Linear Viscoelastic Region Research Articles

Synthetic oil gels with organoclays in the formulation of magnetorheological fluids

Magnetorheological fluids (MRF) are smart composite materials that, under an external magnetic field, show a reversible solid-liquid transition in less than 10 ms. This study aimed to evaluate which organoclays would jellify a synthetic oil for the formulation of MRF. Three dispersant additives for carbonyl iron powder were evaluated. Fifteen different gelling additives from four clay families, bentonites, hectorites, montmorillonites, and mixed mineral thixotropes (MMT), were dispersed in oil only, keeping the same concentration, without iron particles. The gels were then tested through amplitude and frequency sweeps in oscillatory rheometry to evaluate their viscoelastic behavior. The thixotropy of the gels was measured through the “three-interval” test in a rheometer. After selecting the best gelling additive to prepare the MRF, three dispersing additives had their rheology evaluated to determine the best magnetorheological effect and redispersibility after 1 year of sample preparation. In the linear viscoelastic region, all MMT clays resulted in a weak viscoelastic gel (G′∼100 to 300 Pa and G″∼30 to 50 Pa). Some of the bentonite clays jellified, and others did not. The best organoclays were montmorillonites and hectorites, which formed consistent viscoelastic gels (G′∼1 to 5 kPa and G″∼70 to 250 Pa). The best organoclay presented a yield stress σ0 = (42 ± 3) Pa, a storage modulus G′ = (2690 ± 201) Pa, and a cohesive energy density (CED) = 98 mJ/m3, and it was selected to explore the rheology of MRF with three dispersant additives: octan-1-ol, octan-1-amine, and L-α-Phosphatidylcholine. All the MRFs were prepared using carbonyl iron powder HS (BASF SE) in oil gels and with the same organoclay. All three dispersant additives showed a thixotropic recovery above 100% in the three-interval test. Regarding the redispersibility after 1 year, the MRF formulations with octan-1-amine and lecithin were reproved, as they reached normal force peaks of 19 and 24 N, while the work was 28 and 415 mJ, respectively. The best MRF was formulated with octan-1-ol, and resulted in a normal force of 0.33 N and 3.4 mJ at 35 mm of vane penetration. Therefore, we conclude that the MRF with octan-1-ol and montmorillonite #6 showed a better balance between thixotropy, MR effect, and, above all, good redispersibility.

Preparation and characterization of Pickering emulsion gel stabilized by WPI/SPI composite particles and encapsulation of milk-derived peptide FDRPFL

In this study, Pickering emulsion (PE) stabilized by whey protein isolate/soybean protein isolate (WPI/SPI) composite particles were used as a template to construct Pickering emulsion gel (PEG). The results showed that the PE stabilized by WPI/SPI composite particles had good centrifugal and storage stability at 4 °C (at least 4 months). Furthermore, When SA concentration was 3% and PE:SA ratio of 5:1, the obtained PEG with water-in-oil type exhibited a smaller droplet size, a denser network structure, and solid-like behavior in the linear viscoelastic region using a laser particle size analyzer, rheometer, and confocal laser scanning microscopy. Moreover, the increase of hydrogen bonds after SA addition confirmed that increased of β-sheet in WPI/SPI by Fourier-transform infrared spectroscopy, as β-sheet structure was stabilized by interchain hydrogen bonds, thus forming a denser network structure. In addition, PEGs could effectively encapsulate peptide FDRPFL, with a highest encapsulation efficiency of 72.8%. In vitro digestion behavior revealed that PEGs could improve the bioaccessibility of peptide FDRPFL and mainly followed the release mechanism of non-Fickian superstate II. Taken together, the present findings provide a theoretical framework for the development and application of PEGs stabilized by WPI/SPI composite particles.

