Fluid Surfactant Research Articles

FAST DISSOLVING TABLET USING SOLID DISPERSION TECHNIQUE: A REVIEW

Fast dissolving tablets are also called as mouth-dissolving tablets, melt-in mouth tablets, orodispersible tablets, quick dissolving etc. Fast dissolving tablets are those when put on tongue disintegrate instantaneously releasing the drug, which dissolve or disperses in the saliva. The faster the drug dissolved into solution, quicker the absorption and onset of clinical effect. Oral routes of drug administration have wide acceptance up to 50-60% of total dosage forms. Fast dissolving tablet containing solid dispersion was developed to improve the dissolution of drug and stability of solid dispersion. They are disintegrating and/or dissolve rapidly in the saliva without the need for water. Thus it is regarded as the safest, most convenient and most economical method of drug delivery having the highest patient compliance. The later part of the article focus on the progress in methods of manufacturing, evaluation and various latest technologies involved in the development of Fast dissolving tablets. Solid dispersion is basically a drug–polymer two-component system; the drug–polymer interaction is the determining factor in its design and performance. It also discusses about modern characterization technique to characterize solid dispersion. In this review, it is intended to discuss the recent advances related on the area of solid dispersion technology. Different methods are also been used for preparation of solid dispersions such as Melting method, Solvent method, Melting solvent method, Melt extrusion method, lyophilisation Technique, Melt Agglomeration Process, The Use Of Surfactant, Electro spinning and Super Critical Fluid Technology. The introduction of fast dissolving dosage forms has solved some of the problems encountered in administration of drugs to the pediatric and elderly patient, which constitutes a large proportion of the world's population. Solid dispersions have attracted considerable interest as an efficient means of improving the dissolution rate and hence the bio availability of a range of poorly water-soluble drugs. The focus of one part of the review article is based on solid dispersion mainly advantages, disadvantages, types, the method of preparation, and characterization of the solid dispersion at laboratory and industrial level.

Effect of multi-walled carbon nanotubes on linear viscoelastic behavior and microstructure of zwitterionic wormlike micelle at high temperature

The effects of hydroxyl functionalized multi-walled carbon nanotubes (MWCNTs) on linear viscoelastic behavior and microstructure of zwitterionic surfactant oleylamido propyl betaine (BET) micellar solutions were investigated by Cryo-Transmission Electron Microscopy (Cryo-TEM), Fourier Transmission Infrared Spectroscopy (FT-IR) and rheological measurements. In this study, the addition of MWCNTs has obvious effects on the rheological behavior of the mixed system: an increase in the zero-shear viscosity of the system, and appearance of shear thinning non-Newtonian behavior instead of Newtonian behavior at dilute micellar solution. The addition of MWCNTs also obviously increases the semidilute micellar solution's relaxation time, reptation time and storage modulus. Moreover, the temperature resistance of the system with MWCNTs is greatly improved compared with that without MWCNTs. The results of Cryo-TEM and FT-IR measurement demonstrate that the MWCNTs can associate with wormlike micelle to form a strong and complex network structure by micellar end-cap adsorption and hydrogen bonding interaction. The synergistic interaction enhances the viscosity and elasticity of the zwitterionic surfactant fluids at high temperature.

Linear and unconditionally energy stable schemes for the binary fluid–surfactant phase field model

In this paper, we consider the numerical solution of a binary fluid–surfactant phase field model, in which the free energy contains a nonlinear coupling entropy, a Ginzburg–Landau double well potential, and a logarithmic Flory–Huggins potential. The resulting system consists of two nonlinearly coupled Cahn–Hilliard type equations. We develop a first and a second order time stepping schemes for this system using the “Invariant Energy Quadratization” approach; in particular, the system is transformed into an equivalent one by introducing appropriate auxiliary variables and all nonlinear terms are then treated semi-explicitly. Both schemes are linear and lead to symmetric positive definite systems in space at each time step, thus they can be efficiently solved. We further prove that these schemes are unconditionally energy stable in the discrete sense. Various 2D and 3D numerical experiments are performed to validate the accuracy and energy stability of the proposed schemes.

