Infiltration of highly concentrated solutions into unsaturated sand is suspected to be affected by the liquid-gas interfacial tension between the resident water and that of the infiltrating solution. The wetting of non-porous solid surfaces by liquids is commonly quantified by contact angle measurements. However, it is well known that wettability of porous solids cannot be accurately obtained by optical inspection because the liquid is penetrating into the pores of the solid in question. The main objective of this investigation was to find an effective method to measure contact angle in coarse porous media such as sandy soils. In this study, we compare both static and dynamic methods to estimate the contact angle formed by solutions of varying surface tension on silica sands. In addition, the contact angle of the imbibing solutions is estimated in both dry and water-wetted sand. Experiments in this study employed three clear acrylic columns of known volume to determine contact angles using two methods, one static method and one dynamic method. The three acrylic columns were packed with the same mass of each grade of Accusand�� (40/50, 30/40, 20/30, and 12/20 grades respectively) for triplicate measurements. The solutions used in this study included (1) pure water and (2) 5 molal NaNO��� and (3) n-hexane as a reference. The static method estimated contact angles in initially dry sand of 23�� for 40/50 sand, and 30�� to 33�� for 12/20, 20/30, and 30/40 sands, with the same values obtained for both solutions. Contact angles of these solutions observed in the dynamic test, were twice those found in the static test (averaging 45�� and 62�� respectively). In the case of pre-wetted sands, dynamic imbibition with water provided an estimated contact angle of 2��, while the NaNO��� solution yielded 21�� contact. Based on relative surface tensions of water and the 5 molal NaNO���, the Young's equation predicts a contact angle of 25��. These results strongly support recent claims of effective contact angles between these miscible, but contracting, fluids. The observed data suggest that the zero contact angle assumption is a poor one even for clean dry silica sand. In a dynamic system, gravitational forces cannot be ignored in course porous media. An analytical method, used to model imbibition of the solutions into the silica sands, was both accurate and useful for estimating contact angle. / Graduation date: 2002

Interactions between single and double stranded oligonucleotides with SiO2 surfaces and the interactions between oligonucleotides and immobilized oligomers have been studied computationally. The oligonucleotide is the 18-base-pair sequence for the survival motor neuron gene SMN1. The oligomer consisted of a 50 unit 2-hydroxyethyl methacrylate (PHEMA) molecule. A linker used to tether the oligonucleotide was either a 10 Å or a 30 Å long succinimdyl 4-[N-maleimidomethyl]cyclohexane-1-caroxylate (sulfo-SMCC-Cn). The surface consisted of a SiO2 crystal that was 50 Å long and 50 Å wide, one unit thick and covered with modified-(3-aminopropyl)trimethoxysilane (m-APTMS) molecules. It was determined that explicit water, sodium counterions and excess salt were necessary to produce computationally stable oligonucleotide structures on surfaces. Artificial partial charges were introduced to the surface, and linkers, oligomers and oligonucleotides were immobilized and studied. The linkers collapsed onto a positive but not onto a negative surface. Oligomers moved closer to the SiO2 surface regardless of the surface charge. Immobilized oligonucleotides tilted significantly from an initial upright position but did not collapse completely onto the surfaces. The interactions between immobilized oligonucleotides and oligomers were examined. The number of oligomers surrounding the oligonucleotide was varied between two and four. Single stranded oligonucleotides were prevented from interacting with the surface as they were inhibited by the presence of oligomers. Double stranded oligonucleotides collapsed onto the surface when only two oligomers were present but remained upright when four oligomers were present. This was due to the four oligomers interacting with one another and effectively shielding the surface. The oligomers interacted with the bases in the single stranded oligonucleotides, making them energetically accessible. Presence of a high density of oligomers prevented the dsDNA from collapsing onto the surface. These results suggest design criteria for preparation of mixed oligonucleotide and oligomer films for use in biosensors.

