Water-induced Swelling Research Articles

A two-scale model describing swelling in porous materials with elongated internal structures

We consider a two-scale parabolic problem describing the water-induced swelling for a class of porous materials with elongated internal structures. The system of evolution equations we are considering here consists of a parabolic equation describing the evolution of the moisture content into a macroscopic domain coupled in a two-scale fashion to a free boundary problem capturing a microscopic swelling process. The macroscopic domain is a three-dimensional object (the target porous material), while the microscopic domains are a stack of elongated pores modeled as one-dimensional halflines connected at an edge to the macroscopic domain. By imposing a flux boundary condition at the edge of each pore, we allow the moisture content to intrude into the respective microscopic domain. In this work, we prove the existence and uniqueness of a solution to our two-scale problem. One key ingredient in our proof is the guarantee that the microscopic solution is measurable with respect to variable pointing out to the macroscopic domain. By using the Banach’s fixed-point theorem, we establish the local-in-time well-posedness of our two-scale problem.

Volume Regulation and Nonosmotic Volume of Individual Human Platelets Quantified by High-Speed Scanning Ion Conductance Microscopy.

Platelets are anucleate cells that play an important role in wound closure following vessel injury. Maintaining a constant platelet volume is critical for platelet function. For example, water-induced swelling can promote procoagulant activity and initiate thrombosis. However, techniques for measuring changes in platelet volume such as light transmittance or impedance techniques have inherent limitations as they only allow qualitative measurements or do not work on the single-cell level. Here, we introduce high-speed scanning ion conductance microscopy (HS-SICM) as a new platform for studying volume regulation mechanisms of individual platelets. We optimized HS-SICM to quantitatively image the morphology of adherent platelets as a function of time at scanning speeds up to 7 seconds per frame and with 0.1 fL precision. We demonstrate that HS-SICM can quantitatively measure the rapid swelling of individual platelets after a hypotonic shock and the following regulatory volume decrease (RVD). We found that the RVD of thrombin-, ADP-, and collagen-activated platelets was significantly reduced compared with nonactivated platelets. Applying the Boyle-van't Hoff relationship allowed us to extract the nonosmotic volume and volume fraction on a single-platelet level. Activation by thrombin or ADP, but not by collagen, resulted in a decrease of the nonosmotic volume, likely due to a release reaction, leaving the total volume unaffected. This work shows that HS-SICM is a versatile tool for resolving rapid morphological changes and volume dynamics of adherent living platelets.

Ammonia permeation and plasticization of glassy polymeric membranes

Ammonia (NH3) is a vital industrial chemical and a potential clean fuel, whose production is increasing globally. The permeation of ammonia through glassy polymeric membranes demonstrates considerable variability, due to hydrogen bonding with both the polymer and residual water. This study reveals the underlying mechanisms for ammonia permeability within membranes, which is strongly correlated with the presence of water and the polymer's chemistry. Three polymers with varying water/ammonia affinity were studied: poly (vinyl alcohol) (PVA), polysulfone (PSU), and Teflon AF 1600. Ammonia was found to readily plasticize PVA, with sorption isotherms that follow Henry's law at conditions below the nominal glass transition temperature. Residual water within the PVA membranes increased ammonia permeability by an order of magnitude greater than that observed for well-dried PVA, due to water-induced swelling. PSU, being hydrophobic, was unaffected by residual water, though ammonia permeability was clearly time-dependent with a 50 % reduction over 4 days. This was attributed to ammonia clustering within the ammonia phobic PSU, which resulted in pore-blocking. The superhydrophobic Teflon AF 1600 membrane demonstrated the same time dependent permeability behaviour, but at a much faster timescale of minutes rather than days. It is suggested that this relates to the rate of formation of ammonia clusters, which is dependent on the degree of ammonia sorption within the polymer.

