Strong Elastic Properties Research Articles

Lightweight, compressible, elastic resorcinol-formaldehyde aerogels with cobalt-ligand-enhanced cross-linked skeletons

Resorcinol-formaldehyde (RF) aerogel materials exhibit remarkable properties such as low density, ablation resistance (high residual carbon rate), easily regulated pore structure and low thermal conductivity, making them promising for applications in adsorption, medicine and aerospace, among others. However, since their inception, RF aerogels have suffered from disadvantages such as brittleness and long preparation cycles, which have severely limited their widespread use. In order to improve the mechanical properties of RF aerogels, this paper presents a new synthetic route for obtaining strong elastic properties without introducing additional fiber reinforcement. Here, a lightweight, compressible, elastic resorcinol-formaldehyde aerogel with cobalt-ligand-enhanced cross-linked skeletons was prepared by sol-gel and freeze-drying methods using an alkali metal salt (cobalt (II) acetate) as a cross-linking agent and sodium acetate as a catalyst. The coordination of metal ions (Co2+) with resorcinol resulted in the formation of a structure analogous to a metal-phenolic network (MPN), which altered the crosslinking mode and degree of crosslinking of the RF aerogel. This process led to the thickening of the skeletal structure of the sample. Concurrently, a multilayered pore structure was generated within the interior under the appropriate pH conditions, which contributed to the strengthening of the skeleton of the samples and a reduction in thermal conductivity. The obtained RF-Co aerogel can withstand 68.6 % compression change without fracture and shows good elastic deformation at 35 % compression rate, while the aerogel exhibits low thermal conductivity (0.039 W (m K)−1) and low density (0.09 g cm−3).

Dynamic modulus characteristics and prediction model of semi-flexible materials filled with high-performance cement paste

The dynamic modulus of asphalt mixture is an important factor in the design of asphalt pavement, and many scholars have proposed different models for estimating the dynamic modulus of asphalt mixture, but there are almost no studies on the prediction of the dynamic modulus of semi-flexible materials. In order to analyze and estimate the dynamic modulus of semi-flexible materials, we set up a high-performance cementitious paste (HPCP) semi-flexible material and a reference group Stone Mastic Asphalt (SMA-16) under multiple conditions, first measured its dynamic modulus in the laboratory, and analyzed the dynamic modulus characteristics of the material, and then used the equation the estimation equation proposed by Witczak et al. (Witczak1-37A) as a benchmark to introduce a new parameter, grouting mass ratio (Pb) to develop a Witczak-G prediction model to compare and validate the predicted dynamic modulus with the measured values. The results show that compared with SMA-16, HPCP semi-flexible material exhibits higher dynamic modulus and lower phase angle, and its temperature sensitivity and deformation resistance are significantly better than those of SMA-16. Under the influence of porosity and Pb factor, the dynamic modulus is positively correlated with both factors, and the phase angle increases first and then decreases, showing strong elastic properties. In this paper, we propose a dynamic modulus prediction model based on viscosity and Pb, Witczak-G, which predicts the highest coefficient of determination (R2) of the predicted dynamic modulus as high as 0.99 after initial fitting and validation, which indicates that the Witczak-G model is suitable for predicting the dynamic modulus of semi-flexible materials injected with HPCP.

Hydrogels based on low-methoxyl amidated citrus pectin and flaxseed gum formulated with tripeptide glycyl-l-histidyl-l-lysine improve the healing of experimental cutting wounds in rats

