Viscosity Enhancement Research Articles

Dry Tablet Formulation of PLGA Nanoparticles with a Preocular Applicator for Topical Drug Delivery to the Eye.

To enhance ocular drug bioavailability, a rapidly dissolving dry tablet containing alginate and drug-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles was proposed. For hygienic and easy administration of an accurate drug-dose with this tablet, the use of a preocular applicator was suggested. Herein, a dry tablet was prepared by embedding dexamethasone-loaded PLGA nanoparticles in alginate, which was deposited on the tip of the applicator. The nanoparticles were loaded with 85.45 μg/mg drug and exhibited sustained drug release for 10 h. To evaluate in vivo efficacy, dexamethasone concentration in the aqueous humor was measured after topical administration of the dry tablet, with the applicator, to rabbit eyes and was compared to that achieved with Maxidex®, a commercially-available dexamethasone eye drops. When applied with the preocular applicator, the dry tablet containing alginate could be fully detached and delivered to the eye surface. In fact, it showed up to 2 h of nanoparticle retention on the preocular surface due to tear viscosity enhancement, causing an estimated 2.6-fold increase in ocular drug bioavailability compared to Maxidex®. Therefore, the preocular applicator combined with a dry alginate tablet containing PLGA nanoparticles can be a promising system for aseptically delivering an accurate dose of ophthalmic drug with enhanced bioavailability.

Thermo-economic performance analysis of Al2O3-water nanofluids — An experimental investigation

This paper reports an experimental investigation on the thermophysical characterization, cooling capability and economic performance of Al2O3-water nanofluid. Al2O3 (20 nm–30 nm) nanoparticles are dispersed in water to prepare nanofluids by two-step method with no application of surfactant. Thermal conductivity and viscosity of Al2O3-water nanofluids were measured at different solid weight fractions of 0.0001, 0.0005, 0.001, 0.005 and 0.01 over the temperature range of 25 °C–60 °C for every 5 °C. The effect of concentration and temperature on thermal conductivity and viscosity of nanofluids were examined thoroughly. Thermal conductivity enhancement in nanofluids was prominent with variation in concentration and temperature. However, viscosity enhancement in nanofluids was only influenced by change in concentration. New correlations of thermal conductivity and viscosity based upon the experimental results have been proposed. Cooling capacity of nanofluids based on properties enhancement ratio (PER) were investigated and finally, economic analysis of the cooling performance of nanofluids has been presented.

High temperature rheological characteristics of plasma-treated crumb rubber modified binders

This study investigated the effect of cold plasma surface treatment of crumb rubber on the high temperature performances of CRM binders at unaged and RTFO-aged states, which were produced with two base asphalts and three crumb rubber sizes. The high temperature performance tests conducted on the rubberized binders included rotational viscosity, failure temperature, rutting factor, phase angle, storage modulus, and loss modulus at different temperatures. According to the result of performance tests and statistical analyses, cold plasma surface treatment on crumb rubber significantly enhanced the high temperature performances of CRM binders, regardless of base asphalt source, crumb rubber size and aging state. The effect of base asphalt source was mainly reflected in determining the high temperature performances of RTFO-aged binders. With respect to the crumb rubber size, the -40 mesh plasma-treated CRM binders were the most desirable. In addition, the RTFO aging caused an enhancement in elasticity and viscosity of plasma-treated CRM binders as expected. Finally, the Gray Relational Analysis (GRA) determined the coupling effect of these variables, indicating that cold plasma surface treatment of -40 mesh crumb rubber and base asphalt A was the most effective combination in terms of high temperature rheological properties of CRM binders.

