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This understanding of nanocellulose can be directly applied in future formulation design to use nanocellulose in polymer nanocomposites, foams, emulsions, latexes, gels and biomedical materials. / In this study, the potential of nanocellulose as a reinforcing agent in composite materials was investigated using atomic force microscopy (AFM). AFM was used to probe the mechanical properties of nanocelluloses and to investigate their interactions and adhesion in liquid media. Amplitude modulated-frequency modulated AFM was used to map the mechanical properties of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs). Results showed Young’s moduli of 90 GPa and 120 GPa for CNCs and CNFs, respectively, which are comparable to literature values determined using other methods. Additionally, colloid probe AFM was implemented to observe the interactions (attractive, repulsive, steric, adhesive) between cellulose and silica colloid probes with anionic CNCs (containing either a Na+ or H+ counterion) and cationic CNCs. Colloid probe AFM measurements were carried out in five different liquid media: two salt solutions (NaCl and CaCl2) and three surfactant solutions (cationic cetyltrimethylammonium bromide, CTAB; anionic sodium dodecyl sulfate, SDS; and nonionic Triton X100). It was found that low salt concentrations resulted in electrostatic repulsion and high adhesion, whereas the reverse was observed at high salt concentrations. On the contrary, an increased surfactant concentration and increased number of surfactant aggregates (micelles, bilayers, etc.) resulted in increased adhesion. Surprisingly, the interactions were strongly dependent on the CNC counterion as surfactant adsorption seemed to be primarily driven by electrostatic interactions; CTAB adsorbed more to anionic CNCs, SDS adsorbed more to cationic CNCs and Triton X100 adsorbed minimally to all CNCs. Electrophoretic mobility and particle size data showed complementary results to colloid probe AFM, indicating that interactions between surfactants and CNC films and CNCs in suspension are closely related. This research suggests that CNCs have potential as reinforcing agents due to their high strength and the tunability of their interactions through the simple addition of salts or surfactants. This understanding can be directly applied in future formulation design to use nanocellulose in polymer nanocomposites, foams, emulsions, latexes, gels and biomedical materials. / Thesis / Master of Applied Science (MASc) / Nanocellulose is a sustainable nanomaterial most commonly extracted from plants and trees. In recent research, nanocellulose has been shown to have potential as a reinforcing agent for materials such as plastics, foams, paints and adhesives. In this study, the potential of nanocellulose was investigated using atomic force microscopy (AFM). As predicted, AFM measurements indicated that nanocellulose has a high stiffness, supporting the substitution of this biobased material in the place of metals and synthetic fibres. AFM was also used to examine particle interactions in salt and soap-like (surfactant) solutions; changes in nanocellulose size and charge were used to support the findings. Negatively charged nanocellulose interacted more with positively charged surfactants and vice versa. Low salt and high surfactant concentrations led to high adhesion and better material compatibility, which is preferred. This understanding can help us design better nanocellulose materials for future applications.

Bundles and networks of semiflexible biopolymers are key elements in cells, lending them mechanical integrity while also enabling dynamic functions. Networks have been the subject of many studies, revealing a variety of fundamental characteristics often determined via bulk measurements. Although bundles are equally important in biological systems, they have garnered much less scientific attention since they have to be probed on the mesoscopic scale. Here, we review theoretical as well as experimental approaches, which mainly employ the naturally occurring biopolymer actin, to highlight the principles behind these structures on the single bundle level.

Nous avons étudié les propriétés volumiques de copolymères diblocs neutres-chargés dissymétriques. Ces molécules sont composées d'une courte partie neutre de poly(éthylène propylène) (PEP) ou de poly(tert-butyl styrène) (PtBs), et d'une longue partie chargée (polyélectrolyte) poly(styrène sulfonate) sodium (PSSNa) de taux de sulfonation supérieur à 80. Des expériences de diffusion de neutrons aux petits angles et de diffusion quasi-élastique de la lumière ont montré que ces copolymères s'auto-assemblent en solution aqueuse en micelles sphériques : coeur composé de l'auto-association des parties neutres en mauvais solvant, duquel émergent les parties chargées en une grande couronne qui peut être vue comme une brosse polyélectrolyte en géométrie sphérique. La forme et la taille des coeurs hydrophobes ont été trouvées invariantes en fonction de la concentration en polymère et de la concentration en électrolyte ajouté (sel monovalent, NaCl). Cette invariance a permis de déterminer les facteurs de structure des solutions (images des interactions) : les interactions électrostatiques ordonnent les solutions même dans le régime dilué (régime sans contact entre micelles). Dans le régime dilué sans sel ajouté, les parties polyélectrolytes (composant la couronne micellaire) ont été trouvées avec une conformation étendue (quasi-bâtons). Avec du sel ajouté, cette conformation devient de plus en plus flexible dès que la concentration en sel est supérieure à la concentration interne en sel d'une micelle. Dans le régime concentré sans sel ajouté, l'apparition d'un pic polyélectrolyte aux petites échelles, typique de la formation d'un semi dilué de polyélectrolytes, a été mise en évidence. De manière surprenante, cet ordre polyélectrolyte coexiste avec l'ordre entre micelles. L'influence du nombre de chaîne par micelle (nombre d'agrégation) a été discutée. Avec du sel ajouté, le pic polyélectrolyte disparaît, tandis que les solutions restent ordonnées. La distribution des contre-ions a été étudiée par des expériences de diffusion de rayons x aux petits angles. Les contre-ions Na+ ont été remplacés par d'autres contre-ions (typiquement Cs+ et TMA+) par dialyse des solutions. Dans le cas des micelles de faible nombre d'agrégation, la distribution des contre-ions a été trouvée en accord avec la distribution donnée par l'équation de Poisson-Bolztmann autour d'un bâton. Dans le cas des micelles de grand nombre d'agrégation, une forte corrélation entre contre-ions, due au recouvrement des différents nuages, a été mise en évidence. Enfin, la concentration micellaire critique (concentration à partir de laquelle des micelles existent) et l'équilibre des solutions ont été étudiés par électrophorèse capillaire. Les résultats ne sont pas encore bien compris : il existe, quelle que soit la concentration en polymère, 20% de chaînes libres (non associées en micelles).