Effect of PCL chain length on rheological and mechanical properties of PCL‐PDMS‐PCL triblock copolymer films

AbstractThe polycaprolactone‐polydimethylsiloxane‐polycaprolactone (PCL‐PDMS‐PCL) triblock copolymer films of variable PCL chain are analyzed for rheological characteristics in this paper. The dynamics of viscoelastic behavior of photocrosslinked films above their crystal melting temperature (Tcm) is measured using oscillatory shear rheology experiments. The frequency sweep tests are analyzed at 0.1% strain as obtained from linear viscoelastic region. Shear thinning is observed in the study of complex viscosity. It has been noted that viscosity rises with increase in crosslink density and decrease in with PCL chain length. Time‐dependent effect on the copolymer films has been analyzed by creep recovery behavior. The Burgers model is fitted in creep compliance data to analyze its viscoelastic and viscous region. An examination of structure recovery revealed that recovery increased as PCL chain length decreased. Tensile strength and percentage elongation are studied at ambient conditions with a universal testing machine, while storage modulus and tan δ are analyzed by a dynamic mechanical analyzer at varying temperatures.

Network homogeneity on linear and nonlinear viscoelasticity of polyethylene terephthalate vitrimers

Designing network topology with tunable dynamics and rheology behaviors is the key for vitrimers applications. In this study, PET vitrimers with varying crosslinking density and network homogeneity were created by using different Mw of precursors and branching agents (catalysts). Our results show that the dynamic network formed by propane-type branching agent such as 1,3-bis[tris(hydroxymethyl) methylamino] propane (BIS-TRIS propane), is more uniform due to steric hindrance effect compared to 2,2-Bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol (BIS-TRIS). The thermal behavior of PET vitrimers was investigated by non-isothermal experiments, including glass transition and crystallization process. In particular, rheology behavior is sensitive to network structure and bond exchange process. The linear viscoelasticity (LVE) region of PET vitrimers is characterized by constructed pseudo-master curves that are guided by two distinct relaxation mechanisms: Rouse-type relaxation of strands and terminal relaxation of the network. Each relaxation mechanism is associated with a unique activation energy. The mechanical and processing properties of the PET vitrimers are reflected in their plateau modulus and characteristic relaxation time, which varies depending on the network topology. Based on the LVE analysis, we further investigated nonlinear rheology of PET vitrimers under extensional flow. Our results indicate that PET vitrimers exhibit significant strain hardening behavior, but display distinct stretching trends, corresponding to polymer melts' ductility. The ductility of materials decreases with a decrease in precursor's molecular weight (Mw), but improved with enhanced network homogeneity. Therefore, the crosslinking density and network homogeneity of dynamic network can be selectively tailored using appropriate precursors and branching agents to meet various industrial applications.

Acid-induced gels from mixtures of micellar casein and pea protein: Effect of protein ratio and preheating route

Enhancing the sustainability of dairy products through the partial substitution of dairy proteins with plant proteins requires exploring formulation and processing strategies. This study investigates the gluconic-δ-lactone (GDL)-induced hybrid gels from commercial micellar casein isolate (M) and pea protein isolate (P) dispersions (5% w/w protein content). Variations in the M/P ratios (3:1, 2:2, and 1:3) and preheating routes (Route 1: preheating M and P dispersions together; Route 2: preheating them separately) impacted the physical/conformational properties of protein dispersions as well as the rheological/structural features of resulting gels. Small and large amplitude oscillatory shear (SAOS and LAOS) tests revealed that lower M/P ratio led to earlier gelling points and increased the stiffness and elasticity of hybrid gels in the linear viscoelastic (LVE) region. All gels transitioned from elastic to plastic behavior in the non-linear viscoelastic (NLVE) region, with lower M/P ratio showing reduced stretchability and faster structural breakdown. Regardless of routes, the preheating step (95 °C, 30 min) disintegrated inherent aggregates/agglomerates in these commercial protein ingredients, leading to smaller particle size, but higher protein solubility, surface hydrophobicity, and |ζ-potential|. Pea proteins formed soluble aggregates during preheating, but the presence of micellar caseins (Route 1) hindered this process. Consequently, mixtures with lower M/P ratio and from preheating route 2, possessed higher quantities of pea protein soluble aggregates, forming a compact gel network with low water mobility, as observed by CLSM, STED, and LF-NMR. These findings show the potential for using pea proteins in acid-induced gel foods like yogurt and paneer-type cheeses.

