Meiyun Zhang

Spontaneous Inertial Imbibition in Porous Media Using a Fractal Representation of Pore Wall Rugosity

Considering the separable phenomena of imbibition in complex fine porous media as a function of timescale, it is noted that there are two discrete imbibition rate regimes when expressed in the Lucas–Washburn (L–W) equation. Commonly, to account for this deviation from the single equivalent hydraulic capillary, experimentalists propose an effective contact angle change. In this work, we consider rather the general term of the Wilhelmy wetting force regarding the wetting line length, and apply a proposed increase in the liquid–solid contact line and wetting force provided by the introduction of surface meso/nanoscale structure to the pore wall roughness. An experimental surface pore wall feature size regarding the rugosity area is determined by means of capillary condensation during nitrogen gas sorption in a ground calcium carbonate tablet compact. On this nano size scale, a fractal structure of pore wall is proposed to characterize for the internal rugosity of the porous medium. Comparative models based on the Lucas–Washburn and Bosanquet inertial absorption equations, respectively, for the short timescale imbibition are constructed by applying the extended wetting line length and wetting force to the equivalent hydraulic capillary observed at the long timescale imbibition. The results comparing the models adopting the fractal structure with experimental imbibition rate suggest that the L–W equation at the short timescale cannot match experiment, but that the inertial plug flow in the Bosanquet equation matches the experimental results very well. If the fractal structure can be supported in nature, then this stresses the role of the inertial term in the initial stage of imbibition. Relaxation to a smooth-walled capillary then takes place over the longer timescale as the surface rugosity wetting is overwhelmed by the pore condensation and film flow of the liquid ahead of the bulk wetting front, and thus to a smooth walled capillary undergoing permeation viscosity-controlled flow.

Toward high-performance poly(para-phenylene terephthalamide) (PPTA)-based composite paper via hot-pressing: the key role of partial fibrillation and surface activation

The inert surface of para-aramid fibers makes para-aramid fiber-based composites suffer from a poor interfacial interaction and limited physical properties. In this work, the influence of hot-pressing on paper structural properties was explored. Without hot-pressing, in comparison with the fibrid paper (Paper-I), the addition of para-aramid chopped-fiber obviously enhanced mechanical properties, but led to slight damage of the dielectric properties of the fiber/fibrid paper (Paper-II) because of voids and defects. After hot-pressing, it was noteworthy that the increased mechanical properties and dielectric properties of the papers were mainly due to the individual pressing treatment and independent of the individual heating treatment. Interestingly, the combined treatment of heating and pressing shows a synergistic effect and results in an increase of paper compactness especially for Paper-II. Meanwhile, the interfacial interaction between different fibers in the composite papers was greatly improved, which is mainly associated with the partial dissociation into a fibrillar structure and the improved surface activation of para-aramid chopped fibers. Therefore, fiber micro-fibrillation is highly effective for improving internal bonding and optimizing physical properties for para-aramid-based composite papers.

UV-curable ladder-like diphenylsiloxane-bridged methacryl-phenyl-siloxane for high power LED encapsulation

A UV curable ladder-like diphenylsiloxane-bridged methacryl-phenyl-siloxane (L-MPS) was synthesized from phenyltrichlorosilane, diphenylsilanediol and methacryloxypropyldimethylmethoxysilane via dehydrochlorination precoupling, supramolecular architecture-directed hydrolysis-condensation and end-capping reactions. The L-MPS has a condensation degree of ∼100%, and can be complete crosslinked by UV curing. XRD, TEM and molecular simulation suggest that the ladder-like molecules are close packed with a periodic distance of ca. 1.2 nm. The L-MPS shows transmittance of 98% and a refractive index of ca. 1.61 at 450 nm. The cured L-MPS with a Td5% value of 465.5 °C showed excellent anti-yellowing and anti-sulfidation properties. The cured L-MPS film and the encapsulated LED samples were compared with those of Dow Corning OE-6630 and OE-7662. It is believed that the dense nano-ladder unit also contributes to the thermal, gas barrier and even optical properties. L-MPS shows promising potential as a high power LED encapsulant and optical coating for use in harsh environments. This work provides an approach to integrate this novel ladder structure with advanced properties.