Determination of Transport Coefficients by Coronal Seismology of Flare-induced Slow-mode Waves: Numerical Parametric Study of a 1D Loop Model

Abstract Recent studies of a flaring loop oscillation event on 2013 December 28 observed by the Atmospheric Imaging Assembly of the Solar Dynamics Observatory have revealed the suppression of thermal conduction and significant enhancement of compressive viscosity in hot (∼10 MK) plasma. In this study we aim at developing a new coronal seismology method for determining the transport coefficients based on a parametric study of wave properties using a 1D nonlinear magnetohydrodynamics (MHD) loop model in combination with the linear theory. The simulations suggest a two-step scheme: we first determine the effective thermal conduction coefficient from the observed phase shift between temperature and density perturbations as this physical parameter is insensitive to the unknown viscosity; then from the loop model with the obtained thermal conduction coefficient, we determine the effective viscosity coefficient from the observed decay time using the parametric modeling. With this new seismology technique we are able to quantify the suppression of thermal conductivity by a factor of about 3 and the enhancement of viscosity coefficient by a factor of 10 in the studied flaring loop. Using the loop model with these refined transport coefficients, we study the excitation of slow magnetoacoustic waves by launching a flow pulse from one footpoint. The simulation can self-consistently produce the fundamental standing wave on a timescale in agreement with the observation.

Electrorheology of a dilute emulsion of surfactant-covered drops

We investigate the effects of surfactant coating on a deformable viscous drop under the combined action of shear flow and a uniform electric field. Employing a comprehensive three-dimensional approach, we analyse the non-Newtonian shearing response of the bulk emulsion in the dilute suspension regime. Our results reveal that the location of the peak surfactant accumulation on the drop surface may get shifted from the plane of shear to a plane orthogonal to it, depending on the tilt angle of the applied electric field and strength of the electrical stresses relative to their hydrodynamic counterparts. The surfactant non-uniformity creates significant alterations in the flow perturbation around the drop, triggering modulations in the bulk shear viscosity. Overall, the shear-thinning or shear-thickening behaviour of the emulsion appears to be greatly influenced by the interplay of surface charge convection and Marangoni stresses. We show that the balance between electrical and hydrodynamic stresses renders a vanishing surface tension gradient on the drop surface for some specific shear rates, rendering negligible alterations in the bulk viscosity. This critical condition largely depends on the electrical permittivity and conductivity ratios of the two fluids and orientation of the applied electric field. Also, the physical mechanisms of charge convection and surface deformation play their roles in determining this critical shear rate. As a consequence, we obtain new discriminating factors, involving electrical property ratios and the electric field configuration, which govern the same. Consequently, the surfactant-induced enhancement or attenuation of the bulk emulsion viscosity depends on the electrical conductivity and permittivity ratios. The concerned description of the drop-level flow physics and its connection to the bulk rheology of a dilute emulsion may provide a fundamental understanding of a more complex emulsion system encountered in industrial practice.

Effects of Temperature and Particles Concentration on the Dynamic Viscosity of Graphene-NiO/Coconut Oil Hybrid Nanofluid: Experimental Study

In practice, lubricants are used to minimize the friction and wear of frictional surfaces. The disposal of mineral-based lubricating oil possesses environmental issues and forced the development of bio-degradable lubricating agents. The simultaneous mono-dispersion of metallic and metal oxides nanomaterials into lubricating agents may concurrently reveal superior thermo-physical and rheological characteristics. This paper proposes an experimental and theoretical investigation on the dynamic viscosity enhancement of flat platelets textured Graphene/NiO-coconut oil hybrid nanofluids. The results reveal that the dynamic viscosity enhancement of hybrid nanofluids increases with nanomaterial concentration and decreases with temperature. The squat hybrid nanomaterial concentration has less collusion probability and dynamic contact between the mono-dispersed hybrid nanomaterials as it has enough interfacing gaps to conquer superficial surface energy. The high nanomaterial concentration revamps the formation of lamellar-composite agglomerated particles and enhances the dynamic viscosity of base fluid. Further, a theoretical correlation is recommended to estimate the dynamic viscosity of hybrid nanofluid with minimum margin of deviation using artificial neural network (ANN).

