Konstantin Kornev - Academia.edu (original) (raw)

Papers by Konstantin Kornev

Frontiers in soft matter, Mar 27, 2024

In insects vulnerable to dehydration, the mechanistic reaction of blood after wounding is rapid. ... more In insects vulnerable to dehydration, the mechanistic reaction of blood after wounding is rapid. It allows insects to minimize blood loss by sealing the wound and forming primary clots that provide scaffolding for the formation of new tissue. Using nano-rheological magnetic rotational spectroscopy with nickel nanorods and extensional rheology, we studied the properties of blood dripping from the wound of caterpillars of the Carolina sphinx moth (Manduca sexta) with a high concentration of blood cells. We discovered that wound sealing followed a two-step scenario. First, in a few seconds, the Newtonian lowviscosity blood turns into a non-Newtonian viscoelastic fluid that minimizes blood loss by retracting the dripping blood back into the wound. Next, blood cells aggregate, starting from the interfaces and propagating inward. We studied these processes using optical phase-contrast and polarized microscopy, X-ray imaging, and modeling. Comparative analyses of the cell-rich and cell-poor blood of different insects revealed common features of blood behavior. These discoveries can help design fast-working thickeners for vertebrate blood, including human blood.

arXiv (Cornell University), Sep 5, 2013

In a non-uniform magnetic field, the droplets of colloids of nickel nanorods and nanoparticles ag... more In a non-uniform magnetic field, the droplets of colloids of nickel nanorods and nanoparticles aggregate to form a cusp at the droplet surface not deforming the entire droplet shape. When the field is removed, nanorods diffuse away and cusp disappears. Spherical particles can form cusps in a similar way, but they stay aggregated after release of the field; finally, the aggregates settle down to the bottom of the drop. X-ray phase contrast imaging reveals that nanorods in the cusps stay parallel to each other without visible spatial order of their centers of mass. Formation of cusps can be explained with a model that includes magnetostatic and surface tension forces. The discovered possibility of controlled assembly and quenching of nanorod orientation under the cusped liquid surface offers vast opportunities for alignment of carbon nanotubes, nanowires and nanoscrolls, prior to spinning them into superstrong and multifunctional fibers. Magneto and electrostatic analogy suggests that similar ideal alignment can be achieved with the rod-like dipoles subject to a strong electric filed.

arXiv (Cornell University), Mar 17, 2015

As one of the characterization tools for nanoscience & nanotechnology, magnetic rotational spectr... more As one of the characterization tools for nanoscience & nanotechnology, magnetic rotational spectroscopy (MRS) with magnetic nanoprobes is a powerful method for in-situ characterization of minute amounts of complex fluids and for study of nanoscale structures in fluids. In MRS, a uniformly rotating magnetic field rotates magnetic micro-or nano-probes in the liquid and one studies rheological properties by analyzing the features of the probe rotation. The technique relies only on full rotations (rather than oscillations) of the magnetic moment of the probes.

Unique highly porous polyvinylidene difluoride (PVDF) nanofibers of about 50-500 nm in diameter w... more Unique highly porous polyvinylidene difluoride (PVDF) nanofibers of about 50-500 nm in diameter were prepared by electrospinning. Electrospinning setup used allows controlling the nanofiber's placement on the gap-type electrodes. Nanofiber arrays and yarns can be freely suspended in the gap between the electrodes. The resulting nanofiber samples are uniform and do not require expensive purification. Electrospun nanofiber yarns are waterproof. Water drop deposited on the yarn's surface does not penetrate into the bulk. The PVDF yarns have high tenacity, can be bent, knotted, or twisted without any breakage. Results of DSC, TGA, and FTIR characterization of the yarns show the presents of crystalline PVDF β-phase responsible for ferroelectric properties of the PVDF material. Porosity of electrospun nanofibers was determined using SEM and AFM.

