Chemical and Biomolecular Engineering - Theses
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ItemNanoparticles and macromolecules in flow( 2016)The optimised fabrication of nanomaterials requires understanding of their behaviors in flow. Here we report on investigations into the flow induced structured changes in colloidal suspensions and polymer solutions. Fabrication of nano-devices requires understanding of the fundamental aspects of flow induced changes in suspensions or polymers. Understanding the behaviors of the dynamics of particles in flow gives insights into fluid mechanics at these length scales. In this work, rheo-optics are combined with numerical simulations to study flow induced phenomena in the colloidal systems. The rheo-optical methods are used to measure the real time optical changes of the sheared nanomaterial suspensions. The simulations are developed to derive the optical changes from the microstructure or motion changes of the suspending nanomaterials in flow. The thesis reports on three main areas of study. The first two studies are on the flow induced alignment of prolate nanoparticles in the red form poly-4BCMU solutions and gold nanorods aqueous sucrose solutions. The absorption spectra have been measured over a range of shear rates using polarized and unpolarized incident light, and the reversible optical changes indicate that the nanoparticles do not undergo aggregation during measurement. The measured absorbance anisotropy is attributed to the flow induced particle alignment which reach the limitation at high Peclet numbers. The spectral changes are consistent with the Jeffery's orbits (cooperating with the Brownian rotation) for large nanoparticles. While, for the nanorods with the long axis <100nm, the spectral shifts are no longer consistent with the modified Jeffery's orbits, but with the rods flipping between extreme orientations of the Jeffery's orbits. This indicates that the effect of the Brownian motion and hydrodynamic forces on the nanoscale rods needs being reconsidered. The viscoelastic effect on the flow-induced aggregation is studied in the dilute colloidal polystyrene nanoparticles suspensions. The real-time aggregation processes have been recorded via measuring optical absorption/scattering in flow. The observed absorbance decreases over time are attributed to the flow-induced coagulation. The aggregation processes still follow the Smoluchowski coagulation equation in a revised version. Suspensions in a series of media are studied to evaluate the effect of the media rheological properties on the particle aggregation. The data shows that elasticity reduces the aggregation while the solution viscosity increases the aggregation rate. In conclusion, the flow induced alignment and aggregation in the nanomaterials suspensions were studied using the rheo-optical method. The classical hydrodynamic theory describes the rotation of larger prolate nanoparticles in flow, but is no longer efficient for the rod like particles with the long axis 100nm. The solution viscosity accelerates the aggregation of nanoparticles while the elasticity has the opposite effect.
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ItemAssembly of polymer matrices enveloping cubic lyotropic liquid crystalline nanoparticles for drug delivery applications( 2012)Cubic lyotropic liquid crystalline nanoparticles (cubosomes™) exhibit great potential as drug delivery vehicles due to their nanoscale size, biocompatible constituents, and high loading potential for hydrophobic, hydrophilic, and amphiphilic agents. However, they also suffer from some limitations which have restricted their clinical effectiveness. For example, they release their cargo in a rapid, uncontrolled manner— a phenomenon known as burst release. In addition, the lipids which form reverse cubic phase typically do not contain surface functional groups for the immobilisation of targeting or stealth providing moieties. Polymeric capsules, in particular those made with the layer-by-layer technique, are able to modify the release properties of a loaded drug according to the number and nature of polymer layers. Many of the polymers employed also contain available functional groups for additional chemistry. However polymeric capsules can be difficult to efficiently load with therapeutic agents, particularly when the drugs are lipid soluble. Additionally, the removal of the capsule core template often requires conditions that can cause instability. This thesis examined the use of polymers to modulate the properties of cubosomes with the intention to aid stability, limit burst release, add potential functionality, and increase the payload. Different methods used to prepare stable, well dispersed amphiphilic cubosomes (high pressure homogenisation, extrusion, and ultrasonication) were analysed and compared. The effect of an additive to the aqueous environment (such as sodium chloride or phosphate buffered saline (PBS)) was also investigated. Certain additives to the amphiphile matrix such as the charged lipids cetyl trimethylammonium bromide (CTAB), dioctadecyl-dimethylammonium bromide (DODAB) or sodium dodecyl sulphate (SDS) were found to cause structural changes to both bulk and dispersed cubic phase but could be tolerated up to a certain quantity before complete destabilisation occurred. Integrating cubic nanoparticles and polymer matrices was first accomplished by coating silica microparticles. This resulted in a multilayered polymer coating representing an embedded layer of cubosomes surrounded by poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) polyelectrolytes. Upon removal of the silica core, stable polymer microcapsules containing embedded cubic nanoparticles were obtained. A diversity of molecular encapsulation matrices is offered through the capsule core, polyelectrolyte layers, and the embedded cubosomes of these sub-compartmentalised, nanostructured microcapsules. Individual cubic nanoparticles surrounded by polyelectrolyte multilayers were prepared next. The polymers were able to interact with the non-charged cubic lipid nanoparticles by utilising a polyelectrolyte modified with hydrophobic side chains (poly(methacrylic acid-co-oleyl methacrylate), PMAO) as an initial layer. Three bi-layers of poly(L-lysine) (PLL) and poly(methacrylic acid) (PMA) were then sequentially added. In order to separate accrued polymer aggregates from the coated lipid nanoparticles, a simple technique was developed whereby centrifugation separated the less dense cubosomes for collection. Modulation of the drug release properties and attenuation of the burst release from coated cubosome particles was demonstrated using two model drugs (fluorescein and perylene). The modified polymer PMAO was then utilised as an alternative stabiliser for lyotropic liquid crystalline nanoparticles. The charge-stabilised particles were tested against the most commonly utilised steric stabiliser Pluronic F127 for stability and drug release characteristics. Although PMAO-stabilised nanoparticles still exhibited burst release, improved particle stability was observed over time and over a range of temperatures, including storage under refrigeration. A lesser amount of PMAO stabiliser and less energy input were also required to disperse the bulk lipid into discrete, uniform nanoparticles compared to Pluronic F127. These studies demonstrate the viability of combining layer-by-layer polymer matrix technology with cubic lyotropic liquid crystalline nanoparticles to enhance the future of drug delivery.