Influence of Surfactant Structure on Polydisperse Formulations of Alkyl Ether Sulfates and Alkyl Amidopropyl Betaines.

Surfactants provide detergency, foaming, and texture in personal care formulations, yet the micellization of typical industrial primary and cosurfactants is not well understood, particularly in light of the polydisperse nature of commercial surfactants. Synergistic interactions are hypothesized to drive the formation of elongated wormlike self-assemblies in these mixed surfactant systems. Small-angle neutron scattering, rheology, and pendant drop tensiometry are used to examine surface adsorption, viscoelasticity, and self-assembly structure for wormlike micellar formulations comprising cocoamidopropyl betaine, and its two major components laurylamidopropyl betaine and oleylamidopropyl betaine, with sodium alkyl ethoxy sulfates. The tail length of sodium alkyl ethoxy sulfates was related to their ability to form wormlike micelles in electrolyte solutions, indicating that a tail length greater than 10 carbons is required to form wormlike micelles in NaCl solutions, with the decyl homologue unable to form elongated micelles and maintaining a low viscosity even at 20 wt % surfactant loading with 4 wt % NaCl present. For these systems, the incorporation of a disperse ethoxylate linker does not enable shorter chain surfactants to elongate into wormlike micelles for single-component systems; however, it could increase the interactions between surfactants in mixed surfactant systems. For synergy in surfactant mixing, the nonideal regular solution theory is used to study the sulfate/betaine mixtures. Tail mismatch appears to drive lower critical micelle concentrations, although tail matching improves synergy with larger relative reductions in critical micelle concentrations and greater micelle elongation, as seen by both tensiometric and scattering measurements.

Comparison of the Anti-inflammatory Activity and Cellular Interaction of Brush Polymer-N-Acetyl Cysteine Conjugates in Human and Murine Microglial Cell Lines.

Microglia-mediated neuroinflammation is commonly associated with neurodegeneration and has been implicated in several neurological disorders, such as Alzheimer's disease and Parkinson's disease. Therefore, it is crucial to develop a detailed understanding of the interaction of potential nanocarriers with microglial cells to efficiently deliver anti-inflammatory molecules. In this study, we applied brush polymers as a modular platform to systematically investigate their association with murine (BV-2) and human (HMC3) microglial cell lines in the presence and absence of the pro-inflammatory inducer lipopolysaccharide (LPS) using flow cytometry. Brush polymers of different sizes and shapes, ranging from ellipsoid to worm-like cylinders, were prepared through a combination of the two building blocks carboxylated N-acylated poly(aminoester)s (NPAEs)-based polymers and poly(2-ethyl-2-oxazoline)-NH2 (PEtOx-NH2) and characterized by 1H NMR spectroscopy, size exclusion chromatography, and small-angle neutron scattering. Generally, ellipsoidal particles showed the highest cellular association. Moreover, while no significant differences in murine cell association were observed, the brush polymers revealed a significant accumulation in LPS-activated human microglia compared to resting cells, emphasizing their higher affinity to activated HMC3 cells. Brush polymers with the highest cell association were further modified with the anti-inflammatory agent N-acetyl cysteine (NAC) in a reversible manner. The brush polymer-NAC conjugates were found to significantly attenuate the production of interleukin 6 (p < 0.001) in LPS-activated HMC3 cells compared to LPS-activated BV-2 cells. Thus, the presented brush polymer-NAC conjugates showed a high anti-inflammatory activity in human microglia, suggesting their potential for disease-targeted therapy of microglial-mediated neuroinflammation in the future.

Frequency Dependent Silica Dissolution Rate Enhancement under Oscillating Pressure via an Electrochemical Pressure Solution-like, Surface Resonance Mechanism.