High-performance cellulose nanofibers-based actuators with multi-stimulus responses and energy storage

Smart actuating materials have received tremendous attention due to their promising applications in miniaturized robots, integrated electronics and wearable devices. However, simultaneously achieving sensitive multi-stimuli responsiveness, preferable energy storage capability and adequate mechanical properties by one material in a simple yet efficient way remains a considerable challenge. Herein, we propose a novel multi-responsive nanocomposite film actuator consisting of negatively charged cellulose nanofibers (CNF), polydopamine-chelated MXene-Fe3O4 nanohybrids (PMF) and positively charged carbon nanotubes (CCNT) via a cost-efficient electrostatic self-assembly approach. Benefiting from the laminated porous structure and compositional superiorities, including the water-induced swelling effect of CNF and PMF, conductive CCNT with countless interior hydrophobic channels and magneto-conductive properties of PMF, the optimized nanocomposite film actuator presents a high bending speed (100.5°/s), ultrashort actuation time (2.0 s), long-term stability (1005 cycles) and good magnetic response. These actuators can be assembled into a supercapacitor exhibiting an areal capacitance of 33.5 mF/cm2 at 0.5 mA/cm2 and good cycling stability with a capacitance retention of 80.5 % after 5000 cycles. Furthermore, the actuators are designed as soft robots with different motion modes, mechanical grippers for performing consecutive actions and an integrated circuit system to monitor surrounding humidity changes. This work provides inspiration to develop advanced nanocomposite materials for smart devices that require multifunction integration.

Nacre-inspired composite film with mechanical robustness for highly efficient actuator powered by humidity gradients

Exploring and fabricating smart actuating materials that strike the perfect balance between humidity response and mechanical integrity (especially wet tensile strength) via reasonable structural design and simple yet low-cost preparation is critical for biomimetic devices, soft robotics, artificial muscles and generators, but it remains challenging. Herein, inspired by the structure of natural nacre, we demonstrated a robust yet highly sensitive composite film-based humidity actuator composed of carboxymethyl cellulose (CMC), MXene nanosheets, and multivalent aluminum ions (Al3+) via a facile evaporation-induced self-assembly method. The synergistic reinforcing effects of MXene nanosheets and Al3+ through hydrogen and ionic bonding as well as the densely hierarchical microstructure endow the composite film with both an ultrahigh mechanical strength (273.6 MPa), a desirable toughness (7.95 MJ/m3) and even an impressive wet tensile strength (154.2 MPa) at 97 % humidity. Interestingly, the unique laminated structure and water-induced swelling effect of CMC and MXene synergistically enable the composite film with large shape deformation, sensitive actuation (less than 2.3 s) and exceptional cycling stability (over 1500 cycles) upon exposure to humidity gradients. Based on the above merits, the composite film actuator can be well constructed to simulate a flying dragonfly, human finger, artificial muscle, and has also been preliminarily employed as a moist-electric generator, which provides new insight for designing comprehensive composite film-based actuators and reveals their extensive applications.

Silver nanowire-based stretchable strain sensors with hierarchical wrinkled structures

As an engineering frontier, highly stretchable sensors are widely applied in many fields, such as human motion detection, personal healthcare monitoring, and human-machine interactions. In this study, novel silver nanowire (AgNW)-based stretchable sensors with hierarchical wrinkled structures were fabricated through a two-step process, namely water-induced swelling and AgNW deposition. As highly soluble additives, sodium chloride particles were incorporated into the elastomer matrix. Upon soaking in dopamine aqueous solution, significant swelling was introduced onto the elastomer substrate. The dopamine deposition is accompanied with the swelling process, which endows the sample surface with ultra-hydrophilicity. Additionally, the dopamine-modified swollen samples “capture” the nanowires when subsequently immersed in AgNW/ethanol suspension, because the dopamine acts as a highly adhesive layer. Finally, the sensors with wrinkled conductive network have been constructed upon removal of residual water. Both films and 3D printed sensors were fabricated and their electrical properties were systematically characterized. The fabricated sensors exhibit high sensitivity when subjected to external deformation from 10% to 100% strains, good electrical repeatability during 8000 stretching/releasing cycles, and reliable electrical responses in different frequencies of stretching/releasing. Human motion detection has been demonstrated using the 3D printed sensors, revealing the potential application in wearable electronics for healthcare monitoring and rehabilitation.

Water-Stable Nanoporous Polymer Films with Excellent Proton Conductivity.

