Material Swelling Research Articles

Demystify radiation-enhanced hydrogen isotope diffusion in Fe-Ni-Cr austenitic stainless steels

Understanding and containing hydrogen isotope diffusion is crucial for many nuclear applications. In situ experiments have consistently shown that radiation significantly enhances isotope diffusion in austenitic stainless steels. Despite extensive research, the mechanism behind this phenomenon remains elusive, as most radiation-induced defects (e.g., vacancies, dislocations, and grain boundaries) typically trap hydrogen, thereby slowing diffusion. While grain boundaries may increase in-plane diffusivity and interstitials may enhance diffusion due to material swelling, these effects are relatively minor. Utilizing an Fe-Ni-Cr-H interatomic potential for stainless steels, we conducted extensive molecular dynamics simulations to investigate the origins of radiation-enhanced diffusion. Our findings reveal that when a system is resolidified, mimicking defects created by radiation displacements, the resulting structure contains a mixture of phases, boundaries, and dislocation networks. This defective structure significantly increases hydrogen diffusivity, enhancing it by approximately 1.7 times at 900 K. These results suggest that the complex defect structures formed during radiation displacements are the primary drivers of the observed diffusion enhancement, providing valuable insights into the mechanisms underlying radiation-enhanced diffusion in nuclear materials.

A Novel Collagen Aerogel with Relevant Features for Topical Biomedical Applications.

Collagen-based aerogels have great potential for topical biomedical applications. Collagen's natural affinity with skin, biodegradability, and gelling behavior are compelling properties to combine with the structural integrity of highly porous matrices in the dry form (aerogels). This work aimed to produce a novel collagen-based aerogel and to perform the material's solid-state and physicochemical characterization. Aerogels were obtained by performing different solvent exchange approaches of a collagen-gelled extract and drying the obtained alcogels with supercritical CO2. The resulting aerogels showed a sponge-like structure with a relatively dense mesoporous network with a specific surface area of 201-203 m2/g, a specific pore volume of 1.08-1.15 cm3/g, and a mean pore radius of ca. 14.7 nm. Physicochemical characterization confirmed that the obtained aerogels are composed of pure collagen, and the aerogel production process does not impact protein tertiary structure. Finally, the material swelling behavior was assessed at various pH values (4, 7, and 10). Collagen aerogels presented a high water uptake capacity up to ~2700 wt. %, pH-dependent stability, and swelling behavior in aqueous media. The results suggest that this collagen aerogel could be a promising scaffold candidate for topical biomedical applications.

Degradable 4D-printed hydration-driven actuators from a single family of amphiphilic star-shaped copolymers

Actuators are largely used in biomedical applications in the presence of sensitive live cells or biomolecules, which makes actuators triggered by water uptake highly appealing. Dual-material printing and hydration driven expansion is a method of choice to produce such actuators, but mostly rely of non-degradable polymers or on the combination of polymers of different nature that may lead to interface incompatibilities. To overcome this challenge, we report here on two photocrosslinkable resins based on a single family of degradable hydrophilic or hydrophobic star-shaped poly(ethylene glycol)-poly(lactide) copolymers. The two materials are first printed individually and characterized to ensure that their properties enable the printing of dual material objects by stereolithographic digital-light processing. Dual-materials actuators are then printed by sequential switching of the hydrophobic and hydrophilic resin baths. Objects of simple and complex shapes are easily obtained and exhibit rapid actuation (<60 s) upon hydration. The swelling-induced shape changes are accurately reproduced by numerical modeling of the printed geometries using the obtained material swelling properties. This set of results offers new perspectives to develop 4D-printed temporary medical devices.