Nanoparticle-Enhanced Hydraulic-Fracturing Fluids: A Review

Summary Hydraulic-fracturing fluids are used to break down subterranean formations where oil and gas are trapped. Pad or prepad fluids are first pumped into the formation to generate the fracture geometry. Once the fracture geometry is created, additional fluid containing proppant is used to transport these solid particles into the fractures. Then, the hydraulic pressure is released and the fracture will tend to close. At that stage, the proppant prevents fracture closure and provides a conductive channel for hydrocarbons to flow into the wellbore. Biopolymers, synthetic polymers, foams, viscoelastic surfactant (VES) fluids, and slickwater are all used as fracturing fluids, each with properties that are beneficial under certain conditions. Today, their formulations are well-developed, and more recently, may incorporate small-sized particles in the nanometer size range. Such nanoparticles have addressed certain technological limitations of fracturing fluids. For example, VES fluids were reported to suffer high leakoff rates in moderate permeability reservoirs (200 md) and were limited in temperature (beyond approximately 220°F, viscosity was diminished significantly). Another challenge is the pressure-dependent behavior of borate-crosslinked gels, where the viscosity was found to drop significantly under high pressures. Also, in high-temperature reservoirs (>350°F), it is very challenging to design a fluid that can sustain enough viscosity for a required period of time. Synthetic polymers (mainly acrylamide-based polymers) are commonly used and have been reported to be used at high concentrations. These high-concentration requirements are imposed by the need for a stable viscosity under high-temperature conditions. High polymer loading increases the potential of formation damage caused by the fluid residue. These challenges, which can be addressed by nanotechnology, could have a major impact on hydraulic-fracturing applications. For instance, the working temperature limit of VES-based fluids was improved from 200 to 250°F (93 to 121°C) by adding zinc oxide (ZnO) and magnesium oxide (MgO) nanoparticles. The borate-crosslinked gels were found to maintain their viscosity at pressures up to 20,000 psi when using boronic acid-functionalized nanolatex silica particles as crosslinkers, while under such high pressures, conventional borate crosslinkers showed more than 80% reduction in viscosity. Moreover, the rheological properties of mixed VES/polymer fluids were enhanced when using nanoparticles. Use of foams can reduce the amount of water consumed in hydraulic fracturing. Alfa olefin sulfonate (AOS) surfactant can be foamed by use of carbon dioxide (CO2). Aluminum oxide nanoparticles were found to stabilize the foams created by AOS, VES, and CO2. This has a potential application in waterless fracturing. This review paper will capture all of these aspects and summarize the most recent experience of nanoparticle usage in hydraulic-fracturing fluids design.

EFFECTS OF NANOPARTICLES AND SURFACTANT CHARGE GROUPS ON THE PROPERTIES OF VES GEL

Abstract - Application of viscoelastic surfactant (VES) fluids in hydraulic fracturing is still in the development stage, though shear thinning behavior and water solubility are the two important characteristics behind increasing interest in their use in fracturing jobs. Effects of ionic characteristics and the concentration of different surfactants on the rheological properties of VES fluid have been investigated in detail in the present study for a number of surfactant systems. Phase behavior of the system was studied and the gel region was identified. Effects of alkali on the viscosity, thermal stability, and miscibility (in water) of the developed gel were also investigated. Dynamic rheological study was carried out to determine the storage modulus and loss modulus. This study shows that mixed anionic-anionic system gives improved rheology compared to single anionic and mixed anionic-zwitterionic surfactant systems. Keywords : Hydraulic Fracturing; Viscoelastic gel; Surfactant based fluids; Rheology; Nanoparticles.

