Marek Dziubiński

Hydrodynamic focusing for micro-rheological single-particle study

Hydrodynamic focusing is a widely used tool in microfluidics world. Typical working models are treating this phenomenon as two-dimensional, however the requirements of high throughput analysis show the urgent need to operate in higher Reynolds number range Re > 10, where the three dimensional effects are no longer negligible. Current work, based on both experimental results of confocal laser scanning microscopy (CLSM) and computational fluid dynamics (CFD) modeling describes the problematic range of flow parameters and presents the model describing the shape of the focused stream. In specific, the discussion is aimed at possible use of the proposed solution in single particle rheology, where such a model gives novel control possibilities over the experimental parameters.

Impact Assessment of Gamma Radiation on Viscoelastic Properties of Amaranth Starch by Means of Fractional Maxwell-Wiechert Model

In this paper the impact of medium doses of gamma radiation (0–10 kGy) on viscoelastic properties of two cultivars of amaranth starch Hy030 (Amaranthus hypochondriacus L.) and Tibet Yellow (Amaranthus paniculatus L.) was discussed. To describe the rheological properties of the starch, the fractional Maxwell-Wiechert model was used. The changes in values of 14 rheological parameters identified on the basis of proposed model, depending on degree of radiation, were also discussed. It allowed for a detailed characterization of a wide variety of rheological and structural properties of amaranth starch that was modified by irradiation.

Rheo-Kinetic Study of Sol-Gel Phase Transition of Chitosan Colloidal Systems

Chitosan colloidal systems, created by dispersing in aqueous solutions of hydrochloric acid, with and without the addition of disodium β-glycerophosphate (β-NaGP), were prepared for the investigation of forming mechanisms of chitosan hydrogels. Three types of chitosan were used in varying molecular weights. The impacts of the charge and shape of the macromolecules on the phase transition process were assessed. The chitosan system without the addition of β-NaGP was characterized by stiff and entangled molecules, in contrast to the chitosan system with the addition of β-NaGP, wherein the molecules adopt a more flexible and disentangled form. Differences in molecules shapes were confirmed using the Zeta potential and thixotropy experiments. The chitosan system without β-NaGP revealed a rapid nature of phase transition—consistent with diffusion-limited aggregation (DLA). The chitosan system with β-NaGP revealed a two-step nature of phase transition, wherein the first step was consistent with reaction-limited aggregation (RLA), while the second step complied with diffusion-limited aggregation (DLA).

Wettability of commercial starches and galactomannans

ABSTRACT This paper describes the wettability of basic commercial polysaccharides: starches (potato PS, wheat WS, corn CS, tapioca TS, kuzu KS) and galactomannans (fenugreek gum FG, guar gum GG, tara gum TG, locust bean gum LBG). The study was conducted using the Washburn capillary rise method and thermal drying. This allowed one to determine the material constant C, contact angle θ, surface free energy of solid SFE, and initial moisture content M. The measured values of contact angle θ and surface free energy SFE indicated that potato starch (70.9°, 41.1 mN · m−1) and wheat starch (88.4°, 30.2 mN · m−1) were characterized by the highest and lowest wettability among the examined starches, respectively. In turn, the galactomannans were poorly wettable substances. Their contact angles θ were approximately equal to 90°, showing a slight increase with increasing substitution degree. The observed decrease in surface free energy SFE from 30 to 29.6 mN · m−1 indicated a very minor hydrophobization of their surfaces. Material constant C was practically independent of temperature, and an increase in initial moisture content M in the examined starches and galactomannans proceeded according to the following schemes: CS < PS < WS < TS < KS and LBG < TG < GG < FG, respectively. GRAPHICAL ABSTRACT

The Application of Small-Angle Light Scattering for Rheo-Optical Characterization of Chitosan Colloidal Solutions

In the recent studies on chitosan hydrogels, it was found that understanding both rheological and structural properties plays an important role in their application. Therefore, a combination of two independent techniques was applied to investigate micro- and macroscopic properties of chitosan colloidal system. Studies on viscous properties, as well as the sol-gel phase transition process, were performed using rheological methods coupled with the small angle light scattering (SALS) technique. Based on the anisotropy of scattering patterns obtained during rotational shear tests, it was found that the chitosan solution reveals two different behaviors delimited by the critical value of the shear rate. Below a critical value, chitosan clusters are deformed without breaking up aggregates, whereas after exceeding a critical value, chitosan clusters apart from deformation also breakup into smaller aggregates. The values of the radius of gyration determined by applying the Debye function allow one to state that with an increase of chitosan concentration, molecule size decreases. An analysis of the light scattering data from the temperature ramp test showed that with an increase of temperature, the level of polymer coil swelling increases. Simultaneously, the supply of thermal energy leads to a neutralization of the charge of chitosan chains. As a consequence, the formation of intermolecular links occurs and a gel structure is formed.

