acase@tulane.edu / Self-assembly driven by the hydrophobic effect is the fascinating phenomenon by which non-polar moieties in aqueous solution form unique structures. Perhaps the best known of these assembly processes is the creation of a micelle in water, where hydrophobic tail groups are forced inward while hydrophilic head groups are attracted to aqueous solvent. Beyond micellization, the hydrophobic effect has a strong effect on supramolecular assemblies where guest and host are driven together through the hydrophobic effect. One such supramolecular host is the deep cavity cavitand Octa-Acid (OA), which can encapsulate a hydrophobic guest. This encapsulation has potential applications in drug delivery, chemical catalysis and smart material polymer hydrogel synthesis. Molecular Dynamics simulations (MD) of this system have also been shown to demonstrate the curious phenomenon of cononsolvency, where addition of organic co- solvent causes non-monotonic changes in thermodynamic trends. Cononsolvency has been studied most notably in the literature through examining poly(n- isopropylacrylamide) (PNIPAM), which features a coil-globule-coil transition as methanol is added to aqueous solution. While current research into cononsolvency centers on structural characteristics of the solute, this research focuses on cononsolvency driving effects of the solvent itself by focusing on attributes such as the speed of sound in mixed solutions, the partial molar volume of a co-solvent and the excess chemical potential of argon in solvent mixtures. A solvent-based approach to understanding cononsolvency can reveal trends applicable to all systems, not simply characteristics of one system at a time. Through this research, we uncover structural signatures correlating with cononsolvency. These new insights not only give a more thorough understanding of hydrophobic guest-host assembly, but into the hydrophobic effect and the nature of solvation. / 1 / Alexander Saltzman

archives@tulane.edu / Solubility is the ability of a molecule to favorably interact with a solvent. While seemingly simple in application many phenomena arise from knife-edge like conditions between solubility and insolubility. Herein, three of these phenomena; co-non-solvency, the hydrophobic effect, and the direct and reverse Hofmeister effects are investigated in detail to parse out a mechanistic view of solubility in each case. The first phenomenon, co-non-solvency, is the insolubility of a thermo-responsive polymer and a mixture of two good cosolvents. Host-guest systems are used to probe small molecule interactions in the presence of cosolvents for co-non-solvent effects. The second phenomenon, the hydrophobic effect, is often colloquially described as “oil and water do not mix.” However, this is much more complex when diving into the energetic contributions. Host-guest systems are used to determine structural effects novel hosts and guests have on the hydrophobic effect in collaboration with the computational community. The third phenomenon, the Hofmeister effects, are explored through the fine tuning of solubility of lysozyme through the addition of sodium perchlorate in varying pHs. This is used to determine a mechanistic view of protein solubility in the presence of salts. / 1 / Nicholas Ernst

The blending or mixing is extensively utilized in diverse processes of polymers to bring about advantageous properties, but the behavior becomes intriguing when associations are involved and multi-solvents are used. Explanations based on chemistry-specific arguments are less than satisfactory in abstracting essential features, and lack the general applicability across various systems. So, this work focuses on capturing the physical force governing the phenomenon of interest by using a generic model. Highly non-trivial behaviors of polymers are often observed in multi-solvent solutions. It is known that polymers swell and dissolve in good solvents, while they tend to collapse and aggregate in poor solvents. But for some specific systems, polymers that collapse in two different poor solvents become soluble in their mixtures, corresponding to cosolvency, and conversely, polymers that swell in two different good solvents become insoluble in their mixtures, pertaining to cononsolvency. The finding suggests that cononsolvency effect relies on the interplay between polymer-cosolvent preferential adsorptions and solvent-cosolvent attractions, which are typically investigated individually. The utilization of cononsolvency effect can either modify or induce micellization, leading to significant differences in morphology and thermodynamic properties compared to conventional micelles driven solely by hydrophobic interactions. The cosolvency project reveals that it arises from the cross competitions of Van der Waals-type interactions and the associative interaction (e.g., hydrogen bonding). The molecular association has long been a classical problem in physical chemistry, as it often gives rise to ”abnormal” phenomena, such as the elevation of boiling points due to hydrogen bonding. But the understanding of its effect on polymer system still remains rudimentary. So, this work tries to answer three fundamental questions by choosing three representative systems: 1. How will supramolecular complexations change the thermodynamics equilibrium morphology; 2. What is the impact of supramolecular bonds on the free energy landscape during the transition process; 3. How will association influence the single chain coil-globule conformational transition. It is found that the association not only results in versatile morphology, but also brings about distinct transition pathways. Besides, the conformational transition shows the dependence on the association pattern, which is actually decided by the statistical nature.

