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Articles 1 - 30 of 43
Full-Text Articles in Engineering
How Super Is Supercontraction? Persistent Versus Cyclic Responses To Humidity In Spider Dragline Silk, Todd Blackledge, Cecilia Bountry, Shing-Chung Wong, Avinash Baji, Ali Dhinojwala, Vasav Sahni, Ingi Agnarsson
How Super Is Supercontraction? Persistent Versus Cyclic Responses To Humidity In Spider Dragline Silk, Todd Blackledge, Cecilia Bountry, Shing-Chung Wong, Avinash Baji, Ali Dhinojwala, Vasav Sahni, Ingi Agnarsson
Ali Dhinojwala
Spider dragline silk has enormous potential for the development of biomimetic fibers that combine strength and elasticity in low density polymers. These applications necessitate understanding how silk reacts to different environmental conditions. For instance, spider dragline silk ;supercontracts' in high humidity. During supercontraction, unrestrained dragline silk contracts up to 50% of its original length and restrained fibers generate substantial stress. Here we characterize the response of dragline silk to changes in humidity before, during and after supercontraction. Our findings demonstrate that dragline silk exhibits two qualitatively different responses to humidity. First, silk undergoes a previously unknown cyclic relaxation-contraction response to …
Dependent Droplet Impact Dynamics On Flat And Textured Surfaces, Ali Dhinojwala
Dependent Droplet Impact Dynamics On Flat And Textured Surfaces, Ali Dhinojwala
Ali Dhinojwala
Dropletimpactdynamics determines the performance of surfaces used in many applications such as anti-icing, condensation, boiling, and heat transfer. We study impactdynamics 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. Dropletretraction shows very strong temperature dependence especially on hydrophilicsurfaces; 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 …
Contact Of Oil With Solid Surfaces In Aqueous Media Probed Using Sum Frequency Generation Spectroscopy, Ping Hsu, Ali Dhinojwala
Contact Of Oil With Solid Surfaces In Aqueous Media Probed Using Sum Frequency Generation Spectroscopy, Ping Hsu, Ali Dhinojwala
Ali Dhinojwala
We have studied the interface between hexadecane droplets and sapphire substrates in water using infrared-visible sum frequency generation spectroscopy (SFG). At high pH and above the isoelectric point of the sapphire substrate, the hexadecane drop is repelled due to electrostatic forces. The SFG measurements are consistent with the observation that a thick layer of water is present between the oil and the sapphire substrate. Below the isoelectric point of the sapphire substrate, the hexadecane drops stick to the sapphire surface. Surprisingly, the SFG results show the presence of a thin layer of water between hexadecane drop and the sapphire substrate. …
Probing Polymer/Polymer Interfaces, Gary Harp, Keshav Gautam, Ali Dhinojwala
Probing Polymer/Polymer Interfaces, Gary Harp, Keshav Gautam, Ali Dhinojwala
Ali Dhinojwala
Infrared-visible sum frequency generation spectroscopy (SFG) has been used to study the interface between poly(vinyl-N-octadecylcarbamate-co-vinyl acetate) (Comb) and deuterated or hydrogenated polystyrene (dPS or hPS) films. Strong methyl symmetric and Fermi resonance bands associated with the alkyl side chains of the Comb polymer are observed in the SFG spectra. In addition, for Comb/hPS spectra, symmetric and asymmetric vibration modes of phenyl groups are observed. The presence of asymmetric modes indicates the phenyl rings are tilted with respect to the interface normal.
