Osmotic Pressure Gradient Research Articles

Quantifying the dynamic transition of hydrogenated castor oil gels measured via multiple particle tracking microrheology.

Rheological modifiers are essential ingredients in commercial materials that exploit facile and repeatable phase transitions. Although rheological modifiers are used to change flow behavior or quiescent stability, the complex properties of particulate gels during dilution is not well studied. We characterize a dynamically evolving colloidal gel, hydrogenated castor oil (HCO), a naturally sourced material, used in consumer products. This HCO scaffold consists of fibrous colloids, a surfactant (linear alkylbenzene sulfonate) and water. The gel undergoes critical transitions, degradation and formation, in response to an osmotic pressure gradient. Multiple particle tracking microrheology (MPT) measures the evolving material properties. In MPT, fluorescent probe particles are embedded into the sample and Brownian motion is measured. MPT data are analyzed using time-cure superposition, identifying critical transition times and critical relaxation exponents for degradation and formation where tc,deg = 102.5 min, ndeg = 0.77 ± 0.09, tc,for = 31.9 min, and nfor = 0.94 ± 0.11, respectively. During degradation and formation HCO gels evolve heterogeneously, this heterogeneity is characterized spatially and temporally. Heterogeneity of the gel is quantified by comparing variances of single particle van Hove correlation functions using an F-test with a 95% confidence interval. HCO transitions have rheological heterogeneous microenvironments that are homogeneously distributed throughout the field of view. Although HCO gels do evolve heterogeneously, this work determines that these heterogeneities do not significantly change traditional MPT measurements but the analysis techniques developed provide additional information on the unique heterogeneous scaffold microenvironments. This creates a toolbox that can be widely applied to other scaffolds during dynamic transitions.

Food Preservation Technology at Subzero Temperatures: A Review

, 2015Purpose: Cold storage is the most popular method used to preserve highly perishable foods such as beef and fish. However, at refrigeration temperatures, the shelf life of these foods is limited, and spoilage leads to massive food waste. Moreover, freezing significantly affects the food’s properties. Ice crystallization and growth during freezing can cause irreversible textural damage to foods through volumetric expansion, moisture migration induced by osmotic pressure gradients, and concentration of solutes,which can lead to protein denaturation. Methods: Although freezing can preserve perishable foods for months, these disruptive changes decrease the consumer’s perception of the food’s quality. Therefore, the development and testing of new and improved cold storage technologies is a worthwhile pursuit. Results: The process of maintaining a food product in an unfrozen state below its equilibrium freezing temperature is known as supercooling. As supercooling has been shown to offer a considerable improvement over refrigeration for extending a perishable product’s shelf life, imple-mentation of supercooling in households and commercial refrigeration units would help diminish food waste. Conclusions: A commercially viable supercooling unit for all perishable food items is currently being developed and fabricated. Buildup of this technology will provide a meaningful improvement in the cold storage of perishable foods, and will have a significant impact on the refrigeration market as a whole.Keywords: Electrochemical impedance spectroscopy, Food quality analysis, Ice crystal nucleation, Superchilling, Supercooling

RETRACTED: Limitations of osmotic gradient resource and hydraulic pressure on the efficiency of dual stage PRO process

Dual stage PRO process has been proposed for power generation from a salinity gradient across a semi-permeable membrane. Closed-loop and open-loop dual stage PRO system were evaluated using 2 M NaCl and Dead Sea as draw solutions whereas the feed solution was either fresh water or seawater. The impact of feed salinity gradient resource and feed pressure on the net power generation and water flux was evaluated. The results showed that power density in stage one reached a maximum amount atΔP = π/2 but the maximum net power generation occurred atΔP < π/2. This was mainly attributed to the variation of net driving pressure in stage one and two of the PRO process. The dual stage PRO process was found to perform better at high osmotic pressure gradient across the PRO membrane, for example when Dead Sea brine or highly concentrated NaCl is the draw solution. Total power generation in the dual stage PRO process is up to 40% higher than that in the conventional PRO process. This was achieved through harvesting the rest of energy remaining in the diluted draw solution. Therefore, dual stage PRO process has the potential of maximizing power generation from a salinity gradient resource.

