Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2007. / Includes bibliographical references. / The study of surface tension and other surface properties is motivated by the large number of industrially relevant processes involving interfaces, such as coating, detergency, printing, foams, and so forth. These surface properties become increasingly important as the length scale of the system is reduced (as in microfluidic devices). Recently, much research has been focused on developing surfactants which respond to a particular stimulus (such as temperature, pH, light, etc.), so that properties such as surface tension and viscosity can be controlled using a convenient external trigger. Using light for this purpose has some advantages over other methods, as light can easily be focused and patterned (using optical lenses, filters, and masks) to give excellent precision for changing solution properties in a targeted area. A nonionic photoresponsive surfactant has been developed which incorporates the light-sensitive azobenzene group into its hydrophobic tail. Cis-trans photo-isomerization of this group causes a change in the structure of the surfactant molecule which alters its aggregation state in bulk solution and its adsorption capacity at an air-water interface. / (cont.) NMR studies indicate that a solution removed from light for an extended period of time is comprised almost entirely of the trans isomer, while samples exposed to light of fixed wavelength eventually reach a photostationary state containing significant amounts of both isomers, with UV illumination producing a mixture dominated by the cis isomer. Surface pressure measurements of adsorbed monolayers of the surfactant under various illumination conditions were made using a Langmuir film balance. The results indicate that adsorbed cis surfactant exerts a greater surface pressure than the adsorbed trans isomer, and that any cis present in a saturated layer tends to dominate the surface pressure behavior of the film. Fluorescence experiments were used to study the aggregation behavior of the surfactant in aqueous solution. The results suggest that the trans and cis isomers segregate into separate, co-existing aggregate phases and that the critical concentration associated with the onset of aggregation is very different for the two isomers. In measurements performed well above the CMC. the dynamic surface tension of surfactant solutions following the creation of a fresh interface was found to depend strongly on the illumination state of the sample, though the same equilibrium tension was reached in all cases. / (cont.) The observed dynamic behavior is consistent with a mechanism in which the cis and trans isomers present in the mixtures compete for adsorption at the air/water interface. Diffusion models were developed to estimate the time scales expected for surfactant adsorption and surface tension relaxation in these systems. These models account for the role of aggregates in the adsorption process, and consider limiting behavior for three aggregate properties: mobility, dissolution rate, and ability to incorporate into the interface. Good agreement is found between the model predictions and the experimentally observed relaxation time scales. The results suggest that trans-rich aggregates are important to the adsorption of trans surfactant, but that aggregates play little or no role in the adsorption of the cis isomer. In other experiments, high-intensity illumination focused on a surface saturated with surfactant was used to drive photoisomerization of adsorbed surfactant, resulting in rapid, substantial changes in surface tension. These changes are consistent with proposed conformations of the adsorbed surfactant, and with earlier monolayer studies. / by Bradley A. Cicciarelli. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1987. / Bibliography: leaves 250-254. / by Robert Howard Hurt. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2002. / Includes bibliographical references. / Microphase-separated morphologies of side-chain liquid crystal (LC) diblock copolymers have been examined as substrate-supported thin films. The film thicknesses ranged from 0.5 to 10 times the block copolymer period (L). These novel materials are of interest because they exhibit self-oriented electro-optical properties in the bulk state, and may exhibit interesting field dependent nanometer-scale ordering as thin films. A primary challenge in taking advantage of these properties involves the fundamental understanding and control of the nano-domain morphology, which is strongly affected by the substrate, block copolymer properties, and LC alignment within the domains. In these studies, an amorphous side-chain LC diblock polymer system has been synthesized containing a side-chain mesogen with a chiral alkyl end. Experiments were conducted using Atomic Force Microscopy, Transmission Electron Microscopy, and X-ray Specular Reflectometry, to determine the complex surface morphology. Contact angle measurements and angle-resolved X-ray Photoelectron Spectrometry were also conducted to determine LC orientation at different interfaces. From this information, final models of complex morphologies were derived for different block copolymer compositions, including lamellar, cylindrical, and new smectic-bilayered morphologies. To better understand the ordering of the LC mesogen at different interfaces, LC homopolymer films were studied. LC anchoring was planar at the substrate, but homeotropic at the air interface due to exposure of the non-polar mesogen tail. Block copolymer thin films were then examined for compositions ranging from 40% to 85% weight fraction of the LC block. / (cont.) Due to the wetting properties of the LC diblock copolymer, novel LC terraces were observed on the top surfaces corresponding to single smectic layer spacing. For diblock thin films, both blocks coexist at the air surfaces to form a mixed surface. Hybrid morphologies, consisting of both symmetrical and anti-symmetrical wettings, were noted for the lamellar morphology with film thicknesses between 0.5 and 1.5Lo. The surface properties are determined by LC orientation, which depends on the film thickness. Homeotropic anchoring of the smectic LC mesogens at the air interface was observed in both the homopolymer and the block copolymers, resulting in smectic terraces on the top surfaces of the films. In thicker films, when the influence of the substrate was decreased, the lamellar orientation was found to undergo a transition from parallel stacking near the substrate to perpendicular arrangement at the air surface. Effects of annealing and solvent exposure on the resulting thin-film behavior were also addressed. / by Jung-Sheng Wu. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1962. / MIT copy bound with: Polyelectrolyte complexes / Stephen C. Root. 1962. / Includes bibliographical references (leaf 33). / by Richard V. B. Rossman. / B.S.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1993. / Includes bibliographical references (leaves 176-191). / by Gordon Christopher Smith. / Sc.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1929. / by E. P. Weatherly, Jr., Wm. H. Jones. / B.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2008. / Includes bibliographical references (p. 225-267). / Comb-like copolymer structures, also known as graft/comb copolymers, have obtained a significant amount of attention in biomedical and industrial applications because of their unique compositional flexibility, which can lead to versatile structures in bulk, melt, and solution states. With biomedical applications (cancer diagnosis and treatment) as the context, this thesis is aimed at characterizing a series of polyethylene glycol (PEG) -based highly adaptable amphiphilic comb copolymer structures in their solution state that can serve as carriers and potentially contrast enhancement agent in magnetic resonance imaging (MRI). To successfully develop and implement such a delivery/contrast agent system, an adequate understanding is needed concerning their physicochemical properties: stability, size, morphology, local structural information, and magnetic resonance characteristics. The stability of these copolymer structures was characterized by their critical micelle concentration (the lower this concentration, the higher the stability), which was determined by total intensity light scattering and surface tension measurement. The size, morphology, and detailed structural information were studied by a combination of techniques, i.e., dynamic light scattering, transmission electron microscopy, cryogenic transmission electron microscopy, and small angle neutron scattering. Furthermore, solutions of polymer structure containing perfluorocarbon blocks were characterized by 19F magnetic resonance spectroscopy to evaluate their application for MRI contrast enhancement. Perfluorocarbon-containing comb copolymers (i.e., PEG-PFC) in solution had a low CMC of about 2 [mu]m. They were found to form two populations of particles - small micelles and large secondary aggregates. Hydrodynamic radius of micelles did not change with polymer concentration, PEG length, sample preparation method, or time after sample preparation. Large secondary aggregates were most likely compound micelles. Sample preparation method, polymer molecular weight, and time after sample preparation could change the proportion of micelles vs. aggregates. / (cont.) Due to its "perfluoroalkyl-philic" property, PEG-PFC copolymer was able to encapsulate a perfluorocarbon compound, 1H, 1H, 2H, 2H-Perfluoro-l-decanol. 19F-NMR spectroscopy of PEG-PFC polymer solution showed significant spectral line broadening and consequent signal to noise (SNR) decrease due to micelle formation. Furthermore, hydrocarboncontaining comb copolymers (i.e., PEG-HyC) in PBS had a CMC of about 12 [mu]M. The micelles formed by PEG-HyC copolymer had an Rh of about 4-5 nm that did not change with polymer concentration. Because of the formation of nano-size micelles, both PEG-PFC and PEG-HyC copolymers are good candidates to be developed as delivery vehicles for imaging and therapeutic agents. Their low CMC is an indication of their potential ability to maintain micelle integrity in situations of massive dilution. PEG-PFC copolymers could also be used to encapsulate insoluble fluorinated drugs. Though micelle formation of PEG-PFC copolymer caused significant 19F-NMR spectral line broadening and consequent SNR reduction, the copolymer can be modified to act as smart 19F-MRI probes for cancer diagnosis. / by Jin Zhou Dawson. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, September 2015. / Cataloged from PDF version of thesis. "August, 2014." / Includes bibliographical references. / Polymer science is exploring advanced materials which combine functional domains such as proteins and semiconducting polymers with traditional flexible polymers in the same molecule. While thermodynamic assemblies of different geometries introduce many interesting new phenomena such as entropic packing and liquid crystalline interactions, dynamic effects are also important to understand for optimal design of material mechanics, processing kinetics, and the new physics that directly arises from the motion of multiple domains of dissimilar geometries. Rod-coil block copolymers are an example of hybrid molecules that have attracted recent interest for organic electronics and biomaterials. This thesis uses theory, simulation, and experiments to better understand the mechanisms of molecular motion in entangled rod-coil block copolymers as a model for this wider class of functional polymeric materials. The large geometrical differences between rigid rods and Gaussian coils cause significant nonlinearities in dynamical behavior as these two motifs are combined on the same molecule. It is shown that the motion of rod-coils is slowed relative to rod and coil homopolymers because of a mismatch between the curvature of the rod and coil entanglement tubes. This mismatch causes different relaxation mechanisms in the small and large rod limits, where either the rod or the coil block is expected to determine the motion of the overall molecule. In the small rod limit where the rod is a perturbation on coil motion, the randomly varying curvature of the coil's tube presents entropic barriers to the reptation of the rod, modifying the unhindered