Thermally expandable microspheres are polymeric core/shell particles in which a volatile hydrocarbon is encapsulated by a thermoplastic shell. When these microspheres are heated, they expand and increase their volume dramatically. This volume increase is retained upon cooling, leading to a density reduction from around 1100 kg m-3 to about 30 kg m-3. Since the development in the early 1970´s, microspheres have been used extensively by the industry as a foaming agent or light weight filler. In this thesis, microspheres with a poly(acrylonitrile-co-methacrylonitrile) shell have been synthesized through free radical suspension polymerization. The microspheres have been characterized with respect to particle morphology and expansion properties in order to deepen the understanding of the microspheres. It was found that the monomer feed ratio and the polymerization temperature are very important parameters with respect to the expansion properties. Excellent expansion could only be accomplished when polymerizing at 62 °C, with the acrylonitrile feed, fAN, being around 60 mol%, even though core/shell microspheres are formed over a much wider range of fAN. Furthermore, no expansion was achieved when polymerizing at 80 °C, even though no noticeable differences were found, compared to the corresponding sample polymerized at 62 °C. It was also shown that the expansion properties can be modified by replacing the encapsulated hydrocarbon by another hydrocarbon with a different boiling point. Not only is the boiling point important, the structure of the hydrocarbon is also important. Isooctane which is highly branched was found to give superior expansion compared to linear or cyclic hydrocarbons having a similar boiling point. Crosslinking of the polymer shell has proven to be very important for the expansion properties. Both the amount and the structure of the crosslinker are important parameters. Especially the maximum expansion can be improved by the crosslinking of the polymer shell. This originates in an increase in the shape persistence of the expanded microspheres at elevated temperatures. By the combination of crosslinkers that are incorporated separately into the polymer shell, the onset temperature of expansion can be increased significantly. Finally, the surface of microspheres has been modified by grafting poly(glycidyl methacrylate) from the surface by ARGET ATRP. Given that the reaction conditions are appropriate, such modifications can be performed with only limited effects on the expansion properties of the microspheres.

The field of micro total analysis systems (μTAS) aims at developments toward miniaturized and fully integrated lab-on-a-chip systems for applications, such as drug screening, drug delivery, cellular assays, protein analysis, genomic analysis and handheld point-of-care diagnostics. Such systems offer to dramatically reduce liquid sample and reagent quantities, increase sensitivity as well as speed of analysis and facilitate portable systems via the integration of components such as pumps, valves, mixers, separation units, reactors and detectors. Precise microfluidic control for such systems has long been considered one of the most difficult technical barriers due to integration of on-chip fluidic handling components and complicated off-chip liquid control as well as fluidic interconnections. Actuation principles and materials with the advantages of low cost, easy fabrication, easy integration, high reliability, and compact size are required to promote the development of such systems. Within this thesis, liquid displacement in microfluidic applications, by means of expandable microspheres, is presented as an innovative approach addressing some of the previously mentioned issues. Furthermore, these expandable microspheres are embedded into a PDMS matrix, which composes a novel thermally responsive silicone elastomer composite actuator for liquid handling. Due to the merits of PDMS and expandable microspheres, the composite actuator's main characteristic to expand irreversibly upon generated heat makes it possible to locally alter its surface topography. The composite actuator concept, along with a novel adhesive PDMS bonding technique, is used to design and fabricate liquid handling components such as pumps and valves, which operate at work-ranges from nanoliters to microliters. The integration of several such microfluidic components promotes the development of disposable lab-on-a-chip platforms for precise sample volume control addressing, e.g. active dosing, transportation, merging and mixing of nanoliter liquid volumes. Moreover, microfluidic pumps based on the composite actuator have been incorporated with sharp and hollow microneedles to realize a microneedle-based transdermal patch which exhibits on-board liquid storage and active dispensing functionality. Such a system represents a first step toward painless, minimally invasive and transdermal administration of macromolecular drugs such as insulin or vaccines. The presented on-chip liquid handling concept does not require external actuators for pumping and valving, uses low-cost materials and wafer-level processes only, is highly integrable and potentially enables controlled and cost-effective transdermal microfluidic applications, as well as large-scale integrated fluidic networks for point-of care diagnostics, disposable biochips or lab-on-a-chip applications. This thesis discusses several design concepts for a large variety of microfluidic components, which are promoted by the use of the novel composite actuator. Results on the successful fabrication and evaluation of prototype devices are reported herein along with comprehensive process parameters on a novel full-wafer adhesive bonding technique for the fabrication of PDMS based microfluidic devices. / QC 20100817

Macroporous ceramic materials have found widespread technological application ranging from particulate filters in diesel engines, tissue engineering scaffolds, and as support materials in carbon capture processes. This thesis demonstrates how the pore space of macroporous alumina can be manipulated, analysed in three-dimensions (3D) using visualisation techniques, and functionalised with a CO2-adsorbing material. A novel method was developed to produce macroporous alumina materials: by combining sacrificial templating with thermally expandable polymeric microspheres and gel-casting of an alumina suspension. This method offers a versatile production of macroporous ceramics in which the level of porosity and the pore size distribution can easily be altered by varying the amount and type of spheres. The permeability to fluid flow could be regulated by controlling the connectivity of the pore space and the size of the smallest constrictions between the pores. Sacrificial templating with particle-coated expandable spheres significantly increased the fraction of isolated pore clusters and reduced both the sizes and the numbers of connections between neighbouring pores, compared to templating with un-coated spheres. The macroporous alumina materials were characterised with X-ray micro-computed tomography (μ-CT). The 3D data-sets obtained by X-ray μ-CT were used to calculate the spatial variation in porosity, the throat and pore size distributions and to calculate the permeability to fluid flow. The throat and pore size distributions were also able to be accurately quantified in only one extrusion and intrusion cycle with water-based porosimetry; a relatively novel and simple characterisation technique. The pore walls of the macroporous alumina materials were also coated with zeolite films by a colloidal processing technique. The CO2-uptake of the coated alumina materials and of hierarchically porous monoliths of zeolites was evaluated and compared. / As the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: Accepted. Paper 5: Manuscript. Paper 6: Submitted.