Mechanism Of Moisture Diffusion Research Articles

Multi-scale moisture diffusion modeling and analysis of carbon/Kevlar-fiber hybrid composite laminates under the hygrothermal aging environment

Hybrid fiber reinforced polymer (HFRP) can have more complex micro moisture diffusion process than single fiber composite, owing to diverse hygroscopic properties of dissimilar fibers. Thus, elucidating the multi-scale moisture diffusion mechanism of HFRP through experimental method becomes a challenging endeavor. To this end, a multi-scale moisture diffusion modeling approach is proposed to investigate the moisture diffusion behavior of carbon/Kevlar HFRP under the hygrothermal aging environment. Leveraging Fick's law as a foundation, a combination of multi-scale moisture diffusion model and finite element method is employed. To validate the effectiveness of model, accelerated aging experiments are conducted on HFRP samples with various stacking sequences. By SEM characterization, the surface aging on aged Kevlar fibers and the debonding of aged fiber/matrix interface are conspicuously observed. Based on this model, the moisture diffusion behaviors in different HFRP configurations are simulated and analyzed to reveal the micro-, meso‑ and macro-scale moisture diffusion and resistance mechanisms. Our findings highlight the profound influence of factors such as fiber type, fiber content, fiber placement, hygroscopic properties of constituents, and their synergistic effects on moisture absorption and saturated moisture absorption rates. Finally, the hygroscopic properties of HFRP laminate with different stacking sequences are predicted by multi-scale model. This work endeavor furnishes valuable insights and guidelines for the design and analysis of moisture-resistant HFRP.

Investigation of the Mechanism of Hidden Defects in Epoxy Asphalt Pavement on Steel Bridge Decks Under Moisture Diffusion Using Nondestructive Detection Techniques

This study conducts a rigorous analysis of the moisture diffusion mechanism that undermines the adhesive layer of epoxy asphalt (EA) pavement on steel bridge decks, thereby fostering latent distresses. Furthermore, a novel and highly efficacious approach for detecting these concealed distresses is introduced. The findings of water vapor permeability tests conclusively reveal that the moisture diffusion coefficients of the upper and lower layers of the EA pavement stand at 0.1238 mm2/s and 0.0879 mm2/s, respectively, highlighting this disparity as the primary trigger for concealed issues like pavement delamination and swelling. Leveraging the combined capabilities of three‐dimensional ground‐penetrating radar (3D‐GPR) and infrared thermography, this research reliably detects, identifies, and pinpoints concealed defects at three strategic locations on the steel bridge deck. The integration of these two technologies has exhibited remarkable proficiency in identifying concealed damages. Consequently, this study lays a substantial foundation for evaluating and detecting concealed distress in EA pavements atop steel bridge decks.

Investigating the degradation mechanisms of moisture on the reliability of integrated low-k stack

This study investigates the phenomenon of moisture diffusion within integrated circuits, focusing on low-k and SiCN dielectric materials. The research confirms the main pathway of moisture diffusion occurring through interfaces between materials. The various steps involved in the moisture diffusion mechanism are identified and linked to electrical characterizations, including variations in capacitance, modifications in leakage current behavior, and dielectric breakdown. A modification in the conduction mechanism is observed. The investigation also highlights different types of bonds formed between the dielectrics and moisture based on literature review and baking process. Saturated samples exhibit a partial reversibility after a 250 °C bake but do not fully recover. Nevertheless, reversibility is shown to be dependent on the moisture content reached prior to baking.

Effect of Ultrasonic Power on Water Removal Kinetics and Moisture Migration of Kiwifruit Slices During Contact Ultrasound Intensified Heat Pump Drying

The experiments of contact ultrasound intensified heat pump drying (CUHPD) of kiwifruit slices were conducted to investigate the effect of ultrasonic power on dehydration process and water migration of kiwifruit during CUHPD. The results clarified that contact ultrasound (CU) application could reduce the drying time of HPD significantly, and the rise of ultrasonic power had stronger reinforcing effect on dehydration rate. Weibull distribution function could simulate the dehydration process of CUHPD of kiwifruit with high precision, and the β values verified that ultrasonic power improvement could transform the moisture diffusion mechanism of CUHPD from total internal moisture diffusion control to partial internal moisture diffusion control. The Dcal values were 2.304 × 10−9~4.026 × 10−9 m2/s and increased as the rise of ultrasonic power. The scanning electron microscopy results illustrated that increasing ultrasonic power could produce more porous and spacious microstructure which was beneficial for water migration. The low-field nuclear magnetic resonance results elucidated that free water, immobilized water, and bound water in kiwifruit migrated and changed during CUHPD. Free water with the highest mobility was the most abundant water in kiwifruit, and was the first kind of water to be completely removed. With drying progressed, the contents of immobilized water and bound water gradually increased and then decreased, but they were not completely removed. The increasing in ultrasonic power was beneficial to promoting internal water migration and shortening the required dehydration time, especially for free water. Proton density images visualized that increasing ultrasonic power could significantly promote the water diffusion from internal kiwifruit outward the surface, and thereby accelerate the rate of water removal. Therefore, CU application is a suitable method to accelerate the water diffusion and moisture migration of HPD process.