Achieving high values for proton conductivity in a material critically depends on providing hopping sites arranged in a regular fashion. Record values reported for regular, molecular crystals cannot yet be reached by technologically relevant systems, and the best values measured for polymer membranes suited for integration into devices are almost two orders of magnitude lower. Here, an alternative polymer membrane synthesis strategy based on the chemical modification of surface-mounted, monolithic, crystalline metal-organic framework thin films is demonstrated. Due to chemical crosslinking and subsequent removal of metal ions, these surface-mounted gels (SURGELs) are found to exhibit high proton conductivity (0.1 S cm-1 at 30 °C and 100% RH (relative humidity). These record values are attributed to the highly ordered polymer network structure containing regularly spaced carboxylic acid side groups. These covalently bound organic frameworks outperform conventional, ion-conductive polymers with regard to ion conductivity and water stability. Pronounced water-induced swelling, which causes severe mechanical instabilities in commercial membranes, is not observed.

Characterization and atomistic modeling of the effect of water absorption on the mechanical properties of thermoset polymers

An extensive experimental program and molecular dynamics (MD) simulations have been conducted to ascertain the effect of water absorption upon the mechanical degradation of thermoset polymers. Mechanical tests were conducted to determine the degradation of the mechanical properties at regular testing intervals for up to 300 days of water immersion. The outcome of our studies reveals the following: (i) a decrease in the elastic modulus and the tensile strength as a result of the plasticization of the considered epoxy caused by water-induced swelling, and (ii) a reduction of approximately 50% in the fracture strain due to water ingression. SEM micrographs of the fracture surface revealed an abundance of aggregates, crazes, and microcracks as a result of aging in water. Meanwhile, AFM images further depicted step and stacked lamellar topological features of the fracture surface. In addition to the plasticization effect, there is a partial recovery of the elastic modulus at certain water absorption content. Such anti-plasticization effect of water molecules on the epoxy was demonstrated by both experiments and MD simulations. The elastic properties of the epoxy with and without different water contents were predicted by MD simulations, and the results corresponded with the experimental aging trend. The MD predictions further revealed that the water diffusion coefficient decreases with the increase in the epoxy density.

Modelling of water transport with convection effects on amylose transfer in a swelling, eroding and gelatinizing starchy matrix

A 1D mechanistic model was developed to describe water, deformation, amylose transport and starch gelatinization inside rice grains during cooking. Four migrating species were considered: two water populations according to the state of the starch, soluble amylose and an insoluble solid phase network. Three coupled mass transport PDE were formulated assuming diffusional mass transport and using a Lagrangian-Eulerian framework. The model integrates the convective effect of a water flux on the transport of soluble amylose. Rice grain deformation was the result of both water-induced swelling and erosion of the surface of the solid phase, assuming a zero-order kinetic process. The model was adjusted on a milled Chil-bo rice cultivar steeped in excess water at 75 °C and 95 °C. After 30 min at 95 °C, which is the standard cooking time, water uptake, leaching of soluble amylose and the amount of eroded material were 3.15 kg kg−1 db, 5.0% and 15.5% (w/w) respectively. Using the predicted distribution of species within the grain, the model could help to control the texture of cooked rice.