Master curves construction for viscoelastic functions of bituminous materials

Abstract The performance of bituminous materials is often evaluated using rheological properties measured within the linear viscoelastic region. If there is a univocal temperature dependence of all the relaxation times, data obtained in different operating conditions can be translated onto a logarithmic scale where they partially overlap and merge into a single master curve. This is the well-known time–temperature superposition principle that has been successfully applied for decades. However, the empirical nature of the method has led to many different procedures being used for the graphical construction of the master curve. In addition, the continuously increasing calculating power has led to new approaches, such as the simultaneous modelling of the represented viscoelastic function. Losing track of the basic statements of the method is the hidden drawback of this wide range of available protocols with the risk of artefacts and incongruences being introduced in the construction of the master curves. This review summarizes these basic statements together with the empirical and phenomenological approaches developed over the years. The aim of this study is to help the reader in choosing the most appropriate method to build the master curves. Although the subject of the review is of general application, the field of bitumen is focused on.

Impact of crystalline domains on long-term stability and mechanical performance of anisotropic silk fibroin sponges.

Sponge-like materials made from regenerated silk fibroin biopolymers are a tunable and advantageous platform for in vitro engineered tissue culture and in vivo tissue regeneration. Anisotropic, three-dimensional (3D) silk fibroin sponge-like scaffolds can mimic the architecture of contractile muscle. Herein, we use silk fibroin solution isolated from the cocoons of Bombyx mori silkworms to form aligned sponges via directional ice templating in a custom mold with a slurry of dry ice and ethanol. Hydrated tensile mechanical properties of these aligned sponges were evaluated as a function of silk polymer concentration (3% or 5%), freezing time (50% or 100% ethanol), and post-lyophilization method for inducing crystallinity (autoclaving, water annealing). Hydrated static tensile tests were used to determine Young's modulus and ultimate tensile strength across sponge formulations at two strain rates to evaluate rate dependence in the calculated parameters. Results aligned with previous reports in the literature for isotropic silk fibroin sponge-like scaffolds, where the method by which beta-sheets were formed and level of beta-sheet content (crystallinity) had the greatest impact on static parameters, while polymer concentration and freezing rate did not significantly impact static mechanical properties. We estimated the crystalline organization using molecular dynamics simulations to show that larger crystalline regions may be responsible for strength at low strain amplitudes and brittleness at high strain amplitudes in the autoclaved sponges. Within the parameters evaluated, extensional Young's modulus is tunable in the range of 600-2800 kPa. Dynamic tensile testing revealed the linear viscoelastic region to be between 0% and 10% strain amplitude and 0.2-2 Hz frequencies. Long-term stability was evaluated by hysteresis and fatigue tests. Fatigue tests showed minimal change in the storage and loss modulus of 5% silk fibroin sponges for more than 6000 min of continuous mechanical stimulation in the linear regime at 10% strain amplitude and 1 Hz frequency. Furthermore, we confirmed that these mechanical properties hold when decellularized extracellular matrix is added to the sponges and when the mechanical property assessments were performed in cell culture media. We also used nano-computed tomography (nano-CT) and simulations to explore pore interconnectivity and tortuosity. Overall, these results highlight the potential of anisotropic, sponge-like silk fibroin scaffolds for long-term (>6 weeks) contractile muscle culture with an in vitro bioreactor system that provides routine mechanical stimulation.

Impact of thermomechanical reprocessing on multilayer plastic packaging blend

Multilayer plastic packaging (MPP) has attracted extensive attention due to its functionality and inherent difficulty in reclamation. One primary concern is the performance of reprocessed MPP since it inherently consists of many dissimilar polymers. This study aims to assess the effect of multiple thermomechanical reprocessing cycles on the properties of a MPP blend. Low density polyethylene (LDPE)/maleic anhydride grafted linear LDPE (LLDPE-g-MA)/ethylene vinyl alcohol (EVOH) blend was manufactured and subjected to thermomechanical reprocessing, including thermal compounding, grinding, and injection molding for six cycles to characterize the impact of thermomechanical reprocessing on the blend's mechanical, morphological, thermal, and rheological properties. The tensile strength and modulus of the reprocessed blend remained consistent throughout six cycles. A pronounced decline in elongation at break was observed after four cycles of reprocessing. Toughness, as represented by the essential work of fracture, increased steadily up to three cycles of processing, followed by a decline in the following reprocessing cycles. The main property change is possibly caused by the gelling of the EVOH in the reprocessed blend, as demonstrated by larger EVOH agglomerates in the LDPE matrix. Differential scanning calorimetry results indicated that the degree of crystallization of the EVOH phase changed with increasing reprocessing cycles, suggesting EVOH degradation. Rheological behavior in the linear viscoelastic region indicated enhanced interfacial interaction between LDPE and EVOH due to the cross-linking of LLDPE-g-MA and rigid EVOH in the early reprocessing stages. After four cycles of reprocessing, decreases in storage and loss moduli were observed, indicating the possibility of phase separation caused by gelling of EVOH. Using polymer blending to reclaim LDPE-based EVOH multilayer is promising for up to four cycles of reprocessing as shown by mechanical, thermal, and rheological behaviors.

