Micro- and nano-fluidic devices represent an exciting field with a wide range of possible applications. These devices, typically made of either silica or glass, ionize when placed in contact with water. Upon the application of an electric field parallel to the wall, a flow is produced by the charged walls called the electro-osmotic flow (EOF). Since electric fields are so often used as the driving force in these devices, EOF is an extremely common phenomenon. For this reason it is highly desirable to be able to control EOF in order to optimize the functioning of these devices. One method which is quite common experimentally is the modification of the surface using polymer coatings. These coatings can be either adsorbed or grafted, and charged or neutral. The first part of this thesis looks at the role of neutral adsorbed polymer coatings for the modulation of EOF. Specifically our simulation results show that for adsorbed coatings made from a dilute polymer solution the strongest quenching of EOF is found for an adsorption strength at the phase transition for adsorption of the polymers. Further evidence is presented that shows that by using a high density of polymer solution and a polymer which has a strong attraction to the surface a very thick polymer layer can be created. Next the case of charged grafted polymer coatings is examined. The variation of the EOF with respect to several key parameters which characterize the polymer coating is investigated and compared to theory. The prediction that the electrophoretic velocity of the polymers is the same as the EOF generated by a coating made up of the same polymers is found to be false though the two values are quite close. The last section presents results which show how hydrodynamic interactions in charged polymer systems can be modeled mesoscopically without the use of explicit charges by forcing a slip between monomers and the surrounding fluid. This model is validated by simulating some surprising predictions made in the literature such as an object with no net charge having a non-zero force when subjected to an electric field, and how the velocity can even be perpendicular to the applied electric field. The thesis can be roughly divided into two topics: using polymer coatings to modulate EOF, and the free solution electrophoresis of polyelectrolytes. While EOF and free solution electrophoresis might seem unrelated it will be shown that the concepts are the same in both cases. In fact while not investigated in this thesis, the mesoscopic simulation methods for electrophoresis could be applied to the modulation of EOF with polymer coatings allowing for the simulation of longer length and time scales or more complex systems such as heterogeneously grafted colloids.

Micro- and nano-fluidic devices represent an exciting field with a wide range of possible applications. These devices, typically made of either silica or glass, ionize when placed in contact with water. Upon the application of an electric field parallel to the wall, a flow is produced by the charged walls called the electro-osmotic flow (EOF). Since electric fields are so often used as the driving force in these devices, EOF is an extremely common phenomenon. For this reason it is highly desirable to be able to control EOF in order to optimize the functioning of these devices. One method which is quite common experimentally is the modification of the surface using polymer coatings. These coatings can be either adsorbed or grafted, and charged or neutral. The first part of this thesis looks at the role of neutral adsorbed polymer coatings for the modulation of EOF. Specifically our simulation results show that for adsorbed coatings made from a dilute polymer solution the strongest quenching of EOF is found for an adsorption strength at the phase transition for adsorption of the polymers. Further evidence is presented that shows that by using a high density of polymer solution and a polymer which has a strong attraction to the surface a very thick polymer layer can be created. Next the case of charged grafted polymer coatings is examined. The variation of the EOF with respect to several key parameters which characterize the polymer coating is investigated and compared to theory. The prediction that the electrophoretic velocity of the polymers is the same as the EOF generated by a coating made up of the same polymers is found to be false though the two values are quite close. The last section presents results which show how hydrodynamic interactions in charged polymer systems can be modeled mesoscopically without the use of explicit charges by forcing a slip between monomers and the surrounding fluid. This model is validated by simulating some surprising predictions made in the literature such as an object with no net charge having a non-zero force when subjected to an electric field, and how the velocity can even be perpendicular to the applied electric field. The thesis can be roughly divided into two topics: using polymer coatings to modulate EOF, and the free solution electrophoresis of polyelectrolytes. While EOF and free solution electrophoresis might seem unrelated it will be shown that the concepts are the same in both cases. In fact while not investigated in this thesis, the mesoscopic simulation methods for electrophoresis could be applied to the modulation of EOF with polymer coatings allowing for the simulation of longer length and time scales or more complex systems such as heterogeneously grafted colloids.

