC/cholesterol bilayers studied via X-ray reflectivity.

The electron density profile of bilayers of DPPC/cholesterol mixtures supported on semiconductor grade silicon substrates were studied with the objective of determining how the proximity of a solid interface modifies the phase diagram of mixed bilayers. The bilayers were studied in situ immersed in water via synchrotron X-ray reflectivity (XRR). Measurements were performed as a function of temperature through the main phase transition and cholesterol mole fractions up to 40%.

The curvature changes induced by grafted polymers in microemulsions.

The results on Winsor phases, droplet and bicontinous microemulsions phases with polymer-grafted lipids studied by Small Angle Neutron Scattering (SANS) are reported below, together with the contrast variation techniques used to characterize the average curvature in the system. We have clearly shown that polymer-grafted lipids change the interaction between microemulsion droplets --it need not be just repulsive but could also be attractive. They induce structural changes or bring about complete phase changes as observed visually in the Winsor phases when added in sufficient amounts.

Microstructural characteristics of surfactant assembly into a gel-like mesophase for application as an oil spill dispersant.

Hypothesis: Polyoxyethylene (20) sorbitan monooleate (Tween 80) can be incorporated into the gel-like phase formed by L-α-phosphatidylcholine (PC) and dioctyl sulfosuccinate sodium salt (DOSS) for potential application as a gel-like dispersant for oil spill treatment. Such gel-like dispersants offer advantages over existing liquid dispersants for mitigating oil spill impacts.

Experiments: Crude oil-in-saline water emulsions stabilized by the surfactant system were characterized by optical microscopy and turbidity measurements while interfacial tensions were measured by the spinning drop and pendant drop techniques.

Modulation of hemoglobin dynamics by an allosteric effector.

Hemoglobin (Hb) is an extensively studied paradigm of proteins that alter their function in response to allosteric effectors. Models of its action have been used as prototypes for structure-function relationships in many proteins, and models for the molecular basis of its function have been deeply studied and extensively argued. Recent reports suggest that dynamics may play an important role in its function.

X-ray coherent diffraction imaging of cellulose fibrils in situ.

Cellulose is the most abundant renewable source of organic molecules on earth[1]. As fossil fuel reserves become depleted, the use of cellulose as a feed stock for fuels and chemicals is being aggressively explored. Cellulose is a linear polymer of glucose that packs tightly into crystalline fibrils that make up a substantial proportion of plant cell walls.

Neutron spin-echo studies of hemoglobin and myoglobin: multiscale internal dynamics.

Neutron spin-echo spectroscopy was used to study structural fluctuations that occur in hemoglobin (Hb) and myoglobin (Mb) in solution. Using neutron spin-echo data up to a very high momentum transfer q ( approximately 0.62 A(-)(1)), we characterized the internal dynamics of these proteins at the levels of dynamic pair correlation function and self-correlation function in the time range of several picoseconds to a few nanoseconds.

Nonamphiphilic assembly in water: polymorphic nature, thread structure, and thermodynamic incompatibility.

Self-assembly of large quantities of entirely water-soluble molecules is entropically challenging. In this work, we describe the design and synthesis of water-soluble aromatic (dichromonyl) molecules that can form nonamphiphilic assemblies and the so-called chromonic liquid crystal phase in water. We discover a new molecule, 5'DSCG-diviol, that exhibits a large birefringent phase, and we show that the formation of this unique class of nonamphiphilic lyotropic liquid crystal shares enormous similarity to the polymorphism observed for crystal formation.

Effects of pH on the interactions and conformation of bovine serum albumin: comparison between chemical force microscopy and small-angle neutron scattering.