Journal of Engineered Fibers and Fabrics, Jun 1, 2012

We developed a Surface Differential Scanning Calorimeter for the quantitative analyses of thermod... more We developed a Surface Differential Scanning Calorimeter for the quantitative analyses of thermodynamic and heat transfer properties of thin fibrous and porous samples. It has been demonstrated that the calorimeter is capable of measuring cooling power as well as temperature decrease in a reliable and reproducible way. Considering its low cost the equipment can be a valuable option for studying cooling/heating systems in laboratory settings.

Scientific Reports, Oct 15, 2015

A low voltage electropolishing of metal wires is attractive for nanotechnology because it provide... more A low voltage electropolishing of metal wires is attractive for nanotechnology because it provides centimeter long and micrometer thick probes with the tip radius of tens of nanometers. Using X-ray nanotomography we studied morphological transformations of the surface of tungsten wires in a specially designed electrochemical cell where the wire is vertically submersed into the KOH electrolyte. It is shown that stability and uniformity of the probe span is supported by a porous shell growing at the surface of tungsten oxide and shielding the wire surface from flowing electrolyte. It is discovered that the kinetics of shell growth at the triple line, where meniscus meets the wire, is very different from that of the bulk of electrolyte. Many metals follow similar electrochemical transformations hence the discovered morphological transformations of metal surfaces are expected to play significant role in many natural and technological applications.

Bulletin of the American Physical Society, Mar 14, 2017

Submitted for the MAR17 Meeting of The American Physical Society Microrheological characterizatio... more Submitted for the MAR17 Meeting of The American Physical Society Microrheological characterization of thin films and nanoliter droplets using Magnetic Rotational Spectroscopy with ferromagnetic nanorods. PAVEL APRELEV, KONSTANTIN KORNEV, Clemson University, KORNEV GROUP TEAM-Recent advances in the fields of soft and composite materials have led to the development of Magnetic Rotational Spectroscopy (MRS)-a technique for analysis of microrheological properties of complex fluids such as gels and polymer solutions. MRS requires minute amounts of liquids to be studied and thus allows for direct characterization of viscosity and elasticity of thin films. It relies on rotation of ferromagnetic nanorods uniformly dispersed in the studied solution with a steadily rotating magnetic field. The rotational behavior of the nanorod when the magnetic and viscous drag torques are nearly the same is very sensitive to the rod's magnetization, the liquid's rheology, and the external magnetic field. We have developed an experimental procedure to accurately control the external magnetic field and carefully study this behavior. We have applied MRS to study microrheology of biofluids as well as kinetics of curing of thin polymer films.

Advanced Functional Materials, Aug 1, 2014

We investigated the mechanism of mass transfer during DC electropolishing of a tungsten wire in 2... more We investigated the mechanism of mass transfer during DC electropolishing of a tungsten wire in 2M KOH electrolyte solution. It appears that a viscous layer formed by the products of electrochemical reaction on anode surface has distinguishable optical and physicochemical properties. The viscous fluid flow is initiated by formation and detaching of a small droplet at the wire tip. Therefore, according to Tate's law, effects of surface tension and gravitational forces exerted on the film are comparable. Using high speed flow imaging, we estimated the density of this layer as 3 / 1075 m kg   and its interfacial tension as m N / 10 82. 5 6     .

Bulletin of the American Physical Society, 2018

Journal of Theoretical Biology, 2021

Proboscises of many fluid-feeding insects share a common architecture: they have a partially open... more Proboscises of many fluid-feeding insects share a common architecture: they have a partially open food canal along their length. This feature has never been discussed in relation to the feeding mechanism. We formulated and solved a fluid mechanics model of fluid uptake and estimated the time required to completely fill the food canal of the entire proboscis through the openings along its length. Butterflies and moths are taken as illustrative and representative of fluid-feeding insects. We demonstrated that the proposed mechanism of filling the proboscis with fluid through permeable lengthwise bands, in association with a thin film of saliva in the food canal, offers a competitive pathway for fluid uptake. Compared with the conventional mechanism of fluid uptake through apically restricted openings, the new mechanism provides a faster rate of fluid uptake, especially for long-tongued insects. Accordingly, long-tongued insects with permeable lengthwise bands would be able to more rapidly exploit a broader range of liquids in the form of films, pools, and discontinuous columns, thereby conserving energy and minimizing exposure to predators, particularly for hovering insects.

