Chemical Engineering Commons^™

Molecular Structure Of An Alkyl-Side-Chain Polymer-Water Interface: Origins Of Contact Angle Hysteresis, Hasnain Rangwalla, Alexander Schwab, Betül Yurdumakan, Dalia Yablon, Mohsen Yeganeh, Ali Dhinojwala

Ali Dhinojwala

A new and direct approach to verify surface heterogeneity as the microscopic origin of contact-angle hysteresis is demonstrated. IR-visible sum-frequency-generation spectroscopy (SFG) was used to selectively probe the molecules at the interface of an alkyl-side-chain polymer [poly(vinyl n-octadecyl carbamate-co-vinyl acetate)] with water. The spectra indicate that in contact with water, the polymer surface is heterogeneous (having areas of differing surface energies). This evidence of surface heterogeneity supports the hysteresis observed in the advancing and receding contact angles of the polymer surface with water. The same measurements made for the chemically and structurally similar surface of an octadecyltrichlorosilane self-assembled monolayer indicates …

Improved Methods And Standards For Telomerase Detection: Quantitative Histopathology Using Antibody Staining, Matthew Becker

Matthew Becker

Evaluation of telomerase as an early detection biomarker for cancer has been hindered by a lack of reliable methods and standards for in situ histochemical measurement. Improved histochemical methods for measuring telomerase could expedite the acceptance of telomerase as a biomarker for use in diagnostic and clinical applications. The lack of a crystal structure for telomerase coupled with high variability in the antibodies available for immunohistochemical analysis has led to confusion in the literature regarding the binding specificity of these antibodies. We have developed an automated fluorescence microscopy protocol to assess the specificity of three fluorescently labeled telomerase antibodies and …

A Reconsideration Of The Measurement Of Polymer Interdiffusion By Fluorescence Nonradiative Energy Transfer, Ali Dhinojwala

Ali Dhinojwala

No abstract provided.

Retardation Of Rotational Reorientation Dynamics In Polymers Near The Glass Transition: A Novel Study Over Eleven Decades In Time Using Second-Order Nonlinear Optics, Ali Dhinojwala

Ali Dhinojwala

A novel protocol has been developed using second harmonic generation to quantify the rotational, reorientation dynamics of second-order non-linear optical chromophores in amorphous polymers. Dynamics are monitored over 11–12 decades in time, from microseconds onwards, allowing characterization both well above and below the glass transition temperature, Tg. The time dependence of the orientational component of the second order macroscopic susceptibility, χ(2), can be represented by a Kohlrausch-Williams-Watts equation from which average rotational reorientational time constants, 〈τ〉, are determined. For the Disperse Red 1-poly(isobutyl methacrylate) (PIBMA) system studied here, 〈τ〉 is shown to be coupled to the α-relaxation dynamics of PIBMA. …

Fluorinated Copolymer Nanoparticles For Multimodal Imaging Applications, Matthew Becker

Matthew Becker

Nanomaterials have emerged as valuable tools in biomedical imaging techniques. Here, the synthesis and characterization of a novel fluorinated nanoparticle with potential applications as an MRI contrast agent is reported. Particles were synthesized using a free radical polymerization technique. Secondary ion mass spectrometry analysis showed that the particles' surface contained fluorinated groups and nitrogen-containing groups. Solid-state NMR spectroscopy suggested the presence of two distinct fluorine resonances, which conforms to the structure of the fluorinated monomer. Ongoing studies aim to evaluate the performance of the nanoparticles as MRI contrast agents both in vitro and in vivo.

Superhydrophobic Conductive Carbon Nanotube-Based Coatings For Steel, Sunny Sethi, Ali Dhinojwala

Ali Dhinojwala

We report the synthesis of superhydrophobic coatings for steel using carbon nanotube (CNT)-mesh structures. The CNT coating maintains its structural integrity and superhydrophobicity even after exposure to extreme thermal stresses and has excellent thermal and electrical properties. The coating can also be reinforced by optimally impregnating the CNT-mesh structure with cross-linked polymers without significantly compromising on superhydrophobicity and electrical conductivity. These superhydrophobic conductive coatings on steel, which is an important structural material, open up possibilities for many new applications in the areas of heat transfer, solar panels, transport of fluids, nonwetting and nonfouling surfaces, temperature resilient coatings, composites, water-walking robots, …