Interfacial Properties Of Free-Standing Poly(3-Hexyl Thiophene) Films, Yeneneh Yimer, Ali Dhinojwala, Mesfin Tsige
Interfacial Properties Of Free-Standing Poly(3-Hexyl Thiophene) Films, Yeneneh Yimer, Ali Dhinojwala, Mesfin Tsige
Ali Dhinojwala
Using full atomistic classical molecular dynamics simulations, the interfacial properties of free-standing poly(3-hexylthiophene) (P3HT) films have been investigated. The orientations of different parts of the P3HT chain and the surface tensions of the films were calculated in a temperature range of 540 K-600 K. At the liquid/vacuum interface, the P3HT chain shows ordering by exposing hexyl groups at the interface, while the chain backbone lays flat with the thiophene ring preferentially tilt toward the surface. At the interface, the terminal methyl groups of hexyl side chains are in excess compared to the methylene groups or thiophene rings. The surface tension …
Direct Probe Of Interfacial Structure During Mechanical Contact Between Two Polymer Films Using Infrared Visible Sum Frequency Generation Spectroscopy, Gary Harp, Ali Dhinojwala
Direct Probe Of Interfacial Structure During Mechanical Contact Between Two Polymer Films Using Infrared Visible Sum Frequency Generation Spectroscopy, Gary Harp, Ali Dhinojwala
Ali Dhinojwala
Infrared-visible sum frequency generation spectroscopy (SFG) has been used to study the interface between poly(vinyl-N-octadecylcarbamate-co-vinyl acetate) (PVNODC) and polystyrene (PS) films during mechanical contact. The films were contacted using a deformable semispherical poly(dimethylsiloxane) (PDMS) lens that can be easily adapted to incorporate friction and adhesion force measurements. A strong methyl symmetric peak and Fermi resonance band associated with the alkyl side chains of PVNODC are observed in the SFG spectrum. This suggests that the interface structure during mechanical contact is more ordered than the structure observed for PS/PVNODC bilayer films annealed above the melting and glass transition temperatures of PVNODC …
Sum Frequency Generation Vibrational Spectroscopy Of Silicone Surfaces And Interfaces, Dongchan Ahn, Ali Dhinojwala
Sum Frequency Generation Vibrational Spectroscopy Of Silicone Surfaces And Interfaces, Dongchan Ahn, Ali Dhinojwala
Ali Dhinojwala
While several general reviews of the applications of sum frequency generation vibrational spectroscopy (SFG) appear in the literature, none have focused specifically on the application of SFG to silicones. The unique and somewhat dichotomous surface properties of silicones, and their ever-increasing use in surface and interface-dependent applications such as lubricants, adhesives, micro-fluidic materials, sensors and matrices or scaffolds for nano-composites, calls for increased fundamental understanding that has motivated the use of SFG analysis. This chapter focuses on the combination of this uniquely surface sensitive tool to study applications using PDMS and other silicone-based materials. Because the interpretation of SFG spectra …
Carbon Nanotube-Based Robust Steamphobic Surfaces, Ila Badge, Sunny Sethi, Ali Dhinojwala
Carbon Nanotube-Based Robust Steamphobic Surfaces, Ila Badge, Sunny Sethi, Ali Dhinojwala
Ali Dhinojwala
The wetting behavior of a surface under steam condensation depends on its intrinsic wettability and micrometer or nanoscale surface roughness. A typical superhydrophobic surface may not be suitable as a steamphobic surface because of the nucleation and growth of water inside the valleys and thus the failure to form an air-liquid-solid composite interface. Here, we present the results of steam condensation on chemically modified nanostructured carbon nanotube (CNT) mats. We used a plasma-enhanced chemical vapor deposition (PECVD) process to modify the intrinsic wettability of nanostructured CNT mats. The combination of low surface energy achieved by PECVD and the nanoroughness of …
Supercontraction Forces In Spider Dragline Silk Depend On Hydration Rate, Ingi Agnarsson, Cecilia Boutry, Shing-Chung Wong, Avinash Baji, Ali Dhinojwala, Andrew Sensenig, Todd Blackledge
Supercontraction Forces In Spider Dragline Silk Depend On Hydration Rate, Ingi Agnarsson, Cecilia Boutry, Shing-Chung Wong, Avinash Baji, Ali Dhinojwala, Andrew Sensenig, Todd Blackledge
Ali Dhinojwala
Spider dragline silk is a model biological polymer for biomimetic research due to its many desirable and unusual properties. 'Supercontraction' describes the dramatic shrinking of dragline silk fibers when wetted. In restrained silk fibers, supercontraction generates substantial stresses of 40-50 MPa above a critical humidity of approximately 70% relative humidity (RH). This stress may maintain tension in webs under the weight of rain or dew and could be used in industry for robotics, sensor technology, and other applications. Our own findings indicate that supercontraction can generate stress over a much broader range than previously reported, from 10 to 140 MPa. …
A Quantitative Analysis Of Rotational Dynamics In Doped Polymers Above And Below The Glass Transition Temperature: A Novel Application Of Second-Order Nonlinear Optics, Ali Dhinojwala
Ali Dhinojwala
No abstract provided.