Micro- and nano-fluidic devices represent an exciting field with a wide range of possible applications. These devices, typically made of either silica or glass, ionize when placed in contact with water. Upon the application of an electric field parallel to the wall, a flow is produced by the charged walls called the electro-osmotic flow (EOF). Since electric fields are so often used as the driving force in these devices, EOF is an extremely common phenomenon. For this reason it is highly desirable to be able to control EOF in order to optimize the functioning of these devices. One method which is quite common experimentally is the modification of the surface using polymer coatings. These coatings can be either adsorbed or grafted, and charged or neutral. The first part of this thesis looks at the role of neutral adsorbed polymer coatings for the modulation of EOF. Specifically our simulation results show that for adsorbed coatings made from a dilute polymer solution the strongest quenching of EOF is found for an adsorption strength at the phase transition for adsorption of the polymers. Further evidence is presented that shows that by using a high density of polymer solution and a polymer which has a strong attraction to the surface a very thick polymer layer can be created. Next the case of charged grafted polymer coatings is examined. The variation of the EOF with respect to several key parameters which characterize the polymer coating is investigated and compared to theory. The prediction that the electrophoretic velocity of the polymers is the same as the EOF generated by a coating made up of the same polymers is found to be false though the two values are quite close. The last section presents results which show how hydrodynamic interactions in charged polymer systems can be modeled mesoscopically without the use of explicit charges by forcing a slip between monomers and the surrounding fluid. This model is validated by simulating some surprising predictions made in the literature such as an object with no net charge having a non-zero force when subjected to an electric field, and how the velocity can even be perpendicular to the applied electric field. The thesis can be roughly divided into two topics: using polymer coatings to modulate EOF, and the free solution electrophoresis of polyelectrolytes. While EOF and free solution electrophoresis might seem unrelated it will be shown that the concepts are the same in both cases. In fact while not investigated in this thesis, the mesoscopic simulation methods for electrophoresis could be applied to the modulation of EOF with polymer coatings allowing for the simulation of longer length and time scales or more complex systems such as heterogeneously grafted colloids.

Micro- and nano-fluidic devices represent an exciting field with a wide range of possible applications. These devices, typically made of either silica or glass, ionize when placed in contact with water. Upon the application of an electric field parallel to the wall, a flow is produced by the charged walls called the electro-osmotic flow (EOF). Since electric fields are so often used as the driving force in these devices, EOF is an extremely common phenomenon. For this reason it is highly desirable to be able to control EOF in order to optimize the functioning of these devices. One method which is quite common experimentally is the modification of the surface using polymer coatings. These coatings can be either adsorbed or grafted, and charged or neutral. The first part of this thesis looks at the role of neutral adsorbed polymer coatings for the modulation of EOF. Specifically our simulation results show that for adsorbed coatings made from a dilute polymer solution the strongest quenching of EOF is found for an adsorption strength at the phase transition for adsorption of the polymers. Further evidence is presented that shows that by using a high density of polymer solution and a polymer which has a strong attraction to the surface a very thick polymer layer can be created. Next the case of charged grafted polymer coatings is examined. The variation of the EOF with respect to several key parameters which characterize the polymer coating is investigated and compared to theory. The prediction that the electrophoretic velocity of the polymers is the same as the EOF generated by a coating made up of the same polymers is found to be false though the two values are quite close. The last section presents results which show how hydrodynamic interactions in charged polymer systems can be modeled mesoscopically without the use of explicit charges by forcing a slip between monomers and the surrounding fluid. This model is validated by simulating some surprising predictions made in the literature such as an object with no net charge having a non-zero force when subjected to an electric field, and how the velocity can even be perpendicular to the applied electric field. The thesis can be roughly divided into two topics: using polymer coatings to modulate EOF, and the free solution electrophoresis of polyelectrolytes. While EOF and free solution electrophoresis might seem unrelated it will be shown that the concepts are the same in both cases. In fact while not investigated in this thesis, the mesoscopic simulation methods for electrophoresis could be applied to the modulation of EOF with polymer coatings allowing for the simulation of longer length and time scales or more complex systems such as heterogeneously grafted colloids.

No description available.

