Rheo-mechanical Properties Research Articles

Rheology and aging of amine functionalized polyolefins

The time dependent rheo-mechanical properties of a class of associating polymers (amine-functionalized polyolefins) are investigated using rheology, differential scanning calorimetry (DSC), infrared microscopy, and small-angle x-ray scattering (SAXS) measurement. The modulus of the sample increases with time and temperature as determined by shear rheology. With higher temperature and longer equilibration time, there is a gradual decrease in the power-law scaling of storage and loss moduli in the terminal flow region and the emergence of an additional low-frequency plateau in the storage modulus. The aging behavior at different temperatures is found to be correlated with the horizontal shift factors obtained from the time-temperature superposition. With increasing aging time, there is an increase in the glass transition temperatures (DSC), and a continuous red shift in the associated amine stretching peak (Fourier-transform infrared). SAXS also shows the emergence of a dominant microstructure after aging of the sample for a long time. Based on the characterization results, an underlying microscopic origin of the aging process is proposed.

Experimental study on the effect of mixing parameters on the rheological behaviour and micro-flocculation structure of ultrafine Portland cement slurry

The penetration diffusion of ultrafine Portland cement (UPC) slurry is closely related to its rheological behaviour and micro-flocculation structure. To date, there has been a need for more research investigating the impact of mixing parameters on the macro-micro hydrodynamic behaviour of UPC slurries. In this study, a series of macroscopic rheomechanical characterisation tests and microscopic in-situ tests of the flocculation structure of UPC slurries under various mixing parameters were conducted systematically by using a rotational rheometer and a focused beam reflectance measurement (FBRM) system. The effects of mixing speeds and times on the macroscopic shear stress-shear rate curves, rheological patterns, rheomechanical parameters, and the distribution of micro-flocculated particles of UPC slurries were investigated. The results indicate that the macroscopic rheomechanical parameters and microscopic flocculation coefficient of UPC slurry exhibit a decrease with increased slurry mixing speed. However, a “decrease and then increase” trend is observed with increased slurry mixing time. The smaller the powder size of cement and the lower the water-cement ratio of the slurry, the more sensitive the rheomechanical properties of the slurry are to the influence of the mixing parameters. A positive correlation exists between the macroscopic rheomechanical properties of UPC slurry and its microscopic flocculation coefficient. Increasing the slurry mixing speed or prolonging the early mixing time can destroy the microscopic flocculation particles of UPC slurry, a reduction in the flocculation coefficient of the slurry, and an improvement in the macroscopic fluidity properties. The research findings provide a foundation for improving the effectiveness of UPC grouting in the engineering field.

The Role of Starch in Shaping the Rheo-Mechanical Properties of Fat-in-Water Emulsions

The DMA technique was used to conduct experiments on the rheo-mechanical properties of emulsified bovine fat meat products stabilised with potato starch. Starch gels with starch concentrations corresponding to the concentration of starch in water in the emulsions under analysis were used as control systems. The research showed that the rheo-mechanical properties of starch gels and starch–fat gels result from the conformational changes occurring within the structural elements of their spatial network. In starch gels, segments formed by complex associations of amylose chains are structural elements, whereas in starch–fat gels (emulsions) these are additionally amylose–fat complexes. Changes occurring during progressive retrogradation increase the degree of cross-linking in them. In starch gels, they are conditioned by the starch concentration, whereas in emulsions they are conditioned by the concentration of starch and the presence of fat. The parameters obtained by adjusting the Avrami equation to the data obtained with the DMA method enabled the determination of three forms of organisation of the dispersion structure of starch–fat systems. Each of these forms of structure organisation is conditioned by the concentration of starch in the emulsion system.

Microrheology of a thermosensitive gelling polymer for cell culture.

