Crystal Network Structure Research Articles

Characterization and electrochemical response of sonogel carbon electrode modified with nanostructured zirconium dioxide film

A new modified carbon electrode was developed by coating sol–gel derived zirconium dioxide film on the top of graphite carbon electrode, which showed good electrochemical activity and reversibility in the redox process of catechol in acidic aqueous solution (0.1 M H 2SO 4), even in the presence of ascorbic acid (a common interferent). Good electrochemical behavior, including relatively small oxidation and reduction peak separation (Δ E p = 71 mV), improved sensitivity, and good operation stability and reproducibility, can be explained by specific physicochemical properties of sol–gel derived ZrO 2 film. Such properties include robust and interconnected crystal network structure with high ZrO 2 purity, relatively high BET surface area/pore volume, larger interfacial contact area and good adhesion between ZrO 2 film and sonogel graphite carbon material. This study proved that zirconium dioxide film prepared by such a sol–gel route is a promising electrode material for the development of novel conducting electrodes based on sonogel graphite carbon for the detection of neurotransmitters.

Effects of tempering and fat crystallisation behaviour on microstructure, mechanical properties and appearance in dark chocolate systems

Fat crystallisation behaviours in dark chocolates from varying particle size distribution (PSD) ( D 90 of 18, 25, 35 and 50 μm) was studied, yielding products from different temper regimes (optimal temper, over-temper and under-temper), and their effects on mechanical properties and appearance evaluated. Microstructures of derived products were determined using stereoscopic binocular microscopy. Wide variations in mechanical properties and appearance were noted in products from different particle size and temper regimes. Particle size (PS) was inversely related with texture and colour, with the greatest effects noted in hardness, stickiness and lightness at all temper regimes. Over-tempering caused significant increases in product hardness, stickiness with reduced gloss and darkening of product surfaces. Under-tempering induced fat bloom in products with consequential quality defects on texture, colour and surface gloss. Micrographs revealed variations in surface and internal crystal network structure and inter-particle interactions among tempered, over-tempered and under-tempered (bloomed) samples. Under-tempering caused whitening of both surface and internal periphery of products with effects on texture and appearance. Thus, attainment of optimal temper regime during pre-crystallisation of dark chocolate was central to the desired texture and appearance as both over-tempering and under-tempering resulted in quality defects affecting mechanical properties and appearance of products.

The effect of supercooling on crystallization of cocoa butter‐vegetable oil blends

AbstractThe solid fat content (SFC), Avrami index (n), crystallization rate (z), fractal dimension (D), and the pre‐exponential term [log(γ)] were determined in blends of cocoa butter (CB) with canola oil or soybean oil crystallized at temperatures (TCr) between 9.5 and 13.5°C. The relationship of these parameters with the elasticity (G′) and yield stress (σ*) values of the crystallized blends was investigated, considering the equilibrium melting temperature (TMo) and the supercooling (i.e., TCro−TMo) present in the blends. In general, supercooling was higher in the CB/soybean oil blend [TMo=65.8°C (±3.0°C)] than in the CB/canola oil blend [TMo=33.7°C (±4.9°C)]. Therefore, under similar TCr values, higher SFC and z values (P<0.05) were obtained with the CB/soybean oil blend. However, independent of TCr TAG followed a spherulitic crystal growth mechanism in both blends. Supercooling calculated with melting temperatures from DSC thermograms explained the SFC and z behavior just within each blend. However, supercooling calculated with TMo explained both the SFC and z behavior within each blend and between the blends. Thus, independent of the blend used, SFC described the behavior of G′eq and σ* and pointed out the presence of two supercooling regions. In the lower supercooling region, G′eq and σ* decreased as SFC increased between 20 and 23%. In this region, the crystal network structures were formed by a mixture of small β′ crystals and large β crystals. In contrast, in the higher supercooling region (24 to 27% SFC), G′eq and σ* had a direct relationship with SFC, and the crystal network structure was formed mainly by small β′ crystals. However, we could not find a particular relationship that described the overall behavior of G′eq and σ* as a function of D and independent of the system investigated.