Template-Induced Enhanced Ordering Under Confinement, Betul Yurdumakan, Gary Harp, Mesfin Tsige, Ali Dhinojwala
Template-Induced Enhanced Ordering Under Confinement, Betul Yurdumakan, Gary Harp, Mesfin Tsige, Ali Dhinojwala
Ali Dhinojwala
We report a surprisingly strong ordering of Si-(CH(3))(2) groups upon confinement between two surfaces, an oxidized poly(dimethyl siloxane) (PDMS(ox)) elastomer and a methyl-terminated self-assembled monolayer (octadecyltrichlorosilane (OTS)) on sapphire substrates. This enhanced ordering is induced by the template of ordered methyl groups of OTS and is not observed for other surfaces (fluorinated monolayers and sapphire substrates). This strong ordering is reminiscent of layering observed for confined symmetric molecules between two mica surfaces but was expected to vanish between rough macroscopic surfaces. These results provide new insights on confined structure at the interface between two solids and are important in the …
Two-Photon Fluorescence Technique To Study Polymer Adsorption At The Toluene-Water Interface, Ashwin Rao, Ali Dhinojwala
Two-Photon Fluorescence Technique To Study Polymer Adsorption At The Toluene-Water Interface, Ashwin Rao, Ali Dhinojwala
Ali Dhinojwala
Adsorption of fluorescein isothiocyanate labeled polystyrene at the toluene−water interface is studied using two-photon fluorescence microscopy. We have developed a protocol to estimate the amount of polymer adsorbed at the interface. The measured surface excess is strongly influenced by fluorescence resonance energy transfer between neighboring fluorescein units. After accounting for this effect, we are able to estimate the surface excess to be approximately 1 mg/m2, which indicates a brushlike conformation for the adsorbed molecules.
Coupling Of Interfacial Motion At Polystyrene-Alkane Interface, Gary Harp, Hasnain Rangwalla, Guifeng Li, Mohsen Yeganeh, Ali Dhinojwala
Coupling Of Interfacial Motion At Polystyrene-Alkane Interface, Gary Harp, Hasnain Rangwalla, Guifeng Li, Mohsen Yeganeh, Ali Dhinojwala
Ali Dhinojwala
No abstract provided.
Changes In The Adhesive Properties Of Spider Aggregate Glue During The Evolution Of Cobwebs, Vasav Sahni, Todd Blackledge, Ali Dhinojwala
Changes In The Adhesive Properties Of Spider Aggregate Glue During The Evolution Of Cobwebs, Vasav Sahni, Todd Blackledge, Ali Dhinojwala
Ali Dhinojwala
We compare the prey capture glues produced by orb-weaving spiders (viscid glue) and their evolutionary descendents, the cobweb-weaving spiders (gumfoot glue). These glues are produced in homologous glands but exhibit contrasting structure, properties and response to changing humidity. Individual glue droplet stretching measurements indicate that the gumfoot glue behaves like a viscoelastic liquid in contrast to the viscid glue, which behaves like a viscoelastic solid. Moreover, the gumfoot glue is largely humidity-resistant - elasticity and adhesion are constant across variation in humidity and there is weak volume-dependence. Viscid glue, however, is highly humidity-sensitive. The glue expands an order of magnitude …
Direct Measurement Of Acid-Base Interaction Energy At Solid Interfaces, Anish Kurian, Shishir Prasad, Ali Dhinojwala
Direct Measurement Of Acid-Base Interaction Energy At Solid Interfaces, Anish Kurian, Shishir Prasad, Ali Dhinojwala
Ali Dhinojwala
We have studied acid-base interactions at solid-liquid and solid-solid interfaces using interface-sensitive sum frequency generation (SFG) spectroscopy. The shift of the sapphire hydroxyl peak in contact with several polar and nonpolar liquids and polymers was used to determine the interaction energy. The trend in the interaction energies cannot be explained by measuring only water contact angles. Molecular rearrangements at the sapphire interface, to maximize the interaction of the acid-base groups, play a dominant role, and these effects are not accounted for in the current theoretical models. These results provide important insights into understanding adhesion, friction, and wetting on solid interfaces.
