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Knowledge of the nanoscale distribution of proteins in chromatographic resins is critical to our mechanistic understanding of separations performance. However, the nano- to mesoscale architecture of these materials is challenging to characterize using conventional techniques. Small-angle neutron scattering was used to probe (1) the nano- to mesoscale structure of chromatographic media and (2) protein sorption in these media in situ with protein-scale resolution. In particular, we characterize the effect of the architecture of cellulose-based and traditional and dextran-modified agarose-based ion-exchange resins on the nanoscale distribution of a relatively small protein (lysozyme) and two larger proteins (lactoferrin and a monoclonal antibody) at different protein loadings. Traditional agarose-based resins (SP Sepharose FF) can be envisioned as comprising long, thin strands of helical resin material around which the proteins adsorb, while higher static capacities are achieved in dextran-modified resins (SP Sepharose XL and Capto S) due to protein partitioning into the increased effective binding volume provided by the dextran. While protein size is shown not to affect the underlying sorption behavior in agarose-based resins such as SP Sepharose FF and XL, it plays an important role in the cellulose-based S HyperCel and the more highly cross-linked agarose-based Capto S, where size-exclusion effects prevent larger proteins from binding to the base matrix resin strands. Based on the data, we propose that entropic partitioning effects such as depletion forces may drive the observed protein crowding. In general, these observations elucidate the structure and point to the mechanism of protein partitioning in different classes of chromatographic materials, providing guidance for optimizing their performance. [ABSTRACT FROM AUTHOR]

The microstructure of mixtures of deuterated water in the ionic liquid [C4mim][BF4] is investigated by small-angle neutron scattering (SANS) measurement. In the salt-rich region, water dissolves in the ionic liquid up to 0.7 mole fraction, whereupon distinct, nanometer-sized water clusters are observed. These water nanoclusters increase in size with increasing water addition while the mole ratio of water dissolved into the ionic liquid nanostructure increases from 2 to 4. These results provide direct confirmation for recent simulations as well insight into the source of nonidealities in some thermophysical and transport properties (e.g., density and viscosity) of salt-rich aqueous mixtures reported in the literature. [ABSTRACT FROM AUTHOR]

The microstructure of mixtures of deuterated water in the ionic liquid [C4mim][BF4] is investigated by small-angle neutron scattering (SANS) measurement. In the salt-rich region, water dissolves in the ionic liquid up to 0.7 mole fraction, whereupon distinct, nanometer-sized water clusters are observed. These water nanoclusters increase in size with increasing water addition while the mole ratio of water dissolved into the ionic liquid nanostructure increases from 2 to 4. These results provide direct confirmation for recent simulations as well insight into the source of nonidealities in some thermophysical and transport properties (e.g., density and viscosity) of salt-rich aqueous mixtures reported in the literature. [ABSTRACT FROM AUTHOR]

Oppositely charged polyelectrolyte-surfactant mixtures are ubiquitous in biology and the basis of numerous consumer healthcare products. Despite their broad use, however, a rational approach to their formulation remains challenging because of the complicated association mechanisms. Through compilation and analysis of literature reports and our own research, we have developed a semiempirical correlation of the binding strength of surfactants to polyelectrolytes in salt-free mixtures as a function of the polyion linear charge density and the surfactant hydrophobicity. We have found that the cooperative binding strength increases as the square of the polyelectrolyte's linear charge density and in proportion to the surfactant's hydrophobicity, such that a quantitative relationship holds across a broad range of polyelectrolytes. Deviations from the correlation reveal the role of system-specific interactions not considered in the analysis. This engineering relationship aids in the rational design of oppositely charged polyelectrolyte-surfactant formulations for consumer products and biomedicines by enabling the prediction of binding strengths in polyelectrolyte-surfactant mixtures based on mesoscale parameters determined from the chemical composition. [ABSTRACT FROM AUTHOR]

