Influence of high pressure processing on the linear viscoelastic properties of egg yolk dispersions

The effect of high-pressure treatments on the gelation of egg yolk dispersions was studied by using differential scanning calorimetry (DSC) and small amplitude oscillatory shear (SAOS). The influence of pressure of processing and pH were analysed. The DSC results suggest a progressive decrease in thermal denaturation enthalpy as pressure level increases related to protein denaturation. SAOS was used to evaluate the effect of different pressure levels on the linear viscoelastic behaviour of egg yolk dispersions. An increase in the pressure level produces a dramatic change in the linear viscoelastic behaviour undergoing a sol–gel transition. High hydrostatic pressure (HHP) processing was also analysed as a function of pH and solids content. The results obtained confirm that the impact of high pressure on aggregation and network formation can be modulated by pH. HHP processing of egg yolk systems is highly affected by protein concentration particularly when it is compared to heat processing.     

Rheology and microstructure of heat-induced egg yolk gels

The evolution of native egg yolk undergoing a thermal-induced sol-gel transition was studied by using temperature controlled small amplitude oscillatory shear measurements. The critical gel point was determined according to Winters criterion: 1) from the measurements of storage and loss moduli as a function of heating time at different frequencies, and 2) from the exponents of the power law mechanical spectra obtained after cure experiments performed up to a maximum temperature (60–90 °C) followed by a sudden decrease in temperature up to 20 °C. Differential Scanning Calorimetry (DSC) was performed in order to investigate thermal transitions in egg yolk. Microstructure of gels was evaluated by Transmission and Scanning Electron Microscopy. The results obtained were discussed in terms of the processes involved in protein gelation: change in the protein system, aggregation of partially denaturated protein molecules and association of aggregates. As a result, an elastic gel network was always obtained. The influence of frequency, heating rate, solids concentration and maximum temperature of processing, was analysed. Most of the transformations found during thermal processing were found to be basically irreversible, even at the sol state and gel point. However, some reversible phenomena were detected during constant temperature processing depending on the maximum temperature performed.     

离子液体作为聚乙二醇（PEG）添加剂的摩擦学性能

本文研究了作为聚乙二醇（PEG）添加剂的离子液体的摩擦学性能,并用扫描电镜和XPS研究了磨斑形貌和磨斑表面的元素种类及化学状态。结果表明:离子液体作为聚乙二醇添加剂时具有优异的减摩抗磨能力,这是因为在摩擦过程中,离子液体容易吸附在摩擦表面,进一步与摩擦副发生摩擦化学反应,形成1层稳定的保护膜而起到减摩抗磨作用。     

Rheological behaviour of spray-dried egg yolk/xanthan gum aqueous dispersions

This paper provides information on the microstructure of, and reports particle size distributions and rheological results for, aqueous dispersions of spray-dried egg yolk and xanthan gum prepared on a laboratory scale using two types of homogenisers. Laser light scattering results demonstrated that higher energy input during homogenisation yielded a dispersion with a lower average particle size and a wider polydispersity, slightly influencing the linear dynamic viscoelastic functions due to the low concentration of egg yolk particles. These dispersions exhibited weak gel properties at the composition studied. The mechanical spectrum and the corresponding relaxation spectrum were dominated by the xanthan/gum-water matrix which controls the structure of the continuous phase. This fact explained the lack of any wall depletion effects. Several controlled-rate and controlled-stress rotational rheometers and a capillary rheometer were used to obtain information on flow properties. The shear rate dependence of steady state viscosity was determined through twelve decades, and was fitted using the Carreau equation. The kinetics of structural recovery after steady-state shear was studied by start-up at the inception of shear and flow interrupted experiments under controlled shear history. The results were analysed in terms of the ratio of a time-dependent amount of overshoot to the amount of overshoot of the original sample, using the addition of two first order equations. Additionally, combined steady state flow properties at fixed shear stress/oscillatory shear experiments were also used. The increase of the storage modulus with time, checking a linear viscoelastic response, tracked the structural recovery after steady shear. Laser light scattering of sheared samples helped gain a better understanding of the role of egg yolk particles on the rheology of these dispersions. Received: 6 February 2000 Accepted: 5 September 2000     

Effects of the pH on the mechanical behavior of articular cartilage and corneal stroma

