Gravity-driven instabilities in fibrillar colloidal gels containing a second disperse phase

Fibrillar networks are of great importance for biological systems and many industrial applications. We investigate gravity-driven instabilities in fibrilalr colloidal gels containing a second disperse phase. We use a model system containing a surfactant-stabilized oil-in-water emulsion dispersed in a gel of cellulose microfibrils in the presence of carboxymethyl cellulose. Optical scanning of the creaming emulsion containing gels along the height was used to quantify the network evolution over time. We find a remarkable correlation between the concentration of microfibrils and creaming behaviour such as initial creaming speed and final gel height. We compare this behaviour to the theoretical model of gravitational stability of poroelastic gels, which was extended to account for particle shape anisotropy and the presence of a second disperse phase. Please click Additional Files below to see the full abstract

Post-fire forest restoration in the humid tropics: A synthesis of available strategies and knowledge gaps for effective restoration

Humid tropical forests are increasingly exposed to devastating wildfires. Major efforts are needed to prevent fire-related tipping points and to enable the effective recovery of fire-affected areas. Here, we provide a synthesis of the most common forest restoration strategies, thereby focusing on post-fire forest dynamics in the humid tropics. A variety of restoration strategies can be adopted in restoring humid tropical forests, including natural regeneration, assisted natural regeneration (i.e. fire breaks, weed control, erosion control, topsoil replacement, peatland rewetting), enrichment planting (i.e. planting nursery-raised seedlings, direct seeding) and commercial restoration (i.e. plantation forests, agroforestry). Our analysis shows that while natural regeneration can be effective under favourable ecological conditions, humid tropical forests are often ill-adapted to fire, and therefore less likely to recover unassisted after a wildfire event. Active restoration practices may be more effective, but can be costly and challenging to implement. We also identify gaps in knowledge needed for effective restoration of humid tropical forests after fire, hereby taking into account the ecosystems and socio-economic conditions in which these fires occur. We suggest to incorporate fire severity in future studies, to better understand and predict post-fire ecosystem responses. In addition, as fire poses a recurring and intensifying threat throughout the recovery process, more emphasis should be placed on post-restoration management and the prevention of fire throughout the different phases of the restoration process. Furthermore, as tropical wildfires are increasing in scale, establishing collaborative capacity and setting priorities for efficient resource allocation should become a major priority for restoration practitioners in the humid tropics. Finally, as global fire regimes are changing and expected to intensify in the context of climate change, land use and land cover change, we suggest to put continuous effort into fire monitoring and modelling to inform the development of effective restoration strategies in the long-run

Nematic ordering of polarizable colloidal rods in an external electric field : Theory and experiment

We employ the coupled dipole method [B. W. Kwaadgras, et al., J. Chem. Phys., 2011, 135, 134105] to calculate the orientation-dependent interaction of polarizable colloidal rods with an external electric field. We project the angular distribution function of a system of such rods on a quasi-two-dimensional slab, corresponding to the focal plane of a microscope, and show that the 3D nematic order parameter and its measurable projected analogue are very similar. We compare our results to confocal microscopy measurements on the orientation distribution function of systems of polarizable colloidal silica rods in an external electric field, demonstrating reasonably good agreement between theory and experiment without any free fit parameter

Effect of external electric fields on the phase behavior of colloidal silica rods

We examine the effect of external electric fields on the behavior of colloidal silica rods. We find that the electric fields can be used to induce para-nematic and para-smectic phases, and to reduce the number of defects in smectic phases. At high field strengths, a new crystal structure was observed that consisted of strings of rods ordered in a hexagonal pattern in which neighboring rods were shifted along their length. We also present a simple model to describe this system, which we used in computer simulations to calculate the phase diagram for rods of L/D = 6, with L the end-to-end length of the rods and D the diameter of the rods. Our theoretical predictions for the phase behavior agree well with the experimental observations. This journal i

Visual interstitial fibrosis assessment as continuous variable in protocol renal transplant biopsies

INTRODUCTION: In current renal transplant pathology practice interstitial fibrosis is visually assessed in categories according to the Banff classification. As this has a moderate reproducibility, which is little ameliorated by morphometric analysis, we investigated whether visual renal fibrosis assessment is feasible on a continuous scale, i.e. as percentage affected area of the cortex. METHODS: Protocol renal biopsies taken at transplantation (n=125), three (n=73) and twelve months (n=88) after transplantation were visually scored in categories (Banff), and percentages for interstitial fibrosis (ci). Interobserver variation (ICC and weighted κ) was assessed, and morphometric analysis on Sirus Red stained sections was performed. Correlations between the different methods and their association with donor age and eGFR 1 year and 5 year post transplant were analyzed using Pearson's or Spearman's rho. RESULTS: Interobserver agreement was equivalent for Banffci and %ci (κ0.713 vs. ICC 0.792), and for BanffIF/TA and %IF/TA (κ0.615 vs. ICC 0.743). Both Banffci and %ci were associated with Sirius Red morphometry in three and twelve month. With all three methods, a significant correlation was found between donor age and fibrosis in the implantation biopsy, and between fibrosis in the 12 month biopsy and eGFR at 1 and 5 years (eGFR at 1 year: Sirius Red ρ-0.487, %ci ρ-0.393, Banffci ρ-0.413, all p<0.01, eGFR at 5 years: Sirius Red ρ-0.392, %ci ρ-0.333, Banffci ρ-0.435, all p<0.01. CONCLUSION: Interstitial fibrosis assessment on a continuous scale can be used next to scoring in categories according to the Banff classification in protocol renal transplant biopsies