Micellar solutions of hexadecyltrimethylammonium bromide(CTAB)in a protic ionic liquid, ethylammonium nitrate (EAN), are studiedby shear rheology, polarizing optical microscopy (POM), conductivitymeasurements, and small angle neutron scattering (SANS). Three concentrationregimes are examined: A dilute regime (with concentrations [CTAB]< 5 wt %) consisting of noninteracting spherical micelles, a semidiluteregime (5 wt % ≤ [CTAB] ≤ 45 wt %) where micelles interactvia electrostatic repulsions, and a concentrated regime (45 wt % <[CTAB] ≤ 62 wt %) where a reversible, temperature-dependentisotropic (L1) to hexatic (Hex) phase transition is observed.The L1–Hex transition, which has been predictedbut not previously observed, is characterized by (1) a sharp increasein the shear viscosity, (2) the formation of focal conical birefringencetextures (observed by POM), and (3) enhancement of the crystallineorder, evidenced by the appearance of Bragg reflections in the SANSprofiles. Ionic conductivity is not sensitive to the L1–Hex transition, which corroborates the absence of topologicaltransitions. [ABSTRACT FROM AUTHOR]

In this Article, we report the dielectrophoretic assemblyof colloidalparticles and show how the kinetics of assembly and degree of orderingdepend on the particle size, charge, solution ionic strength, andfield strength and frequency. A special dielectrophoresis (DEP) samplecell is constructed and validated to quantitatively measure directedself-assembly via sequential light scattering and optical microscopymeasurements. Our results confirm the recently established scalingfor the order–disorder transition and extend it to higher scaledfrequencies. The limiting scaling of the order–disorder transitionand particle electrophoretic mobility are correctly predicted by thestandard electrokinetic model (SEKM). In particular, the order–disordertransition line is predicted from the particle properties using arecently proposed empirical scaling law and the SEKM over an orderof magnitude in particle size. [ABSTRACT FROM AUTHOR]

Dynamic arrest transitions of colloidal suspensions containing nonspherical particles are of interest for the design and processing of various particle technologies. To better understand the effects of particle shape anisotropy and attraction strength on gel and glass formation, we present a colloidal model system of octadecyl-coated silica rods, termed as adhesive hard rods (AHR), which enables control of rod aspect ratio and temperature-dependent interactions. The aspect ratios of silica rods were controlled by varying the initial TEOS concentration following the work of Kuijk et al. (J. Am. Chem. Soc., 2011, 133, 2346-2349) and temperature-dependent attractions were introduced by coating the calcined silica rods with an octadecyl-brush and suspending in tetradecane. The rod length and aspect ratio were found to increase with TEOS concentration as expected, while other properties such as the rod diameter, coating coverage, density, and surface roughness were nearly independent of the aspect ratio. Ultrasmall angle X-ray scattering measurements revealed temperature-dependent attractions between octadecyl-coated silica rods in tetradecane, as characterized by a low-q upturn in the scattered intensity upon thermal quenching. Lastly, the rheology of a concentrated AHR suspension in tetradecane demonstrated thermoreversible gelation behavior, displaying a nearly 5 orders of magnitude change in the dynamic moduli as the temperature was cycled between 15 and 40 °C. The adhesive hard rod model system serves as a tunable platform to explore the combined influence of particle shape anisotropy and attraction strength on the dynamic arrest transitions in colloidal suspensions with thermoreversible, short-range attractions. [ABSTRACT FROM AUTHOR]

The self-assembly of an end-functionalized PEO106-PPO70-PEO106 triblock copolymer (BCP) with acrylic end groups (Pluronic F127 diacrylate or FDA) in a protic ionic liquid (deuterated ethylammonium nitrate, dEAN) is studied using small-angle neutron scattering, shear rheology, and dielectric spectroscopy. This functionalization constitutes less than 1 wt % of the copolymer and has no effect on micelle formation in dEAN. The sol-gel transition and the supramolecular crystal structure of the concentrated FDA/dEAN solutions are also found to be unaffected by the acrylation of the end groups. Photo-cross-linking results in viscoelasticity enhancement of the FDA/dEAN solutions with FDA contents below the gel point. Cross-linking gels produces soft elastomers with exceptional elasticity and conductivity comparable to the un-cross-linked solutions. Tuning BCP microstructure via self-assembly in ionic liquids followed by chemical cross-linking is shown to be a promising route for the design of materials with specific mechanical properties and ionic conductivities. [ABSTRACT FROM AUTHOR]

