Characteristics and safety of nano-sized cellulose fibrils

A finely ground fibrillated cellulose was fractionated into separate size fractions. The characteristics of the smallest size fractions were studied, and the toxicity to humans was tested as part of a safety assessment. Morphological studies performed with state-of-the-art methods, such as scanning electron microscopy and atomic force microscopy, showed that the fraction obtained consisted of long thin fibrils but also larger fibril agglomerates, and spherical particles were present. The finest fraction did not show any sub-lethal effects as assessed by RNA inhibition test in vitro, nor were there any indications of genotoxicity as tested by the Ames test in vitro. Systemic effects tested in vivo with the nematode were also absent. No cytotoxic effects were seen in the highest tolerated dose test in vitro, but some indication of cytotoxicity was observed in the total protein content test in vitro at the highest sample concentration. The significance of this toxicity test result should be addressed in relation to the other toxicity tests, in which no toxicity was observed, with special emphasis on the in vivo test. Given this, the overall toxicity analyses support the conclusion that nano-scale cellulose fibrils can be considered to be safe towards humans. However, the reason for the positive cytotoxicity test result and, in addition, the effect of the biocide used in sample preservation on the toxicity tests need to be clarified before generalizing these results and declaring nanocellulose to be unambiguously safe.     

Avoiding eddy-current problems in ultra-low-field MRI with self-shielded polarizing coils

In ultra-low-field magnetic resonance imaging (ULF MRI), superconductive sensors are used to detect MRI signals typically in fields on the order of 10-100 μT. Despite the highly sensitive detectors, it is necessary to prepolarize the sample in a stronger magnetic field on the order of 10-100 mT, which has to be switched off rapidly in a few milliseconds before signal acquisition. In addition, external magnetic interference is commonly reduced by situating the ULF-MRI system inside a magnetically shielded room (MSR). With typical dipolar polarizing coil designs, the stray field induces strong eddy currents in the conductive layers of the MSR. These eddy currents cause significant secondary magnetic fields that may distort the spin dynamics of the sample, exceed the dynamic range of the sensors, and prevent simultaneous magnetoencephalography and MRI acquisitions. In this paper, we describe a method to design self-shielded polarizing coils for ULF MRI. The experimental results show that with a simple self-shielded polarizing coil, the magnetic fields caused by the eddy currents are largely reduced. With the presented shielding technique, ULF-MRI devices can utilize stronger and spatially broader polarizing fields than achievable with unshielded polarizing coils.     

A Notion of Fine Continuity for BV Functions on Metric Spaces

In the setting of a metric space equipped with a doubling measure supporting a Poincaré inequality, we show that BV functions are, in the sense of multiple limits, continuous with respect to a 1-fine topology, at almost every point with respect to the codimension 1 Hausdorff measure.     

A Federer-style characterization of sets of finite perimeter on metric spaces

In the setting of a metric space equipped with a doubling measure that supports a Poincaré inequality, we show that a set E is of finite perimeter if and only if \({\mathcal {H}}(\partial ^1 I_E)<\infty \), that is, if and only if the codimension one Hausdorff measure of the 1-fine boundary of the set’s measure theoretic interior \(I_E\) is finite. To obtain the necessity of the above condition, we prove a suitable characterization of the 1-fine boundary, analogously to what is known in the case \(p>1\), and apply a quasicontinuity-type result for \(\mathrm {BV}\) functions proved in the metric setting by Lahti and Shanmugalingam (J Math Pures Appl (9) 107(2):150–182, 2017). To obtain the sufficiency, we generalize further results of fine potential theory from the case \(p>1\) to the case \(p=1\), including weak analogs of a Cartan property for solutions of obstacle problems, and of the Choquet property for finely open sets.     

Percolation and jamming in structures built through sequential deposition of particles

The strength of attractive interaction among particles on a surface, which was studied in our previous work, leads to different degrees of clustering and ordering. A growing structure percolates when all clusters connect and become one and finally the structure is jammed when there is no space large enough to accommodate one more particle. The lowest jamming limit reported is for structures from the random sequential adsorption. We studied here, by means of Monte Carlo simulation, structures built through sequential deposition of particles, into which surface diffusion and various degrees of attractive forces are incorporated and reported jamming limits along with the percolation thresholds. The higher the strength of attractive interactions, the larger the percolation densities and jamming limits are. These results were shown in a diagram as a function of temperature (or equivalently the strength of attractive interaction), ranging from very low temperature to very high temperature (RSA limit).     

Nanoporous Network Channels from Self‐Assembled Triblock Copolymer Supramolecules

Supramolecular complexes of a poly(tert‐butoxystyrene)‐block‐polystyrene‐block‐poly(4‐vinylpyridine) triblock copolymers and less than stoichiometric amounts of pentadecylphenol (PDP) are shown to self‐assemble into a core–shell gyroid morphology with the core channels formed by the hydrogen‐bonded P4VP(PDP)complexes. After structure formation, PDP was removed using a simple washing procedure, resulting in well‐ordered nanoporous films that were used as templates for nickel plating.

     

Sequential deposition of polydisperse particles with double layer interactions: An integral-equation theory

Adsorption of charged colloidal particles to oppositely charged surfaces is usually an irreversible process. The interaction between a pair of particles can be modeled with an exponentially decaying potential originating from double layer interactions. This work explored the effect of the Debye length on monolayer structures using the integral-equation theory which was successfully developed based on a binary-mixture approximation to include the effect of particle size polydispersity. The theoretical results from the integral equations with a Percus-Yevick closure showed that upon increasing the Debye length, the radial distribution functions, g(r), as well as the structure factor, S(k), decreased, in good agreement with simulation results. When the effect of size distributions was investigated, the prominent peak of the radial distribution function increased non-linearly with the product κσ_av, which followed the same trend as was reported for the case of the jamming coverage of the monolayer film.     

Reversibility in particle deposition: the effect of mobile fraction of particles on monolayer structures

In this work, the degree of reversibility in particle deposition was introduced by surface diffusion. The effect of mobile fraction of triangular-well particles on the surface among the immobile ones was explored by varying number of particles added at a time in modified sequential quenching model. It was found that at low temperatures, as the number of added mobile particles increased, the structures was composed of more compact clusters connecting to one another, thereby, decreasing the percolating density while at high temperatures, the structures are more disordered and the final structures were independent on the deposition flux, leading to the unchanged percolating density.