Omid Arjmandi-Tash

Surfactant-enhanced spreading: Experimental achievements and possible mechanisms.

Surfactants are broadly used to improve wetting properties of aqueous formulations. The improvement is achieved by essential reduction of liquid/air and solid/liquid interfacial tensions resulting in the decrease of contact angle. For moderately hydrophobic substrates, there is a range of surfactants providing complete wetting of substrate. With the decrease of substrate surface energy, this range of surfactants reduces very quickly and only trisiloxane surfactant solutions are capable to wet completely such highly hydrophobic substrates as polypropylene and parafilm. That is why these surfactants are referred to as superspreaders. The most intriguing feature of wetting surfactant solutions is their ability to spread much faster than pure liquids with spread area, S, being proportional to time, t, S~t, as compared to S~t(0.2) for pure liquids, which wet completely the solid substrate. Trisiloxane surfactant solutions spread faster than other aqueous surfactant solutions, which also provide complete wetting, being superspreaders in the sense of spreading rate as well. The mechanism of fast spreading of surfactant solutions on hydrophobic substrates and much higher spreading rates for trisiloxane solutions are to be explained. Below the available experimental data on superspreading and surfactant-enhanced spreading are analysed/summarised, and possible mechanisms governing the fast spreading are discussed.

Spreading of blood drops over dry porous substrate: Complete wetting case

HYPOTHESIS The process of dried blood spot sampling involves simultaneous spreading and penetration of blood into a porous filter paper with subsequent evaporation and drying. Spreading of small drops of blood, which is a non-Newtonian liquid, over a dry porous layer is investigated from both theoretical and experimental points of view. EXPERIMENTS AND THEORY A system of two differential equations is derived, which describes the time evolution of radii of both the drop base and the wetted region inside the porous medium. The system of equations does not include any fitting parameters. The predicted time evolutions of both radii are compared with experimental data published earlier. FINDINGS For a given power law dependency of viscosity of blood with different hematocrit level, radii of both drop base and wetted region, and contact angle fell on three universal curves if appropriate scales are used with a plot of the dimensionless radii of the drop base and the wetted region inside the porous layer and dynamic contact angle on dimensionless time. The predicted theoretical relationships are three universal curves accounting satisfactorily for the experimental data.

Kinetics of Wetting and Spreading of Droplets over Various Substrates

There has been a substantial increase in the number of publications in the field of wetting and spreading since 2010. This increase in the rate of publications can be attributed to the broader application of wetting phenomena in new areas. It is impossible to review such a huge number of publications; that is, some topics in the field of wetting and spreading are selected to be discussed below. These topics are as follows: (i) Contact angle hysteresis on smooth homogeneous solid surfaces via disjoining/conjoining pressure. It is shown that the hysteresis contact angles can be calculated via disjoining/conjoining pressure. The theory indicates that the equilibrium contact angle is closer to a static receding contact angle than to a static advancing contact angle. (ii) The wetting of deformable substrates, which is caused by surface forces action in the vicinity of the apparent three-phase contact line, leading to a deformation on the substrate. (iii) The kinetics of wetting and spreading of non-Newtonian liquid (blood) over porous substrates. We showed that in spite of the enormous complexity of blood, the spreading over porous substrate can be described using a relatively simple model: a power low-shear-thinning non-Newtonian liquid. (iv) The kinetics of spreading of surfactant solutions. In this part, new results related to various surfactant solution mixtures (synergy and crystallization) are discussed, which shows some possible direction for the future revealing of superspreading phenomena. (v) The kinetics of spreading of surfactant solutions over hair. Fundamental problems to be solved are identified.