Experiments show that MgSO4 salt has a non-monotonic effect as a function of MgSO4 concentration on the ejection of DNA from bacteriophage lambda. There is a concentration, N0, at which the minimum amount of DNA is ejected. At lower or higher concentrations, more DNA is ejected. We propose that this non-monotonic behavior is due to the overcharging of DNA at high concentration of Mg⁺² counterions. As the Mg⁺² concentration increases from zero, the net charge of ejected DNA changes its sign from negative to positive. N0 corresponds to the concentration at which DNA is neutral. Our theory fits experimental data well. The DNA-DNA electrostatic attraction is found to be -0.004 kBT/nucleotide. Simulations of DNA-DNA interaction of a hexagonal DNA bundle support our theory. They also show the non-monotonic DNA-DNA interaction and reentrant behavior of DNA condensation by divalent counterions. Three problems in understanding the capsid assembly for a retrovirus are studied: First, the way in which the viral membrane affects the structure of in vivo assembled HIV-1 capsid is studied. We show that conical and cylindrical capsids have similar energy at high surface tension of the viral membrane, which leads to the various shapes of HIV-1 capsids. Secondly, the problem of RNA genome packaging inside spherical viruses is studied using RNA condensation theory. For weak adsorption strength of capsid protein, most RNA genomes are located at the center of the capsid. For strong adsorption strength, RNA genomes peak near the capsid surface and the amount of RNA packaged is proportional to the capsid area instead its volume. Theory fits experimental data reasonably well. Thirdly, the condensation of RNA molecules by nucleocapsid (NC) protein is studied. The interaction between RNA molecules and NC proteins is important for the reverse transcription of viral RNA which relates to the viral infectivity. For strong adsorption strength of the NC protein, there is a screening effect by RNA molecules around a single NC protein.

Boîtes quantiques (QDs) et nanoparticules fluorescentes de silice (NPs) ont influencé le domaine de la bioimagerie de par leur forte luminosité et photostabilité. Par rapport aux QDs, les NPs organiques peuvent s’avérer être encore plus brillantes et entièrement biodégradables, avec une bonne biocompatibilité et sans contenir aucun élément toxique. Nous avons développé quatre types de ces NPs : en premier, des nano-gouttelettes lipidiques chargées de colorants lipophiles (flavone et Nil Rouge) pour l'imagerie in vivo chez le poisson zèbre ; en second, l’association ionique entre rhodamine B alkylée et tétraphénylborate fluoré (TPB) donne des NPs de 11-20 nm avec un rendement quantique de ~60% ; une troisième type de NPs consiste en des micelles de 7 nm obtenus par co-assemblage de cyanine amphiphiles et contre-ions TPB ; enfin, la polymérisation de micelles de calix[4]arène par agents de réticulation bi-fonctionnels à base de cyanine donne des NPs de 7 nm présentant un comportement fluorogène et une bonne stabilité en milieu intracellulaire. Ces NPs plus brillantes et de taille inférieure aux QDs apparaissent comme des outils prometteurs en bioimagerie. / Quantum dots (QDs) and fluorescent silica nanoparticles (NPs) have impacted the domain of bioimaging by their high brightness and robust photostability. In comparison to QDs, organic NPs can be even brighter and fully biodegradable, as well biocompatible and not containing toxic elements inside. Herein, we developed four types of these NPs. At first, lipid nano-droplets loaded with lipophilic flavone and Nile Red dyes for in vivo imaging in zebrafish; second, ion-association of alkyl rhodamine B with fluorinated tetraphenylborate (TPB) counterions result in 11-20 nm NPs with fluorescence quantum yield up to 60%; third, 7 nm micellar NPs obtained by co-assembly of cyanine amphiphiles with TPB counterions; finally, polymerization of calix[4]arene micelles using bi-functional cyanine crosslinkers giving 7 nm NPs, that show fluorogenic behavior and high intracellular stability. These NPs, being of smaller size and brighter than QDs, have emerged as promising tools for bioimaging.