With the aim of developing a deeper understanding of particle behaviour within nano-hybrid materials, this thesis investigates the particle-particle and particle-polymer interactions that influence and control cellulose nanocrystal dispersion in aqueous and non-aqueous environments. / Cellulose nanocrystals (CNCs) are rigid rod-shaped nanoparticles derived from bio-based resources and are considered an emerging nanomaterial based on their commercial availability and favourable properties. CNCs have great potential as reinforcing agents in hybrid materials and composite applications if they are well-dispersed. Whereas colloidal stability is effectively described by established theories, dispersing nanoparticles from an aggregated state, and their interaction with polymers can be difficult to predict and control. Herein, the particle-particle and particle-polymer interactions that govern CNC dispersibility in aqueous and non-aqueous environments are examined. The surface chemistry, morphology and colloidal/thermal stability of CNCs from North American industrial producers were extensively characterized such that particle interactions could be reproducibly measured from a known starting material. Industrially produced CNCs compared well to those produced at the bench-scale, implying that laboratory results should be translatable to the development of new CNC-based products. To examine particle-particle interactions within dry CNC aggregates, a surface plasmon resonance-based platform was developed to monitor CNC film swelling in a range of solvents and salt solutions. Water was observed to interrupt particle-particle hydrogen bonding most effectively, however film stability, and ultimately particle aggregation, was maintained by strong van der Waals interactions. Moreover, particle spacing and overall film thickness was found to be independent of the CNC surface chemistries and surface charge densities examined, yet the rate of film swelling scaled with the ionic strength of the surrounding media. Polyethylene glycol (PEG) was used as a model, non-ionic, water-soluble polymer to investigate polymer adsorption to CNC surfaces in water. PEG did not adsorb to CNCs despite the abundance of hydroxyl groups, which is in direct contrast to silica particles that are well known to hydrogen bond with PEG. Combining the knowledge of both particle-particle and particle-polymer interactions, PEG nanocomposites reinforced with CNCs and silica were compared and particle dispersibility was related to composite performance. Although PEG does not adsorb to CNCs in aqueous environments, polymer adsorption does occur in dry polymer nanocomposites leading to good dispersibility and improved mechanical properties. Overall, the work presented here yields new insight into the forces that govern CNC dispersion and provides a foundation from which a variety of new CNC-based products can be developed. / Thesis / Doctor of Philosophy (PhD) / Using particles derived from renewable resources to reinforce plastics and other materials has the potential to make products lighter, stronger and more environmentally friendly. However, to make these products we need to understand how to control and distribute particles uniformly throughout hybrid/composite materials. This work uses particles extracted from trees and cotton, known as cellulose nanocrystals, to reveal which factors govern particle dispersion in reinforced composite materials. To do so, first the properties and performance of commercially available cellulose nanocrystals were extensively analyzed and compared to form the basis from which interactions can be understood. Next, particle films were measured in water, organic solvents and salt solutions to better understand how aggregated cellulose nanocrystals can be separated within composite materials. The interactions between water-soluble polymers and cellulose nanocrystals were then investigated to reveal how polymer adsorption impacts particle dispersibility. Finally reinforced polymer composites were prepared with uniformly distributed cellulose nanocrystals and the crystallization and mechanical properties were investigated. By developing a deeper understanding of the factors that control cellulose nanocrystal dispersion we can learn how to make a variety of new and improved environmentally conscious products.

Le microscope à force atomique (AFM) est un outil privilégié pour sonder la matière à l'échelle nanométrique. Dans cette thèse, nous l'utilisons comme instrument de mesure de force. Nous montrons que la mesure des fluctuations thermiques des ressorts permet de déterminer précisément leur raideur à condition d'utiliser un modèle qui prend en compte la forme des modes et la méthode de détection. A l'aide de nouvelle méthodes d'analyse des courbes de rétraction, nous étudions la conformation de polymères et de copolymères adsorbés, ainsi que l'interaction spécifique entre un complexe du nickel (Ni-NTA) et l'acide aminé histidine. Nous mettons en évidence des comportements inattendus en présence de liens multiples et nous en proposons une interprétation basée sur un équilibre entre formations et ruptures des liaisons. Nous présentons des premiers résultats expérimentaux concernant la transition conformationnelle de la polylysine sous étirement.

Attractive particle interactions which lead to the hetero-aggregation or 'sliming' of silicate clay gangue and valuable sulphide mineral particles are encountered in a number of hydrometallurgical and flotation processes. Sliming leads to poor recovery of the valuable minerals and high recovery of the clay gangue minerals in flotation concentrates. In the present work, the hetero-aggregation mechanism of hydrophilic mica clay mineral sericite (or muscovite) and hydrophobic chalcocite was investigated by probing the particle interactions and the prevailing interfacial chemistry under dispersion conditions where the individual chalcocite and sericite particles displayed negative zeta potentials. The mitigation/suppression of the hetero-aggregation was examined via the prudent control of dispersion conditions and pulp chemistry (i.e., pH modification and solution speciation control) and the use of two, anionic, polymeric dispersants with different molecular weight and functionality (carboxylate-substituted polyacrylamide, Cyquest 3223 and sulphonate-substituted polymaleic acid, P80 co-polymers) as dispersants. The adsorption behaviour of both polymers onto both minerals under industrially relevant suspension conditions have been quantified in terms of the polymer adsorption density and the adsorbed layer characteristics. These interfacial layer properties which impact on the mineral particles' zeta potentials and interactions, and also underpin the dispersion efficacy of polymers were characterized, using interfacial and solution analytical methods and TM-AFM imaging analysis.

