Microfluidic device construction uses certain critical structures throughout many different applications. The valve structure remains one of the primary structures that present a barrier to miniaturization and portability. The extensive support devices required to power common microfluidic valves remove a significant amount of freedom from microfluidic device design. Moving to electrostatic methods of actuation could reduce the overall footprint of the microfluidic valve. This thesis covers three concept prototypes. Concept I presents an attempt at inlaying gold electrodes into polydimethylsiloxane substrates. Concept II attempts to use liquid silver injected into channels as electrode materials. Concept III uses aluminum sputtering to fabricate valve electrodes. Each device encountered complications during fabrication which led to improved fabrication guidelines for future devices. Designing and fabricating these concept devices required the development of several new processes in the clean room, including RIE Plasma bonding, PDMS sputtering techniques, and multilayer PDMS thin film fabrication. The PDMS sputtering technique in particular allows profilometry measurement of PDMS surfaces without risk of damaging the profilometer tip, a development that could allow for much more control over PDMS film thicknesses in future projects.

Mechanical rubbing alignment is the most common used method in the liquid crystal display manufacturing process. However, it may cause dust and electrostatic problem. In this study, we investigate effects of low surface free energy Polydimethylsiloxane (PDMS) on orientation of liquid crystal molecules in a confined structure and fabricate alignment layer using PDMS. In the present study, we show that liquid crystal molecules are arranged in consistency without rubbing process and it may be a new homogeneously aligned mode in liquid crystal display. In this thesis, liquid crystal textures were observed using polarizing optical microscopy (POM). It was found that liquid crystal molecules were homogeneously aligned in PDMS holes. In addition, this thesis indicated that how liquid crystal alignment affected by PDMS layer thickness and surface treatment. We learned that using treatment of JALS-9800 film on the bottom substrate from liquid crystal texture can obtain the arrangement of expected liquid crystal molecules. The liquid crystal device can be produced using PDMS structure. The measurement of electro-optic characteristics showed that the circular shape in the confined structure had better transmittance and contrast ratio.

Controlling the orientation of liquid crystal molecules in LC displays is extremely important for optimizing device performance. The method most commonly used in industry today involves rubbing the surface of the polymer-coated glass substrates used in the displays with a velvet cloth to create microscopic grooves. Berreman theory states that the liquid crystal molecules then align along the direction of the grooves. Alternatively, some literature shows that the friction caused by rubbing aligns the polymer chains in the surface layer which then attract and align the liquid crystal molecules along the direction of the chains. Even now, it is still unclear exactly how the process of rubbing the surface causes the liquid crystal molecules to align in an orderly manner. This thesis describes a systematic study of the physical and chemical influence of the substrate on the alignment and orientation of liquid crystal molecules. We used Fourier Transform Infrared spectroscopy (FTIR) to identify surface chemistry, contact angle measurements to determine the surface energy, and atomic force microscopy (AFM) to observe the alignment of liquid crystal on the surfaces. In the course of this study, we have gained insight into how the physical and chemical properties of the surface affect the molecular arrangement in the solid-liquid interface. Our results can be applied not only to LCD technology, but more generally to biochips and biosensor devices.