Contrasting liquid imbibition into uncoated versus pigment coated paper enables a description of imbibition into new-generation surface-filled paper

Abstract.The transport of print fluids into paper is directly dependent on the imbibition characteristic of the paper including both the z-, x- and y-directions. As the measurement of free liquid imbibition into the paper thickness (z-direction) is difficult experimentally, due to the thin nature of paper, in this paper we resort to imbibition along the y-direction of paper to analyse and explore the possibility of understanding the mechanistic differences between wicking into uncoated unfilled paper versus that of controllable pigment-filled paper and paper coating. Considering the classical imbibition dynamic, the measured imbibition was characterised firstly with respect to

Toward high-performance fibrillated cellulose-based air filter via constructing spider-web-like structure with the aid of TBA during freeze-drying process

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Fabrication of mechanically robust and UV-resistant aramid fiber-based composite paper by adding nano-TiO 2 and nanofibrillated cellulose

√t and secondly with respect to linear t. It is shown that the wicking behaviour of uncoated unfilled paper follows neither the classical viscous drag balance model of Lucas-Washburn (

Fabrication and characterization of differentiated aramid nanofibers and transparent films

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Revealing the Components at Work in Classical Liquid Imbibition Models: Inertial, Bosanquet and Viscous Lucas-Washburn Applied to Printing

√t) nor the more comprehensive inertia-included imbibition described by Bosanquet. However, by increasing the filler load into the surface layer of the paper, the imbibition dynamic is seen to revert to the Bosanquet model. Thus, when using highly filled papers, the imbibition dynamic for printing liquid shows a fast imbibition at the initial stages dominated by inertial plug flow, and then transits to the Lucas-Washburn viscosity-dominated imbibition component over longer time.Graphical abstract

Engineered porous calcium silicate as paper filler: effect of filler morphology on paper properties

In consideration of the healthcare issues caused by Particulate Matter (PM) pollution, developing high-performance air-filter materials especially aiming at filtering PM2.5 has attracted great attention. In this work, we fabricated a novel air filter with spider-web-like structure based on renewable and biodegradable fibrillated cellulose fibers, and demonstrated an effective strategy for network structure regulation during freeze-drying process. The results showed that the air filter with spider-web-like structure, whose filtration efficiency for model PM particles with the diameter of 300xa0nm could exceed 99%, was obtained from a fibrillated cellulose fiber/water/Tert-Butyl Alcohol (TBA) mixture by freeze-drying. The role of TBA in the construction of spider-web-like structure was mainly due to the following two aspects: (1) TBA molecules could promote the separation of microfibrils which acted as the cobwebs in spider-web-like structure. (2) The presence of TBA resulted in air filter transformed from lamellar porous architecture into spider-web-like structure by changing the morphologies and growth kinetics of ice-crystals. Herein, this work paves a way to fabricate high-performance air filters based on renewable materials and the pore-formation mechanism can provide a guide for structure regulation in porous materials.

Analysis and Measurement of the Imbibition Characteristic of Paper Based in the y-Direction

AbstractAramid fiber-based composite paper is widely used as an engineering material that is often used in outdoor environments. This inevitably cause ultraviolet (UV) damage to aramid fibers. In this work, nanotitanium dioxide (nano-TiO2) was introduced to endow the composite a good UV-resistance while nanofibrillated cellulose (NFC) was used to disperse and deposit TiO2 nanoparticles onto aramid fibers by physical interaction. Firstly, TiO2 nanoparticles were treated by (γ-aminopropyl) triethoxysilane to achieve abundant amino-groups (–NH2), which can interact with hydroxyl groups (–OH) of NFC. The results showed that NFC can significantly suppress nano-TiO2 aggregation and result in a well-defined core–shell structure of TiO2 nanoparticles uniformly coated onto aramid fibers. Also, the bridge effect of NFC and the reinforcing effect of nano-TiO2 benefit the mechanical properties the aramid/NFC/TiO2 composite. The maximum tensile index (~u200916.42xa0Nxa0m/g) and maximum tearing index (~u20099.28xa0mNxa0m2/g) of aramid/NFC/TiO2 composites increase by ~u200943.4 and ~u200926.1% in comparison with the control sample (~u200911.45xa0Nxa0m/g and ~u20097.36xa0mNxa0m2/g), respectively. Meanwhile, the aramid/NFC/nano-TiO2 composite achieves a good UV-resistant property because of the dominant light-absorbing ability of well-dispersed TiO2 nanoparticles. Therefore, our work presents a green and damage-free approach to achieve high-performance aramid fiber composite especially with great UV resistance.nGraphical Abstract