The microstructure and rheologicalproperties of micellar solutionsof Pluronic block copolymers (PEOx–PPOy–PEOx)in deuterated ethylammonium nitrate (dEAN, a protic ionic liquid)are studied by small- and ultrasmall-angle neutron scattering (SANSand USANS), fluorescence microscopy, and shear rheology. A homologousseries of three Pluronics with similar PPO block length (F127 (PEO106–PPO70–PEO106), P123(PEO20–PPO70–PEO20),and L121 (PEO5–PPO70–PEO5)) are examined to explore the effect of the relative balance ofsolvophilic to solvophobic block size on the self-assembled microstructure.Both F127 and P123 form spherical micelles in dEAN that assemble intoface-centered and body-centered cubic supramolecular crystals, respectively,upon increasing concentration or temperature. The transition fromdisordered to crystalline (ordered) structures manifests as a sol–gelrheological transition. A richer phase diagram is observed in theL121/dEAN system: due to its low solvophilicity in dEAN, L121 self-assemblesinto structures with low curvatures, namely, vesicles in the diluteregime, elongated (wormlike) micelles at intermediate concentrationsand low temperatures, a nematic phase in concentrated solutions, andmultilamellar phases at high temperatures. Highly viscoelastic solutionsare created by the self-assembly of entangled L121 wormlike micelles.Structural length scales of the three Pluronic/dEAN systems in thevarious mesophases are determined from SANS and USANS. [ABSTRACT FROM AUTHOR]

The assembly of ordered dicolloid monolayers is directedby anelectric field. The dicolloid particles are polystyrene latex witha maximum equatorial diameter 3.45 μm and length 4.63 μm.The monolayer structure is characterized using small-angle light scatteringand bright-field microscopy. With increasing field strength from 26.7to 200 VRMS/cm, a transition from a disordered monolayer,to first orientationally ordered, and then translationally orderedtwo-dimensional (2D) arrays occurs. A c2mmplane group symmetry dominates the ordered structure but is presentalongside structures with p2 symmetry, leading toa spread in the angular distribution of the light scattering peaks.The order–disorder transition dependence on field strengthand frequency is similar to that observed for colloidal spheres; athigher frequencies, stronger fields are required to assemble particles.Optimal ordered structures reflect a balance between inducing sufficientlystrong interparticle interactions while limiting the rate of formationto ensure the growth of large crystalline domains. [ABSTRACT FROM AUTHOR]

The micellization of dilute solutions of Pluronic block copolymers P123 (EO20–PO70–EO20) and F127 (EO106–PO70–EO106) and comicellization of binary mixtures in partially deuterated ethylammonium nitrate (d3EAN, a protic ionic liquid) are studied by small-angle neutron scattering. The average Pluronics composition in micelles shows a linear dependence on the bulk Pluronic composition. The mole ratio between P123 molecules in the micelles to those existing as unimers in solvent increases with temperature and P123 concentration. At a fixed F127/P123 ratio, the micelle core radius, the micelle corona thickness, and the aggregation number decrease with increasing temperature, while the total micelle volume fraction increases. At a fixed temperature, increasing P123 content in the binary mixtures leads to a weak minimum in micelle core size and aggregation number and a weak maximum in micelle corona thickness and total volume fraction of micelles. The comicellization behavior in d3EAN resembles that in aqueous solutions reported experimentally and theoretically. To our knowledge, this is the first experimental report on comicellization behavior of Pluronic triblock copolymers in a protic ionic liquid. [ABSTRACT FROM AUTHOR]

High-structured carbon fillers are ubiquitous as the conductive additive comprising suspension-based electrochemical energy storage technologies. Carbon black networks provide the necessary electrical conductivity as well as mechanical percolation in the form of a yield stress. Despite their critical role in determining system performance, a full mechanistic understanding of the relationship between the electrical transport characteristics of the percolated, conductive networks of carbon black, and the rheological properties is lacking, which hinders the rational design and optimization of flowable electrodes and the processing of electrolytes for batteries. Here, we report on the microstructural origin of the rheological and electrical properties of two commonly used conductive additives in neat propylene carbonate. From quiescent mechanical and structural studies, we find that the gelation of these carbon black suspensions is best described by the dynamic arrest of a clustered fluid phase. In contrast, the temperature and frequency dependence of the ac conductivity near this transition shows that mesoscale charge transport is determined by hopping between localized states that does not require a stress-bearing network. This unique combination of microstructural characterization with rheological and electrical measurements enables testing prevailing theories of the connection between electrical and mechanical percolation as well as improving conductive additives to enhance electrochemical performance. [ABSTRACT FROM AUTHOR]