Analogous to the extracellular matrix (ECM) of natural tissues, properties of a tissue engineering scaffold direct cell behavior and thus regenerated tissue properties. These include both physical properties (e.g. morphology and modulus) and chemical properties (e.g. hydrophobicity, hydration and bioactivity). Notably, recent studies suggest that scaffold properties (e.g. modulus) may be as potent as growth factors in terms of directing stem cell fate. Thus, 3D scaffolds possessing specific properties modified for optimal cell regeneration have the potential to regenerate native-like tissues. Photopolymerizable poly(ethylene glycol) diacrylate (PEG-DA)-based hydrogels are frequently used as scaffolds for tissue engineering. They are ideal for controlled studies of cell-material interactions due to their poor protein adsorption in the absence of adhesive ligands thereby making them “biological blank slates”. However, their range of physical and chemical properties is limited. Thus, hydrogel scaffolds which maintain the benefits of PEG-DA but possess a broader set of tunable properties would allow the establishment of predictive relationships between scaffold properties, cell behavior and regenerated tissue properties. Towards this goal, this work describes a series of unique hybrid inorganic-organic hydrogel scaffolds prepared using different solvents and also in the form of continuous gradients. Properties relevant to tissue regeneration were investigated including: swelling, morphology, modulus, degradation rates, bioactivity, cytocompatibility, and protein adhesion. These scaffolds were based on the incorporation of hydrophobic, bioactive and osteoinductive methacrylated star polydimethylsiloxane (PDMSstar-MA) [“inorganic component”] into hydrophilic PEG-DA [“organic component”]. The following parameters were varied: molecular weight (Mn) of PEG-DA (Mn = 3k & 6k g/mol) and PDMSstar-MA (Mn = 1.8k, 7k, 14k), ratio of PDMSstar-MA to PEG-DA (0:100 to 20:80), total macromer concentration (5 to 20 wt%) and utilizing either water or dichloromethane (DCM) fabrication solvent. The use of DCM produced solvent induced phase separation (SIPS) resulting in scaffolds with macroporous morphologies, enhanced modulus and a more homogenous distribution of the PDMSstar-MA component throughout. These hybrid hydrogel scaffolds were prepared in the form of continuous gradients such that a single scaffold contains spatially varied chemical and physical properties. Thus, cell-material interaction studies may be conducted more rapidly at different “zones” defined along the gradient. These gradients are also expected to benefit the regeneration of the osteochondral interface, an interfacial tissue that gradually transitions in tissue type. The final aspect of this work was focused on enhancing the osteogenic potential of PDMS via functionalization with amine and phosphonate. Both amine and phosphonate moieties have demonstrated bioactivity. Thus, it was expected that these properties will be enhanced for amine and phosphonate functionalized PDMS. The subsequent incorporation of these PDMS-based macromers into the previously described PEG-DA scaffold system is expected to be valuable for osteochondral tissue regeneration.

No description available.

Universiẗat, Diss.--Dortmund, 2007.

Zugl.: Freiburg (Breisgau), Univ., Diss., 2007

Techn. Hochsch., Diss., 2004--Aachen.

Orientador: José Alberto Fracassi da Silva / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-20T05:22:01Z (GMT). No. of bitstreams: 1 Campos_RichardPifferSoaresde_M.pdf: 3349460 bytes, checksum: 5efdb4dd4409b9d1b6771593c8874edf (MD5) Previous issue date: 2012 / Resumo: Os micro sistemas de análise total consistem de dispositivos da ordem de centímetros que tem como objetivo a integração de várias etapas analíticas em um único chip, tais como etapas de tratamento de amostra, separação por eletroforese capilar, ou mesmo a integração de sensores em canais microfluídicos. O poli(dimetilsiloxano), PDMS, é um dos polímeros mais adotados para a fabricação destes microdispositivos, devido a suas propriedades elastoméricas, transparência óptica, permeabilidade gasosa, biocompatibilidade, fácil moldagem, relativa alta resistência química e baixo custo de fabricação, além de poder ser facilmente moldado e selado, resultando em microcanais com boa resolução. Além disso, é possível a fabricação de canais por ablação a laser sobre o polímero curado. Entretanto, a característica altamente hidrofóbica do PDMS faz com que sua aplicação para soluções aquosas seja problemática e analitos pouco polares possam sofrer forte adsorção nas paredes do canal, tornando pobre a reprodutibilidade do processo. Neste sentido, estratégias para modificar o material nativo ou mesmo a superfície dos canais vêm sendo estudadas. Neste trabalho, foi inicialmente estudada a modificação estrutural do PDMS, que consiste na utilização de um reticulante (contendo função orgânica polar metacrilato ou amina) na formação do substrato. Também foi realizada a modificação da superfície do substrato de PDMS por reação topológica, com a introdução de polietileno glicol, além da modificação do processo convencional de reticulação do PDMS Sylgard 184, pela adição do surfactante Silwet-L77 a este processo. O PDMS modificado foi avaliado quanto a sua hidrofobicidade, por medida do ângulo de contato com a água, em relação às propriedades do fluxo eletrosmótico gerado no microcanal e as modificações foram estudadas por métodos espectroscópicos. A reação de modificação de superfície do PDMS com divinil éter de polietileno glicol apresentou as melhores características hidrofílicas dentre as modificações estudadas e mobilidade do fluxo eletrosmótico com valor de 3,6x10 cm V s. Em adição, as modificações puderam ser caracterizadas por métodos de espectroscopia (IR e Raman), que se mostraram eficientes na avaliação tanto da rota de modificação quanto do produto final / Abstract: The micro total analysis systems consist of devices in the order of centimeters that aim to integrate several analytical steps on a single substrate, such as sample treatment, injection, or even integrated sensors on microfluidic channels. Poly(dimethylsiloxane), PDMS, is one of the most used polymers for microfabrication due to its elastomeric properties, optical transparency, gas permeability, biocompatility, relatively high chemical resistance and low fabrication costs. PDMS can also be easily cast and sealed, resulting in microchannels with good resolution. On top of that, it is possible to fabricate the microchannels using the lase ablation technique on the cured PDMS. However, the highly hydrophobic characteristic of PDMS makes its aqueous applications problematic. Moreover, non-polar analytes can adsorb on the channel walls, leading to poor reproducibility. In this sense, strategies to modify the raw material or channel surface have been proposed. In this work, the structural modification of PDMS, involving the use of a crosslinking agent (containing the methacrylate or amine polar functions) was studied. In addition, the surface modification of PDMS by topologic reaction with polyethylene glycol and the modification of the conventional PDMS Sylgard 184 crosslinking by the addition of Silwet-L77 surfactant were also performed. The hydrophobicity of modified PDMS was evaluated by water contact angle measurements and the modifications were studied by spectroscopic methods. The electroosmotic flow (EOF) generated in the microchannels was also evaluated. The best hydrophilic characteristic among the studied modifications were obtained with the polyethylene glycol divinyl ether PDMS modification. This device presented an EOF of 3,6x10 cm V s. In addition, the modifications could be characterized by spectroscopic methods (Raman and IR) and those techniques were efficient in the evaluation of the reaction routes as well as the final products / Mestrado / Quimica Analitica / Mestre em Química