Effects of cyclic deformation on a barrier thin film for flexible organic optoelectronic devices

Effects of cyclic bending on the encapsulation properties of a barrier thin film are investigated. Water vapor transmission rate (WVTR) of the given barrier film is measured after variously cyclic bending conditions using a calcium corrosion test technique. Experimental results show that microcracks in the barrier thin film are found after applying a certain number of bending cycles. They are responsible for an increase in WVTR. Given a bending radius, a greater number of bending cycles leads to a larger amount of damage, and consequently a greater extent of moisture ingress. A smaller bending radius produces a greater amount of damage than a larger one, in a short period of loading time (≤104 cycles). However, after 105 cycles of cyclic bending, the amount of damage reaches a saturated level regardless of bending radius, as all the WVTR values become comparable. A simplified 3D finite element analysis (FEA) model is established in microscale to analyze the moisture diffusion mechanism. Numerical results show that, with the presence of cracking and delamination, the WVTR value increases significantly. Good agreement between the simulation and experimental measurements on WVTR confirms that the failure mechanism involves cracking and delamination under cyclic bending. The 3D FEA modeling developed could offer a method to predict the change of WVTR in correlation with cracking and delamination in the barrier thin film.

Correction: Analysis of moisture diffusion mechanism in structured lipids using magnetic resonance imaging

Correction for ‘Analysis of moisture diffusion mechanism in structured lipids using magnetic resonance imaging’ by Sravanti Paluri et al., RSC Adv., 2015, 5, 76904–76911.

Analysis of moisture diffusion mechanism in structured lipids using magnetic resonance imaging

The mechanism of moisture migration from a high water-content gel-layer to an adjacent lipid layer was characterized.

Mathematical and Simulation Modelling of Moisture Diffusion Mechanism during Plastic IC Packages Disassembly

Reuse of plastic IC packages disassembled from printed circuit boards (PCBs) has significant environmental benefits and economic value. The interface delamination caused by moisture diffusion is the main failure mode of IC packages during the disassembling process, which greatly reduces the reusability and reliability of disassembled IC packages. Exploring moisture diffusion mechanism is a prerequisite to optimize prebaking processes before disassembling that is an effective way to avoid the interface delamination. To this end, a computational model with variable boundary conditions is developed based on the different combination state of water in IC packages. The distribution characteristics and mechanism of moisture diffusion behavior are analyzed including the humidity distribution field and the relation among baking temperature, water loss rate, and baking time during baking process, and then the results are validated by FEA simulation based on the improved definition of relative moisture concentration. Baking under variable temperature is proposed and compared with the baking process and baking efficiency under constant temperature to find out the optimized baking parameters. Finally, a set of curves which indicate the relation between baking energy consumption and temperature are determined under actual industrial baking experiments, which could be used as references to develop industrial standards for PCB disassembling process.

Process Modeling and Optimization Studies in Drying of Current Transformers

The vacuum drying process for drying of paper in current transformers was modeled with an aim to develop an understanding of the drying mechanism involved and also to predict the water collection rates. A molecular as well as macroscopic approach was adopted for the prediction of drying rate. Ficks law of diffusion was adopted for the prediction of drying rates at macroscopic levels. A steady state and dynamic mass transfer simulation was performed. The bulk diffusion coefficient was calculated using weight loss experiments. The accuracy of the solution was a strong function of the relation developed to determine the equilibrium moisture content. The actually observed diffusion constant was also important to predict the plant water removal rate. Thermo gravimetric studies helped in calculating the diffusion constant. In addition, simulation studies revealed the formation of perpetual moisture traps (loops) inside the CT. These loops can only be broken by changing the temperature or pressure of the system. The change in temperature or pressure changes the kinetic or potential energy of the effusing vapor resulting in breaking of the loop. The cycle was developed based on this mechanism. Additionally, simulation studies also revealed that the actual mechanism of moisture diffusion in CT's is by surface jumps initiated by surface diffusion balanced against the surrounding pressure. Every subsequent step in the cycle was to break such loops. The effect of change in drying time on the electrical properties of the insulation was also assessed. The measurement of capacitance at the rated voltage and one third of the rated voltage demonstrated that the capacitance change is within the acceptance limit. Hence, the new cycle does not affect the electrical performance of the CT.

Mechanism of Heat and Mass Transfer in Moist Porous Materials

A mathematical simulatin carried out to study the physical mechanisms of moisture diffusion into hygroscopic fabric during humidity transients. On the basis of a mathematical model developed to describe the coupled heat and moisture transfer in wool fabric, the moisture–sorption mechanisms are investigated for fabrics made from fibers with different degrees of hygroscopicity. Theoretical predictions on the moisture uptake and temperature changes under humidity transients are compared with those measured previously in a sorption–cell experiment for fabrics made from wool, cotton, acrylic fiber, and polypropylene fiber. It is concluded that hte physical mechanism of moisture diffusion into highly hygroscopic fibers such as wool and cotton can be described by a two stage moisture diffusion process: a fast Fickian diffusion with a concentration–dependent diffusion coeffecient and slow diffusion with a time–dependent diffusion coefficient. For weakly hygroscopic fibers such as polypropylene fiber, the moisture sorption process can be described by a single Fickian diffusion with a constant diffusion coefficient. Heat transfer in moist textiles takes place by conduction, infra–red radiation, and distillation. Until the fiber is saturated, the evaporation process is determined mainly by the fiber’s sorption properties. Conductivity increases with water content and also depends on a fiber’s sorption properties. Key words: Moisturediffusion; hygrospic fabrics; humidity transients

Mechanism analysis of ultrasonic treatment on SU-8 swelling in UV-LIGA technology

In SU-8 UV-LIGA technology, the precision and controllability of electroformed metal structure are not satisfied because of SU-8 photoresist swelling during electroforming process. To reduce SU-8 swelling and further improve the dimensional precision of electroformed microstructure, the authors originally introduce ultrasonic treatment in the fabrication process of SU-8 mould. The experimental results indicate that the swelling property of cross-linked cured SU-8 varies with ultrasonic time. SU-8 swelling is diminished when it is treated less than 15 min by ultrasonic, but the swelling is increased if the ultrasonic time is extended to 20 min. To explore ultrasonic treatment mechanism of SU-8 swelling, the contact angle between SU-8 and electroforming solutions in different ultrasonic time was measured, and the result presents that SU-8 surface hydrophilicity is affected by ultrasonic treatment. Besides, the contact angle trend is consistent with the curve of SU-8 swelling removal ratio in different ultrasonic time. Subsequently, ultrasonic treatment mechanism of SU-8 swelling is proposed based on ultrasonic mechanical scission of polymer chain and moisture diffusion mechanism.

Determination of the Bulk Moisture Diffusion Coefficient for Corn Starch Using an Automated Water Sorption Instrument

The bulk moisture diffusion coefficient (Db) is an important physical parameter of food ingredients and systems. However, the traditional method of measuring Db using saturated salt solutions is very time-consuming and cumbersome. New automated water sorption instruments, which can be used to conveniently and precisely control both relative humidity and temperature, provide a faster, more robust method for collecting the data needed for determining Db. Thus, the objectives of this study were to (1) investigate the use of the DVS instrument for collecting the data needed for determining the adsorption (Dba) and desorption (Dbd) bulk moisture diffusion coefficients for dent corn starch as a function of relative humidity and (2) determine the effect of temperature on Dba for dent corn starch at a constant relative humidity. Kinetic water sorption profiles of dent corn starch were obtained at eight relative humidity values ranging from 10 to 80% at 10% intervals at 25 degrees C and at five temperatures, 15, 20, 25, 30, and 35 degrees C, at 50% relative humidity using a DVS instrument. Db was calculated from the kinetic water sorption profiles using the full solution of Fick's second law for the thin slab model, as well as the slope method, a simplification of the full model. The Dba of dent corn starch at 25 degrees C reached a maximum at intermediate relative humidity values, after which Dba decreased due to a change in the moisture diffusion mechanism from vapor to liquid diffusion. The Dbd of dent corn starch at 25 degrees C remained nearly constant as a function of relative humidity. The Dba for dent corn starch increased as temperature increased from 15 to 35 degrees C, with an activation energy of 38.85 +/- 0.433 kJ/mol.

Anomalous debonding behavior of a polymer/inorganic interface

Adhesion and subcritical debonding at the interface between a thin diglycidyl ether of bisphenol F polymer layer and either SiN x or SiO 2 passivated silicon substrates are described. The interface is characterized by weak hydrogen bonding. Prolonged exposure to a moist environment resulted in a time-dependent decrease in adhesion. Subcritical debond-growth rates as a function of applied loads were sensitive to temperature and relative humidity, and greatly accelerated in the presence of cyclic loading. Of particular interest was the occurrence of an anomalous region of persistent debonding that developed below ∼10 −8 m s −1 under both monotonic and cyclic loading. In this region, debond-growth rates were characterized by a weak dependence on the applied loads, a strong dependence on moisture activity, and the absence of a measurable threshold below which debonding could not be measured. We propose a new stress-dependent transport model that describes the moisture diffusion mechanism responsible for this anomalous behavior.

Composite degradation due to fluid absorption

This experimental study investigated the combined effects of liquid (water, Skydrol, fuel, and dichloromethane) absorption, impact damage and drilling on aramid and carbon fibre/epoxy composites. The static and fatigue behaviour of the composite samples was determined after the treatments. The response to impacts was analysed, and elastic and absorbed energy were measured. The mechanism of moisture diffusion into the composites was studied and a method for the accelerated ageing of the composites applied. Penetrant radio-opaque dye and stereo-radiography were used to determine the onset and growth of damage during fatigue life and the decay of mechanical characteristics. Optical microscopy was used to investigate the microscopic mechanisms of absorption and damage, in order to propose interpretative models.

Physical Mechanisms of Moisture Diffusion into Hygroscopic Fabrics during Humidity Transients

A mathematical simulation carried out to study the physical mechanisms of moisture diffusion into hygroscopic fabrics during humidity transients is reported. On the basis of a mathematical model developed to describe the coupled heat and moisture transfer in wool fabric, the moisture-sorption mechanisms are investigated for fabrics made from fibers with different degrees of hygroscopicity. Theoretical predictions on the moisture uptake and temperature changes under humidity transients are compared with those measured previously in a sorption-cell experiment for fabrics made from wool, cotton, acrylic fiber, and polypropylene fiber. It is concluded that the physical mechanism of moisture diffusion into highly hygroscopic fibers such as wool and cotton can he described by a two-stage moisture-diffusion process: a fast Fickian diffusion with a concentration-dependent diffusion coefficient and a slow diffusion with a time-dependent diffusion coefficient. For weakly hygroscopic fibers such as polypropylene fiber, the moisture-sorption process can be described by a single Fickian diffusion with a constant diffusion coefficient. Through theoretical calculations of the distributions of moisture concentration in the air of fabric void space, fiber moisture content, and temperature through fabric thickness, we show that moisture diffusion into a fabric through air is a fast process for all the fabrics studied. Meanwhile, the moisture diffusion into fibers is coupled with the heat-transfer process, which is much slower and is dependent on the ability of fibers to absorb moisture. The strength of the coupling effect is a function of a number of fiber properties, such as the moisture-sorption isotherms, water-diffusion coefficient, fiber diameter, and heat of sorption.

The effect of hygrothermal fatigue on physical/mechanical properties and morphology of neat epoxy resin and graphite/epoxy composite

AbstractThe effect of moisture absorption, desorption, and thermal spiking on the physical/mechanical properties of TGDDM/DDS epoxy resin was investigated and compared to the Gr/Ep composite. The mechanism of moisture diffusion in the neat resin was described on the morphological level. The diffusion rate of moisture in epoxy resin was found to depend on the mobility of molecular chains within an inhomogeneous epoxy network. Two well‐known concepts of plasticization of amorphous polymers, the lubricity theory and the gel theory, were invoked to describe the interactions between the absorbed moisture and the resin network. Slight permanent changes in properties of the neat resin were observed after one absorption‐desorption cycle. In the thermal spiking experiment, only the spiking temperature above the glass transition of the moisture saturated epoxy resins changed their internal structure and produced very small (thin) microcracks. By comparison with the neat epoxy resin, the Gr/Ep composites contain the reinforcement‐matrix boundary region, characterized by the highest restrictions to molecular mobility. The absorbed moisture during the static hygrothermal fatigue cannot effectively plasticize this region. But during thermal spiking, the formation of microcracks is observed within the reinforcement‐matrix boundary region as well as an increase in the moisture content.