A new method for judging and predicting the stability of ceramic suspensions by rheological tests

In preparing stable ceramic suspensions, the interactions of particles and polymer chains should be emphatically considered, which depends on DLVO stabilization theory. However, DLVO stabilization theory are qualitative and lack quantitative methods for judging and predicting stability. The present study introduced a new method for directly judging and predicting suspension stability based on rheological tests and established a correlation between measured data and the state of ceramic suspensions. Among rheological properties, the dominance of the storage modulus G' is more conducive to the realization of steric stabilization, whereas the loss modulus G" exerts a more significant influence in bridging and depletion flocculation states. The stability of suspensions with a given particle size can be judged and predicted by comparing the value of tan δ (the ratio of G" and G') under identical measurement conditions. Lower values of tan δ indicate better stability of the ceramic suspensions. The new method has been verified by experiments of classical alumina suspensions. The results indicate that the alumina suspensions with 14, 17, 20, and 23 vol% of solid particles exhibit optimal stability when combined with PVA concentrations of 3.5, 3.0, 2.5, and 2.0 wt%. Meanwhile, this combination leads to the minimum values of tan δ within the linear viscoelastic region (0.71, 0.45, 0.33, and 0.31, respectively). The universality of the method has been further demonstrated in zirconia suspensions dispersed with Dolapix CE64 dispersant. The application of this method has demonstrated its significance in judging and predicting the stability of ceramic suspensions.

Effect of cellulose ether emulsion and oleogel as healthy fat alternatives in cream cheese. Linear and nonlinear rheology, texture and sensory properties

The suitability of oil-in-water (o/w) hydroxypropyl methylcellulose (HPMC)-based emulsions and oleogels to reduce total fat and saturated fat content in cream cheese was studied. The effect of HPMC emulsions and oleogels on spreadability, viscoelasticity, and sensory acceptability of cream cheese was evaluated. Small-amplitude oscillatory shear (SAOS) and large-amplitude oscillatory shear (LAOS) tests were performed to investigate linear and nonlinear rheology. All cheeses showed a predominance of G’ versus G” with a light dependence of both moduli with frequency in the linear viscoelastic region (LVR). Fat replacement with emulsion or oleogel significantly reduces the values of G’ and G” at the LVR, yield point, and flow point, and increases spreadability. This effect was greatest for the oleogel substitution. However, incorporation of emulsion or oleogel did not significantly affect tan δ, yield stress, yield strain, flow stress, and flow strain. The elastic and viscous evolution during the transition from SAOS to LAOS was similar in all cheeses, despite their differences in spreadability. At large deformation, all samples showed strain-stiffening and shear-thinning behavior. Similar sensory acceptability was found among the oleogel and emulsion cheeses and the control. The similar nonlinear rheological properties among cheeses do not explain the differences in spreadability properties, but explain their similar sensory acceptability. Furthermore, the purchase intention for oleogel and emulsion cheeses increases when consumers receive information on the type and amount of fat.