In this dissertation, the mechanisms of nanosuspension stabilization via polymer adsorption on nanoparticle surface were investigated. As the electrokinetic behavior and colloidal stability depend on the surface characteristics, altering the surface adsorbed polymers affords the different surface properties of nanoparticles and leads to the insight on the mechanism of nanoparticle stabilization. Drug nanosuspensions were prepared by wet milling of drug with water as medium and polymers as stabilizers. Block copolymers were evaluated based on varying the hydrophobic and hydrophilic amounts, polymer concentration, and polymer affinity differences onto the nanoparticle surface. Specifically, block copolymers of ethylene oxide (EO) and propylene oxide (PO) with different EO chain lengths were used to modify the nanoparticle surface and investigate the mechanisms of stabilization by varying the ratio of hydrophobic (PO) and hydrophilic (EO) units. It was hypothesized that the PO chain of block copolymers adsorb at the solid-solution interface and the EO chain provides steric hindrance preventing aggregation. Block copolymer adsorption layer thicknesses were experimentally determined with adsorption layer thicknesses increasing from 4.7 to 9.5 nm as the number of EO increase from 26 to 133 monomer units. Nanoparticle aggregation occurred with insufficient polymer monolayer coverage and electrokinetic zeta potential greater than -20 mV. The amount of block copolymers on the surface of nanoparticles was quantified and the affinity of polymer adsorption increased as the copolymer hydrophobic units increased. The amount adsorbed and affinity provides a qualitative ranking of the affinities between a specific polymer and nanoparticle substrate to provide a method in determining the mechanism of stabilization, where specific functional groups for adsorption could be selected for maximum nanoparticle stability. A molecular modeling was conducted to visualize and support the mathematical model and the proposed mechanism of block copolymer adsorption onto a nanoparticle surface. The time lapse molecular modeling of a block copolymer in an aqueous media showed the hydrophobic units adsorbing onto the nanoparticle surface with the hydrophilic units projecting into the aqueous media. For the first time in pharmaceutical research, a systematic series of studies were conducted to elucidate the mechanisms of adsorption with both surface charge and polymer affinity analyses. A series of studies evaluating the adsorption properties polymer stabilizers provided useful information on how a block copolymer comprised of both hydrophilic and hydrophobic domains adsorbs onto an active pharmaceutical ingredient. A systematic set of experimental techniques were presented with novel analysis tools and predictors to construct stable nanoparticle formulations.

Στην εργασία αυτή μελετήθηκε o ρυθμός ροής υδατικών διαλυμάτων, σε διάφορα pH περιβάλλοντος, διαμέσου ενός νανοπορώδους υλικού τροποποιημένου με πολυμερικές ψήκτρες. Ειδικότερα, ερευνήθηκε το σύστημα του σύνθετου υλικού πορώδους ανοδικής αλουμίνας με πολυμερικές ψήκτρες του γραμμικού δισυσταδικού συμπολυμερούς πολύ(Ισοπρένιου)–b–πολυ(Ακρυλικού Οξέους) (ΙΑΟ). Η προσρόφηση καθώς και η κινητική προσρόφησης του IAO στο νανοπορώδες υλικό διερευνήθηκε κυρίως μέσω τεχνικών δονητικής φασματοσκοπίας. Πιο συγκεκριμένα με τεχνικές υπερύθρου μετασχηματισμού κατά Φουριέ (Fourier Transform Infrared Spectroscopy ή FT-IR), εγγύ υπερύθρου (N-IR) και Αποσβεννύμενη Ολική Ανάκλαση στο μέσο υπέρυθρο (ATR-IR). Ακόμη, με σκοπό την ποσοτικοποίηση της προσροφημένης ποσότητας του ΙΑΟ εφαρμόστηκε η τεχνική της θερμοσταθμικής ανάλυσης (TGA). Τέλος, για την απόκτηση μιας λεπτομερούς εικόνας σχετικά με τη δομή του σύνθετου νανο-πορώδους υλικού τα δείγματα χαρακτηρίστηκαν και με ηλεκτρονική μικροσκοπία (SEM/EDS). / In the present study the flow rate of aqueous solutions of different pH values through a nanoporous material functionalized with polymeric brushes was investigated using spectroscopic and thermogravimetric methods. In particular, the system under study was a composite material of porous anodic alumina with polymeric brushes of the diblock copolymer poly(Isoprene)–b–poly(Acrylic Acid) (IAO). The adsorption and adsorption kinetics of the IAO onto nanoporous alumina were explored mainly through techniques of vibrational spectroscopy. More specifically Fourier Transformed Infrared Spectroscopy (FT-IR), Near Infrared (N-IR) and Attenuated Total Reflectance (ATR-IR) were employed for this purpose. Moreover, for the quantification of the adsorbed amount of IAO, thermogravimetric analysis was applied (TGA). Finally, to obtain a comprehensive picture of the structure of the nanoporous composite materials used in this study, samples were additionally characterized by electron microscopy (SEM/EDS).