The goal of this research project is to determine the fractal nature, if any, which certain surface water waves exhibit when viewed on a microscopic scale. We make use of the mathematical formulation of non-viscous fluids describing their physical properties. Using these expressions and including boundary conditions for free surfaces as well as taking the surface tension into consideration, we obtain a partial differential equation describing the dynamics of surface water waves. A brief introduction to the study of fractal geometry with several examples of well-known fractals is included. An important property of fractals is their non-integral dimension. Several methods of determining the dimension of a curve are described in this paper. Our wave equation is examined under different assumptions representing the conditions of a surface water wave near its breaking point. Solutions are developed using analytical and numerical methods. We determine the dimension of 'rough' solutions using one of the methods introduced and conclude that under certain conditions, surface water waves near their breaking point exhibit a fractal structure on a microscopic scale. / Graduation date: 1994

In a first step, the surfaces of polyethylene films have been modified by grafting urethane monoacrylate monomer under UV irradiation in ambient air. For native films, this grafting was successfully realized but the grafted surface was heterogeneous. To overcome this drawback and obtain a smooth and homogeneous coating, a wet oxidation method using sodium hypochlorite through two different processes was developed. The oxidation mechanism of the PE films has been established. As a consequence of the oxidation, the wettability of the grafted films was strongly increased as measured by sessile drop technique and Wilhelmy plate method. The hydrophilicity is due to carbonyl and carboxylic groups created on the treated surface. Grafting of several formulations containing different amounts of monomer, carrier and photosensitizer was successfully evidenced by analyzing the residues obtained from PE extraction in hot toluene. Indeed, FTIR, XPS, DSC and elementary analysis showed that the polyacrylate was effectively grafted on PE pre-oxidized films. Moreover, the obtained grafted surfaces corresponding to important oxidation time were homogeneous as shown by SEM and AFM. In a second step, acrylate grafting was used to induce specific properties onto the surface. This study was focused on antibacterial effect. The process starts by a dissolution of poly(4-vinylbenzyl chloride) (PVBC) in the urethane monoacrylate monomer followed by photopolymerisation of the latter. Anchoring of different PVBC based formulations was confirmed by FTIR analysis, performed onto obtained residues after extraction in hot toluene and dichloromethane. In a last step, the grafted coatings were quaternized by using triethylamine in N, N-dimethyl formamide by a nucleophilic displacement reaction. Antibacterial effect of the quaternized samples was measured by Kirby Bauer method.

We report on a new class of nonionic, photosensitive surfactants consisting of a polar di(ethylene oxide) head group attached to an alkyl spacer of between two and eight methylene groups, coupled through an ether linkage to an azobenzene moiety. Structural changes associated with the interconversion of the azobenzene group between its cis and trans forms as mediated by the wavelength of an irradiating light source cause changes in the surface tension and self-assembly properties. Differences in saturated surface tensions (surface tension at concentrations above the CMC) were as high as 14.4 mN/m under radiation of different wavelengths. The qualitative behavior of the surfactants changed as the spacer length changed, attributed to the different orientations adopted by the different surfactants depending on their isomerization states, as revealed by neutron reflection studies. The self-assembly of these photosensitive surfactants has been investigated by light scattering, small angle neutron scattering, and cryo-TEM under different illuminations. The significant change in the self-assembly in response to different illumination conditions was attributed to the sign change in Gaussian rigidity, which originated from the azobenzene photoisomerization. / Singapore-MIT Alliance (SMA)

Recent studies showed that evaporation of water can induce surface tension gradients along the water surface and ultimately lead to convection, known as Marangoni convection. This study was devoted to visualization and characterization of the evaporation-induced, surface-tension-driven convection in water using laser-based measurement techniques. The evaporation of water at various low vapor-phase pressures in the absence of buoyancy driven flow was investigated. Strong symmetric convection was observed and its velocity field was measured using stereo particle image velocimetry. The temperature field obtained from using both a thermocouple and planar laser induced fluorescence indicated that no buoyancy driven flow was generated. The strength of the convection was found to be correlated with the evaporation rate of water. In addition, the estimated Marangoni number exceeded the critical value for onset of Marangoni convection. It can be concluded that the observed evaporative convection of water can only be Marangoni convection.

Thesis (Ph. D.)--University of Delaware, 2006. / Principal faculty advisor: Andrew V. Teplyakov, Dept. of Chemistry & Biochemistry and Raul F. Lobo, Dept. of Chemical Engineering. Includes bibliographical references.

