Differences In Viscoelastic Properties Research Articles

Dynamically Asymmetric Phase Separation and Morphological Structure Formation in the Epoxy/Polysulfone Blends

A thermoplastic polysulfone was used to blend with epoxy resin, and both the curing reaction and phase separation of the epoxy/polysulfone blend were investigated. Polysulfone did not alter the mechanism of curing reaction; however, it did depress the reaction rate. The details of the dynamically asymmetric phase separation, which was caused by the large differences in viscoelastic properties between epoxy and polysulfone component, were observed and studied. During the structure evolution, volume-shrinking behavior of the dynamically slow polysulfone component always existed even at fairly low (but still above the entanglement concentration) concentrations. More interestingly, when the curing temperature was higher than the glass transition temperature of polysulfone, volume shrinking with the consequence of layered structure formation was also observed as long as the viscoelastic asymmetry was maintained. These results indicated the generality of the mechanism of the dynamically asymmetric phase separation in this type of reactive system. Also, the influence of curing temperature was studied, and it was found that phase separation was promoted more than the curing reaction as the temperature was increased.

Interfacial and Oil/Water Emulsions Characterization of Potato Protein Isolates

Interfacial and emulsifying properties of potato protein isolate (PPI) have been studied to evaluate its potential application to stabilize oil/water emulsions at two pH values (2 and 8). The amount, type, and solubility of proteins and the size of aggregates have been determined in aqueous dispersion. Air-water and oil-water interfacial properties (adsorption, spreading, and viscoelastic properties) have been determined as a function of concentration and pH using soluble phases of PPI. The behavior of PPI stabilized oil/water emulsions has been then analyzed by droplet size distribution measurements and interfacial concentration. PPI exhibits low solubility over a wide range of pH values, with the presence of submicrometer aggregates. The pH value exerts a negligible effect on interfacial tension (oil-water) or surface pressure (air-water) but displays very important differences in viscoelastic properties of the interfacial films formed between oil and water. In this sense, pH 8 provides a major elastic response at oil-water interfaces as compared to pH 2. In relation with this result, a much higher ability to produce fine and stable emulsions is noticed at pH 8 as compared to pH 2. Consequently, there is an evident relationship between the rheological properties of the oil-water interfacial films and the macroscopic emulsion behavior.

Rheometric properties of canine vocal fold tissues: Variation with anatomic location

Objective To evaluate the in vitro rheometric properties of the canine vocal fold lamina propria and muscle at phonatory frequencies, and their changes with anatomic location. Methods Six canine larynges were harvested immediately postmortem. Viscoelastic shear properties of anterior, middle, and posterior portions of the vocal fold cover (lamina propria) as well as those of the medial thyroarytenoid (TA) muscle (vocalis muscle) were quantified by a linear, controlled-strain simple-shear rheometer. Measurements of elastic shear modulus ( G′) and dynamic viscosity ( η′) of the specimens were conducted with small-amplitude sinusoidal shear deformation over a frequency range of 1–250 Hz. Results All specimens showed similar frequency dependence of the viscoelastic functions, with G′ gradually increasing with frequency and η′ decreasing with frequency monotonically. G′ and η′ of the canine vocalis muscle were significantly higher than those of the canine vocal fold cover, and η′ of the canine vocal fold cover was significantly higher than that of the human vocal fold cover. There were no significant differences in G′ and in η′ between different portions of the canine vocal fold cover. Conclusion These preliminary data based on the canine model suggested that the vocalis muscle, while in a relaxed state in vitro, is significantly stiffer and more viscous than the vocal fold cover during vibration at phonatory frequencies. For large-amplitude vocal fold vibration involving the medial portion of the TA muscle, such distinct differences in viscoelastic properties of different layers of the vocal fold should be taken into account in multi-layered biomechanical models of phonation.