Hydrogels based on natural and modified polysaccharides represent growing group of suitable matrices for the construction of effective wound healing materials. Bioactive tripeptide glycyl-l-histidyl-l-lysine and amino acid α-l-arginine are known to accelerate wound healing and skin repair. In this study, hydrogels based on low-methoxyl amidated citrus pectin or flaxseed gum were prepared and used for the transport of these healing agents to the experimental cutting wounds affected by extensive skin damage. Fourier-transform infrared spectroscopy, rheology, differential scanning calorimetry, scanning electron microscopy, swelling and release tests confirmed that these hydrogels differed in structure and physical properties. The cationic tripeptide was found to bind to carboxylic groups in LMA pectin, and the C3OH hydroxyl and ring oxygen O5 are involved in this interaction. The pectin hydrogel showed high viscosity and strong elastic properties, while the flaxseed gum hydrogel was characterised as a viscoelastic system of much lower viscosity. The former hydrogel released the drugs very slowly, while the latter hydrogel demonstrated zero order releasing kinetics optimal for drug delivery. In the in vivo wound healing testing on rats, both polysaccharide hydrogels improved the healing process mediated by the mentioned biomolecules. The tripeptide applied in the hydrogels showed significantly higher healing degree and lower healing time than in the control animals without treatment and when it was applied in an aqueous solution. Despite the absence of a synergistic effect, the mixture of the tripeptide and α-l-arginine in the hydrogels was also quite effective in wound healing. According to histological analysis, complete healing was achieved only when using the tripeptide in the flaxseed gum hydrogel. These observations might have an important prospect in clinical application of polysaccharide hydrogels.

Pseudo-laminarization effect of dilute and ultra-dilute polymer solutions on flows in narrow pipes

The properties of dilute and ultra-dilute polymer solutions flowing in a narrow pipe (inner diameter: 680, 400, and 125 μm) were evaluated experimentally by measuring the pressure drop at constant flow rate. Deionized water, silicone oil, and several aqueous solutions of polyacrylamide (PAA), polyethylene oxide (PEO), and xanthan gum (X-Gum) were used. In viscosity measurements, 100- and 10-ppm solutions exhibited non-Newtonian viscosities whereas 1-ppm solutions exhibited Newtonian viscosities. We applied a power-law model to the non-Newtonian viscosities and estimated a generalized Reynolds number. Moreover, we focused on the transition and turbulent regions because the flows being observed were through narrow pipes. For water and silicone oil, good agreement was obtained between the resultant pressure drop and the predicted value. Furthermore, the critical Reynolds number for water and silicone oil was approximately 1.8×103. In contrast, laminar flow was maintained in the transition region for the dilute and ultra-dilute polymer solutions. In the 125- μm capillary flows, the maximum critical Reynolds numbers for the ultra-dilute polymer solutions were 2.4×103 (PAA), 3.9×103 (PEO), and 3.0×103 (X-Gum). Even though ultra-dilute solutions were used, pseudo-laminarization was obtained. To understand the experimental results, we estimated the first normal stress difference. All such values were correlated with the wall shear rate. We conclude that the pseudo-laminarization can be associated with the elasticity of the polymer solutions and is typified by the appearance of strong elastic properties in small-scale flows.

Hypothetical planar and nanotubular crystalline structures with five interatomic bonds of Kepler nets type

The possibility of metastable existence of planar and non-chiral nanotubular crystalline lattices in the form of Kepler nets of 34324, 3342, and 346 types (the notations are given in Schläfly symbols), using ab initio calculations, has researched. Atoms of P, As, Sb, Bi from 15th group and atoms of S, Se, Te from 16th group of the periodic table were taken into consideration. The lengths of interatomic bonds corresponding to the steadiest states for such were determined. We found that among these new composed structures crystals encountered strong elastic properties. Besides, some of them can possess pyroelectric and piezoelectric properties. Our results can be used for nanoelectronics and nanoelectromechanical devices designing.

Effect of elastic properties on the propagation of gelled and in-situ gelled acids in carbonate cores

Abstract Polymer-based acids exhibit some viscoelastic properties. Therefore, the objectives of this study are to determine the elastic and viscous properties of these acids, how these properties change as the acid reacts with carbonate formations, and their effect on the propagation of the acid inside 20-in. long carbonate cores. Live gelled and in-situ gelled acids had weak elastic properties, while partially neutralized (pH 3.2) in-situ gelled acid had strong elastic properties. Polymer filter cake was observed for the cores that were treated with gelled acid while the cores that were treated with in-situ gelled acids did not form this filter-cake. In-situ gelled acid formed a thin layer of gel that minimized leakoff, which prevented the formation of filter cake. For gelled acid, the polymer filter cake reduced the core permeability to zero. The wormhole obtained in the case of gelled acid was nearly linear and thinner than those created by in-situ gelled acid. The strong elastic properties enhanced the ability to get the gel to remain around the wormhole, which forced the next acid stage to change its direction.

