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.

Microstructure and rheology of microfibril-polymer networks.

By using an adsorbing polymer in combination with mechanical de-agglomeration, the microstructure and rheological properties of networks of microfibrils could be controlled. By the addition of sodium carboxymethyl cellulose during de-agglomeration of networks of bacterial cellulose, the microstructure could be changed from an inhomogeneous network with bundles of microfibrils and voids to a more homogeneous spread and alignment of the particles. As a result the macroscopic rheological properties were altered.

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.

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.

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.

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.

Dispersions of attractive semiflexible fiberlike colloidal particles from bacterial cellulose microfibrils.

We prepared dispersions from bacterial cellulose microfibrils (CMF) of a commercial Nata de Coco source. We used an ultra-high-energy mechanical deagglomeration process that is able to disperse the CMFs from the pellicle in which they are organized in an irregular network. Because of the strong attractions between the CMFs, the dispersion remained highly heterogeneous, consisting of fiber bundles, flocs, and voids spanning tens to hundreds of micrometers depending on concentration.

Synthesis of monodisperse, rodlike silica colloids with tunable aspect ratio.

Although the experimental study of spherical colloids has been extensive, similar studies on rodlike particles are rare because suitable model systems are scarcely available. To fulfill this need, we present the synthesis of monodisperse rodlike silica colloids with tunable dimensions. Rods were produced with diameters of 200 nm and greater and lengths up to 10 μm, resulting in aspect ratios from 1 to ∼25.