Electro-Coalescence Fireworks

Electro-coalescence is the application of an electric field onto coalescing fluid bodies. The following fluid dynamics videos show a droplet coalescing into a fluid bath while embedded into a viscous medium and subject to a very high electric field. The concentration of electric stresses at the apex of the droplet cause it to break apart. The droplet is glycerol and the viscous medium is silicone oil

An interferometric study of spreading liquid films

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.Includes bibliographical references (p. 201-212).Moving contact line problems involving polymeric materials and other complex fluids are encountered in many applications such as coating flows, gravity-driven drainage, and spin-coating operations. Viscous, capillary, inertial and gravitational forces can all be important in these flows depending on the scale and speed of the spreading process. In this research, a number of benchmark problems involving moving contact lines of viscous Newtonian and non-Newtonian polymeric fluids have been studied using non-invasive optical techniques. A detailed study of viscous Newtonian and non-volatile liquids spreading on smooth horizontal and inclined substrates is presented. A phase-modulated interference microscope was used to enable the simultaneous measurement of both the inner (microscopic) length scale and the outer (macroscopic) flow scale in addition to the intermediate matching region. The resulting measurements of both the apparent contact angle and lateral scale of the precursor wetting film agree quantitatively with theoretical predictions for the spreading of a van der Waals fluid over a wide range of capillary numbers (10-6 10) on a solid surface is also considered. Our experiments confirm the existence of a non-Newtonian 'foot' region in the vicinity of the moving contact line for highly entangled polymer melts. Our experimental results of the lateral and vertical scales of this 'foot' are in fair agreement with available theoretical predictions. The transient spreading motion of an ideal elastic 'Boger' fluid (consisting of a dilute solution of high molecular weight polymer dissolved in a viscous Newtonian solvent) is also investigated. It is shown that the spreading rate of this model elastic fluid is smaller than is observed for corresponding Newtonian fluid drops of similar size and viscosity due to the viscoelastic effects. A foot-like structure is detected at the leading edge of the droplet for these unentangled, elastic fluids as well ...by Hossein Pirouz Kavehpour.Ph.D

Effect of relative humidity on the evaporation of a colloidal solution droplet

International audienceBackground The deposition of uniform layers of colloids on a solid surface is a major challenge for several industrial processes such as glass surface treatment and creating optical filters. One strategy involves the deposition of the colloids behind a contact line that recedes due to hydrodynamic reasons and evaporation (drying). The interaction between deposition, evaporation and hydrodynamics is a complex matter. We need to get a better understanding of the mechanisms at the contact line and the role they play in coating an organized deposit [1]

Fabrication and biocompatibility of BNNT supramolecular complexes and PCL/BNNTs nanofibers

Hyphenated electrospinning electrospraying is a versatile method for synthesizing polymeric functional materials with fascinating and tuneable characteristics. In this paper, previously unreported clusters of boron nitride nanotubes (BNNTs) and their hybrid nanofibers with ɛ-polycaprolactone (PCL) were fabricated successfully. For instance, this biocompatible nano fibrous mat may have a potent to encapsulate common anticancer drugs such as doxorubicin (DOX), cisplatin and Fluorouracil (5FU) to minimize their the most lethal side effect, cardiotoxicity, and to improve chemotherapy and manage cardiotoxicity in cancer patients. BNNTs supramolecular solution was prepared with controllable dispersion and agglomeration features. Furthermore, the synthesized PCL nanofibers including BNNTs clusters (PCL/BNNTs) exhibit favourable qualities in the terms of mechanical and thermal strength, hydrophobicity and biocompatibility. Different microscopic and analytical examinations such as: Field emission scanning electron microscopy (FESEM), Furrier transform spectroscopy (FT-IR), Dynamic scanning calorimetry (DSC) and MTT assay were performed. BNNTs clusters were synthesized and then subjected to electrospraying. Simultaneously electrospinning of PCL solution was conducted to provide nanofiber net-like film consisting of BNNT nano-capsulated beads (∼100 nm to ∼1 µm). PCL/BNNTs nanofibers with average diameters of 350 ± 50 nm were synthesized depended on various electrospinning conditions. The results of cytotoxicity assay on cardiac cell line (H9c2 cells) reveal that prepared BNNTs clusters and PCL/BNNTs nanofibers are more biocompatible rather than isolated BNNTs

Non-Newtonian thin films with normal stresses: dynamics and spreading

The dynamics of thin films on a horizontal solid substrate is investigated in the case of non-Newtonian fluids exhibiting normal stress differences, the rheology of which is strongly non-linear. Two coupled equations of evolution for the thickness of the film and the shear rate are proposed within the lubrication approximation. This framework is applied to the motion of an advancing contact line. The apparent dynamic contact angle is found to depend logarithmically on a lengthscale determined solely by the rheological properties of the fluid and the velocity of the contact line

Incorporation of Active DNA/Cationic Polymer Polyplexes into Hydrogel Scaffolds

The effective and sustained delivery of DNA and siRNAs locally would increase the applicability of gene therapy in tissue regeneration and cancer therapy. One promising approach is to use hydrogel scaffolds to encapsulate and deliver nucleotides in the form of nanoparticles to the disease sites. However, this approach is currently limited by the inability to load concentrated and active gene delivery nanoparticles into the hydrogels due to the severe nanoparticle aggregation during the loading process. Here, we present a process to load concentrated and un-aggregated non-viral gene delivery nanoparticles, using DNA/polyethylene imine (PEI) polyplexes as an example, into neutral polyethylene glycol (PEG), negatively charged hyaluronic acid (HA) and protein fibrin hydrogels crosslinked through various chemistries. The encapsulated polyplexes are highly active both in vitro and in vivo. We believe this process will significantly advance the applications of hydrogel scaffold mediated non-viral gene delivery in tissue regeneration and cancer therapy

A thermodynamic unification of jamming

Fragile materials ranging from sand to fire-retardant to toothpaste are able to exhibit both solid and fluid-like properties across the jamming transition. Unlike ordinary fusion, systems of grains, foams and colloids jam and cease to flow under conditions that still remain unknown. Here we quantify jamming via a thermodynamic approach by accounting for the structural ageing and the shear-induced compressibility of dry sand. Specifically, the jamming threshold is defined using a non-thermal temperature that measures the 'fluffiness' of a granular mixture. The thermodynamic model, casted in terms of pressure, temperature and free-volume, also successfully predicts the entropic data of five molecular glasses. Notably, the predicted configurational entropy avoids the Kauzmann paradox entirely. Without any free parameters, the proposed equation-of-state also governs the mechanism of shear-banding and the associated features of shear-softening and thickness-invariance.Comment: 16 pgs double spaced. 4 figure