Paul Takhistov - Academia.edu (original) (raw)

Papers by Paul Takhistov

We experimentally and theoretically examine two static means of mixing liquids in microchannels u... more We experimentally and theoretically examine two static means of mixing liquids in microchannels using electrokinetic flow. A diffusive interface between two regions of unequal concentration and conductivity is shown to be unstable to a normal electric field in the direction of the lower conductivity. The resulting instability is analogous to viscous fingering between miscible fluids and is analyzed with a special spectral analysis of the self-similar diffusive front to provide conditions for maximum fingering and mixing. An alternating transverse field provided by analysis of the self-similar diffusive front to provide conditions for maximum fingering and mixing. An alternating transverse field provided by a local electrode induces an oscillating non-uniform electrokinetic velocity profile. The resulting Taylor dispersion is shown to effectively mix slugs of reactants.

Polymer blends are created by mixing polymers with different chemical structures together in orde... more Polymer blends are created by mixing polymers with different chemical structures together in order to create new properties intermediate between the two individual polymer components. Film structure, surface properties, and stability of immiscible hydroxypropyl cellulose (HPC) polyethylene glycol (PEG) polymeric blend films were investigated. The effect of substrate properties on the phase separation behavior of a polymer films has been investigated. We found that the amplitude of this process may be modified by a substrate material. This is due to the reduced surface attraction of HPC for the increased surface coverage by PEG. It was observed that regime of spinodal decomposition of films could be controlled through manipulation of key parameters of film formation process. Control of these parameters result in guided surface morphology where surface roughness, pore size, and segregation can be predicted and directed

Personalized medicine, in terms of personalized dosing, can increase the effectiveness of medicat... more Personalized medicine, in terms of personalized dosing, can increase the effectiveness of medications while simultaneously lowering the risk of adverse side effects. The accurate dosing of small amounts of solutions and suspensions is a prerequisite and this can be achieved using Drop on Demand(DoD)technology. In DOD printing, each type of nozzle has its uniqueness and limitations based upon specific driving parameters, ejected droplet dimension,and dispensed material properties. We have implemented three different microdosing technologies (solenoid, positive displacement, and piezoelectric) to dispense both single-phase and multi-phase pharmaceutical compounds. These systems can dispense droplets with volumes ranging from picoliters to microliters. We have characterized their performance with respect to changes in formulation parameters such as viscosity, particle size and surface tension. Based on the experimental results we have determined the process map and parametric window fo...

The hydrophobic properties of substrates are known to affect wetting behavior of the deposited mu... more The hydrophobic properties of substrates are known to affect wetting behavior of the deposited multiphase droplets. In this study, decomposition of O/W nano-emulsion droplets placed onto various wettable surfaces with controlled hydrophobicity is investigated. It was found that thin film spreading of the oil phase over the substrate surfaces is one of the primary reasons for emulsion decomposition. Our data shows that decomposition occurs first near the droplet pole and not at the contact line. Various techniques (phase contrast optical microscopy, gravimetric measurements and Raman spectroscopy) have been used to reveal the mechanism of the emulsion destabilization. It was found that process of nano-emulsion decomposition on highly hydrophobic surfaces can be described as two-stage process with critical point at which the value of dynamic contact angle is suddenly increased. We propose a simple mass balance model to explain observed phenomena.

We developed a lab-scale setup for fabrication of thin films (~0.1mm) by drying multicomponent po... more We developed a lab-scale setup for fabrication of thin films (~0.1mm) by drying multicomponent polymer solutions over a wide range of drying regimes. The drying chamber is equipped with a heater, an air blower with adjustable flow rate and temperature, a humidifier to vary the partial pressures of water and organic solvent, a balance to automatically monitor the sample weight, and sensors to control the temperature, airflow, and the atmosphere composition in the process of drying. We will report on the drying kinetics and mechanical properties of films prepared by drying aqueous HPMC solutions without and with additions of sodium dodecyl sulfate and polyethylene glycol over a broad range of operating regime. The work was supported by NSF Engineering Research Center on Structured Organic Particulate Systems.

With the advent and completion of the human genome project researchers are predicting that person... more With the advent and completion of the human genome project researchers are predicting that personalized medicine can be used to target specific ailments and disease populations. Although personalized medicine has the potential to revolutionize healthcare, currently there exists no platform for mass manufacturing of personalized drugs due to the lack of available technology at many large scale pharmaceutical manufacturing plants. This problem exemplifies the need for building a bridge between traditional engineering and biomedical research. A viable solution is to utilize Drop on Demand (DoD) technology in conjunction with ink jet printing. Applied to precision dosage formulation, ink jet technology can be used to drop accurate dosages of drug formulation onto biopolymeric substrates to create functional and convenient drug delivery systems. The goal of this research is to develop an automated manufacturing platform which can be used for precision dosage and controlled drug delivery ...

