Chemical vapor deposition of a thin titanium dioxide (TiO2) film on lightweight native nanocellulose aerogels offers a novel type of functional material that shows photoswitching between ...water‐superabsorbent and water‐repellent states. Cellulose nanofibrils (diameters in the range of 5–20 nm) with native crystalline internal structures are topical due to their attractive mechanical properties, and they have become relevant for applications due to the recent progress in the methods of their preparation. Highly porous, nanocellulose aerogels are here first formed by freeze‐drying from the corresponding aqueous gels. Well‐defined, nearly conformal TiO2 coatings with thicknesses of about 7 nm are prepared by chemical vapor deposition on the aerogel skeleton. Weighing shows that such TiO2‐coated aerogel specimens essentially do not absorb water upon immersion, which is also evidenced by a high contact angle for water of 140° on the surface. Upon UV illumination, they absorb water 16 times their own weight and show a vanishing contact angle on the surface, allowing them to be denoted as superabsorbents. Recovery of the original absorption and wetting properties occurs upon storage in the dark. That the cellulose nanofibrils spontaneously aggregate into porous sheets of different length scales during freeze‐drying is relevant: in the water‐repellent state they may stabilize air pockets, as evidenced by a high contact angle, in the superabsorbent state they facilitate rapid water‐spreading into the aerogel cavities by capillary effects. The TiO2‐coated nanocellulose aerogels also show photo‐oxidative decomposition, i.e., photocatalytic activity, which, in combination with the porous structure, is interesting for applications such as water purification. It is expected that the present dynamic, externally controlled, organic/inorganic aerogels will open technically relevant approaches for various applications.
Photoswitching between a water‐superabsorbing state and a water‐repellent state is demonstrated using highly porous, native nanocellulose aerogels coated with a thin TiO2 film by chemical vapor deposition. The nanofibril aggregations and porosity at different length scales are compared to those of similarly treated nanocellulose films and filter paper references.
The rapid development of the electronic packaging industry has necessitated the production of epoxy resin insulation materials with high heat resistance and low water absorption. In this study a new ...cross‐linking composite composed of polyhedral oligomeric silsesquioxane (POSS) functionalized with isocyanate groups and epoxy resin (EP) containing phenolic hydroxyl groups. By employing an isocyanate‐hydroxyl process, the cage structure of Ph7POSS with isocyanate functionalization (MP) can be suspended on EP, leading to a significant improvement in the thermal and moisture resistance of the MP/EP composite. Our DSC and TGA studies revealed that the addition of 3% MP to the epoxy resin increased the glass transition temperature by 27.1°C and raised the initial thermal breakdown temperature to 334.5°C. We also utilized a novel quartz crystal microbalance (QCM) technique to continuously monitor the moisture resistance of the composite, and our results showed that the composite absorbed only 0.03% of water. Moreover, the porosity and cross‐linking of the POSS molecules further restricted the movement of the polymer chains, thereby reducing the dielectric constant and dielectric loss of the composite. Consequently, the MP‐modified epoxy composites exhibit excellent properties, which suggest promising applications in the field of electronic packaging.
•The silane-based emulsion has low penetration depth due to the large micelle size.•The water absorption can be significantly suppressed by the hydrophobic agent.•The agent has excellent thermal, ...low-temperature, UV, alkali and acid resistances.•The waterborne hydrophobic agent possesses good water penetrability.•The surface impregnation increases the compactness of cement based materials.
The physicochemical properties of a self-developed, waterborne, saline-based hydrophobic agent and the chloride resistance of concrete treated with the waterborne hydrophobic agent are presented in this paper. The low penetration depth of the waterborne hydrophobic agent is found to be primarily determined by the large micelle size. Moreover, the capillary water absorption is significantly suppressed by the surface treatment of the cement-based substrates with the waterborne hydrophobic agent. In terms of the water penetrability, the waterborne hydrophobic agent has remarkable thermal, low-temperature, ultraviolet, alkali and acid resistances. The compactness of the mortar specimen impregnated with the waterborne hydrophobic agent is improved, resulting in the unexpected increase in the water impermeability of the impregnated mortar. In addition, the impregnated concrete specimen has a pronounced chloride resistance. The penetration depth of the waterborne hydrophobic agent developed in this work is as low as 0.43mm, yet it is still more than qualified to serve asa waterproofing product.