We investigate the rheo-mechanical properties of Mebiol Gel®, a thermosensitive gel-forming polymer extensively used as a medium for cellular culture, using passive microrheology made either by standard dynamic light scattering or by photon correlation imaging. In the dilute limit, Mebiol displays a Newtonian behavior with an effective viscosity that decreases with temperature, consistent with a peculiar aggregation mechanism characterized by an increase of the molecular weight with a simultaneous reduction of the aggregate size. By increasing concentration and approaching gelation, both the storage and loss moduli show a nonmonotonic dependence with temperature, with a pronounced maximum around Tm ≃ 28-30 °C, the value above which, in the dilute limit, the individual Mebiol chains are fully compacted. Such a distinctive trend of the elastic and viscous properties persists within the gel, which, therefore, becomes "softer" above Tm. Although when temperature changes are performed adiabatically, the transition from the fluid to the gel phase takes place without any apparent discontinuity, a rapid T-jump leads to the formation of a hard gel at a concentration where a low heating rate conversely yields a fluid phase. This is a visible manifestation of the nonequilibrium nature of these physical gels.

DMA Study of the Molecular Structure of Porcine Fat in-Water Emulsions Stabilised by Potato Starch.

The aim of the study was to determine how the molecular structure of porcine fat-in-water type emulsions stabilised with potato starch affected their rheomechanical properties. Dynamic mechanical analysis (DMA) and instrumental analysis of the texture were the method used in experiments. Starch gels with concentrations corresponding to the water starch concentration of the examined emulsions were used as control systems. The analysis of the starch and starch–fat systems showed that the values characterising their rheomechanical and textural properties reflected the spatial reaction of the amylose matrix to dynamic mechanical interactions. Changes in their values resulted from conformational changes in the structure of segments and nodes of the lattice, conditioned by the concentration of starch and the presence of fat. As a result of these changes, starch–fat emulsions are distinguished by greater densities of network segments and nearly two times greater functionalities of nodes than starch gels. The instrumental analysis of the texture showed that the values of the texture parameters in the starch gels were greater than in the starch–fat emulsions. The high values of the correlation coefficients (R~0.9) between the texture determinants and the rheological parameters proved that there was a strong correlation between the textural properties of the tested systems and their rheomechanical properties.

Phase Behavior and Microscopic Dynamics of a Thermosensitive Gel-Forming Polymer

Soft adaptive networks like polymer gels are almost ideal candidates as surrogates for the extracellular matrix, more so when their rheo-mechanical properties can be carefully tuned by temperature. Using both dynamic light scattering and photon correlation imaging, we have investigated the phase behavior and the microscopic dynamics of a thermoresponsive network, Mebiol Gel, extensively and effectively used as a three-dimensional scaffold for cell growth. In the dilute limit, Mebiol displays a temperature-driven association process characterized by a significant increase of the molecular weight, which is not accompanied, however, by a concurrent increase of the aggregate size. This peculiar behavior is consistent with numerical simulations of a simpler but structurally homologous block-copolymer system. By increasing concentration and approaching gelation, the polymer solution progressively attains the structure of a percolating network, as witnessed by the logarithmic decay of the intensity correlation functions extending over many time decades, a relaxation behavior that is found well within the gel phase too. No evidence of a discontinuous transition to a fully arrested gel phase is, however, detectable in the microscopic dynamics.

Classification of hydrocolloids based on small amplitude oscillatory shear, large amplitude oscillatory shear, and textural properties.

Dynamic rheological and mechanical properties of seven commercial (xanthan [XG], guar [GG], high methoxylated pectin [HMP], κ-carrageenan [κ-Car], agar [AG], alginate [ALG], and carboxymethylcellulose [CMC]) and four emerging hydrocolloids (basil seed gum [BSG], sage seed gum [SSG], Balangu-Shirazi seed gum [BSSG], and cress seed gum [CSG]) were investigated and the classification of the hydrocolloids were carried out based on them. AG belonged to the first class with 0.81 membership function (MF), κ-Car and HMP grouped in the second class with 0.68 and 0.71 MFs, respectively, XG, BSG, and SSG were depended to the third class with 0.61-0.70 MFs, finally, CMC, GG, BSSG, ALG, and CSG related to the fourth class, as the most populated class, with MF > 0.61. The first class contained the highest amount of hardness parameter (43.40 ± 2.76 g), the second class included the highest pseudoplasticity parameter (shear-thinning ratio = -0.54 ± 0.03) and relaxation time (66.25 ± 2.61 s) and the fourth cluster comprised the highest frequency dependency of viscous modulus (exponent of power-law model for viscous modulus vs. frequency = 0.30 ± 0.05). In addition, the results of this study showed that there was a distinct relationship between nonlinear harmonics in the stress wave and fundamental characteristics of hydrogel networks. The investigation of the rheo-mechanical properties of biopolymers in large deformation under shear and normal forces can have an important role in the prediction of the behavior of the material in real processes and application conditions, especially in the food industry. Due to the inconvenience of large deformation mechanical tests, such as Weissenberg effect, the complication of the results analyzing and sampling difficulty of semi-dilute samples; herein, we determined the correlation between large deformation (LAOS and texture analysis) and small deformation (SAOS) tests properties. The studied rheo-mechanical parameters showed high correlation with the four mentioned network parameters (more than 65% similarity index). Using these results, other scientists could rationally design the experiments and avoid experiments with similar parameters.