Interactions between single and double stranded oligonucleotides with SiO2 surfaces and the interactions between oligonucleotides and immobilized oligomers have been studied computationally. The oligonucleotide is the 18-base-pair sequence for the survival motor neuron gene SMN1. The oligomer consisted of a 50 unit 2-hydroxyethyl methacrylate (PHEMA) molecule. A linker used to tether the oligonucleotide was either a 10 Å or a 30 Å long succinimdyl 4-[N-maleimidomethyl]cyclohexane-1-caroxylate (sulfo-SMCC-Cn). The surface consisted of a SiO2 crystal that was 50 Å long and 50 Å wide, one unit thick and covered with modified-(3-aminopropyl)trimethoxysilane (m-APTMS) molecules. It was determined that explicit water, sodium counterions and excess salt were necessary to produce computationally stable oligonucleotide structures on surfaces. Artificial partial charges were introduced to the surface, and linkers, oligomers and oligonucleotides were immobilized and studied. The linkers collapsed onto a positive but not onto a negative surface. Oligomers moved closer to the SiO2 surface regardless of the surface charge. Immobilized oligonucleotides tilted significantly from an initial upright position but did not collapse completely onto the surfaces. The interactions between immobilized oligonucleotides and oligomers were examined. The number of oligomers surrounding the oligonucleotide was varied between two and four. Single stranded oligonucleotides were prevented from interacting with the surface as they were inhibited by the presence of oligomers. Double stranded oligonucleotides collapsed onto the surface when only two oligomers were present but remained upright when four oligomers were present. This was due to the four oligomers interacting with one another and effectively shielding the surface. The oligomers interacted with the bases in the single stranded oligonucleotides, making them energetically accessible. Presence of a high density of oligomers prevented the dsDNA from collapsing onto the surface. These results suggest design criteria for preparation of mixed oligonucleotide and oligomer films for use in biosensors.

<p>Denna avhandling presenterar experimentella studier av polyelektrolytadsorption på motsatt laddade ytor, där substrat av både kiseloxid och blekt barrsulfatmassa har använts. Ett huvudsakligt syfte med denna forskning var att karaktärisera konformationen hos adsorberade skikt av katjonisk polyakrylamid (CPAM) i jämförelse med katjonisk dextran (Cdextran) och relatera denna information till inbindningskapaciteten av kolloidal kiselsyra. Ett andra syfte i denna avhandling var att studera kinetiken för sekventiell adsorption av polyamidamin epiklorhydrin (PAE) och karboxymetyl cellulosa (CMC) på massafibrer och att bestämma adsorptionsisotermer för deponering av polyelektrolyter skikt för skikt på massafibrer.</p><p>Adsorptionen av CPAM på kiseloxidytor studeras med stagnationspunkts-reflektometri och kvartskristalls-mikrogravimetri för att bestämma adsorptionskinetiken och mättnadsadsorptionens beroende av polyelektrolytens laddningstäthet, pH och NaCl koncentration. Konformationen hos adsorberade skikt av CPAM och Cdextran bestämdes både före och efter sekundär tillsats av kolloidal kiselsyra (CS) och adsorptionen av CS kvantifierades också som funktion av yttäckningen av polyelektrolyt.</p><p>Resultaten indikerar att laddningstätheten hos CPAM kontrollerar den adsorberade mängden på kiseloxidytor vid låga NaCl koncentrationer. Både adsorptionen av CPAM och Cdextran på kiseloxid visades vara effektiv i NaCl koncentrationer upp till 1 M, vilket indikerar ett signifikant bidrag av icke-jonisk interaktion mellan polyelektrolyterna och kiseloxid. Adsorptionen av CS var högre på föradsorberad CPAM än Cdextran. Konformationen hos de adsorberade skikten efter tillsats av CS sågs expandera signifikant för skikt baserade på CPAM medan skikt av Cdextran vid låga salthalter verkade återta sin konformation efter en temporär expansion.