Dominant Flow Structures in Gas–Solid Fluidized Beds Using Time and Frequency Domains Analyses

Time series analysis techniques in time domain and average cycle frequency were applied to characterize bubbling fluidization. The experiments were carried out in a laboratory scale fluidized bed, operated under ambient conditions and various sizes of particles, measurement heights, and different superficial gas velocities. It was found that a minimum in average cycle frequency and flatness and a shift of skewness from negative to positive against velocity correspond to shift from macrostructures and finer structures of the flow rather than transition velocity from the bubbling to turbulent regime. The power spectrum estimation of the measured pressure fluctuations shows that the peak dominant frequency of the pressure fluctuations is about 1.5–2.5 Hz which is corresponding to the macrostructures of the bed. Accordingly, the onset of turbulent fluidization regime was detected through standard deviation analysis. It was shown that the simple analysis techniques still have interesting information about hydrodynamics of fluidization and they can accurately estimate transition between dominant flow structures of a gas–solid fluidized bed.

Possibility of Atherosclerosis in an Arterial Bifurcation Model

INTRODUCTION Arterial bifurcations are susceptible locations for formation of atherosclerotic plaques. In the present study, steady blood flow is investigated in a bifurcation model with a non-planar branch. METHODS The influence of different bifurcation angles and non-planar branch is demonstrated on wall shear stress (WSS) distribution using three-dimensional Navier-Stokes equations. RESULTS The WSS values are low in two locations at the top and bottom walls of the mother vessels just before the bifurcation, especially for higher bifurcation angles. These regions approach the apex of bifurcation with decreasing the bifurcation angle. The WSS magnitudes approach near to zero at the outer side of bifurcation plane and these locations are separation-prone. By increasing the bifurcation angle, the minimum WSS decreases at the outer side of bifurcation plane but low WSS region squeezes. WSS peaks exist on the inner side of bifurcation plane near the entry section of daughter vessels and these initial peaks drop as bifurcation angle is increased. CONCLUSION It is concluded that the non-planarity of the daughter vessel lowers the minimum WSS at the outer side of bifurcation and increases the maximum WSS at the inner side. So it seems that the formation of atherosclerotic plaques at bifurcation region in direction of non-planar daughter vessel is more risky.

Prediction and control of drop formation modes in microfluidic generation of double emulsions by single-step emulsification

HYPOTHESIS Predicting formation mode of double emulsion drops in microfluidic emulsification is crucial for controlling the drop size and morphology. EXPERIMENTS AND MODELLING A three-phase Volume of Fluid-Continuum Surface Force (VOF-CSF) model was developed, validated with analytical solutions, and used to investigate drop formation in different regimes. Experimental investigations were done using a glue-free demountable glass capillary device with a true axisymmetric geometry, capable of readjusting the distance between the two inner capillaries during operation. FINDINGS A non-dimensional parameter (ζ) for prediction of double emulsion formation mode as a function of the capillary numbers of all fluids and device geometry was developed and its critical values were determined using simulation and experimental data. At logζ>5.7, drops were formed in dripping mode; the widening jetting occurred at 5<logζ<5.7; while the narrowing jetting was observed at logζ<5. The ζ criterion was correlated with the ratio of the break-up length to drop diameter. The transition from widening to narrowing jetting was achieved by increasing the outer fluid flow rate at the high capillary number of the inner fluid. The drop size was reduced by reducing the distance between the two inner capillaries and the minimum drop size was achieved when the distance between the capillaries was zero.

Simulation of Blood Flow Coronary Artery with Consecutive Stenosis and Coronary-Coronary Bypass

INTRODUCTION In this research the behavior of coronary arteries has been studied with symmetric and asymmetric consecutive stenosis, and grafted vessels. METHODS The incompressible Navier-Stokes and energy equations were discretized with second-order upwind method. Assumptions such as Newtonian fluid, wall rigidity and steady-flow were used. RESULTS All the calculations showed the same results with Newtonians and non- Newtonian fluids. It was found that the possibility of stenosis be reduced by increasing the graft angle. However, there exists further stenosis possibility. Among the three graft angles 20, 30 ˚ and 40, the 30 ˚ was found to be the reliable ones. CONCLUSION Based on these findings, it can be deduced that there would be a high risk of further atherosclerosis when the first stenose has the maximum percentage.