In a first step, the surfaces of polyethylene films have been modified by grafting urethane monoacrylate monomer under UV irradiation in ambient air. For native films, this grafting was successfully realized but the grafted surface was heterogeneous. To overcome this drawback and obtain a smooth and homogeneous coating, a wet oxidation method using sodium hypochlorite through two different processes was developed. The oxidation mechanism of the PE films has been established. As a consequence of the oxidation, the wettability of the grafted films was strongly increased as measured by sessile drop technique and Wilhelmy plate method. The hydrophilicity is due to carbonyl and carboxylic groups created on the treated surface. Grafting of several formulations containing different amounts of monomer, carrier and photosensitizer was successfully evidenced by analyzing the residues obtained from PE extraction in hot toluene. Indeed, FTIR, XPS, DSC and elementary analysis showed that the polyacrylate was effectively grafted on PE pre-oxidized films. Moreover, the obtained grafted surfaces corresponding to important oxidation time were homogeneous as shown by SEM and AFM. In a second step, acrylate grafting was used to induce specific properties onto the surface. This study was focused on antibacterial effect. The process starts by a dissolution of poly(4-vinylbenzyl chloride) (PVBC) in the urethane monoacrylate monomer followed by photopolymerisation of the latter. Anchoring of different PVBC based formulations was confirmed by FTIR analysis, performed onto obtained residues after extraction in hot toluene and dichloromethane. In a last step, the grafted coatings were quaternized by using triethylamine in N, N-dimethyl formamide by a nucleophilic displacement reaction. Antibacterial effect of the quaternized samples was measured by Kirby Bauer method.

Pattern formation, i.e., the outcome of self-organization, has fascinated scientists for centuries. A large effort was devoted to understand the formation of regular patterns in dissipative structures. More recently, it appears that self-organized structures could also be achieved near equilibrium. There is a great variety of physical and chemical systems that, near equilibrium, exhibit periodic patterns. For instance, stripes or bubbles could be observed in thin films of magnetic garnet, superconducting materials, block copolymers, liquid crystals, phospholipids, and ferrofluids. Wrinkling instability of compressed rigid membranes on soft elastic substrates leads also to the formation of periodic patterns near equilibrium. Since the seminal paper of Bowden et al. (Nature 1998), various systems were proposed to generate nano- and micrometric wrinkles via the application of compressive stresses to multilayers. In addition to its purely fundamental interest, these instabilities also offer a new route to build in a simple, cost-effective, and well-defined way nano- and microstructured surfaces without the use of the traditional, robust techniques developed in the microelectronics industry. In this thesis, we develop a new system, metal-polymer-substrate trilayers, that exhibit wrinkling when heated above the glass transition temperature of the polymer. We explain in detail the mechanism at the origin of wrinkling and expand existing models to obtain a complete description of the relevant parameters that govern both the amplitude and the wavelength of the obtained pattern. In light of this, we show that by playing with the rheological properties of the polymer we are able to control precisely the geometry of the wrinkles. Furthermore, to generate surfaces with a tailor-made buckling pattern, we develop an original variant of the experiments. We tune the boundary conditions at the polymer-substrate interface by chemically patterning the substrates with regions of high and low adhesion. In this way, we obtain patterns with wrinkles being oriented differently above the sticky and the slippery regions. This last result is very surprising since it seems, at first sight, unrealistic to imagine that the chemical nature of the substrate could affect the elastic instability of the skin through a micron-thick polymer film. To explore wrinkled patterns with complex morphologies, we couple the wrinkling instability with solvent diffusion. Molecular diffusion in the polymer layer triggers the transition from an unwrinkled to a wrinkled state, provided that stimuloresponsive mutlilayers are used. The wrinkled pattern obtained is determined by the geometry of the diffusion process. To understand this surprising observation, we explain in detail how the scalar field related to the solvent concentration affects so strongly the elastic instabilities usually determined by the tensorial stress field. This mechanism allows us thus to grant exotic stress distributions which lead to very intriguing patterns (e.g. parallel or radial folds, herringbones). Interestingly, we find that under specific conditions, a hierarchical wrinkled morphology, i.e. pattern of wrinkles branching into generations of ever-higher folds, develops. We study other manifestations of hierarchical structures existing around us. In this frame, we derive a general concept that a plate constrained at one edge (with a fixed wavelength) but free at the opposite one evolves naturally to larger wavelengths to minimize its bending energy. We show theoretically that the evolution results from a compromise between the gain in bending energy and the energetic penalties related to the change of wavelength. We demonstrate the universality of these concepts by showing that our commonplace suspended curtain behaves like nanometer-thick polystyrene films deposited on water and further compressed. We close this thesis by making a short review of the main applications related to wrinkling that are already described in literature and develop in detail one of them, the use of wrinkling to investigate cell contact guidance.

