Diffusion-relaxation Model Research Articles

Interplay between the Glass Transition Temperature, Analyte Diffusion, and Fluorescence Quenching for Detection of Nitro-Group Containing Explosives Using Organic Semiconducting Films.

Efficient detection of chemical analytes using fluorescence-based sensors necessitates an in-depth understanding of the physical interaction between the analyte molecules and the sensor films. This study explores the interplay between the thermal properties of a series of triphenylamine-centered fluorescent dendrimers with different glass transition temperatures (Tg) for detecting nitroaromatic explosives. When exposed to 4-nitrotoluene (pNT) vapors, biphasic diffusion kinetics were observed for all the dendrimers, corresponding to Super Case II kinetics, suggesting rapid film swelling during initial analyte uptake. The diffusion kinetics were further analyzed using a diffusion-relaxation model, where a strong Tg dependence was observed for both the initial concentration-driven diffusion phase and the slower film relaxation phase. Additionally, a difference in kinetics between analyte uptake and release was observed. The photoluminescence (PL) kinetics also showed a Tg dependence, with more efficient PL recovery observed for films composed of dendrimers that had a lower Tg. Rapid quenching of over 40% with little PL recovery was seen in the dendrimer with the highest Tg (107 °C), while a smaller quench with efficient PL recovery was observed in the dendrimer that had a Tg close to room temperature. The results highlight the critical role of the thermal properties of sensor films in achieving rapid and sensitive detection.

Estimating axon radius using diffusion-relaxation MRI: calibrating a surface-based relaxation model with histology.

Axon radius is a potential biomarker for brain diseases and a crucial tissue microstructure parameter that determines the speed of action potentials. Diffusion MRI (dMRI) allows non-invasive estimation of axon radius, but accurately estimating the radius of axons in the human brain is challenging. Most axons in the brain have a radius below one micrometer, which falls below the sensitivity limit of dMRI signals even when using the most advanced human MRI scanners. Therefore, new MRI methods that are sensitive to small axon radii are needed. In this proof-of-concept investigation, we examine whether a surface-based axonal relaxation process could mediate a relationship between intra-axonal T2 and T1 times and inner axon radius, as measured using postmortem histology. A unique in vivo human diffusion-T1-T2 relaxation dataset was acquired on a 3T MRI scanner with ultra-strong diffusion gradients, using a strong diffusion-weighting (i.e., b = 6,000 s/mm2) and multiple inversion and echo times. A second reduced diffusion-T2 dataset was collected at various echo times to evaluate the model further. The intra-axonal relaxation times were estimated by fitting a diffusion-relaxation model to the orientation-averaged spherical mean signals. Our analysis revealed that the proposed surface-based relaxation model effectively explains the relationship between the estimated relaxation times and the histological axon radius measured in various corpus callosum regions. Using these histological values, we developed a novel calibration approach to predict axon radius in other areas of the corpus callosum. Notably, the predicted radii and those determined from histological measurements were in close agreement.

Anomalous Water-Sorption Kinetics in ASDs.

Anomalous water-sorption kinetics in amorphous solid dispersions (ASDs) are caused by the slow swelling of the polymer. In this work, we used a diffusion–relaxation model with the Williams–Landel–Ferry (WLF) equation and the Arrhenius equation to predict the anomalous water-sorption kinetics in ASDs of poly(vinyl-pyrrolidone)-co-vinyl-acetate (PVPVA) and indomethacin (IND) at 25 °C. These predictions were based on the viscosities of pure PVPVA and pure IND, as well as on the water-sorption kinetics in pure PVPVA. The diffusion–relaxation model was able to predict the different types of anomalous behavior leading to a qualitative and quantitative agreement with the experimental data. Predictions and experiments indicated more pronounced anomalous two-stage water-sorption behavior in the ASDs than in pure PVPVA. This was caused by a higher viscosity of glassy ASD–water mixtures compared to glassy PVPVA–water mixtures at the same distance from their glass transition temperature. These results suggest that this ASD swells more slowly than the polymer it is composed of. The modeling approach applied in this work can be used in the future for predicting diffusion-controlled release behavior or swelling-controlled release behavior of ASDs.