Atomistic Simulation Of Orientation Of Methyl Groups And Methylene Bisectors, And Surface Segregation, In Freely Standing Thin Films Of Atactic Poly(Ethylene-Co-Propylene), Sagar Rane, Wayne Mattice, Ali Dhinojwala
Atomistic Simulation Of Orientation Of Methyl Groups And Methylene Bisectors, And Surface Segregation, In Freely Standing Thin Films Of Atactic Poly(Ethylene-Co-Propylene), Sagar Rane, Wayne Mattice, Ali Dhinojwala
Ali Dhinojwala
Atomistically detailed models of free-standing thin films of random poly(ethylene-co-propylene) were produced using a method recently applied to atactic polystyrene (Clancy, et al. J. Phys. Chem. B 2001, 105, 11493). Monte Carlo simulations of the copolymer were carried out at ethylene fractions that cover the entire range of composition investigated in a recent experimental work (Opdahl, et al. J. Phys. Chem. B 2002, 106, 5212) based on sum-frequency generation (SFG) spectroscopy. We find that there is a minor enrichment of methyl groups on the surface, as compared to the bulk composition. Interestingly, the orientation distribution of methyl and methylene units …
Orientation Of Phenyl Rings And Methylene Bisectors At The Free Surface Of Atactic Polystyrene, Thomas Clancy, Jee Jang, Ali Dhinojwala, Wayne Mattice
Orientation Of Phenyl Rings And Methylene Bisectors At The Free Surface Of Atactic Polystyrene, Thomas Clancy, Jee Jang, Ali Dhinojwala, Wayne Mattice
Ali Dhinojwala
Atomistically detailed models of free-standing thin films and the bulk structure of amorphous atactic polystyrene have been produced by reverse mapping from equilibrated coarse-grained models. The bridging technique employed in the simulation allows the generation of a moderate sized atomistic system (six independent parent chains of C400H402, 4812 atoms) with a more reasonable computational effort than is required when all of the construction is performed on chains expressed with atomistic detail. Reverse mapping from the coarse-grained model to the atomistically detailed model is found to be straightforward, without ring piercing or concatenation. The calculated surface energy (38 ± 10 erg/cm2) …
Probing Hidden Polymeric Interfaces Using Ir-Vis Sum-Frequency Generation Spectroscopy, Hasnain Rangwalla, Ali Dhinojwala
Probing Hidden Polymeric Interfaces Using Ir-Vis Sum-Frequency Generation Spectroscopy, Hasnain Rangwalla, Ali Dhinojwala
Ali Dhinojwala
Understanding the molecular-level processes underlying interfacial phenomena is important in the area of adhesion. We briefly introduce IR–visible sum-frequency generation spectroscopy (SFG) using a total-internal-reflection geometry for the study of polymer–air, polymer–solid, and polymer–polymer interfaces. The following examples, predominantly of work done in our lab, illustrating differences in molecular structure and dynamic properties at interfaces are presented: the air- and solid-interface structure of an amorphous polystyrene (PS) and a semicrystalline polymer with side-chain crystallinity, poly(octadecyl acrylate) (PA- 18); structure of a polymer–polymer interface between thin films of a semicrystalline polymer with side-chain crystallinity, poly(vinyl-N-octadecylcarbamateco-vinyl acetate), and an amorphous PS; thermal …
Structure Of Poly(Methyl Methacrylate) Chains Adsorbed On Sapphire Probed Using Infrared-Visible Sum Frequency Generation Spectroscopy, Ashwin Rao, Hasnain Ranwalla, Vikas Varshney, Ali Dhinojwala
Structure Of Poly(Methyl Methacrylate) Chains Adsorbed On Sapphire Probed Using Infrared-Visible Sum Frequency Generation Spectroscopy, Ashwin Rao, Hasnain Ranwalla, Vikas Varshney, Ali Dhinojwala
Ali Dhinojwala