Phase Transitions in Cellulose Microfibril Dispersions by High-Energy Mechanical Deagglomeration

It is shown that dispersions of cellulose microfibrils display gel–sol and direct gel–colloidal liquid crystalline structure transitions. This is achieved by applying high-energy mechanical deagglomeration to bacterial cellulose (BC) networks in the presence of sodium carboxymethyl cellulose (CMC). At high CMC content adsorption of the polymer leads to a significant increase in the ζ potential. The resulting apparent phase diagram shows transitions from aggregates to single microfibril dispersions with increasing the CMC/BC weight ratio at low microfibril concentrations. At higher concentrations, liquid crystalline ordering was observed and the microstructure becomes more homogeneous with increasing the CMC content. The observed liquid crystalline ordering was found to be reminiscent of nematic gels. Applying deagglomeration in the presence of CMC, thus, transitions the system from aggregates and gels to dispersions of single microfibrils and nematic gel-type structures

Revealing and Quantifying the Three-Dimensional Nano- and Microscale Structures in Self-Assembled Cellulose Microfibrils in Dispersions

Cellulose microfibrils (CMFs) are an important nanoscale building block in many novel biobased functional materials. The spatial nano- and microscale organization of the CMFs is a crucial factor for defining the properties of these materials. Here, we report for the first time a direct three-dimensional (3D) real-space analysis of individual CMFs and their networks formed after ultrahigh-shear-induced transient deagglomeration and self-assembly in a solvent. Using point-scanning confocal microscopy combined with tracking the centerlines of the fibrils and their junctions by a stretching open active contours method, we reveal that dispersions of the native CMFs assemble into highly heterogeneous networks of individual fibrils and bundles. The average network mesh size decreases with increasing CMF volume fraction. The cross-sectional width and the average length between the twists in the ribbon-shaped CMFs are directly determined and compared well with that of fibrils in the dried state. Finally, the generality of the fluorescent labeling and imaging approach on other CMF sources is illustrated. The unique ability to quantify in situ the multiscale structure in CMF dispersions provides a powerful tool for the correlation of process–structure–property relationship in cellulose-containing composites and dispersions

Orientation of a dielectric rod near a planar electrode

We present experimental and theoretical results on suspensions of silica rods in DMSO-water, subjected to an applied electric field. The experimental results indicate that, if the electrode used for generating the electric field is in direct contact with the suspension, a fraction of the rods close to the electrode surface does not stand parallel to the field but instead lies flat on the electrode when the field is switched on. To explain these results theoretically, we modify the coupled dipole method to include "image dipoles", and find that a rod close to the electrode experiences not only the expected global potential energy minimum at an orientation parallel to the electric field, but also a local minimum several times the thermal energy in depth for orientations parallel to the electrode surface. Additionally, we indicate how the magnitude of the potential energy depends on the electric field strength and include results not only for negatively polarizable (which correspond to the aforementioned experimental system), but also for positively polarizable rods

Revealing and Quantifying the Three-Dimensional Nano- and Microscale Structures in Self-Assembled Cellulose Microfibrils in Dispersions

Cellulose microfibrils (CMFs) are an important nanoscale building block in many novel biobased functional materials. The spatial nano- and microscale organization of the CMFs is a crucial factor for defining the properties of these materials. Here, we report for the first time a direct three-dimensional (3D) real-space analysis of individual CMFs and their networks formed after ultrahigh-shear-induced transient deagglomeration and self-assembly in a solvent. Using point-scanning confocal microscopy combined with tracking the centerlines of the fibrils and their junctions by a stretching open active contours method, we reveal that dispersions of the native CMFs assemble into highly heterogeneous networks of individual fibrils and bundles. The average network mesh size decreases with increasing CMF volume fraction. The cross-sectional width and the average length between the twists in the ribbon-shaped CMFs are directly determined and compared well with that of fibrils in the dried state. Finally, the generality of the fluorescent labeling and imaging approach on other CMF sources is illustrated. The unique ability to quantify in situ the multiscale structure in CMF dispersions provides a powerful tool for the correlation of process–structure–property relationship in cellulose-containing composites and dispersions