Electro-chemo-mechanical couplings in articular cartilages and corneal stroma are due to the presence of electric charges on proteoglycans. In addition, at non-physiological pH, collagen molecules become charged as well. Variation of the pH of the electrolyte has strong implications on the electric charge of these tissues, and by the same token, on their transport and mechanical properties. Indeed, articular cartilages and corneal stroma swell and shrink depending on the composition of the electrolyte, they are in contact with.Emphasis is laid here on the combined effects of pH, ionic strength, calcium and chloride binding on mechanical properties.The tissues are viewed as three-phase multi-species porous media. The constitutive framework is phrased in the theory of thermodynamics of deformable porous media. Acid–base reactions, as well as ion binding, are embedded in this framework. Although, macroscopic in nature, the approach accounts for a number of biochemical details defining collagen and proteoglycans.The model is used to simulate laboratory experiments where specimens of articular cartilages and corneal stroma are put in contact with a bath of controlled chemical composition. Chemical loadings, where the ionic composition and pH of the bath are varied, are intermingled with mechanical loadings. The variations of the stress and strain are observed to depend strongly on the ionic strength and ion type present in the bath: sodium chloride leads to a stiffer response than calcium chloride and hydrochloric acid. Moreover, when the bath changes from basic to acidic, the change of sign of the fixed charge across the isoelectric point has definite mechanical implications, and it gives rise to non-monotonous evolutions of the stress, strain and chemical content.While the chemo-mechanical effect is a key phenomenon that governs the behavior of tissues with fixed charges, the converse mechano-chemical effect is significant in corneal stroma due to its low stiffness.     

The effect of pH,ionic strength,and temperature on the rheology and stability of aqueous clay suspensions

The effect of pH level, ionic strength, and temperature on the theology and stability of aqueous suspensions of attapulgite clay was systematically investigated. A Rheometrics Mechanical Spectrometer with cone and plate fixtures was used to measure the steady shear viscosity of the system. The edge charges of the clay particles can be adjusted by changing the pH level of the suspending medium so as to influence the flocculation state and, consequently, the rheological behavior of the suspension. This pH effect may be counteracted by the ionic strength effect at both very high and very low pH levels where the ionic strength is high enough to cause flocculation of the electrostatically stabilized suspension. The temperature effect study indicates that the relative contribution of Brownian motion and shear flow to the viscosity is dependent on the flocculation state of the suspension.     

45#钢等离子渗氮在不同润滑剂下的摩擦磨损性能研究

利用脉冲直流等离子对45#钢进行等离子渗氮,用X射线散射分析等离子渗氮表面成分,并测量了渗氮前后表面硬度,利用SRV摩擦磨损试验机考察45#钢等离子渗氮前后在含磷酸三甲酚酯、硫化异丁烯和离子液3种润滑剂润滑下的摩擦磨损性能,通过扫描电子显微镜和X射线光电子能谱仪对3种润滑剂的抗磨减摩机理进行分析.结果表明:等离子渗氮后可以提高45#钢表面的硬度;在磷酸三甲酚酯、硫化异丁烯和离子液润滑下,其抗磨性能大幅度提高,等离子渗氮层具有良好的抗磨性能,其中1-丙基-3-辛基咪唑六氟磷酸盐离子液具有优良的抗磨减摩性能.这是由于润滑油中活性元素与渗氮层协同作用的结果.     

铜和石墨对铁基含油自润滑复合材料机械及摩擦学性能的影响

采用粉末冶金工艺制备了铁基含油自润滑复合材料,考察了Cu与石墨的含量对铁基含油自润滑复合材料的机模样性能、摩擦学性能及组织结构的影响,并利用X射线衍射仪、扫描电子显微镜及光学显微镜等对材料的组分、显微组织形态和结构以及磨损表面形貌等进行了系统的观察和分析,结果表明：添加适量Cu的Fe-Cu二元系材料的机械性能和摩擦学性能明显优于Fe系材料,这主要是因为Cu的加入改变了材料的微观结构。添加适量石墨的Fe-Cu-石墨三元系材料比Fe-Cu二元系材料具有更优异的摩擦学性能,但机械性能有所下降,这主要是由于石墨与油的协同润滑效应和石墨的加入改变了材料的微观结构所致。     

Modeling of the pH-sensitive behavior of an ionic gel in the presence of diffusion

