Water Diffusion Kinetics Research Articles

Hygrothermal ageing of reprocessed polylactide

The influence of an accelerated hygrothermal ageing simulation test on a commercial PLA and its three subsequent mechanically-reprocessed materials was studied. The analysis was focused on the water diffusion kinetics and the physico-chemical changes induced by the hygrothermal degradation. Water diffusion proceeded faster than chain relaxation processes, as defined by a Case II absorption model. It was proved that the water diffusion rate decreased with subsequent reprocessing cycles and increased with higher hygrothermal ageing temperatures. Hydrolytic chain scission provoked significant molar mass decays and consequent general losses of thermal and mechanical performance. The rearrangement into crystalline fractions of shorter chains provoked by hygrothermal ageing was qualitatively and quantitatively followed by both Fourier-Transform Infrared Spectroscopy and Differential Scanning Calorimetry. The microstructural changes were monitored by the cold-crystallization temperature, the crystallinity degree XC and the absorbance intensity ratio I921/I955. A Weibull model showed that the crystallites were formed faster at higher reprocessing cycles and at lower hygrothermal ageing temperatures. All these effects were particularly significant for PLA reprocessed more than one time.

Preparation of Acetylated Guar Gum – Unsaturated Polyester Composites & Effect of Water on Their Properties

Article history: Received June 25, 2012 Received in Revised form September 21, 2012 Accepted 21 September 2012 Available online 22 September 2012 Guar gum has seen extensive use in blends, however, its application as a filler in thermoset composites has as yet not been investigated. The effect of the addition of guar gum and its acetyl derivatives on the kinetics of water diffusion in unsaturated polyester composites was studied. The effect of water on the mechanical properties of the composites was studied with respect to the nature of filler, filler concentration and time of immersion. All the mechanical properties were observed to decrease on exposure to water. Further, it was observed that acetylated guar gum, with a degree of substitution of 0.21, showed the best mechanical properties, surpassing the other filled composites and that of the pure unsaturated polyester. Thus, acetylated guar gum showed promise as eco-friendly filler in composite formulation.

Diffusion and solubility of commercial poly(methyl methacrylate) denture base material modified with dimethyl itaconate and di‐n‐butyl itaconate during water absorption/desorption cycles

AbstractThis study evaluated the water absorption, solubility, kinetics of water diffusion and residual monomer content of commercial poly(methyl methacrylate) (PMMA) denture base material modified with dimethyl itaconate (DMI) and di‐n‐butyl itaconate (DBI). Water absorption and solubility were measured gravimetrically while the residual monomer content was analysed using high‐performance liquid chromatography with ultraviolet detection. It was found that the addition of di‐n‐alkyl itaconates significantly decreases the residual methyl methacrylate (MMA) content in the polymerized material. Maximum uptake (M∞) and loss (M′∞), and diffusion coefficients for absorption (Da) and desorption (Dd) of water through all materials were established. M∞ shows a linear decrease with increasing amount of itaconate in the system while Da shows a linear increase with increasing amount of itaconate, both of these effects being more pronounced when DBI is present compared to DMI. M∞ is a linear function of the value of Hoy's solubility parameter. The reduction in residual MMA promoted by addition of a small amount of di‐n‐alkyl itaconates can improve the applicative properties and biocompatibility of the PMMA denture base material. Also, it is shown that modification of the denture base material with di‐n‐alkyl itaconates can enable precise control of water absorption in the system. Copyright © 2012 Society of Chemical Industry

Kinetics of water diffusion in corn grain during the alkaline cooking at different temperatures and calcium hydroxide concentration

The kinetics of corn grains hydration during the nixtamalization process is described for different temperatures, cooking times and Ca(OH) 2 concentrations. Samples were prepared using different cooking times from 0 to 120 min; cooking temperatures of 62, 72, 82, and 92 °C, and Ca(OH) 2 concentrations of 0.0%, 0.8%, 1.0%, and 2.0% related to the mass of corn grains. The fitting of the experimental data to the empirical Michaelis–Menten equation gives a good approach of the hydration process. From the first derivate of the Michaelis–Menten equation the rate of the corn grain hydration can be obtained. This mathematical model predicts the hydration and hydration rate of the corn grains during the cooking time of the nixtamalization process. Furthermore, with this proposed model, we can predict that for short times the rate reaches its maximum, and tends to zero for long times as the saturation of the grain is reached. It is concluded that hydration and hydration rate of white corn grains depends significantly on the temperature and cooking water lime concentration ( P < 0.005).

Effect of Water on Mechanical Properties of Unsaturated Polyester—Acetylated Hydroxypropyl Guar Gum Composites

The use of natural, eco-friendly, renewable resources in composites, as a reinforcing material, requires chemical or physical treatment to improve compatibility with the polymer matrix. In the present study hydroxypropyl guar gum (HPG) was acetylated to investigate its influence on the behavior of its unsaturated polyester (UPR) composites on exposure to water. The kinetics of water diffusion and effect on mechanical properties were studied with respect to the degree of acetylation and filler concentration. The absorption behavior of all composites was found to follow Fick’s law. Mechanical properties of HPG composites were found to be superior compared to pure UPR and acetylated HPG composites.

