Gleb Vasilyev

Rheological Properties and Electrospinnability of High-Amylose Starch in Formic Acid

Starch derivatives, such as starch-esters, are commonly used as alternatives to pure starch due to their enhanced mechanical properties. However, simple and efficient processing routes are still being sought out. In the present article, we report on a straightforward method for electrospinning high-amylose starch-formate nanofibers from 17 wt % aqueous formic acid (FA) dispersions. The diameter of the electrospun starch-formate fibers ranged from 80 to 300 nm. The electrospinnability window between starch gelatinization and phase separation was determined using optical microscopy and rheological studies. This window was shown to strongly depend on the water content in the FA dispersions. While pure FA rapidly gelatinized starch, yielding solutions suitable for electrospinning within a few hours at room temperature, the presence of water (80 and 90 vol % FA) significantly delayed gelatinization and dissolution, which deteriorated fiber quality. A complete destabilization of the electrospinning process was observed in 70 vol % FA dispersions. Optical micrographs showed that FA induced a disruption of starch granule with a loss of crystallinity confirmed by X-ray diffraction. As a result, starch fiber mats exhibited a higher elongation at break when compared to brittle starch films.

Pressure losses in flow of viscoelastic polymeric fluids through short channels

We propose a new alternative method for calculating the resistance of short channels (capillaries) in the flow of viscoelastic polymeric fluids (solutions and melts). The method is based on the assumption that pressure losses in short channels are determined by average time of deformation in passing a fluid through a channel and linear viscoelastic properties of a material. Experiments carried out with a series of moderately concentrated polymer solutions and three polymer melts, as well as literature data, confirmed that pressure losses (expressed via the apparent shear stress at a capillary wall) in flow through capillaries of different length are an unique function of the average residence time in passing through a capillary. Experimental data for every viscoelastic polymeric material form a scaling dependence on the Deborah number calculated as the product of the average residence time and relaxation time found in the periodic oscillation measurements. For different polymeric materials, a master curve can be built by normalizing the apparent shear stress by the characteristic elastic modules at the crossover point.

Structure Evolution and Drying Dynamics in Sliding Cholesteric Cellulose Nanocrystals

The study of colloidal liquid crystals (LCs) reveals fundamental insights into the nature of ordered materials, giving rise to emergent properties with fascinating applications in soft matter nanotechnology. Here we investigate the shape instabilities, layer undulations, dynamic assembly, and collective behaviors in evaporating a cellulose nanocrystal-based cholesteric LC drop. During the drying process, the drop edges are pinned to the substrate with spontaneous convective flow occurring along the drop, which leads to nonequilibrium sliding of the individual cholesteric fragment with active ordering as well as hydrodynamic fluctuations and flow transitions in the bulk cholesteric phase.

Controlled Assembly of Nanocellulose-Stabilized Emulsions with Periodic Liquid Crystal-in-Liquid Crystal Organization

Colloidal particles combined with a polymer can be used to stabilize an oil-water interface forming stable emulsions. Here, we described a novel liquid crystal (LC)-in-LC emulsion composed of a nematic oil phase and a cholesteric or nematic aqueous cellulose nanocrystal (CNC) continuous phase. The guest oil droplets were stabilized and suspended in liquid-crystalline CNCs, inducing distortions and topological defects inside the host LC phase. These emulsions exhibited anisotropic interactions between the two LCs that depended on the diameter-to-pitch ratio of suspended guest droplets and the host CNC cholesteric phase. When the ratio was high, oil droplets were embedded into a cholesteric shell with a concentric packing of CNC layers and took on a radial orientation of the helical axis. Otherwise, discrete surface-trapped LC droplet assemblies with long-range ordering were obtained, mimicking the fingerprint configuration of the cholesteric phase. Thus, the LC-in-LC emulsions presented here define a new class of ordered soft matter in which both nematic and cholesteric LC ordering can be well-manipulated.

Tunable pH-Responsive Chitosan-Poly(acrylic acid) Electrospun Fibers

The macromolecular organization in system composed of anionic poly(acrylic acid) (PAA) and cationic chitosan (Cs), with different degrees of deacetylation (DD), under extensive elongational flow, is described. Cs/PAA nanofibers were obtained, and polyelectrolyte complexation only occurred when fibers were immersed in fluid media of a certain pH. Assembled polyelectrolytes complexes formed a pH-triggered system, as demonstrated by reversible change of the swelling degree, by 3 orders of magnitude, and a change on the elastic modulus, by 2 orders of magnitude. Both the swelling degree and the elastic modulus proved sensitive to the DD of Cs. Rheological measurements showed that increased DD of Cs resulted in a decrease in viscosity of both pure Cs and precursor Cs/PAA solutions, attributed to repulsive interactions between ionized amino groups in Cs. At the same time, a DD-dependent change in balance between hydrogen bonding and ion-dipole interactions between the components in Cs/PAA, was responsible for the more pronounced viscosity decrease in these solutions.

Differentiation of Pancreatic Cyst Types by Analysis of Rheological Behavior of Pancreatic Cyst Fluid

Differentiation between mucinous and non-mucinous pancreatic cysts is exceedingly important and challenging, particularly as the former bears malignant transformation potential. Pancreatic cyst fluid (PCF)-based diagnostics, including analyses of biochemical markers, as well as cytology, has shown inadequate accuracy. Herein, a preliminary single-center study of 22 PCF samples, collected by endoscopic ultrasound-guided fine needle aspiration (EUS-FNA), assessed the rheological behavior of PCF and its correlation with lesion type. The dependence of PCF shear viscosity on shear rate was found to follow a power law and could be fitted using Ostwald–de Waele model. Three types of flow curves were identified, where two types correlated with non-mucinous cysts, differing by their power law exponent, and the third type corresponding to mucinous cysts. Viscosity measured at a high shear rate was shown to serve as an accurate and independent marker distinguishing between mucinous and non-mucinous cysts, with an optimal cutoff value of ηc = 1.3 cP The accuracy of this novel technique proved superior to string-sign, cytology, carcinoembryonic antigen, and amylase assessments. Moreover, the combined predictive value of ηc and patient age provided for sensitivity and specificity of 100% and 95.5%, respectively. This simple and rapid diagnostic tool can be immediately implemented after EUS-FNA sampling.