Evaluation of the Physical Stability of Zinc Oxide Suspensions Containing Sodium Poly-(acrylate) and Sodium Dodecylsulfate

The physical stability of zinc oxide (ZnO) aqueous suspensions has been monitored during two months by different methods of investigation. The suspensions were formulated with ZnO at a fixed concentration (5 wt%), sodium poly-(acrylate), as a viscosifier, and sodium dodecylsulfate (SDS), as a wetting agent. The rheological study shows that the suspensions exhibit a non-Newtonian, most often shear-thinning behavior and their apparent viscosity increases with polymer concentration. The rheograms of most of the ZnO suspensions do not vary during the experimental period. The viscoelastic properties of these suspensions, such as elastic or storage modulus (G′), viscous or loss modulus (G″) and phase angle (δ) were also examined. For% strains lower than 10%, all the formulations show strong elastic properties (G′ > G″, δ varies between 5 and 15°). Beyond 10% strain, the rheological behavior changes progressively from elastic to viscous (G″ > G′ for % strain >80%). Consistently, δ increases and reaches the 50–70° zone. Multiple light scattering (back-scattered intensity), measured with the Turbiscan ags, was used to characterize suspension physical stability (early detection of particle or aggregate size variations and particle/aggregate migration phenomena). Suspensions containing 0.4 and 0.6 wt% polymer remain stable and macroscopically homogeneous, without being affected by the change of particle size observed with a laser particle sizer. Sedimentation tests, pH, and ζ potential measurements versus time, also confirmed these findings.

Some novel aspects of DNA physical and chemical gels

DNA chemical and physical networks have been investigated with respect to their stability and swelling, and rheological properties. Chemical networks were prepared by cross-linking DNA with ethylene glycol diglycidyl ether (EGDE), and physical networks by association with cationic polymers. Both types of gels display strong elastic properties and have a shear thinning behaviour. Addition of cationic surfactants effectively collapses the chemical gels, de-swelling starting from a critical aggregation concentration (cac) much lower than the critical micelle concentration (cmc) but similar to that for binding of surfactant to DNA in solution. The swelling-deswelling process appears to be reversible; thus the addition of an anionic surfactant to a gel collapsed by cationic surfactant gives a gel volume close to that of the original gel. Physical networks prepared by mixing DNA (either single- or double-stranded) with cationic polyelectrolytes, both derivatives of hydroxyethyl cellulose, one of them carrying hydrophobic groups, show an intriguing asymmetric phase separation and a very different rheological response from that of the polymers alone. Phase maps of the mixtures show three distinctive regions, a two-phase region, a bluish one-phase region and a transparent one-phase region. Effects due to hydrophobic groups on the polymers are relatively minor. (Less)

Structure of cubic phases in ternary systems Glucopone/water/hydrocarbon

Phase diagrams for the ternary systems of Glucopone, water and several hydrocarbons are reported. Four different types of hydrocarbon are used namely; heptane, octane, dodecane and tetradecane. Small angle X-ray scattering (SAXS) and polarizing microscope are used for phase identification and structure characterization. The ternary systems are shown to form different liquid crystalline phases with the increase of concentration in the following order—cubic, hexagonal, and lamellar. The liquid crystalline phases present in the ternary phase diagrams have been characterized by SAXS and further analyzed in terms of lattice parameters and area per surfactant head-group. An optical isotropic gel phase with strong elastic properties is found in these systems and identified as cubic phase. The cubic phase is optically isotropic, transparent and highly viscous phase with three-dimensional structure. The cubic samples showed several diffraction peaks and can be assigned to the Ia3 d space group. The rheological study on the cubic phase is performed. All cubic samples behave as solid-like material with storage modulus G′∼0.7×10 6 Pa typical of cubic lyotropic materials. The effect of the oil concentration and oil types on the storage and loss moduli for the cubic liquid crystalline phases is examined. For all systems, the elastic modulus and the complex viscosity are found to increase with oil concentration while decrease with increasing the length of hydrocarbon chain. Tetradecane ternary system shows completely opposite behaviors. The elastic modulus decreased when the oil content is increased. The effect of temperature on the dynamic moduli of the systems is also studied. The systems show very sharp melting transition. Both, storage and loss modulus are found to decrease as the temperature increased. It was possible to deduce the influence of the alkane chain lengths in the phase and rheological behaviors of the Glucopone surfactant. Generally, the ternary systems show similar rheological behaviors except for tetradecane system, which found to show completely opposite behaviors. The cubic phase region is found to shift to higher oil content with the increase in the alkane chain length of hydrocarbon. Finally, it is worth to mention that no cubic phases are found with toluene and cyclohexane as oil phase.