Incorporating soy protein hydrolysate and temperature-induced gelling polysaccharide as partial egg replacements for enhanced texture in sponge cake

This study investigated the influence of hydroxypropyl methylcelluloses (HPMCs), temperature-induced gelling polysaccharides, on the air-water interfacial properties and foaming properties of four soy proteins. Two HPMCs with different relative molecular masses (F50, lower; K4M, higher) were combined with soy protein isolate (SPI), 7S fraction (7S), selective hydrolysate by pepsin (SPSH), and limited hydrolysate by papain (SPLH). Interfacial shear rheology results showed that SPSH exhibited the highest G′ value, indicating a multi-layer adsorption structure formed due to both 7S and low molecule peptides in SPSH. Adding F50 to SPI, 7S, and SPSH improved foam expansion and stability while adding K4M negatively impacted the foam expansion of SPI, 7S, and SPSH but enhanced the foam expansion of SPLH. These findings suggest that the interfacial interaction patterns between HPMCs and soy proteins are significantly influenced by the molecular weight of HPMCs and the structure of the protein. Incorporating F50 into SPSH decreased the gelation temperature, shortened the formation time of a solid-like layer at the air-water interface, and expanded the linear viscoelastic region during structural fraction testing. Consequently, the combination of F50 and SPSH was chosen as the viable alternative to egg protein in sponge cake, as it facilitated rapid foam stability and prevented collapse during baking. The resulting sponge cake, with half of the egg replaced by the SPSH/F50 mix, exhibited a similar appearance and texture to that with only the egg added. Thus, combining temperature-induced gelling polysaccharides with SPSH offers a promising alternative to egg protein in aerated bakery food production.

Impact of Lallemantia royleana seed mucilage on the physicochemical, textural, rheological, and in-mouth breakdown behavior properties of cold-set whey protein isolate emulsion-filled gel

This work focused on the Lallemantia royleana seed mucilage (LRSM) effect on the rheological, physicochemical, and microstructural attributes, and the in vivo oral breakdown of cold-set emulsion-filled gel (EFG) based on the whey protein isolate (WPI). Emulsions containing 0.1 and 0.5% LRSM displayed the largest and smallest droplet sizes (3.38 vs. 1.26 μm) and polydispersity index (0.60 vs. 0.23), respectively. Also, the 0.1–0.5% LRSM-WPI EFGs compared to the control had greater elastic modulus in the linear viscoelastic (LVE) region (7006.1–7167.8 vs. 4438.3 Pa), flow-point stress (484.6–540.1 vs. 327.8 Pa), network strength (7227.8–7451.2 vs. 5380.1 Pa.s1z), network extension (10.91–11.44 vs. 10.05), lower LVE limit (1.74–2.26 vs. 2.53 %), same loss tangent (0.17), similar frequency dependence of elastic modulus (0.087–0.091 vs. 0.095), and inhomogeneous microstructures. Hardness, springiness, and chewiness at 0.1% and adhesiveness and cohesiveness at 0.5% LRSM-WPI EFGs were the highest. Raising the LRSM from 0% to 0.5% improved the water-holding capacity (75.49%–87.68%), swelling ratio (0.20%–2.59%), and decreased syneresis (11.08%–9.13%). The 0.5% LRSM-WPI EFG compared to the control needed a higher chew duration (16.22 vs. 11.80 s) and chew cycle (24.76 vs. 18.31), and its bolus had a smaller particle size (0.94 vs. 1.65 mm).

Effects of wheat protein on hot-extrusion 3D-printing performance and the release behaviours of caffeic acid-loaded wheat starch

In this study, the effects of wheat protein (WP) on the hot-extrusion 3D-printing (HE-3DP) performance of wheat starch (WS) gels, as well as effects of such gels on the encapsulation of caffeic acid, were investigated for the first time. The HE-3DP results show that the addition of WP can reduce print-line width and improve printing accuracy and fidelity, and the best printing results were achieved when using gels with 10 % WP. The rheological results show that WP reduced the gels' linear viscoelastic region (LVR), yield stress (τy), flow stress (τf) and consistency factor (K) but increased their structural recovery rate, which facilitated smooth extrusion during 3D printing and, thus, improved printing accuracy. The analysis of X-ray diffraction and small-angle X-ray scattering indicates that adding WP to WS could increase the mass fractal dimension and lead to denser gel network structures. The results regarding release kinetics demonstrate that the maximum release of caffeic acid from gels decreased by 28 % with the addition of WP, indicating slow-release behaviour. This study provided valuable information about processing wheat products via 3D printing.