Effects of hydrosoluble calcium ions and organic acids on citrus oil emulsions stabilized with citrus pectin

Citrus fruits are rich in nutritional substances, including various hydrosoluble and liposoluble components, and many of these are subject to enormous waste in the food industry. To make full use of these components and produce novel, high value-added citrus products, an emulsion-based delivery system containing both hydrosoluble (Ca2+, citric acid, ascorbic acid, and citrus pectin) and liposoluble (citrus oil) components was fabricated. In this paper, we investigated the effects of hydrosoluble calcium ions and organic acids on the properties and stability of citrus oil emulsions stabilized by citrus pectin. The effects of varying the adding order of Ca2+ and organic acids were analyzed for the first time. Ca2+ can interact with citrus pectin, resulting in large emulsion droplets. Adding Ca2+ prior to emulsification resulted in an emulsion that was stable with respect to phase separation for 20 days, due to the enhancement of the continuous phase viscosity. The addition of organic acids (citric acid and ascorbic acid) reduced the droplet size and improved the emulsion stability, and the benefits were more evident when acids were added prior to emulsification (from 1.47 to 0.83 μm with 1 wt% ascorbic acid added), due to the enhancement of the emulsifying capacity caused by the acidic environment. Notably, the degradation of d-limonene was reduced by adding 1 wt% ascorbic acid to the citrus oil emulsion. Furthermore, the large droplets formed due to the addition of Ca2+ can be avoided by the simultaneous addition of organic acid. This study details a novel emulsion product prepared using endogenous citrus nutrient components, which may improve the utilization and added value of citrus fruits.

Characterization of magnesium ferrite nanofluids for heat transfer applications

This study intends to examine the suitability of magnesium ferrite nanofluid for heat transfer applications by measuring the thermophysical properties. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) are used to determine the surface morphology and size of magnesium ferrite nanoparticle. The ferrofluid is prepared by dispersing MgFe2O4 nanoparticles of size 80 nm in the Deionized water. The thermal conductivity, viscosity and surface tension of MgFe2O4 ferrofluid were investigated for five different volume fractions 0.01, 0.05, 0.10, 0.15, and 0.20, respectively. The hydrothermal synthesis method is employed for the preparation of magnesium ferrite nanoparticles. The outcome of the study indicates that thermal conductivity and viscosity of the ferrofluid is improved proportionally with intensification in volume fraction. Also noticed that the surface tension is decreased with the increasing volume fraction. The maximum enhancement of thermal conductivity and viscosity is 9.88% and 49% at the highest volume fraction of 0.20. The percentage of decrease in surface tension of the ferrofluid is observed as 45.8% at 0.20 volume fraction. The surface tension of ferrofluid decreases in connection with the rise in temperature from 293 to 333 K.

A RECENT OVERVIEW OF LOCALLY ADMINISTERED TOPICAL OTIC DOSAGE FORMS

Ear diseases can significantly affect the life quality of patient, so the need for effective treatment encourages the development of new active substances and new dosage forms. Otic dosage forms may be solutions, suspensions, or emulsions of drops or spray for washing the ear or for administration to the ear canal. They may be ear-wash preparations in the form of solution or emulsion, or medicated semi-solid or solid preparations in the form of gel, cream, ointment, powders, sticks or buffers. These preparations can contain one or much more active ingredients in a suitable vehicle and additionally may contain different excipients for isotonisation, pH adjustment, viscosity or solubility enhancement, buffering, preservation, etc. These excipients should not alter the pharmacological effect of active substances and should not be toxic or irritating. Ear preparations can be packaged in single or multiple doses. It is anticipated that otic dosage forms will be improved and the importance of locally applied, safe and highly controlled drug delivery systems will increase in the future.