Rheologische Eigenschaften von Dimersäurebetainlösungen / Rheological Properties of Dimer Acid Betaine Solutions

This paper presents a detailed study of the rheological properties of aqueous dimer acid betaine solutions. Even at very low surfactant concentrations, these systems exhibit strong elastic properties. In contrast to anionic or cationic surfactants, where stress decay may proceed through chemical pathways, the amphoteric betaine solutions do not show monoexponential relaxation processes. The dynamic features of these solutions can be characterized by stretched exponential decays. Typical properties such as zero shear viscosity, relaxation time or equilibrium shear modulus scale with exponents which were originally derived from reptation theories.

Ringing gels and their fascinating properties

Phase diagrams for the ternary systems of tetradecyldimethylamine oxide (C 14DMAO), water and several hydrocarbons are reported. An optical isotropic gel phase with strong elastic properties is found in these systems. In the triangular phase diagrams the gel phases are located at the intersection of the solubilization line of the L 1-phase with the 55% water composition line. For tetradecane as the hydrocarbon, the gel phase contains about 35% surfactant, between 5 and 10% hydrocarbon and between 50 and 60% water. For hydrocarbons with smaller chain lengths, the location of the gel phases is shifted to regions with a higher hydrocarbon content. The properties of the micelles in the isotropic solution phase L 1 and the properties of the gel phase have been studied. Solutions of the binary system C 14DMAO/H 2O contain rod-like micelles. The rods are transformed to globular aggregates by solubilization of the hydrocarbons. With decreasing chain length of the hydrocarbon, more hydrocarbon on a molar or weight ratio of hydrocarbon to surfactant is necessary for the transformation to take place. For all hydrocarbons investigated, between tetradecane and octane, and also for cyclohexane, globular aggregates were present at the solubilization line. For a given hydrocarbon/surfactant ratio, the size of the particles remained the same with increasing concentration of surfactant. The solubilization capacity of the micellar solution and the transformation point for the rod/sphere transition correlate with the value for interfacial tension of the micellar solution against the hydrocarbon. The gel phase has been investigated with SANS and SAXS measurements. Some samples clearly showed several diffraction peaks and the gel phase could clearly be identified as a cubic phase. The evaluated dimensions of the aggregates in the gel phase were in agreement with the dimensions of the spherical aggregates in the isotropic solution. It is therefore concluded that the gel phase consists of the same globular structures that are present in the isotropic solution adjacent to the gel phase. In other samples only a single scattering peak was visible and it was thus not possible to associate it with a particular cubic structure. 13C-NMR spectra gave narrow lines in the gel phase and separate lines could be resolved for the C-atoms of the solubilized hydrocarbon and the surfactant chains. The elasticity moduli for some samples have been measured. They were in the range of 5 · 10 5 Pa. In shear experiments, the gel phases begin to flow when the deformation reaches ∼ 1.5%. It has been recognized that the elasticity modulus of the gels is determined by the Laplace pressure in the globules. The experimental values agree with the theoretical values, which are calculated from the interfacial tension of a micellar solution against a hydrocarbon. Dynamic light scattering measurements have been made in the micellar L 1-phase and in the gel phase. Surprisingly, the correlation times were very similar in both phases.

Elastic and Rheological Properties of Hydrocarbon Gels

AbstractWe have investigated high elastic gels which can be formed from biphasic systems of hydrocarbon, water and surfactant. These new phases contain up to 99% hydrocarbon, but there exists a well defined upper limit for the incorporation of excess oil. – The hydrocarbon gels exhibit strong elastic properties which can be described by a frequency independent static shear modulus. The influence of the surfactant concentration, the surfactant chainlength and the volume fraction of hydrocarbon on the modulus was systematically investigated. The experimental data are in fairly good agreement with theoretical models which have been derived for such hydrocarbon rich gels.