Open Access. Powered by Scholars. Published by Universities.®
- Discipline
- Keyword
-
- Supercontraction (3)
- Alkyl side chain polymer (2)
- Biophysics (2)
- Humidity (2)
- Nonlinear optics (2)
-
- Polymer adhesion (2)
- Polymer interface (2)
- Polymer surface (2)
- Spider silk (2)
- Surface restructuring (2)
- Surface transition (2)
- Adhesion (1)
- Adhesives (1)
- Biomaterial (1)
- Biomaterials (1)
- Biomimetic fiber (1)
- Biomimetic muscle (1)
- Chain Molecules (1)
- Diffraction (1)
- Friction (1)
- Hierarchical (1)
- Infrared Spectra (1)
- Interface Phenomena (1)
- Interfaces (1)
- Liquid Films (1)
- Major ampullate fibroin (1)
- Major ampullate silk (1)
- Materials science (1)
- Nanomaterials (1)
- Nephila clavipes (1)
- File Type
Articles 1 - 30 of 94
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 …
Rotational Diffusion Of Nonlinear Optical Chromophores In Rubbery And Glassy Polymers: Ï¡-Relaxation Dynamics Probed By Second Harmonic Generation And Dielectric Relaxation, Ali Dhinojwala
Ali Dhinojwala
No abstract provided.
In Dynamics In Small Confining Systems Ii, Ali Dhinojwala
In Dynamics In Small Confining Systems Ii, Ali Dhinojwala
Ali Dhinojwala
No abstract provided.
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 …
Small Molecule Probe Diffusion In Thin Polymer Films Near The Glass Transition: A Novel Approach Using Fluorescence Nonradiative Energy Transfer, Ali Dhinojwala
Small Molecule Probe Diffusion In Thin Polymer Films Near The Glass Transition: A Novel Approach Using Fluorescence Nonradiative Energy Transfer, Ali Dhinojwala
Ali Dhinojwala
A novel experimental approach involving fluorescence nonradiative energy transfer (NRET) is employed to study the Fickian diffusion of small molecules in rubbery polymer films near the glass transition. A theoretical formalism has been developed which directly relates the small molecule translational diffusion coefficient, , to changes in the energy transfer efficiency, E. Values of as low as 5 × 10-16 cm2/s have been measured. In this approach, two thin polymer films are sandwiched together, one labeled with either NRET donor or acceptor chromophores and the second doped with the complementary chromophore. Upon annealing for a time t, dopant chromophore diffusion …
Cobweb-Weaving Spiders Produce Different Attachment Discs For Locomotion And Prey Capture, Vasav Sahni, Jared Harris, Todd Blackledge, Ali Dhinojwala
Cobweb-Weaving Spiders Produce Different Attachment Discs For Locomotion And Prey Capture, Vasav Sahni, Jared Harris, Todd Blackledge, Ali Dhinojwala
Ali Dhinojwala
Spiders' cobwebs ensnare both walking and flying prey. While the scaffolding silk can entangle flying insects, gumfoot silk threads pull walking prey off the ground and into the web. Therefore, scaffolding silk needs to withstand the impact of the prey, whereas gumfoot silk needs to easily detach from the substrate when contacted by prey. Here we show that spiders accomplish these divergent demands by creating attachment discs of two distinct architectures using the same pyriform silk. A 'staple-pin' architecture firmly attaches the scaffolding silk to the substrate and a previously unknown 'dendritic' architecture weakly attaches the gumfoot silk to the …
In Dynamics In Small Confining Systems Iii, Ali Dhinojwala
In Dynamics In Small Confining Systems Iii, Ali Dhinojwala
Ali Dhinojwala
No abstract provided.
Adsorption, Ali Dhinojwala
New Approaches To Measure Interfacial Rheology Of Confined Fluids, Ali Dhinojwala
New Approaches To Measure Interfacial Rheology Of Confined Fluids, Ali Dhinojwala
Ali Dhinojwala
Several instrumental developments to examine the rheology of ultrathin confined liquids are described. These include capacitance sensing of the film thickness, concurrent measurement of normal and shear forces by piezoelectric methods, application of periodic forces in the normal direction to determine dynamic oscillatory shear moduli, and quantification of apparatus misalignment. The method to separate apparatus from sample contributions is stressed.
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. …
Translation-Rotation Paradox For Diffusion In Glass-Forming Polymers: The Role Of The Temperature Dependence Of The Relaxation Time Distribution, Ali Dhinojwala
Translation-Rotation Paradox For Diffusion In Glass-Forming Polymers: The Role Of The Temperature Dependence Of The Relaxation Time Distribution, Ali Dhinojwala
Ali Dhinojwala
Comparisons are made of the translational and rotational diffusion of small-molecule probes in a polymer near its glass transition temperature, Tg. In the rubbery state, 1.1Tg>T>Tg, translational diffusion is much less temperature dependent than rotational reorientation; in a ``quenched'' glass, translation and rotation have similar temperature dependencies. This is explained to be a consequence of the fact that in the rubbery state near Tg the breadth of the polymer relaxation distribution is strongly temperature dependent, while in the quenched glass it is temperature invariant.
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.