We have studied the orientation of the train segments of a poly(methyl methacrylate) (PMMA) adsorbed layer at the CCl4-sapphire interface using surface-sensitive IR-visible sum frequency generation (SFG) spectroscopy. The SFG spectra of PMMA chains adsorbed on sapphire indicate ordered ester methyl groups. In comparison, we did not observe any significant contributions from the backbone methylene and alpha methyl groups, suggesting that these groups are disordered. No change in the structure of the adsorbed layer is observed upon cooling the solvent below the theta temperature; this is consistent with the picture of flat adsorbed chains on the surface. Interestingly, the orientation …
Origin Of Higher Friction For Elastomers Sliding On Glassy Polymers, Betul Yurdumakan, Kumar Nanjundiah, Ali Dhinojwala
Origin Of Higher Friction For Elastomers Sliding On Glassy Polymers, Betul Yurdumakan, Kumar Nanjundiah, Ali Dhinojwala
Ali Dhinojwala
We have designed a novel approach to couple infrared−visible sum frequency generation (SFG) spectroscopy with adhesion and friction measurements to determine the molecular structure of the surface molecules at the contact and sliding interfaces. The frictional force of crosslinked poly(dimethyl siloxane) (PDMS) lens sliding on poly(styrene) (PS) is a factor of 4 higher than that of PDMS sliding on poly(vinyl n-octadecyl carbamate-co-vinyl acetate) (PVNODC). This higher frictional force of PDMS/PS interface cannot be explained by its adhesion energy or hysteresis. The SFG results indicate that the hydrocarbon PVNODC surface consists of well-ordered crystalline side chains that do not restructure upon …
Observation Of Novel Smectic-Like Phase Above The Bulk Melting Temperature, Keshav Gautam, Satyendra Kumar, Didier Wermeille, Doug Robinson, Ali Dhinojwala
Observation Of Novel Smectic-Like Phase Above The Bulk Melting Temperature, Keshav Gautam, Satyendra Kumar, Didier Wermeille, Doug Robinson, Ali Dhinojwala
Ali Dhinojwala
In this paper, we show that a noncrystalline but ordered smectic-like phase exists above the bulk-melting temperature (T(m)) at poly(n-alkyl acrylates)-air interface. The surface ordered phase is one monolayer thick and undergoes a sharp transition from order to disorder 10 degrees C above T(m) for n=22. The presence of a surface phase that does not exist in the bulk has important implications in the design of thermally responsive adhesives.
Dynamic Interfacial Tension At The Oil/Surfactant-Water Interface, Guifeng Li, Shishir Prasad, Ali Dhinojwala
Dynamic Interfacial Tension At The Oil/Surfactant-Water Interface, Guifeng Li, Shishir Prasad, Ali Dhinojwala
Ali Dhinojwala
We have used dynamic interfacial tension measurements to understand the structure of the ordered monolayer at the hexadecane/water interface induced by the presence of surfactant molecules. No abrupt changes in the interfacial tension (gamma) are observed during the expansion and contraction cycle below the interfacial ordering temperature (Ti) as observed for alkanes in contact with air. The lack of an abrupt change in gamma and the magnitude of this change during the expansion process indicate that the ordered phase may not be crystalline. The change in the interfacial tension is due to an increase in contact between water and hexadecane …
Chain Orientation And Its Effects On Mobility At A Rubbed Surface, Y. Pu, H. White, M. Rafailovich, J. Sokolov, S. Schwarz, Ali Dhinojwala, D. M. Agra, S. Kumar
Chain Orientation And Its Effects On Mobility At A Rubbed Surface, Y. Pu, H. White, M. Rafailovich, J. Sokolov, S. Schwarz, Ali Dhinojwala, D. M. Agra, S. Kumar
Ali Dhinojwala
We have measured the tracer diffusion coefficient in PS films oriented by surface rubbing. The results show that the diffusion perpendicular to the rubbed surface is slower in oriented than in nonoriented chains. The decrease of the diffusion coefficient was correlated with the total oriented volume as determined by birefringence measurements.