Title: The Study of Dynamic Behaviour and Interactions During the Tempera- ture-Induced Phase Separation in Polymer Solutions Author: Hana Kouřilová Department / Institute: Charles University in Prague, Faculty of Mathemat- ics and Physics, Department of Macromolecular Physics Supervisor of the doctoral thesis: doc. RNDr. Lenka Hanyková, Dr. Abstract: 1 H and 13 C high-resolution NMR spectroscopies were used for the phase separation investigation in three types of polymer solutions: i) poly(N -isopropylmethacrylamide)/D2O/ethanol with or without negatively charged comonomer sodium methacrylate, ii) random copolymers poly(N -isopro- pylmethacrylamide-co-acrylamide) in D2O, D2O/ethanol and D2O/acetone and iii) D2O solutions of polymer mixtures poly(N -isopropylmethacrylamide)/poly(N - vinylcaprolactam). For i) cononsolvency effect and influence of temperature on the phase separation was studied. Differences between mesoglobules formed as a consequence of cononsolvency effect and of temperature were found. While inside the cononsolvency-induced mesoglobules no bound ethanol molecules were detect- ed, in the mesoglobules formed by the effect of temperature ethanol molecules were present. The charge introduced into the polymer chains strenghtens polymer- solvent interactions. For ii) mesoglobules were found to be...

Cononsolvency occurs if a mixture of two good solvents causes the collapse or demixing of polymers into a polymer-rich phase in a certain range of compositions of these two solvents. The better solvent is usually called cosolvent and another common solvent is called solvent. So far, the phase-transition mechanism behind cononsolvency is still rather controversially debated in literature. In this thesis, I experimentally investigated the cononsolvency effect of poly(N-isopropylacrylamide) (PNiPAAm) brushes with different grafting density in aqueous alcohol mixtures. I have used Vis-spectroscopic ellipsometry measurements and proved the hypothesis that the cononsolvency transition of PNiPAAm brushes consists of a volume phase-like equilibrium transition. I found a strong collapse transition in PNiPAAm brushes followed by a reentry behavior as observed by ellipsometry measurements. Using a series of alcohols with increasing alkyl-chain length I have demonstrated that the cononsolvency effect is enhanced and shifted to smaller volume fractions of the alcohol. Particularly for the alcohol with increasing hydrophobic property this is correlated with an increasing tendency of demixing between the cosolvent and water. This is apparently in contrast to the hypothesis of strongly associative solvents being the origin of the cononsolvency effect. The hypothesis of preferential adsorption, on the other hand, can account for this case by assuming an increasing hydrophobically driven adsorption of the cosolvent on the polymer chains. The recently proposed adsorption-attraction model based on the concept of preferential adsorption, can be used to predict the corresponding phase-transition behavior. In particularly the model predictions for variation of the grafting density is in agreement with the experimental findings. However, to reflect the imperfect mixing of the longer alcohols in water as well as finite miscibility of the polymers in the common solvent, extensions of the model have to be considered. I have shown that the simplest extension of the model taking into account the Flory-Huggins parameter for polymer and water can account for the qualitative changes observed for temperature changes in my experiments. Both a theoretical analysis and experimental observations show that the phase-transition mechanism of cononsolvency depends on the relative strengths of various interactions in the polymer solutions. A cononsolvency transition can be driven by a strong cosolvent-solvent attraction