Linear viscoelastic and morphological description of multiphase systems affected by processing parameters

AbstractInfluence of processing methods, in terms of comparing compression and injection moldings, on the rheological behavior of polycarbonate (PC)/acrylonitrile‐butadiene‐styrene (ABS) blends and PC/ABS/glass fibers composites is presented. Blend compositions and fiber content are considered as material variables. For blends, the effect of the processing route on the viscoelastic functions is evident only for low shearing frequencies. Injection molding created morphology with cocontinuous character, while compression molded blends have “relaxed” structure, where dispersed phase domains are several times larger than in injection molded ones. The glass fiber reinforcement led to the significant differences in viscoelastic properties of composites processed by injection and compression molding. Injected composites have both moduli always higher than compression molded. Also, fiber lengths are reduced more for compressing molding. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Relationship Bewteen Viscoelastic Stress Relaxation and Passive Stiffness in Single Muscle Fibers of Human Skeletal Muscles

Human performance requires muscles to store energy when deformed or stretched and to recoil after being stretched. The association of viscoelastic and elastic properties with stiffness or extensibility still remains unclear in human single muscle fibers. PURPOSE: To evaluate the viscoelastic stress relaxation and passive stiffness of human single skeletal muscle fibers and to find the relationship between stress relaxation and stiffness. METHODS: Chemically skinned single muscle fibers (n=107) were prepared from biopsy specimens obtained from vastus lateralis muscles of 6 healthy volunteers (3 females and 3 males; mean age: 24.3±4.1 yr). Slack tests were used to determine specific force (maximal force/cross-sectional area, CSA) and unloaded shortening velocity. Stress relaxation and passive force were measured at pCa 9.0 using a stepwise stretch with 0.2 μm increments of muscle length from 2.4 to 4.2 μm. Peak responses to each ramp stretch and steady state force at the end of stress relaxation (after 1 min) were measured to obtain passive tension (steady state force/CSA), passive stiffness (slope of length-tension curve), peak steady-state force ratio (PSSFR, peak force/steady state force) and viscoelastic absorption (tension decayxt1/2). The myosin heavy chain isoform of each fiber was identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. RESULTS: Specific force and unloaded shortening velocity were not significantly different between females and males for type I (n=29 for females and 20 for males) and IIa (n= 15 and 18) fibers. There were no sex and fiber type differences in passive tension and PSSFR. Passive stiffness and viscoelastic absorption were greater in type IIa, but not type I fibers of males vs. females. PSSFR at maximum stretch was 5.61±1.99 suggesting 82.2% loss of peak response during stress relaxation. PSSFR was negatively correlated with stiffness (r = -0.369, p = 0.001) but not passive tension. Viscoelastic absorption was correlated with stiffness (r = 0.432, p < 0.001). CONCLUSION: We found a sex difference in viscoelastic properties and stiffness only for type IIa fibers. PSSFR indicating relative force loss during stress relaxation can be useful to assess viscoelastic and elastic properties along with passive stiffness.

Functional morphology of the sound‐generating labia in the syrinx of two songbird species

In songbirds, two sound sources inside the syrinx are used to produce the primary sound. Laterally positioned labia are passively set into vibration, thus interrupting a passing air stream. Together with subsyringeal pressure, the size and tension of the labia determine the spectral characteristics of the primary sound. Very little is known about how the histological composition and morphology of the labia affect their function as sound generators. Here we related the size and microstructure of the labia to their acoustic function in two songbird species with different acoustic characteristics, the white-crowned sparrow and zebra finch. Histological serial sections of the syrinx and different staining techniques were used to identify collagen, elastin and hyaluronan as extracellular matrix components. The distribution and orientation of elastic fibers indicated that the labia in white-crowned sparrows are multi-layered structures, whereas they are more uniformly structured in the zebra finch. Collagen and hyaluronan were evenly distributed in both species. A multi-layered composition could give rise to complex viscoelastic properties of each sound source. We also measured labia size. Variability was found along the dorso-ventral axis in both species. Lateral asymmetry was identified in some individuals but not consistently at the species level. Different size between the left and right sound sources could provide a morphological basis for the acoustic specialization of each sound generator, but only in some individuals. The inconsistency of its presence requires the investigation of alternative explanations, e.g. differences in viscoelastic properties of the labia of the left and right syrinx. Furthermore, we identified attachments of syringeal muscles to the labia as well as to bronchial half rings and suggest a mechanism for their biomechanical function.