Enhanced gelled hydrocarbon well treatment fluids

Abstract Compared with water-based well treatment fluid systems, hydrocarbon-based fluids possess advantages such as better fluid compatibility and lower formation damage, especially in water-sensitive formations. Hydrocarbon-based fluids are therefore often used in oilfield operations including hydraulic fracturing, sand control, and coiled tubing cleanout. The metal-crosslinked, phosphate ester-based gelled hydrocarbon (or gelled oil) fluids have been the preferred choice among hydrocarbon-based fluids since they are cost effective, robust at elevated temperatures, and operationally simple as only a couple of fluid additives are involved. Functioning as the gelling agent in gelled oil fluids, phosphate ester could cause fouling in refinery equipment. It is therefore desirable to lower the dosage of the phosphate ester-based gelling agent as much as possible, but without adversely affecting the fluid performance. A number of materials have been identified that could enhance the gelled oil viscosity and stability, which in turn translates into the reduction of the phosphate ester needed in the gelled oil. Among these enhancing materials, a type of aluminum pillared montmorillonite clay (the additive) was found to enhance the gelled oil viscosity to the largest extent. In laboratory tests, 30 ppt (30 pounds per thousand gallons) of the additive increased the gelled oil viscosity by 84% (± 5%) at 250 °F when compared with the baseline gelled oil without the additive. With the additive dosage at 30 ppt, the amount of the phosphate ester in the gelled oil could be reduced by 25% without decreasing the fluid viscosity. The additive was successfully applied to the crude oil-based gelled fluid, resulting in multiple times of viscosity increase in the study. In addition to the gelled oil viscosity enhancement, the additive also increased the regained permeability in the coreflow tests to near 3 times.

On the thermal characteristics of a manifold microchannel heat sink subjected to nanofluid using two-phase flow simulation

The main objective of the present study is to numerically simulate the heat transfer and fluid flow characteristics of water/CuO nanofluid under laminar flow regime in a manifold microchannel. Ensuring the accuracy of the numerical procedure, the obtained results have been compared with the experimental data available in the literature. The Euler multi-phase method considering temperature-dependent thermophysical properties have been employed to simulate the fluid flow and heat transfer. The effects of in/out ratio, Reynolds number, and solid concentration of nanoparticles as independent parameters on the heat transfer and flow field characteristics have been investigated. The obtained results revealed that the heat transfer and friction coefficient had been enhanced by increasing the in/out ratio at a constant Reynolds number. Furthermore, it is observed that by increasing the Reynolds number, the effects of in/out ratio becomes more considerable. According to obtained results, by increasing the solid concentration of the nanoparticles, the friction coefficient increases due to the enhancement of the effective viscosity. Based on the present investigation, in/out ratio equal to 0.25 provides the maximum amount of performance evaluation criterion at the Reynolds number of 100 and solid concentration 2 vol%. Thus, under the studied conditions, the heat transfer enhancement, due to adding the nanoparticles, is higher than that of the pressure drop.

Development of a Self‐Assembled Peptide/Methylcellulose‐Based Bioink for 3D Bioprinting

AbstractThe introduction of 3D bioprinting to fabricate living constructs with tailored architecture has provided a new paradigm for biofabrication, with the potential to overcome several drawbacks of conventional scaffold‐based tissue regeneration strategies. Hydrogel‐based materials are suitable candidates regarding cell biocompatibility but often display poor mechanical properties. Self‐assembling peptides are a promising source of biomaterials to be used as 3D scaffolds based on their similarity to extracellular matrices (structurally and mechanically). In this study, an advanced bioink for biofabrication is presented based on the optimization of a RAD16‐I‐based biomaterial. The strategy followed to build 3D predefined structures by 3D printing is based on an enhancement of bioink viscosity by adding methylcellulose (MC) to a RAD16‐I solution. The resultant constructs display high shape fidelity and stability and embedded human mesenchymal stem cells present high viability after 7 days of culture. Moreover, cells are also able to differentiate to the adipogenic lineage, suggesting the suitability of this novel biomaterial for soft tissue engineering applications.

Proposing a nano-approach to modify viscosity behavior of SAE 5W50 as light road vehicles lubricant

In this paper, viscosity of MWCNT (%50)–TiO2 (%50)/5W50 is investigated in temperature range of 5–55 °C, solid volume fractions of 0.05%, 0.1%, 0.25%, 0.5%, 0.75% and 1%, and shear rate range of 666.5–10,664 (s−1). Experimental results showed non-Newtonian behavior of enriched nano-engine oil. Nano-engine oil viscosity reduction (compared to 5W50 base oil) in some specific temperatures and solid volume fractions is one of the unique and interesting results of this research. Maximum viscosity reduction (− 11%) occurred in 15 °C and solid volume fraction of 0.05%, and maximum viscosity enhancement (+ 17%) was observed in 25 °C and solid volume fraction of 1%. The main goal of present study is to control viscosity increase of nanofluid after adding nanoparticles to the oil. Modeling and prediction of results were achieved via RSM and ANN methods.