Fluid Interaction with Tight Rocks to Induce Energy Recovery

The research using aqueous surfactant fluid to interact with tight rocks to increase petroleum production was conducted from our group in 2009. As part of our effort to assess the potential for imbibition to recovery oil from shale, we studied the porosity, permeability to oil, permeability to waters (brine water, and surfactants), and spontaneous surfactant intake for Bakken and Niobrara rocks. We observed that porosities for Niobrara cores were generally higher than those from Bakken cores. Consistent with the Darcy equation, rate-independent water and oil permeability was noted. Cores from the Niobrara and Bakken formations exhibited a broad range of permeability, ranging from 0.11 to 26 microdarcys (μD). In the Niobrara formation, permeability was least in marl (0.1-4 μD), larger in chalk (1-15 μD), and greatest in sandstone (8-26 μD). Although variations occurred, the absolute permeability to water, permeability to oil, and permeability to surfactant formulations were all comparable. The surfactant formulations tested exhibited a favorable potential for fluid flowing in both formations by spontaneous imbibition. The average oil recovery by spontaneous imbibition of the selected surfactants was ranged from 13 to 57% OOIP at optimal salinity, at least 5 percentage incremental in oil recovery over brine water imbibition.

Flow-induced proppant carrying capacity

A subclass of viscoelastic surfactant fluids are investigated as flow-dependent proppant carrying fluids. Shear-induced structure networks have the potential to eliminate the need for cross linkers and viscosity breakers associated with traditional fluids because they shear-thicken and shear-thin depending on the fluid pump rates in the fracture. Particle tracking velocimetry is used to visualize proppant settling velocity inside a fracture flow cell. We show that settling velocities in high shear flows are reduced by a factor 20 compared to settling in low shear ones and fluids at rest. Couette cell and oscillatory rheometry are used to investigate the induced viscoelasticity. The critical shear rate required for fluid thickening and the succeeding viscosity contrast ratio determine the extra proppant carrying capacity.

Environmental Pollutant Ozone Causes Damage to Lung Surfactant Protein B (SP-B).

Lung surfactant protein B (SP-B) is an essential protein found in the surfactant fluid at the air–water interface of the lung. Exposure to the air pollutant ozone could potentially damage SP-B and lead to respiratory distress. We have studied two peptides, one consisting of the N-terminus of SP-B [SP-B(1–25)] and the other a construct of the N- and C-termini of SP-B [SP-B(1–25,63–78)], called SMB. Exposure to dilute levels of ozone (∼2 ppm) of monolayers of each peptide at the air–water interface leads to a rapid reaction, which is evident from an increase in the surface tension. Fluorescence experiments revealed that this increase in surface tension is accompanied by a loss of fluorescence from the tryptophan residue at the interface. Neutron and X-ray reflectivity experiments show that, in contrast to suggestions in the literature, the peptides are not solubilized upon oxidation but rather remain at the interface with little change in their hydration. Analysis of the product material reveals that no cleavage of the peptides occurs, but a more hydrophobic product is slowly formed together with an increased level of oligomerization. We attributed this to partial unfolding of the peptides. Experiments conducted in the presence of phospholipids reveal that the presence of the lipids does not prevent oxidation of the peptides. Our results strongly suggest that exposure to low levels of ozone gas will damage SP-B, leading to a change in its structure. The implication is that the oxidized protein will be impaired in its ability to interact at the air–water interface with negatively charged phosphoglycerol lipids, thus compromising what is thought to be its main biological function.

Combined soil washing and CDEO for the removal of atrazine from soils

In this work, it is studied the removal of atrazine from spiked soils by soil washing using surfactant fluids, followed by the treatment of the resulting washing waste by electrolysis with boron doped diamond (BDD) anode. Results confirm that combination of both technologies is efficient for the removal and total mineralization of atrazine. Ratio surfactant/soil is a key parameter for the removal of atrazine from soil and influences significantly in the characteristic of the wastewater produced, affecting not only to the total organic load but also to the mean size of micelles. The higher the ratio surfactant soil, the lower is the size of the particles. Electrolyses of this type of waste attain the complete mineralization. TOC and COD are removed from the start of the treatment but the key of the treatment is the reduction in size of the micelles, which lead to a higher negative charge in the surface and to the faster depletion of the surfactant as compared with the pesticide.