Effect of temperature on water sorption and solubility of dental adhesive resins

Objective This study examined the effect of temperature on water sorption and solubility characteristics of four commercial dental adhesives. The null hypothesis tested was that temperature has no effect on the water sorption and solubility characteristics of these adhesives. Methods The tested materials were: three-step etch-and-rinse (All-Bond 2, AB), two-step etch-and-rinse (One-Step, OS), two-step self-etch (Clearfil SE Bond, SE) and one-step self-etch (Clearfil S3 Bond, S3) adhesives. Seven resin disks (6 mm in diameter × 1 mm in thickness) were prepared from each tested material and were stored in deionized water at 23 °C, 37 °C and 55 °C. Water sorption and solubility of the resin disks were measured before and after water immersion and desiccation following two consecutive sorption and desorption cycles. The water sorption and solubility values obtained were analyzed using two-way ANOVA and Tukey's multiple comparison tests. The relationships between maximum water sorption, solubility and kinetics of water diffusion with temperature were evaluated by means of Pearson correlation statistic. Results OS exhibited the highest water sorption and solubility values in the second sorption–desorption cycle at 55 °C ( p < 0.001). This is followed by S3, SE and AB with no significant difference between SE and AB. Significant positive correlations were observed between maximum water sorption ( r = 0.307, p < 0.01), solubility ( r = 0.244, p < 0.05), water sorption ( r = 0.651, p < 0.001) and desorption ( r = 0.733, p < 0.001) diffusion coefficients (obtained using Fick's law of diffusion) with temperature in the second cycle. Significance High temperatures increased water sorption of simplified adhesives. Such water sorption may contribute to the failure of resin–dentin bonds.

Volcanic eruptions fromghostmagma chambers

[1] Recent studies have proposed that magma reservoirs crystallized to a virtually rigid crystal-mush can be partially remelted by diffusion of hot fluids. We show that for a crystal mush with the composition of a K-trachyte from the Campanian Ignimbrite (CI) Eruption, remelting can occur without a significant increase of the magma temperature, but simply by diffusion of H2O by the magmatic gases feeding the system. The CI origin is not the issue here, but rather the chemical and physical behavior of an almost solidified magma mass left over in a reservoir after a major eruption. To test our hypothesis, we run high pressure/high temperature laboratory experiments to study the kinetics of water diffusion, together with thermodynamics and fluid diffusion modelling. For small diffusivities, or large diffusion time, the remelting mechanism proposed above needs to be replaced by other processes as gas percolation or intrusion of a magmatic mass.

Glucose and water diffusion kinetics study in a fluorosilicone acrylate contact lens material by positron lifetime spectroscopy

A comparative study of water and glucose sorption in a rigid gas-permeable contact lens polymer, Fluoroperm 92, has been carried out using positron annihilation lifetime spectroscopy, gravimetric analysis and refractive index measurements. The water sorption in FP92 is non-Fickian, whereas for glucose sorption it changes to Fickian. Glucose molecules reduce the interaction of water molecules with the polymer, resulting in more free water than bound water. It is observed that lenses which contain more bulk-water are prone to lens dehydration and corneal desiccation. The present results indicate that, in case of diabetics, as the glucose level increases in the aqueous humor, there would be more free water than bound water, which increases the propensity for corneal desiccation. The change in refractive index with increase in glucose content indicates decrease in optical transparency of the material.

Water sorption/solubility of dental adhesive resins

Objectives This study evaluated the water sorption, solubility and kinetics of water diffusion in commercial and experimental resins that are formulated to be used as dentin and enamel bonding agents. Methods Four commercial adhesives were selected along with their solvent–monomer combination: the bonding resins were of Adper Scotchbond Multi-Purpose (MP) and Clearfil SE Bond (SE) systems, and the “one-bottle” systems, Adper Single Bond (SB) and Excite (EX). Five experimental methacrylate-based resins of known hydrophilicities (R1, R2, R3, R4 and R5) were used as reference materials. Specimen disks were prepared by dispensing the uncured resin into a mould (5.8 mm × 0.8 mm). After desiccation, the cured specimens were weighed and then stored in distilled water for evaluation of the water diffusion kinetics over a 28-day period. Results Resin composition and hydrophilicity (ranked by their Hoy's solubility parameters) influenced water sorption, solubility and water diffusion in both commercial and experimental dental resins. The most hydrophilic experimental resin, R5, showed the highest water sorption, solubility and water diffusion coefficient. Among the commercial adhesives, the solvated systems, SB and EX, showed water sorption, solubility and water diffusion coefficients significantly greater than those observed for the non-solvated systems, MP and SE ( p < 0.05). In general, the extent and rate of water sorption increased with the hydrophilicity of the resin blends. Significance The extensive amount of water sorption in the current hydrophilic dental resins is a cause of concern. This may affect the mechanical stability of these resins and favor the rapid and catastrophic degradation of resin–dentin bonds.