Bundles and networks of semiflexible biopolymers are key elements in cells, lending them mechanical integrity while also enabling dynamic functions. Networks have been the subject of many studies, revealing a variety of fundamental characteristics often determined via bulk measurements. Although bundles are equally important in biological systems, they have garnered much less scientific attention since they have to be probed on the mesoscopic scale. Here, we review theoretical as well as experimental approaches, which mainly employ the naturally occurring biopolymer actin, to highlight the principles behind these structures on the single bundle level.

Polyelektrolyte (PEs) bilden eine große Klasse von Materialien, die in der wissenschaftlichen Forschung immer mehr Beachtung findet. Aufgrund der Lange-Bereich Elektrostatic ist das theoretische Verständnis von PE-Lösungen im Vergleich zu ihren neutralen Gegenstücken noch relativ schlecht gewesen, dadurch die Rationalisierung der Gegenionskondensation auf hochgeladenen PEs herausfordern. Die Komplexität des Problems wird noch zusätzlich durch die gleichzeitige Anwesenheit monovalenter und divalenter Gegenionen in der Lösung, was vielen biologische Umgebungen entspricht, erhöht. Dies beeinflusst die PE-Protein Komplexierungen, damit ihren Funktionen und Anwendungen in der Biomedizin und Biotechnologie. In dieser Arbeit führen wir eine umfassende Analyse der Ladungs- und Hydratationsstruktur von dendritischen PEs in einem monovalenten Salz unter Verwendung von atomistischen Molekulardynamik (MD) Computersimulationen mit explizitem Wasser durch. Darüber hinaus untersuchen der kompetitiven Adsorption der monovalenten und divalenten Gegenionen am globulären PE mit Hilfe theoretischer Mean-Field-Modelle, vergröberter und atomistischer (expliziter) Wasser-Simulationen und Kalorimetrie-Experimenten. Wir befassen uns mit der Herausforderung, eine genau definierte effektive Ladung und ein Oberflächenpotential der PEs für praktische Anwendungen zu finden, und präsentieren ein neuartiges kompetitives Ionenbindungsmodell, das einen aussagekräftigen Vergleich zwischen Theorie, Simulationen und Experimenten gewährleistet. Diese Arbeit stellt eine systematische elektrostatischen Beschreibung von PE vor, untersucht die thermodynamische PE-Wasser Signatur und analysiert die kompetitiven Bindung von monovalenten und divalenten Gegenionen an PEs. Es wird ein tieferer Einblick in die physikochemischen Aspekte von PE-Gegenionen- und PE-Wasser-Wechselwirkungen erhalten, was für das rationale Design von PEs auf einer gezielten Anwendungsbasis von entscheidender Bedeutung ist. / Polyelectrolytes (PEs) represent a broad class of materials that are getting an increasing attention in the scientific community. However, due to the long-range electrostatics, the theoretical understanding of PE solutions has been relatively poor compared to their neutral counterparts, thereby challenging the rationalization of the counterion condensation on highly charged PEs. Moreover, the counter-intuitive footprint of PE-water thermodynamics, and the simultaneous presence of the divalent and the monovalent counterions in the solution, as is reminiscent of many biological environments, escalates the complexity and richness of the problem. This affects the PE-proteins complexations, and thus their functions, applications in biomedicine and biotechnology. In this thesis, we conduct a comprehensive analysis of the charge and hydration structure of dendritic PEs in a monovalent salt using all-atom explicit-water molecular dynamics computer simulations, and investigate a competitive sorption of mono- versus divalent ions on globular PEs using mean-field theoretical models, all-atom and coarse-grained simulations and calorimetry experiments. We address the challenges of obtaining a well-defined effective charge and surface potential of the PE for practical applications and present a novel competitive ion binding model, ensuring a meaningful comparison between theory, simulations and experiments. This thesis lays out a systematic PE electrostatic characterization, explores PE-water thermodynamics, and analyses the competitive binding of divalent and monovalent counterions on the PE. A deeper insight into the physicochemical aspects of PE-counterion and PE-water interactions is achieved, which is vital towards the rational design of PEs on a targeted application basis.

Mixed association of calix[4]resorcinarene with ethyl sulfonate groups on the lower rim and dimethylaminomethyl groups on the upper rim (CR) and cationic surfactant 4-aza-1-hexadecyl-azoniabicyclo[2.2.2]octane bromide (DABCO-16) is studied by methods of tensiometry, conductometry, potentiometry and NMR spectroscopy at fixed CR concentration and varied surfactant concentration. Beyond ca. 0.4 mM of DABCO-16, mixed aggregates enriched by CR are proved to be formed due to electrostatic forces, while beyond ca. 5 mM, aggregates enriched by surfactant occur due to the hydrophobic effect. Spectrophotometry monitoring of the solubilization of a hydrophobic dye, Orange OT, demonstrated that only the second type of mixed aggregate enriched by DABCO-16 is capable of binding the organic probe, while the mixed system where the surfactant is a minor component shows no binding capacity towards Orange OT. This finding can be used for the design of nanocontainers with controllable binding/release properties. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.