Evolution and Competition of Block Copolymer Nanoparticles

Nanoparticle structures formed in a mixture of diblock copolymer and solvent are investigated using a three-phase density functional model and its sharp interface approximation. A wide variety of equilibria described by localized domain patterns are quantified both numerically and analytically. Competition among multiple particles is shown to occur through mass diffusion driven by differences in chemical potential, which may or may not lead to Ostwald ripening behavior. Late stage rigid body dynamics is shown to result from interaction through dipolar fields, leading to orientational alignment and long-range attraction.NSF [DMS-1514689]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Membrane and Bioseparation

Although one of the strongest methods of purification is chromatography, the major problem of porous bed chromatography is that purification takes place using the diffusion. This will prolong the purification process and bring down the efficiency. In recent years, membrane methods have greatly overcome this limitation due to low membrane thickness, low pressure drop, and convective flow, and they are a great alternative to chromatography columns. Unfortunately, the membranes have a low surface area. For solving such problem, membrane modification with polymeric brushes and layer-by-layer adsorption in polyelectrolyte films can be attractive. Accordingly, in this chapter we introduce types of biomolecule purification methods, the best purification method, membrane modification techniques, and their limitations and assets. Also, we introduce the membrane as an attractive tool for selective purification and separation of biomolecules

A closer physico-chemical look to the Layer-by-Layer electrostatic self-assembly of polyelectrolyte multilayers

The fabrication of polyelectrolyte multilayer films (PEMs) using the Layer-by-Layer (LbL) method is one of the most versatile approaches for manufacturing functional surfaces. This is the result of the possibility to control the assembly process of the LbL films almost at will, by changing the nature of the assembled materials (building blocks), the assembly conditions (pH, ionic strength, temperature, etc.) or even by changing some other operational parameters which may impact in the structure and physico-chemical properties of the obtained multi-layered films. Therefore, the understanding of the impact of the above mentioned parameters on the assembly process of LbL materials plays a critical role in the potential use of the LbL method for the fabrication of new functional materials with technological interest. This review tries to provide a broad physico-chemical perspective to the study of the fabrication process of PEMs by the LbL method, which allows one to take advantage of the many possibilities offered for this approach on the fabrication of new functional nanomaterials.Comment: Published Pape

High-pressure rheological analysis of CO2-induced melting point depression and viscosity reduction of poly(ε-caprolactone)

High-pressure rheology has been used to assess the effects of supercritical carbon dioxide (scCO2) on the melting point (Tm) and viscosity of poly (ε-caprolactone) (PCL) over a range of temperatures and pressures up to 300 bar over a wide range of shear rates. Plots of the storage and loss moduli against temperature show a significant shift of Tm to lower temperatures in the presence of CO2, indicating that the polymer crystals melt at temperatures much lower than the ambient pressure Tm. