Guggenheim Anderson De Boer Research Articles

Determination of Moisture Sorption Isotherm using Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) Models, Germination Capacity and Index Vigor of Soybean during Storage

Understanding the interaction between the equilibrium moisture content of a product and the surrounding air is crucial for guaranteeing product quality and preserving its characteristics throughout storage. The study of this tendency may be conducted utilizing sorption isotherms. This research aimed to study the moisture sorption characteristics of soybeans during storage, identify the most suitable mathematical model for the experimental data, and examine the relationship between the germination capacity and vigor index of soybeans with their moisture content and water activity. Moisture sorption characteristics of soybean, Anjasmara variety, were investigated at temperatures of 30ᵒC, 40ᵒC, and 50ᵒC, and water activities of 0.08 to 0.80, and were modelled using two different mathematical models, Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB). Both two mathematical models, BET and GAB, were found to effectively describe the moisture sorption data based on regression analyses and goodness of fit. Each model was statistically evaluated by coefficient of determination and deviation standard. The moisture sorption behaviour of soybean seeds displayed a sigmoidal pattern. The GAB models have been suggested to estimate the moisture content at certain humidity levels at 30ᵒC, 40ᵒC, and 50ᵒC temperatures. The BET models were suitable for temperatures between 30ᵒC and 40oC. The vigor and germination indicated exhibited a progressive and optimal trend at a water activity level of 0.32, followed by a decline at all three temperatures.

Physical Properties of Selected Fruit Fibre and Pomace in the Context of Their Sustainable Use for Food Applications

Pomace, a waste product, generates a huge problem in the fruit and vegetable industry. Numerous studies prove that pomace and fibre are valuable sources of many nutrients. Due to their properties, their popularity is growing in many industries. Water vapour isotherms and kinetics were determined for selected fruit fibre and pomace. The activity and water content, colour, apparent and bulk density, and material structure were also investigated. In addition, the thermal stability of the tested fibres and pomace was examined. Fibre and pomace from chokeberries, apples and currants were used in the research. The determined kinetic curves proved that apple fibre absorbed more water vapour. The isotherms were found to have a shape characteristic of type III sorption isotherms. The Guggenheim–Anderson–de Boer model (GAB) described experimental data for sorption isotherms well (taking an RMS value of less than 10% as a good fit of the model to the sorption data). Thermogravimetric analysis showed good thermal stability, and all analysed fruit fibre and pomace showed similar behaviour in the three main stages of weight loss. The results suggest that the analysed waste materials can be used for different applications, including flour replacements for food products or filling materials in edible packaging films.

Antimicrobial gelatin-based films with cinnamaldehyde and ZnO nanoparticles for sustainable food packaging

Cinnamaldehyde (CIN), a harmless bioactive chemical, is used in bio-based packaging films for its antibacterial and antioxidant properties. However, high amounts can change food flavor and odor. Thus, ZnO nanoparticles (NPs) as a supplementary antimicrobial agent are added to gelatin film with CIN. The CIN/ZnO interactions are the main topic of this investigation. FTIR-Attenuated Total Reflection (ATR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were utilized to investigate CIN/ZnO@gelatin films. Transmission electron microscope (TEM) images revealed nanospheres morphology of ZnO NPs, with particle sizes ranging from 12 to 22 nm. ZnO NPs integration increased the overall activation energy of CIN/ZnO@gelatin by 11.94%. The incorporation of ZnO NPs into the CIN@gelatin film significantly reduced water vapour permeability (WVP) of the CIN/ZnO@gelatin film by 12.07% and the oxygen permeability (OP) by 86.86%. The water sorption isotherms of CIN/ZnO@gelatin were described using Guggenheim-Anderson-de Boer (GAB) model. The incorporation of ZnO NPs into the CIN@gelatin film reduced monolayer moisture content (M0) by 35.79% and significantly decreased the solubility of CIN/ZnO@gelatin by 15.15%. The inclusion of ZnO into CIN@gelatin film significantly decreased tensile strength of CIN/ZnO@gelatin by 13.32% and Young`s modulus by 18.33% and enhanced elongation at break by 11.27%. The incorporation of ZnO NPs into the CIN@gelatin film caused a significant decrease of antioxidant activity of CIN/ZnO@gelatin film by 9.09%. The most susceptible organisms to the CIN/ZnO@gelatin film included Candida albicans, Helicobacter pylori, and Micrococcus leutus. The inhibition zone produced by the CIN/ZnO@gelatin film versus Micrococcus leutus was 25.0 mm, which was comparable to the inhibition zone created by antibacterial gentamicin (23.33 mm) and cell viability assessment revealed that ZnO/CIN@gelatin (96.8 ± 0.1%) showed great performance as potent biocompatible active packaging material.

Evaluation of surface structure, water sorption properties, water plasticizing effect, and color stability of dried chrysanthemums

The storage stability of two varieties of chrysanthemum (Chrysanthemum morifolium Ramat. cv. HSGJ and C. morifolium Ramat. cv. JSHJ)was evaluated in this study through an analysis of their water binding behavior. This involved examining the surface structure of the powdered dried chrysanthemums, studying the water sorption characteristics, and quantifying the water plasticizing effect. In comparison to JSHJ, powdered HSGJ had a smaller particle size and more hydrophilic groups on its surface. Additionally, it exhibited significantly higher characteristic values of adsorbed water, excluding the number of adsorbed monolayers (Nam). The sorption of water by the powdered chrysanthemums conformed to a type II isotherm. The Guggenheim–Anderson–deBoer (GAB) model was trustworthy for predicting water sorption within the range of aw from 0.112 to 0.907 and temperatures between 20 and 40 °C. The exothermic interactions between water molecules and the primary sorption sites of the powdered samples became more powerful when the temperature decreased. Powdered chrysanthemums can be preserved at 30 °C if the humidity is below 0.0852 g/g for HSGJ and 0.0766 g/g (d.b) for JSHJ. The color changes of powdered samples were not significantly affected when stored in a glassy state. This study is significant for identifying the drying endpoint, predicting shelf life, and choosing suitable packaging materials for dried chrysanthemums.

Water sorption modeling and monolayer of biological and food materials

Despite water molecules are strongly hydrogen bonding to hydrophilic solids, the Brunauer-Emmet-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) surface adsorption models have been widely accepted to describe water sorption properties of biological and food materials. These mathematically quite similar models use parameters which include a theoretical ‘monolayer’ value and one or two other parameters which describe ‘surface affinity’ in thermodynamic terms as heat of sorption. A high surface affinity indicates a strong surface binding of water molecules and preferential monolayer adsorption prior to multilayer sorption. Conversely, biological materials are water plasticized and suffer physicochemical changes at various stages of water sorption. Dynamic water sorption measurements often show regions where time-dependent changes in material characteristics, such as viscous flow and crystallization, may occur as a result of the glass transition. The two or three parameters of the BET and GAB models, respectively, are useful in the analysis of water sorption characteristics of individual substances, although the existence of a monolayer particularly in multicomponent materials may not be justified. Fitting the models to experimental data may occur rather for empirical than theoretical reasons.

Impact of maltodextrin, egg white protein addition and microwave-assisted foam mat drying on drying kinetics, microstructures, physicochemical and quality attributes of jackfruit juice powder

This study aimed to analyze the effect of maltodextrin and egg white protein addition on the physicochemical, functional, microstructures, and drying characteristics of microwave-assisted foam mat-dried (MFD) jackfruit juice powders. A microwave intensity of 1 W/g was employed to obtain optimal yield and high quality of the powders. The concentration of maltodextrin influenced the drying rate of the jackfruit juice powders, with higher concentrations resulting in a faster drying rate. The data obtained from Microwave-assisted foam mat drying of the jackfruit juice powder data were best fitted by the Page and Logarithmic kinetic models. The moisture content of the jackfruit powders ranged from 1.323 ± 0.75 g/100 g (w.b.) to 1.712 ± 0.72 g/100 g (w.b.). Powders produced at higher maltodextrin/egg white protein ratios exhibited superior flowability, lower cohesiveness, smoother and smaller particle sizes, but degraded color quality. The maltodextrin concentration significantly influences the antioxidant properties of the powders. The water sorption of jackfruit juice powder was determined, and the findings showed a good fit with the Guggenheim–Anderson–de Boer (GAB) model.

Effects of dextran molecular weight on starch retrogradation and technological properties of Chinese steamed bread: Based on the rubber/glass transition

From the perspective of rubber/glass transition, this study clarified that the impact of dextran on retarding hardening behavior and slowing starch retrogradation of Chinese Steamed Bread (CSB) depended on its molecular weight and concentration level. Guggenheim-Anderson-de Boer (GAB) model was fitted to explore critical behavior changes in rubber/glass transition of CSB. Incorporation of high molecular weight dextran enhanced the elasticity of dough and porosity of CSB, reduced the aging and hardening degree of CSB at appropriate addition levels. CSB hardness showed a growing tendency during storage, while macromolecular dextran reduced the hardness and retrogradation degree by 22.87 % and 67.53 %. Dextran with high molecular weights lowered the glass transition temperature (Tg) and improved the moisture sorption and molecular mobility of CSB under various relative humidity (RHs) conditions by providing hydrophilic sites or intermolecular space to bind water molecules. Meanwhile, it reinforced the binding between denatured gluten and gelatinized starch. Both of them devoted to starch retrogradation inhibition and stable quality maintenance of CSB. CSB is suggested to maintain stable quality at room temperature with RHs ≤33 % to prevent rubber/glass transition. This work provided theoretical guidance for fractionation application of dextran to regulate the quality and extend the shelf-life of flour products.

Study on the mechanism and law of temperature, humidity and moisture content on the mechanical properties of molded fiber products

The change of temperature, humidity and moisture content (MC) will lead to the change of mechanical properties of molded fiber products (MFP). However, it is difficult to decouple the effects of temperature, humidity and MC on the mechanical properties of MFP, and predict the mechanical properties of MFP during the use. In this study, the laws and mechanism of mechanical properties of MFP with ambient temperature, humidity and MC were studied. The results showed that the direct effect of temperature (20−70 °C) on mechanical properties of MFP was insignificant, and the mechanical properties of MFP were mainly changed by MC. The MC was related to ambient temperature and humidity, and the relationship between the three could be described by the modified Guggenheim-Anderson-de Boer (GAB) model (20−70 °C and 30 %–90 % relative humidity). With the increase of MC, the elastic modulus and fracture strain was increased and decreased linearly, the yield strength and failure strength were presented GaussAmp laws, and the failure strain was presented asymptotic regressed distribution law. Two fracture modes of MFP, brittle fracture and ductile fracture, were revealed by the scanning electron microscopy of the mesoscopic fiber structure of sugarcane bagasse molded fiber products. The mathematical models and the changes of fiber structure were verified by wheat straw molded fiber products and waste paper molded fiber products. This study was contributed to understand the effects and mechanism of the change of temperature, humidity and MC on the mechanical properties of MFP.

Hygroscopicity of nitrocellulose with different nitrogen content

AbstractResearch on the hygroscopic behavior of NC is essential because it affects the mechanical properties, combustion properties, and safe storage of NC‐based products. In this study, Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) are used to characterize the chemical structure, crystal structure, and microscopic morphology of NC, respectively. The moisture adsorption isotherms of NC fibers with different nitrogen content are determined by dynamic vapor sorption (DVS) and fitted with Hailwood‐Horrobin (H−H) and Guggenheim‐Anderson‐de Boer (GAB) models. The specific surface area and surface energy of NC are also measured by inverse gas chromatography (IGC). The results show that as the nitrogen content of NC increases, the intensity of the −OH characteristic absorption peak is weakened, the crystallinity does not change much, the number of cracks and pores on the NC fiber surface increases, and the equilibrium moisture content (EMC) of the NC decreases in general. In addition, the fitting results based on the H−H and GAB models show that, under low humidity conditions, the EMC value of NC is determined by the adsorbed water content of the monolayer, which is mainly related to the −OH content in NC. However, with the increase of humidity, the EMC value of NC is gradually determined by the multilayer adsorbed water content, which is influenced by both the nitrogen content and the fiber cleavage structure. Meanwhile, the IGC results show that the surface energy of the NC consists mainly of the dispersive surface energy (values >46 mJ m−2), with the specific surface energy contributing approximately 25 mJ m−2. The total surface energy of NC and the bonding strength between NC molecules and water molecules decrease with increasing nitrogen content.

A novel poly(vinyl alcohol)/silica composite film with “spherical crystal interlocking structure” and its barrier and enhancement mechanism

Using the semi-crystalline poly(vinyl alcohol) (PVA) as the polymer matrix and silica nanoparticles (SNPs) as the reinforcing filler, composite films with excellent water vapor barrier, high tensile strength, visible light transmission and ultraviolet (UV) shielding performances were constructed via a simple heat treatment process, during which the films underwent dehydration cross-linking and isothermal recrystallization to form a "spherical crystal interlocking structure". Both the dosage and average particle size of SNPs significantly affected the barrier property, and the optimal values were 7 wt% and 15 nm, respectively. The heat treatment further improved the water resistance, mechanical strength, and barrier property to a great extent. Moreover, different theoretical models including Guggenheim Anderson de Boer (GAB), Brunauer Emmett and Teller (BET), Hailwood-Horribon (H-H) model, crystallinity model and Fick's law model were successfully used to explain the water vapor barrier mechanism. The water vapor permeability (WVP) of the optimized composite film was reduced to 2.20 × 10−12 g·m/(m2·Pa·s) at 37°C and 65% RH, while the tensile strength was increased up to 116.8 MPa. In addition, the absorption rate of ultraviolet of the film after heat treatment increased from 13% to 92.0%, while the transmittance of visible light remained above 78%.

Assessment of the performance of Cromarty's equation to predict seed equilibrium moisture content during drying

For conventional seed (gene)banking of orthodox seeds, it is essential to effectively dry the seeds and maintain a low moisture content (MC). Cromarty's equation describes the MC and relative humidity (RH) relationship of drying seeds, based on their oil content, and can be used to predict the MC seeds would reach when dried to equilibrium in a controlled environment (RH, temperature). However, the equilibrium MC-RH relationship ('isotherm') varies not only between seeds of different species and depending on temperature, but also on whether seeds are losing (desorbing) or gaining (adsorbing) moisture. The reliability of Cromarty's equation in predicting the equilibrium MC for drying different seed species was examined and compared with the Guggenheim-Anderson-De Boer (GAB) equation, to model both desorption and adsorption data. Cromarty's equation provided a good fit to the desorption data for oilseed rape and barley (R 2 = 0.98). For yellow mustard, seed MC was overestimated and for lupin, wheat, buckwheat and pea, the MC equilibria predicted by Cromarty's equation were closer to the adsorption data. Overall, the GAB equation provided a better fit of the data. While Cromarty's equation is a useful tool for estimating the MC of seeds under a given environment, it should be used with caution in critical situations.

Effect of Posidonia oceanica on the hygrothermal characterization of compacted earth blocks

A hygrothermal characterization of new construction materials, namely unstabilized and Posidonia oceanica fiber stabilized compressed earth blocks, were studied in this work. In the first part, the sorption-desorption isotherms of unstabilized blocks were compared with others stabilized with raw and treated fibers to detect the effect of adding fibers. The results revealed an improvement in hygric properties after the addition of raw fibers. Moreover, the Guggenheim-Anderson-de Boer (GAB), the Oswin, and Brunauer, Emmet, and Teller (BET) models successfully fitted experimental sorption-desorption isotherms curves. In the second step, the moisture buffer value and water vapor permeability were evaluated under dynamic conditions. According to the classification of the NORDTEST project, the innovative and new compacted earth blocks studied in this paper seem to be excellent moisture regulators because they have an MBV greater than 2 g/ (m2. %RH). In fact, BAFBB samples (block with crushed Posidonia oceanica) achieved the best results. These formulations recorded an ideal water buffer coefficient equal to 2.66 g/ (m2.%RH)

Influence of plant proteins blend or polydextrose on freeze-dried açaí (Euterpe oleracea) sorption isotherms and thermal properties

The influence of polydextrose or plant proteins blend, as a drying aid in freeze-dried açaí pulp, was evaluated regarding stability by vapor sorption isotherms at 20 °C in a water activity range of 0.1–0.95, obtained by vapor sorption analyzer and by saturated salt solutions, and the enthalpic properties were obtained by differential scanning calorimetry.The experimental isotherms data presented a good fit to the Peleg and Guggenheim-Anderson-de Boer (GAB) equations, açaí powder with polydextrose presented a Brunauer-Emmett-Teller (BET) type III, while the açaí powder without and with a plant proteins blend, type II. The freeze-dried açaí powders showed two endothermic peaks between −15 °C and 10 °C, probably related to linoleic and oleic fatty acids fusion. Fusion enthalpies of these peaks were lower when a carrier agent was used, which could be explained by a lower lipids content (25.0 J/g and 3.5 J/g for powder without the carrier and 12.0 J/g and 1.5 J/g for powder with plant proteins blend). The glass transition temperatures were between 49 °C and 58 °C, depending on the water activity, for powder without carriers and from 45 °C to 54 °C for the one with proteins.

Physical origin of adsorption heat and its significance in the isotherm equation

Adsorption heat is a cornerstone concept underpinning almost all the existing theoretical isotherms for porous media. Yet, it remains elusive what this concept stands for and what are the physical sources for it. Here, a rigorous thermodynamic formulation is derived for the adsorption process with the aid of the law of mass action, leading to an expression of adsorption heat as the external chemical potential difference between two adjacent adsorbate layers. The interaction between adsorbent and adsorbates like van der Waals is theoretically identified as the intermolecular source for the change of adsorption heat. Thereby, adsorption heat is formulated as a spatially varied function of the distance to adsorbent surfaces. This adsorption heat function facilitates the establishment of a two-parameter sorption isotherm equation. The equation can be theoretically converted to two widely used adsorption isotherm equations, namely Brunauer–Emmet–Teller (BET) and Guggenheim-Anderson-de Boer (GAB) equations, and shows excellent performance in capturing experimental isotherm data of a wide array of materials. The comparative analysis demonstrates that the derived two-parameter isotherm equation outperforms the two-parameter BET equation and the three-parameter GAB equation in most cases. Such performance verifies the generality of the derived isotherm equation, thus further confirming the validity of the derived formulation of adsorption heat.

Model-based investigation of water adsorption in Achira (Canna edulis K.) biscuits

The water adsorption properties of Achira biscuits were investigated using a mathematical model-based strategy to understand the relationship between water activity and moisture content due to the fact that it is highly relevant for its storage. For this purpose, the water adsorption isotherms of commercial Achira biscuits were firstly experimentally determined by the dynamic dew point (DDI) method at 25, 35, and 45 °C and ATR–FTIR spectroscopy was used to detect the functional groups. Secondly, the Guggenheim-Anderson-de Boer (GAB) equation, 4 empirical models (Smith, Oswin, Peleg and DLP), and 5 machine-learning techniques (Regression trees, Random Forest, k-Nearest Neighbors, Artificial Neural Networks and Support Vector Machine) were used to model the isotherms. The fundamentals of water adsorption were analyzed via GAB model parameters, adsorption surface area, spreading pressure, effective pore size, and thermodynamic properties, such as enthalpy-entropy and Gibbs free energy. The experimental results reflected a type III water isotherm and a moderate temperature effect. The GAB model quantified the effect of temperature on the adsorption properties, which reflected a lower degree of hygroscopicity at high temperatures. The Support Vector Machine Learning model provided the best mathematical description of the water adsorption isotherms considering the temperature effect (MRE<3% and R2adj>99%).

Effect of Germinated Sorghum Extract on the Physical and Thermal Properties of Pre-Gelatinized Cereals, Sweet Potato and Beans Starches.

Starches from different botanical sources are affected in the presence of enzymes. This study investigated the impact of α-amylase on several properties of pre-gelatinized starches derived from chickpea (Cicer arietinum L.), wheat (Triticum aestivum L.), corn (Zea mays L.), white beans (Phaseolus vulgaris), and sweet potatoes (Ipomoea batatas L.). Specifically, the water holding capacity, freezable water content, sugar content, and water sorption isotherm (adsorption and desorption) properties were examined. The source of α-amylase utilized in this study was a germinated sorghum (Sorghum bicolor L. Moench) extract (GSE). The starch samples were subjected to annealing at temperatures of 40, 50, and 60 °C for durations of either 30 or 60 min prior to the process of gelatinization. A significant increase in the annealing temperature and GSE resulted in a notable enhancement in both the water-holding capacity and the sugar content of the starch. The ordering of starches in terms of their freezable water content is as follows: Chickpea starch (C.P.S) > white beans starch (W.B.S) > wheat starch (W.S) > chickpea starch (C.S) > sweet potato starch (S.P.S). The Guggenheim-Anderson-de Boer (GAB) model was only employed for fitting the data, as the Brunauer-Emmett-Teller (BET) model had a low root mean square error (RMSE). The application of annealing and GSE treatment resulted in a shift of the adsorption and desorption isotherms towards greater levels of moisture content. A strong hysteresis was found in the adsorption and desorption curves, notably within the water activity range of 0.6 to 0.8. The GSE treatment and longer annealing time had an impact on the monolayer water content (mo), as well as the C and K parameters of the GAB model, irrespective of the annealing temperature. These results can be used to evaluate the applicability of starch in the pharmaceutical and food sectors.

Impact of instant controlled pressure drop texturing on the drying of yellow mealworms

Abstract Insects are increasingly being evaluated as promising protein sources for the food and feed sectors. However, to be accepted as a viable food source, insects must undergo proper processing. Drying is a crucial step in insect processing, as it inhibits the growth of harmful microorganisms, improves their stability and extends their shelf life. After drying, insects can be further processed into various forms, to make them more socially acceptable as food and feed. During drying, biological materials are prone to shrinking, which usually affects their quality. Shrinkage of dried biological material results in a compact structure and causes a significant reduction in water diffusivity. It is typically escorted with unsatisfactory organoleptic quality and problems with grinding. Therefore, including retexturing and structure-expanding techniques in regular drying procedures is becoming essential. The instant controlled pressure drop (DIC) technique was suggested as a texturing technique for yellow mealworms. DIC treatment successfully overcame shrinkage at treatment conditions of 0.194 MPa/32 s and above, resulting in enhanced water diffusivity of 1,833 and 682% for DIC-treated larvae at 0.45 MPa/25 s, dried at 50 and 60 °C, respectively, as compared to blanched larvae. Furthermore, DIC caused a 125% increase in the specific surface area of the dried meal, and a more uniform particle size distribution, both of which reflect the influence of this pretreatment on grinding and, consequently, the end product’s quality. Finally, experimental data of sorption isotherms at 20, 30, and 40 °C were fitted with Brunauer-Emmett-Teller (BET), Guggenheim-Anderson-de Boer (GAB), and Oswin models to represent the sorption behaviour.

Improvement of microporous structure and impermeability of cement mortars using fly ash and blast furnace slag under low curing pressures

Low air pressures in high plateau will degrade the impermeability and air void structure of cement mortars. In this study, the feasibility and mechanism of fly ash (FA) and ground granulated blast furnace slag (GGBFS) improving the microporous structure and impermeability of cement mortars under low curing pressure were investigated. Results showed that the slag significantly improved the impermeability and air voids distribution of cement mortars, while the fly ash did not benefit the impermeability, as well as the air void in mixed mortars. The heat releasing rate and hydration product composition of the slag mixed paste were superior to that of the FA. The reduction of Ca(OH)2, gentler hydration rate, and filling effect of fine slag particles are believed to contribute to the improvement of impermeability. The water vapor isotherm sorption test demonstrated that low curing pressure changed the surface characteristics of hydrates, and inhibited the adsorption and desorption process (including the capillary condensation process and ink-bottle effect) with the range of relative humidity (RH) > 40%. Meanwhile, the titting parameters variation certified according to Guggenheim-Anderson-deBoer (GAB) model certified that the addition of slag achieved the same result as increasing curing pressure. Moreover, futher analysis showed that if partial OPC was replaced by slag, it could befinit energy consumption, CO2 emission, and materials cost compared with pure OPC. This study provides an initial evidence for applications of slag in low air pressure conditions.

Study on water absorption and dielectric response of epoxy resin impregnated paper bushing

AbstractEpoxy‐impregnated paper transformer bushings are prone to water absorption due to the presence of water‐attracting moieties in the cellulose chemical structure and epoxy resin, leading to moisture‐induced insulation defects. To understand the mechanism of moisture's impact on epoxy‐impregnated paper, this study developed a testing platform that integrated moisture diffusion, adsorption, and dielectric properties of insulating materials. Insulation specimens made of epoxy resin and epoxy‐impregnated paper were prepared and their water diffusion characteristics were investigated using the Fick diffusion model and the Langmuir model, respectively. The Guggenheim–Anderson–de Boer equation was used to examine the vacuum vapour adsorption characteristics of the materials, providing a theoretical foundation for examining the form of water present within them. The dielectric response of materials with varying moisture levels was then tested to study the effect of water on the dielectric spectrum curve. Using the Extended Derivative Method, the characteristic frequency reflecting the water content of the epoxy‐impregnated paper was extracted. The results demonstrate that 0.01‐Hz characteristic frequency provides superior accuracy for moisture assessment in epoxy resins compared to 50 Hz, and extracting and fitting the relaxation peak characteristic frequency in epoxy‐impregnated paper moisture evaluation yields higher accuracy than using tan δ at the power frequency.

Protein Adsorption on Carboxy-Functionalized Microparticles Revealed by Zeta Potential and Absorption Spectroscopy Measurements

Abstract Addition of micro/nanoparticles to a protein solution leads to the formation of a protein layer on the particle surface, called a protein corona. We investigate here the adsorption behavior of myoglobin, hemoglobin, cytochrome-c, and lysozyme on carboxy-functionalized polystyrene microparticles using zeta potential and absorption spectroscopy measurements. The observed adsorption behavior differs according to the method of detection: monolayer for zeta potential and multilayer for absorption spectroscopy. Langmuir-type monolayer adsorption is observed with zeta potential measurements, because zeta potential (ζ) responds only to the charge density at the outermost protein layer. Multilayer adsorption is observed by absorption spectroscopy. Spectroscopic results were analyzed by the Guggenheim-Anderson-de Boer (GAB) model, which comprises a hard corona formed by strong interaction between the protein and the particle surface and a soft corona formed by weak interaction between adsorbed and bulk-solution proteins. The extent of hard and soft corona formation depends on pH. When a protein monolayer is prepared by covalent modification of the particle surface, the number of layers in the protein corona decreases relative to the case of protein adsorption on bare particles. This result demonstrates that electrostatic interactions between the protein and particle surface play a key role in the formation of a protein corona.