Mung Bean Starch and Mung Bean Starch Sheet Jelly: NaCl-Based Characteristics Variation.

Empirical evidence indicates that NaCl can improve the quality of mung bean starch sheet jelly (MBSS) when properly incorporated. In this study, by comparison with a sample without NaCl, the influences of NaCl (1.5-8%, w/w) on the physicochemical and structural properties of mung bean starch (MBS) and the quality of MBSS were investigated. MBS with added NaCl had greater gelatinization temperature and pasting parameters but lower gelatinization enthalpy than native MBS. With the addition of NaCl, the drying rate of MBSS first accelerated and then declined in the oven-drying process. The addition of NaCl improved the cooking properties of MBSS but decreased the hardness of cooked MBSS. Rheological results implied that the linear viscoelastic region of cooked MBSS decreased with the NaCl addition, and the storage modulus and tan δ were more frequency-dependent than the loss modulus of cooked MBSS. The addition of NaCl gradually increased the toughness of dried MBSS and the overall acceptability of cooked MBSS. Furthermore, NaCl decreased the structure order degree of starch in MBSS. Correlation analysis demonstrated that the quality of MBSS had a significant correlation with the molecular and lamellar order of starch. Overall, NaCl could improve the quality of MBSS by regulating the thermal, gelatinizing, and structural properties of MBS.

Influence of asphalt mixture nonlinearity on pavement mechanical response

In view of the influence of asphalt mixture nonlinearity on the mechanical response of pavement structure, the creep compliance of AC-16 under 0.1, 0.3, 0.5, 0.7 and 0.9 MPa is studied first. The results show that the asphalt mixture is in the linear viscoelastic region, when the load is in the 0.1-0.5 MPa interval. When the load is greater than 0.5 MPa, the creep compliance increases significantly, and asphalt mixture presents a nonlinear property. The Prony series is used to fit the creep compliance data, and the relaxation modulus is calculated based on the convolution relationship between creep compliance and relaxation modulus in viscoelastic mechanics. The relaxation modulus under different loads is introduced into the mechanical calculation of layered viscoelastic system. The calculation results show that the nonlinearity of asphalt mixture significantly affects the permanent deformation of asphalt layer, but has little effect on the fatigue problem of the asphalt base. In the design of pavement structure, attention should be paid to the nonlinearity of asphalt mixture.

Effects of electrochemical treatment and Epigallocatechin-3-gallate on emulsification, rheological and oxidation stability of soybean oil body

In this study, the soybean oil body (SOB) was placed in the cathode chamber of an electrochemical reactor, H+ enters the cathode chamber through the proton exchange membrane to undergo reduction reaction. The complex of SOB and Epigallocatechin-3-gallate (EGCG) was prepared on the basis of electrochemical treatment (ESOB-EGCG). The effects of two treatment on the structure and thermal properties of SOB protein were analyzed, which provided a basis for the study on the emulsification, rheological and oxidation stability of SOB emulsion. The results showed that the EAI of ESOB-EGCG was 108% higher than that of SOB, and the emulsion showed greater viscosity and the largest linear viscoelastic region. Through the determination of oxidation stability and fitting of oxidation kinetic model, it was found that ESOB-EGCG sample showed the best oxidation stability, which provided support for fitting and predicting the oxidation stability of SOB.

Concentration-dependent rheological characteristics of chickpea (Cicer arietinum L.) flour dispersion in steady and dynamic shear

Chickpea (Cicer arietinum L.) flour (CF) is the basic raw material used in the form of dispersion in varied concentrations for making promising oriental sweets and snacks in the Asian subcontinent. The finished product quality of these fried food items thus mainly depends on the consistency of flour dispersions. Therefore, a concentration-dependent steady-state and dynamic rheological study, along with the pasting behaviour, was carried out. Steady shear rheology exhibited concentration-dependent pseudoplastic behaviour with significantly higher apparent viscosity for 40 - 45% CF dispersions, and a desirable consistency to be used in making fried sweets and snacks. The Herschel-Bulkley model described dispersions better at 5 - 20%, while Mizrahi-Berk at 25 - 50%. Hahn Ree-Erying's model described thixotropic behaviours for time-dependent flow; increasing CF concentration from 30 - 50% and increasing storage (G') and loss (G'') modulus in the linear viscoelastic region. However, G' values were dominant over G'' values in the small amplitude region, showing elastic behaviour, whereas viscous behaviour was exhibited in the higher amplitude region. During heating (30 - 80°C) in the temperature sweep test, concentrated samples (30 - 50%) showed a drastic increase in G' and complex viscosity (η*), while in cooling stages (95 - 25°C), a 25% concentration sample resulted in the highest values of G', G'', and η*.