Study on Mechanism of Desorption Behavior of Saturated Superabsorbent Polymers in Concrete

The effect of several potential factors on the desorption behavior of saturated superabsorbent polymers (SAPs) in concrete was studied by simulating the internal saline concentration, alkalinity, and relative humidity. Results indicate that the desorption of SAP is mainly decided by osmotic pressure and humidity gradient. The desorption process of SAP is divided into three stages: the leading factor is the osmotic pressure during the first stage; humidity gradient during the third stage; and a relatively low-level combination of these two factors during the second stage. At the same time, the desorption is not decided by pH value, and the factor with the most effect is the osmotic pressure. The water release rate Rt of saturated SAP influenced by humidity shows the following trends: Rt indicates a clear linear trend as a function of time, and an approximate logarithm correlation exists between Rt and the relative humidity (Rt = A • ln(RH) + B).

Design and modeling of a light powered biomimicry micropump

The design of compact micropumps to provide steady flow has been an on-going challenge in the field of microfluidics. In this work, a novel micropump concept is introduced utilizing bacteriorhodopsin and sugar transporter proteins. The micropump utilizes light energy to activate the transporter proteins, which create an osmotic pressure gradient and drive the fluid flow. The capability of the bio inspired micropump is demonstrated using a quasi 1D numerical model, where the contributions of bacteriorhodopsin and sugar transporter proteins are taken care of by appropriate flux boundary conditions in the flow channel. Proton flux created by the bacteriorhodopsin proteins is compared with experimental results to obtain the appropriate working conditions of the proteins. To identify the pumping capability, we also investigate the influences of several key parameters, such as the membrane fraction of transporter proteins, membrane proton permeability and the presence of light. Our results show that there is a wide bacteriorhodopsin membrane fraction range (from 0.2 to 10%) at which fluid flow stays nearly at its maximum value. Numerical results also indicate that lipid membranes with low proton permeability can effectively control the light source as a method to turn on/off fluid flow. This capability allows the micropump to be activated and shut off remotely without bulky support equipment. In comparison with existing micropumps, this pump generates higher pressures than mechanical pumps. It can produce peak fluid flow and shutoff head comparable to other non-mechanical pumps.

Decoupling of mass transport mechanisms in the stagewise swelling of multiple emulsions.

This contribution reports on the mass transport kinetics of osmotically imbalanced water-in-oil-in-water (W1/O/W2) emulsions. Although frequently studied, the control of mass transport in W1/O/W2 emulsions is still challenging. We describe a microfluidics-based method to systematically investigate the impact of various parameters, such as osmotic pressure gradient, oil phase viscosity, and temperature, on the mass transport. Combined with optical microscopy analyses, we are able to identify and decouple the various mechanisms, which control the dynamic droplet size of osmotically imbalanced W1/O/W2 emulsions. So, swelling kinetics curves with a very high accuracy are generated, giving a basis for quantifying the kinetic aspects of transport. Two sequential swelling stages, i.e., a lag stage and an osmotically dominated stage, with different mass transport mechanisms are identified. The determination and interpretation of the different stages are the prerequisite to control and trigger the swelling process. We show evidence that both mass transport mechanisms can be decoupled from each other. Rapid osmotically driven mass transport only takes place in a second stage induced by structural changes of the oil phase in a lag stage, which allow an osmotic exchange between both water phases. Such structural changes are strongly facilitated by spontaneous water-in-oil emulsification. The duration of the lag stage is pressure-independent but significantly influenced by the oil phase viscosity and temperature.

