Rheological Measurements Research Articles

Hydrogels Powered by Nanoemulsion Technology for the Topical Delivery of Acmella oleracea Extract

Background/Objectives: Natural products are gaining increasing importance due to the large variety of biological activities exerted by their constituents. Among these, the products deriving from Acmella oleracea (L.) R.K. Jansen can be exploited for their local anaesthetic, myorelaxant, anti-inflammatory/analgesic, and antifungal properties. In this regard, there is a need to develop novel formulations for the topical delivery of A. oleracea-derived extracts to widen their use in the pharmaceutical and cosmetic fields. Methods: Nanoformulations, i.e., nanoemulsions (NEs) and microemulsions (MEs), were investigated as a strategy to encapsulate an extract from A. oleracea at the nanoscale level in water and then incorporated into xanthan gum-based hydrogels. Results: Only NEs provided a physically stable formulation, while the precipitation of solid hydrophobic components from the extract was observed during ME preparation under all tested conditions despite the use of ethyl oleate as an oily co-solvent. The optimized NE-based hydrogel remained physically stable over six months, as confirmed by rheological measurements and polarized optical microscope observation, without a phase separation phenomenon. Therefore, NEs resulted more suitable nanodispersed systems than MEs for the encapsulation of A. oleracea extract, which contains a large amount of hydrophobic constituents that are solid at room temperature. Furthermore, the sustained spilanthol release across an artificial membrane (Franz cell apparatus) and the cytotoxic profile on HaCaT cell line support its potential topical application. Conclusions: The outcomes of this study provided valuable insights into the formulation of A. oleracea extract, broadening its fields of applicability, including topical administration.

Effect of Quinoa Protein Concentrate in Particulate and Fibrillar Forms on the Physico-Chemical Properties of Quinoa Starch Gels

Abstract The current study investigates the interactions between quinoa protein—both in particulate (protein concentrate, QPC) and fibrillar (QPF) forms—and quinoa starch (QS) gels, and how these interactions influence the thermal, pasting, and rheological properties of the gels. Gels were made by adding three different concentrations of QPC or QPF to a 10% QS dispersion (10, 25, and 50% w/w of starch). DSC results suggested an enhancement of amylopectin thermal stability and an acceleration of retrogradation upon a cooling stage by the addition of quinoa protein. FTIR spectra indicated that QS and QPC/QPF mostly interacted through hydrogen bonds. According to rheological measurements, in contrast to the increased G′ due to the addition of QPC (50%), only a slight increase in G′ was observed due to the addition of QPF (50%). Notably, this study is the first to directly compare the effects of QPC and QPF on starch gel properties, revealing that QPC markedly enhances gel elasticity. These findings highlight the potential application of the optimized quinoa starch-protein-based gels as functional ingredients in plant-based meat analogues, where improved textural and nutritional attributes are critical.

Rheological and structural characterization of emulsion-based paints.

Paints obtained by dispersing pigments in emulsions of egg yolk and vegetable oil have been used by 20th century artists, likely drawing on techniques dating back to the 15th century. Understanding their flow behavior is key to shedding light on artists' material choices, gestures, and the resulting visual effects. In this study, we investigate two modern recipes that yield either oil-in-water (o/w) or water-in-oil (w/o) emulsions, formulated with egg yolk and linseed oil-raw or cooked with lead oxide following a historical process designed to accelerate drying. Stable, homogeneous paints were successfully prepared by dispersing lead-tin yellow pigment into these emulsions. The volume fraction of the dispersed phase, which includes solid pigment particles and emulsion droplets, emerged as a critical parameter for stable shear flow. Higher volume fractions resulted in increased yield stress, consistency, and viscosity across a wide range of shear rates. Dynamic rheological measurements further revealed the significant influence of the nature of the continuous phase on the viscoelastic properties of the paints. Finally, confocal microscopy on model systems (using glass microspheres as pigment analogs) showed preferential localization of particles within one emulsion phase. These observations offer new insights into how preparation protocols influence the microstructure-and subsequently the working properties-of historical emulsion paints.