Recently, reversible cluster formation was identified as an underlying cause of anomalously large solution viscosities observed in some concentrated monoclonal antibody (mAb) formulations, which poses a major challenge to the use of subcutaneous injection for some mAbs. A fundamental understanding of the structural and dynamic origins of high viscosities in concentrated mAb solutions is thus of significant relevance to mAb applications in human health care, as well as being of scientific interest. Herein, we present a detailed investigation of an IgG1-based mAb to relate the short-time dynamics and microstructure to significant viscosity changes over a range of pharmaceutically relevant physiochemical conditions. The combination of light scattering, small-angle neutron scattering, and neutron spin echo measurement techniques conclusively demonstrates that, upon addition of Na2SO4, these antibodies form strongly bound reversible dimers at dilute concentrations that interact with each other to form large, loosely bound, transient clusters when concentrated. This hierarchical structure formation in solution causes a significant increase in the solution viscosity. [ABSTRACT FROM AUTHOR]

The formation of multilamellar vesicles(MLVs) from the lamellar phase of nonionic surfactant system C12E5/D2O under shear flow is studiedby time-resolved small angle neutron and light scattering during shearflow. A novel small angle neutron scattering sample environment enablesthe tracking of the lamellae alignment in the velocity–velocitygradient (1–2) plane during MLV formation, which was trackedindependently using flow small angle light scattering commensuratewith rheology. During the lamellar-to-multilamellar vesicle transition,the primary Bragg peak from the lamellar ordering was observed totilt, and this gradually increased with time, leading to an anisotropicpattern with a primary axis oriented at ∼25° relativeto the flow direction. This distorted pattern persists under flowafter MLV formation. A critical strain and critical capillary numberbased on the MLV viscosity are demonstrated for MLV formation, whichis shown to be robust for other systems as well. These novel measurementsprovide fundamentally new information about the flow orientation oflamellae in the plane of flow that cannot be anticipated from thelarge body of previous literature showing nearly isotropic orientationin the 2,3 and 1,3 planes of flow. These observations are consistentwith models for buckling-induced MLV formation but suggest that theinstability is three-dimensional, thereby identifying the mechanismof MLV formation in simple shear flow. [ABSTRACT FROM AUTHOR]

The search for stable vesicular structures is a long-standing topic of research because of the usefulness of these structures and the scarcity of surfactant systems that spontaneously form vesicles in true thermodynamic equilibrium. We report the first experimental evidence of spontaneous formation of vesicles for a pure cationic double tail surfactant (didodecyldimethylammonium bromide, DDAB) in a protic ionic liquid (ethylammonium nitrate, EAN). Using small and ultra-small angle neutron scattering, rheology and bright field microscopy, we identify the coexistence of two vesicle containing phases in compositions ranging from 2 to 68 wt %. A low density highly viscous solution containing giant vesicles (D ∼ 30 μm) and a sponge (L3) phase coexists with a dilute high density phase containing large vesicles (D ∼ 2.5 μm). Vesicles form spontaneously via different thermodynamic routes, with the same size distribution, which strongly supports that they exist in a true thermodynamic equilibrium. The formation of equilibrium vesicles and the L3 phase is facilitated by ion exchange between the cationic surfactant and the ionic liquid, as well as the strength of the solvophobic effect in the protic ionic liquid. [ABSTRACT FROM AUTHOR]

The self-assembly of didodecyldimethylammonium bromide (DDAB) in a protic ionic liquid, ethylammonium nitrate (EAN), in the high surfactant concentration regime is studied using five different experimental techniques. A thermoreversible first-order sponge (L3) to lamellar (Lα) transition occurring at [DDAB] > 80 wt % was identified by (1) a sharp increase in the elastic and viscous moduli, (2) a transition peak recorded by differential scanning calorimetry, (3) formation of Maltese cross birefringence textures observed via polarizing optical microscopy, (4) a decrease in the interbilayer mean distance measured by small angle neutron scattering, and (5) an abrupt increase in the conductivity obstruction factor. In contrast to aqueous DDAB solutions, this surfactant forms a stable L3phase in EAN in a wide window of compositions and temperatures, which is potentially useful for the synthesis of nanoporous materials. To the best of our knowledge, this is the first evidence of the formation of the L3phase in an ionic liquid. [ABSTRACT FROM AUTHOR]