or by the preferential adsorption of cosolvent onto the polymer. By an extension of the adsorption-attraction model, I report on a comprehensive and quantitative theoretical study of the cononsolvency effect of neutral polymers such as PNiPAAm brushes, macro-gels and single long chains. The extended adsorption-attraction model is able to describe and predict the phase-transition behaviors of these systems in various aqueous alcohol solutions quantitatively. My analysis showed that besides the dominant role of polymer-cosolvent preferential adsorption and the monomer-cosolvent-monomer triple contacts (cosolvent-assisted temporary cross-linking effect) that define the strength of the collapse-transition in the cosolvent-poor region, other effects are shown to be of relevance: The non-ideal mixing between polymer and solvent plays a role in shifting the collapse transition to the lower-concentration region of cosolvent, and an increase of the demixing tendency between cosolvent and solvent on the polymer chains reduces the window width of the cononsolvency transition. Using data from my own experiments and literature I can show that the cononsolvency response of brushes, gels and single long polymer chain can be consistently described with the same model. The model parameters are consistent with their microscopic interpretation. In addition, weakening of the cononsolvency transition in cosolvent-poor aqueous solutions at high hydrostatic pressure can be explained by the suppression of demixing tendency between cosolvent and water, and between polymer and water in the case of PNiPAAm. An investigation of the grafting-density effect in the cononsolvency transition of grafted PNiPAAm polymer, showed that a decrease of grafting density at the collapse state as well as the temperature is fixed, the swollen polymer chains can show various morphologies not limited to collapse brush. In addition, my experimental results clearly showed that the strongest collapse state can be only realized by polymer brushes with moderate grafting densities. My results display the universal character of the cononsolvency effect with respect to series of cosolvents and show that PNiPAAm brushes display a well-defined and sharp collapse transition. This is most pronounced for 1-propanol as cosolvent which is still fully miscible in water. Potential applications are switches built from implementation of brushes in pores and similar concave geometries can be realized by harnessing the cononsolvency effect of stimuli-responsive polymers such as PNiPAAm. As an example of application of cononsolvency effect of grafted polymers, different molecular-weight PNiPAAm polymers are grafted around the rim of solid-state nanopores by using grafting-to method. I demonstrate that small amounts of ethanol admixed to an aqueous solution can trigger the translocation of fluorescence DNA through polymer-decorated nanopores. I can identify the cononsolvency effect as being responsible for this observation which causes an abrupt collapse of the brush by increasing the alcohol content of the aqueous solution followed by a reswelling at higher alcohol concentration. For the first time, I provide a quantitative method to estimate hydrodynamic thickness of a polymer layer which is grafted around the rim of nanopores. Regardless of the grafting density of a grafted PNiPAAm polymer layer around the rim of nanopores, in the alcohol-tris buffer mixtures, the polymer layer displays solvent-composition responsive behaviors in the range of metabolic pH values and room temperatures. Although in this study PNiPAAm was chosen as a model synthetic polymer, I believe in that the conclusions made for PNiPAAm can be also in general extended to other synthetic polymers as well as to biopolymers such as proteins. As a proof of concept of using synthetic