Optimisation-based strategies to identification of material parameters of hygro-thermo-mechanical problems

Applications involving hygro-thermo-mechanical models are found in engineering fields as diverse as electronic packaging, concrete structures, composite materials and wood structures. Within the framework of wood processing, hygro-thermo-mechanical problems account for the cross-dependence of moisture content, temperature and dimensional changes of wooden components. Numerical simulation plays an important role in predicting the behaviour of wooden structures and, therefore, use of appropriate process and material parameters is essential for a successful prediction. The present work is inserted in this context and addresses application of optimisation techniques to identification of heat transfer, moisture diffusion and moisture-dependent swelling/shrinkage parameters. The direct problem is formulated based on a fully coupled transient solution of the energy, moisture and momentum transfer conservation laws. A global–local hybrid optimisation technique is proposed combining swarm intelligence and deterministic approaches, respectively based on particle swarm optimisation and the Nelder–Mead (NM) technique. The first stage aims at reducing the search space, so that the NM algorithm is able to determine the global minimum with acceptable accuracy. The strategy is both robust and efficient, being able to avoid local minima with reduced number of fitness computations. An illustrative example featuring a moisture-gaining process is also discussed, in which special attention is placed on the elastic and material swelling coupled effects caused by moisture transfer.

Temperature Evolution of Sorbonorit-4 Methane-Induced Deformation through the Eyes of Classical Density Functional Theory.

Activated carbons are widely used industrial adsorbents due to their attractive sorption properties. Although extensive research on activated carbon has been carried out for several centuries, some aspects of the adsorption-induced deformation of activated carbon remain unclear. The puzzling temperature dependence of the methane-induced deformation of activated carbon is investigated in the present work. Several experimental studies have shown that an increase in temperature leads to a reversal of the sign of adsorption strain at low pressures, i.e., the contraction turns into an expansion. Here we suggest a possible explanation for this effect by applying classical density functional theory to the adsorption isotherms of nitrogen, carbon dioxide, and methane as well as to methane-induced deformation isotherms. Our calculations show that the adsorption stress generated in the smallest pores predominates at higher temperatures and leads to material swelling. Lowering the temperature, on the other hand, leads to a predominance of larger pores and compression of the activated carbon material. We also investigated the possibility of determining the pore size distribution from methane-induced deformation and adsorption data and the predictive capabilities of our theoretical approach.

Hemicellulose additive to chitosan-based bioplastic improved the tensile strength and allowed to control the material swelling

Hemicellulose additive to chitosan-based bioplastic improved the tensile strength and allowed to control the material swelling

Evaluation of Thermodynamic and Kinetic Contributions to Over-Extraction of Extractables by Nonpolar Organic Solvents in Comparison to Lipids in Exhaustive and Exaggerated Extractions of Medical Devices Based on Abraham Solvation Model and Solvent–Material Interactions Using Low-Density Polyethylene as a Representative Material

The thermodynamic and kinetic contributions to the over-extraction of extractables by nonpolar organic solvents relative to biological lipids in exhaustive and exaggerated extractions of medical devices are studied based on the Abraham solvation model and solvent–material interactions, using low-density polyethylene (LDPE) as an exemplary material. The thermodynamic effect is evaluated by the partition constant of extractables between LDPE and extraction solvents, hexane and lipids, defined as the concentration in the polymer phase divided by the concentration in the solvent phase. The Abraham solvation model is used to correlate the measured LDPE-lipid partition constant (log10Pldpe/lipid) to construct the predictive model. Similar models are also derived from the thermodynamic cycle conversion, using the system constants of LDPE-water and Lipid-water partition systems. These constructed models, together with the predictive LDPE-hexane (log10Pldpe/hexane) model established from a previous study, are used to predict and compare the ranges and values of Pldpe/s (s = lipids and hexane) for the observed LDPE extractables over a wide hydrophobicity range in log10Po/w from zero to 30. The solvent-LDPE interactions are examined by the degree of swelling of LDPE by hexane (or other nonpolar solvents) and lipids, including the solvent diffusion rates into the material. These parameters allow the evaluation of kinetic effect on the over-extraction. The extent of over-extraction is compiled directly by experimental “overall” or “specific” migration data or indirectly calculated by the diffusion coefficient of extractables when extracted by hexane or lipids. It is concluded from this study that the extractables distribution between LDPE and lipids highly favors the lipid phase thermodynamically (Pldpe/lipid&lt;1), and the values of Pldpe/lipid are always lower than those of Pldpe/hexane, thereby indicating that the thermodynamic effect is not the cause of over-extraction. It is the kinetic effect that dominantly contributes to the over-extraction, as supported by the material swelling and solvent diffusion rates. Finally, the extent of over-extraction has been established from a few folds to over a hundred-fold, and the median value is 7. Furthermore, the methods adopted and developed in this study can be invaluable tools in other disciplines such as the reliable prediction of extractables from other device materials and environmental sampling.