Pulmonary Atelectrauma. Biophysical Insights into Mechanisms of Damage and Prevention

Mechanical ventilation is inarguably a necessary life-sustaining medical treatment for acute respiratory distress syndrome. However, mechanical stresses and strains exerted on the delicate tissues of the airways and alveoli may result in ventilation-induced lung injury (VILI). This presentation describes the coupling between fluid flows, mechanical stresses, and surfactant biophysical interactions that occurs during the recruitment of obstructed airways and alveoli that can result in atelectrauma. Our investigations couple computational simulation with in vitro experimental investigations. We idealize the system as an airway that is lined with epithelial cells, with reopening occurring through the migration of a finger of air that displaces the obstruction. Mechanical stress fields and surfactant transport processes are assessed by computational fluid dynamic simulation, flow visualization is completed with microparticle image velocimetry, and cell damage is evaluated using biomimetic airway constructs of respiratory bronchioles. These studies demonstrate the strong coupling between interfacial flows and atelectrauma. Finally, we asked whether it is possible to enhance the surface activity of endogenous surfactant, using unsteady flows to reduce atelectrauma. Our investigations demonstrate that the use of pulsatile flow to enhance surfactant function provides an opportunity for “endogenous surfactant delivery” that diminishes epithelial damage and thus may reduce VILI.

Lung development in the late preterm

An increasing incidence of moderate-to-late prematurity is observed worldwide (6-7% of all births). Moderate-to-late prematurity is a cause of important mortality and morbidity, even when it is just a few weeks before term gestation [1]. Respiratory issues related to moderate prematurity include delayed neonatal transition to air breathing, respiratory distress resulting from delayed fluid clearance, surfactant deficiency, and pulmonary hypertension. There is increasing evidence to support the hypothesis that preterm delivery, even in the absence of any neonatal respiratory disease, may have adverse effects on subsequent lung growth and development, and that these alterations may persist during the early years of life. Premature birth interrupts normal in utero lung development and results in an early transition from the hypoxic intrauterine environment to a comparatively hyperoxic atmospheric environment [2]. Alveolar walls may be thicker, impairing optimal gas exchange. Colin et al. proposed that preterm birth leads to decreased parenchyma elasticity and subsequent airway tethering, a mechanism by which airway wall compliance keeps surrounding alveoli well opened [3]. The long-term significance of reduced airway function early in life has been emphasized in a longitudinal study involving a large group of non-selected infants who had participated in the Tucson Children’s Respiratory study [4]. In this study Stern et al. showed that infants whose pulmonary function was in the lowest quartile also had pulmonary function in the lowest quartile through the years of follow-up until early adulthood. These findings in a normal unselected population, suggest that the level of pulmonary function in early life tracks and changes little with growth. Several authors suggest that deficits in lung function during early life, especially if associated with lower respiratory illnesses, increase the risk of chronic obstructive pulmonary disease in late adult life [5-7]. Of particular importance in this context may be the role played by RSV, which affects most children during their first year of life. The risk of life-threatening RSV infection appears relevant up to a post-conceptional age of 44 weeks. Stein et al. reported that RSV lower respiratory tract illness during the first 3 years of life in a healthy birth cohort was associated with recurrent wheeze up to age 11 [8]. In conclusion altered lung development is a characteristic feature of the late preterm infants and its impact on neonatal and postnatal morbidity needs to be considered.

Phospholipid composition and kinetics in different endobronchial fractions from healthy volunteers

