A Review On Spider Silk Adhesion,
2014
University of Akron
A Review On Spider Silk Adhesion, Ali Dhinojwala
Ali Dhinojwala
Spiders employ clever behavioral strategies combined with almost invisible custom-made adhesive silk fibers to spin prey capture webs. The adhesives used in these webs evolved over millions of years into a class of natural materials with outstanding properties. Here, we review how spiders use different adhesives to capture prey. We show how spiders take advantage of the elasticity of both the capture silk and the glue to enhance adhesive forces, thereby providing important insights in designing new synthetic adhesives.
High-Content Profiling Of Cell Responsiveness To Graded Substrates Based On Combinatorially Variant Polymers,
2014
University of Akron
High-Content Profiling Of Cell Responsiveness To Graded Substrates Based On Combinatorially Variant Polymers, Matthew Becker
Matthew Becker
We have developed a novel approach combining high information and high throughput analysis to characterize cell adhesive responses to biomaterial substrates possessing gradients in surface topography. These gradients were fabricated by subjecting thin film blends of tyrosine-derived polycarbonates, i.e. poly(DTE carbonate) and poly(DTO carbonate) to a gradient temperature annealing protocol. Saos-2 cells engineered with a green fluorescent protein (GFP) reporter for farnesylation (GFP-f) were cultured on the gradient substrates to assess the effects of nanoscale surface topology and roughness that arise during the phase separation process on cell attachment and adhesion strength. The high throughput imaging approach allowed us to …
A Device For Surface Spectroscopic Study Of Micron Thin Films,
2014
University of Akron
A Device For Surface Spectroscopic Study Of Micron Thin Films, Ali Dhinojwala
Ali Dhinojwala
A device to probe the molecular structure of materials next to a solid interface in a thin film geometry has been developed. The device can produce controlled thicknesses as small as 1 μm with parallelity better than 0.003°. We have shown that the thickness and the parallelity of the film produced between two optical surfaces can be quantified using white light and monochromatic light interferometry, respectively. In addition, this apparatus allows the study of these films in a static state or under shear using spectroscopic techniques involving transmission or reflection measurements.
Gecko-Inspired Carbon Nanotube-Based Self-Cleaning Adhesives,
2014
The University Of Akron
Gecko-Inspired Carbon Nanotube-Based Self-Cleaning Adhesives, Sunny Sethi, Liehui Ge, Lijie Ci, P. Ajayan, Ali Dhinojwala
Ali Dhinojwala
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.
Dynamics Of Ice Nucleation On Water Repellent Surfaces,
2014
The University Of Akron
Dynamics Of Ice Nucleation On Water Repellent Surfaces, Azar Alizadeh, Masako Yamada, Ri Li, Wen Shang, Shourya Otta, Sheng Zhong, Liehui Ge, Ali Dhinojwala, Ken Conway, Vaibhav Bahadur, A. Vinciquerra, Brian Stephens, Margaret Blohm
Ali Dhinojwala
Prevention of ice accretion and adhesion on surfaces is relevant to many applications, leading to improved operation safety, increased energy efficiency, and cost reduction. Development of passive nonicing coatings is highly desirable, since current antiicing strategies are energy and cost intensive. Superhydrophobicity has been proposed as a lead passive nonicing strategy, yet the exact mechanism of delayed icing on these surfaces is not clearly understood. In this work, we present an in-depth analysis of ice formation dynamics upon water droplet impact on surfaces with different wettabilities. We experimentally demonstrate that ice nucleation under low-humidity conditions can be delayed through control …
Polycarbonate Of Tetra:Methyl Spiro:Bi:Indane Bisphenol,
2014
University of Akron
Polycarbonate Of Tetra:Methyl Spiro:Bi:Indane Bisphenol, Ali Dhinojwala
Ali Dhinojwala
No abstract provided.
Cooperative Adhesion And Friction Of Compliant Nanohairs,
2014
The University Of Akron
Cooperative Adhesion And Friction Of Compliant Nanohairs, Liehui Ge, Lijie Ci, Anubha Goyal, Rachel Shi, L. Mahadevan, P. Ajayan, Ali Dhinojwala
Ali Dhinojwala
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 …
Peg-Hydrogels: Synthesis, Characterization, And Cell Encapsulation,
2014
University of Akron
Peg-Hydrogels: Synthesis, Characterization, And Cell Encapsulation, Matthew Becker
Matthew Becker
No abstract provided.