A Novel Approach for Characterizing Epoxy Mold Compound High Temperature Swelling

In this paper, a novel method for measuring hightemperature material swelling of an epoxy mold compound is explored. This work attempts to extend the swelling characterization beyond the capability of typical commercial tools. The approach uses a high-pressure chamber to maintain a saturated liquid environment for the specimen. Digital image correlation is used to measure in-situ strain change in the specimen due to hygro-thermal expansion. The results show moisture-induced swelling increases with temperature and is significant compared with thermal expansion. Results are compared against other measurement methods and published data. This has yielded good fundamental learnings for the novel concept and identified areas for future work.

Mechanically-reinforced biocompatible hydrogels based on poly(N-isopropylacrylamide) and star-shaped polycaprolactones

The aim of this work was to improve the properties of hydrogels based on poly(N-isopropyl acrylamide) (PNIPAAm) in terms of mechanical features and functionality by combining the polymer with a star-shaped tetrafunctional polycaprolactone (PCL), which was synthesized ad-hoc and introduced into the reaction mixture. The synthesized PCL (coded as PCL-COOH), selected to maintain the biocompatibility of the final material, was designed with a star structure characterized by four strong arms ending with maleic groups to increase the functionalization potential capable of participating in the radical polymerization and adding acid groups to the system. Specifically, various hydrogels were prepared by partially replacing pentaerytritol tetraacrylate (PE-TA), a commercial crosslinker, with increasing concentrations of PCL-COOH in the presence of trihexyl(tetradecyl)phosphonium persulfate (TETDPPS) as non-gas-releasing radical initiator. In addition, frontal polymerization (FP) was employed, a fast and energy efficient technique, potentially capable of promoting the dispersibility of PCL in the polymer matrix.The influence of the star-shaped PCL on the polymerization process as well as on the hydrogel properties in terms of chemical structure, swelling behaviour, thermal and mechanical features was investigated. Indeed, it was found that the presence of PCL allowed the formation of a stable polymerization front up to a concentration of 25 wt%. FT-IR measurements allowed to evaluate the fraction of PCL effectively bonded to the hydrogel structure, while the morphological analysis performed by FE-SEM characterization revealed that the hydrogel pore size tended to decrease as the amount of PCL in the system increased. In addition, the star-shaped PCL was found to affect the material swelling properties, by reducing the swelling ratio without affecting the thermoresponsive behavior. Mechanical tests performed on the neat PNIPAAm hydrogels and on PCL-containing hydrogels, showed a relevant increase in the material stiffness due to the PCL-COOH addition. The DSC characterization results showed a decrease in the glass transition temperature with increasing PCL-COOH content, indicating a partial miscibility of the two polymers likely due to a compatibilization effect of a copolymer formed during the polymerization process. To demonstrate the capability of the hydrogels to retain positively charged molecules, the prepared systems were contacted with solutions containing pararosaniline hydrochloride. The retention capacity as well as the kinetic release were investigated. The measurements evidenced a higher retaining capacity and a lower release rate in the PCL-containing hydrogels. Finally, the biocompatibility and the low citoxicity of the PNIPAAm/PCL hydrogels were confirmed by a cell viability assay using the SH-SY5Y cell line.