BackgroundAlterations in surfactant phospholipid compositions are a recognized feature of many acute and chronic lung diseases. Investigation of underlying mechanisms requires assessment of surfactant phospholipid molecular composition and kinetics of synthesis and turnover. Such studies have recently become possible in humans due to the development of stable isotope labelling combined with advances in analytical methods in lipidomics. The objectives of this study are to compare phospholipid molecular species composition and phosphatidylcholine synthesis and turnover in surfactant isolated from various endobronchial compartments in healthy adults.MethodsHealthy adults (N = 10) were infused with methyl-D9-choline chloride and samples of induced sputum, tracheal wash and small volume bronchoalveolar lavage fluid were obtained subsequently at intervals up to 96 hours. Surfactant phospholipid composition and incorporation of stable isotope into surfactant phosphatidylcholine were determined by electrospray ionisation mass spectrometry.ResultsWhile molecular species compositions of phospholipids were similar for all three sample types, dipalmitoylphosphatidylcholine content was highest in lavage, intermediate in tracheal wash and lowest in sputum. Methyl-D9-choline incorporation into surfactant phosphatidylcholine was lower for sputum at 24 hours but reached equilibrium with other sample types by 48 hours. Fractional methyl-D9-dipalmitoylphosphatidylcholine incorporation for all sample types was about 0.5% of the endogenous composition. Lysophosphatidylcholine enrichment was twice than that of phosphatidylcholine.ConclusionsTracheal secretions may be of value as a surrogate to assess bronchoalveolar lavage fluid surfactant molecular composition and metabolism in healthy people. Despite minor differences, the phospholipid molecular composition of induced sputum also showed similarities to that of bronchoalveolar lavage fluid. Detailed analysis of newly synthesized individual phosphatidylcholine species provided novel insights into mechanisms of surfactant synthesis and acyl remodelling. Lysophosphatidylcholine methyl-D9 incorporation patterns suggest that these species are secreted together with other surfactant phospholipids and are not generated in the air spaces by hydrolysis of secreted surfactant phosphatidylcholine. Application into patient populations may elucidate potential underlying pathophysiological mechanisms that lead to surfactant alterations in disease states.

0106 PIVによるバックステップを通過する粘弾性流体乱流の不安定性に関する研究

This paper presents experimental investigations of flow instability due to the viscoelasticity in backward-facing step turbulent flow of surfactant fluid. We measured spatial distribution of statistical quantities including Reynolds stress and examined those variations by adding surfactant additives with using PIV. We found the condition (parameter range) in terms of shear rate and the surfactant concentration of viscoelastic fluid for the flow instability.

Shear banding in time-dependent flows of polymers and wormlike micelles

We study theoretically the formation of shear bands in time-dependent flows of polymeric and wormlike micellar surfactant fluids, focussing on the protocols of step shear stress, step shear strain (or in practice a rapid strain ramp), and shear startup, which are commonly studied experimentally. For each protocol we perform a linear stability analysis to provide a fluid-universal criterion for the onset of shear banding, following our recent Letter [Phys. Rev. Lett. 110 (2013) 086001]. In each case this criterion depends only on the shape of the experimentally measured rheological response function for that protocol, independent of the constitutive properties of the material in question. (Therefore our criteria in fact concern all complex fluids and not just the polymeric ones of interest here. A separate manuscript [in preparation] will explore them in a broad class of disordered soft glassy materials including foams, dense emulsions, dense colloids, and microgel bead suspensions.) An important prediction is that pronounced banding can arise transiently in each of these protocols, even in fluids for which the underlying constitutive curve of stress as a function of strain-rate is monotonic and a steadily flowing state is accordingly unbanded. For each protocol we provide numerical results in the rolie-poly and Giesekus models that support our predictions. We comment on the ability of the rolie-poly model to capture the observed experimental phenomenology, and on the failure of the Giesekus model.

Adaptations to hibernation in lung surfactant composition of 13-lined ground squirrels influence surfactant lipid phase segregation properties