The aim of this thesis work was to systematically investigate the physico-chemical properties of polyelectrolyte complexes (PECs) formed by bottle brush and linear polyelectrolytes in solution and at solid / liquid interfaces. Electrostatic self-assembly of oppositely charged macromolecules in aqueous solution is a versatile strategy to construction of functional nanostructures with easily controlled properties. Bottle brush architecture, introduced into the PEC, generates a number of distinctive properties of the complexes, related to a broad range of application, such as colloidal stability and protein repellency to name a few. To utilize these materials in a wide range of applications e.g. drug delivery, the understanding of the effects of polymer architecture and solution parameters on the properties of bottle brush PECs is of paramount importance. This thesis constitutes a systematic investigation of PECs formed by a series of cationic bottle-brush polyelectrolytes and a series of anionic linear polyelectrolytes in aqueous solution. The focus of the first part of the thesis was primarily on formation and characterization of PECs in solution, whereas the adsorption properties and adsorption kinetics of bottle-brush polyelectrolytes and their complexes was investigated in the second part of the thesis work. In particular, effects of the side-chain density of the bottlebrush polyelectrolyte, concentration, mixing ratio and molecular weigh of the linearpolyelectrolyte on formation, solution properties, stability and adsorption of PECs were addressed. The pronounced effect of the side-chain density of the bottle-brush polyelectrolyte on the properties of stoichiometric and nonstoichiometric PECs was demonstrated. Formation of PECs by bottle-brush copolymers with high density of side-chains results in small, watersoluble, molecular complexes having nonspherical shape, independent of concentration. Whereas formation of PEC-aggregates was revealed by bottle-brush polyelectrolytes with low side chain density, the level of aggregation in these complexes is controlled by polyelectrolyte concentration. The structure of the PECs formed with low molecular weight polyanions is consistent with the picture that several small linear polyelectrolyte molecules associate with the large bottle-brush. In contrast, when complexation occurs between polyanions of high molecular weigh and the bottle-brush polymers considerably larger PECs are formed, consistent with several bottle-brush polymers associating with one high molecular weight polyanion. / QC 20110516

The focus in this thesis has been to gain a fundamental understanding of how different type of salts affect preadsorbed polyelectrolytes, both natural and synthetic. The knowledge from the fundamental work is then applied on a commercial system to investigate if the efficiency can be enhanced. We built thin films using the synthetic polyelctrolytes by using layer-by layer (LbL) deposition. The formed film is commonly known as a polyelectrolyte multilayer. The LbL method allows the incorporation of proteins, polymers, polyelectrolytes with different functions and so on within the film, thus achieving multilayers with different functions. The major measuring technique used within this thesis is the quartz crystal microbalance with dissipation (QCM-D), which measures mass adsorbed on a surface including the trapped solvent and the viscoelastic properties of an adsorbed film. The QCM-D measurements were complemented with an optical technique, dual polarization interferometry (DPI), which measures the change in refractive index and thickness. From these parameters the dry mass and relative water content of the film can be calculated. The Atomic Force Microscopy (AFM) further gave information about forces acting between preadsorbed films. We investigated the effect of salt on synthetic polyelectrolyte poly(allylamine hydrochloride)/poly(sodium 4-styrenesulfonate) built with the LbL technique, thus forming polyelectrolyte multilayers. We concluded that the multilayer build-up was linear and that the internal structure of the multilayer is of a compact and rigid nature. However, the type of rinsing protocol (termination of adsorption by: salt, water and salt first followed by water) has a significant effect on the outer layer of the formed multilayer. Interestingly, the structural changes only applied when poly(allylamine hydrochloride) was at the outermost layer and the most significant when water was used. We suggest that it is only the top layer that swells due to the removal of counterions resulting in increased intrachain repulsion. We further performed two-layer model calculations with the Voight model to confirm the QCM-D results as well as a novel two layer model simulation for the DPI data in order to resolve the thickness. The model calculations were in good agreement with each other thus we concluded that only the outer layer swells for this particular multilayer system. In a related experiment we studied the adsorption of bovine submaxillary mucin (BSM), which has an important mucousal function, to different thiol modified gold surfaces as well as the effect of electrolytes (NaCl, CaCl2, LaCl3) on preadsorbed mucin to a hydrophobic thiol-modified Au surface. The salt induced an expansion at low concentrations; higher concentrations resulted in a compaction. Increasing the valence of the counter ion resultedin a compaction at low concentrations. The structural change of preadsorbed BSM was reversible for NaCl, partially reversible for CaCl2 and irreversible for LaCl3. Interestingly, the swelling of BSM could not be fully understood by using the QCM-D and thus AFM force curves of the same system were taken and the results showed that NaCl does decrease the tail length due to the effective screening of charged sites within the BSM molecule. Increasing the valence resulted in a notable compaction already at very low concentrations suggesting that the ions bind to the anionic sites on BSM. In the last work we attempted to combine the gained knowledge from the previous studies by using the LbL-buildup on an actual commercial health care application. The above-mentioned mutlilayer were used to coat polystyrene wells in order to increase the binding of immunoglobulin (IgG). The main goal was to increase the sensitivity of the conventional enzymelinked immunosorbent spot assay (ELISpot) and subsequently the modified polystyrene wells were used with the ELISpot test with human peripheral blood mononuclear cells (PBMC) to measure the cytokine response. We suggested that the main driving force for adsorption for IgG on a PAH terminated multilayer is electrostatic attraction, whereas on PSS terminated multilayer the driving force is hydrophobic. Further, we suggested that IgG  does not overcharge the surface and the linearity of the multilayer build-up is not altered when IgG is incorporated within the multilayer structure. We concluded that the cytokine response (spots) on the built multilayers regardless thickness or adsorbed IgG is significantly less than the regular polyvinyldiene fluoride (PVDF) backed ELISpot wells. We suggested that due to the compact and rigid nature of the PAH/PSS multilayer structure it is unable to form the kind of three-dimensional antibody-binding support found in the PVDF membrane. PSS terminated PAH/PSS multilayer did not induce any cytokine response whereas PAH terminated did, which suggests that PSS totally covers the surface from the cells point of view. / QC20100705