The molecular structure and charge on solid surfaces in aqueous environments is of fundamental importance to various scientific research and applications, yet remain not sufficiently understood. The research herein uses sum frequency generation spectroscopy to reveal the molecular structure of the mineral and polymer surfaces, and also probes the water molecules near the charged aqueous interfaces to get information about the surface charge. The application of visible-infrared sum-frequency generation spectroscopy to polymer thin-films requires a careful interpretation of the results, as the electric field magnitude and phase at each interface must be determined in a manner that takes thin film interference effects into account. A straightforward method that has a concise analytic solution in the case of a single thin film that exhibits interference effects was proposed. This method enabled selective probing of transparent thin-films using sum frequency generation spectroscopy, hence eliminated the ambiguity of the contribution of signal from two interfaces. The method was then extended to multiple polarization schemes, enabling easier and more comprehensive study of the molecular orientation on thin-films. Nonlinear vibrational spectroscopy has also been used to study the temperature-dependent surface structure of polydimethylsiloxane when exposed to water and a perfluorinated hydrophobic liquid. Quantitative analysis of the methyl plane orientation was performed using a combination of vibrational peak ratios and peak amplitudes that enable proposed structures to be identified. For both environments, the tilt and twist of the methyl plane was found to increase with temperature in a reversible manner. This has been attributed to be a consequence of the backbone reorganization due to temperature-dependent density changes. At charged aqueous interfaces, the structure of water adjacent to solid interface is sensitive to the surface potential. As a result, close inspection of signals originating from these water molecules can be used to reveal the surface charge density. Nonlinear vibrational spectroscopy was used to monitor the water O-H stretching band over a temperature range of 10-75°C to account for the increase in surface potential from deprotonation. It has been demonstrated that the behavior at the silica surface is a balance between increasing surface charge, and a decreasing contribution of water molecules aligned by the surface charge. Together with a model that accounts for two different types of silanol sites, the change in enthalpy and entropy for deprotonation at each site were reported. The surface charge density of untreated polydimethylsiloxane surface in water with various ionic strengths was also determined. It was found that the surface charge could be explained with an ion adsorption model. A relationship between the surface potential and measured nonlinear optics response that is valid at high potentials and low ionic strength was proposed. Finally, a universal method was demonstrated to derive the surface potential with nonlinear optics by modulating the coherence length. / Graduate / 2022-09-07