From atomic force microscopy (AFM) experiments, we report a new phenomenon in which the dissolution rate of fused silica is enhanced by more than 5 orders of magnitude by simply pressing a second, dissimilar surface against it and oscillating the contact pressure at low kHz frequencies in deionized water. The silica dissolution rate enhancement was found to exhibit a strong dependence on the pressure oscillation frequency consistent with a resonance effect. This harmonic enhancement of the silica dissolution rate was only observed at asymmetric material interfaces (e.g., diamond on silica) with no evidence of dissolution rate enhancement observed at symmetric material interfaces (i.e., silica on silica) within the experimental time scales. The apparent requirement for interface dissimilarity, the results of analogous experiments performed in anhydrous dodecane, and the observation that the silica "dissolution pits" continue to grow in size under contact stresses well below the silica yield stress refute a mechanical deformation or chemo-mechanical origin to the observed phenomenon. Instead, the silica dissolution rate enhancement exhibits characteristics consistent with a previously described 'electrochemical pressure solution' mechanism, albeit, with greatly amplified kinetics. Using a framework of electrochemical pressure solution, an electrochemical model of mineral dissolution, and a recently proposed "surface resonance" theory, we present an electro-chemo-mechanical mechanism that explains how oscillating the contact pressure between dissimilar surfaces in water can amplify surface dissolution rates by many orders of magnitude. This reaction rate enhancement mechanism has implications not only for dissolution but also for potentially other reactions occurring at the solid-liquid interface, e.g. catalysis.

Synthesis and Characterization of Polyethylenimine-Silica Nanocomposite Microparticles.

A novel procedure for the synthesis of polyethylenimine (PEI)-silica nanocomposite particles with high adsorption capacities has been developed based on an emulsion templating concept. The exceptional chelating properties of PEI as the parent polymer for the particle core promote the binding abilities of the resulting composite for charged species. Further, the subsequent introduction of silica via the self-catalyzed hydrolysis of tetraethoxysilane facilitates production of robust composite particles with smooth surfaces, enabling potential use in multiphase environments. To enable tailored application in solid/liquid porous environments, the production of particles with reduced sizes was attempted by modulating the shear rates and surfactant concentrations during emulsification. The use of high-speed homogenization resulted in a substantial decrease in average particle size, while increasing surfactant loading only had a limited effect. All types of nanocomposites produced demonstrated excellent binding capacities for copper ions as a test solute. The maximum binding capacities of the PEI-silica nanocomposites of 210-250 mg/g are comparable to or exceed those of other copper binding materials, opening up great application potential in resources, chemical processing, and remediation industries.

Copper-Binding Properties of Polyethylenimine-Silica Nanocomposite Particles.

Increasing demand for copper resources, accompanied by increasing pollution, has resulted in an urgent need for effective materials for copper binding and extraction. Polyethylenimine (PEI) is one of the strongest copper-chelating agents but is not suitable directly (as is) for most applications due to its high solubility in water. PEI-based composite materials show potential as efficient and practical alternatives. In the present work, the interaction of copper ions with PEI-silica nanocomposite particles and precursor PEI microgels (as a reference) is investigated. It is hypothesized that the main driving force of the reaction is chelation of copper ions by amino groups in the PEI network. The presence of silica in the PEI-silica composites was shown to increase the copper-binding capacity in comparison with the parent microgel. The copper-binding behavior of etched (PEI-free "ghost") composite particles in comparison with the original composites and microgel particles shows that silica nanoparticles in the composite structure increase the number of copper-binding sites in the PEI network rather than adsorbing copper themselves. PEI-silica composites can be easily recycled after copper adsorption by simply washing in 1 M nitric acid, which results in complete copper extraction. Employing this recovery method, PEI-silica composite particles can be used for multiple, efficient cycles of copper removal and extraction.

Structure-Performance Relationships for Tail Substituted Zwitterionic Betaine-Azobenzene Surfactants.

Azobenzene-containing surfactants (azo-surfactants) have garnered significant attention for their use in generating photoresponsive foams, interfaces, and colloidal systems. The photoresponsive behavior of azo-surfactants is driven by the conformational and electronic changes that occur when the azobenzene chromophore undergoes light-induced trans ⇌ cis isomerization. Effective design of surfactants and targeting of their properties requires a robust understanding of how the azobenzene functionality interacts with surfactant structure and influences overall surfactant behavior. Herein, a library of tail substituted azo-surfactants were synthesized and studied to better understand how surfactant structure can be tailored to exploit the azobenzene photoswitch. This work shows that tail group structure (length and branching) has a profound influence on the critical micelle concentration of azo-surfactants and their properties once adsorbed to an air-water interface. Neutron scattering studies revealed the unique role that intermolecular π-π azobenzene interactions have on the self-assembly of azo-surfactants, and how the influence of these interactions can be tuned using tail group structure to target specific aqueous aggregate morphologies.