polymers to mimic biological functions of cell-membrane channels, my study clearly transpired that cononsolvency effect of polymers can be used as a trigger to change the size of nanopores in analogy to the opening and closure of the gates of cell-membrane channels.:Chapter 1 Background and motivation 4 1.1 Liquid-liquid phase separation 4 1.2 Polymer phase separation in a pure solvent 5 1.3 Polymer phase separation in mixtures of two good solvents 10 1.4 Characterizing cononsolvency transition in experimental study 14 1.5 Research motivation 16 Chapter 2 Phase behaviors of PNiPAAm brushes in alcohol/water mixtures: A combined experimental and theoretical study 17 2.1 Introduction 17 2.2 Materials and Methods 17 2.2.1 Materials 17 2.2.2 Preparation of Polymer Brushes 18 2.2.3 VIS-Spectroscopic Ellipsometry Measurement 18 2.2.4 Determining a polymer brush’s overlap grafting density 19 2.2.5 Test of PNiPAAm solubility in short-chain polyols 20 2.3 The adsorption-attraction model 20 2.4 Equilibrium behavior of cononsolvency transition of PNiPAAm brushes 22 2.5 Role of volume of solvent molecules in the swelling of PNiPAAm brushes 24 2.6 Cononsolvency transition of PNiPAAm brushes in aqueous solutions of a series of alcohol 24 2.7 Isomer effect of alcohol in the cononsolvency transition of PNiPAAm brushes 27 2.8 Role of alcohol-water interaction in the cononsolvency transition of PNiPAAm polymers 28 2.9 Temperature effect in the cononsolvency transition of PNiPAAm brushes 30 2.10 Grafting-density effect in the cononsolvency transition of PNiPAAm brushes 33 2.11 Octopus-shape-micelle morphology of grafted PNiPAAm polymers 34 2.12 Chapter summary 35 2.13 Chapter appendix 37 2.13.1 Data extraction and reprocessing for the molar Gibbs free energy of mixing 37 2.13.2 Temperature effect in the cononsolvency transition of PNiPAAm gels 37 Chapter 3 The extended adsorption-attraction model 41 3.1 Introduction 41 3.2 An extension of the adsorption-attraction model 43 3.3 Numerical solution of the extended adsorption-attraction model 47 3.4 Validation of the extended adsorption-attraction model 50 3.4.1 Cononsolvency transition of polymer brushes and macro-gels in different alcohol-water mixtures 51 3.4.2 An analysis of the enthalpic interaction between cosolvent and solvent 57 3.4.3 The window width of the cononsolvency transition 60 3.4.4 Pressure effect in the cononsolvency transition of PNiPAAm polymers 61 3.4.5 Cononsolvency transition of a single long polymer 65 3.5 Chapter summary 66 3.6 Chapter appendix 67 3.6.1 Chemical potential change of mixing two components 67 3.6.2 The Enthalpic Wilson model 68 3.6.3 Estimation of effective Flory-interaction parameter 73 3.6.4 Crosslink-density effect in the cononsolvency transition of poly(N-isopropylacrylamide) micro-gel and macro-gel 74 3.6.5 Pressure effect on the dimensionless chemical potential change (μ) 75 3.6.6 Pressure effect on the cosolvent-solvent interaction (χcs) 76 3.6.7 Pressure effect on the polymer-solvent interaction (χps) 77 3.6.8 Chemical potential change of DMSO/water mixtures 78 Chapter 4 Gating the translocation of DNA through poly(N-isopropylacrylamide) decorated nanopores using the cononsolvency effect in aqueous environments 80 4.1 Introduction 80 4.2 Methods 80 4.2.1 Preparation of polymer-grafted gold membrane 80 4.2.2 Translocation experiments of fluorescence λ-DNA through nanopores 82 4.2.3 Method of identification and counting of DNA translocation events 84 4.3 Results and discussion 86 4.3.1 Grafting density effect on the swollen behaviors of PNiPAAm polymers around the rim of nanopores 86 4.3.2 Switching effect of polymer chains around the rim of nanopores in the tri-buffer/ethanol mixtures 88 4.3.3 Switching effect of polymer brushes on the flat surface in the tri-buffer/ethanol mixtures 92 4.3.4 An attempt of numerical fit of experimental data using the extended adsorption-attraction model 94 4.4 Chapter summary 95 4.5 Chapter appendix 96 4.5.1 An estimation of grafting density 96 4.5.2 The method of processing data 97 Chapter 5 Concluding remarks and outlooks 100 5.1 Concluding remarks 100 5.2 Outlooks: A preliminary discussion of the cononsolvency transition of polymer solutions 102 References and notes 108 List of figures 119 List of tables 128 Acknowledgements 130 List of publications 131 Erklärung 132