Natural fibres (NFRs) composite materials are acquiring popularity in the modern world due to their eco-friendliness and superior mechanical properties. Although it has been shown that determining ...this is a herculean endeavour in the literature, the water absorption (WA) qualities of the natural fibre (NFR) are crucial in the progressive degradation of the features of the resulting composites. This article seeks to report exhaustively on studies pertaining to the WA attributes of polymer composites reinforced with NFRs. This article provides an overview of NFR, its characterization, and the issues related to its addition to the matrix. The primary purpose of this research study is to investigate existing studies on the problems associated with the creation of cellulosic fibre hybrid composites, water absorption, and its impact on the tensile (TS), flexural (FS), and impact strength (IS) of NFR reinforced composites. We reviewed various surface treatments (ST) applied to NFR, including alkali treatment, silane treatment, acetylation, as well as recent advancements aimed at mitigating WA, enhancing hydrophobicity, and improving the interfacial bonding (IB) between NFR and the polymer matrix (PM). Additionally, we assessed the effectiveness of utilizing nanoparticles (NAPs) in specific ST of NFR to minimize water absorption.
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•Introduction of the natural fiber, its characteristics.•Investigate the effects of surface modifications on aspects such as hydrophilicity.•The specifics of each surface treatment technique, along with the pros and cons of it.•The application of nanoparticles enhances the hydrophobicity.
•Influence of fly ash and GW, separately and jointly, on the fresh and hardened properties of SCC were examined.•Incorporation of fly ash in granite based SCC mixes improved the fresh ...characteristics.•Granite based SCC mixes prepared with fly ash showed higher UPV and superior resistance to water absorption.•Granite based SCC mixes prepared with fly ash exhibited the dense microstructure.
This research intends to use granite waste (GW) and fly ash as alternatives for fine aggregate and cement, respectively, for the sustainable production of self-compacting concrete (SCC). The fresh properties were evaluated using slump flow, T500 flow, V-funnel, J-ring, and L-box tests, while the hardened properties were evaluated in terms of using compressive strength, flexural strength, water absorption, and ultrasonic pulse velocity tests. The results of the fresh properties showed that they were adversely affected by the incorporation of GW. However, the incorporation of fly ash improved the fresh properties and mitigated to some extent the negative effect of GW on the fresh properties. The incorporation of GW in SCC mixes augmented the hardened properties. The incorporation of fly ash further enhanced the hardened properties (except strength properties). The findings of this study revealed that the combined use of GW and fly ash in SCC has the potential to considerably enhance the fresh and hardened properties (without adversely affecting the strength characteristics).
•Designed, fabricated, and tested a flat plate manifold microchannel heat exchanger.•Developed a specially designed manifold to allow distribution of the flow.•Achieved heat transfer coefficients as ...high as 66,000 W/m2K for water.•Demonstrated reasonable agreement between the experimental and the numerical results.•Potential use is in process, air conditioning and refrigeration applications.
The design and performance testing of a single-phase, flat plate, manifold microchannel heat exchanger with water as the working fluid are discussed in this paper. The aim of this study was to explore the use of manifolding of microchannels for performance enhancement of plate heat exchangers for single-phase, low heat flux (process type) applications operating in a counter flow configuration. The paper discusses the design of the heat exchanger, followed by the experimental testing and numerical simulation results. The experimental tests reveal that the heat exchanger is capable of delivering an overall heat transfer coefficient of close to 20,000 W/m2K at flow rates as low as 20 g/s (corresponding to a microchannel Reynolds number of 30) and a pressure drop per length value of 5.85 bar/m. The experimental results also are compared with established counter flow heat exchanger ε-NTU correlations to verify counter flow performance. Further, numerical simulation results for a single unit cell of the same geometry, which show reasonable agreement with the experimental results, are also described in this paper. The current work demonstrates successful use of microgrooves/microchannels for performance enhancement of plate heat exchangers for diverse industrial applications, including the refrigeration/air conditioning, process, and power production sectors.
•Mycorrhizal hyphae have the role in water absorption from soil.•Hyphal water absorption rate was 0.126–1.973mg H2O/h/mm in trifoliate orange.•Drought significantly elevated hyphal water absorption ...rate by 2.3–6.6 times.•Hyphal water contribution to host plants is more important under DS than under WW.