In this paper, we develop a model for swelling of an ionic gel in a solvent of varying pH and diffusion of the solvent through the swollen gel by applying a variational method originally presented by Baek and Srinivasa (Int. J. Nonlinear Mech. 39 (2004) 201). The approach presented here, based on the balance laws of a single continuum with mass diffusion and ionic chemical reactions, delivers system equations and boundary conditions by assuming two constitutive scalar functions for the free energy of the system and the rate of dissipation, instead of assuming osmotic pressure, electrostatic repulsive force, etc. In the equilibrium case, the model describes pH-dependent behavior and the effect of other counterions on the swelling of ionic gels. In the non-equilibrium case, it accounts for the pH-dependent mass flux through ionic gels. Moreover, the model shows that the mass flux can be induced by the gradient of chemical potential, the concentration of the mobile species and ionic charges. This model is applied to a typical carboxylated copolymer gel, and compared with an experiment for equilibrium swelling, and predicts the pH-dependence for a pressure-induced mass flux.     

Structure and dynamics of ovalbumin gels

Solvent effects on dynamical and thermal behaviors of ovalbumin (OVA) gels induced by thermal denaturation at high temperature of 160°C were studied from dynamic shear modulus measurement, shear creep and creep recovery measurement, and DSC measurement. Two organic solvents, glycerin (G) and ethylene glycol (EG), and their mixtures with water (W)(G/W and EG/W) were used as solvent for preparation of gels. Stable gels formed in pure glycerin took a fractal structure at OVA concentration C range of 15–45wt% at a temperature specific to respective C, whereas a fractal structure was not observed for gels prepared in EG, G/W, and EG/W. The results were consistent with thermal denaturation behaviors of OVA in these solvents. Morphologies of two gels prepared in water and glycerin were explored using high resolution SEM, which showed that a basic unit responsible for formation of OVA gels was spheres with a diameter ranging from 20 to 40 nm, being much larger than 5.6 nm of the diameter of native OVA, and a fractal structure was related to network formation accompanied by melting of those spheres.Dedicated to Prof. John D. Ferry on the occasion of his 85th birthday.     

静态热老化对锂-钙基润滑脂微观结构和流变性的影响

采用静态热老化模拟润滑脂在轴承中的热老化过程,通过红外光谱特征波峰面积变化、扫描电镜和差热分析表征热老化后润滑脂微观结构,并采用流变测试仪考察热老化过程中润滑脂流变性能的变化.结果发现：随着老化时间延长,基础油分子碳链发生断裂,稠化剂浓度下降,产生含羰基类氧化产物,该类物质浓度逐渐增强;老化后的润滑脂晶体结构遭到严重破坏,皂纤维网状结构逐渐瓦解,润滑脂结构稳定性变差,剪切过后,结构恢复速率变慢;超过热老化288 h润滑脂热稳定临界点后,润滑脂老化反应加剧,易从润滑部位流失,润滑失效.     

DIC Strain Measurements at the Micro-Scale in a Semi-Crystalline Polymer

To improve physical motivation of mechanical modeling for semi-crystalline polymers, a better understanding of micro-mechanisms and a quantification of the mechanical response at the microstructure scale are needed. Strain field evolutions during deformation would be useful information but experimental techniques are still lacking for these materials. In this paper, an in-situ Digital Image Correlation (DIC) technique in the Scanning Electron Microscope (SEM) was developed to access strain fields at the spherulitic scale of a polypropylene. The evolution of strain heterogeneities during deformation were analyzed and correlated to the microstructure.     

Epoxy-based electroactive polymer gels

We describe a new type of electroactive polymer gel. In contrast to cross-linked polyacrylates, this system is based on triepoxides cross-linked with polyfunctional amines. The stoichiometry is selected to form a cross-linked gel with excess amino hydrogens. In acid solutions these become cationic and the ionic interactions cause the gel to swell. We describe the mechanical properties of the gels, their response to changes in pH and to electrical activation. The response time is in rough agreement with what would be expected for a diffusional process through a gel of this size (about 100 μm). Samples of smaller dimensions would be expected to respond more rapidly.     

Rheology of gel-like materials in textile printing

Printing of fabrics made of cellulose fibres involves printing pastes mainly containing the dyer and thickeners which are generally polysaccharides. The process is a sequence of several operations in order to obtain the penetration and the fixation of the dyer molecule in the fibre. Firstly, the paste is deposited on the fabric and dried. Then, there is a gelation phase by means of a cross-linking agent. This paper presents experimental results obtained with thickeners used in textile industry. The rheological properties of the thickeners and of the gels are characterised by oscillatory measurements. The influence of the pH and of the presence of salt is discussed.     

