Stability and Interfacial Viscoelasticity of Oil-Water Nanoemulsions Stabilized by Soy 2 Lecithin and Tween 20 for the Encapsulation of Bioactive Carvacrol

The rheology of oil-in-water (O/W) droplet interfaces stabilized by food-grade emulsifiers (soy lecithin or Tween 20) under controlled aqueous conditions was investigated to elucidate its contribution in the kinetic stabilization of nanoemulsion-based delivery systems containing carvacrol, a naturally-derived antimicrobial compound. Dilational rheology of surfactant-laden O/W interfaces was measured using axisymmetric drop shape analysis. The kinetic stability of corresponding nanoemulsions (containing mixtures of carvacrol and medium-chain triglyceride (MCT) oil dispersed in water (pH 7)) was characterized using dynamic light scattering. Zwitterionic lecithin molecules adsorbed to the O/W interface for 24 h formed a notably viscoelastic layer, compared to nonionic Tween 20 molecules. The kinetic stability within the first 24 h for each nanoemulsion was strongly dependent upon encapsulated carvacrol concentration, with higher carvacrol concentrations leading to lower kinetic stability. Lecithin-stabilized nanoemulsions (pH 7) were highly stable, yielding monodispersed droplet size distributions and high resistance to increases in droplet size over 30 days. Contrarily, corresponding Tween 20-stabilized nanoemulsions showed large increases in the droplet size and developed a bimodal droplet size distribution over time. The initial size of oil droplets stabilized by lecithin was slightly dependent on pH, yielding smaller droplets at pH 7 and larger droplets at pH 3; however, the extended kinetic stability was not greatly impacted by pH modulation. Determining a positive association between interfacial viscoelasticity and nanoemulsion stability may potentially be very useful for food manufacturers seeking to optimize the encapsulation and delivery of lipophilic antimicrobial molecules using food-grade emulsifiers

Interfacial Rheological Mechanics of a Non-ionic, Tri-block Copolymer at Water/Hexadecane Interface

Growing interest on the stability of foams and emulsions has lead to concentrated research of interfacial rheology. The response of an interfacial layer to mechanical deformation in size and shape is dependent on its composition. [Miller 2010] This research analysis focused on the adsorption and rheological mechanics of the non-ionic, tri-block copolymer, Pluronic 17R4 at the water/hexadecane interface. The adsorption and viscoelastic properties of the interface were measured via methods of pendant drop tensiometry and dynamic oscillation with drop shape analysis software. Interfacial tension measurements were taken to study the surface pressures of Pluronic 17R4 solutions with concentrations ranging from 1x10-6 M to 1x10-2 M. Dynamic oscillation experiments were conducted to study the elastic and viscous responses of the Pluronic 17R4 solutions subjected to a series of sinusoidal area deformations at frequencies ranging from 0.01 Hz to 1 Hz. Experimental analysis showed that as concentration and deformation rates increase, the elastic response of the interfacial layer decreases and the viscous response increases. This implies that at higher concentrations and deformation rates, the interfacial layer is behaving more like a viscous film than an elastic solid

Characterization of Superabsorbent Poly(Sodium-Acrylate Acrylamide) Hydrogels and Infuence of Chemical Structure on Internally Cured Mortar

Internal curing of mortar through superabsorbent polymer hydrogels is explored as a solution to self-desiccation. Four different hydrogels of poly(sodium-acrylate acry- lamide) are synthesized and the impact of chemical composition on mortar is assessed with relative humidity and autogenous shrinkage testing. The hydrogels are characterized with swelling tests in different salt solutions and compression tests. Chemical composition af- fected both swelling kinetics and gel network size. Mortar containing these hydrogels had increased relative humidity and markedly reduced autogenous shrinkage. Additionally, the chemical structure of the hydrogels was found to signifcantly impact the mortar’s shrink- age. Hydrogels that quickly released most of their absorbed fuid were able to better reduce autogenous shrinkage compared to hydrogels that retained fuid for longer periods (\u3e 4 hours), although this performance was highly sensitive to total water content. The release of absorbed water in hydrogels is most likely a function of both Laplace pressure of emptying voids and chemically-linked osmotic pressure developing from an ion concentration gradient between the hydrogels and cement pore solution. If the osmotic pressure is strong enough, the hydrogels can disperse most of the absorbed water before the depercolation of capillary porosity occurs, allowing the water to permeate the bulk of the mortar microstructure and most effectively reduce self-desiccation and autogenous shrinkage

