Polymeric biomaterials represent the leading technologies available today for the repair of tissue damage and for targeted drug delivery. Perhaps the most valuable aspect of polymer-based systems is the extent to which their physical properties (e.g. elasticity, porosity, etc.) can be controlled and tuned by regulating experimental parameters during their synthesis. Biomaterial performance can be improved further still by including supplementary components resulting in a composite material. Synergetic interactions between the constituents of composite materials often results in bulk physical properties that are substantially more than the sum of individual parts. Through understanding and exploiting these sympathetic relationships, novel biocomposites can be developed which exhibit improved efficacy and biocompatibility. Here we report on the synthesis strategies and characterization of novel biocomposites from our laboratory. We look specifically at hydrogel composites containing a physically-associated network of Pluronic® block copolymer along with a calcium-phosphate mineral component. Rheological results show that composites containing an in situ deposited mineral exhibit a significantly higher elastic modulus than composites of similar composition formed by conventional means. Moreover, analysis of the calcium-phosphate phase of in situ composites revealed that system parameters such as acidity play an integral role in determining the size and stability of the resultant mineral and subsequently the materials' expected in vivo performance. Changes to the structure in Pluronic®/calcium-phosphate composite hydrogels during dehydration was investigated to provide a look into the mechanisms involved in composite formation. Small angle X-ray scattering analysis of these systems shows that hydrogen bonding interactions between phosphate ions and the polyethylene oxide (PEO) polymer block significantly impact the nanoscale structure and long-range order contained in these materials. Phosphate groups are preferentially sequestered into the PEO phase in the gel and overall structural changes can be directly related to the average number of hydrogen bonds each phosphate ion experiences. Our results indicate that by understanding how mineralization occurs in simplified systems we may be able to provide insight into the complex mechanisms involved in natural tissue formation. Moreover, we show that by utilizing novel synthesis routes we are able to manufacture new biomaterials with desirable and tunable physical properties.

Semiconductor nanocrystals, or quantum dots (QDs), are interesting nanomaterials whose size-dependent, tunable optical and electronic properties make them ideal for applications in biological sensing and imaging, light-emitting devices, displays, and solar cells. The commercial exploitation of these materials requires the development of synthesis techniques that are scalable, economical, and environmentally friendly, while enabling precise control of the size, shape and size distribution of the nanocrystals. The most common synthesis technique for these nanocrystals employs small batch reactors in which nanocrystals grow as a function of time following a rapid injection of organometallic precursors into a hot coordinating solvent. The limitations of this process for large-scale commercial exploitation stem from the incomplete mixing of the precursors in large batches that can lead to non-uniform nucleation and broad particle size distributions. Limitations also include the high cost, flammability, and toxicity of the organometallic precursors and its operator-intensive nature. Templated synthesis techniques for nanocrystals have distinct advantages over other methods, including more precise control of particle size, shape, and size distribution and easier scalability for commercial applications. This thesis presents the templated synthesis of semiconducting nanocrystals in stable microemulsions and liquid crystals, formed by the self-assembly of an amphiphilic block copolymer in the presence of a polar and non-polar solvent. The work of this thesis investigates microemulsion templates for the scalable synthesis of semiconductor nanocrystals including: materials composition and particle size control, continuous production of nanocrystals, improvement of optical properties, and alternative non-toxic reactants. The nanocrystals were formed by reacting a group-II salt dissolved in the dispersed phase of the template with a group-VI hydride gas inside the nanodomains. The versatility of nanomaterials and precision of size control of this synthesis method were demonstrated by adjusting the metal salt composition and concentration. The scalability of this technique was displayed by developing a counter-current flow, packed-bed reactor for continuous synthesis of nanocrystals in templating microemulsions. Limitations of the optical properties of nanoparticles synthesized with microemulsion template were addressed by post-processing techniques including extraction and functionalization of the nanocrystals, annealing, and overcoating the quantum dots with an inorganic shell to optimize fluorescence emission and quantum yield. This post-process annealing allowed for the investigation of Mn-dopant incorporation and expulsion from the ZnSe nanocrystal. To eliminate the toxic and flammable group-VI hydride gases, a microwave-assisted templated synthesis route was developed. This employed bursts of microwaves to selectively heat the aqueous, dispersed droplets of water-in-oil microemulsions that contain the water-soluble precursors of the group-II and VI elements, thus leading to nucleation and formation of a single nanocrystal inside each nanodomain.