Models to Couple Mechanics and Electrochemical Transport in Solid Electrolytes

Electrolytic transport models available in the literature primarily deal with liquid media; models for solid electrolytes in polymer-electrolyte-membrane (PEM) fuel cells [1] largely derive from theories originally formulated to describe fluids. Since a solid can sustain a deformation at equilibrium under an applied stress or strain, there is a fundamental difference in the transport physics. Accurately modelling water-induced swelling in ionomer membranes requires that solid mechanics be reconciled with the transport and kinetic behaviour of electrochemical systems [2]. Previous efforts made to consider membrane swelling usually operate on a global basis, accounting only for an overall volume change; it is not clear whether models that include local swelling effects do so in thermodynamically consistent ways. This talk will deal specifically with swollen ionomers, although the principles introduced apply equally well to other solid ion conductors. In the case of Nafion, as Fig. 1 shows, water and ionic transport can produce, and dynamically interact with, non-uniform local volume changes and associated distributions of stress, making electrochemical/mechanical coupling significant. Our strategy is to return to first principles, identifying and undoing the assumptions made specifically for liquid mixtures, and finding ways to ensure that the simultaneous use of ostensibly independent theories of kinematics, thermodynamics, and transport does not induce internal inconsistencies in the model. The incorporation of additional state variables such as pressure, stress, and strain requires the inclusion of new balance equations and constitutive laws: one must carry along a local balance of momentum, which relates the local pressure within the electrolyte to the distributions of stress and inertia; there must be a stress constitutive law that characterises the mechanical response (viscous, elastic, viscoelastic etc.); and strain must be defined in such a way that it ties deformed coordinates to a reference state while simultaneously abiding by the thermodynamic volume-explicit equation of state. Modifying the system of equations in the manner discussed above and tackling questions of model closure have helped us to produce a more robust and comprehensive set of equations to model Nafion. The underlying aim is to combine developments in continuum poroelasticity theory with advanced electrochemical transport models. Ultimately, such a model will help us rationalise the physics associated with swollen vapour-equilibrated Nafion-like membranes in fuel cells under isothermal, non-isobaric, and constrained or free-swelling conditions. Such a model could inform better water management schemes and efforts to improve membrane durability. It will also be useful to have a general framework for modelling solid electrolytes that can be applied to materials beyond Nafion where electrochemical/mechanical coupling is important. [1] Weber, A.Z. and J. Newman, Transport in polymer-electrolyte membranes - II. Mathematical model. Journal of the Electrochemical Society, 2004. 151(2): p. A311-A325. [2] Kusoglu, A. and A.Z. Weber, Electrochemical/Mechanical Coupling in Ion-Conducting Soft Matter. The Journal of Physical Chemistry Letters, 2015. 6(22): p. 4547-4552. Figure 1

The effects of water on the morphology and the swelling behavior of sulfonated poly(ether ether ketone) films

Thin sulfonated poly(ether ether ketone) films swell excessively in water. The extent of water-induced swelling is shown to be correlated with the optical anisotropy of the films, due to two distinct phenomena. Firstly, the optical anisotropy is directly related to the amount of water taken up from the surrounding ambient atmosphere, and thus to amount of water present in the material just prior to swelling. Secondly, the optical anisotropy corresponds to internal stresses in the film that affect the free energy of the film, and thus the potential of the film to swell. The anisotropy vanishes upon sorption of liquid water and returns when the water is desorbed. When the water is completely removed, the film changes from more or less colorless to an intense yellow color that can be attributed to molecular assembly of the aromatic rings in the polymer backbone. The color change is reversible and occurs immediately upon exposure to low humidity. For films prepared in the absence of water, the lack of hydration of the sulfonic acid groups affects the microphase separation behavior of the polymer. This is manifested by an apparent lower propensity to water-induced swelling. The possibility to affect the properties of sulfonated polymer films by varying the hydration state of the polymer during preparation can have important implications for applications of such films.

Anionic surfactant-doped Pebax membrane with optimal free volume characteristics for efficient CO2 separation

Calcium lignosulfonate (CaLS) is an organic anionic surfactant, which has been used for the first time as a charged additive to improve the performance of Pebax membranes for CO2 separation. Owing to the abundant hydrophobic groups and low charge density of lignosulfonate ion (LS2−), CaLS was found to efficiently interrupt the chain packing of Pebax 1657 matrix via both metal-organic complexation and hydrophobic interaction, endowing membranes with tunable fractional free volume (FFV). For dry membranes, CaLS could slightly enlarge membrane FFV without forming highly crosslinked structures. For humidified membranes, water-induced swelling led to a remarkable enhancement of FFV, while the hydrophobic interaction between CaLS and Pebax avoided excessive swelling. With the coexistence of CaLS and water, optimal FFV and moderate salting-out effect were acquired, resulting in very high CO2 permeability (3585Barrer) and fairly good CO2/gas selectivity (29 for CO2/CH4 and 71 for CO2/N2). The separation mechanism was discussed by analyzing the relationship between salting-out effect and the well-known solution-diffusion mechanism. Based on the performance comparison of Pebax–CaLS membrane with the previously reported Pebax–salt membranes, the guideline about the design of polymer electrolyte membranes for CO2 capture was tentatively proposed.