Reactive Oxygen Species and NFkB Increase Peritoneal Filtration and Generate Ascites in Nephrotic Syndrome

Clinical and experimental observations suggest that nephrotic ascites is not accounted for by hypoalbuminemia but by changes of the capillary endothelium permeability. We investigated the mechanism of these changes in puromycin aminonucleoside (PAN) nephrotic rats. The peritoneal filtration coefficient (Kf) was estimated by the slope of the regression line connecting the trans‐peritoneal gradient of osmotic pressure which was varied experimentally to the trans‐peritoneal water flux measured by osmotic dilution.Kf doubled and expression of aquaporin 1 (AQP1) increased in peritoneum of PAN rats. PAN rats displayed peritoneal oxidative stress attested by ROS accumulation and dysregulation of NADPH oxidase and ROS detoxifying enzymes expression. The ROS scavenger N‐acetyl cysteine (NAC) prevented the increase in Kf and in AQP1 expression. It also reduced by half the volume of ascites without changing renal sodium handling, albuminuria or hypoalbuminemia. PAN rats peritoneum also displayed activation of NFkB attested by increased nuclear labeling with anti‐p50 antibody. Activation of NFkB was blunted in NAC‐treated PAN rats. JSH‐23, an inhibitor of NFkB transcriptional activity, mimicked all the effects of NAC.These results show that nephrotic syndrome is associated with increased filtration coefficient of the peritoneal barrier which stems in part from increased expression of AQP1. These changes are triggered by oxidative stress and subsequent activation of NFkB. They account for at least half of increased filtration rate, the remaining stemming possibly from decreased plasma oncotic pressure.

Organic fouling in forward osmosis (FO): Membrane flux behavior and foulant quantification

Forward osmosis (FO) is an emerging membrane technology with potential applications in desalination and wastewater reclamation. The osmotic pressure gradient across the FO membrane is used to generate water flux. In this study, flux performance and foulant deposition on the FO membrane were systematically investigated with a co-current cross-flow membrane system. Sodium alginate (SA), bovine serum albumin (BSA) and tannic acid (TA) were used as model foulants. Organics adsorbed on the membrane were peeled off via oscillation and characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). When an initial flux of 8.42 L/m2h was applied, both flux reduction and foulant deposition were slight for the feed solution containing BSA and TA. In comparison, flux reduction and foulant deposition were much more severe for the feed solution containing SA, as a distinct SA cake-layer was formed on the membrane surface and played a crucial role in membrane fouling. In addition, as the initial SA concentration increased in FS, the thickness of the cake-layer increased remarkably, and the membrane fouling became more severe.

Microfluidic generation of PEG-b-PLA polymersomes containing alginate-based core hydrogel.

Herein, we demonstrate a novel method for the generation of monodisperse cell-like structures containing a biocompatible hydrogel matrix surrounded by a membrane responsive to chemical cues. Specifically, we employ droplet-based microfluidics to generate PEG-PLA polymersomes encapsulating alginate in liquid form. We investigate alginate core gelation by creating an osmotic pressure gradient across the polymeric membrane that, through expansion, allows the passage of calcium ions. The effects of calcium concentration on the core gelation are explored.

Numerical modelling of concentration polarisation and cake formation in membrane filtration processes

A model capable of predicting concentration polarisation and cake formation in cross-flow membrane filtration is proposed. The cross-flow hydrodynamics is resolved by solving the Navier–Stokes equations and convection–diffusion equation is used to resolve the solute distribution. A Lattice-Boltzmann (LB) scheme is used for the hydrodynamics and this is coupled with an LB scheme or a finite volume (FV) scheme for modelling the cake formation. The equations are coupled through the velocity and the viscosity, which is assumed to vary with the solute concentration. Concentration polarisation is modelled for interacting nano-particles by using concentration dependence on diffusion coefficient and osmotic pressure gradient as a function of solute concentration. Cake formation phenomenon is predicted for interacting nano-particles and non-interacting solute particles using the same approach. The proposed model is validated by comparing the results obtained for a number of problems with the predictions produced by other computational models and experimental results available in literature.

New Thermal Energy Converters Based on Polyelectrolyte Hydrogels

The theory of thermal energy converters based on polyelectrolyte hydrogels has been developed. The possibility of providing the circulation of a fluid in the contour by controlled variations of the local value of concentrations of the mobile ions that cause an osmotic pressure gradient was shown. On the basis of the solution of motion equations of the mobile ions the numerical estimates of parameters of proposed type of circulation contour are given.