Synthesis and Characterization of Polymer-Silica Composite Hydrogel Particles and Influence of Hydrogel Composition on Cement Paste Microstructure

The objective of this research is to define the fundamental structure-property relationships of water-swollen polymer hydrogel particles that are employed as internal curing agents in cementitious mixtures, in addition to reporting a novel synthesis procedure for combining pozzolanic materials with hydrogel particles. Solution polymerization was performed to incorporate amorphous nanosilica particles within acrylic-based polymer hydrogel particles of varying chemical compositions (i.e., monomer ratio of acrylic acid (AA) to acrylamide (AM)). Experiments were designed to measure the absorption capacity and kinetics of hydrogel particles immersed in pure water and cementitious pore solution, as well as determine the impact of particles on cement paste microstructure. While majority-AM hydrogel particles displayed relatively stable absorption values during immersion in pore solution, majority-AA hydrogel particles desorbed fluid over time, most likely due to the interactions of multivalent cations in the absorbed solution with the anionic polymer network. Interestingly, the addition of negatively charged nanosilica particles accelerated and enhanced this desorption response. When incorporated into cement paste, majority-AM hydrogel particles encouraged the formation of calcium hydroxide and calcium silicate hydrate within the void space previously occupied by the swollen particles. When nanosilica was added to the hydrogel particles, a 53 % increase in the number of hydrogel voids containing hydrated product was observed for the 17 % AA hydrogel particles, and a 140 % increase was observed for the 83 % AA hydrogel particles. These results suggest that the combination of nanosilica with polymeric hydrogel particles provides a favorable environment for the pozzolanic reaction to proceed and that nanosilica aids in the replenishment of hydrogel void space with hydrated cement phases

Controllable Internal Mixing in Coalescing Droplets Induced by The Solutal Marangoni Convection of Surfactants with Distinct Headgroup Architectures

Through several complementary experiments, an investigation of the bulk and interfacial flows that emerged during the coalescence of two water-in-oil droplets with asymmetric compositional properties was performed. By adding surfactant to one of the coalescing droplets and leaving the other surfactant-free, a strong interfacial tension gradient (i.e., solutal Marangoni) driving energy between the merging droplets generated pronounced internal mixing. The contributions of two distinct types of surfactant, anionic ammonium lauryl sulfate (ALS) and cationic cetyltrimethylammonium bromide (CTAB) on the rate of coalescence bridge expansion and on the generation of opposing flows during coalescence were investigated. All coalescence experiments supported the power law relation between the radius of the expanding connective liquid bridge and time, rb ∝ t1/2. However, the presence of surfactant decreased the magnitude of the prefactor in this relationship due to induced interfacial solutal Marangoni convection. Experiments showed that packing efficiency, diffusivity, and bulk concentration of the selected surfactant are vital in solutal Marangoni convection and thus the degree and timescale of internal mixing between merging droplets, which has yet to be adequately discussed within the literature. Denser interfacial packing efficiency and lower diffusivity of CTAB produced stronger opposing bulk and interfacial flow as well as greater bulk mixing. A discussion of how optimized surfactant selection and solutal Marangoni convection can be used for passively inducing convective mixing between coalescing drops in microfluidic channels when viscosity modulation is not feasible is provided

Characterization of Superabsorbent Polymers in Aluminum Solutions

Over the past few decades, super absorbent polymers (SAPs) have been the topic of research projects all around the world due to their incredible ability to absorb water. They have applications in everything from disposable diapers to high performance concrete. In concrete, aqueous cations permeate the polymer network, reducing swelling and altering properties. One of these ions, aluminum, alters SAP properties by creating a stiff outer shell and greatly reducing absorbency, but these effects have not been well characterized. One method of characterizing the effects of aluminum on SAP hydrogels was performing gravimetric swelling tests to determine equilibrium water capacity at different aluminum ion concentrations. Compressive strength was also determined for swollen particles using a rheometer to perform compression tests. Results from this testing show that low concentration solutions take several hours to permeate the polymer network and reduce swelling capacity, while high concentration solutions are able to limit swelling immediately. The compressive strength of the gel was increased greatly in polymers containing mostly poly(acrylic acid), while SAPs containing more poly(acrylamide) did not have their strength as greatly influenced by the aluminum ions. These results help elucidate the negative effects that may be caused by multivalent cations in concrete. Further research will include studying the interactions of aluminum ions with polymer strands using polymer brushes on a quartz crystal microbalance. This will hopefully reveal the mechanism and kinetics of salt absorption in polymer networks