Pulmonary surfactant lines the entire alveolar surface, serving primarily to reduce the surface tension at the air–liquid interface. Surfactant films adsorb as a monolayer interspersed with multilayers with surfactant lipids segregating into different phases or domains. Temperature variation, which influences lipid physical properties, affects both the lipid phase segregation and the surface activity of surfactants. In hibernating animals, such as 13-lined ground squirrels, which vary their body temperature, surfactant must be functional over a wide range of temperatures. We hypothesised that surfactant from the 13-lined ground squirrel, Ictidomys tridecemlineatus, would undergo appropriate lipid structural re-arrangements at air–water interfaces to generate phase separation, sufficient to attain the low surface tensions required to remain stable at both low and high body temperatures. Here, we examined pressure–area isotherms at 10, 25 and 37°C and found that surfactant films from both hibernating and summer-active squirrels reached their highest surface pressure on the Wilhelmy–Langmuir balance at 10°C. Epifluorescence microscopy demonstrated that films of hibernating squirrel surfactant display different lipid micro-domain organisation characteristics than surfactant from summer-active squirrels. These differences were also reflected at the nanoscale as determined by atomic force microscopy. Such re-arrangement of lipid domains in the relatively more fluid surfactant films of hibernating squirrels may contribute to overcoming collapse pressures and support low surface tension during the normal breathing cycle at low body temperatures.

EARLY AIRWAY PRESSURE RELEASE VENTILATION PREVENTS ARDS—A NOVEL PREVENTIVE APPROACH TO LUNG INJURY

Acute respiratory distress syndrome (ARDS) afflicts 200,000 patients annually with a mortality rate of 30% to 60% despite wide use of low tidal volume (LTV) ventilation, the present standard of care. High-permeability alveolar edema and instability occur early in the development of ARDS, before clinical signs of lung injury, and represent potential targets for therapy. We hypothesize that early application of a protective ventilation strategy (airway pressure release ventilation [APRV]) will stabilize alveoli and reduce alveolar edema, preventing the development of ARDS. Yorkshire pigs (30-40 kg) were anesthetized and subjected to two-hit injury: (a) intestinal ischemia-reperfusion, (b) peritoneal sepsis, or sham surgery. Following surgery, pigs were randomized into APRV (n = 4), according to current published guidelines for APRV; LTV ventilation (n = 3), using the current published ARDS Network guidelines (6 mL/kg); or sham (n = 5). The clinical care of all pigs was administered per the Surviving Sepsis Campaign guidelines. Animals were killed, and necropsy performed at 48 h. Arterial blood gases were measured to assess for the development of clinical lung injury. Lung tissue epithelial cadherin (E-cadherin) was measured to assess alveolar permeability. Bronchoalveolar lavage fluid (BALF) surfactant protein A was measured to assess alveolar stability. Lung edema content and histopathology were analyzed at 48 h. Airway pressure release ventilation pigs did not develop ARDS. In contrast, pigs in the LTV ventilation met ARDS criteria (PaO2/FIO2 ratio) (APRV: baseline = 471 ± 16; 48 h = 392 ± 8; vs. LTV ventilation: baseline = 551 ± 28; 48 h = 138 ± 88; P < 0.001). Airway pressure release ventilation preserved alveolar epithelial integrity demonstrated by higher levels of E-cadherin in lung tissue as compared with LTV ventilation (P < 0.05). Surfactant protein A levels were higher in BALF from the APRV group, suggesting APRV preserved alveolar stability. Quantitative histologic scoring showed improvements in all stigmata of ARDS in the APRV group versus the LTV ventilation (P < 0.05). Airway pressure release ventilation had significantly lower lung edema (wet-dry weight) than LTV ventilation (P < 0.05). Protective ventilation with APRV immediately following injury prevents development of ARDS. Reduction in lung edema, preservation of lung E-cadherin, and surfactant protein A abundance in BALF suggest that APRV attenuates lung permeability, edema, and surfactant degradation. Protective ventilation could change the clinical paradigm from supportive care for ARDS with LTV ventilation to preventing development of ARDS with APRV.