Geometry Optimization of Dispersed U[sbnd]Mo Fuel for Light Water Reactors

The Uranium/Molybdenum metallic fuel has been proposed as promising advanced fuel concept especially in the dispersed fuel geometry. The fuel is manufactured in the form of small fuel droplets (particles) placed in a fuel pin covered by a matrix. In addition to fuel particles, the pin contains voids necessary to compensate material swelling and release of fission gases from the fuel particles. When investigating this advanced fuel design, two important questions were raised. Can the dispersed fuel performance be analyzed using homogenization without significant inaccuracy and what size of fuel drops should be used for the fuel design to achieve optimal utilization? To answer, 2D burnup calculations of fuel assemblies with different fuel particle sizes were performed. The analysis was supported by an additional 3D fuel pin calculation with the dispersed fuel particle size variations. The results show a significant difference in the multiplication factor between the homogenized calculation and the detailed calculation with precise fuel particle geometry. The recommended fuel particle size depends on the final burnup to be achieved. As shown in the results, for lower burnup levels, larger fuel drops offer better multiplication factor. However, when higher burnup levels are required, then smaller fuel drops perform better.

In-situ TEM investigation of void swelling in nickel under irradiation with analysis aided by computer vision

Understanding the stability of irradiation-induced voids in materials is important for engineering material's swelling behavior under irradiation. In-situ TEM offers a spatial and temporal resolution that is suitable for investigating the evolution of voids under irradiation. However, the in-situ videos have often been too large to be analyzed manually, leaving the valuable data underutilized. We developed a deep learning-based semantic segmentation model to consistently study the growth and shrinkage of voids in nickel under 1 MeV krypton ion irradiation at various temperatures from 525 °C to 650 °C. With a foil thickness near 100 nm and ion flux of 6.3 × 1011 ions⋅ cm−2⋅s−1, the pre-existing voids, which were created beforehand by irradiation at 600 °C to 0.5 dpa, shrank at low temperatures and grew at high temperatures under irradiation, where the transition occurred at 575 °C (∼0.5 TM). The observed stability transition provided new insight for the shrinkage mechanism of voids under irradiation. In addition, an annealing experiment on nickel, previously irradiated at 600 °C to 3 dpa, was performed sequentially at 650 °C to 720 °C to reveal the shrinkage rate of void as a function of temperature and void size. The advantage of combining computer vision and in-situ TEM to obtain comprehensive void evolution was demonstrated.

Hydraulic conductivity, microstructure and texture of compacted claystone/ bentonite mixtures saturated with different solutions

The French reference concept for the disposal of intermediate- and high-level nuclear waste in the Callovo-Oxfordian sedimentary rock formation (COX-claystone) considers the employment of crushed COX-claystone and its mixture with MX80-bentonite as potential backfill materials installed in drifts and shafts upon termination of the operational phase of the future repository. The fraction of MX80-bentonite in the mixture is limited to 30% in wet weight. Over time, the backfill will be saturated with solutions that originate in the surrounding rock formation and percolate through the concrete lining left in place. The main characteristic of the leachate will be its high pH-value. In addition to the swelling pressure, the sealing properties of the backfill are determined by the hydraulic conductivity. This laboratory experimental study aimed to understand the hydraulic conductivity evolution of potential backfill materials under realistic conditions in terms of compaction conditions, solution chemistry, temperature and hydraulic gradient, and to relate results determined at the macroscale to results of microstructural and textural analysis. Also, the impact of the solution chemistry was evaluated by these means. In the case of mixture-samples, no stabilization of hydraulic conductivity was detected, despite the duration of the experiments being about one year. There was no detectable impact of the solution chemistry in the course of experiments attributable to low reaction kinetics under imposed conditions. Subsequent microstructural analysis indicated material swelling triggering rearrangements in the pore space and lowering the fraction of hydraulic conductive voids. Interestingly, neither the saturation nor the solution chemistry had an impact on the texture of materials.

Theoretical studies on the stabilization and diffusion behaviors of helium impurities in 6H-SiC by DFT calculations

In fusion environments, large scales of helium (He) atoms are produced by a radical transformation along with structural damage in structural materials, resulting in material swelling and degradation of physical properties. To understand its irradiation effects, this paper investigates the stability, electronic structure, energetics, charge density distribution, PDOS and TDOS, and diffusion processes of He impurities in 6H-SiC materials. The formation energy indicates that a stable, favorable position for interstitial He is the HR site with the lowest energy of 2.40 eV. In terms of vacancy, the He atom initially prefers to substitute at pre-existing Si vacancy than C vacancy due to lower substitution energy. The minimum energy paths (MEPs) with migration energy barriers are also calculated for He impurity by interstitial and vacancy-mediated diffusion. Based on its calculated energy barriers, the most possible diffusion path includes the exchange of interstitial and vacancy sites with effective migration energies ranging from 0.101 eV to 1.0 eV. Our calculation provides a better understanding of the stabilization and diffusion behaviors of He impurities in 6H-SiC materials.