Generalized Diffusion–Relaxation Model for Solvent Sorption in Polymers

Generalized Diffusion–Relaxation Model for Solvent Sorption in Polymers

Anomalous, Multistage Liquid Water Diffusion and Ionomer Swelling Kinetics in Nafion and Nafion Nanocomposites

The advent of commercially viable vanadium redox flow batteries has generated interest in improving upon existing membrane materials utilized in this grid-scale energy storage technology. Elucidating structure–transport relationships in perfluorosulfonated ionomer nanocomposites is of particular importance for the development of next-generation membranes, as there is a limited understanding of how nanoparticles alter transport in these membranes. In the present study, we attempt to resolve the impact of silica nanoparticles (SiNPs) on liquid water transport in Nafion–SiNP membranes. Specifically, liquid water sorption and ionomer swelling kinetics in a series of Nafion–SiNP membranes were evaluated using time-resolved attenuated total reflectance–Fourier transform infrared spectroscopy. Anomalous, multistage water uptake and swelling kinetics were observed for both Nafion and Nafion–SiNP membranes at all SiNP loadings. The first stage of the kinetic data was regressed to a diffusion–relaxation model, as water diffusion and resulting diffusion-induced polymer relaxation kinetics during this first stage were found to be highly coupled. Suppressed water transport and swelling kinetics were observed with the introduction of SiNPs, though this trend did not hold true for higher SiNP loadings. Thermal annealing of the membranes was also observed to impact the transport and swelling properties of the Nafion and Nafion–SiNP membranes, exhibiting a synergistic effect with the SiNPs at low nanoparticle loadings. Finally, the multistage water uptake mechanism in dry Nafion and Nafion–SiNP nanocomposites was understood to be governed by the time-dependent local water activity in the membrane. Overall, this study presents a clear framework that can be employed to characterize and tune aqueous transport through Nafion nanocomposite membranes.

Anomalous water diffusion in epoxy/carbon nanoparticle composites

Water absorption-desorption-resorption and swelling were studied for a DGEBA-based amine-cured epoxy resin filled with four types of carbon nanoparticles: multiwall carbon nanotubes (MWCNT), graphite nano-platelets (GnP), expanded graphite platelets, and carbon black. Nanocomposites are characterised by lower diffusivity (down to 20% for epoxy/GnP) and increased water sorption capacity compared to the neat epoxy. Anomalous water absorption and swelling of nanocomposites is finely described by the diffusion-relaxation model. The relaxation times, considered as quantitative indicators of changes in segmental mobility of the polymer, increased with addition of nanoparticles and decreased with temperature. Epoxy/MWCNT composites are characterised by the longest relaxation times (twofold increase) and highest Deborah numbers compared to the neat epoxy and other nanocomposites. Hydrothermal ageing effects and efficiency of nanoparticles on thermal and thermomechanical properties of the epoxy were estimated. Water uptake in nanocomposites is accompanied by several competing processes: plasticization, after-cure, and physical ageing of the polymer matrix.

Design of fast ion conducting cathode materials for grid-scale sodium-ion batteries.

The obvious cost advantage as well as attractive electrochemical properties, including excellent cycling stability and the potential of high rate performance, make sodium-ion batteries prime candidates in the race to technically and commercially enable large-scale electrochemical energy storage. In this work, we apply our bond valence site energy modelling method to further the understanding of rate capabilities of a wide range of potential insertion-type sodium-ion battery cathode materials. We demonstrate how a stretched exponential function permits us to systematically quantify the rate performance, which in turn reveals guidelines for the design of novel sodium-ion battery chemistries suitable for high power, grid-scale applications. Starting from a diffusion relaxation model, we establish a semi-quantitative prediction of the rate-performance of half-cells from the structure of the cathode material that factors in dimensionality of Na+ ion migration pathways, the height of the migration barriers and the crystallite size of the active material. With the help of selected examples, we also illustrate the respective roles of unoccupied low energy sites within the pathway and temperature towards the overall rate capability of insertion-type cathode materials.

Long term performance study of glass reinforced composites with different resins under marine environment

For marine structural applications which poses significant challenges to the choice of materials due to presence of corrosive seawater, polymer matrix based fiber reinforced composites are increasingly becoming the material of choice. However the performance properties of composites are greatly influenced by the moisture absorbed by the composite. In the current study, the long term performance is assessed by determining the amount of moisture absorbed and the reduction of mechanical properties over 12 months in a simulated sea-water environment at different temperatures. Three commonly used thermoset resins with different chemistry such as unsaturated polyester (USP), epoxy resin (EP) and vinylester (VE) are chosen. The effect of fiber reinforcement on the long term performance is investigated. A suitable method for manufacturing glass reinforced composite with good interfacial bonding and high volume fraction is also developed in current study. It is observed that vinylester plaques and composites absorb lesser moisture compared to USP and Epoxy systems resulting in lesser reduction in flexural strength and making the best performing among polymers studied. It is also found that sea-water diffusion into the composite follows non-Fickian behaviour and diffusion relaxation model fits well with the experimental data and corresponding model parameters are evaluated.