La poly(2-isopropyl-2-oxazoline) (PIPOZ) est un polymère thermosensible qui possède une température de solution critique inférieure (LCST) autour de 40 °C en solution aqueuse. Les travaux présentés s’intéressent aux propriétés en solution aqueuse et aux interfaces, de l’homopolymère PIPOZ, d’une PIPOZ fonctionnalisée avec un groupement lipidique (lipo-PIPOZ) et de copolymères à blocs à base de poly(éthylène glycol) et de PIPOZ. Si elle est régulièrement comparée à son isomère structurel le poly(N-isopropylacrylamide) (PNIPAM), les études sur les propriétés en solution de la PIPOZ sont cependant moins complètes que celles sur le PNIPAM. Le premier objectif des travaux présentés ici est de parfaire la connaissance du comportement en solution de la PIPOZ en présence d’additifs. Les effets de sels et de solvants hydromiscibles sur la solubilité de la PIPOZ ont été investigués par turbidimétrie et microcalorimétrie sur trois homopolymères de masses moléculaires différentes. Contrairement aux solutions de PNIPAM, l’ajout de méthanol à la solution de PIPOZ ne conduit pas au phénomène de cononsolvency où la solubilité du polymère diminue pour une certaine gamme de fractions volumiques de cosolvant. L’effet a néanmoins été observé dans le cas de système PIPOZ/Eau/THF. L’effet de sels sur la solubilité de la PIPOZ suit la série Hofmeister. La présence de sels chaotropes (NaI et NaSCN) en solution ont révélé un effet bien plus important sur la solubilité de la PIPOZ que pour son isomère. Les valeurs de point troubles de la solution de PIPOZ augmentent de plus de 30 °C pour une concentration en sel supérieure à 1 M. L’autre objectif de cette thèse est de synthétiser un système à base de PIPOZ capable de s’auto-assembler à l’interface air-eau afin de former des films interfaciaux par la technique Langmuir-Blodgett. A cette fin, un amorceur contenant un groupement lipidique (2 chaînes alkyles et un groupement phosphate) a été synthétisé et utilisé pour la polymérisation cationique par ouverture de cycle (CROP) du monomère 2-isopropyl-2-oxazoline conduisant à l’obtention d’un lipo-PIPOZ (Mn = 10 kg.mol-1). L’effet de deux sels (NaSCN et NaCl) sur les films interfaciaux a été étudié. Malgré leur effet opposé sur la solubilité de la PIPOZ en solution, ils conduisent tous les deux à l’expansion de la monocouche de lipo-PIPOZ. Transférés sur des substrats de mica, ces films ont été visualisés par microscopie à force atomique (AFM). La iv présence de sels dans la sous-phase lors de la formation de monocouches conduit à la formation d’agrégats d’épaisseur ~ 10 nm dont le diamètre augmente avec la concentration en sel. Enfin, le dernier objectif est de caractériser les propriétés en solutions de copolymères à blocs PIPOZ-b-PEG-b-PIPOZ. La polymérisation par CROP de la 2-isopropyl-2-oxazoline a été amorcée à partir d’un PEG (Mn = 2 kg.mol-1) bifonctionnel, Le polymère synthétisé (TrOH, Mn = 11 kg.mol-1) a ensuite subit une fonctionnalisation des extrémités de chaînes par des groupements octadécyles conduisant à l’obtention d’un copolymère à blocs téléchélique amphiphile et thermosensible (TrC18). Les propriétés des copolymères en solution aqueuse ont été étudiées par turbidimétrie, diffusion dynamique de la lumière (DLS), microcalorimétrie (DSC), microscopie électronique à transmission et spectroscopie à sonde