Measurement of the average shear rate around a microparticle in the shear thinning medium with laser tweezers

ABSTRACT A novel method for the determination of the average shear rate around a microparticle moving in the fluid is presented. Although the shear rate around a particle moving in the fluid is a parameter of paramount importance in sedimentation studies, its determination is time-consuming, thus model-based solutions are preferred. However, the current literature models require still rigorous validation. The presented technique relies on optical tracking of a laser-tweezers trapped particle suspended in the liquid medium. The obtained experimental results for spherical particles of 1 micron diameter show a good agreement with the classical rheology and literature correlation models. The new method is a valuable tool for determination of sedimentation parameters as it reduces the time of experiments and the sample volume by order(s) of magnitude when compared to classical methods.

Analyses of LPG Dispersion During Its Accidental Release in Enclosed Car Parks

Abstract Despite the fact that LPG (Liquefied Petroleum Gas) is used in a large number of cars, tests have not yet been carried out to ascertain how hazardous can be the release of LPG from the car when parked in enclosed garages. The problem applies to both public and industrial parking areas, especially in Poland, where more than 10% cars are fueled by LPG. The paper describes full scale experiments, which demonstrate conditions that may occur in a garage in the event of accidental LPG release from the car installation. Over the course of the tests, a series of six LPG spillage tests were performed to study emission time and flammable cloud formation depending on the accidental gap diameter. Additionally, to enable the visual observation of the gas dispersion and influence of the ventilation system the experiment was conducted using well visible CO2 gas cloud, produced from dry ice. The experiments have shown that without ventilation LPG can accumulate on the floor of the enclosed garage for a long time, which generates a high explosive hazard. However, good ventilation (especially jet fan systems) can quickly remove hazardous flammable LPG clouds. Moreover, very important for effective LPG detection is the location of detectors closer to the floor than is currently recommended - at a height of 30 cm.

Structural analysis of gluten-free doughs by fractional rheological model

This study examines the effects of various components of tested gluten-free doughs, such as corn starch, amaranth flour, pea protein isolate, and cellulose in the form of plantain fibers on rheological properties of such doughs. The rheological properties of gluten-free doughs were assessed by using the rheological fractional standard linear solid model (FSLSM). Parameter analysis of the Maxwell-Wiechert fractional derivative rheological model allows to state that gluten-free doughs present a typical behavior of viscoelastic quasi-solid bodies. We obtained the contribution dependence of each component used in preparations of gluten-free doughs (either hard-gel or soft-gel structure). The complicate analysis of the mechanical structure of gluten-free dough was done by applying the FSLSM to explain quite precisely the effects of individual ingredients of the dough on its rheological properties.

Evaluation Of Transport Mechanism Of Contaminant Particles In Small Water Systems In Poland

Abstract The change in water quality in small water systems is strongly affected by sediment particles. Their transport, deposition and re-suspension due to variability in water demand has a significant impact on the change in water quality. Two significant mechanism of deposit transport and deposition i.e. turbophoresis and turbulent diffusion have been described in the literature. The paper presents the mechanisms of turbophoresis and turbulent diffusion. These phenomena have an impact on the quality of water in small water systems. The aim of the study is to propose procedures of identifying areas of mechanism of particle movement and their accumulation in small water system networks. Simulation of the flow of small water-pipe network at Niewiesz was used for the study. That water pipeline is situated in the central Poland. Many rural areas in Poland have a similar architecture. Modeling of movement of contaminant in close wall areas in pipelines is presented. The article presents the discussion concerning the areas where the mechanisms of turbophoresis and turbulent diffusion occur in the transport of solid particles in water supply systems. The relations between deposition and transporting of particles in turbulent flows depend on a number of parameters, including: particle size, localization of particles in the pipe (at given time), as well as the turbulence of flow. These parameters change depending on the water demand. The type of these changes depends on pipe diameters, material from which the pipes and the fittings are made, water demand and initial quality of water.