Design of High Rate Performance Sodium-Ion Battery Cathode Materials

Sodium ion batteries (NIB) remain attractive to many battery researchers because the earth-abundance of Na opens up a pathway for significant cost reductions in the fabrication of batteries that maintain a high energy density. The cost advantage of Na over Li will only translate into low cost batteries if the concept of earth-abundance is applied consistently. This implies moving away from electrode materials analogous to those in Li-ion batteries which typically contain costly transition metals such as Co. Materials designs starting from LIB analogues also appears to be problematic due to the differences in reaction mechanisms of the Na analogues to the Li transition metal oxides and different structural requirements for Na+ mobility. This approach also overlooks a particular strength of sodium compounds compared to LIB materials, in structures with suitable ion transport pathways the heavier and more polarisable Na+ can move faster than Li+ ions and thus can yield promising candidates for high rate performance batteries. We previously employed the bond valence (BV) method to analyse and predict ionic transport properties in solids from static and dynamic structure models [1]. Here we present an extension of the approach allowing for a rational and quantitative characterization of insertion-type NIB cathode materials in terms of rate performances based on a diffusion relaxation model.Bond-valence site energy (BVSE) modelling and DFT simulations were used to probe Na+ ion migration paths in over 20 sodium-ion battery cathode materials based on earth-abundant transition metals for which experimental rate performance data were available. The migration barriers calculated based on our BVSE approach matches closely those based on DFT studies. Together with the help of the proposed diffusion relaxation model, this allows for a semi-quantitative prediction of the rate performance of half-cells directly from local structure models. The overall approach is computationally cheap and thus allows for fast screening of candidate structure databases as well as for testing of a series of local structure models (e.g. to investigate the role of antisite defects or stoichiometry deviations towards ionic transport properties) for each structure type. Both molecular dynamics and Kinetic Monte Carlo simulations were also employed to test the rate performances predictions. Finally, specific guidelines are established for the design of novel sodium-ion battery cathode materials in terms of pathway dimensionality, migration barriers, the effect of low-lying unoccupied sites, dopants or antisite defects as well as particle sizes.For one of the candidate materials that showed strong potential for high rate performance in the computational study, alluaudite-type non-stoichiometric Na2+xFe2-x/2(SO4)3 (wherein Fe vacancies and NaFe’ antisite defects cross-link the otherwise independent 1D Na+ pathways [2]), we tested our prediction by building a room-temperature all-solid state sodium-ion battery combining the alluaudite-type cathode with Na3PS4 as the solid electrolyte and Na2Ti3O7 as the anode. We also report an alternative synthesis of the alluaudites by mechanical milling of Na2SO4 and FeSO4 followed by annealing at 400°C under argon atmosphere. Favourable rate performance of the all-solid state sodium-ion battery was demonstrated. [1] S. Adams, R. Prasada Rao, “Understanding ionic conduction and energy storage materials with bond valence-based methods”, Bond Valences (Edited by I. D. Brown et al.), Structure and Bonding 158, pp. 129-160, Springer (2014).[2] L.L. Wong, H. Chen, S. Adams, “Sodium-ion diffusion mechanisms in the low cost high voltage cathode material Na2+dFe2-d/2(SO4)3” Phys. Chem. Chem. Phys. 17 (2015), 9186-9193.