Nanoparticle Assisted EOR during Sand-Pack Flooding: Electrical Tomography to Assess Flow Dynamics and Oil Recovery.

Silica nanoparticles have been shown to exhibit many characteristics that allow for additional oil to be recovered during sand-pack flooding experiments. Additionally various imaging techniques have been employed in the past to visually compare flooding procedures including x-ray computed tomography and magnetic resonance imaging; however, these techniques require the sample to be destroyed or sliced after the flooding experiment finishes. Electrical resistance tomography (ERT) overcomes these limitations by offering a non-destructive visualization method allowing for online images to be taken during the flooding process by the determination of spatial distribution of electrical resistivity, thus making it suitable for sand-packs. During the scope of this research a new sand-pack system and methodology was created which utilized ERT as a monitoring tool. Two concentrations, 0.5 wt% and 1.0 wt%, of SiO2 nanoparticles were compared with runs using only brine to compare the recovery efficiency and explore the ability of ERT to monitor the flooding process. Electrical resistance tomography was found to be an effective tool in monitoring local recovery efficiency revealing 1.0 wt% SiO2 to be more effective than 0.5 wt% and brine only runs during the scope of this research. A new method involving the slope function in excel was used to compare the effects of nanofluids on resistivity trends also revealing information about the rate of recovery against time. SiO2 nanofluid recovery mechanisms such interfacial tension reduction and viscosity enhancement were then considered to explain why the nanofluids resulted in greater oil recovery.

Effect of the alumina nanofluid concentration on minimum quantity lubrication hard machining for sustainable production

The use of vegetable oil-based nanofluids for minimum quantity lubrication hard machining has become a new research trend, proven to bring out very promising results and attained much attention to reduce the negative effects of using cutting fluids on the environment. The enhancement of thermal conductivity and viscosity of nanofluids helps to reduce the values of the friction coefficient, and the cooling lubricant properties are significantly improved when compared to the base fluids. In this paper, a set of optimized minimum quantity lubrication hard milling parameter combinations is obtained by using response surface methodology. Based on the optimized results, the study of the concentration effect of Al2O3 soybean oil-based nanofluid used for minimum quantity lubrication hard milling performance of 60Si2Mn hardened steel is investigated to validate and make further observations. It is noted that the appropriate nanoconcentration (1.0–1.5 wt%) and cutting conditions are observed to improve the cutting performance using soybean oil-based nanofluid. Increasing the nanoparticle concentration enhances the thermal conductivity and viscosity of the base fluids, which lead to reduce the cutting temperature and cutting forces and prolong the tool life from 80 to 115 min (increasing about 43.8%). Especially, the surface roughness ( Ra, Rz) improves and remains stable during hard cutting. Hence, the application of soybean oil-based nanofluid in minimum quantity lubrication hard machining is enlarged without losing anti-toxic, economic, and environment-friendly properties.

Effect of CuO Nanoparticles on Rheological Behavior of ISO VG46, Jatropha Oil, and Their Blend