Macadamia (Macadamia integrifolia) shell and castor (Rícinos communis) oil based sustainable particleboard: A comparison of its properties with conventional wood based particleboard

The present study examines the suitability of particleboard made from ground macadamia nut shells bonded with castor oil derived resin as an environmentally sustainable substitute for conventional wood fiber/urea formaldehyde particleboards. The properties of the macadamia shell castor oil resin particleboard were compared with those of a wood fiber/castor oil resin particleboard and a conventional wood fiber/urea formaldehyde particleboard.The density of the macadamia shell particleboard was 43% higher than that of its wood fiber counterpart, in keeping with the higher density of the macadamia shells. Water absorption and water-induced swelling were much lower in the macadamia shell particleboard, being only one quarter of the value obtained for the wood fiber particleboard. This is consistent with the lower moisture absorption reported previously for macadamia shells.The internal bond strength was similar for the macadamia shell and wood fiber particleboards bonded with castor oil based polyurethane. The modulus of rupture and modulus of elasticity were however about 50% lower for the macadamia shell particleboard than for its wood fiber counterpart. This is considered to be due, at least in part, to the lower cellulose content of macadamia shells.Formaldehyde emissions from the castor oil resin particleboards were less than 5% of those typical of urea formaldehyde particleboards.Based on these findings it is considered that macadamia shell/castor oil particleboards have acceptable properties for use in the built environment. Their good moisture resistance makes them particularly attractive for use in humid environments, such as in bathroom and kitchen applications. Moreover, they have much lower environmental impact than conventional particleboards.

Sorption, swelling, and free volume of polybenzimidazole (PBI) and PBI/zeolitic imidazolate framework (ZIF-8) nano-composite membranes for pervaporation

We have studied alcohol- and water-induced swelling and sorption of PBI and PBI/ZIF-8 nano-composite membranes and characterized both dry and wet membranes by positron annihilation lifetime spectroscopy (PALS). The degrees of membrane swelling after immersing in alcohols and water follow the order of ethanol > methanol > water > n-butanol. Addition of ZIF-8 particles into PBI membranes suppresses the ethanol-, methanol- and water-induced PBI swelling. The water-induced swelling is subdued most severely because of the hydrophobic nature and rigid structure of ZIF-8 particles, while the n-butanol-induced swelling is enhanced owing to a greater free volume in the PBI/ZIF-8 membrane. The PALS studies confirm that the high pervaporation permeability of PBI/ZIF-8 membranes is attributed to the high fractional free volume (FFV) created by large cavities of ZIF-8 particles. In addition, the alcohol saturated PBI/ZIF-8 membranes have significantly smaller free volume radii than alcohol saturated PBI membranes. A correlation among FFV, pervaporation permeability and sorption diffusion coefficient has been developed. This study also demonstrates the importance of using PALS to characterize membrane structure changes in solvent-saturated membranes at a molecular level and to correlate pervaporation performance with solvent-induced swelling.

Water Penetration—Its Effect on the Strength and Toughness of Silica Glass

When a crack forms in silica glass, the surrounding environment flows into the crack opening, and water from the environment reacts with the glass to promote crack growth. A chemical reaction between water and the strained crack-tip bonds is commonly regarded as the cause of subcritical crack growth in glass. In silica glass, water can also have a secondary effect on crack growth. By penetrating into the glass, water generates a zone of swelling and, hence, creates a compression zone around the crack tip and on the newly formed fracture surfaces. This zone of compression acts as a fracture mechanics shield to the stresses at the crack tip, modifying both the strength and subcritical crack growth resistance of the glass. Water penetration is especially apparent in silica glass because of its low density and the fact that it contains no modifier ions. Using diffusion data from the literature, we show that the diffusion of water into silica glass can explain several significant experimental observations that have been reported on silica glass, including (1) the strengthening of silica glass by soaking the glass in water at elevated temperatures, (2) the observation of permanent crack face displacements near the crack tip of a silica specimen that had been soaked in water under load, and (3) the observation of high concentrations of water close to the fracture surfaces that had been formed in water. These effects are consistent with a model suggesting that crack growth in silica glass is modified by a physical swelling of the glass around the crack tip. An implication of water-induced swelling during fracture is that silica glass is more resistant to crack growth than it would be if swelling did not occur.