Physical Review E, 2019

Magnetic nanorods rotating in a viscous liquid are very sensitive to any ambient magnetic field. ... more Magnetic nanorods rotating in a viscous liquid are very sensitive to any ambient magnetic field. We theoretically predicted and experimentally validated the conditions for two-dimensional synchronous and asynchronous rotation as well as three-dimensional precession and tumbling of nanorods in an ambient field superimposed on a planar rotating magnetic field. We discovered that any ambient field stabilizes the synchronous precession of the nanorod so that the nanorod precession can be completely controlled. This effect opens up different applications of magnetic nanorods as sensors of weak magnetic fields, for microrheology, and generally for magnetic levitation.

Soft Matter, 2018

Using theoretical and computational modeling, we focus on dynamics of gels filled with uniformly ... more Using theoretical and computational modeling, we focus on dynamics of gels filled with uniformly dispersed ferromagnetic nanoparticles subjected to electromagnetic (EM) irradiation within the GHz frequency range.

Particle & Particle Systems Characterization, 2013

In this paper, the kinetics of ordering of an assembly of non‐interacting nanorods suspended in a... more In this paper, the kinetics of ordering of an assembly of non‐interacting nanorods suspended in a solidifying liquid film is studied theoretically. Assuming random orientation of nanorods at the initial moment of time, the time needed for nanorods to align along the direction of an external magnetic field is estimated. In the solidifying films with exponentially increasing viscosity, the viscous drag significantly resists the nanorod alignment. Therefore, some nanorods might be quenched halfway to the equilibrium orientation even before complete solidification of the film. Different regimes of ordering have been revealed and classified and the criterion for the alignment of nanorods prior to the film solidification has been introduced.

Nanotechnology, 2013

We show that electrochemical formation of long probes with nanosharp tips can be controlled by ch... more We show that electrochemical formation of long probes with nanosharp tips can be controlled by choosing an appropriate thermodynamic pathway of metal to metal oxide and hydroxide transformation. Currently, convection-limited electropolishing (CLE) is extensively used. Nanosharp probes are produced by electrochemically etching a wire until it breaks into two pieces. This process is difficult to control because of the complexity of the associated hydrodynamic flows. We introduce transport-limited electropolishing (TLE), where the electrochemical reaction results in the formation of metal oxides and hydroxides which form a porous surface layer hindering the flow of electrolyte. The developed TLE method enables one to make long tapered needles. The taper can spread over more than 6 mm while the radius of tip curvature can be decreased down to 30 nm. These needles are strong and were successfully applied for piercing single smooth vascular muscle cells.

Nanoscale, 2011

We describe a method of fabrication of nanoporous flexible probes which work as artificial probos... more We describe a method of fabrication of nanoporous flexible probes which work as artificial proboscises. The challenge of making probes with fast absorption rates and good retention capacity was addressed theoretically and experimentally. This work shows that the probe should possess two levels of pore hierarchy: nanopores are needed to enhance the capillary action and micrometer pores are required to speed up fluid transport. The model of controlled fluid absorption was verified in experiments. We also demonstrated that the artificial proboscises can be remotely controlled by electric or magnetic fields. Using an artificial proboscis, one can approach a drop of hazardous liquid, absorb it and safely deliver it to an analytical device. With these materials, the paradigm of a stationary microfluidic platform can be shifted to the flexible structures that would allow one to pack multiple microfluidic sensors into a single fiber.