Kinetic and equilibrium sorption of organic liquids and vapors in Matrimid

This work examines the kinetic and equilibrium sorption characteristics of a variety of chemical penetrants in the polyimide polymer Matrimid. Liquid equilibrium sorption for dense films with thicknesses of 50µm for a large variety of organic species including alkanes, alcohols, acetates, furans, and ionic liquids is presented. Vapor equilibrium sorption isotherms and kinetic sorption behavior for water and C1-C6 alcohols as a function of chemical activity from 0 to 0.9 were measured using a quartz crystal microbalance with films ranging in thickness from 0.07 to 2.0µm. Diffusion coefficients and relaxation parameters were calculated according to the diffusion-relaxation model for penetrants in glassy polymers. Diffusion coefficients at infinite dilution for water and C1-C6 alcohols are given as a function of van der Waals molar volume and a clear dependency is shown ranging from 2E-11 to 6.5E-13cm2/s for water and hexanol, respectively, for 0.26µm thick films. Diffusion coefficients for all studied vapor penetrants displayed a marked dependence on thickness spanning approximately two orders of magnitude for each respective vapor penetrant over the range 0.1–1.0µm. Penetrant-induced relaxation behavior accounts for the majority of mass sorption at chemical activities of 0.2 and above for the C1-C6 alcohol vapors.

Rational Design of Cathode Materials for High Rate Performance Sodium-Ion Batteries

Sodium ion batteries attracted a large research community because of earth-abundance, low cost and possibility of high energy density batteries. Despite the cost motivation of the research a considerable fraction of this activity still focuses on electrode materials analogous to those in Li-ion batteries often containing costly transition metals such as Co, which appears problematic for various reasons: differences in reaction mechanisms of the Na analogues to the Li transition metal oxides, different structural requirements for Na+ mobility, the fact that a cost advantage of Na over Li will only translate into low cost batteries if the concept of earth-abundance is applied consistently. Understanding of transport in solids both electrode and electrolyte is pivotal in designing such batteries. The analysis and prediction of ion transport in solids from static and dynamic structure models has become an interesting application for the bond valence (BV) approach [1]. Here we present a rational and quantitative characterization of rate performances of insertion-type cathode materials based on the diffusion relaxation model. Bond-valence site energy modelling and DFT simulations were employed to clarify Na+ ion migration barriers in more than 20 sodium-ion battery cathode materials based on earth-abundant elements. Migration energy barriers calculated from our bond valence site energy models closely agree with the DFT models and with the help of the diffusion relaxation model allow for a direct semi-quantitative prediction of the rate performance of half-cells based on local structure models. The demonstrated method is computationally cheap enough to be applied for the fast screening of candidate structure databases and to allow for the testing of a series of local structure models (e.g. to explore the role of antisite dopants or stoichiometry deviations) for each structure type. Rate performance predictions are tested with molecular dynamics and Kinetic Monte Carlo simulations and yield specific guidelines for the design of novel sodium-ion battery cathode materials in terms of pathway dimensionality, migration barriers the effect of low-lying unoccupied sites, dopants or antisite defects as well as particle sizes. As an example of the materials identified by the computational study as promising for high rate performance the alluaudite-type non-stoichiometric Na2+xFe2-x/2(SO4)3, (wherein Fe vacancies and NaFe / antisite defects cross-link the otherwise one-dimensional Na+ pathways [2]) was synthesized by mechanical milling of Na2SO4 and FeSO4 followed by annealing at 400ºC under argon environment and its favourable rate performance is demonstrated in a room-temperature all-solid state sodium-ion battery using Na3PS4 as the solid electrolyte.

Long-distance transport of magnon spin information in a magnetic insulator at room temperature

The transport of spin information has been studied in various materials, such as metals, semiconductors and graphene. In these materials, spin is transported by diffusion of conduction electrons. Here we study the diffusion and relaxation of spin in a magnetic insulator, where the large bandgap prohibits the motion of electrons. Spin can still be transported, however, through the diffusion of non-equilibrium magnons, the quanta of spin wave excitations in magnetically ordered materials. Here we show experimentally that these magnons can be excited and detected fully electrically in linear response, and can transport spin angular momentum through the magnetic insulator yttrium iron garnet (YIG) over distances as large as 40 micrometer. We identify two transport regimes: the diffusion limited regime for distances shorter than the magnon relaxation length, and the relaxation limited regime for larger distances. With a model similar to the diffusion-relaxation model for electron spin transport in (semi)conducting materials, we extract the magnon relaxation length lambda = 9.4 micrometer in a 200 nm thin YIG film at room temperature.