motion of the coil along its tube into an activated reptation process. In the large rod limit where the coil is a perturbation on rod motion, the long rod cannot rotate around the surrounding entanglements so motion is only possible when the coil moves into a straightened entanglement tube in an arm retraction process. These mechanisms were first explored in molecular dynamics simulation using the Kremer- Grest model of entangled polymers, which showed that the tracer diffusion of coil-rod-coil triblock copolymers was slower than both rod and coil homopolymers. This observation was verified experimentally by forced Rayleigh scattering in both the small and large rod limits. Using additional simulations and experiments, the theories were applied to more complex configurations such as diblock copolymers and self-diffusion in polymer melts, where additional effects including molecular asymmetry and the motion of the surrounding chains were incorporated. Finally, a more detailed and quantitative analysis of the mechanisms both individually and in combination was performed using a coarse-grained slip-link model which matched the previous simulations and experiments. / by Muzhou Wang. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 171-176). / Growing concerns due to rising CO2 emissions have made biomass an indispensable source of renewable fuels and chemicals. However, biomass inherently has high oxygen content, which translates to low energy density, thereby necessitating a deoxygenation step before being utilized as fuels. Recently, MoO3 and Mo2C have emerged as promising earth-abundant cheap catalysts that perform hydrodeoxygenation (HDO) at relatively low temperatures ( 673 K) and ambient H2 pressures wherein oxygen is selectively removed as water. However, there exists a significant knowledge gap in understanding the stability and the active phases responsible for HDO of these catalysts. Furthermore, their applicability for real biomass conversions has not been largely demonstrated. In this thesis, first, HDO of m-cresol, a biomass-derived model compound, is investigated over bulk and supported MoO 3 catalysts. Detailed reactivity and characterization studies reveal that Mo5+ species plays a critical role during HDO. Specifically, TiO2 and ZrO2 are identified as ideal supports as they feature superior HDO reactivity and stability over bulk MoO3 by stabilizing intermediate Mo oxidation states (i.e. Mo5+) while bulk MoO 3 over-reduces to inactive metallic Mo. Translating from model compound studies, supported MoO3 catalysts are demonstrated to be effective in converting biomass (pine) pyrolysis vapors to hydrocarbons (ca. 30 % yield). In comparison with MoO 3, Mo2C is significantly more stable and selective for HDO of 4-methylanisole to toluene under identical reaction conditions. Mo2C predominantly breaks the stronger phenolic C-0 bond while MoO 3 also breaks the weaker aliphatic C-0 bond, likely due to the presence of Bronsted acid sites. To gain insights into the surface active sites, operando near-ambient XPS is employed during HDO and this technique revealed that HDO seems to operate via distinct active sites over both these materials. Finally, Mo2C is shown to be effective in upgrading real lignin streams to a single product propylbenzene, a precursor for renewable polymer. Overall, this thesis demonstrates the applicability of MoO3 and Mo2C in real biomass conversions and provides insights on the working nature of these catalysts, which will enable the design of more effective HDO catalysts. / by Karthick Murugappan. / Ph. D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2001. / Includes bibliographical references (p. 256-275). / The production of proteins in recombinant host cells has become an invaluable tool to obtain significant amounts of protein for therapeutic and other applications. Efforts to increase expression of foreign proteins in Escherichia coli, however, put an increasing burden on protein synthesis and processing. This can result in the production of improper or misfolded forms of protein that are degraded by host cell proteases. Proteolytic degradation may be enhanced by cellular stresses caused by the metabolic burden of protein overproduction and the dynamic bioreactor environment. Thus, the emergence of protein degradation and poor or variable product quality issues is a natural consequence of efforts to increase recombinant protein production to unnaturally high levels in a host cell. Protein degradation is an important consideration in bioprocess design as it influences the yield of product from th~ bioreactor and the distribution of degraded product fragments that ultimately must be removed during purification. This work characterizes the effect of dissolved oxygen, an important bioprocess scale-up parameter, on the degradation of recombinant [alpha]1-antitrypsin ([alpha]1AT) during production in E. coli. a 1-antitrypsin degradation increases with dissolved oxygen concentration, with -20% degraded under anaerobic conditions and approximately -50% degraded in cultures sparged with pure oxygen. Radioactive pulse-chase experiments indicate that newly synthesized protein is particularly susceptible to the oxygen-enhanced degradation. Protein engineering was used to create a 1AT variants to probe the degradation mechanism. [alpha]1AT degradation was reduced in a strain deficient in the ATP-dependent protease ClpP. It could be eliminated completely by production of [alpha]1AT with an N-terminal OmpT fusion peptide. The yield of [alpha]1AT was influenced by elimination of cytoplasmic oxidoreductases that increased the redox potential of the cytoplasm, perhaps indicating an interaction between cellular redox status and the observed degradation and yield of a 1AT. Low molecular weight fragments of [alpha]1AT were eliminated from the process by plasmid and purification improvements. I_n summary, the effect of dissolved oxygen on [alpha]1AT degradation was characterized and a variety of strategies were used to improve process quality, including dissolved oxygen control, plasmid design, protein engineering, strain improvement, and optimization of chromatography. / by Michael Edward Laska. / Ph.D.