Polymer and foams in hair care products [Abstract]

Hair care products are expected to wet well human hair, even when the hair is hydrophobic. Thus, wetting properties of human hair are very important, as they influence consumer satisfaction with the products. Wettability of a hair tress is an important characteristic. The wetting behavior of polymer solutions on hair is less studied than surfactant solutions. The wetting of hair tresses by aqueous solutions of commercially available polymers AculynTM 22 (A22) and AculynTM 33 (A33) has been investigated. Both experimental studies and numerical simulations of behavior of polymer solutions and foams on tresses of human hair has been investigated including drainage of foams produced from solutions of those polymers and interaction of foams with hair stresses are presented. Both A22 and A33 solutions demonstrate well pronounced shear thinning behavior. Initial contact angle of the A22 and A33 solutions on undamaged hair tresses is about 100 o. The A22 droplets remained on the hair tress after spreading for at least half an hour. However, a fast penetration of the A33 droplet inside the hair tresses was observed when advancing contact angle in the course of spreading reaches a critical value of about (60 o). Pure solutions of A22 and A33 have higher initial contact angle and longer penetration time on hair tresses compared with the solutions containing i-propanol or sodium dodecyl sulphate. The results demonstrate that wetting kinetics of the polymer solution on hair tresses drastically different depending on the formulation and can vary from a rapid imbibition to a spreading only.One of the major disease manifestations of systemic lupus erythematosus (SLE) is lupus nephritis (LN), and the underlying mechanisms are not yet understood. Epstein-Barr virus (EBV) reactivation was associated with the induction of SLE, with EBV-encoded latent membrane protein1 (LMP1) plays a vital role in this process. Although it was reported that LN was associated with LMP1, most of these results are from patients with ages differed greatly (range, 10-56 years). Given the increased prevalence of EBV infection in young patients, we focused on the association of LN and LMP1 expression in the renal tissues of young patients (range, 6-16 years) in this study. We found that the positive rate of LMP1 in the renal tissues was significantly higher in patients with LN compared with control (P<0.001), which is consistent with the previous reports. The positive rates of LMP1 were similar between the patients of initial onset and relapse, and there was no detectable difference between the patients with and without concurrent infection (P>0.05). However, we reported for the first time about the positive correlation of LMP1 with classification of LN. The proportion of young patients positive for anti‑Sm antibody was significantly higher in the LMP1 positive group compared with the LMP1 negative control (P>0.05). These results indicate that EBV infection in the renal of young patients may lead to the increased severity of LN, and the expression of anti-Sm is likely contributed to this process.Human hair is a nanocomposite biological fiber. Maintaining the health, feel, shine, color, softness, and overall aesthetics of the hair is highly desired. Hair care products such as shampoos and conditioners, along with damaging processes such as chemical dyeing and permanent wave treatments, affect the maintenance and grooming process and are important to study because they alter many hair properties. Nanoscale characterization of the cellular structure, mechanical properties, and morphological, frictional, and adhesive properties (tribological properties) of hair are essential to evaluate and develop better cosmetic products, and to advance the understanding of biological and cosmetic science. The tensile response of hair is of considerable interest. Another property of interest is the surface charge of hair, which has a significant effect on manageability, feel, and appearance. For this reason, controlling charge buildup to improve these factors is an important issue in the commercial hair care industry. The atomic/friction force microscope (AFM/FFM) and nanoindenter have recently become important tools for studying the micro/nanoscale properties of human hair. In this talk, we present a comprehensive review of the cellular structural, nanomechanical, and nanotribological properties of various hair and skin as a function of ethnicity, damage, conditioning treatment, and various environments1-2. Various cellular structures of human hair and fine sublamellar structures of the cuticle are identified and studied. Nanomechanical properties such as hardness, elastic modulus, creep and scratch resistance are discussed. Nanotribological properties such as roughness, friction, and adhesion are presented, as well as investigations of conditioner distribution, thickness, and binding interactions.