Compatibilization of poly(lactic acid)/poly(3‐hydroxybutyrate‐co‐hydroxyvalerate) blends using multifunctional epoxy‐based chain extender

AbstractIn this study, the influence of the multifunctional epoxy‐based Joncryl ADR‐4468 as a chain extender (CE) for homopolymers and compatibilizer for blends of polylactide (PLA) and poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) is investigated. Firstly, dissolving Joncryl in acetone enabled precise dosing through the extruder feed zone during reactive extrusion of various blends with low Joncryl concentrations. The chosen composition ratio with 30 wt% PHBV led to a droplet‐matrix morphology with spherical PHBV droplets in the matrix of PLA. The increased compatibility of the PLA/PHBV blends was achieved by the addition of Joncryl. The average size of PHBV droplets decreased with increasing Joncryl concentration. Rheological measurements clearly revealed the influence of the interfacial tension between PLA and PHBV on the storage modulus. Specifically, the shoulder of the storage modulus at low frequencies shifts to lower frequencies with an increasing concentration of Joncryl in the blend. Moreover, an improvement of compatibility and interfacial adhesion between the PLA and PHBV phases is demonstrated by tensile tests under uniaxial loading, as the blends clearly become more ductile with higher Joncryl concentration.Highlights Dissolving Joncryl in acetone ensures precise low dosing in reactive extrusion. Joncryl reduces PHBV droplet size in the PLA matrix. Joncryl compatibilizes PLA/PHBV blends, enhancing adhesion and strain at break. Joncryl increases dynamic moduli and viscosity of PLA, PHBV, and their blends.

Carbon Fiber‐Reinforced Silicon Carbide (C/C‐SiC) Fabrication Derived From Polyetherketoneketone (PEKK) as an Alternative Thermoplastic Carbon Precursor

ABSTRACTThis study shows the first successful fabrication of a carbon fiber‐reinforced silicon carbide (C/C‐SiC) via the liquid silicon infiltration process using two thermoplastic polyetherketoneketone (PEKK) powders as carbon precursors. Samples are analyzed after each processing step and compared to polyetheretherketone (PEEK)‐derived reference samples. The carbon yield was above 65% for PEKK and 54% for PEEK, possibly due to the greater crosslinking potential of PEKK. Rheological measurements showed a higher melt viscosity of PEKK 60/40 (which consists of 60% terephtalic and 40% isophtalic moieties) than PEEK. The higher viscosity of PEKK 60/40 affected the carbon fiber‐reinforced plastic (CFRP) microstructure because it resulted in more matrix pores and some partly saturated fiber tows in the PEKK 60/40‐derived CFRP. The incomplete infiltration of fiber tows by PEKK in the CFRP state led to the undesirable reaction of the single carbon fibers during final siliconization. However, the effect was of minor influence, and the microstructure and phase composition remained unaffected. Mechanical testing of PEEK‐ and PEKK‐derived C/C‐SiC showed excellently comparable properties with a mean flexural strength above 200 MPa and a strain to failure above 0.55%. Thus, PEKK‐derived C/C‐SiC is a suitable alternative thermoplastic polymer for C/C‐SiC fabrication.

The Impact of DNA as a Chemical Admixture for Cementitious Materials

AbstractViscosity modifying agents (VMA) and superplasticizers (SP) are two common macromolecular admixture types for cementitious materials. VMAs are used to stabilize fresh cementitious materials, while SPs are used to disperse them. Most VMAs are bio‐based polysaccharides that act in the water phase between particles; while most SPs are synthetic comb polymers, consisting of negatively charged backbones that help their adsorption to the cement particles' surface. The molecular structure of DNA contains elements of VMA – as it is a polysaccharide – and SP – as it is a polyanion. In this study, rheological measurements are used to compare how these three types of macromolecules (VMA, SP, and DNA) affect cementitious materials. It is found that DNA shows the combined effects of VMAs and SPs on cement paste: it lowers yield stress while at the same time maintaining or even increasing its viscosity, which permits reducing water content while avoiding bleeding or segregation of samples. Yet, the presence of DNA has a significant retardation impact on cement hydration, which is also a common side effect of VMAs and SPs.

Fabrication of pullulan-chitosan fiber membranes for enhanced hemostatic applications.

Fabrication of pullulan-chitosan fiber membranes for enhanced hemostatic applications.

Preparation and characterization of thermosensitive phase-transition hydrogel based on decanoic acid-modified chitosan and methyl cellulose for wound healing.

Preparation and characterization of thermosensitive phase-transition hydrogel based on decanoic acid-modified chitosan and methyl cellulose for wound healing.

Effects of ionic liquids with different alkyl chain lengths and heat treatment on the physicochemical properties of high amylose maize starch and its resultant inclusion complex.

Effects of ionic liquids with different alkyl chain lengths and heat treatment on the physicochemical properties of high amylose maize starch and its resultant inclusion complex.

Hyperelastic Swelling of Stiff Hydrogels.