A critical study of the nonlinear rheological properties in major classes of foods using the Sequence of Physical Processes (SPP) method and the Fourier Transform Coupled with Chebyshev Decomposition (FTC) method

The nonlinear rheological behaviors of three different classes of foods (emulsion, suspension, and elastic network) were studied and analyzed using the Rogers Sequence of Physical Processes (SPP) method and the Ewoldt-McKinley method of coupling Fourier Transform with Chebyshev Decomposition (FTC). SPP analysis led to instantaneous rheological parameters G′t and G″t at any point in time, providing a more accurate picture of the linear viscoelastic region and crossover points by the 3D amplitude sweep. When G′t is plotted against G″t, the resulting graph is a deltoid which offers a detailed and distinctive intracycle behavior of each class of food. Analyzing the revolution of deltoids with increasing strain allows for the determination of a critical strain, beyond which irreversible network breakdown occurs. The strain range between the linear viscoelastic limit and the critical strain found in SPP is comparable to the MAOS region as determined with FTC. Under increasing amplitude, predominantly elastic networks showed a gradual structural rearrangement, while more erratic and abrupt changes were observed in the suspension and emulsion we studied. Under increasing frequency, elastic responses dominate viscous responses in all samples due to the shorter experimental time, allowing less relaxation.

Mechanism and Development of Thermo-Rheological Properties of Asphalts Modified by Reactive Polymer Systems.

The new class of reactive polymers is designed to modify asphalt through chemical reactions with asphalt components. The complexity of such systems and the long experience with thermoplastic elastomers as well as with some other "classical" modifiers, and to a degree that our present testing methods and even specifications revolve around these materials, might obscure the fact that we are dealing with rather different modification systems and possibly with new emerging asphalt paving technologies. Our present work attempted to compare two different reactive polymer systems with the "classical" system which uses thermoplastic elastomer. The impact of reactive polymer systems on asphalt was studied through material properties manifested by specification tests and through the development of thermo-rheological properties in linear and non-linear viscoelastic regions. As expected, the behavior of reactive polymeric systems with different chemistries also differed among themselves. The available results showed that the reactive groups of polymers react with polar components of asphalt leading to higher stiffness at elevated pavement temperatures and differing impact on low temperature properties. The data point to a significantly improved resistance to plastic deformation of pavement in the case of reactive polymers, despite the fact that elastic recovery-based specification tests failed to identify this improvement.

Rheological and Viscoelastic Analysis of Hybrid Formulations for Topical Application.

The rheological and viscoelastic properties of hybrid formulations composed of vehicles designed for cutaneous topical application and loaded with ultradeformable liposomes (UDL) were assessed. UDL were selected for their established ability to transport both lipophilic and hydrophilic compounds through the skin, and are applicable in pharmaceuticals and cosmetics. Formulations underwent flow analysis and were fitted to the Herschel-Bulkley model due to their prevalent non-Newtonian behavior in most cases. Linear viscoelastic regions (LVR) were identified, and G' and G″ moduli were determined via frequency sweep steps, considering the impact of temperature and aging. The formulations exhibited non-Newtonian behavior with pseudoplastic traits in most cases, with UDL incorporation inducing rheological changes. LVR and frequency sweep tests indicated predominantly elastic solid behavior, with G' higher than G″, at different temperatures and post-production times. Tan δ values also illustrated a predominant solid-like behavior over liquid. This study provides pivotal insights into the rheological and viscoelastic features of topical formulations, emphasizing the crucial role of meticulous vehicle and formulation selection when incorporating UDL or analogous liposomal drug delivery systems.