We studied the drying process of dopamine solution drops put by means drop-on-demand tecnique on ... more We studied the drying process of dopamine solution drops put by means drop-on-demand tecnique on a wettable solvent cast biopolymeric films. Three stages can be identified. First, the droplet spreads until a maximum radius where evaporation becomes dominant. The second phase is characterized by a constant radius due to competition between spreading and evaporation of the solvent. Finally, the contact line recedes until complete evaporation of the solvent. During evaporation process we have observed the transformation of a studied system from one phase to another. Furthermore, we have shown that the observed 1st order phase transition can be manipulated via interfacial characteristics of substrate to produce amorphous or crystalline structures upon droplet impingement. In general there exists three regions for which the structure of the splat will exist as either as a structure lacking long range order of the positions of the atoms, a semi crystalline structure with limited long rang...

Biopolymer can improve the solubility of the poor-soluble drugs. This work focus on how polyethyl... more Biopolymer can improve the solubility of the poor-soluble drugs. This work focus on how polyethylene glycol 3350 (PEG3350), a polymer widely applied in drug delivery, combines with Ibuprofen (IBU) by hot melt in region I and region II of a eutectic mixture. The experiments demonstrate that the amorphous IBU separates from PEG and locates at the boundary of PEG crystals for mixture in region I while in region II some amorphous IBU is in the PEG crystal the other concentrate at PEG crystals' boundary. Phase diagram of PEG3350-IBU as well as a model is built to integrate the process of phase separation during solidification. Phase contrast optical microscopy technique is applied to analyze the mechanism of non-isothermal solidification of PEG3350-IBU mixture. It was found that the homogeneous nucleation crystallization occurs in region I mixture crystallization while both homogenous and heterogeneous nucleation crystallization appear in the solidification of mixture in region II. P...

Probiotics and Antimicrobial Proteins, 2009

Food Biophysics, 2006

... is the function of pdV, the work of expansion (dV) under the pressure p; 8dQ ... following ch... more ... is the function of pdV, the work of expansion (dV) under the pressure p; 8dQ ... following chemicals were used to prepare surfac-tant and electrolyte stock solutions: potassium chlo-ride ... The patterns of droplet flow were observed under an optical microscope (Model 441824, Nikon ...

Journal of Food Science, 2014

The impedimetric characteristics of an immunosensor depend on the electrical properties of an imm... more The impedimetric characteristics of an immunosensor depend on the electrical properties of an immunosensor substrate. The impedimetric characteristics of an immunosensor compared with adsorption of Listeria monocytogenes were investigated on an aluminum surface insulated with an electrically resistive aluminum oxide layer. Antibody for L. monocytogenes (anti-L. monocytogenes) was immobilized on an aluminum surface that was insulated with a native air-formed aluminum oxide layer. The resistance of impedance (R) value of an aluminum-based immunosensor decreased, especially at 10(4) to 10(6) Hz, where the effect of the reactance of impedance (X) was minimal when L. monocytogenes was adsorbed on the immunosensor surface. The R value of the immunosensor at 81 kHz decreased proportionally to the concentration of L. monocytogenes from 1.3 to 4.3 log CFU mL(-1) . The adsorption of L. monocytogenes produced local protrusions on the immunosensor surface, causing physicochemical changes in the ionic layer formed on the immunosensor surface by a sinusoidal electrical signal input, which might help electrical current to flow and cause the R value to decrease.

ABSTRACT Nanotechnology has the potential to revolutionize the global food and agricultural syste... more ABSTRACT Nanotechnology has the potential to revolutionize the global food and agricultural system. Nanoscale control of food molecules could allow the modification of many macroscale characteristics of foods, such as texture, sensory attributes, processability, and shelf life. The tools of nanotechnology have already allowed scientists to better understand the way in which food components are structured and how they interact with each other. This understanding is expected to enable a more precise manipulation of food molecules for the design of healthier, tastier, and safer foods. Some of the benefits of nanotechnology will be conveyed to the food system directly through agriculture and agricultural research. Newly created tools in molecular and cellular biology will enable significant advances in reproductive science and technology, disease prevention, and treatment of plants and animals and potentially boost the production of raw food materials. The development of biosensors for pathogen and contaminant detection in agricultural products will help ensure the safety of the food supply. Conversion of renewable agricultural materials or food waste into energy and useful by-products is an environmentally oriented area of research that could be greatly enhanced by nanotechnology.