Polyurethane-acrylate based films as humidity sensors

Fluorescence spectroscopy, together with a conventional gravimetric method, were employed to study the mechanism and kinetics of water diffusion in UV-cured polyurethane-acrylate based adhesive films doped with organic fluorescent sensors. The diffusion of water through the films followed Fick's law during almost the whole mass sorption curve. Whilst the fluorescence data showed that boundary conditions are more complex and Fickian behaviour is only observed after different periods, depending on the molar volume of the fluorescent probe and the adhesive composition. The influence of hydrophilic monomers is discussed. Good correlation between diffusion coefficients by both methods is obtained in the range where water uptake is diffusion controlled. The fluorescence of the studied probes or labels in these films shows high sensitivity to humidity, good long-term stability and fast response time. Therefore, it appears that these doped films can be used as efficient humidity sensors.

The diffusion of calcium ion into the organic layers studied by a differential photoacoustic system

Kinetics of water and calcium ion diffusion into biological layer (pericarp) exposed to different thermal treatments was investigated using the novel concept of differential photoacoustic cell (DPC). The latter enabled the real time measurements of amplitude and phase of PA signals originating from the reference and test samples. The uptake of calcium ion and water into kernel during the cooking of maize occurs predominantly through the pericarp. This process affects the physiochemical properties of kernel causing the corresponding changes of the signal and the phase of PA signal in time. The novel concept of DPC including temperature profiles is an excellent tool to study in-situ kinetics and thermal properties of material.

The States, Diffusion, and Concentration Distribution of Water in Radiation‐Formed PVA/PVP Hydrogels

Hydrogels with various compositions of polyvinyl alcohol (PVA) and poly(1‐vinyl‐2‐ pyrrolidinone) (PVP) were prepared by irradiating mixtures of PVA and PVP in aqueous solutions with gamma‐rays from 60Co sources at room temperature. The states of water in the hydrogels were characterized using DSC and NMR T2 relaxation measurements and the kinetics of water diffusion in the hydrogels were studied by sorption experiments and NMR imaging. The DSC endothermic peaks in the temperature range −10 to +10°C implied that there are at least two kinds of freezable water present in the matrix. The difference between the total water content and the freezable water content was referred to as bound water, which is not freezable. The weight fraction of water at which only nonfreezable water is present in a hydrogel with FVP=0.19 has been estimated to be gH2O/gPolymer=0.375. From water sorption experiments, it was demonstrated that the early stage of the diffusion of water into the hydrogels was Fickian. A curve‐fit of the early‐stage experimental data to the Fickian model allowed determination of the water diffusion coefficient, which was found to lie between 1.5×10−11 m2 s−1 and 4.5×10−11 m2 s−1, depending on the polymer composition, the cross‐link density, and the temperature. It was also found that the energy barrier for diffusion of water molecules into PVA/PVP hydrogels was ≈24 kJ mol−1. Additionally, the diffusion coefficients determined from NMR imaging of the volumetric swelling of the gels agreed well with the results obtained by the mass sorption method.

Comparison of pretreatment methods on water and solid diffusion kinetics of osmotically dehydrated mangos

This study compared mass transfer during osmotic dehydration (OD), as well as some quality indices, of untreated mango samples to those pretreated by applying high intensity electric field pulses (HELPs), high pressure (HP) or supercritical carbon dioxide having the same initial cell disintegration index ( Z p ) in the range 0.50–0.58. HELP and HP pretreated samples had a higher water loss (WL) and higher solid gain (Sg) than the untreated samples. Applying supercritical carbon dioxide did not improve water loss but facilitated higher sugar gain (8–42%) than in the other pretreated samples. HP and supercritical carbon dioxide pretreatments increased the red intensity ( a values) of the mangos. The breaking force of HELP and HP pretreated samples increased with OD time.

Kinetics of water diffusion across phospholipid membranes. 1H- and 17O-NMR relaxation studies

Nuclear relaxation measurements of 1H and 17O of water have been applied to study the kinetics of water diffusion across vesicular lipid membranes. Differentiation between the intra- and extravesicular media was achieved by entrapping Mn 2+ inside the vesicles. The water permeability of egg phosphatidylcholine vesicles was found to be 2.9 · 10 −3 cm/s at 25°C, with an activation energy of 10.5 kcal/mol which remains constant through the temperature range 0–65°C. The water permeability across vesicular bilayers of L-α-dipalmitoyl phosphatidylcholine exhibited a sharp change through the lipid phase transition. The permeability in the lipid crystalline phase (45°C) was found to be 7.2 · 10 −3 cm/s with an activation energy of 7.2 kcal/mol. Below the transition at the gel phase (35°C) a permeability of 1.0 · 10 −3 cm/s was determined. The results indicate that water diffuses through lipid membranes in the liquid crystalline phase in a similar fashion to its diffusion in hydrocarbon liquids. However, when the lipids undergo a phase transition to the gel state, this similarity does not hold any more and water diffusion becomes much more restricted than in hydrocarbon liquids. The change in water permeability through the phase transition was correlated with the changes observed in the lipid segmental motion determined from 13C T 1 measurements.