Hydraulicity of wet-milling ultra-fine grouting cement

The physical and mechanical properties of wet-milling ultra-fine grouting cement were studied, and its microstructure was observed through modern instrumentation analysis such as scanning electronic microscopy (SEM), X-ray diffraction and Hg-intrusion micromeritics. The experimental results indicate that wet-milling ultra-fine cement possesses high rheological properties and groutability. It can be filled densely in cracks of rock and hydrate fully, which may endow hydrated cement with high mechanical strength. Main hydration products of wet-milling ultra-fine cement are poorly crystalline C-S-H(I), acicular AFt and plank-shape Ca(OH)2. The dense crystal-network structure can be formed in the rock gaps filled with cement paste, but some weak regions exist owing to Ca(OH)2. The features of micro-pore structure of hydrated wet-milling ultra-fine cement are few big harmful pores, abundant harmless micro pores and little most possible pore radius.

Rheometry and polymorphism of cocoa butter during crystallization under static and stirring conditions

AbstractIn this work the association between polymorphism and the crystal network structure developed by the TAG of cocoa butter (CB) was investigated under static and stirring crystallization conditions using a dynamic mechanical spectrometer. The results obtained showed that parameters obtained through oscillatory rheometry (i.e., phase shift angle, δ) followed the polymorphism of CB during static crystallization. Although standard DSC was not capable of differentiating the α to β′ phase transformation from the direct β′ crystallization from CB melt, δ rheograms measured these two processes separately. Additionally, through oscillatory rheometry, we followed the dimensionality of the crystal network during CB crystallization. Within this context, the pre‐exponential term (In γ) from the weak‐link regime equation for colloidal dispersions was much more sensitive than the fractal dimension (D) to differences in crystal size, spatial distribution of the crystal network, and melting temperature of the β′ phase of CB. On the other hand, torque measurements obtained during CB crystallization under stirring conditions showed a shear rate effect that favored TAG development in the β phase at temperatures of 19, 22, and 26.5°C, particularly at shear rates of 120 and 400 rpm. In contrast, under static conditions CB did not develop in the β phase at any of the crystallization temperatures investigated (i.e., 18 to 26.5°C).

Influence of SFC, microstructure and polymorphism on texture (hardness) of binary blends of fats involved in the preparation of industrial shortenings

Several binary blends of vegetable oils commonly used in industrial shortenings (i.e., palm oil (PO), hydrogenated palm oil (HPO), soybean oil (SO), hydrogenated soybean oil (HSO), low-erucic acid rapeseed oil (LERO), hydrogenated low-erucic acid rapeseed oil (HLERO)) were studied for their physical properties such as solid fat content (SFC) by nuclear magnetic resonance (NMR) and textural properties (hardness). Microstructure was also observed by microscopy in order to explain the variability in hardness for samples having the same SFC values. The blends studied by microscopy were the following: HSO, HPO and HLERO diluted in LERO. For these three blends which had the same SFC, the level of network structure was different. HSO diluted in LERO had more crystals, closer to each other and overlapped. This can explain that HSO has a higher hardness than HPO or HLERO, for a same SFC value, when diluted in LERO. Polymorphism was also observed by powder X-ray diffraction. The variability in hardness for samples having the same SFC is due to various crystal types and/or network structures that are formed upon crystallization of hard fats. This work demonstrates that for binary blends of studied oils, changes in the hardness are controlled mostly by the SFC, polymorphism and also by the material’s microstructure.