Helium production and material damage rate assessment in EU DEMO HCPB divertor

EU DEMO should be the first demonstrative fusion power plant, and it is expected to show that net electric energy can be produced and supplied to the grid. The availability and lifetime of the plant will be comparable to that of a commercial fusion power plant. The capacity to provide considerable net electric power safely and continuously to the grid (from 100 MW to 500 MW) is one of DEMO's significant purposes. The neutrons cause defects, leading to the transmutation of elemental atoms when interacting with the divertor component materials. These reactions produce gases, notably helium, which can induce material swelling and embrittlement. In this paper, the DPA and helium production in divertor has been assessed, mainly focusing on the structural material: EUROFER. Helium production rates reach around 117 appm/fpy as the peak, while DPA values reach about 4 dpa/fpy as the maximum value. These calculations were performed using the MCNP6 code with FENDL 3.2 nuclear data and the ADVANTG tool.

Materials swelling revealed through automated semantic segmentation of cavities in electron microscopy images

Accurately quantifying swelling of alloys that have undergone irradiation is essential for understanding alloy performance in a nuclear reactor and critical for the safe and reliable operation of reactor facilities. However, typical practice is for radiation-induced defects in electron microscopy images of alloys to be manually quantified by domain-expert researchers. Here, we employ an end-to-end deep learning approach using the Mask Regional Convolutional Neural Network (Mask R-CNN) model to detect and quantify nanoscale cavities in irradiated alloys. We have assembled a database of labeled cavity images which includes 400 images, > 34 k discrete cavities, and numerous alloy compositions and irradiation conditions. We have evaluated both statistical (precision, recall, and F1 scores) and materials property-centric (cavity size, density, and swelling) metrics of model performance, and performed targeted analysis of materials swelling assessments. We find our model gives assessments of material swelling with an average (standard deviation) swelling mean absolute error based on random leave-out cross-validation of 0.30 (0.03) percent swelling. This result demonstrates our approach can accurately provide swelling metrics on a per-image and per-condition basis, which can provide helpful insight into material design (e.g., alloy refinement) and impact of service conditions (e.g., temperature, irradiation dose) on swelling. Finally, we find there are cases of test images with poor statistical metrics, but small errors in swelling, pointing to the need for moving beyond traditional classification-based metrics to evaluate object detection models in the context of materials domain applications.

Effects of Porous Supports in Thin-Film Composite Membranes on CO2 Separation Performances

Despite numerous publications on membrane materials and the fabrication of thin-film composite (TFC) membranes for CO2 separation in recent decades, the effects of porous supports on TFC membrane performance have rarely been reported, especially when humid conditions are concerned. In this work, six commonly used porous supports were investigated to study their effects on membrane morphology and the gas transport properties of TFC membranes. Two common membrane materials, Pebax and poly(vinyl alcohol) (PVA), were employed as selective layers to make sample membranes. The fabricated TFC membranes were tested under humid conditions, and the effect of water vapor on gas permeation in the supports was studied. The experiments showed that all membranes exhibited notably different performances under dry or humid conditions. For polyacrylonitrile (PAN) and poly(ether sulfones) (PESF) membranes, the water vapor easily condenses in the pores of these supports, thus sharply increasing the mass transfer resistance. The effect of water vapor is less in the case of polyvinylidene difluoride (PVDF) and polysulfone (PSF), showing better long-term stability. Porous supports significantly contribute to the overall mass transfer resistance. The presence of water vapor worsens the mass transfer in the porous support due to the pore condensation and support material swelling. The membrane fabrication condition must be optimized to avoid pore condensation and maintain good separation performance.