Dynamic Monte Carlo Modeling Of Exciton Dissociation In Organic Donor Acceptor Solar Cells,
2014
The University Of Akron
Dynamic Monte Carlo Modeling Of Exciton Dissociation In Organic Donor Acceptor Solar Cells, Michael Heiber, Ali Dhinojwala
Ali Dhinojwala
A general dynamic Monte Carlo model for exciton dissociation at a donor-acceptor interface that includes exciton delocalization and hot charge separation is developed to model the experimental behavior observed for the poly(3-hexylthiophene):fullerene system and predict the theoretical performance of future materials systems. The presence of delocalized excitons and the direct formation of separated charge pairs has been recently measured by transient photo-induced absorption experiments and has been proposed to facilitate charge separation. The excess energy of the exciton dissociation process has also been observed to have a strong correlation with the charge separation yield for a series of thiophene based …
Relative Contribution Of The Third-Order Effect To The Second Harmonic Signal In Doped, Poled Amorphous Polymers,
2014
University of Akron
Relative Contribution Of The Third-Order Effect To The Second Harmonic Signal In Doped, Poled Amorphous Polymers, Ali Dhinojwala
Ali Dhinojwala
A novel approach involving a delay-trigger method and doped, glassy polymers has been developed to determine the contribution of the electric-field-induced third-order effect to the second-order macroscopic susceptibility χ(2) of nonlinear optical dyes. A submillisecond, variable time delay is employed for switching on or off the electric poling field with respect to the laser pulse. For the several dyes tested at 30 °C the contribution of the electric-field-induced third-order effect (second-harmonic wavelength = 532 nm) ranges from (6 ± 2)% of χ(2) 4-(dimethylamino)benzylidenemalononitrile to (20 ± 3)% of χ(2) for 4-(dimethylamino)-4′-nitrostilbene.
Quantitative Rational Predictions Of The Long-Term Temporal Decay Properties Of Second-Order Nonlinear Optical Polymers From The Analysis Of Relaxation Dynamics,
2014
University of Akron
Quantitative Rational Predictions Of The Long-Term Temporal Decay Properties Of Second-Order Nonlinear Optical Polymers From The Analysis Of Relaxation Dynamics, Ali Dhinojwala
Ali Dhinojwala
An accelerated method of testing has been developed which allows quantitative, rational prediction of the temporal decay properties of second-order nonlinear optical (NLO) polymers under conditions of technological interest but which are experimentally inaccessible. This is accomplished by using a novel delay-trigger technique to monitor the reorientation of NLO chromophores doped and labeled in amorphous polymers over 12 decades in time (10-6 to 106 sec). By fitting the time-dependent orientational component of the second-order macroscopic susceptibility, χ(2), to the Kohlrausch-Williams-Watts expression, an average reorientation relaxation time, <τ>, is determined in both the glassy and rubbery states. The reorientation dynamics of …
Surface Dynamics In Rubbed Polymer Thin Films Probed With Optical Birefringence Measurements,
2014
The University Of Akron
Surface Dynamics In Rubbed Polymer Thin Films Probed With Optical Birefringence Measurements, Alexander Schwab, Dena Mae Agra, Jae-Hoon Kim, Satyendra Kumar, Ali Dhinojwala
Ali Dhinojwala
Measurements of the optical birefringence were used to probe the relaxation of rubbed ultrathin polystyrene (PS) films on glass substrates. It was found that the glass transition temperature, Tg, of the films dropped by 15−20 K as the film thickness decreased from 10 μm to 5.8 nm. Experiments on thick films (10 μm) revealed that molecules closer to the polymer−air interface relax more quickly than molecules farther from the interface. These results are explained in the context of past experimental studies of thermal properties of similar ultrathin polymer films.