Spontaneous surface adsorption of aqueous graphene oxide by synergy with surfactants.

The spontaneous adsorption of graphene oxide (GO) sheets at the air-water interface is explored using X-ray reflectivity (XRR) measurements. As a pure aqueous dispersion, GO sheets do not spontaneously adsorb at the air-water interface due to their high negative surface potential (-60 mV) and hydrophilic functionality. However, when incorporated with surfactant molecules at optimal ratios and loadings, GO sheets can spontaneously be driven to the surface. It is hypothesised that surfactant molecules experience favourable attractive interactions with the surfaces of GO sheets, resulting in co-assembly that serves to render the sheets surface active. The GO/surfactant composites then collectively adsorb at the air-water interface, with XRR analysis suggesting an interfacial structure comprising surfactant tailgroups in air and GO/surfactant headgroups in water for a combined thickness of 30-40 Å, depending on the surfactant used. Addition of too much surfactant appears to inhibit GO surface adsorption by saturating the interface, and low loadings of GO/surfactant composites (even at optimal ratios) do not show significant adsorption indicating a partitioning effect. Lastly, surfactant chemistry is also a key factor dictating adsorption capacity of GO. The zwitterionic surfactant oleyl amidopropyl betaine causes marked increases in GO surface activity even at very low concentrations (≤0.2 mM), whereas non-ionic surfactants such as Triton X-100 and hexaethyleneglycol monododecyl ether require higher concentrations (ca. 1 mM) in order to impart spontaneous adsorption of the sheets. Anionic surfactants do not enhance GO surface activity presumably due to like-charge repulsions that prevent co-assembly. This work provides useful insight into the synergy between GO sheets and molecular amphiphiles in aqueous systems for enhancing the surface activity of GO, and can be used to inform system formulation for developing water-friendly, surface active composites based around atomically thin materials.

Norepinephrine derived carbon dots for live-cell imaging and effective hemoglobin determination.

Recently, carbon dots (CDs) have attracted wide attention for their potential use as fluorescence probes in biological and analytical chemistry due to their great stability and high fluorescence quantum yields. In our work, norepinephrine (NE)-derived CDs with green luminescence and an average size of 10 nm were fabricated using a one-step hydrothermal route. As-prepared CDs show a strong emission at a wavelength of 520 nm when excited at 420 nm, and demonstrate pH and concentration dependent fluorescence behaviour. Multiple functional groups on the CDs allow their protonation/deprotonation and thus alter fluorescence intensity and peak position in different pH conditions. Prepared CDs show significant potential to be used as a live-cell imaging agent with long-term photostability. Furthermore, a simple but effective method to determine the concentration of hemoglobin (Hb) in diluted human blood samples was also developed based on the inner filter effect (IFE). The method demonstrates good linearity from 0.01-10 µM, with a limit of determination (LOD) of 52 nM.

A rapid paper-based blood typing method from droplet wicking.

Paper-based diagnostics are leading the field of low-cost, point of care analytical techniques. However, large scale testing facilities such as hospitals are still primarily using the gel column agglutination technique. This is because paper-based systems are single use tests that are generally more time consuming and less automatable than traditional methods. Here, we present a novel, rapid and scalable, paper-based blood typing method that can produce test results in under ten seconds. We believe this is the fastest blood typing test that is appropriate for large scale automation. The test consists of placing a drop of antibody solution on paper, followed by a drop of blood on the same locus, and measuring the evolution of blood stain area as a function of time. Positive reactions for both forward and reverse tests have significantly slower growth rates and smaller final stain sizes when compared to negatives. We analyse the effect paper type, red blood cell concentration, antibody specificity (A, B and D) and antibody dilution have on the sensitivity and reproducibility of the technique. A high sensitivity is found in papers with a low density and thickness. The optimum red blood cell concentration is determined from a balance between wicking rate, strength of reaction and optical contrast. A and B antibodies give more sensitive results than D; however, the D antigen can still be successfully identified. This technique has the potential to significantly cut down the time and cost of blood typing tests and enable design of a new high throughput and fully automatable system.

Droplet-based blood group antibody screening with laser incubation.