</p><p>I den andra delen av avhandlingen studerades sekventiell adsorption av PAE och CMC på massafibrer. Adsorptionsisotermer skikt för skikt på avkryllad massa visade att PAE adsorberade i större mängd än CMC, både i hänseende av massa och laddning. Adsorptionen av PAE var signifikant långsammare än CMC och adsorptionstiden till 90% av mättnadsadsorptionen bestämdes till 3 respektive 1 minut. Zetapotentialen för kryll bestämdes för adsorption av de två första polyelektrolytskikten och resultaten tydde på att kryllmaterialet omladdade inom en minut efter tillsatserna av polyelektrolyt. Reflektometriförsök inom sekventiell adsorption av PAE och CMC på kiseloxid antydde att den låga molekylviktsfraktionen av PAE störde uppbyggnaden av polyelektrolyt-multiskikten.</p> / <p>This thesis presents experimental studies of polyelectrolyte adsorption on oppositely charged surfaces, where substrates of both silica and bleached softwood kraft pulp were used. A major aim of this research was to characterise the conformation of adsorbed layers of cationic polyacrylamide (CPAM), in comparison to cationic dextran (Cdextran), and relate this information to the binding capacity of colloidal silica. A second aim in this thesis was to study the kinetics of the sequential adsorption of polyamide epichlorohydrine (PAE) and carboxymethyl cellulose (CMC) on pulp fibres, and to determine the adsorption isotherms for the layer-by-layer deposition of polyelectrolytes on pulp fibres.</p><p>The adsorption of CPAM on silica surfaces was studied using stagnation point adsorption reflectometry and quartz crystal microgravimetry to determine its adsorption kinetics as well as the dependencies of polyelectrolyte charge densities, pH, and NaCl concentration on saturation adsorption. The conformation of adsorbed layers of CPAM and Cdextran, analysed in terms of amount of water and layer thickness, was determined both before and after the secondary adsorption of colloidal silica (CS), and the adsorption of CS was also quantified as a function of the surface coverage of the polyelectrolyte.</p><p>Results indicate that the charge density of CPAM controlled the amount of the polyelectrolyte adsorbed on silica surfaces at low NaCl concentrations. The adsorption of both CPAM and Cdextran on silica was shown to be effective at up to 1 M NaCl concentrations, which indicates that non-ionic interactions between the polyelectrolytes and silica contribute significantly. CS adsorption was higher on pre-adsorbed CPAM than on Cdextran. The conformation of the adsorbed layer after CS addition was seen to expand significantly in CPAM-based layers, while the Cdextran layer appeared to restore its conformation after a temporary expansion at low salt concentrations.</p><p>In the second part of the thesis, the sequential adsorption of PAE and CMC on pulp fibres was determined using the polyelectrolyte titration technique. Layer-by-layer adsorption isotherms derived on fractionated pulp showed that PAE adsorbed in higher amounts than CMC did, both in terms of adsorbed mass and adsorbed charge. The adsorption of PAE was significantly slower compared to CMC, and the adsorption times required to reach 90% of the saturation adsorption were 3 and 1 min, respectively. The zeta potential of pulp fines was determined for the adsorption of the two first polyelectrolyte layers, and data indicated that the fines recharge within one minute after the polyelectrolyte additions. Reflectometry experiments regarding the sequential adsorption of PAE and CMC on silica indicated that the low-molecular-weight fraction of PAE disturbed the formation of polyelectrolyte multilayers.</p>

No description available.

