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Hypothesis: A process to fabricate structures on inclined substrates has the potential to yield novel applications for colloidal-based structures. However, for conventional techniques, besides the coffee ring effect (CRE), anisotropic particle deposition along the inclination direction (IE) is expected to occur. We hypothesize that both effects can be inhibited by reducing the dispense volume during printing by direct writing. Experiments: We combined an additive manufacturing technique, namely direct writing, with colloidal assembly (AMCA) for an automated and localized drop-cast of polystyrene and silica suspensions onto inclined surfaces. Herein, we investigated the influence of the substrate tilting angle and the dispense volume on the printing of colloids and the resulting structures’ morphology. Findings: The results demonstrate that a reduction in the dispense volume hinders the CRE and IE for both particles’ systems, even though the evaporation mode is different. For polystyrene, the droplets evaporated solely in stick-mode, enabling a “surface capturing effect”, while for silica, droplets evaporated in mixed stick–slip mode and a “confinement effect” was observed, which improved uniformity of the deposition. These findings were used to generate a model of the critical droplet radius needed to print homogeneous colloidal-based structures onto inclined substrates., Deutsche Forschungsgemeinschaft (DFG)

Passive surface thermal regulation is an area of critical interest, with many potential applications ranging from the design of energy efficient building coatings to applications such as thermo camouflage. The thermoregulation of a surface requires the dynamic modulation of emissivity and reflectivity of the material; these changes are achieved via the manipulation of the surface morphology of the material. The work presented in this thesis used a strain driven CNT film to achieve the said morphology changes. In the experimental characterization of CNT films, a 0.047 increase in the average solar reflectivity was observed when strain up to 80%. When exposed to direct sunlight, this change in reflectivity was manifested as a temperature change of 2.8℃. Following the experimental work, a 3D model was developed to represent the CNT film. The developed model was simulated using raytracing under varying levels of strain, these results were used to develop a hypothesis. The developed hypothesis viewed the surface of the CNT films to be composed of many pit-like structures; the shallowing of the pit depth when strained was determined to be the driving mechanism of increased reflectivity. Later based on the developed hypothesis a simpler periodic model was created to provide an enhanced strain-dependent reflectivity increase of 0.145 in the solar region. This model was further improved by adding a silver backed layer to provide an increased averaged solar reflectivity of 0.6826 resulting in a surface temperature change of nearly 61℃.

Passive surface thermal regulation is an area of critical interest, with many potential applications ranging from the design of energy efficient building coatings to applications such as thermo camouflage. The thermoregulation of a surface requires the dynamic modulation of emissivity and reflectivity of the material; these changes are achieved via the manipulation of the surface morphology of the material. The work presented in this thesis used a strain driven CNT film to achieve the said morphology changes. In the experimental characterization of CNT films, a 0.047 increase in the average solar reflectivity was observed when strain up to 80%. When exposed to direct sunlight, this change in reflectivity was manifested as a temperature change of 2.8℃. Following the experimental work, a 3D model was developed to represent the CNT film. The developed model was simulated using raytracing under varying levels of strain, these results were used to develop a hypothesis. The developed hypothesis viewed the surface of the CNT films to be composed of many pit-like structures; the shallowing of the pit depth when strained was determined to be the driving mechanism of increased reflectivity. Later based on the developed hypothesis a simpler periodic model was created to provide an enhanced strain-dependent reflectivity increase of 0.145 in the solar region. This model was further improved by adding a silver backed layer to provide an increased averaged solar reflectivity of 0.6826 resulting in a surface temperature change of nearly 61℃.

We present our recent results on the fabrication of photonic devices such as single-mode and few-mode waveguides, Ycouplers as well as integrated interferometric sensor devices. The devices were created by means of a fabrication method based on maskless lithography, which allows for fabricating embedded integrated polymer elements on a scale of several square centimeters with a resolution down to one micron. We demonstrate the versatility of our approach by presenting first results on photonic structures created by maskless lithography. © 2016 SPIE.

Photonic crystals due to their angular bandgaps and quasi-bandgaps can provide spatial (angular) filtering of light. Two-dimensional photonic crystals (photonic structures modulated along the longitudinal and along one transverse dimension) can provide spatial filtering in one one-dimensional, decreasing the beam divergence in one quadrature. Three-dimensional crystals can provide two-dimensional filtering, with the shape of the filtering window corresponding to the symmetry of photonic crystal (e.g. forming a quadratic, or hexagonal shape beams). For many applications axisymmetric spatial filtering is required, in order to obtain diffraction limited axisymmetric Gaussian beams. For that purpose we developed and fabricated axisymmetric photonic crystal-like structures (periodic in longitudinal direction, but aperiodic in transverse direction). We overview the axisymmetric filtering: physical principles, simulations, fabrication, and experimental measurements, Peer Reviewed, Postprint (published version)