Use of Micellar Solutions as Draw Agents in Forward Osmosis

AbstractRecent advances in membrane technologies have enhanced the viability of water treatment strategies that employ semipermeable barriers. Forward osmosis (FO), which exploits the natural osmotic pressure gradient between a “draw” solution and a “feed” solution to produce potable water, offers a low‐energy, low‐cost alternative to more conventional treatment methods. Surfactants, because of their tendencies to aggregate into micelles and to adsorb at interfaces, provide intriguing osmotic pressures and offer exploitable properties by which draw solutions can be regenerated. The effectiveness of surfactant‐based FO using cellulose triacetate membranes has been assessed in terms of water flux and reverse surfactant diffusion using cetylpyridinium chloride, sodium dodecylsulfate, and Triton X‐100. The ratios of water flux to surfactant flux exceeded 600 L mol−1 for all surfactants studied. Surfactant recoveries of over 99 % were achieved by ultrafiltration using regenerated cellulose membranes.

Electro-Osmotic-Based Catholyte Production By Microbial Fuel Cells

Introduction & Objectives Research in the field of Bioelectrochemical Systems (BES) has focused on utilising compounds in wastewater to bioelectricity either by Microbial Fuel Cells (MFCs) or biosynthesis using Microbial Electrolysis Cells (MECs). The latter requires electrical input, whereas the former generates electricity, with both technologies resulting in valuable product recovery such as hydrogen gas or caustic soda [1,2]. The proton selective membrane properties and its configuration in dual-chamber MFCs, allows the extraction of cations other than protons from the anode to the cathode. The current-dependent transport results in electro-osmotically dragged water molecules reaching the cathode [3]. The current study reports on the production of catholyte on the surface of the cathode electrode, which was achieved as a direct result of electricity generation using MFCs fed with wastewater and employing Pt-free carbon based electrodes. Materials & Methods Twelve MFCs were tested in triplicate groups assembled with 25mL anodes, which were inoculated with activated sludge. The cathode chambers were empty and closed - but not air-tight, and contained electrodes as follows: Carbon cloth with Microporous Layer (MPL), carbon fibre veil (CV), carbon fibre veil with MPL (CV MPL) and activated carbon (AC). All cathodes had a geometric surface area of 10cm2 and were mechanically pressed against the CEM membrane. Results & Discussion All tested MFCs presented herewith showed a catholyte production directly on the surface of the corresponding electrode, with AC being the best (see Fig.1). The data presented in Fig.1 show the correlation between catholyte generation and power production for each MFC. It clearly shows that the more powerful the MFC unit is, the more catholyte it produces. Moreover, the produced catholyte’s pH (12.9-13.3 suggesting caustic content) and conductivity, showed gradual increase with power (data not shown), which suggest that the cationic transport might present a mechanism of water extraction from the anolyte via electro-osmotic drag (under load) and osmotic pressure (under open-circuit). The total charge transfer in the MFC is related to the electro-osmotic drag of water through the membrane [3], whereas osmotic pressure gradient that exists between dissimilar solutions is dominant under open-circuit conditions, where no electron transfer occurs.Figure 1. Amount of catholyte produced by the MFCs, normalised against open-circuit conditions, during a 7-day operation. Conclusions MFCs were shown to produce useful catholyte whilst generating electricity, with plain Pt-free electrodes, thereby representing a promising route for sustainable electricity production and water recycling. References Logan, B. E et al. (2008) Microbial electrolysis cells for high yield hydrogen gas production from organic matter. Environ. Sci. Technol., 42, 23: 8630–40.Rabaey, K et al. (2010) High current generation coupled to caustic production using a lamellar bioelectrochemical system. Environ. Sci. Technol., 44, 11: 4315–21.Kim, J. R., et al. (2009) Development of a tubular microbial fuel cell (MFC) employing a membrane electrode assembly cathode. Power Sources, 187, 2: 393-399.