Mycorrhizal hyphae have the functioning on water absorption from soil, while the information regarding hyphal water absorption rate is not fully known. In this study, 37-μm nylon meshes were positioned in a pot bottom to allow mycorrhizal extraradical hyphae, but not roots, to pass through the mesh. The whole pot was placed in a beaker, where distilled water was supplied, reaching a 0.5-cm air gap between the pot bottom and water surface of the beaker. Citrus rootstock, trifoliate orange (Poncirus trifoliata) seedlings of pots were inoculated with Funneliformis mosseae and Paraglomus occultum and also exposed to well-watered (WW) and drought stress (DS). The 71-days soil DS significantly inhibited root mycorrhizal colonization and hyphal length in soil and mesh, regardless of mycorrhizal fungal species. The hyphal water absorption rate was 0.607–1.973mg H2O/h/mm for F. mosseae and 0.126–0.963mg H2O/h/mm for P. occultum, respectively. The DS treatment significantly elevated hyphal water absorption rate by 2.3–6.6 times. The increase of leaf water potential by mycorrhization was higher under DS than under WW. Our results provide a quantitative estimation of water absorption rate by mycorrhizal extraradical hyphae and also suggest more important water contribution of hyphae to the host plant under DS than under WW.
This paper focuses on modeling the water absorption and the resulting internal stress behavior of steel/rubber composites. A three-dimensional finite element model, which includes the internal ...microstructure of bundled long steel wire reinforced composite, is established to accurately simulate water diffusion behavior. The water diffusion coefficient and rubber matrix's hygroscopic expansion parameter are estimated by experiments. The outcomes demonstrated that the earliest stages of water diffusion of steel/rubber composites conformed to the Fickian model. Then the weight gain continued to increase and followed the Langmuir model instead of Fickian model owing to the presence of bound water. Both the free water and bound water in steel/rubber composites were modeled by FE software. The internal stress caused by the differential swelling between steel and rubber was revealed and quantitatively analyzed through finite element simulation. The internal stress is the main cause of damage initiation in the steel/rubber composites, which was in good agreement with experimental measurements.
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•The water absorption mechanisms of steel/rubber composites were systematically studied.•There were two stages of water absorption behavior of steel/rubber composites due to the existence of free and bound water.•The FE model of composite's true internal geometry were established to simulate the water diffusion behavior.•The evolution of internal stress analysis by FE method was in good agreement with experimental results.•The internal stress is the main cause of damage initiation in the steel/rubber composites.
This work presents an experimental investigation into the effect of cornhusk fibre (CHF) content upon the mechanical properties, water absorption behaviour, and swellability of CHF/polyester (PE) ...composites used in water environments. The CHF/PE was prepared at different volume fractions using hot compression (~175 °C). To investigate the rate of water absorption and swellability behaviours, composites were immersed in water for varying durations. The mechanical properties of composites (i.e. tensile, bending and compression strengths) immersed in water were carefully evaluated. The results indicate that the composites with an increased CHF content and a longer immersion time are prone to lower mechanical properties. The large amount of water absorbed by the composite reduces the bonding interface between CHF and PE, which is responsible for the damage. Moreover, the amount of water absorbed and the swellability increase with a corresponding increase in the CHF content. The lowest water absorption (2.39%) was detected in 20% CHF and 80% PE composite immersed for 6 days. The findings gathered in this research endorse CHF/polyester thermoset composites as a viable alternative for construction applications.
•Investigation of the effect of corn husk fiber (CHF) content on the mechanical properties.•The capacity of water absorption and swelling thickness is directly related to the density of sample.•The CHF composites was found to be a viable alternative for construction application.
Moisture and water transport in clay bricks are essential contributing factors towards brick decay in buildings. Experimental work is reported comparing water absorption and porosity of handmade and ...solid fired clay bricks from Paraguay. Their respective porosities were estimated by gravimetric test and, their pore distribution, degree of anisotropy and morphology were examined by SEM. Although it was found that both samples have a common composition (XRD), a higher degree of porosity was found in handmade bricks, which also absorb water at a higher rate accelerating the decay process. Experimental data is reported on the exponential kinetics behavior of water absorption similar to the one observed in capillary tubes, but with an additional diffusive process. A phenomenological model is proposed for water absorption in both types of bricks which compared with the standard model of water absorption available in the literature, produces a better representation of the experimental data.