Adsorbed Gels versus Brushes: Viscoelastic Differences

It is of fundamental importance to be able to easily distinguish between the viscoelastic properties of a molecular gel (noncovalent cross-linked three-dimensional polymer structure) and a brush (polymer structure that emanates from a surface in three dimensions without cross-linking). This has relevance in biology and in designing surfaces with desired chemical and viscoelastic properties for nano and genomic technology applications. Agarose and thiol-tagged poly(ethylene glycol) were chosen as model systems, as they are known, on adsorption, to behave like a molecular gel and brush, respectively. Here, we focus on their viscoelastic differences using a quartz crystal microbalance with dissipation monitoring (QCM-D). Changes in resonance frequency and dissipation for three overtones using QCM-D were fitted with the Voigt viscoelastic model to calculate the shear viscosity and shear modulus for the adsorbed agarose gel and the PEG brush. At a surface coverage of 500 ng/cm2, the shear viscosities and shear moduli were 0.0025 +/- 0.0002 Pa-s and 2.0 +/- 0.17 x 105 Pa and 0.0010 +/- 0.0001 Pa-s and 5.0 +/- 0.3 x 104 Pa for the gel and brush, respectively. Thus, the adsorbed agarose gel layer was far more rigid than that of the covalently bound PEG brush due to its cross-linked network. Also, the diffusivity of agarose and PEG in solution was compared during adsorption onto a bare gold surface. The estimated value for the effective diffusivity of the PEG (without a thiol tag) and of the agarose gel was on the order of 10(-11) and 10(-15) m2/s, respectively. This low diffusivity for agarose supports the contention that it exists as a molecular gel with a H-bonded cross-linked network in aqueous solution. With the methods used here, it is relatively easy to distinguish the differences in viscoelastic properties between an adsorbed gel and brush.

Crystal-like pattern formation in polymerization-induced phase separation

A unique domain structure was found in liquid-liquid phase separation induced by radical polymerization of 4-chlorostyrene monomer in the presence of random copolymer poly(dimethylsiloxane-co-diphenylsiloxane). Droplets with a narrow size distribution were generated by phase separation, and these droplets hardly coalesced by collisions. With the growth of droplet size, droplets gradually filled the space and spontaneously arranged themselves in a regular array like a crystal. The mechanism of regular array formation was discussed based on the large difference in viscoelastic properties between two segregating components.

Pattern formation and ordering in thin films of crystallisable block copolymers

We show that tapping-mode atomic force microscopy provides real-space and time-resolved observations of morphology and pattern formation resulting from crystallisation of annealed thin films of polyethelenoxide or microphase-separated low-molecular-weight hydrogenated poly(butadiene-b-ethyleneoxide) diblock copolymers. Differences in viscoelastic properties allow distinguishing crystalline and molten (amorphous) areas with a nanometer resolution.

Differences in Viscoelastic Properties of Periodontium between Japanese and Chinese

Purpose : This study examined differences in the viscoelasticity of the periodontium between Japanese and Chinese subjects and the influence of their living environment on the periodontium.Materials and Methods : We selected 93 and 113 upper central incisors, 100 and 100 upper canines, and 104 and 98 upper first molars of the Japanese and Chinese subjects, respectively, for examination in this study. The viscoelasticity of the periodontium was measured using an automatic diagnostic system that measured tooth mobility. The evaluated parameters were viscosity c1, c2 and elasticity k. An analysis of variance was used to compare the upper central incisors, canines, and first molars in the Japanese and Chinese subjects. An unpaired t-test was used for comparison between sexes and between Japanese and Chinese.Results : The viscoelastic parameters showed significant differences among central incisors, canines, and first molars in both the Japanese and Chinese. Almost all periodontal viscoelastic parameters were significantly different between Japanese males and females, while only a few such parameters showed significant gender differences in the Chinese. All parameters except c1 of the central incisors in men and all parameters in women showed significant differences between the Japanese and Chinese subjects.Conclusion : There were differences in the viscoelastic properties of the periodontium between Japanese and Chinese subjects.

Synthesis of Hydroxypropyl Methacrylate/Polysaccharide Graft Copolymers as Matrices for Controlled Release Tablets

ABSTRACTHydrophilic matrices are an interesting option when developing drug delivery systems. With this aim, hydroxypropyl methacrylate was grafted onto hydroxypropyl starch and hydroxypropyl cellulose substrates by following the Ce(IV) redox initiation method. Different amounts of ethyleneglycol dimethacrylate, 7 and 34 mol%, as the crosslinking monomer, were also added. The drying of grafted products was carried out by lyophilization, obtaining white powders. Reaction yields (percent grafting, grafting efficiency, etc.) and some physical characteristics of the powders (particle size, moisture uptake, density, morphology, etc.) were determined. These parameters indicate how useful these products may be as potential matrices for direct compressed tablets. In this light, the powder flowability and the binding properties of each copolymer were determined. The graft copolymers can be considered of great interest as direct compression excipients. Due to their different chemical structure and composition, they showed differences in viscoelastic properties that revealed an interesting range of possibilities for use in drug delivery formulations. Tablets formulated with conventional excipients were also tested. Dissolution tests of various tablets were carried out. In 12 hr, 60–80% of the model drugs was released.

