Guodong Liu

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.

Micro nanofibrillated cellulose (MNFC) gel dewatering induced at ultralow-shear in presence of added colloidally-unstable particles

Aqueous nanogels are notoriously difficult to dewater. An example of such a gel is that of a suspension of micro nanofibrillated cellulose, in which water is both bound to the fibrillar surface and held within the interfibril matrix. We demonstrate a phenomenon in which dewatering of nanocellulose based gel-like suspensions can be induced by adding a colloidal particulate component, which itself can undergo autoflocculation when suspended in water. The mechanism is exemplified by the addition of undispersed precipitated calcium carbonate, which in equilibrium remains stabilised in the gel, but when the gel mix is exposed to ultralow shear, acting below the yield stress, demixing of the combination between the nanofibrils and the autoflocculating pigment leads to separation of the unbound water phase. This novel mechanism is proposed to enhance the dewatering capability in general of complex gel-like water-holding suspensions.

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

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

\surd{} t

A promising transparent and UV-shielding composite film prepared by aramid nanofibers 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 (

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

\surd{} t

The fractal characteristic of porous coatings prepared with ground calcium carbonate

√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

Pore wall rugosity: The role of extended wetting contact line length during spontaneous liquid imbibition in porous media

The classical imbibition models: inertial, Bosanquet and the later dominance of viscous flow, thus following the Lucas-Washburn regime, frequently are employed to characterise the imbibition behaviour of printing fluids in paper or paper-based materials. To explore the interaction relationship among these imbibition models, theoretical simulation regarding the imbibition process based on these three models is discussed and analysed in this paper under uniform physical parameters. Additionally, their mutual relationship also was displayed by means of analysis and simulation results with different radii of the equivalent capillary tube aiming at different papers or paper-based materials, with focus on coated grades. It is found that these classical imbibition models indeed have an interaction relationship in the whole imbibition process, which is that Bosanquet is a more general form to characterize imbibition behaviour both inertial and viscous, each of which describe the dominant imbibition stages during the absorption process and have an overlapping area at initial stages and times of geometrical change within the structure related to the inertial regime respectively. The overlapping point timescale changes, and is extended when the equivalent radius of capillary tube of print materials is relatively large or small. It means that the consistency of this circumstance between inertial and viscous behaviour would extend into longer periods when having a large equivalent radius of capillary tube. By contrast, if the equivalent radius is small, the inertial and viscous regimes would reach a parallel situation at an earlier point of imbibition time. It also indicates that inertial imbibition and the viscous imbibition model enable one solve the Bosanquet imbibition at the initial stage and later imbibition during some specific cases, but the permeability and viscous flow dominate at the later bulk volume imbibition stage. In addition, Bosanquet takes care of transitions between the inertial model and the L-W model due to including both effects in its expression. Thus, when the whole imbibition process needs to be characterised, the Bosanquet would be the optimal choice if the complex network structure is well characterized and the computational model available.

Structural evidence for the timescale separated liquid imbibition phenomenon in porous media

An aramid nanofibers (ANFs)-functionalized nanofibrillated cellulose (NFC) composite film is effectively fabricated by the incorporation of ANFs into nanocellulose matrix. The fabrication of the composite film imitates the traditional paper-making process after homogenous mixing. The as-prepared composite film shows excellent UV-shielding performance due to the incorporation of ANFs. Thus the effect of ANFs contents is evaluated in aspects of the surface morphology, physicochemical properties including crystallinity, chemical structure and photothermal stability of composite film. Results show that the composite film with 2 wt.% of ANFs has improved mechanical properties, surface wettability compared to pure NFC film, and presents excellent UV-shielding performance ranging up to 400 nm while still retaining its high transparency. Moreover, the composite film shows high photostability even after continuous UV irradiation (365 nm) for over 12 h. The findings in the present work indicate that the ANFs-functionalized NFC composite films are promising as UV-shielding and transparent materials.