Spider Silk As A Novel High Performance Biomimetic Muscle Driven By Humidity,
2014
The University Of Akron
Spider Silk As A Novel High Performance Biomimetic Muscle Driven By Humidity, Ingi Agnarsson, Ali Dhinojwala, Vasav Sahni, Todd Blackledge
Ali Dhinojwala
The abrupt halt of a bumble bee's flight when it impacts the almost invisible threads of an orb web provides an elegant example of the amazing strength and toughness of spider silk. Spiders depend upon these properties for survival, yet the impressive performance of silk is not limited solely to tensile mechanics. Here, we show that silk also exhibits powerful cyclic contractions, allowing it to act as a high performance mimic of biological muscles. These contractions are actuated by changes in humidity alone and repeatedly generate work 50 times greater than the equivalent mass of human muscle. Although we demonstrate …
Optical Anisotropy Of Aligned Single Wall Carbon Nanotubes,
2014
University of Akron
Optical Anisotropy Of Aligned Single Wall Carbon Nanotubes, Matthew Becker
Matthew Becker
The optical properties of single wall carbon nanotubes (SWCNTs) are of significant importance for a variety of applications, particularly for fractions containing well defined tube lengths and chiralities. In this work, stable suspensions of DNA wrapped SWCNTs were mechanically aligned by dispersing them in amorphous polymer films, and their intrinsic optical anisotropy measured through a combination of polarized light spectroscopy, polarized Raman spectroscopy, and small-angle neutron scattering (SANS). Conventional measures of nematic alignment in the stretched polymer films typically varied from 0.7 to 0.9. The quality of the nanotube dispersion within the centimeter scale polymer film samples was also directly …
Direct Evidence Of Phospholipids In Gecko Footprints And Spatula-Substrate Contact Interface Detected Using Surface-Sensitive Spectroscopy Techniques,
2014
The University Of Akron
Direct Evidence Of Phospholipids In Gecko Footprints And Spatula-Substrate Contact Interface Detected Using Surface-Sensitive Spectroscopy Techniques, Ping Hsu, Liehui Ge, Xiaopeng Li, Alyssa Stark, Chrys Wesdemiotis, Peter Niewiarowski, Ali Dhinojwala
Ali Dhinojwala
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 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 …
Rheo-Optical Studies Of Carbon Nanotube Suspensions,
2014
University of Akron
Rheo-Optical Studies Of Carbon Nanotube Suspensions, Matthew Becker
Matthew Becker
We use a polarization-modulation technique to investigate the optical anisotropy of multi- and single-wall carbon nanotubes suspended in a variety of solvents under simple shear flow. Measurements of birefringence and dichroism are performed as a function of shear rate, tube concentration, and solvent viscosity. At fixed volume fraction, the anisotropy increases with increasing shear stress due to enhanced flow alignment. At fixed shear stress, the anisotropy increases with volume fraction due to rotational excluded-volume interactions. By considering the rotational diffusivity as a function of nanotube length, diameter, concentration, and solvent viscosity, we demonstrate a leading-order scaling relation for the optical …
Surface Segregation Induced By Surface Freezing,
2014
The University Of Akron
Surface Segregation Induced By Surface Freezing, Shishir Prasad, Lauri Hanne, Ali Dhinojwala
Ali Dhinojwala
No abstract provided.
Length Fractionation Of Single Wall Carbon Nanotubes Using Centrifugation,
2014
University of Akron
Length Fractionation Of Single Wall Carbon Nanotubes Using Centrifugation, Matthew Becker
Matthew Becker
Scalable separation of single-walled carbon nanotubes (SWCNTs)by length and chirality is critical to the adaptation of these materials for applications. Ultracentrifugation of SWCNTs within a density gradient produces chiral separation of the NTs, and it is shown here that ultracentrifugation can also be used to produce length fractionated SWCNTs by exploiting their transient motion in response to applied centripetal acceleration.
Infrared-Visible Sum Frequency Generation Spectroscopic Study Of Molecular Orientation At Polystyrene/Comb-Polymer Interfaces,
2014
The University Of Akron
Infrared-Visible Sum Frequency Generation Spectroscopic Study Of Molecular Orientation At Polystyrene/Comb-Polymer Interfaces, Gary Harp, Hasnain Rangwalla, Moshen Yeganeh, Ali Dhinojwala
Ali Dhinojwala
Surface-sensitive infrared-visible sum frequency generation spectroscopy (SFG) in total internal reflection geometry has been used to study the structure of poly(vinyl n-octadecyl carbamate-co-vinyl acetate) (PVNODC) or poly(octadecyl acrylate) (PA-18) in contact with a deuterated or hydrogenated polystyrene (dPS or hPS) layer. SFG spectra from the PVNODC (or PA-18)/hPS interface show methyl and methylene peaks corresponding to PVNODC (or PA-18) and phenyl peaks corresponding to the PS. Analysis suggests that the methyl groups are tilted at angles less than 30 degrees with respect to the surface normal. The presence of a strong methylene peak suggests the PVNODC alkyl side chains contain …
Length-Dependent Uptake Of Dna-Wrapped Single-Walled Carbon Nanotubes,
2014
University of Akron
Length-Dependent Uptake Of Dna-Wrapped Single-Walled Carbon Nanotubes, Matthew Becker
Matthew Becker
A length threshold for cell uptake of DNA-wrapped single-walled carbon nanotubes (SWNTs) by human lung fibroblasts (IMR90) is identified. Competitive uptake experiments with well-defined and characterized length fractions show that SWNTs above the length threshold are excluded from the cell, whereas SWNTs labeled with Cy3-derivatized DNA below the threshold are able to access the cell interior, as shown in the fluorescence image and on the cover.
