TiO(2) nanoparticles of different phases play a key role in property alteration of nanocomposite fibers. Polycaprolactone (PCL)/TiO(2) composite fibers were prepared using the electrospinning method. Pure anatase and rutile phases were synthesized using the sol-gel route for nanocomposite synthesis. The Effect of nanoparticle phases on crystallinity of fibers and interaction with polymer molecules have been studied using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, morphology through SEM, surface properties using BET method and wetting property of fibers commencing from contact angle measurement. Biocompatibility and biodegradation of hybrid materials have been studied in simulated body fluid (SBF) and phosphate buffer (PBS), respectively. The anatase phase with smaller particle dimensions exhibited significant improvement of most of the properties as compared to composites made of the rutile phase. Better interaction between polymer chain and anatase particle PCL-A nanocomposite fibers leads to better mechanical property and biocompatibility vis-à-vis PCL-R and pristine PCL fibers. Biocompatibility of PCL nanocomposite has been testified through proliferation of fibroblast cell and its adhesion; MTT (3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay demonstrates good proliferation rate for cells on PCL-A nanocomposite fibres.

A counterintuitive, thermocapillary-induced limit to heat- pipe performance was observed that is not predicted by current thermal-fluid models. Heat pipes operate under a number of physical constraints including the capillary, boiling, sonic, and entrainment limits that fundamentally affect their performance. Temperature gradients near the heated end may be high enough to generate significant Marangoni forces that oppose the return flow of liquid from the cold end. These forces are believed to exacerbate dry out conditions and force the capillary limit to be reached prematurely. Using a combination of image and thermal data from experiments conducted on the International Space Station with a transparent heat pipe, we show that in the presence of significant Marangoni forces, dry out is not the initial mechanism limiting performance, but that the physical cause is exactly the opposite behavior: flooding of the hot end with liquid. The observed effect is a consequence of the competition between capillary and Marangoni-induced forces. The temperature signature of flooding is virtually identical to dry out, making diagnosis difficult without direct visual observation of the vapor-liquid interface.

A wickless heat pipe was operated on the International Space Station to provide a better understanding of how the microgravity environment might alter the physical and interfacial forces driving evaporation and condensation. Traditional heat pipes are divided into three zones: evaporation at the heated end, condensation at the cooled end, and intermediate/adiabatic in between. The microgravity experiments reported herein show the situation may be dramatically more complicated. Beyond a threshold heat input, there was a transition from evaporation at the heated end to large-scale condensation, even as surface temperatures exceeded the boiling point by 160 K. The hotter the surface, the more vapor was condensed onto it. The condensation process at the heated end is initiated by thickness and temperature disturbances in the thin liquid film that wet the solid surface. Those disturbances effectively leave the vapor "superheated" in that region. Condensation is amplified and sustained by the high Marangoni stresses that exist near the heater and that drive liquid to cooler regions of the device.

The Constrained Vapor Bubble (CVB) experiment concerns a transparent, simple, "wickless" heat pipe operated in the microgravity environment of the International Space Station (ISS). In a microgravity environment, the relative effect of Marangoni flow is amplified because of highly reduced buoyancy driven flows as demonstrated herein. In this work, experimental results obtained using a transparent 30 mm long CVB module, 3 mm × 3 mm in square cross-section, with power inputs of up to 3.125 W are presented and discussed. Due to the extremely low Bond number and the dielectric materials of construction, the CVB system was ideally suited to determining if dry-out as a result of Marangoni forces might contribute to limiting heat pipe performance and exactly how that limitation occurs. Using a combination of visual observations and thermal measurements, we find a more complicated phenomenon in which opposing Marangoni and capillary forces lead to flooding of the device. A simple one-dimensional, thermal-fluid flow model describes the essence of the relative importance of the two stresses. Moreover, even though the heater end of the device is flooded and the liquid is highly superheated, boiling does not occur due to high evaporation rates.

No abstract