Distinct structural and optical regimes in natural silk spinning

This study investigates the relationship between birefringence and mechanical properties in the dragline silk of the gold orb weaving spider Nephila edulis. Using a custom birefringence-tensile testing device, we probed the orientation and water-induced swelling of fibers spun at variety of drawing rates ranging from 0.003 to 400 mm s(-1). Our results indicate that based upon drawing rate, silk fibers fall into three distinct regimes each with characteristic orientation and swelling properties. Further investigation using in situ tensile testing reveals interactions between a fiber's drawing speed, mechanical properties, and orientation that support previous model predictions. We propose that simultaneous birefringence-tensile testing provides a unique and readily accessible insight into the structural behavior of this interesting and important biomaterial.

Distribution Analysis of Triglyceride Having Repair Effect on Damaged Human Hair by TOF-SIMS

This study showed that hydrogenated palm oil was an effective conditioning agent for repair of damaged hair because it inhibits water-induced swelling of damaged hair. To understand the functional mechanism of hydrogenated palm oil, we conducted TOF-SIMS analysis of the penetration of this oil into damaged hair. TOF-SIMS analysis revealed that tripalmitin, a constituent of hydrogenated palm oil, penetrated into the cuticle and the outer cortex of damaged hair. This is considered as the mechanism responsible for inhibition of hair swelling by hydrogenated palm oil.

Gas permeation measurement under defined humidity via constant volume/variable pressure method

Many industrial gas separations in which membrane processes are feasible entail high water vapour contents, as in CO 2-separation from flue gas in carbon capture and storage (CCS), or in biogas/natural gas processing. Studying the effect of water vapour on gas permeability through polymeric membranes is essential for materials design and optimization of these membrane applications. In particular, for amine-based CO 2 selective facilitated transport membranes, water vapour is necessary for carrier-complex formation (Matsuyama et al., 1996; Deng and Hägg, 2010; Liu et al., 2008; Shishatskiy et al., 2010) [1–4]. But also conventional polymeric membrane materials can vary their permeation behaviour due to water-induced swelling (Potreck, 2009) [5]. Here we describe a simple approach to gas permeability measurement in the presence of water vapour, in the form of a modified constant volume/variable pressure method (pressure increase method).

Chlorhexidine release and water sorption characteristics of chlorhexidine-incorporated hydrophobic/hydrophilic resins

Objectives The aim of this study was to evaluate chlorhexidine release from unfilled non-solvated methacrylate-based resins of increasing hydrophilicity and to examine relationships among Hoy's solubility parameters, water sorption, solubility and the rate of chlorhexidine release. Methods Resin discs were prepared from light-cured, experimental resin blends (R1, R2, R3, R4 and R5) containing 0.0, 0.2, 1.0 and 2.0 wt.% chlorhexidine diacetate (CDA). Discs were immersed in distilled water at 37 °C, and mass changes were recorded at different periods. Spectral measurements were made to follow change in optical densities of storage solution to examine chlorhexidine release kinetics. After a 28-day period, water sorption, solubility, and the cumulative chlorhexidine release were obtained. Additionally, antibacterial study was performed by observing the presence of inhibition zone against Streptococcus mutans. Results The most hydrophilic resin (R5) exhibited the highest chlorhexidine release rate. The most hydrophobic resin (R1) exhibited the lowest rate. However, no inhibition zone was produced by any specimens stored in water for 2 weeks. The addition of CDA increased solubility significantly but had no effect on water sorption. Significant positive correlations were seen between water sorption and the cumulative chlorhexidine release. Significance Chlorhexidine release from resins may be related to water-induced swelling, which in turn is enhanced by the hydrophilicity of cured polymer matrix.

Water-Induced Swelling Displacements in Core Drilling Method

This paper discusses the nondestructive technique of core drilling to evaluate stresses in concrete. Core drilling measures the displacements found near a hole drilled in concrete and relates this to stresses present in the structure by using elasticity theory. During core drilling, the introduction of water causes concrete to swell. These swelling displacements directly lead to errors in estimating the stresses. In this paper, the author provides a way to correct these water-induced swelling displacement errors. Using the values presented in the research literature as a basis, the author estimates the depth of water penetration and the swelling strain due to water exposure. The apparent stresses are estimated using finite element modeling. Results, which are applied to an earlier non-related hole-drilling investigation, show that proper accounting for water-induced swelling displacements significantly improves accuracy in prediction.