Viscoelastic properties of chondrocytes from normal and osteoarthritic human cartilage.

The deformation behavior and mechanical properties of articular chondrocytes are believed to play an important role in their response to mechanical loading of the extracellular matrix. This study utilized the micropipette aspiration test to measure the viscoelastic properties of chondrocytes isolated from macroscopically normal or end-stage osteoarthritic cartilage. A three-parameter standard linear solid was used to model the viscoelastic behavior of the cells. Significant differences were found between the mechanical properties of chondrocytes isolated from normal and osteoarthritic cartilage. Specifically, osteoarthritic chondrocytes exhibited a significantly higher equilibrium modulus (0.33 +/- 0.23 compared with 0.24 +/- 0.11 kPa), instantaneous modulus (0.63 +/- 0.51 compared with 0.41 +/- 0.17 kPa), and apparent viscosity (5.8 +/- 6.5 compared with 3.0 +/- 1.8 kPa-s) compared with chondrocytes isolated from macroscopically normal, nonosteoarthritic cartilage. The elastic moduli and relaxation time constant determined experimentally in this study were used to estimate the apparent biphasic properties of the chondrocyte on the basis of the equation for the gel relaxation time of a biphasic material. The differences in viscoelastic properties may reflect alterations in the structure and composition of the chondrocyte cytoskeleton that have previously been associated with osteoarthritic cartilage. Coupled with earlier theoretical models of cell-matrix interactions in articular cartilage, the increased elastic and viscous properties suggest that the mechanical environment of the chondrocyte may be altered in osteoarthritic cartilage.

Effect of Long-chain Branching and Microgels in the Viscoelastic Behavior of Ethylene—Propylene—Diene Copolymers

Ethylene—propylene-diene (EPDM) terpolymers with different amounts of microgel and long-chain branching have been characterized by dynamic mechanical experiments. Low frequency measurements were found particularly useful for revealing differences in viscoelastic properties of the samples Loss factor values were of limited use, as they are influenced by sample molecular weights. Modified Cole—Cole plots were verified to be molecular weight independent, and could therefore be employed to detect molecular architecture variations. It was determined that long-chain branching and microgels are almost entirely localized in the higher molecular weight fractions of the investigated EPDM samples.

Collection and Analysis of Respiratory Mucus from Subjects without Lung Disease

We collected the respiratory mucus coating the endotracheal tubes used during short surgical procedures in 27 patients with no clinical evidence of respiratory disease. Twelve were male and 15 were female, and they ranged from 1 to 64 yr of age (mean, 28.7 yr). The viscoelastic properties, frog palate transport rate, and percent solid composition were in the normal range reported for both canine and human mucus collected using the bronchoscopy brush technique. There were no significant differences noted between male and female patients, and there were no changes in mucus or transport properties seen with aging. Mucus was also collected separately from the inside of the tube exposed to constant gas flow (13 patients), and from the outside of the endotracheal tubes in 25 patients. Although there were no significant differences in viscoelastic properties between inside and outside mucus, there was a greater thread formation (filance, 45 versus 26 mm; p less than 0.005) and a higher percentage of solids in mucus from the inside of the endotracheal tube (15.9 versus 11.4%; p less than 0.05), which is compatible with reduced hydration. The duration of anesthesia ranged from 25 to 195 min (mean, 85 min). There was no effect of duration of anesthesia on any of the measured mucus properties. This technique for mucus collection allows us to study alterations in mucus properties in patients with and without pulmonary disease at the time of incidental surgery.(ABSTRACT TRUNCATED AT 250 WORDS)

The viscoelastic properties of rubber–resin blends. I. The effect of resin structure