Paper and board are hydrophobized (sized) to control the spreading and absorption of waterbased inks and retard the absorption and edge penetration of liquid packaging by aqueous liquids. Alkenyl ketene dimers (AKD) and alkenyl succinic anhydride (ASA) are synthetic sizing agents that are generally used under neutral or slightly alkaline papermaking conditions. The overall objective of this thesis is to improve understanding of the internal sizing of paper and board by AKD and ASA by establishing a link between the sizing mechanism on one hand, and properties of sized papers, such as surface chemistry, wettability and friction, on the other. Fundamental research has been conducted in parallel with more applied research on laboratory and pilot papers. Significant effort has been expended to study the spreading behavior of AKD. The main instrument to characterize the surface chemical composition of AKD and ASA sized papers was X-ray photoelectron spectroscopy (XPS). By combination with time-of-flight secondary ion mass spectrometry (ToF-SIMS) we have been able to determine the lateral distribution and the chemical state of the sizing agent at the paper surface. Combined with contact angle measurements using liquids with different surface tensions, and other methods to analyze the amounts of size in paper, this has enabled us to obtain a deeper knowledge of the sizing mechanisms of AKD and ASA. The results indicate a definitive relationship between the redistribution of AKD at the surface of pilot papers and the drying profile used during papermaking. However, the spreading was not complete, as also seen on a model surface. Further spreading of AKD was shown to occur via surface diffusion in the form of an autophobic monolayer precursor. The spreading rate increased linearly with temperature and showed an inverse proportionality with respect to the melting point of the AKD. This monolayer spreading is relatively slow the diffusion coefficient being of the order 10-11 m2/s. AKD spreading was not hindered by hydrolyzed AKD (ketone) that spread as well. Moreover, AKD spread on the surface of crystalline calcium carbonate. In laboratory papers, the extractives present on CTMP fiber surfaces appeared to have enhanced the spreading of AKD when the fibers were in water. In spite of a slightly lower retention, ASA covered the surface of unfilled and PCC-filled pilot papers to a significantly higher extent than AKD. The ASA sized papers, however demonstrated slightly lower resistance to water. This was attributed to formation of hydrolyzed ASA products. The results obtained confirm the proposed sizing mechanism for ASA, where the hydrolyzed ASA plays a key role. The sizing level of these papers stored wrapped in aluminium foil at 23 °C and 5O %RH was nearly unchanged over prolonged storage time. In contrast, the papers exposed to ambient conditions suffered from sizing loss, most likely due to hydrolysis and migration. The reduction of the sizing degree was higher for the AKD than ASA sized unfilled papers and the catalytic effect of PCC contributed to the hydrolysis of AKD in PCC-filled papers. As expected, the use of sizing agent reduced the surface energy of paper. The higher the sizing degree of paper the lower the surface energy, and thus the higher the resistance to wetting. This was particularly seen in the contact angles with ethylene glycol having a lower surface tension than water. AKD significantly decreased the friction between unfilled papers, whereas ASA had no impact. This difference was attributed to surface chemical composition. Friction reduction for the AKD sized papers started at the AKD coverage normally found in paper produced for low water absorption. As expected, PCC