Critique Of The Friction Coefficient Concept For Wet (Lubricated) Sliding, Ali Dhinojwala

Ali Dhinojwala

Complications in the traditional definitions of static and kinetic friction are discussed as they pertain to lubricated sliding. First, we discuss rate criteria to observe stick−slip motion and show that stick−slip occurs only when thin liquid films are deformed faster than their intrinsic relaxation time. This conclusion comes from experiments with confined aqueous films in a surface forces apparatus modified to measure interfacial rheology. The observation offers a new strategy to look for methods to avoid stick−slip motion by engineering the relaxation time of a confined fluid. Second, we consider the issue of transients and show, for the case of …

Isothermal Relaxation Of Rubbed Polystyrene Thin Films Probed With Optical Birefringence Measurements, Alexander Schwab, Bharat Acharya, Satyendra Kumar, Ali Dhinojwala

Ali Dhinojwala

Optical birefringence measurements were used to observe the isothermal relaxation of rubbed polystyrene films on silica substrates below the glass transition temperature. The relaxation dynamics were described by the Kohlrausch-Williams-Watts relaxation function with Arrhenius temperature dependence on relaxation time. The isothermal results were in good agreement with results obtained using a 1 K min -1 heating rate.

Emission-Tunable Microwave Synthesis Of Highly Luminescent Water Soluble Cdse/Zns Quantum Dots, Matthew Becker

Matthew Becker

Water soluble CdSe/ZnS nanoparticles with emission maxima from 511 nm to 596 nm and quantum efficiencies ranging from 11% to 28% are synthesized in a facile two-step method in ambient atmospheric conditions using a commercially available microwave reactor.

Carbon Nanotube/Polymer Composite Material For Carbon Nanostructure Adhesive And Field-Emission Device, Comprises Carbon Nanostructures Formed Into Preset Architecture Embedded In Polymer Matrix Such That Architecture Is Stabilized, Ali Dhinojwala

Ali Dhinojwala

No abstract provided.

Comment On How Water Meets An Hydrophobic Surface, Ali Dhinojwala

Ali Dhinojwala

No abstract provided.

Universal Gradient Substrates For Click Biofunctionalization, Matthew Becker

Matthew Becker

Versatile templates for gradient immobilization of biomolecules by click chemistry are easily generated from reproducible and tunable surface energy gradients. An arginine–glycine–aspartate (RGD) peptide density gradient controls cell adhesion (see figure), and demonstrates the utility of this fabrication process for making substrates that can screen cell response to bioactive materials.

High Fidelity Detection Of Defects In Polymer Films Using Surface-Modified Nanoparticles, Matthew Becker

Matthew Becker

Surface defects are ubiquitous for most thin films, yet their systematic detection poses one of the most difficult challenges even to modern day technology. Polymer thin films are no exception to these problems. We address this issue by developing a novel, efficient method for the optical detection of surface topographical features using fluorescent nanoprobes, which are surface-modified CdSe quantum dots whose ability to detect surface features can be tuned via size and chemical properties. We have successfully applied this approach to detect numerous types of artificial and natural defects in polymer films including lines, pinholes, sharp edges, and chemically variant …

Study Of High Pressure Steaming On Lipid Recovery From Microalgae, Ana-Maria Aguirre

Electronic Thesis and Dissertation Repository

Sustainable and clean fuels are in demand due to the perceived negative effects on health and environment with current use of fossil fuels. Lipids from microalgae offer a potential approach to obtain sustainable biofuels. In this study a two step process was adopted: investigation of culture conditions to find optimal points for lipid productivity and cellulose content, followed by an investigation of microalgae disruption for lipid recovery.