fluorescente, FT-IR et AFM. Les deux copolymères sont thermosensibles et présentent des valeurs de points troubles de ~ 48 °C pour le copolymère TrOH et de ~ 38 °C pour le copolymère amphiphile. Ce dernier s’auto-assemble à température ambiante et forme, en solution aqueuse, des micelles de type fleurs de rayon hydrodynamique RH ~ 8 nm. L’effet prolongé de la température sur la cristallisation des blocs de PIPOZ a aussi été examinée. Les deux polymères cristallisent en solution aqueuse conduisant à la formation de fibres insolubles dans l’eau. Mots- / Poly(2-isopropyl-2-oxazoline) (PIPOZ) is a thermosensitive polymer whose lower critical solution temperature (LCST) in water is ~ 40 °C. This thesis focuses on the properties in aqueous solution and on interfaces of new poly(2-isopropyl-2-oxazoline) systems. PIPOZ is often compared to its structural isomer, the renowned poly(N-isopropylacrylamide) (PNIPAM). If PNIPAM has been the center of thermosensitive polymer research for the last three decades, it is PIPOZ which has recently been gaining interest. The first aim of the thesis is to improve on the knowledge on PIPOZ properties in aqueous solution in the presence of water-soluble additives. Effect of salts and cosolvents were investigated by turbidimetry and microcalorimetry (DSC) on PIPOZ homopolymers of different molecular weights. Effect of salts on PIPOZ solubility follows the Hofmeister series. Chaotropic anions (SCN-, I-) induce a large increase (up to 30 °C) of the cloud point temperature of PIPOZ solution which is 10 times larger than for PNIPAM. Adding methanol into PNIPAM aqueous solution leads to a decrease in solubility of the polymer. This phenomena is called cononsolvency. Unlike PNIPAM solutions, the addition of methanol in PIPOZ solution does not lead to a cononsolvency effect. Nevertheless, cononsolvency has been observed in the case of THF addition into PIPOZ aqueous solutions. The second aim of this work was to design and synthesize an amphiphilic PIPOZ able to anchor itself at the air-water interface and to form stable monolayer via the Langmuir-Blodgett technique. For that purpose, a lipidic initiator containing two alkyl chains and a phosphate group, was synthesized and used to initiate the cationic ring opening polymerization (CROP) of 2-isopropyl-2-oxazoline. The obtained amphiphilic (lipo-PIPOZ, Mn = 10 kg.mol-1) forms stable monolayers at the air-water interface. The presence of salt (NaCl or NaSCN) in the sub-phase during the compression of the films leads to expansion of the monolayer even if the salts have opposite effect on PIPOZ solubility in solution. The interfacial films were then transferred onto mica substrates and captured by atomic force microscopy (AFM). The salts induced the formation of aggregates (height ~ 10 nm) whose diameter depends on the salt and its concentration. At last, a block copolymer, TrOH, containing a central poly(ethylene glycol) (PEG) (Mn = 2 kg.mol-1) and two PIPOZ blocks was obtained by CROP of 2-isopropyl-2-oxazoline initiated vi by a bi-functionnal PEG. The total molecular weight was Mn ~ 11 kg.mol-1. Hydrophobic chain ends modification has been performed onto TrOH to bring amphiphilicity and to get a telechelic octadecyl-end capped block copolymer TrC18. The properties of these two block copolymers in water were characterized by dynamic light scattering (DLS), microcalorimetry (DSC), electronic transmission microscopy (TEM) and fluorescence spectroscopy, FT-IR and AFM. Cloud point temperature of copolymer solutions was found to be around 48 °C for TrOH and around 38°C for the amphiphilic analogue TrC18. The latter self-assembles at room temperature into flower micelles whose hydrodynamic radius is RH ~ 8 nm. Extended heating of both copolymer solutions leads to crystallization of PIPOZ block and insoluble fibers form in solution.