Cr靶电流对Cr改性类石墨薄膜摩擦磨损性能的影响

采用闭合场非平衡磁控溅射离子镀设备,在不同Cr靶电流参数下制备Cr改性类石墨薄膜,测试了薄膜的硬度、结合强度、摩擦系数和比磨损率,采用扫描电子显微镜和透射电子显微镜观察薄膜的显微结构.结果表明:改变Cr靶电流不仅能够改变薄膜的化学成分,而且能够改变薄膜的显微结构;随着Cr靶电流增加,薄膜的断口出现纤维状结构,并逐渐发展为柱状结构;Cr的加入使得类石墨薄膜形成周期性层状结构;在干摩擦条件下,随着Cr靶的电流增加,GLC膜的摩擦系数先减小而后增大;当载荷较小时,薄膜的比磨损率随Cr靶电流的增加而增大,载荷较大时薄膜的比磨损率变化不大.化学成分和显微结构的变化引起GLC膜硬度和韧性的变化,从而改变了薄膜的摩擦磨损性能.     

高速车削300M超高强度钢时的Al2O3 基陶瓷刀具磨损机理研究

使用Al2O3基陶瓷刀具对300M超高强度钢进行了干切削试验,采用电子扫描显微镜（SEM）观察刀具的磨损形貌,并通过能谱分析仪（EDS）测量了陶瓷刀具磨损微区的各元素含量,分析了陶瓷刀具的主要磨损机理.结果表明：陶瓷刀具磨损的主要机理为粘结磨损、磨粒磨损和氧化磨损.粘结磨损主要发生在前刀面上,且受刀具材料和工件材料接触点应力状态的影响.刀具前、后刀面的磨损边缘区易发生氧化磨损.     

含盐量对水泥土强度影响的室内试验研究

通过含盐量对非有机质土加固强度影响的试验研究,得到了含盐量对水泥土强度的提高或减小的阈值为3.5%。当盐渍土的含盐量低于这个阈值时,盐渍土的加固强度会因可溶性盐的结晶膨胀作用,提高水泥土的强度;相反当盐渍土的含盐量高于该阈值时,盐渍土的强度会因可溶性盐的过多的结晶膨胀作用,使水泥土的结构遭到破坏,从而使水泥土的强度大大降低。同时分析了可溶性硫酸盐、镁盐和氯盐对水泥土的浸蚀性作用,并从盐类对水泥土强度的影响从机理上进行了阐释,提出了高含盐量对水泥土破坏作用的对策。     

Quantitative Strain Analysis of the Large Deformation at the Scale of Microstructure: Comparison between Digital Image Correlation and Microgrid Techniques

A comparative study has been carried out to assess the accuracy of the Digital Image Correlation (DIC) technique for the quantification of large strains in the microstructure of an Interstitial Free (IF) steel used in automotive applications. A microgrid technique has been used in this study in order to validate independently the strain measurements obtained with DIC. Microgrids with a pitch of 5 microns were printed on the etched microstructure of the IF steel to measure the local in-plane strain distribution during a tensile test carried out in a Scanning Electron Microscope (SEM). The progressive deformation of the microstructure with microgrids has been recorded throughout the test as a sequence of micrographs and subsequently processed using DIC to quantify the distribution of local strain values. Strain maps obtained with the two techniques have been compared in order to assess the accuracy of the DIC measurements obtained using the natural patterns of the revealed microstructure in the SEM micrographs. The results obtained with the two techniques are qualitatively similar and thus, demonstrate the reliability of DIC applied to microstructures, even after large deformations in excess of 0.7. However, an average error of about 16?% was found in the strain values calculated using DIC.     

Obtaining metal-based composites with hardening by titanium diboride nanoparticles

The mechanism of obtaining high-strength mesocomposite materials with a cellular microstructure is studied. It is shown that the formation of the mesocomposite microstructure is determined by the method of pressing characterized by high strains and strain rates, and also by the mesocomposite composition; the high-plasticity matrix and nondeformable particles of the hardening phase, which are not bonded to the mesocomposite matrix, assist in the process of self-organization, i.e., formation of a cellular microstructure. The set of mesocomposite properties is studied to understand the general laws of mesocomposite formation and optimize the composition. A composite with an optimal composition is obtained, which retains high electrical conductivity of copper and sufficiently high plasticity necessary for its effective application; its strength is greater than the base strength by an order of magnitude; moreover, its strength and wear resistance are much higher than those of dispersion-hardened alloys obtained by the method of internal oxidation. The results obtained can be used for creating new composite materials.