Novel Experimental Protocol For Studying Temporal Decay Of Second-Order Nonlinear Optical Polymer Properties: Quantitative Analysis Of Coupling To Polymer Dynamics And Conditions For Temporal Stability, Ali Dhinojwala
Ali Dhinojwala
A new experimental approach has been developed which allows characterization of rotational dynamics of NLO chromophores in amorphous polymers over 12 decades in time, from 10-6 to 106 sec. Measurements over such a broad distribution in relaxation times are important not only in determining how the chromophore orientational dynamics are coupled to polymer dynamics but also in making accurate predictions of the temporal stability of technological interest. In particular, accurate characterization over a broad range of time scales reveals that NLO polymers meet technological requirements more easily than is predicted using a less complete characterization.
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 …
Optorheological Studies Of Sheared Confined Fluids With Mesoscopic Thickness, Ali Dhinojwala
Optorheological Studies Of Sheared Confined Fluids With Mesoscopic Thickness, Ali Dhinojwala
Ali Dhinojwala
Fluids of mesoscopic thickness can be sheared and their molecular orientation probed concurrently with the new instrument described in this paper. The fluid is confined between parallel optically flat windows whose spacing is controlled, using piezoelectric inchworms, from submicrometer thickness to 500 μm, with no essential lower limit apart from surface roughness. Capacitance sensors or optical interferometry is used to monitor spacing between the windows with submicrometer accuracy. Piezoelectric bimorphs are used to apply periodic shear displacements with amplitude 0.l−10 μm and frequency 0.1−700 Hz. Shear-induced molecular alignment during sinusoidal shear cycles is determined, with up to 5 μs time …
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 …
Rotational Dynamics In Polystyrene Above And Below The Glass Transition Temperature: Second Harmonic Generation And Dielectric Relaxation Measurements, Ali Dhinojwala
Ali Dhinojwala
No abstract provided.
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 …
Implementing Carbon Nanotube Thermal Interface Material Onto Heat Sink Involves Growing Nanotubes On Sink By Chemical Vapor Deposition; And Compressing Nanotube Onto Metallic Surface To Increase Contact Surface Area Between Nanotube/Surface, Ali Dhinojwala
Ali Dhinojwala
No abstract provided.
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. …
Probe Translational And Rotational Diffusion In Polymers Near Tg: Role Of Probe Size, Shape, And Secondary Bonding In Deviations From Debye-Stokes-Einstein Scaling, Ali Dhinojwala
Ali Dhinojwala
Rotational and translational dynamics of a variety of probes are compared in several polymers near the glass transition temperature, Tg. Second harmonic generation was used to measure the rotational relaxation distribution and average rotational relaxation time, 〈τ〉, and fluorescence nonradiative energy transfer was used to measure Dtrans, the translational diffusion coefficient. Dtrans is affected greatly by probe size and shape, typically with a temperature dependence in the rubbery state near Tg which violates Debye–Stokes–Einstein (DSE) scaling and an apparent enhancement in translational diffusion; in contrast, 〈τ〉 is largely unaffected by probe size and shape (for the ranges studied), as long …
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.
Humidity Responsive Material Composition For Fibrous Body Or System, And Biomimetic Fiber Product, Comprises Aqueous Solution Of Silk Protein Formed To Have Predetermined Contraction/Relaxation Characteristics, 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 …
Relaxation Time Of Confined Water, Ali Dhinojwala
Relaxation Time Of Confined Water, Ali Dhinojwala
Ali Dhinojwala
No abstract provided.
Generalized Effects In Confined Fluids: New Friction Map For Boundary Lubrication, Ali Dhinojwala
Generalized Effects In Confined Fluids: New Friction Map For Boundary Lubrication, Ali Dhinojwala
Ali Dhinojwala
Recent advances in measuring the rheology and tribology of thin liquid films between shearing surfaces have enabled previously-inaccessible parameters to be measured accurately during frictional sliding. These include the real area of contact, the local asperity load and pressure, and the sheared film thickness. The results show striking non-continuum, non-bulk like effects when the thicknesses of sheared films approach molecular dimensions as occurs under most tribological conditions. Based on these new results, we assess the validity of current presentations of friction processes, such as the Stribeck curve, and propose new constitutive relations and a dynamic friction map, including an alternative …
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.
Molecular Structure Of Hydrophobic Alkyl Side Chains At Comb Polymer-Air Interface, Keshav Gautam, Ali Dhinojwala
Molecular Structure Of Hydrophobic Alkyl Side Chains At Comb Polymer-Air Interface, Keshav Gautam, Ali Dhinojwala
Ali Dhinojwala
Surface sensitive sum-frequency generation (SFG) spectroscopic technique has been used to study the orientation of alkyl side chains for comb polymers at polymer-air interface. The SFG spectra at 24oC for thick spin-coated polymer films and adsorbed layer (on mica substrate) show strong signals associated with methyl asymmetric and symmetric vibrations indicating ordered methyl terminal groups. However, the ratio of methylene to methyl stretch vibrations is higher for the adsorbed layer than that observed for spin-coated films. This spectroscopic evidence of poor packing of alkyl chains with enhanced gauche defects correlates well with low water contact angles measured for the adsorbed …