Projecting long-term non-Fickian diffusion behavior in polymeric composites based on short-term data: a 5-year validation study

The slow approach to equilibrium concentration indicative of non-Fickian diffusion in polymer composites necessitates experimental time frames which are often of limited feasibility. As a result, experimental studies are terminated prematurely due to time constraints or incorrect identification of equilibrium. Here, the three-dimensional anisotropic diffusion behaviors of six-, twelve-, and forty-ply quartz-reinforced bismaleimide laminates are quantified through a 5-year, full-immersion gravimetric absorption study. The applicability of the three-dimensional hindered diffusion model is investigated, while projections of future absorption behavior made at 21 months are revisited in light of 3 years of additional data. The mathematical equivalency of the hindered diffusion model and a diffusion–relaxation model under certain conditions is discussed. Moisture content rises continuously throughout the 5-year experiment for all samples. In the six-ply case, the standard termination criterion for the equilibrium condition is met before 6 months and 1.38 % moisture content by weight. Actual moisture content reaches 1.56 % after 5 years. The hindered diffusion model and associated forward projections of moisture content are found to conform well to experimental results.

Effect of the weight ratio of alginate-modified tapioca starch on the physicochemical properties and release kinetics of chlorogenic acid containing beads

Sodium alginate (SA)-modified tapioca starch (TS) solutions (RSA/TS) in different weight ratios (1/0, 0.75/0.25, 0.5/0.5 and 0.25/0.75), added with chlorogenic acid (CGA), were dripped into CaCl2 solution for obtaining calcium alginate (CA) hydrogel beads filled with TS containing chlorogenic acid (HBCA/TS). The beads size, morphology, encapsulation efficiency, textural and viscoelastic properties, CGA release in simulated gastrointestinal conditions, and the molecular interactions between beads components using DSC and FTIR were evaluated. The sphericity of the HBCA/TS filled with TS was lower than that made with only calcium alginate, but the diameter was larger. CGA release from the beads was due to a complex interplay between matrix porosity and tortuosity. Highest release % of CGA occurred for HB0.75/0.25 which showed the lowest Tan δ-strain %, hardness and cohesiveness values. The diffusion-relaxation model involving two mechanisms described better the CGA release experimental data.

A pressure and concentration dependence of CO2 diffusion in two Australian bituminous coals

Gas diffusion in coals plays an important role in enhanced coalbed methane production, fugitive gas emissions from coal, and gas release in coal mines. However, a consistent picture of diffusion behaviour in coals is yet to emerge. For example, the adequacy of describing diffusion by a single coefficient is debated. Moreover, some researchers have reported diffusion coefficients as increasing with rising pressure, others report the opposite. This variation may be due to the choice of the model, coal, or experimental conditions. In this study, experimental CO2 kinetic sorption data was obtained for two Australian bituminous coals over a range of pressure conditions and analysed using three different models. We found that the unipore model, which uses only one characteristic diffusion coefficient, does not adequately capture the sorption kinetics. Using a bidisperse model, two characteristic coefficients can describe the diffusion process. The pressure dependence of the fast diffusion coefficient decreases as the system pressure rises. However, the slow diffusion coefficient is not solely dependent on pressure, but is influenced by additional sorption by the coal, which is introduced during the pressure step. Depending on the amount of gas sorbed in a single sorption step, the magnitude of the slow diffusion component will change. This diffusion coefficient exhibits concentration dependence; it varies depending on whether small or large pressure steps are applied. This suggests that the bidisperse model used is inappropriate for examining the pressure dependence of diffusion coefficients at these conditions. Experiments were repeated using a microporous activated carbon, where CO2 uptake displayed rapid kinetics, with no evidence of a slower component. This indicates that the slower uptake of CO2 observed in coal is due to specific properties of the coals. A Fickian diffusion-relaxation model (FDR) developed for studying anomalous diffusion in glassy polymers is proposed instead, ascribing the diffusion in the primary stage to Fickian diffusion, and in the second stage due to slow rearrangement of the coal structure possibly associated with swelling. Additionally, the rapid uptake of gas by the coals (investigated by the model fits) is found to be very sensitive to measured sorption values immediately after gas exposure. This affects the magnitude of calculated diffusion coefficients.

Non-Fickian Diffusion of Water in Polylactide

The diffusion of water in polylactide (PLA) was measured at various external water vapor activities (0–0.85) and temperatures (25, 35, 45 °C) using three separate experimental techniques: quartz spring microbalance (QSM), quartz crystal microbalance (QCM), and time-resolved Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Non-Fickian sorption kinetic behavior was observed with all the experimental techniques used over the observed experimental time scales, which was a result of the nonequilibrium state of the glassy polymer. Two phenomena were observed over two distinct time periods (two-stage sorption kinetics), where early time data revealed diffusion driven by a water concentration gradient and later time data revealed diffusion driven by slow polymer relaxation or swelling due to additional water ingress over time. Diffusion coefficients and relaxation time constants were determined by regressing the early time data to a Fickian model and the data over the entire observed experimental time scale to a diffusion-relaxation model, respectively. Diffusion coefficients increased with temperature, were constant with activity and concentration of water in the polymer, and were similar among all three experimental techniques. The high Deborah numbers (relaxation time/diffusion time) determined from the diffusion-relaxation model confirm the observed two-stage non-Fickian behavior.