Detection of blood group antibodies is a crucial step for blood transfusion recipients and pregnant women to prevent potentially fatal haemolytic reactions. Due to the short, non-bridging structure of such antibodies (IgG), the indirect antiglobulin test (IAT) is required, complete with a thermal incubation phase. This incubation step, where the sample must be heated to 37 °C for several minutes, has hitherto prevented chip- and paper-diagnostics from performing a complete IAT and instead required the IAT to be performed away from the patient beside in a laboratory setting with specialist equipment - significantly delaying blood transfusions. With recent laser technology for immunohaematology, a single blood droplet can be heated. This study presents a simple diagnostic where a single 15 µL droplet sits on hydrophobic PTFE film and is heated by laser. The result of the test is then determined via placement of a paper strip where passive wicking and filtration of the sample separates positive from negative results. We demonstrate that this diagnostic can accurately and sensitively detect blood group antibodies, with results quickly read by eye without further specialist equipment or training, with potential to lead to a point-of-care antibody screen.

Pattern formation in drying blood drops.

Patterns in dried droplets are commonly observed as rings left after spills of dirty water or coffee have evaporated. Patterns are also seen in dried blood droplets and the patterns have been shown to differ from patients afflicted with different medical conditions. This has been proposed as the basis for a new generation of low-cost blood diagnostics. Before these diagnostics can be widely used, the underlying mechanisms leading to pattern formation in these systems must be understood. We analyse the height profile and appearance of dispersions prepared with red blood cells (RBCs) from healthy donors. The red cell concentrations and diluent were varied and compared with simple polystyrene particle systems to identify the dominant mechanistic variables. Typically, a high concentration of non-volatile components suppresses ring formation. However, RBC suspensions display a greater volume of edge deposition when the red cell concentration is higher. This discrepancy is caused by the consolidation front halting during drying for most blood suspensions. This prevents the standard horizontal drying mechanism and leads to two clearly defined regions in final crack patterns and height profile. This article is part of a discussion meeting issue 'A cracking approach to inventing new tough materials: fracture stranger than friction'.

Exploring the transition of polydopamine-shelled perfluorohexane emulsion droplets into microbubbles using small- and ultra-small-angle neutron scattering.

Perfluorocarbon emulsion droplets are interesting colloidal systems with applications, ranging from diagnostics and theranostics to drug delivery, due to their controllable phase transition into microbubbles via heat application or acoustic droplet vapourisation. This work highlights the application of small- and ultra-small-angle neutron scattering (SANS and USANS, respectively), in combination with contrast variation techniques, in observing the in situ phase transition of polydopamine-stabilised perfluorohexane (PDA/PFH) emulsion droplets into microbubbles during heating. Results show peak USANS intensities at temperatures around 90 °C, which indicates that the phase transition of PDA/PFH emulsion droplets occurs at significantly higher temperatures than the bulk boiling point of pure liquid PFH (56 °C). Analysis and model fitting of the SANS and USANS data allowed us to estimate droplet sizes and interfacial properties at different temperatures (20 °C, 90 °C, and 20 °C after cooling), giving valuable insights about the transformation of these polydisperse emulsion droplet systems.

Radial Wicking of Biological Fluids in Paper.

In this study, we analyze stain growth kinetics from droplets of biological fluids such as blood, plasma, and protein solutions on paper both experimentally and numerically. The primary difference of biological fluids from a simple fluid is a significant wetting/dewetting hysteresis in paper. This becomes important in later stages of droplet wicking, after the droplet has been completely absorbed into paper. This is shown by anomalous power dependence of area with time in the later stages of radial wicking. At early stages, current numerical wicking models can predict stain growth of biological fluids. However, at later stages, the introduction of hysteresis complicates modeling significantly. We show that the cause of the observed hysteresis is due to contact angle effects and that this is the dominant mechanism that leads to the anomalous stain growth kinetics measured uniquely in biological fluids. Results presented will streamline the design process of paper-based diagnostics, allowing a modeling approach instead of a trial and error method.

In Situ Nanostructural Analysis of Concentrated Wormlike Micellar Fluids Comprising Sodium Laureth Sulfate and Cocamidopropyl Betaine Using Small-Angle Neutron Scattering.