Cristalização de lipídios estruturados obtidos a partir de gordura do leite e óleo de milho

A partir da mistura de óleos e gorduras e de posterior interesterificação podem ser obtidos lipídios estruturados, que são compostos que apresentam características físicas, químicas e nutricionais diferentes daquelas dos lipídios que lhes deram origem. As principais propriedades físicas destes lipídios, como consistência e plasticidade, podem ser influenciadas por sua estrutura cristalina. O objetivo deste trabalho foi observar modificações na estrutura cristalina de lipídios estruturados obtidos a partir de gordura do leite e óleo de milho. As curvas de cinética de cristalização foram construídas a partir do conteúdo de gordura sólida das amostras em função do tempo. A utilização do cálculo dos parâmetros de Avrami permitiu determinar a velocidade de cristalização e os tipos de nucleação e dos cristais formados. A microscopia sob luz polarizada forneceu imagens dos cristais formados pelos métodos de resfriamento lento e rápido, a partir das quais foram determinados os seguintes itens: número de cristais, área cristalizada e dimensões fractais das amostras. A correlação obtida entre os resultados indicou que a adição de óleo de milho não provocou mudanças substanciais na estrutura da rede cristalina da gordura do leite, apenas diminuiu a quantidade de gordura cristalizada. As reações de interesterificação e a adição de óleo de milho não alteraram o tamanho e a forma dos cristais.

Effect of interfacial stress on the crystalline structure of the matrix and the mechanical properties of high‐density polyethylene/CaCO3 blends

AbstractA series of high‐density polyethylene (HDPE)/CaCO3 blends were prepared with different kinds of coupling agents, with CaCO3 particles of different sizes, and with matrixes of different molecular weights during the melt‐mixing of HDPE and CaCO3 particles. The mechanical properties of these blends and their dependence on the interfacial adhesion and matrix crystalline structure were studied. The results showed that the Charpy notched impact strength of these blends could be significantly improved with an increase in the interfacial adhesion or matrix molecular weight or a decrease in the CaCO3 particle size. When a CaCO3 surface was treated with a compounded coupling agent, the impact strength of the HDPE/CaCO3(60/40) blend was 62.0 kJ/m2, 2.3 times higher than that of unimproved HDPE; its Young's modulus was 2070 MPa, 1.07 times higher than that of unimproved HDPE. The heat distortion temperature of this blend was also obviously improved. The improvement of the mechanical properties and the occurrence of the brittle–tough transition of these blends were the results of a crystallization effect induced by the interfacial stress. When the interfacial adhesion was higher and the CaCO3 content was greater than 30%, the interfacial stress produced from matrix shrinkage in the blend molding process could strain‐induce crystallization of the matrix, leading to an increase in the matrix crystallinity and the formation of an extended‐chain (or microfibrillar) crystal network. The increase in the critical ligament thickness with an increasing matrix molecular weight was attributed to the strain‐induced areas becoming wider, the extended‐chain crystal layers becoming thicker, and the interparticle distance that formed the extended‐chain crystal network structure becoming larger with a higher matrix molecular weight. The formation of the extended‐chain crystal network and the increase in the matrix crystallinity were also the main reasons that Young's modulus and the heat distortion temperature of this blend were improved. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2120–2129, 2003

FAT CRYSTAL NETWORKS: STRUCTURE AND RHEOLOGICAL PROPERTIES

ABSTRACTThe solid character of plastic fats is the result of the presence of a certain percentage of crystallized fat. Although methods are now available to measure solid/liquid ratios without difficulty, there is no conclusive theory which will relate crystal size and shape, solid fat content and rheological properties. It is generally assumed that plastic fats contain a three‐dimensional network of fat crystals, held together by primary (nonreversible) and secondary (reversible) bonds. This paper highlights the hypotheses that have been put forward concerning the forces existing between fat crystals, the rheological properties of plastic fats, and recent information on crystal network structure.

Viscoelastic properties of plastic fat products

AbstractAn instrument is described for the creep analysis of plastic fat products. The instrument records the deformation of a sample under constant force. Deformation is sensed by a displacement transducer. Instantaneous elasticity, retarded elasticity and plastic flow can be calculated. The extent of instantaneous elasticity of plastic fat products was found to be dependent on loading time. At longer loading times, the instantaneous elasticity as a percentage of total deformation decreased, with a corresponding increase in permanent deformation. The effects of temperature, magnitude of force and work softening were investigated. The results are discussed in relation to the nature of the crystal network structure in plastic fat products.