Physicochemical and rheo-mechanical properties of titanium dioxide reinforced sage seed gum nanohybrid hydrogel

Sage seed gum (SSG) is a promising biopolymer candidate for utilization and substitution prevalent galactomannan gels of interest in soft biomaterial applications. Herein, physicochemical and rheo-mechanical properties of SSG matrix reinforced by various titanium dioxide (TiO2) nanoparticles loading (0–25wt%) were monitored. Particle size and density of the nanocomposite increased with raising TiO2 content, due to the creation of more compact agglomerated and aggregated microstructure. Increasing the particle size resulted in lower electrophoretic mobility of SSG-TiO2 systems upon nanoparticles addition, confirmed the adsorption of TiO2 on the SSG macromolecule. Mechanical spectra of the SSG-based nanocomposites demonstrated a more solid-like behavior by lower frequency-dependent viscoelastic moduli, suggested a structural decoration of the nanohybrid gels discussed in terms of polymer bridging effect and formation of percolated matrix-particle superstructure. Crucial textural parameters improved with increasing TiO2 until a critical level (15 wt%), after which further increments in filler resulted in a reduction of hardness, adhesiveness and apparent modulus of elasticity. Deformation of rod-like junction zones acting as physical crosslinks in the system and fracture theory were used to explain the strain-stiffening and adhesive behavior of SSG-based gels, respectively. The nanocomposite gels with tunable functional properties might be ideal candidates for biomaterial industry.

Novel nanobiocomposite hydrogels based on sage seed gum-laponite: Physico-chemical and rheological characterization

In this study, the physico-chemical and rheo-mechanical properties of sage seed gum hydrogel, reinforced by various ratios (0–25 wt.%) of Laponite, were investigated. Particles size measurements indicated the formation of large SSG-Laponite microstructures upon nanoparticle adding, due to the interactions generated between the anionic SSG and the charged surfaces of clay platelets. Laponite affected the surface tension and density of the SSG-based systems significantly, but only influenced the ζ-potential above 20 wt.%. The dynamic rheological behavior of SSG-based nanocomposites reflected the reinforcing effect of secondary structures and percolated three-dimensional network, suggested a structural modification of the hydrogels with the Laponite loading. An improvement in texture profile analysis parameters was observed in Laponite content ≤5 wt.%, whereas for nanoparticles >5 wt.%, a significant decrease was obtained. In conclusion, Laponite improved the rheological and physico-chemical properties of SSG-based hydrogel and extended its potential as promising future bio-products for industrial applications.

Investigation of rheo-mechanical properties of cement suspensions activated in a hydrodynamic cavitator

The object of research is cement suspensions activated in a hydrodynamic cavitator. One of the most problematic places of the proposed method of activation is the slowing of the kinetics of the strength of astringents on days 2 and 7 of hardening. It is possible to speed up the set of strength by studying the processes of structure formation occurring in activated suspensions and hardening mixtures, and also to enhance physical effects by improving the design of the cavitator and the mixing chamber. During the study, activated water and 10 % cement-water suspension are used. After 10 minutes of cavitation treatment at pressures of 0.63–1.4 MPa and a temperature of 28–32 °C, the pH of the medium increases (pH+7.56) and decreases by a factor of 10.38 times the dynamic viscosity of the suspensions. This is due to the fact that the increase in pressure and temperature in the cement-water suspension contributes to the intensification of the dispersion of cement particles in the frequency range 700–800 Hz and the passage of intensive mass-transfer processes in the frequency range 1.9–3.5 kHz, leading to the formation of primary crystallization structures. Due to this, it is possible to obtain dilatant liquids with a viscosity of 160 to 273.5 cP and control the rate of agitation in the speed range from 50 to 200 min -1 . Compared to similar activation methods, the approach under study provides an increase in brand strength of 1.14 times compared to an unactivated cement system and contributes to a decrease in the amount of Portland cement from 10 to 14 %.