Concentrated wormlike micellar fluids form the basis for a vast array of formulated products, from liquid soaps and shampoos to drag reduction and drilling fluids. Typically, these systems are analyzed using bulk rheological measurements to determine their flow properties and cryo-microscopy to detect their nanostructure. Small-angle neutron scattering provides an opportunity to directly and nonperturbatively analyze nanostructure in situ but is complicated for concentrated systems by correlations from interparticle volume exclusion. Here, we use small-angle and ultra-small-angle neutron scattering to probe directly for the first time the nanostructure of concentrated wormlike micellar fluids composed of the widely used surfactant pair sodium laureth sulfate and cocamidopropyl betaine in aqueous electrolytes. Obtained data are analyzed using different approaches to determine scattering contributions from the wormlike particles themselves and interactions between them. It is found that approximating worms as locally rigid cylinders offers some insight into their aggregation dimensions at short length scales, and both volume exclusion and screened Coulombic interaction potentials describe interactions reasonably well. Using the semi-empirical polymer reference interaction site model (PRISM) gives excellent agreement with observed scattering, and physical insight obtained using this approach is discussed in detail. A drawback of this method is the significant complexity in coding the model in order to fit data, so to facilitate this for future researchers, we provide with this paper a fully operational, open-source code to utilize this model.

Tuning Cellular Interactions of Carboxylic Acid-Side-Chain-Containing Polyacrylates: The Role of Cyanine Dye Label and Side-Chain Type.

Cellular uptake and intracellular targeting to specific organelles are key events in the cellular processing of nanomaterials. Herein, we perform a detailed structure-property relationship study on carboxylic acid-side-chain-bearing polyacrylates to provide design criteria for the manipulation of their cellular interactions. Redox-initiated reversible addition-fragmentation chain-transfer (RRAFT) polymerization of three tert-butyl-protected N-acylated amino ester-based acrylate monomers of different substitutions and degrees of polymerization (DPs) yielded defined and pH-responsive carboxylic acid-side-chain polymers upon deprotection (N-acetyl, DP 1: P(M1); N-propionyl, DP 1: P(E1), DP 2: P(E2)). Flow cytometry studies revealed time-dependent cell association with P(E2) > P(E1) > P(M1) at any given time point. Importantly, the type of cyanine dye used for labeling was found to significantly influence the cellular processing of the polymers. Changing the dye from Cy5 to its sulfonated version sulfoCy5 resulted in a much lower cellular association. Moreover, Cy5-labeled polymers were targeted to mitochondria, while sulfoCy5 modification caused a significant change in the cellular fate of polymers toward lysosome trafficking. This study highlights the importance of selecting a suitable dye but also demonstrates the possibilities for the rational design of organelle-specific targeting of carboxylated polyacrylates.

Spontaneous Self-Assembly of Thermoresponsive Vesicles Using a Zwitterionic and an Anionic Surfactant.

Spontaneous formation of vesicles from the self-assembly of two specific surfactants, one zwitterionic (oleyl amidopropyl betaine, OAPB) and the other anionic (Aerosol-OT, AOT), is explored in water using small-angle scattering techniques. Two factors were found to be critical in the formation of vesicles: surfactant ratio, as AOT concentrations less than equimolar with OAPB result in cylindrical micelles or mixtures of micellar structures, and salt concentration, whereby increasing the amount of NaCl promotes vesicle formation by reducing headgroup repulsions. Small-angle neutron scattering measurements reveal that the vesicles are approximately 30-40 nm in diameter, depending on sample composition. Small-angle X-ray scattering measurements suggest preferential partitioning of OAPB molecules on the vesicle inner layer to support vesicular packing. Heating the vesicles to physiological temperature (37 °C) causes them to collapse into smaller ellipsoidal micelles (2-3 nm), with higher salt concentrations (≥10 mM) inhibiting this transition. These aggregates could serve as responsive carriers for loading or unloading of aqueous cargoes such as drugs and pharmaceuticals, with temperature changes serving as a simple release/uptake mechanism.

Capture of Perfluorooctanoic Acid Using Oil-Filled Graphene Oxide-Silica Hybrid Capsules.

