Some challenges in the naming and measuring of nanocellulose

Due to its renewable nature, its inherent strength, and many other favorable attributes, nanocellulose (NC) has drawn increasing attention for many potential applications. A diverse and complex assortment of NC products have been reported, and these are most commonly classified based on some contrasting procedures of preparation. The research community is facing a continuing challenge to adequately measure and quantify morphological features of various NC products. In principle, it ought to be possible to quantify and name NC based on such attributes as “degree of branching,” “breadth of particle size,” and “aspect ratio distribution,” etc. However, the ability to measure and compute such quantities still lies beyond what can be achieved in practical amounts of time in typical laboratories. Meanwhile, there has been tension between researchers proposing additional descriptive names, while at the same time there have been efforts at achieving uniformity and simplicity in nomenclature. It is proposed in this essay that this state of affairs is largely a reflection of complexity itself, such that NC products that have the same nominal description can be very different from each other when examined closely. The diversity itself may turn out to be a good thing, as researchers work to come up with varieties of NC that can survive an expected relentless competition from existing plastic-based or cellulose-based materials.

Estimation of Aspect Ratio of Cellulose Nanocrystals by Viscosity Measurement: Influence of Aspect Ratio Distribution and Ionic Strength

The influence of the cellulose nanocrystal (CNC) aspect ratio (L/d) distribution and ionic strength of different salts on the L/d estimation by viscosity measurement were investigated. The L/d distribution was controlled by mixing two CNC, with different L/d, which were prepared by acid hydrolysis from wood and bacterial cellulose. The results demonstrated that the L/d distribution did not affect the accuracy of the CNC L/d estimated by viscosity measurements using the Batchelor equation, and the calculated L/d was the number-average L/d. Moreover, monovalent (NaCl), divalent (CaCl2), and trivalent (AlCl3) salts were chosen to study the influence of ionic strength on the CNC L/d estimation by viscosity measurement. It was found that NaCl and CaCl2 could be added to the CNC suspension to screen the electro-viscous effect and estimate the actual physical CNC L/d by viscosity measurement, and the content of NaCl and CaCl2 can be predicted by the Debye–Hückel theory. However, a small amount of AlCl3 induced CNC aggregation and increased intrinsic viscosity and predicted L/d.

A General Method for Estimating Bulk 2D Projections of Ice Particle Shape: Theory and Applications

The orientation of falling ice particles directly influences estimates of microphysical and radiative bulk quantities as well as in situ retrievals of size, shape, and mass. However, retrieval efforts and bulk calculations often incorporate very basic orientations or ignore these effects altogether. To address this deficiency, this study develops a general method for projecting bulk distributions of particle shape for arbitrary orientations. The Amoroso distribution provides the most general bulk aspect ratio distribution for gamma-distributed particle axis lengths. The parameters that govern the behavior of this aspect ratio distribution depend on the assumed relationship between mass, maximum dimension, and aspect ratio. Individual spheroidal geometry allows for eccentricity quantities to linearly map onto ellipse analogs, whereas aspect ratio quantities map nonlinearly. For particles viewed from their side, this analytic distinction leads to substantially larger errors in projected aspect ratio than for projected eccentricity. Distribution transformations using these mapping equations and numerical integration of projection kernels show that both truncation of size distributions and changes in Gaussian dispersion can alter the modality and shape of projection distributions. As a result, the projection process can more than triple the relative entropy between the spheroidal and projection distributions for commonly assumed model and orientation parameters. This shape uncertainty is maximized for distributions of highly eccentric particles and for particles like aggregates that are thought to fall with large canting-angle deviations. As a result, the methods used to report projected aspect ratios and the corresponding values should be questioned.

Characterization and analysis of the aspect ratio of carbide grains in WC–Co composites

To study the aspect ratio distribution of carbide grains in WC–Co composites, two novel approaches, namely grain shape ellipse calculation and five parameter analysis (FPA) methods, are reported in this work.