Denna avhandling presenterar experimentella studier av polyelektrolytadsorption på motsatt laddade ytor, där substrat av både kiseloxid och blekt barrsulfatmassa har använts. Ett huvudsakligt syfte med denna forskning var att karaktärisera konformationen hos adsorberade skikt av katjonisk polyakrylamid (CPAM) i jämförelse med katjonisk dextran (Cdextran) och relatera denna information till inbindningskapaciteten av kolloidal kiselsyra. Ett andra syfte i denna avhandling var att studera kinetiken för sekventiell adsorption av polyamidamin epiklorhydrin (PAE) och karboxymetyl cellulosa (CMC) på massafibrer och att bestämma adsorptionsisotermer för deponering av polyelektrolyter skikt för skikt på massafibrer. Adsorptionen av CPAM på kiseloxidytor studeras med stagnationspunkts-reflektometri och kvartskristalls-mikrogravimetri för att bestämma adsorptionskinetiken och mättnadsadsorptionens beroende av polyelektrolytens laddningstäthet, pH och NaCl koncentration. Konformationen hos adsorberade skikt av CPAM och Cdextran bestämdes både före och efter sekundär tillsats av kolloidal kiselsyra (CS) och adsorptionen av CS kvantifierades också som funktion av yttäckningen av polyelektrolyt. Resultaten indikerar att laddningstätheten hos CPAM kontrollerar den adsorberade mängden på kiseloxidytor vid låga NaCl koncentrationer. Både adsorptionen av CPAM och Cdextran på kiseloxid visades vara effektiv i NaCl koncentrationer upp till 1 M, vilket indikerar ett signifikant bidrag av icke-jonisk interaktion mellan polyelektrolyterna och kiseloxid. Adsorptionen av CS var högre på föradsorberad CPAM än Cdextran. Konformationen hos de adsorberade skikten efter tillsats av CS sågs expandera signifikant för skikt baserade på CPAM medan skikt av Cdextran vid låga salthalter verkade återta sin konformation efter en temporär expansion. I den andra delen av avhandlingen studerades sekventiell adsorption av PAE och CMC på massafibrer. Adsorptionsisotermer skikt för skikt på avkryllad massa visade att PAE adsorberade i större mängd än CMC, både i hänseende av massa och laddning. Adsorptionen av PAE var signifikant långsammare än CMC och adsorptionstiden till 90% av mättnadsadsorptionen bestämdes till 3 respektive 1 minut. Zetapotentialen för kryll bestämdes för adsorption av de två första polyelektrolytskikten och resultaten tydde på att kryllmaterialet omladdade inom en minut efter tillsatserna av polyelektrolyt. Reflektometriförsök inom sekventiell adsorption av PAE och CMC på kiseloxid antydde att den låga molekylviktsfraktionen av PAE störde uppbyggnaden av polyelektrolyt-multiskikten. / This thesis presents experimental studies of polyelectrolyte adsorption on oppositely charged surfaces, where substrates of both silica and bleached softwood kraft pulp were used. A major aim of this research was to characterise the conformation of adsorbed layers of cationic polyacrylamide (CPAM), in comparison to cationic dextran (Cdextran), and relate this information to the binding capacity of colloidal silica. A second aim in this thesis was to study the kinetics of the sequential adsorption of polyamide epichlorohydrine (PAE) and carboxymethyl cellulose (CMC) on pulp fibres, and to determine the adsorption isotherms for the layer-by-layer deposition of polyelectrolytes on pulp fibres. The adsorption of CPAM on silica surfaces was studied using stagnation point adsorption reflectometry and quartz crystal microgravimetry to determine its adsorption kinetics as well as the dependencies of polyelectrolyte charge densities, pH, and NaCl concentration on saturation adsorption. The conformation of adsorbed layers of CPAM and Cdextran, analysed in terms of amount of water and layer thickness, was determined both before and after the secondary adsorption of colloidal silica (CS), and the adsorption of CS was also quantified as a function of the surface coverage of the polyelectrolyte. Results indicate that the charge density of CPAM controlled the amount of the polyelectrolyte adsorbed on silica surfaces at low NaCl concentrations. The adsorption of both CPAM and Cdextran on silica was shown to be effective at up to 1 M NaCl concentrations, which indicates that non-ionic interactions between the polyelectrolytes and silica contribute significantly. CS adsorption was higher on pre-adsorbed CPAM than on Cdextran. The conformation of the adsorbed layer after CS addition was seen to expand significantly in CPAM-based layers, while the Cdextran layer appeared to restore its conformation after a temporary expansion at low salt concentrations. In the second part of the thesis, the sequential adsorption of PAE and CMC on pulp fibres was determined using the polyelectrolyte titration technique. Layer-by-layer adsorption isotherms derived on fractionated pulp showed that PAE adsorbed in higher amounts than CMC did, both in terms of adsorbed mass and adsorbed charge. The adsorption of PAE was significantly slower compared to CMC, and the adsorption times required to reach 90% of the saturation adsorption were 3 and 1 min, respectively. The zeta potential of pulp fines was determined for the adsorption of the two first polyelectrolyte layers, and data indicated that the fines recharge within one minute after the polyelectrolyte additions. Reflectometry experiments regarding the sequential adsorption of PAE and CMC on silica indicated that the low-molecular-weight fraction of PAE disturbed the formation of polyelectrolyte multilayers. / QC 20101112