Proceedings of The Royal Society A: Mathematical, Physical and Engineering Sciences, Aug 8, 2014

Using the method of matched asymptotic expansions, the problem of the capillary rise of a meniscu... more Using the method of matched asymptotic expansions, the problem of the capillary rise of a meniscus on the complex-shaped fibres was reduced to a nonlinear problem of determination of a minimal surface. This surface has to satisfy a special boundary condition at infinity. The proposed formulation allows one to interpret the meniscus problem as a problem of flow of a fictitious non-Newtonian fluid through a porous medium. As an example, the shape of a meniscus on a fibre of an oval cross section was analysed employing Chaplygin's hodograph transformation. It was discovered that the contact line may form singularities even if the fibre has a smooth profile: this statement was illustrated with an oval fibre profile having infinite curvature at two endpoints.

Micromachines

Films formed by dip coating brass wires with dilute and semi-dilute solutions of polyvinyl butyra... more Films formed by dip coating brass wires with dilute and semi-dilute solutions of polyvinyl butyral in benzyl alcohol were studied in their liquid and solid states. While dilute and semi-dilute solutions behaved as Maxwell viscoelastic fluids, the thickness of the liquid films followed the Landau-Levich-Derjaguin prediction for Newtonian fluids. At a very slow rate of coating, the film thickness was difficult to evaluate. Therefore, the dynamic contact angle was studied in detail. We discovered that polymer additives preserve the advancing contact angle at its static value while the receding contact angle follows the Cox–Voinov theory. In contrast, the thickness of solid films does not correlate with the Landau-Levich-Derjaguin predictions. Only solutions of high-molecular-weight polymers form smooth solid films. Solutions of low-molecular-weight polymers may form either solid films with an inhomogeneous roughness or solid polymer domains separated by the dry substrate. In technologi...

Physics of Fluids, 2022

Drop-on-demand (DOD) printing is a versatile manufacturing tool, which has been widely used in ap... more Drop-on-demand (DOD) printing is a versatile manufacturing tool, which has been widely used in applications ranging from graphic products to manufacturing of ceramics, even for cell engineering. However, the existing DOD methods cannot be applied for highly viscous materials: the printing technologies are typically limited to the inks with the water level viscosity and fall short to eject jets from thick fluids and break them into droplets. To address this challenge, a new wire-in-a-tube technology for drop generation has been developed replacing the nozzle generator with a wire-in-a-tube drop generator. We successfully formed droplets on demand from highly viscous (∼10 Pa s) liquids and studied the mechanisms of drop formation in the wire-in-a-tube drop generators. These mechanisms couple unique fluid mechanics, capillarity, and wetting phenomena providing a new platform that can be used in different microfluidic applications.

Insect Mouthparts, 2019

Fluid feeders represent more than half of the world’s insect species. We review current understan... more Fluid feeders represent more than half of the world’s insect species. We review current understanding of the physics of fluid-feeding, from the perspective of wetting, capillarity, and fluid mechanics. We feature butterflies and moths (Lepidoptera) as representative fluid-feeding insects. Fluid uptake by live butterflies is experimentally explained based on X-ray imaging and high-speed optical microscopy and is augmented by modeling and by mechanical and physicochemical characterization of biomaterials. Wetting properties of the lepidopteran proboscis are reviewed, and a classification of proboscis morphology and wetting characteristics is proposed. The porous and fibrous structure of the mouthparts is important in determining the dietary habits of fluid-feeding insects. The fluid mechanics of liquid uptake by insects cannot be explained by a simple Hagen–Poiseuille flow scenario of a drinking-straw model. Fluid-feeding insects expend muscular energy in moving fluid through the proboscis or through the sucking pump, depending primarily on the ratio of the proboscis length to the food canal diameter. A general four-step model of fluid-feeding is proposed, which involves wetting, dewetting, absorbing, and pumping. The physics of fluid-feeding is important for understanding the evolution of sucking mouthparts and, consequently, insect diversification through development of new fluid-feeding habits.