Unusual Surface Aging Of Poly(Dimethylsiloxane) Elastomers, Anish Kurian, Shishir Prasad, Ali Dhinojwala
Unusual Surface Aging Of Poly(Dimethylsiloxane) Elastomers, Anish Kurian, Shishir Prasad, Ali Dhinojwala
Ali Dhinojwala
We have observed an unusual increase in adhesion hysteresis and frictional forces for poly(dimethylsiloxane) (PDMS) lenses sliding on smooth glassy surfaces after a period of aging in a laboratory environment. X-ray photoelectron spectroscopy, contact angle, and in situ surface-sensitive sum frequency generation spectroscopy (SFG) measurements show no differences between an aged and unaged lens, indicating that these changes in tribological properties cannot be due to surface contaminant or degradation. Instead, we observed that the SFG intensity of the PDMS Si−CH3 symmetric band is 3 orders of magnitude higher after sliding the aged lenses. Such a large increase in the SFG …
Interfacial Structure And Melting Temperature Of Alkane And Alcohol Molecules In Contact With Polystyrene Films, Guifeng Li, Ali Dhinojwala, Mohsen Yeganeh
Interfacial Structure And Melting Temperature Of Alkane And Alcohol Molecules In Contact With Polystyrene Films, Guifeng Li, Ali Dhinojwala, Mohsen Yeganeh
Ali Dhinojwala
Infrared-visible sum-frequency-generation spectroscopy (SFG) is used to investigate the interfacial structure of hexadecanol (C16H33OH) and heneicosane (C21H44) in contact with polystyrene films (PS) spin coated on a sapphire substrate. The interfacial structure of hexadecanol is very different from heneicosane in contact with PS. In the crystalline state, the hexadecanol molecules are oriented with the C-C-C axis parallel to the surface plane in contact with PS. For the crystalline heneicosane/PS interface, the SFG spectra are very similar to those observed for molecules oriented with the symmetry axis of the methyl groups parallel to the surface normal. The structure of both hexadecanol …
Molecular Origin Of Solvent Resistance Of Polyacrylonitrile, Veronique Lachat, Vikas Varshney, Ali Dhinojwala, Mohsen Yeganeh
Molecular Origin Of Solvent Resistance Of Polyacrylonitrile, Veronique Lachat, Vikas Varshney, Ali Dhinojwala, Mohsen Yeganeh
Ali Dhinojwala
We report on the first in-situ sum frequency generation (SFG) spectroscopy characterization of polyacrylonitrile (PAN) interfacial interactions with air, sapphire, water, and heptane. Using the shift in the resonance frequency of CN at various interfaces, we demonstrated that PAN interacts with the surface hydroxyl of sapphire substrate through the lone pair orbital of nitrogen in the “end-on” configuration (σ-H bond). We also demonstrated that the CN−CN interaction is the main reason for the superior chemical resistance property of PAN. At room temperature the interaction between the polymer chains is much stronger than the interaction between the polymer and solvent molecules …
Spider Silk Inspired Functional Microthreads, Vasav Sahni, Disha Labhasetwar, Ali Dhinojwala
Spider Silk Inspired Functional Microthreads, Vasav Sahni, Disha Labhasetwar, Ali Dhinojwala
Ali Dhinojwala
We employ the adhesive web building strategy used by modern orb-weaving spiders to produce functional microthreads that are similar in structure (beads-on-a-string (BOAS) morphology) and adhesive properties to the capture-silk threads of the spider web. The diameter and spacing of droplets (beads) are controlled by varying the viscosity, velocity, and surface tension of the coating fluid. Using these functional threads, we also describe the behavior of the BOAS morphology during contact (mimicking the collision of an insect with the web) and during separation (mimicking insect rescue from the web). Our results show that the BOAS structure performs better than a …
A Device For Surface Spectroscopic Study Of Micron Thin Films, Ali Dhinojwala
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, Sunny Sethi, Liehui Ge, Lijie Ci, P. Ajayan, Ali Dhinojwala
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.
Cooperative Adhesion And Friction Of Compliant Nanohairs, Liehui Ge, Lijie Ci, Anubha Goyal, Rachel Shi, L. Mahadevan, P. Ajayan, Ali Dhinojwala
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 …