Long-term colloidal stability of polymer-grafted silica nanoparticles in concentrated brine at elevated temperatures

Random copolymer poly(AA-co-AMPS) chains were grafted covalently onto amine coated individual ~20 nm silica nanoparticles (NPs) without forming aggregates. The hydrodynamic diameter of the grafted silica NPs remained constant at ~25 nm for over six weeks up to 90°C in 100% API brine indicating electrosteric stabilization. The grafting efficiency was enhanced by catalysis with EDC and N-hydroxysuccinimide to increase the half-life of the intermediates on the AA groups to form negatively charged intermediates on the AA groups to attract the protonated amines on the NPs. The higher reaction rate for the activated AA groups, relative to the collision rate of the NPs favored multiple grafting of a bound polymer to the same nanoparticle versus bridging of the polymer chain to a second nanoparticle. After extreme dilution, the particles were still stable in brine indicating the chains were permanently grafted. The random copolymer poly(AA-co-AMPS) was found to be able to stay swelled and elongated in a wide range of pH (pH 4 to 12) and provide colloidal stability for the silica NPs due to the high solvation of the AMPS groups.Chemical Engineerin

Biodegradable NIR-active contrast agents for photoacoustic imaging

Biodegradable contrast agents are of great interest in biomedical imaging, in specific photoacoustic imaging, for early detection of cancer. The ideal contrast agent should exhibit sufficiently high adsorption in the near infrared (NIR) window (700–1000 nm), high photostability, and efficient conversion of heat energy to produce strong acoustic waves. Various organic and inorganic contrast agents have been studied in this thesis, including gold nanoclusters, PEG-PLGA nanocapsules loaded with copper sulfide nanoclusters, and PEG-PLGA nanocapsules loaded with ICG J-aggregates. Biodegradable NIR-active nanoclusters of 4 nm ligand-coated gold nanoparticles (NPs) were assembled in aqueous solution by controlling the interparticle interactions through varying the pH, ionic strength, and the surface ligands. These nanoclusters can fully dissociate in the physiological environment back to primary 4 nm gold NPs, which may allow for renal clearance. The spacing between NPs inside the gold nanoclusters must be less than 1 nm to achieve the required surface plasmon resonance (SPR) shift into the NIR window. Binary surface ligand coatings of thioctic acid zwitterion and citrate were used to help achieve the required interparticle spacing, allowing both for high NIR adsorption and reversible assembly/dissociation. In contrast to gold nanoclusters, close interparticle separations are not necessary to achieve strong NIR adsorption in copper sulfide nanoclusters, since the primary copper sulfide NPs already exhibit this behavior. Therefore, longer surface-passivating ligands can be employed for copper sulfide nanoparticles to effectively prevent protein opsonization in the physiological environment to facilitate successful renal clearance. Copper sulfide nanoclusters were encapsulated in PEG-PLGA nanocapsules to improve their stability and control the degradation kinetics inside the body. Finally, indocyanine green J-aggregates encapsulated in PEG-PLGA nanocapsules were synthesized as organic contrast agents made of FDA-approved constituents. These nanocapsules exhibit a sharp peak in the NIR window with favorable stability and degradation kinetics in the physiological environment. Overall, this thesis demonstrates important advances toward synthesis of biocompatible nanoscale contrast agents with control over size, stability and degradation kineticsChemical Engineerin

Two-fold enhancement in tensile strength of carbon nanotube–carbon fiber hybrid epoxy composites through combination of electrophoretic deposition and alternating electric field

AbstractA new carbon nanotube (CNT)–hybridized carbon fiber (CF) was introduced in an attempt to improve interfacial strength between CF and polymeric matrix. Amine-functionalized CNTs was radially deposited on the CF surface through a combination of alternating electric field with electrophoretic deposition process. Radial deposition of CNTs on CF formed a unique porous structure around CF that could significantly increase the interfacial adhesion through interlocking of polymeric matrix. Tensile properties and fatigue life of the reinforced composites were investigated in order to study the effect of interfacial adhesion on mechanical properties of reinforced composites. Results indicate that the radial deposition of CNT on CF can remarkably enhance the compatibility of polymeric matrix with CF. This improvement in compatibility of polymeric matrix with CNT–hybridized CF resulted in considerable enhancement in mechanical properties of composites. The interfacial reinforcing mechanism was explored through fractography of reinforced composites and possible failure modes have been precisely discussed