Levofloxacin Release, Antibacterial Activity and Cytotoxicity Studies on a Novel Wound Dressing

A novel functional material was fabricated by combining levofloxacin microspheres with viscose nonwoven fabrics. The complex microspheres were made by w/o emulsion crosslinking technique. The morphologies of both microspheres and fabric composite were investigated by SEM. The drug release property was evaluated by UV. The antibacterial activity and cytotoxicity were tested by spread plate and cell culture method. The results showed that the microspheres had spherical shape and could be embedded into the viscose fabrics. The levofloxacin was released gradually within 168 hours and its release kinetics corresponded to diffusion-relaxation model. In addition, the antibacterial activity of the fabric was increased with prolonged drug releasing time and the complex fabrics had no obvious cytotoxicity. The functional material has great potential to be used as a wound dressing with antibacterial property.

Liquid Water Transport in Polylactide Homo and Graft Copolymers

The successful design of new biodegradable, renewable resource plastics as replacements to commodity barrier plastics would benefit from an accurate measurement of sorption and diffusion of liquids. In this study, the diffusion of liquid water in amorphous polylactide [PLA] and a PLA graft copolymer, poly(1,5-cyclooctadiene-co-5-norbornene-2-methanol-graft-dl-lactide) [PCNL], was examined with time-resolved Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. Non-Fickian behavior was observed for all experiments, indicated by a slow approach to steady state due to diffusion and polymer relaxation occurring on similar time scales. This non-Fickian behavior highlights the variability of the sorption isotherms reported in the literature, where others have collected nonequilibrium sorption behavior (instead of true steady-state equilibrium sorption) at different time points and film thicknesses. The dynamic infrared data provided direct evidence for both water diffusion and water-induced polymer relaxation, where both were quantified and regressed to a diffusion-relaxation model to determine the diffusion coefficient and the polymer relaxation time constant. In addition to the successful measurement and modeling of the diffusion-relaxation phenomena for diffusion of a liquid in a nonequilibrium state glassy polymer, this study also determined that the diffusivity of water in the PLA graft copolymer (with only 5 wt % rubber) was 3-fold lower than in the PLA homopolymer.

The influence of thermal history on structure and water transport in Parylene C coatings

Poly(monochloro- p-xylylene) (Parylene C) coatings are commonly used in a number of applications due to their robust properties and unique ability to be deposited directly from the vapor phase. Recently, Parylene C has been used in new medical devices, where an accurate assessment and understanding of liquid transport and its relationship to the polymer structure is critical in design and evaluation. In this study, the diffusion of liquid water in Parylene C coatings was examined as a function of the thermal history with in situ time-resolved Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy, while the polymer structure was investigated with in situ X-ray scattering. Anomalous transport behavior was observed, where dynamic infrared spectra provide evidence of water diffusion and water-induced polymer relaxation occurring on similar time scales. Both of these phenomena were quantified and regressed to a diffusion–relaxation model to determine the diffusion coefficient and polymer relaxation time constant. After thermal treatment of the Parylene C coating, the water diffusivity reduced by 2-fold, which can be attributed to the increase in crystallinity and the evolution of a new crystalline phase in Parylene C.

Dynamic and Equilibrium Swelling of Biodegradable Starch-Based Superabsorbent Polymers

A series of biodegradable superabsorbent polymers (SAP’s) based on starch grafted with acrylic acid (AA) and crosslinked with N,N’-methylenebisacrylamide (MBIS) were obtained. The parameters that define SAP’s properties, such as starch type, amount of initiator, acrylic acid and crosslinker concentrations, and degree of neutralization were varied. The dynamic swelling was interpreted in terms of both a simple power of time equation and a more detailed model based on a coupled diffusion–relaxation mechanism. The diffusivity coefficients calculated from diffusion–relaxation model were compared with the microimages obtained by optical microscopic.