A Systematic Analysis of the Effect of Extraction Solvents on the Chemical Composition of Extraction Solutions and the Analytical Implications in Extractables and Leachables Studies

Assessment of extractables and leachables (E&L) released from the pharmaceutical container closure systems (CCS), single-use polymeric processing materials (PPM), and medical devices is one of regulatory requirements in the submission and approval of pharmaceutical products and medical devices. The analytical activities involved in E&L studies are the solvent extraction of test articles, followed by instrumental analysis to determine both concentration and identities. Most E&L publications today are centered around the latter part, and the effect of extraction solvents on the chemical composition of extracts in the number, concentration and molecular weight (MW) has not been systematically delineated and conceptualized to the best of our knowledge. The focus of this study is on a systematic review and analysis of the effect of solvents on the composition of extracts based on an extensive collection and study of relevant publications. The details of the discussions include: (1) the solvent extraction processes; (2) the degree of solvent-material interactions; (3) the material swelling and diffusion rate of material constituents; (4) the MW impact from swelling; and (5) finally, the conclusion of the dependency of chemical compositions in final extracts on solvent. Experimental data have also been collected and presented to support the conclusions of the study. The implications of the solvent-dependent chemical composition on analytical measurements of E&L by using both chromatography-based and gravimetric methods are briefly and critically discussed at the end.

Uncovering the morphological effects of high-energy Ga+ focused ion beam milling on hBN single-photon emitter fabrication.

Many techniques to fabricate complex nanostructures and quantum emitting defects in low dimensional materials for quantum information technologies rely on the patterning capabilities of focused ion beam (FIB) systems. In particular, the ability to pattern arrays of bright and stable room temperature single-photon emitters (SPEs) in 2D wide-bandgap insulator hexagonal boron nitride (hBN) via high-energy heavy-ion FIB allows for direct placement of SPEs without structured substrates or polymer-reliant lithography steps. However, the process parameters needed to create hBN SPEs with this technique are dependent on the growth method of the material chosen. Moreover, morphological damage induced by high-energy heavy-ion exposure may further influence the successful creation of SPEs. In this work, we perform atomic force microscopy to characterize the surface morphology of hBN regions patterned by Ga+ FIB to create SPEs at a range of ion doses and find that material swelling, and not milling as expected, is most strongly and positively correlated with the onset of non-zero SPE yields. Furthermore, we simulate vacancy concentration profiles at each of the tested doses and propose a qualitative model to elucidate how Ga+ FIB patterning creates isolated SPEs that is consistent with observed optical and morphological characteristics and is dependent on the consideration of void nucleation and growth from vacancy clusters. Our results provide novel insight into the formation of hBN SPEs created by high-energy heavy-ion milling that can be leveraged for monolithic hBN photonic devices and could be applied to a wide range of low-dimensional solid-state SPE hosts.

Material swelling with partial confinement in the internally balanced generalization of hyperelasticity

The internally balanced material theory, which can be viewed as a generalization of hyperelasticity, is extended to treat material swelling. Swelling problems involving eventual contact with fixed rigid surfaces are considered, first for a situation where the post-contact deformation is homogeneous, and then for a situation where the post-contact deformation is not homogeneous. The latter requires the solution of a boundary value problem in the internally balanced material setting. Both situations are considered in detail for a neo-Hookean-like constitutive specification in the internally balanced material framework.

Dandelion pappus morphing is actuated by radially patterned material swelling.

Plants generate motion by absorbing and releasing water. Many Asteraceae plants, such as the dandelion, have a hairy pappus that can close depending on moisture levels to modify dispersal. Here we demonstrate the relationship between structure and function of the underlying hygroscopic actuator. By investigating the structure and properties of the actuator cell walls, we identify the mechanism by which the dandelion pappus closes. We developed a structural computational model that can capture observed pappus closing and used it to explore the critical design features. We find that the actuator relies on the radial arrangement of vascular bundles and surrounding tissues around a central cavity. This allows heterogeneous swelling in a radially symmetric manner to co-ordinate movements of the hairs attached at the upper flank. This actuator is a derivative of bilayer structures, which is radial and can synchronise the movement of a planar or lateral attachment. The simple, material-based mechanism presents a promising biomimetic potential in robotics and functional materials.