Laszlo Tisza and Irwin Manning. / "March 15, 1957." "Reprinted from The Physical Review, Vol. 105, No. 6, 1695-1705, March 15, 1957." "This paper is a development of the Ph.D. thesis submitted by Irwin Manning to the Dept. of Physics, Massachusetts Institute of Technology." / Army Signal Corps Contract No. W-36-039 sc-32037 Project No. 102B. Dept. of the Army Project No. 3-99-10-022 and DA 3-99-10-000.

Adsorption-mediated self-assembly of nanoparticles at fluid interfaces, driven by reduction in interfacial energy, leads to stabilization of emulsions and foams and can be used for the bottom-up fabrication of functional nanostructured materials. Improved understanding of the parameters that control the self-assembly, the structure of nanoparticles at the interface, the barrier properties of the assembly and the rate of particle attachment and exchange is needed if such nanoparticle assemblies are to be employed for the design and fabrication of novel materials and devices. Here, I report on the use of dynamic surface tension (DST) measurements to probe the kinetics of irreversible adsorption and self-assembly of hydrophobic ethyl-cellulose (EC) nanoparticles at the air-water interface. Using thermodynamic arguments, I make a direct connection between the DST and the time-dependent surface coverage. I show that adsorption models appropriate for surfactants (e.g., Ward and Tordai model) break down for irreversible adsorption of nanoparticles, when the adsorption energy far exceeds the mean energy of thermal fluctuations (kBT) and surface blocking effects give rise to a steric barrier to adsorption. I show instead that irreversible adsorption kinetics are unequivocally characterized in terms of the adsorption rate constant and the maximum (jamming) coverage, both of which are determined on the basis of DST data using the generalized random sequential adsorption theory (RSA) for the first time. Novel accurate estimates of the adsorption energy of 42 nm and 89 nm EC nanoparticles are also provided. Coverage of the interface to the jamming limit of 91%, corresponding to a triangular lattice in 2D, is experimentally demonstrated. Colloidal solutions of EC nanoparticles are stabilized at neutral pH by electrostatic repulsive forces. Strong adsorption of these particles at an interface of like charge suggests the parallel action of attractive hydrophobic forces.

Adsorption-mediated self-assembly of nanoparticles at fluid interfaces, driven by reduction in interfacial energy, leads to stabilization of emulsions and foams and can be used for the bottom-up fabrication of functional nanostructured materials. Improved understanding of the parameters that control the self-assembly, the structure of nanoparticles at the interface, the barrier properties of the assembly and the rate of particle attachment and exchange is needed if such nanoparticle assemblies are to be employed for the design and fabrication of novel materials and devices. Here, I report on the use of dynamic surface tension (DST) measurements to probe the kinetics of irreversible adsorption and self-assembly of hydrophobic ethyl-cellulose (EC) nanoparticles at the air-water interface. Using thermodynamic arguments, I make a direct connection between the DST and the time-dependent surface coverage. I show that adsorption models appropriate for surfactants (e.g., Ward and Tordai model) break down for irreversible adsorption of nanoparticles, when the adsorption energy far exceeds the mean energy of thermal fluctuations (kBT) and surface blocking effects give rise to a steric barrier to adsorption. I show instead that irreversible adsorption kinetics are unequivocally characterized in terms of the adsorption rate constant and the maximum (jamming) coverage, both of which are determined on the basis of DST data using the generalized random sequential adsorption theory (RSA) for the first time. Novel accurate estimates of the adsorption energy of 42 nm and 89 nm EC nanoparticles are also provided. Coverage of the interface to the jamming limit of 91%, corresponding to a triangular lattice in 2D, is experimentally demonstrated. Colloidal solutions of EC nanoparticles are stabilized at neutral pH by electrostatic repulsive forces. Strong adsorption of these particles at an interface of like charge suggests the parallel action of attractive hydrophobic forces.

Two of the most robust results from dynamic competitive models of industrial organization suggest that higher sunk cost industries should exhibit (1) higher intertemporal variability in the market value of their firms, and (2) lower intertemporal variability in the size of their industries. These predictions have done well empirically. This paper argues on theoretical and empirical grounds that depreciation generates countervailing effects.

Increased interest in and use of additive manufacturing has made it an important component of advanced manufacturing in the last decade. Material Extrusion Additive Manufacturing (MatEx) has seen a shift from a rapid prototyping method harnessed only in parts of industry due to machine costs, to something widely available and employed at the consumer level, for hobbyists and craftspeople, and industrial level, because falling machine costs have simplified investment decisions. At the same time MatEx systems have been scaled up in size from desktop scale Fused Filament Fabrication (FFF) systems to room scale Big Area Additive Manufacturing (BAAM). Today MatEx is still used for rapid prototyping, but it has also found application in molds for fiber layup processes up to the scale of wind turbine blades. Despite this expansion in interest and use, MatEx continues to be held back by poor part performance, relative to more traditional methods such as injection molding, and lack of reliability and user expertise. In this dissertation, a previously unreported phenomenon, irreversible thermal strain (ITε), is described and explored. Understanding ITε improves our understanding of MatEx and allows for tighter dimensional control of parts over time (each of which speaks to extant challenges in MatEx adoption). It was found that ITε occurs in multiple materials: ABS, an amorphous polymer, and PLA, a semi-crystalline one, suggesting a number of polymers may exhibit it. Control over ITε was achieved by tying its magnitude back to part layer thickness and its directionality to the direction of roads within parts. This was explained in a detail by a micromechanical model for MatEx described in this document. The model also allows for better description of stress-strain response in MatEx parts broadly. Expanding MatEx into new areas, one-way shape memory in a commodity thermoplastic, ABS, was shown. Thermal history of polymers heavily influences their performance and MatEx thermal histories are difficult to measure experimentally. To this end, a finite element model of heat transfer in the part during a MatEx build was developed and validated against experimental data for a simple geometry. The application of the model to more complex geometries was also shown. Print speed was predicted to have little impact on bonds within parts, consistent with work in the literature. Thermal diffusivity was also predicted to have a small impact, though larger than print speed. Comparisons of FFF and BAAM demonstrated that, while the processes are similar, the size scale difference changes how they respond to process parameter and material property changes, such as print speed or thermal diffusivity, with FFF having a larger response to thermal diffusivity and a smaller response to print speed. From this experimental and simulation work, understanding of MatEx has been improved. New applications have been shown and rational design of both MatEx processes and materials for MatEx has been enabled.