Fluorinated hydrocarbon (FHC) contamination has attracted global attention recently because of persistence within the environment and ecosystems of many types of FHC. The surfactant perfluorooctanoic acid (PFOA) is particularly commonly found in contaminated sites, and thus, urgent action is needed for its removal from the environment. In this study, water dispersible hybrid capsules were successfully prepared from an oil-in-water emulsion stabilized by graphene oxide and including a silicate precursor to grow a strong, mesoporous capsule shell surrounding the droplets. These capsules were decorated with amine groups to present a positively charged outer corona that attracts negative PFOA molecules. The aminated capsules were effectively applied as a novel technology to adsorb and sequester PFOA contamination in water. It was confirmed that PFOA removal by the capsules was pH and PFOA concentration dependent, with adsorption efficiencies of >60 mg g-1 under ideal conditions. PFOA removal kinetics followed using high-performance liquid chromatography and liquid chromatography-mass spectrometry showed that capture of PFOA by the capsules reached a maximum of >99.9% in 2-3 days.

Structural relationships for the design of responsive azobenzene-based lyotropic liquid crystals.

Light-responsive binary (azobenzene + solvent) lyotropic liquid crystals (LCs) were investigated by structural modification of simple azobenzene molecules. Three benzoic acid-containing azobenzene molecules 4-(4-(hydroxyphenyl)diazenyl)benzoic acid (AZO1), 3-(4-(hydroxyphenyl)diazenyl)benzoic acid (AZO2) and 5-(4-(hydroxyphenyl)diazenyl)isophthalic acid (AZO3) were produced with various amide substitutions to produce tectons with a variety of hydrophobicity, size and branching. The LC mesophases formed by binary (azobenzene + solvent) systems with low volatility solvents dimethylsulfoxide (DMSO) and N,N-dimethylformamide (DMF) as well as the protic ionic liquids ethylammonium formate (EAF) and propylammonium formate (PAF), were investigated using a combination of small-angle X-ray and neutron scattering (SAXS and SANS) as well as polarising light microscopy (PLM). Increasing alkyl group length was found to have a strong influence on LC phase spacing, and changes in the position of substitution on the benzene ring influenced the preferred curvature of phases. UV-induced trans to cis isomerization of the samples was shown to influence ordering and optical birefringence, indicating potential applications in optical devices.

Favored local structures in amorphous colloidal packings measured by microbeam X-ray diffraction.

Local structure and symmetry are keys to understanding how a material is formed and the properties it subsequently exhibits. This applies to both crystals and amorphous and glassy materials. In the case of amorphous materials, strong links between processing and history, structure and properties have yet to be made because measuring amorphous structure remains a significant challenge. Here, we demonstrate a method to quantify proportions of the bond-orientational order of nearest neighbor clusters [Steinhardt, et al. (1983) Phys Rev B 28:784-805] in colloidal packings by statistically analyzing the angular correlations in an ensemble of scanning transmission microbeam small-angle X-ray scattering (µSAXS) patterns. We show that local order can be modulated by tuning the potential between monodisperse, spherical colloidal silica particles using salt and surfactant additives and that more pronounced order is obtained by centrifugation than sedimentation. The order in the centrifuged glasses reflects the ground state order in the dispersion at lower packing fractions. This diffraction-based method can be applied to amorphous systems across decades in length scale to connect structure to behavior in disordered systems with a range of particle interactions.

Enhancing Printing Resolution on Hydrophobic Polymer Surfaces Using Patterned Coatings of Cellulose Nanocrystals.

High-resolution inkjet printing of a hydrophobic polymer surface (polystyrene, PS) was accomplished using a patterned coating of cellulose nanocrystals (CNCs) that prevents the ink from bleeding. A periodically crack-free, wrinkled (wavelength of around 850 nm) stamp was prepared by surface oxidation of an uniaxially stretched poly(dimethylsiloxane) elastomeric substrate and was used as a template to transfer aligned patterns of cellulose nanocrystals (CNCs) onto PS surfaces by wet stamping. The morphology of the aligned CNC coatings on PS was then compared with randomly deposited CNCs on PS using atomic force microscopy. The wettability of the CNCs and polymer surfaces with water and ink was measured and analyzed in the context of inkjet printing. This biomaterial coating technique enables high-resolution printing of modern water-based inks onto hydrophobic surfaces for applications in renewable packaging and printing of biomolecules for high throughput diagnostics. Further, with suitable modifications, the technology is scalable to roll-to-roll manufacturing for industrial flexo printing.