The conformation of bovine serum albumin (BSA), as well as its interactions with negatively charged mica surfaces in saline solutions of different pH values, have been studied by small-angle neutron scattering (SANS) and chemical force microscopy (CFM), respectively. A new approach to extract the contribution of elementary interactions from the statistically averaged force-extension curves through self-consistent fitting was proposed and used to understand the effects of pH on the interactions and conformation of BSA in saline solutions. When pH increases, the SANS results reveal that the sizes of BSA molecules increase slightly, while the statistical analysis of the CFM results shows that the averaged pull-off force for the elongation monotonously decreases.

Why the wrinkling transition in partially polymerized membranes is not universal? Fractal-multifractal hierarchy.

When partially polymerized membranes wrinkle they exhibit a passage from a conventional buckling (due to an instability caused by chiral symmetry breaking) at low polymerization to a local roughening (due to a frustration in the local packing of the chiral molecules composing the membrane) as a function of the polymerization of the lipids aliphatic tails. This transition was found to be non-universal and here we used neutron scattering to elucidate that this behavior is due to the onset of stretching in the membrane accompanied by a bilayer thickness variation. Close to the percolation limit this deformation is plastic similar to mutated lysozymes.

PEO-PPO block copolymer vectors do not interact directly with DNA but with lipid membranes.

Small angle neutron (SANS) and light scattering was used to study the interaction between fragments of double stranded deoxyribonucleic acid (DNA) and a synthetic triblock [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)] amphiphilic polymer, known as L64, a potential vector for gene therapy. The mechanism of action of this vector is yet unknown. The contrast variation method was used to separate the partial structure factors of the different components in mixtures of triblock and DNA.

Microstructure of beta-lactoglobulin/pectin coacervates studied by small-angle neutron scattering.

Small-angle neutron scattering (SANS) has been used to investigate the microstructure of beta-lactoglobulin/pectin coacervates prepared by different initial protein/polysaccharide weight ratio (r), sodium chloride concentration (C(NaCl)), and pectin charge density. The higher r and higher pectin charge density lead to higher scattering intensity at small q range (0.007 Angstrom(-1) < q < 0.

Observation of a low-viscosity interface between immiscible polymer layers.

X-ray photon correlation spectroscopy was employed in a surface standing wave geometry in order to resolve the thermally driven in-plane dynamics at both the surface/vacuum (top) and polymer/polymer (bottom) interfaces of a thin polystyrene (PS) film on top of Poly(4-bromo styrene) (PBrS) and supported on a Si substrate. The top vacuum interface shows two relaxation modes: one fast and one slow, while the buried polymer-polymer interface shows a single slow mode. The slow mode of the top interface is similar in magnitude and wave vector dependence to the single mode of the buried interface.

Interactions of membrane-active peptides with thick, neutral, nonzwitterionic bilayers.

Alamethicin is a well-studied channel-forming peptide that has a prototypical amphipathic helix structure. It permeabilizes both microbial and mammalian cell membranes, causing loss of membrane polarization and leakage of endogenous contents. Antimicrobial peptide-lipid systems have been studied quite extensively and have led to significant advancements in membrane biophysics.

Resonantly enhanced off-specular X-ray scattering from polymer/polymer interfaces.

We have used measurements of the absolute intensity of diffuse X-ray scattering to extract the interfacial tension of a buried polymer/polymer interface. Diffuse scattering was excited by an X-ray standing wave whose phase was adjusted to have a high intensity at the polymer/polymer interface and simultaneously a node at the polymer/air interface. This method permits the capillary-wave-induced roughness of the interface, and hence the interfacial tension, to be measured independently of the polymer/polymer interdiffusion.

Self-assembled liquid-crystalline gels designed from the bottom up.

Liquid crystals are often combined with polymers to influence the liquid crystals' orientation and mechanical properties, but at the expense of reorientation speed or uniformity of alignment. We introduce a new method to create self-assembled nematic liquid-crystal gels using an ABA triblock copolymer with a side-group liquid-crystalline midblock and liquid-crystal-phobic endblocks. In contrast to in situ polymerized networks, these physical gels are homogeneous systems with a solubilized polymer network giving them exceptional optical uniformity and well-defined crosslink density.