The effects of the interface on microstructure and rheo-mechanical properties of polyamide 6/cellulose nanocrystal nanocomposites prepared by in-situ ring-opening polymerization and subsequent melt extrusion

Polyamide 6 (PA6) nanocomposites containing cellulose nanocrystals (CNCs) were prepared via a multi-step process consisting of in-situ anionic ring-opening polymerization and subsequent melt extrusion. The effect of surface modification of the CNCs with aminopropyl triethoxysilane (APS) was studied in detail using microscopic, mechanical and rheological techniques and compared with that of the neat CNC nanocomposites. Solid-state 29Si NMR analysis was used to confirm the interfacial bond formation between the PA6 matrix and surface modified CNCs. SEM images showed that upon surface modification, the morphology of CNCs within the matrix transformed from a fibrillar structure towards more individually dispersed nanocrystals with enhanced dispersion and higher interfacial area. The matrix-particle interphase was further investigated using quantitative nanomechanical mapping (QNM) to study the role of interfacial modification on thickness of interphase and development of a broader modulus gradient across the interface. The quality of dispersion and development of the rigid interfacial layer in the modified system resulted in significant improvement in solid-state mechanical properties of the nanocomposites. In addition, melt rheological studies showed significant improvements of melt elasticity and strength in shear and elongational flow in the nanocomposites systems.

Dissipative-particle-dynamics model of biofilm growth

A dissipative-particle-dynamics model for the quantitative simulation of biofilm growth controlled by substrate (nutrient) consumption, advective and diffusive substrate transport, and hydrodynamic interactions with fluid flow (including fragmentation and reattachment) is described. The model was used to simulate biomass growth, decay, and spreading. It predicts how the biofilm morphology depends on flow conditions, biofilm growth kinetics, the rheomechanical properties of the biofilm, and adhesion to solid surfaces. The morphology of the model biofilm depends strongly on its rigidity and the magnitude of the body force that drives the fluid over the biofilm.

Effects of nanofiller morphology and aspect ratio on the rheo-mechanical properties of polyimide nanocomposites

New polyimide nanocomposites containing organically modified montmorillonite (MMT), synthetic silicate (chrysotile) nanotubes (SNT), and zirconium dioxide (ZrO2) were prepared to investigate the influence of the nanoparticle morphology on the nanocomposite rheology and mechanical properties under selected conditions that the materials are likely to encounter during use. The efficiency of homogeneous dispersion of the nanoparticles in the polyimide matrix was studied by measuring the rheology of model oligoimides (OI) dispersions containing the desired amounts of the nanoparti- cles. The OI/nanoparticles dispersions showed significant increase in complex viscosity with increasing concentration of the nanoparticles that depended strongly on the nanoparticle morphology and aspect ratio. Polyimide nanocomposite films (PI-PM) prepared from the poly(amic acid) of poly(pyromellitic dianhydride-co-4,4'-oxydianiline) (PM) filled with the desired concentration of the nanoparticles showed an increase in tensile modulus with increasing nanoparticle concentra- tion in the order MMT>SNT>ZrO2. In contrast to the PI-PM/MMT films, the PI-PM films filled with 10 vol% of SNT and ZrO2 showed higher sample failure strains, suggesting that the SNT and ZrO2 may be more effective in improving the duc- tility of the polyimide nanocomposites for applications where the relatively brittle polyimide/MMT nanocomposites films are not useable.

Structural transitions in aqueous suspensions of natural graphite

The electric conductivity σ and viscosity η of aqueous suspensions at different volume fraction of graphite ϕ and concentration of nonionic surfactant (Triton X-305) are investigated. The correlations between conductivity and rheological properties are discussed. A model of structural transitions in aqueous graphite suspensions is discussed. Two structural transitions, corresponding to changes in electrical and rheomechanical properties, are identified as electrical connectivity and rigidity (or sol–gel) percolation transitions, respectively. An unusual initial decrease of the bulk electrical conductivity with graphite volume fraction ϕ increase was observed in the surfactant solution. This fact is explained as a result of an isolating coating formation around the graphite particles.