Hydrogels are swollen polymer networks where elastic deformation is coupled to nanoscale fluid flow. As a consequence, hydrogels can withstand large strains and exhibit nonlinear, hyperelastic properties. Previous studies have shown that low-modulus hydrogels and semiflexible biopolymer networks universally contract when sheared on timescales much longer than the poroelastic relaxation timescale. Using rheological and tribological measurements, we find that stiff polyacrylamide and polyacrylic acid hydrogels, with moduli of order ∼10-100 kPa, exclusively swell (dilate) when sheared. Poroelastic relaxation was examined using strain-controlled compression, indicating a volumetric diffusion constant of order 10^{-9} m^{2}/s. Upon shearing, we observed an increase in normal stress that varied quadratically with shear strain, which persisted for hours. Moreover, we show that this dilatant behavior manifests as swelling during tribological sliding, imbibing the hydrogel with fluid. We suggest that this inherent, hyperelastic dilatancy is an important feature in all stiff hydrogels, and may explain rehydration and mechanical rejuvenation in biological tissues such as cartilage.

Robust Self-Healing Metallo-Supergels of Folic Acid: Potential Sustainable Gelator for Oilfield Applications.

The majority of known metallosupramolecular gels are based on carefully designed ligands using extensive chemical synthesis. Their gelation is often limited to a certain specific metal salt. We demonstrate that in the presence of a wide group of metal salts natural and readily available folic acid (FA) can act as a supergelator. We report a systematic investigation of 17 mechanically robust FA-based metallogels at extremely low concentrations (<0.2 wt%). Using oscillatory rheological measurements, we further show that these metallogels undergo rapid recovery and self-healing, recovering up to 95% of their original stiffness within 1 min. Among the metallogels studied, FA-chromium(III) acetate gel (0.4 wt%) displayed the highest stiffness with a storage modulus of 4kPa. More importantly, the stiffness, recovery, and sol↔ gel transitions can be readily tuned by changing either the metal salt or the concentration. Using a combination of various analytical methods, we also suggest a structure of self-assembly in the metallogel network. This study defines non-toxic FA as a robust and sustainable building block for metallogels-mechanically tunable, multi-responsive soft materials. Finally, as a proof-of-concept experiment, we demonstrate that the FA-chromium(III) acetate gel can be considered as a potent sustainable gellator for enhanced oil recovery applications.

Closed‐Loop Recycling of Covalent Adaptable Network (CAN) Derived From Dopamine and Waste PET

ABSTRACTCovalent adaptable networks (CANs) have established a unique paradigm for developing recyclable thermosets. However, the majority of the CANs are derived from non‐renewable resources. Incorporating bio‐based feedstock in the design of CANs would further enhance sustainability. To this end, this work introduces a strategy to construct a CAN from bio‐based dopamine and plastic (PET) waste. The pursuit of novel molecules for the derivation of CAN motivated us to introduce dopamine in this report. The dopamine was transformed into a tetra‐functional alcohol monomer, which resulted in CAN upon polymerization with pyromellitic dianhydride. The CAN exhibited appreciable thermal stability, noteworthy mechanical properties, and excellent chemical and solvent resistance. The catalyst‐free reprocessing of the CAN was demonstrated. The viscoelastic behavior of the CAN was examined using rheological measurements. Finally, toward achieving the closed‐loop circular economy, the CAN was chemically degraded, and the monomer was recovered in high yield (91%) and purity, allowing the remaking of CAN. Our exploration expands the scope of diverse bio‐derived feedstock toward the synthesis of CANs. To the best of our knowledge, this is the first report that describes the derivation of reprocessable thermoset‐like CAN from dopamine and waste plastic and their subsequent chemical recycling.

Application of Quantitative EHL to the Bearing Life Analysis in a Refrigerant Compressor

ABSTRACT Standard rolling element bearing life calculations, as outlined in ISO 281, are not accurate for bearings used in refrigerant systems, because the lubrication quality parameter, κ, does not account for the behavior of refrigerant-oil mixtures. The presence of refrigerant reduces the viscosity and piezo-viscosity while increasing the compressibility of the mixtures. This paper presents a novel method for determining the reliability of rolling bearings using rheological measurements and elastohydrodynamic lubrication (EHL) simulations to produce a numerical value of the viscosity parameter κ, as opposed to the standard analytical one, based on a numerical estimation of the film parameter Λ. The proposed approach was validated with compressor tests using polyolester oil and R-1234ze(E) refrigerant under actual operating conditions from a real air-conditioning application. Scanning electron microscope examinations of the rolling bearings post-tests showed that the numerical κ from the new method predicted bearing condition more accurately than the standard κ. Although the example listed here uses a specific refrigerant-oil mixture, the method can be applied to other combinations of refrigerants and oils.

Simultaneous Effects of Thermal Cycling and Shear on Flow Instabilities of Phase-Change Nanoemulsions Measured by Rheo-NMR and MRI Velocimetry.