In the first phase of the research the effect of culture conditions on Chlorella vulgaris biomass concentration and the ratio of lipid productivity/cellulose content were studied. Response surface methodology was applied to optimize …

Solar And Visible Light Driven Photocatalysis For Sacrificial Hydrogen Generation And Water Detoxification With Chemically Modified Ti02, Pankaj Chowdhury

PC

Photocatalysis is a recognized approach where light energy is employed to excite the semiconductor material producing electron/hole pair which eventually involves in the detoxification of pollutants and/or water splitting producing hydrogen. Existing photocatalysts suffer from poor activity or no activity in visible light irradiation which restricts them from solar light utilization. This work is focused on two key applications of photocatalysis (i) sacrificial hydrogen generation, and (ii) phenol degradation in visible and/or solar light. Platinum was loaded on TiO2 photocatalyst by solar photo-deposition method. Eosin Y dye was used as a sensitizer for sensitization of platinum loaded TiO2 photocatalyst. The …

Computational Modeling Of In Vitro Biological Responses On Polymethacrylate Surfaces, Abraham Joy

Abraham Joy

The objective of this research was to examine the capabilities of QSPR (Quantitative Structure Property Relationship) modeling to predict specific biological responses (fibrinogen adsorption, cell attachment and cell proliferation index) on thin films of different polymethacrylates. Using 33 commercially available monomers it is theoretically possible to construct a library of over 40,000 distinct polymer compositions. A subset of these polymers were synthesized and solvent cast surfaces were prepared in 96 well plates for the measurement of fibrinogen adsorption. NIH 3T3 cell attachment and proliferation index were measured on spin coated thin films of these polymers. Based on the experimental results …

Poly (Ethylene Glycol) As A Sensitive Regulator Of Cell Survival Fate On Polymeric Biomaterials: The Interplay Of Cell Adhesion And Pro-Oxidant Signaling Mechanisms, Abraham Joy

Abraham Joy

Poly(ethylene glycol) (PEG) is one of the most widely used compounds across a variety of platforms and is increasingly found in medical applications. Polycarbonates containing varying mol% of PEG (Mw 1000) were used to probe the effects of PEG on cell adhesion, proliferation, spreading, and survival. Two contrasting PEG-mediated cell signaling elements affected these cellular behaviors: (i) integrin α5 receptor mediated cellular focal adhesions to the biomaterial surface and (ii) modulation of cellular redox and apoptosis through generation of reactive oxygen species (ROS). At lower PEG1k mol% (5% and 8%) cell attachment and spreading decreased concomitantly due to ROS, whereas …

Simple, Rapid, And Highly Sensitive Detection Of Diphosgene And Triphosgene By Spectrophotometric Methods, Abraham Joy

Abraham Joy

Methods for the detection and estimation of diphosgene and triphosgene are described. These compounds are widely used phosgene precursors which produce an intensely colored purple pentamethine oxonol dye when reacted with 1,3-dimethylbarbituric acid (DBA) and pyridine (or a pyridine derivative). Two quantitative methods are described, based on either UV absorbance or fluorescence of the oxonol dye. Detection limits are approximately 4 micromol/L by UV and <0.4 micromol/L by fluorescence. The third method is a test strip for the simple and rapid detection and semi-quantitative estimation of diphosgene and triphosgene, using a filter paper embedded with dimethylbarbituric acid and poly(4-vinylpyridine). Addition …

Predicting Biomaterial Property-Dendritic Cell Phenotype Relationships From The Multivariate Analysis Of Responses To Polymethacrylates, Abraham Joy

Abraham Joy

Dendritic cells (DCs) play a critical role in orchestrating the host responses to a wide variety of foreign antigens and are essential in maintaining immune tolerance. Distinct biomaterials have been shown to differentially affect the phenotype of DCs, which suggested that biomaterials may be used to modulate immune response towards the biologic component in combination products. The elucidation of biomaterial property-DC phenotype relationships is expected to inform rational design of immuno-modulatory biomaterials. In this study, DC response to a set of 12 polymethacrylates (pMAs) was assessed in terms of surface marker expression and cytokine profile. Principal component analysis (PCA) determined …

Long-Range Radical Cation Migration In Dna: Investigation Of The Mechanism, Abraham Joy

Abraham Joy

During the past decade, long-range radical cation migration in DNA has been an area of extensive experimental and theoretical examination. The motivations for the vigorous investigation of this topic are its potential to yield a deeper understanding of the processes that cause oxidative damage of genomic DNA and the potential for use of DNA architectures in molecular electronics. This investigation has revealed the mechanisms of charge transport and the limitations of DNA as a functional element in devices. In this article we discuss various aspects of the radical cation migration process and present the plausible mechanism by which this process …