Abstract This article presents experimental results on the mixing of CuO nanoparticles in ISO VG 46 oil, Jatropha oil, and a blend of the two oils. Initially, blend oil was prepared by mixing ISO VG46 and Jatropha oil in a fixed proportion. This blending caused a reduction in the viscosity of the oil mix as compared to the ISO VG46 oil. Therefore, to bring the viscosity of the blend oil to the level of the ISO VG46 oil, various concentrations of CuO nanoparticles were added to the blend to prepare stable nano-blend oils. The stability of the blend oil, ISO VG46, and Jatropha oil-based nano-lubricants was checked by measuring viscosity at regular intervals of time, and it is observed that stability decreases with the increase of CuO loading in base fluid. Viscosity values of nano-blend oils for various concentrations of CuO ranging from 0 to 3 wt. % were measured. These values were compared to the viscosity values of ISO VG46 and Jatropha oil-based nano-lubricants with the same CuO concentrations. About 19, 17, and 20 % enhancement in viscosity was observed in the blend oil, ISO VG46 oil, and Jatropha oil-based nano-lubricants, respectively, for 3 wt. % concentrations of CuO at 30°C. The nano-blend oil showed inferior performance up to 2 wt. % concentration of CuO in the entire temperature range (30 to 60°C). The viscosity of the nano-blend oil dispersing with 3 wt. % concentration matched well with the viscosity of ISO VG46 mineral oil. Furthermore, the experimental viscosity data of all the types of nano-lubricants are compared to the different viscosity models, and it is observed that the viscosity of the nano-lubricants closely matched with a viscosity model available in the literature. It is observed from viscosity sensitivity analysis that viscosity is more sensitive to greater concentration. The studies on the effects of nanoparticles’ concentration on density and friction coefficients revealed that the addition of nanoparticles in base oils had a small impact on pumping power.

Experimental Investigation of Recycled Machining Coolant Mixed with Nanofluids Based Al2O3

Machining coolant is used in manufacturing industry for lubrication, rusting control and cooling which are crucial in operations such as grinding and cutting process. However, the machining coolant lose efficiency in months due to the thermal degradation and contamination. To recycle the used of machining coolant while enhancing the performance, the mixture of nanofluids (N) based Al2O3 with better thermal properties to synthesize with the recycled machining coolant (RMC). This study suspended Al2O3 nanofluids in four base ratios of recycled machining coolant (i.e. 0:100, 20:80, 40:60 and 60:40) by ultrasonic homogenies. The three main parameters in cooling rate performance and rusting control are thermal conductivity, dynamic viscosity and pH indication, respectively. The thermal conductivity and dynamic viscosity are then measured at temperature range of 30 to 60°C. The highest enhancement of thermal conductivity was evaluated to be 37.9% higher than machining coolant base fluid at the temperature of 60°C in 60:40 (N:RMC). However, the enhancement of dynamic viscosity was measured to be 4.5% for 60:40 (N:RMC) at 60°C. The pH value of 60:40 (N:RMC) at ambient temperature obtained 8.18 value was nearly neutral and decreased the rusting process. Therefore, this study recommends the use of recycled machining coolants based Al2O3 as cutting fluid in the ratio of 60:40 for application in machining operations.

Rheological properties of super critical CO2 with Al2O3: Material type, size and temperature effect

CO2 liquid is applied as an Enhanced Oil Recovery (EOR) method in oil reservoirs to increase the displacement efficiency. Because of the high temperature and pressure in the reservoirs, the viscosity of the CO2 decreases leading to poor macroscopic sweep efficiency. We study the effect of morphology of aluminum oxide nanoparticle (Al2O3 NP) on the rheological properties of super critical (SC)-CO2 such as viscosity and self-diffusion coefficient using molecular dynamic (MD). We investigate these properties in detail for relevant temperature (350, 380, and 410) K, pressure, 200 bar, and spherical diameter (1.0, 2.0, and 3.0 nm) at 1% volume fraction. Molecular dynamic (MD) simulates Al2O3 SC-CO2 nanofluid by using two force fields such as condensed-phase molecular potentials for atomistic simulation studies (COMPASS) and Charge optimization many body (COMB). The results show that the viscosity of the nanofluid has a direct proportional to temperature and reversely proportional to NP size. Moreover, NP-based material and NP shape exhibit significant effect of enhancement in the nanofluid viscosity in comparison with the cylindrical CuO NP in our previous study. The relative viscosity is enhanced almost 3.6 times for smallest NP at 380 K. Also, implementing 1.0 nm Al2O3 SC-CO2 nanofluid improves the relative viscosity from 1.94 to 3.59 and then to 3.67 by increasing temperature from 350 to 380 to 410 K.