Padua/Nanotechnology Research Methods for Foods and Bioproducts, 2012

Page 1. Nanotechnology Research Methods for Foods and Bioproducts, First Edition. Edited by Graci... more Page 1. Nanotechnology Research Methods for Foods and Bioproducts, First Edition. Edited by Graciela W. Padua and Qin Wang. © 2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc. 5 Nanotechnology–enabled delivery systems for food functionalization ...

The Journal of Physical Chemistry B, 2005

We have used phosphorescence from erythrosin B (tetraiodofluorescein) dispersed in amorphous thin... more We have used phosphorescence from erythrosin B (tetraiodofluorescein) dispersed in amorphous thin films of maltose and maltitol at mole ratios of 0.8:10(4) dye:sugar to monitor the molecular mobility of these matrixes over the temperature range from -25 to over 110 degrees C. Analysis of the emission peak frequency and bandwidth (full width at half-maximum) and time-resolved intensity decay parameters provided information about thermally activated modes of matrix mobility that enhanced the rate of dipolar relaxation around the triplet state and the rate of intersystem crossing to the ground state (k(TS0)). Detectable dipolar relaxation began in the glassy state about 50 degrees C below T(g) in both maltose and maltitol; the relaxation rate, however, while 3-4 orders of magnitude slower than literature values for the beta relaxation determined from dielectric relaxation, had an activation energy only 2-fold smaller. Dipolar relaxation was further enhanced in the melt above T(g); the dipolar relaxation rates in the melt scaled nearly exactly with rates for the alpha relaxation determined from dielectric relaxation. Intensity decays were well fit using a stretched exponential decay function in which the lifetime (tau) and the stretching exponent (beta) were the physically significant parameters. In maltose, the magnitude of k(TS0) was essentially constant in the glass and increased dramatically at the T(g); in maltitol k(TS0) increased moderately at T(g) = -50 degrees C and more dramatically in the melt at T(g) = +20 degrees C. The value of k(TS0) in maltose:maltitol mixtures was significantly smaller than that seen in pure maltose and maltitol, suggesting that specific interactions decreased the mobility of the mixed sugar matrix; this phenomenon was comparable to the antiplasticization seen in mixtures of small molecule plasticizers with synthetic polymers and starch. The extent of inhomogeneous broadening and dynamic heterogeneity were essentially constant in the glass and increased dramatically in maltose and more gradually in maltitol at the glass transition.

Soil Science Society of America Journal, 2012

ABSTRACT Volume of soil aggregates can be determined with a combination of two immiscible liquids... more ABSTRACT Volume of soil aggregates can be determined with a combination of two immiscible liquids by saturating aggregates with one of the liquids and measuring buoyancy while submerged in the second one. The saturating liquid may get displaced from pores resulting in volume measurements that do not remain constant in time. Theory predicts a faster rate of displacement when the saturating liquid has a smaller viscosity than the displacing liquid. Our objective was to test the effect of two liquid combinations on the dynamics of liquid displacement from soil pores. Kerosene was used alternatively as the saturating (C-1) and the displacing (C-2) liquid and a glycerin–ethanol mix (1:1, v/v) as the complementary immiscible liquid. For each combination, nine aggregates from an unplowed native prairie (NP) and eight from an agricultural field (AG) ranging in mass from 0.1 to 15 g were saturated in the saturating liquid and submerged for 15 min in the displacing liquid. Aggregate volume change was about nine times faster in liquid combination C-1 than in C-2 (P < 0.001), validating theoretical predictions. Also, aggregates of mass <1 g from both soils showed a greater change in volume with combination C-1 than larger aggregates (P ≤ 0.003). When selecting a combination of two immiscible liquids it is important that the viscosity of the saturating liquid be greater than that of the displacing liquid to assure constant values of aggregate volume that are independent of aggregate size.

Journal of Food Engineering, 2007

Electric field-based food processing technologies have recently caught the attention of food indu... more Electric field-based food processing technologies have recently caught the attention of food industry that wishes to fulfill consumers' demands for high-quality and safety of food products. Numerous research groups have recently demonstrated the possibility to inactivate different ...

Journal of Colloid and Interface Science, 2001