Increased interest in and use of additive manufacturing has made it an important component of advanced manufacturing in the last decade. Material Extrusion Additive Manufacturing (MatEx) has seen a shift from a rapid prototyping method harnessed only in parts of industry due to machine costs, to something widely available and employed at the consumer level, for hobbyists and craftspeople, and industrial level, because falling machine costs have simplified investment decisions. At the same time MatEx systems have been scaled up in size from desktop scale Fused Filament Fabrication (FFF) systems to room scale Big Area Additive Manufacturing (BAAM). Today MatEx is still used for rapid prototyping, but it has also found application in molds for fiber layup processes up to the scale of wind turbine blades. Despite this expansion in interest and use, MatEx continues to be held back by poor part performance, relative to more traditional methods such as injection molding, and lack of reliability and user expertise. In this dissertation, a previously unreported phenomenon, irreversible thermal strain (ITε), is described and explored. Understanding ITε improves our understanding of MatEx and allows for tighter dimensional control of parts over time (each of which speaks to extant challenges in MatEx adoption). It was found that ITε occurs in multiple materials: ABS, an amorphous polymer, and PLA, a semi-crystalline one, suggesting a number of polymers may exhibit it. Control over ITε was achieved by tying its magnitude back to part layer thickness and its directionality to the direction of roads within parts. This was explained in a detail by a micromechanical model for MatEx described in this document. The model also allows for better description of stress-strain response in MatEx parts broadly. Expanding MatEx into new areas, one-way shape memory in a commodity thermoplastic, ABS, was shown. Thermal history of polymers heavily influences their performance and MatEx thermal histories are difficult to measure experimentally. To this end, a finite element model of heat transfer in the part during a MatEx build was developed and validated against experimental data for a simple geometry. The application of the model to more complex geometries was also shown. Print speed was predicted to have little impact on bonds within parts, consistent with work in the literature. Thermal diffusivity was also predicted to have a small impact, though larger than print speed. Comparisons of FFF and BAAM demonstrated that, while the processes are similar, the size scale difference changes how they respond to process parameter and material property changes, such as print speed or thermal diffusivity, with FFF having a larger response to thermal diffusivity and a smaller response to print speed. From this experimental and simulation work, understanding of MatEx has been improved. New applications have been shown and rational design of both MatEx processes and materials for MatEx has been enabled.

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No description available.

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Conventional methods of cancer therapy have been severely limited by inefficient delivery of therapeutic doses without incidence of harsh and toxic side effects in normal tissues. Consequently, countless new methods for early detection and drug delivery have been investigated in the area of nanoparticles and hydrogels. Although many of these methods are promising, the complex nature of cancer increases the difficultly for the development of the perfect system. Cellulose nanocrystals (CNCs) have been studied widely for a variety of applications. Despite their advantages, investigations of their abilities in the biomedical field have not been explored. The goal of this project is to delve into the potential uses of CNCs in detection, targeted drug delivery, and potentiation of irreversible electroporation (IRE)-induced cell death in folate receptor (FR)-positive cancers. To accomplish this task we have prepared stable and reproducible CNCs from wood pulp via sulfuric acid hydrolysis. Furthermore, we have functionalized the surface of these nanoparticles and conjugated them with the targeting ligand folic acid (FA) and the fluorescent imaging agent fluorescein-5\'-isothiocyanate (FITC) to create FITC-CNC-FA; CNCs have also been conjugated with doxorubicin (DOX), a potent chemotherapeutic (DOX-ALAL-CNC-FA). We have determined FITC-CNC-FA's and DOX-ALAL-CNC-FA's ability to specifically target FR-positive cancer cells in vitro; meanwhile non-targeted CNCs (FITC-CNC) were shown unable to bind to these cell types. In addition, we have investigated FITC-CNC-FA's pharmacokinetic activity in vivo. To properly model the CNC conjugate's activity in vivo, a physiologically based pharmacokinetic (PBPK) model has been constructed. We have also examined CNCs' ability to potentiate a new technique for tumor ablation, IRE. Pre-incubation with FA-conjugated CNCs (CNC-FA) have shown an increase in cytotoxicity in FR-positive cancer cells induced by IRE. In addition, CNC-FA did not potentiate IRE-induced cytotoxicity in a FR-negative cancer cell type. For a more comprehensive understanding of CNC-FA's ability to potentiate IRE induced cytotoxicity, we optimized a 3D in vitro hydrogel system. Preliminary data suggest this method of experimentation will be more realistic to in vivo studies to be completed in the future. Together, these studies showcase CNCs as efficient and effective nano-carriers in tumor detection and treatment. / Ph. D.