Apoplastic and symplastic phloem loading in Quercus robur and Fraxinus excelsior

Whereas most of the research on phloem loading is performed on herbaceous plants, less is known about phloem loading strategies in trees. In this study, the phloem loading mechanisms of Quercus robur and Fraxinus excelsior were analysed. The following features were examined: the minor vein structure, the sugar concentrations in phloem sap by the laser-aphid-stylet technique, the distribution of photoassimilates in the mesophyll cells by non-aqueous fractionation, gradients of sugar concentrations and osmotic pressure, and the expression of sucrose transporters. The minor vein configurations of Q. robur and F. excelsior belong to the open type. Quercus robur contained companion cells in the minor veins whereas F. excelsior showed intermediary cells in addition to ordinary companion cells. The main carbon transport form in Q. robur was sucrose (~1M). In F. excelsior high amounts of raffinose and stachyose were also transported. However, in both tree species, the osmolality of phloem sap was higher than the osmolality of the mesophyll cells. The concentration gradients between phloem sap and the cytoplasm of mesophyll cells for sucrose were 16-fold and 14-fold for Q. robur and F. excelsior, respectively. Independent of the type of translocated sugars, sucrose transporter cDNAs were cloned from both species. The results indicate that phloem loading of sucrose and other metabolites must involve active loading steps in both tree species. Quercus robur seems to be an apoplastic phloem loader while F. excelsior shows indications of being a symplastic or mixed symplastic-apoplastic phloem loader.

Influence of Organic Matters on Forward Osmosis Membrane Performance

Forward osmosis is an emerging membrane technology with potential applications in desalination and wastewater reclamation, osmotic pressure gradient cross the FO membrane is used to generate water flux. In contrast with conventional pressure-driving membrane process, the advantage of FO is significant: energy saving, high solute rejection and low fouling propensity. In this study, alginic acid (AA), boving serum albumin (BSA), humic acid (HA) and tannic acid (TA) were used to investigate the influence of organic fouling. The flux changed obviously, the rejection was approving and the absorption of organics was observed in the study. Ultrasonic oscillation was employed to wipe the organics off the fouling membranes, which was intend to study the quality of absorption of organic matters.

Pressure retarded osmosis in closed circuit: a new technology for clean power generation without need of energy recovery

Power generation from salinity gradients by means of Pressure Retarded Osmosis (PRO) is currently preformed by conventional methods, wherein Energy Recovery (ER) is an essential feature without which such a process is impossible. The newly conceived Closed Circuit (CC) Pressure Retarded Osmosis technology (CC-PRO) described herein is based on a continuous consecutive sequential batch process; wherein, pressurized high salinity feed (HSF) is continuously supplied to the inlets of PRO modules and pressurized effluent removed from their outlets through internal circulation means by the alternating engagement/disengagement of two side conduits (SC). This process proceeds with high energy conservation without need of ER means. The new CC-PRO technology enables high operational flexibility achieved by set point selection of the permeation flux; the circulation flow; the applied pressure of power generation; and the flow ratio circulation/permeation which defines the salinity and osmotic pressure gradients inside the PRO modules. The high flexibility is manifested by the availability of an infinite number of set point combinations for the optimization of the process with respect to maximum power production under lower membrane detrimental effects and reduced fouling factors.

Desalination by forward osmosis using nonionic surfactants

An adequate and dependable supply of fresh water is critical for human health and prosperity. As traditional water resources have become scarcer, processing seawater into fresh water has become essential for many nations. Recent advances in membrane technologies have enhanced the viability of desalination strategies that employ semipermeable barriers. Forward osmosis (FO), which exploits the natural osmotic pressure gradient between a solution and saline to produce potable water, offers a low-energy, low-cost alternative to more conventional desalination methods. Explored herein is the use of t-octylphenoxypolyethoxyethanol surfactants as osmotic agents in draw solutions. Surfactants, because of their tendencies to aggregate into micelles and to adsorb at interfaces, offer exploitable properties by which draw solutions can be regenerated. The effectiveness of surfactant-based FO using Hydration Technology Innovations cellulose triacetate membranes has been assessed in terms of water flux and revers...