Organic phase change materials (PCMs) for thermal energy storage can be emulsified in water in the presence of surfactants to enable their use as pumpable heat transfer fluids. However, PCM nanoemulsions often exhibit instabilities during thermal cycling and shear flow that limit their use. To investigate their combined effects, rheological nuclear magnetic resonance (rheo-NMR) spectroscopy and magnetic resonance imaging (MRI) velocimetry methods were applied on a model octadecane-water-stearic acid system. Rheology measurements indicated that the viscosity exhibited hysteresis during thermal cycling, which correlated with the solid fraction of octadecane. Fluid velocity profiles and concentration distributions of liquid octadecane were noninvasively measured in a Searle cell. Nonlinear fluid velocity profiles developed after the octadecane solid-to-liquid phase transition, which recovered to linear profiles after octadecane melting at lower shear rates but notably not at higher shear rates. Nonuniform concentrations of liquid octadecane were measured during thermal cycling, a result of shear-induced mass transport, which causes local viscosity gradients that can lead to hydrodynamic instabilities and nonlinear fluid velocity profiles. The results not only show how shear affects flow instabilities in PCM nanoemulsions during thermal cycling but also demonstrate that this NMR methodology is a powerful tool for noninvasively measuring flow and concentration profiles in complex fluids.

Development and application of a time-temperature hydroxyethyl cellulose ink based on Clitoria ternatea L. blue petals anthocyanin and N-Hydroxyphthalimide for food freshness monitoring.

Development and application of a time-temperature hydroxyethyl cellulose ink based on Clitoria ternatea L. blue petals anthocyanin and N-Hydroxyphthalimide for food freshness monitoring.

Serial Extraction of Pectin and Polyphenols From Watermelon Rind for Use in Strawberry Preservation Film.

The aim of this study was to extract watermelon rind (WR) pectin (WRP) and watermelon rind polyphenols (WRE) and evaluate the effect of pectin/sodium alginate composite films (WRPSA) with or without WRE on strawberry preservation. WRP was extracted using citric acid, whereas WRE was obtained through ethyl acetate extraction. The extracted WRP was characterized for composition and structural properties, multi-angle laser light scattering (MALLS), Fourier Transform Infrared Spectroscopy (FTIR), differential scanning calorimetry (DSC), x-ray diffraction (XRD), ζ-potential analysis, and rheological measurements. The pectin/SA film (WRPSA) and pectin/SA composite film containing WRE (WRPESA) were prepared. Both films were analyzed for physical properties and structurally characterized. Strawberries were wrapped with either WRPSA, WRPESA, or no treatment (exposed) and stored under lightproof conditions at 4°C for 12 days. The results showed that WRP was a low-ester pectin (degree of methylation [DM]=38.7%) with a molecular weight of 683kDa. WRP had typical polysaccharide characteristic peaks and good thermal stability that could be used as a film-forming substrate. WRPESA showed better mechanical strength and antioxidant capacity than that of WRPSA, indicating that WRE showed synergistic effects on the improvement of composite films. Additionally, WRPESA effectively reduced strawberry softening, color deterioration, and weight loss, in addition to the delay in the dynamic changes in sugar content and pH and accumulation of malondialdehyde (MDA). WRPESA also helped maintain the total phenolic content of the strawberries. These findings suggest that watermelon byproducts could be valorized for sustainable food packaging, reducing both agricultural waste and reliance on synthetic materials. Practical Application: This article confirmed the feasibility of a sequential extraction process for watermelon rind pectin and polyphenols, which can later be applied to industrial production lines to increase the utilization rate of watermelon rind. The practical application value of this research lies in the development of biodegradable packaging materials. By extracting pectin and polyphenols from watermelon rind, the resulting films can effectively extend the shelf life of strawberries and reduce food waste. Furthermore, this study promotes the utilization of agricultural waste, enhances the nutritional value of food, and provides new opportunities for local economic development. Additionally, it offers a scientific basis for advancing sustainable packaging technology and food preservation innovations, which is significant for environmental protection and healthy consumption.

Direct visualization of the side-by-side self-assembly of high and low acyl gellan gum by AFM.

Direct visualization of the side-by-side self-assembly of high and low acyl gellan gum by AFM.

Salt-induced gelation of nonionic sucrose ester dispersions.

Salt-induced gelation of nonionic sucrose ester dispersions.

Harnessing pea proteins for thermo-reversible gels: Novel strategy and molecular principle.

Harnessing pea proteins for thermo-reversible gels: Novel strategy and molecular principle.

Effect of container geometry induced slippage on rheological measurement of fresh cement-based materials using coaxial cylinder rheometer

Effect of container geometry induced slippage on rheological measurement of fresh cement-based materials using coaxial cylinder rheometer