AbstractBlends of elastomers with the proper concentration of appropriate low molecular weight resins exhibit performance as pressure sensitive adhesives. Viscoelastic properties, which may be related to adhesive performance, were measured on 1:l blends of rubber and resin using a mechanical spectrometer. Significant differences in viscoelastic properties were observed depending upon the resin structure. On plots of G′ and tan δ vs. temperature, the addition of a compatible resin produces a pronounced shift of the tan δ peak to a higher temperature and reduces the modulus in the rubbery plateau. An incompatible resin results in a minor shift in the tan δ peak of the elastomer along with the appearance of a second peak at higher temperature, attributed to a second phase which is predominantly resin. Also, the modulus is increased in the rubbery plateau. A polystyrene resin, Mw about 900, is shown to be incompatible with natural rubber but compatible with styrene–butadiene rubber. A cycloaliphatic poly(viny1 cyclohexane) resin, Mw about 650, prepared by hydrogenating the polystyrene resin, is compatible with natural rubber, but incompatible with styrene‐butadiene rubber. An alkyl‐aromatic poly(tert‐butylstyrene) resin, Mw about 850, which is intermediate in aromaticity between the aromatic polystyrene resin and the cycloaliphatic poly(viny1 cyclohexane) resin, is compatible with both natural rubber and styrene‐butadiene rubber. Therefore, the structure of the resin is very important in adjusting the viscoelastic properties of a rubber–resin blend to achieve pressure sensitive adhesive performance.

Fine structure of antennal mechanosensilla of adult Rhodnius prolixus stål (Hemiptera: Reduviidae).

Each antenna of both sexes of adult Rhodnius prolixus has approximately 570 mechanosensitive neurons that innervate five morphologic types of cuticular mechanosensilla: campaniform sensilla, tapered hairs, trichobothria, and type I and type II bristle sensilla. Each campaniform sensillum and tapered hair is presumably innervated by one mechanosensitive bipolar neuron and probably functions in proprioception. The campaniform sensilla being located at the base of the scape could monitor the position of the antenna. Tapered hairs are found at the distal margin of flagellar segment I and projecting laterally from the bases of the pedicel and scape. They probably provide information about the relative positions of the antennal segments. Seven trichobothrium are located on the pedicel and three on flagellar segment I. Each trichobothrium has a long filamentous hair inserted into the base of a socket that extends inwardly as a cuticular tube and is innervated by one bipolar neuron with a tublar body, a parallel arrangement of microtubules associated with electron-dense material. The trichobothria may respond to small variations in air currents. Type I bristles occur at the base of the antenna and are the most numerous type of mechanosensillum; an average of 452 occur on each antenna of females and 440 on males. The bristle is curved toward the antennal shaft and is serrated distally. Type II bristles are located distally and are the second most numerous type of mechanosensillum; an average of 88 were counted on each antenna of females and 94 on males. The type II bristle is straight with small, longitudinal, external grooves and projects laterally from the antennal shaft. Each type I and II bristle sensillum is innervated by a bipolar neuron whose dendrite is divided into an inner and outer segment. The outer segment is encased by a dendritic sheath which may be highly convoluted and distally contains a tubular body. Two sheath cells are associated with each sensillum. Both types of bristle sensilla have a tactile function. The tubular bodies of both types of bristle sensilla have a complex structure indicating that they are very sensitive. Variations in the amount and arrangement of the electron-dense material at the tip of the tubular bodies may reflect differences in viscoelastic properties that underlie functional characteristics.

The viscoelastic properties of the human semilunar cartilage

We performed the experiment to observe the mechanical and physical properties of the semilunar cartilage in the knee of the pig and the human, which were preserved in silicone oil at 4°C for four days. The experiments were all performed in silicone oil and within an hour at room temperature. The observed stress-strain curve for pig menisci was sigmoid and this was proved to be due to its net-like framework of collagenous fibres by wide angle X-ray diffraction and stress relaxation experiments. Young's modulus was calculated from the linear part of stress-strain curve showing 1.75 × 10 8 dyn/cm 2 with 1.7%/sec strain rate. The strain rate dependency of Young's modulus increased very slightly. This is contrary to the suggested idea that the meniscus could mainly play a role of a shock absorber in the knee joint. Stress relaxation tests with tensile load revealed no difference in visco-elastic properties between human normal and torn menisci.

Effect of method of synthesis of unsaturated fatty acid-modified alkyd resin on the crosslinking behavior of prepolymer: Correlation of molecular weight distribution of prepolymer and degree of crosslinking of the derived film

The viscoelastic properties of films of unsaturated fatty acid-modified alkyd resins prepared by different synthetic procedures are examined. The films prepared by the fatty acid method have a higher glass transition temperature and greater degree of crosslinking than those prepared by the monoglyceride method. It is suggested the molecular weight distribution of prepolymer prepared by the monoglyceride method would be broader than that prepared by the fatty acid method, and this was verified by the results of [η]/Mn and fractionation of prepolymers. The differences in viscoelastic properties of films is explainable on the basis of the molecular weight distribution and the distribution of crosslinking functional groups of prepolymers.