Development of a novel compression tester and rheo-mechanical properties of wet-mass powder. I--Effect of kneading time on the rheo-mechanical properties.

In our previous paper [Watano S., et al., Chem. Phram. Bull., 49(1), 64-68, (2001)], a compaction tester was developed to quantitatively evaluate the water dispersion condition of wet kneaded masses prepared by a paddle type kneader. It was also demonstrated that the physical properties of pellets prepared by extrusion granulation after the kneading could be well predicted by the vertical pressure transmission obtained through the compaction tester. However, in this compression tester, the vertical pressure transmission was just obtained and rheological and mechanical properties (so called rheo-mechanical properties) of wet mass-powder that should be the most important to determine the deformation process were not well studied. In this study, a novel compression tester, which can measure both vertical and radial pressure transmissions, has been developed. Based on the compression test, mechanical property (Young's modulus) and rheological property (effective internal friction) of wet mass powder prepared by different kneading times were quantitatively investigated. Granules (pellets) were then obtained through the extrusion granulation and fluidized bed drying, and the physical properties (strength and disintegration time) of the obtained pellet were evaluated. The relationship between the granule (pellet) physical properties and the mechanical and rheological (rheo-mechanical) properties was analyzed.

Development of a novel compression tester and rheo-mechanical properties of wet-mass powder. II--Effect of moisture content on the rheo-mechanical properties.

In our previous paper [Watano S., et al., Chem. Pharm. Bull., 51(7), 747-750 (2003)], a novel compression tester, which enables the vertical and radial pressure transmission measurement, has been developed and quantitative analysis of rheo-mechanical properties of wet-mass powder prepared by different kneading times was conducted. In this study, the compression test was conducted by using the kneaded wet-mass powders prepared by different moisture contents. Pressure transmission characteristics and rheo-mechanical properties have been investigated to characterize the wet-mass powders. The relationship between these parameters and granule physical properties was also investigated.

Influence of chemical structure of polyimide prepolymer on rheo-mechanical properties of polyimide foam composites

A study is reported of the effect of varying chemical composition of foam polyimide prepolymers (H-complex) on the structure and properties of foam polyimide resins and their composites with aromatic polyimide fiber felt. The melt rheological behavior of the H-complex was found to be strongly dependent on its chemical composition and structure reorganization in the melt which is akin to mesophasic structural transition states in liquid crystal polymers. Changing the diamine part of the H-complex from 4,4-methylene dianiline to 1,3-diaminobenzene led to decreased steady shear viscosity at temperatures and shear rates ranging between 95° and 105°C and 0.01 and 1 s−1, respectively. Additionally, changing the dialkyl moiety from dimethyl to diethyl in 3,3′,4,4′-benzophenonetetracarboxylic dialkyl ester (precursor to the H-complex) increased gelation time of the H-complex, enhancing processibility of the foam polyimide composites. The results indicate that novel, lightweight foam polyimide composites with enhanced thermomechanical properties for beneficial uses can be prepared through chemical modification of the H-complex prior to its thermal imidization in the presence of the aromatic polyimide fiber felt.

Comparative Rheomechanical and Adhesive Properties of Two Hydrocolloid Dressings: Dependence on the Degree of Hydration

AbstractHydration is believed to modify the mechanical properties (resistance to stress) and the rheological (viscoelastic) properties of hydrocolloid dressings. Rheomechanical properties in turn influence adhesional properties. In this work the relationships between the degree of hydration and the rheomechanical and the adhesive properties of two different commercial dressings (regular and nondispersive) were investigated. The two dressings showed different hydration characteristics. The regular dressing takes up water rapidly and tends to reach saturation after 12 hr. As the dressing swells and loses its integrity there is an accompanying reduction of both rheomechanical and adhesive properties. The nondispersive dressing exhibits a linear water uptake profile over extended periods of hydration up to 4 days. It does not swell and its rheomechanical and adhesive properties remain unchanged after hydration, The comparative evaluation of the results obtained with the various methods points to the relevance...