filler increased paper-to-paper friction. / Papper och kartong hydrofoberas (limmas) för att kontrollera spridning och absorption avvattenbaserade tryckfärger och hindra kantinträngning av vattenbaserade vätskor ivätskekartong. Alkylketendimer (AKD) och alkylbärnstensyra anhydrid (ASA) är syntetiskahydrofoberingsmedel som allmänt används under neutrala eller något alkaliska förhållandenvid papperstillverkning.Arbetets övergripande målsättning var att förbättra förståelse för mäldhydrofobering avpapper och kartong med AKD och ASA genom att upprätta ett samband mellanhydrofoberingsmekanism på ena sida och ytkemi hos hydrofoberat papper och dessvätningsförmåga och friktion på den andra sidan. Grundläggande studier parallellt med mertillämpade undersökningar på laboratorie- och pilotpapper har utförts. En betydande strävanhar använts för att studera spridning av AKD. Huvudinstrumentet för att karakterisera kemisksammansättning av ytan av pilotpapper hydrofoberade med AKD och ASA var röntgenfotoelektron spektroskopi (XPS). Genom att kombinera det med sekundär jonmasspektrometri (ToF-SIMS) har lateral fördelning och kemiskt tillstånd av AKD och ASAvid en yta av papper kunnat bestämmas. Kombinerat med mätningar av kontaktvinkel medvätskor med olika ytspänning och andra metoder för att analysera halten avhydrofoberinsgmedel i papper har gjort det möjligt att erhålla djupare kunskap omhydrofoberingsmekanismer av AKD och ASA.Resultaten indikerar en klar koppling mellan omfördelning av AKD på ytan av pilotpapperoch torkningsprofil vid papperstillverkning. Emellertid, spridningen var inte fullständig, vilketvar fallet även på modellytor. Fortsatt spridning av AKD visades ske som ytdiffusion i formav ett autofobiskt monoskikt (precursor film). Spridningshastigheten ökade linjärt medtemperatur och visade omvänd proportionalitet med avseende på AKD:s smältpunkt. Dennamonoskiktspridning är relativt långsam, diffusionshastighet är i storleksordningen 10-11 m2/s.Hydrolyserat AKD (keton) hindrade inte AKD:s spridning utan spred även den. Dessutomspred AKD på ytan av kristallina kalciumkarbonat. I laboratoriepapper är extraktivämnennärvarande på ytor av CTMP fiber och tycktes ha förbättrat AKD:s spridning när fibrerna varunder vatten.ivTrots något lägre retention täckte ASA ytan av icke-fyllda och PCC-fyllda papper tillsignifikant högre grad än AKD. ASA-papperen visade dock något lägre motstånd mot vatten.Detta var hänvisat till bildning av hydrolyserade ASA-produkter. De uppnådda resultatenbekräftar den föreslagna hydrofoberingsmekanismen för ASA, där hydrolyserat ASA spelaren avgörande roll. Hydrofoberingsgraden av papper lagrade inlindade i aluminiumfolie vid23 °C och 50 RH var nästan oändrad över den förlängda lagringstiden. Som motsatsgenomgick papperen som exponerats mot omgivande atmosfärsförhållanden genomgick enminskning av hydrofoberingsgraden, troligen på grund av hydrolys och migrering. Minskningav hydrofoberingsgraden var större för icke-fyllda papper av AKD än av ASA. PCC:skatalytiska effekt bidrog till hydrolys av AKD i PCC-fyllda papper.Som förväntat reducerade användning av hydrofoberingsmedel reducerade ytenergin avpapper. Ju högre hydrofoberingsgrad desto lägre var ytenergin och därmed desto högremotstånd mot vätning. Detta sågs särskilt i kontaktvinklar med etylenglykol som har lägreytspänning än vatten.AKD minskade signifikant friktionen mellan icke-fyllda papper, medan ASA inte hadeinverkan. Denna skillnad hänfördes till skillnad i ytsammansättning. Minskning av friktion förAKD-hydrofoberade papperen påbörjades vid en sådan yttäckning av AKD som är normaltför papper tillverkat för låg vattenabsorption. Som förväntat ökade PCC-fyllmedel friktionenmellan papperen. / QC 20100817