Water Uptake along the Length of Grapevine Fine Roots: Developmental Anatomy, Tissue-Specific Aquaporin Expression, and Pathways of Water Transport

To better understand water uptake patterns in root systems of woody perennial crops, we detailed the developmental anatomy and hydraulic physiology along the length of grapevine (Vitis berlandieri × Vitis rupestris) fine roots from the tip to secondary growth zones. Our characterization included the localization of suberized structures and aquaporin gene expression and the determination of hydraulic conductivity (Lpr) and aquaporin protein activity (via chemical inhibition) in different root zones under both osmotic and hydrostatic pressure gradients. Tissue-specific messenger RNA levels of the plasma membrane aquaporin isogenes (VvPIPs) were quantified using laser-capture microdissection and quantitative polymerase chain reaction. Our results highlight dramatic changes in structure and function along the length of grapevine fine roots. Although the root tip lacked suberization altogether, a suberized exodermis and endodermis developed in the maturation zone, which gave way to the secondary growth zone containing a multilayer suberized periderm. Longitudinally, VvPIP isogenes exhibited strong peaks of expression in the root tip that decreased precipitously along the root length in a pattern similar to Arabidopsis (Arabidopsis thaliana) roots. In the radial orientation, expression was always greatest in interior tissues (i.e. stele, endodermis, and/or vascular tissues) for all root zones. High Lpr and aquaporin protein activity were associated with peak VvPIP expression levels in the root tip. This suggests that aquaporins play a limited role in controlling water uptake in secondary growth zones, which contradicts existing theoretical predictions. Despite having significantly lower Lpr, woody roots can constitute the vast majority of the root system surface area in mature vines and thus provide for significant water uptake potential.

Minimizing the Instant and Accumulative Effects of Salt Permeability to Sustain Ultrahigh Osmotic Power Density

We have investigated the instant and accumulative effects of salt permeability on the sustainability of high power density in the pressure-retarded osmosis (PRO) process experimentally and theoretically. Thin-film composite (TFC) hollow-fiber membranes were prepared. A critical wall thickness was observed to ensure sufficient mechanical stability and hence a low salt permeability, B. The experimental results revealed that a lower B was essential to enhance the maximum power density from 15.3 W/m(2) to as high as 24.3 W/m(2) when 1 M NaCl and deionized water were feeds. Modeling work showed that a large B not only causes an instant drop in the initial water flux but also accelerates the flux decline at high hydraulic pressures, leading to reduced optimal operating pressure and maximal power density. However, the optimal operating pressure to harvest energy can be greater than one-half of the osmotic pressure gradient across the membrane if one can carefully design a PRO membrane with a large water permeability, small B value, and reasonably small structural parameter. It was also found that a high B accumulates salts in the feed, leads to the oversalinization of the feed, and largely lowers both the water flux and power density along the membrane module. Therefore, a low salt permeability is highly desirable to sustain high power density not only locally but also throughout the whole module.

Anti VEGF: When, which effect?

AbstractFluid accumulation in the retina is a multi‐factorial process that involves the breakdown of the blood‐retina barrier in retinal capillaries or the retinal pigment epithelium. Hydrostatic pressure gradient and the colloid osmotic pressure gradient lead to diffusion of fluid across capillary walls. Damage to tight junctions enhances the rate of capillary filtration, which exceeds the rate of fluid removal from the retina. Fluid accumulates in the outer plexiform layer and pools into cystic space. Accumulated fluid is visible on optical coherence tomography and fluorescein angiogram, but unlike clinical edema, its finding on imaging studies does not always correlate with changes in visual acuity. For that reason, periodical follow‐up is required. Decision to initiate treatment or re‐treatment to prevent progression to edema with subsequent deterioration of visual acuity may be difficult. Intravitreal injections with anti‐VEGF agents have become the first‐line treatment for macular edema. Combination therapy with corticosteroids may be successful in chronic edema that has been found to be somewhat resistant to treatment. Early treatment for macular edema was shown to be beneficial for optimal visual outcomes. Commercial interest