Sterilizing Filtration of Liposome and Related Lipid-Containing Solutions: Enhancing Successful Filter Qualification

Bacterial penetration of integral sterilizing-grade 0.2 μm rated filters, although rare, is not a new phenomenon in the biopharmaceutical industry. It is recognized by both the Parenteral Drug Association and the Food and Drug Administration via recommended bacterial retention qualification (also commonly called filter validation) performed in relevant product fluids or suitable surrogates when necessary (1-3). As noted in recent work, formulations such as some adjuvanted vaccines, liposome-based drug delivery solutions, and similar surfactant or emulsion-based product fluids increase the likelihood of such penetration events (4). Here we demonstrate that some 0.2 μm rated sterilizing-grade filters from different filter manufacturers may perform less effectively than expected when their membranes are challenged with one of these bacterial penetration risk-related solutions. Some filters provided very little sterility assurance (titer reductions < 6 logs) and others provided substantial sterility assurance (titer reduction > 8 log). From this, it is clear that the product formulation most likely to lead to filter penetration must be identified early in the design process to facilitate process design and minimize qualification costs. In this way, the solution can be matched with the appropriate sterilizing-grade filter and the appropriate process conditions. Bacterial penetration of intact sterilizing-grade filters during filter qualification, although rare, is not a new phenomenon in the biopharmaceutical industry. Because these incidences are identified in the filter validation process, there is no risk to the drug product end-user, but these failures do incur additional expense to the pharmaceutical manufacturer and could prevent the manufacture of very important drug formulations. Formulations such as some adjuvanted vaccines, liposome-based drug delivery solutions, and similar surfactant or emulsion-based product fluids have been documented to lead to an increased risk of penetration events. Here we demonstrate that some sterilizing-grade filters may perform differently from expected when their membranes are challenged with one of these solutions related to bacterial penetration risk. Some filters provided very little sterility assurance and others provided substantial sterility assurance. From this, it is clear that the pharmaceutical products and product formulation most likely to lead to filter penetration must be identified early in the design process to facilitate process design and minimize qualification costs. Moreover, that solution should be matched with the appropriate sterilizing-grade filter and process conditions to ensure expected sterility.

Nanochannel with Uniform and Janus Surfaces: Shear Thinning and Thickening in Surfactant Solution

On basis of molecular simulation of confined surfactant solutions, we show that by adding chemical patterns on the inner surface of nanochannels dynamical properties of the confined surfactant solutions could be modified from shear thinning to shear thickening. To this end, we select uniformly hydrophobic and hydrophilic surfaces as well as a stripe-patterned Janus surface as three prototype confining surfaces of nanochannels. In all three nanochannels, when the surfactant solution is under relatively low shear rates, it shears thin. Under moderate shear rates, a sharp decrease in the shear viscosity could occur due to surfactant morphology transition. Under relatively high shear rates, a shear-thinning-to-thickening transition can emerge due to the tendency of stratification normal to the confining surface. Our simulation study offers a guide to steering dynamic properties of surfactant fluids in nanofluidic devices through engineering surfaces of nanochannels by design.

Switchable bistable ordering and real-time alignment dynamics in wormlike micelles

Using a combination of rheology and magnetic resonance known as “rheo-NMR” we observe, in real time, the shear- and field-dependent dynamics of orientational order in a wormlike micelle (WLM). We construct a dynamical phase diagram, yielding a range where bistable shear-activated phase switching occurs in which WLMs are stably isotropic (> 12 h) before shearing, and yet realign with B0 after shearing. Furthermore, we extract anisotropic viscoelastic coefficients for the first time in a WLM by precisely fitting nonlinear realignment data. This deepened understanding of complex surfactant fluid dynamics lights a path toward increased materials control in advanced lubricants and coatings, drug delivery, and tissue engineering.

Protein assembly at the air-water interface studied by fluorescence microscopy.

Protein assembly at the air-water interface (AWI) occurs naturally in many biological processes and provides a method for creating biomaterials. However, the factors that control protein self-assembly at the AWI and the dynamic processes that occur during adsorption are still underexplored. Using fluorescence microscopy, we investigated assembly at the AWI of a model protein, human serum albumin minimally labeled with Texas Red fluorophore. Static and dynamic information was obtained under low subphase concentrations. By varying the solution protein concentration, ionic strength, and redox state, we changed the microstructure of protein assembly at the AWI accordingly. The addition of pluronic surfactant caused phase segregation to occur at the AWI, with fluid surfactant domains and more rigid protein domains revealed by fluorescence recovery after photobleaching experiments. Protein domains were observed to coalesce during this competitive adsorption process.