Synthysis of polymer/nano-droplet composites from reverse microemulsion polymerization

L1 and L2 domains of the water/AOT/MMA ternary system were investigated at 22±1°C. Free radical polymerizations were conducted in L2 domain. Only opaque polymer rods were obtained. Acrylamide, a water soluble monomer, plays a role of co-surfactant which greatly expands the L2 domain. However, polymerizations only yielded opaque material. SEM showed images of phase separation. MDOS (2-Methacryloyloxy)ethyl trimethylammonium bis(2-ethylhexyl) sulfosuccinate, was synthesized by ion exchange method. L1 and L2 domains of the water/MDOS/MMA ternary system were also investigated at 22±1°C. Free radical polymerizations were conducted in L2 domain. Transparent polymer was produced. The “L2” domain after polymerization was almost as large as L2 domain. Polymerizations with acrylamide in the aqueous phase also produced transparent copolymer with up to 14% water. Polymer materials so produced were characterized by TGA, DSC, SEC, SEM

Sticky Gecko Feet: the Role of Temperature and Humidity

Gecko adhesion is expected to be temperature insensitive over the range of temperatures typically experienced by geckos. Previous work is limited and equivocal on whether this expectation holds. We tested the temperature dependence of adhesion in Tokay and Day geckos and found that clinging ability at 12 degrees C was nearly double the clinging ability at 32 degrees C. However, rather than confirming a simple temperature effect, our data reveal a complex interaction between temperature and humidity that can drive differences in adhesion by as much as two-fold. Our findings have important implications for inferences about the mechanisms underlying the exceptional clinging capabilities of geckos, including whether performance of free-ranging animals is based solely on a dry adhesive model. An understanding of the relative contributions of van der Waals interactions and how humidity and temperature variation affects clinging capacities will be required to test hypotheses about the evolution of gecko toepads and is relevant to the design and manufacture of synthetic mimics

Temperature Dependent Droplet Impact Dynamics on Flat and Textured Surfaces

Droplet impact dynamics determines the performance of surfaces used in many applications such as anti-icing, condensation, boiling, and heat transfer. We study impact dynamics of water droplets on surfaces with chemistry/texture ranging from hydrophilic to superhydrophobic and across a temperature range spanning below freezing to near boiling conditions. Droplet retraction shows very strong temperature dependence especially on hydrophilic surfaces; it is seen that lower substrate temperatures lead to lesser retraction. Physics-based analyses show that the increased viscosity associated with lower temperatures combined with an increased work of adhesion can explain the decreased retraction. The present findings serve as a starting point to guide further studies of dynamic fluid-surface interaction at various temperatures. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3692598

Sticky Gecko Feet: The Role of Temperature and Humidity

Gecko adhesion is expected to be temperature insensitive over the range of temperatures typically experienced by geckos. Previous work is limited and equivocal on whether this expectation holds. We tested the temperature dependence of adhesion in Tokay and Day geckos and found that clinging ability at 12°C was nearly double the clinging ability at 32°C. However, rather than confirming a simple temperature effect, our data reveal a complex interaction between temperature and humidity that can drive differences in adhesion by as much as two-fold. Our findings have important implications for inferences about the mechanisms underlying the exceptional clinging capabilities of geckos, including whether performance of free-ranging animals is based solely on a dry adhesive model. An understanding of the relative contributions of van der Waals interactions and how humidity and temperature variation affects clinging capacities will be required to test hypotheses about the evolution of gecko toepads and is relevant to the design and manufacture of synthetic mimics

Gecko-Inspired Carbon Nanotube-Based Self-Cleaning Adhesives

The design of reversible adhesives requires both stickiness and the ability to remain clean from dust and other contaminants. Inspired by gecko feet, we demonstrate the self-cleaning ability of carbon nanotube-based flexible gecko tapes

Cooperative Adhesion and Friction of Compliant Nanohairs

The adhesion and friction behavior of soft materials, including compliant brushes and hairs, depends on the temporal and spatial evolution of the interfaces in contact. For compliant nanofibrous materials, the actual contact area individual fibers make with surfaces depends on the preload applied upon contact. Using in situ microscopy observations of preloaded nanotube hairs, we show how nanotubes make cooperative contact with a surface by buckling and conforming to the surface topography. The overall adhesion of compliant nanohairs increases with increasing preload as nanotubes deform and continuously add new side-wall contacts with the surface. Electrical resistance measurements indicate significant hysteresis in the relative contact area. Contact area increases with preload (or stress) and decreases suddenly during unloading, consistent with strong adhesion observed for these complaint nanohairs

Direct Evidence of Phospholipids in Gecko Footprints and Spatula– Substrate Contact Interface Detected Using Surface-Sensitive Spectroscopy

Observers ranging from Aristotle to young children have long marvelled at the ability of geckos to cling to walls and ceilings. Detailed studies have revealed that geckos are ‘sticky’ without the use of glue or suction devices. Instead, a gecko’s stickiness derives from van derWaals interactions between proteinaceous hairs called setae and substrate. Here, we present surprising evidence that although geckos do not use glue, a residue is transferred on surfaces as they walk—geckos leave footprints. Using matrix-free nano-assisted laser desorption-ionization mass spectrometry, we identified the residue as phospholipids with phosphocholine head groups.Moreover, interface-sensitive sum-frequency generation spectroscopy revealed predominantly hydrophobic methyl and methylene groups and the complete absence of water at the contact interface between a gecko toe pad and the substrate. The presence of lipids has never been considered in current models of gecko adhesion.Our analysis of gecko footprints and the toe pad–substrate interface has significant consequences for models of gecko adhesion and by extension, the design of synthetic mimics

Sex, size, and toe pad area of geckos used in experimental trials. Toe pad area is an estimate of maximal area of scansors visible on scans.

<p>Sex, size, and toe pad area of geckos used in experimental trials. Toe pad area is an estimate of maximal area of scansors visible on scans.</p

Direct Evidence of Phospholipids in Gecko Footprints and Spatula-Substrate Contact Interface Detected Using Surface-Sensitive Spectroscopy Techniques

Observers ranging from Aristotle to young children have long marvelled at the ability of geckos to cling to walls and ceilings. Detailed studies have revealed that geckos are \u27sticky\u27 without the use of glue or suction devices. Instead, a gecko\u27s stickiness derives from van der Waals interactions between proteinaceous hairs called setae and substrate. Here, we present surprising evidence that although geckos do not use glue, a residue is transferred on surfaces as they walk-geckos leave footprints. Using matrix-free nano-assisted laser desorption-ionization mass spectrometry, we identified the residue as phospholipids with phosphocholine head groups. Moreover, interface-sensitive sum-frequency generation spectroscopy revealed predominantly hydrophobic methyl and methylene groups and the complete absence of water at the contact interface between a gecko toe pad and the substrate. The presence of lipids has never been considered in current models of gecko adhesion. Our analysis of gecko footprints and the toe pad-substrate interface has significant consequences for models of gecko adhesion and by extension, the design of synthetic mimics