Porous materials have long been a research interest due to their practical importance in traditional chemical industries such as catalysis and separation processes. The successful synthesis of porous materials requires further understanding of the fundamental physics that govern the formation of these materials. In this thesis, we apply molecular modeling methods and develop novel models to study the formation mechanism of ordered porous materials. The improved understanding provides an opportunity to rational control pore size, pore shape, surface reactivity and may lead to new design of tailor-made materials. To attain detailed structural evolution of silicate materials, an atomistic model with explicitly representation of silicon and oxygen atoms is developed. Our model is based on rigid tetrahedra (representing SiO4) occupying the sites of a body centered cubic (bcc) lattice. The model serves as the base model to study the formation of silica materials. We first carried out Monte Carlo simulations to describe the polymerization process of silica without template molecules starting from a solution of silicic acid in water at pH 2. We predicted Qn evolutions during silica polymerization and good agreement was found compared with experimental data, where Qn is the fraction of Si atoms with n bridging oxygens. The model captures the basic kinetics of silica polymerization and provides structural evolution information. Next we generalize the application of this atomic lattice model to materials with tetrahedral (T) and bridging (B) atoms and apply parallel tempering Monte Carlo methods to search for ground states. We show that the atomic lattice model can be applied to silica and related materials with a rich variety of structures including known chalcogenides, zeolite analogs, and layered materials. We find that whereas canonical Monte Carlo simulations of the model consistently produce the amorphous solids studied in our previous work, parallel tempering Monte Carlo gives rise to ordered nanoporous solids. The utility of parallel tempering highlights the existence of barriers between amorphous and crystalline phases of our model. The role of template molecules during synthesis of ordered mesoporous materials was investigated. Implemented surfactant lattice model of Larson, together with atomic tetrahedral model for silica, we successfully modeled the formation of surfactant-templated mesoporous silica (MCM-41), with explicit representation of silicic acid condensation and surfactant self-assembly. Lamellar and hexagonal mesophases form spontaneously at different synthesis conditions, consistent with published experimental observations. Under conditions where silica polymerization is negligible, reversible transformation between hexagonal and lamellar phases were observed by changing synthesis temperatures. Upon long-time simulation that allows condensation of silanol groups, the inorganic phases of mesoporous structures were found with thicker walls that are amorphous and lack of crystallinity. Compared with bulk amorphous silica, the wall-domain of mesoporous silicas are less ordered withlarger fractions of three- and four-membered rings and wider ring-size distributions. It is the first molecular simulation study of explicit representations of both silicic acid condensation and surfactant self-assembly.

Block copolymer (BCP) nanocomposites are an important class of hybrid materials in which the BCP guides the spatial location and the periodic assembly of the additives. High loadings of well-dispersed nanofillers are generally important for many applications including mechanical reinforcing of polymers. In particular the composites shown in this work might find use as etch masks in nanolithography, or for enabling various phase selective reactions for new materials development. This work explores the use of hydrogen bonding interactions between various additives (such as homopolymers and non-polymeric additives) and small, disordered BCPs to cause the formation of well-ordered morphologies with small domains. A detailed study of the organization of homopolymer chains and the evolution of structure during the process of ordering is performed. The results demonstrate that by tuning the selective interaction of the additive with the incorporating phase of the BCP, composites with significantly high loadings of additives can be formed while maintaining order in the BCP morphology. The possibility of high and selective loading of additives in one of the phases of the ordered BCP composite opens new avenues due to high degree of functionalization and the proximity of the additives within the incorporating phase. This aspect is utilized in one case for the formation of a network structure between adjoining additive cores to derive mesoporous inorganic materials with their structures templated by the BCP. The concept of additive-driven assembly is extended to formulate BCPadditive blends with an ability to undergo photo-induced ordering. Underlying this strategy is the ability to transition a weakly interacting additive to its strongly interacting form. This strategy provides an on-demand, non-intrusive route for formation of well-ordered nanostructures in arbitrarily defined regions of an otherwise disordered material. The second area explored in this dissertation deals with the incorporation of additives into photoresists for next generation extreme ultra violet (EUV) photolithography applications. The concept of hydrogen bonding between the additives and the polymeric photoresist was utilized to cause formation of a physical network that is expected to slow down the diffusion of photoacid leading to better photolithographic performance (25-30 nm resolution obtained).