A Threshold-Limited Fluorescence Probe for Viscosity.

Viscosity of body fluid is an established biomarker of pathological conditions. Abnormality of cellular viscosity occurs when cells are challenged with external stresses. Small molecule probes to assess the viscosity are sought after for both disease diagnostics and basic studies. Fluorescence based probes are particular attractive due to their potentials for convenient and high spatiotemporal resolution microscopic monitoring of biological samples. The dyes with a floppy push-pull backbone or dyes with a rotatable substituent exhibits a viscosity responsive fluorescence enhancement and therefore viable viscosity probes. The scaffold of the existing viscosity probes contains typically one such floppy site. Therefore, they typically linearly respond to log(viscosity). We argue that minor viscosity fluctuation could potentially be physiological as the biological system is dynamic. We wish to develop a type of conceptually-new, threshold-limited viscosity probes, to complement the existing probes. Such probes do not exhibit a fluorescence enhancement when challenged with minor and presumably physiological enhancement of viscosity. When the viscosity is higher than a certain threshold, their fluorescence turns on. We hypothesize that a dye with two far-apart floppy sites could potentially yield such a threshold-limited signal and designed VPZ2 and VPZ3. Through spectral titration, VPZ3 was found to yield the desired threshold-limited signal. VPZ3 was suitable for in vitro bioimaging of viscosity under one-photon or two-photon excitation. VPZ3 is potentially useful in many downstream applications. Future work includes fine-tune of the threshold to allow tailored limit for fluorescence turn-on to better meet the need of different applications. Besides the implications in the real-world applications, the design concept could also be translated to design of alternative substrates.

Surfactant modulated interactions of hydrophobically modified ethoxylated urethane (HEUR) polymers with penetrable surfaces

HypothesisAdsorption of hydrophobically modified ethoxylated urethane polymers (HEURs) at the soft colloid interfaces of emulsion droplets will stabilise oil-in-water emulsions (a) via steric stabilisation induced by adsorption of the polymer at the droplet surfaces through the hydrophobic groups, and (b) via continuous phase viscosity enhancement through polymer self-association. Both of these mechanisms will be modulated by the presence of the surfactant, sodium dodecylsulfate (SDS). ExperimentsDodecane-in-water emulsions stabilised by three HEUR polymers with different structural composition were examined in the absence and presence of SDS by NMR spectroscopy and small-angle neutron scattering (SANS). The effect of adsorption of the polymer to the dodecane droplet surfaces, and the conformation of the self-associating polymer in the aqueous solution were quantified. FindingsAll emulsions were stable for days-weeks. Diffusion data showed the formation of oil droplets of hundreds of nm in size in the presence of all three HEURs, here denoted C6-L-(EO100-L)9-C6, C10-L-(EO200-L)4-C10, and C18-L-(EO200-L)7-C18, where EOx represents a block of ethylene oxide of x monomers, L denotes the linker group, and Cn the length of the hydrophobic end-group. No significant changes in droplet size across this series of polymers was observed. Collectively, the results point to adsorption of the polymer to the droplet surfaces, which results in a small decrease in the effective polymer solution concentration, thereby driving to significant changes in the structure and dynamics of the system. Evident in the SANS data in particular, is a subtle balance between the characteristic features reflecting polymer self-association, and those associated with polymer structures commensurate with a larger length-scale, dependent on the system composition. Surprisingly, the polymer and polymer/SDS complex in the presence of oil show slightly greater diffusive rates relative to the analogous systems in the absence of the oil.Finally, the partitioning of the three polymers in phase-separated samples was studied by 1H NMR, and it was shown that the C18-L-(EO200-L)7-C18 exhibited a greater partitioning in the oil phase compared with C6-L-(EO100-L)9-C6 and C10-L-(EO200-L)4-C10, an observation that may be understood in terms of the structural composition of the HEURs. The SDS showed a positive correlation between its partitioning in the two layers with the polymer partitioning, evidence of a strong interaction between the surfactant and the polymer, consistent with the behaviour observed in the oil-free system.