Fast Readout of Split-Ring Resonators Made Simple and Low-Cost for Application in HPLC

Split-ring resonators (SRR) are simple electrical circuits that show a significant shift in resonance frequency even with the smallest changes in split capacitance, and thus in permittivity, electric conductivity, and dielectric losses of the split capacitor’s dielectric. Usually, the resonance frequency is derived from the frequency response, but recording the frequency spectrum takes a certain amount of time. Here, we present a new capillary split-ring resonator CaSRR with fast readout for liquid chromatography (LC), which is capable of accurately detecting very fast changes in split capacity. The proposed method is based on the detection of the transmitted signal at a single frequency that is analyzed by demodulation. The demodulated signal changes its amplitude depending on the shift of the resonance frequency. Our simple low-cost electronics enables an average sampling rate of 42 Hz with 128 averages of the demodulated signal and has a frequency stability of 840 mHz. Thus, a minimum change in permittivity of ∆εr,min = 11.26 × 10−3 can be detected. Finally, a chromatogram of one sugar (glucose) and one sugar alcohol (xylitol) is recorded using the SRR and is compared to a standard refractive index detector. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

RP-LC and HPTLC Methods for the Determination of Olmesartan Medoxomil and Hydrochlorothiazide in Combined Tablet Dosage Forms

Two new, rapid, precise, accurate and specific chromatographic methods were described for the simultaneous determination of olmesartan medoxomil and hydrochlorothiazide in combined tablet dosage forms. The first method was based on reversed phase liquid chromatography using an Eurosphere 100 RP C18 column (250 × 4.6 mm ID, 5 μm). The mobile phase was methanol–0.05% o-phosphoric acid (60:40 v/v) at a flow rate of 1.0 mL min−1. Commercially available tablets and laboratory mixtures containing both drugs were assayed and detected using a UV detector at 270 nm. The second method involved silica gel 60 F254 high performance thin layer chromatography and densitometric detection at 254 nm using acetonitrile–ethyl acetate–glacial acid (7:3:0.4 v/v/v) as the mobile phase. Calibration curves ranged between 200–600 and 125–375 ng spot−1 for olmesartan and hydrochlorothiazide, respectively

Applicability of the Long Chain Diol Index (LDI) as a Sea Surface Temperature Proxy in the Arabian Sea

The long-chain diol index (LDI) is a relatively new proxy for sea surface temperature (SST) which has been rarely applied in upwelling regions. Here, we evaluated its application by comparison with other SST records obtained by commonly used proxies, that is, the Mg/Ca ratio of the planktonic foraminifera species Globigerinoides ruber and the alkenone paleothermometer U-37(K '). We focused on the last glacial-interglacial transition of four different sedimentary archives from the western and northern Arabian Sea, which are currently under the influence of monsoon-induced upwelling and the associated development of an oxygen minimum zone. The UK ' 37 ${{\mathrm{U}}{\mathrm{K}\prime }}_{37}$ and Mg/Ca-G.ruber SST records revealed an increase of 0.6-3.4 degrees C from the Last Glacial Maximum to the late Holocene with somewhat higher amplitude in the northern part of the Arabian Sea than compared to the western part. In contrast, the LDI SSTs did not reveal major changes during the last glacial-interglacial transition which was followed by a decreasing trend during the Holocene. The LGM versus the Holocene LDI SSTs ranged between -0.2 and -2.7 degrees C. Particularly at one record, offshore Oman, the SST decrease during the Holocene was high in amplitude, suggesting a potential cold bias, possibly related to changes in upwelling intensity. This indicates that care has to be taken when applying the LDI for annual mean SST reconstruction in upwelling regions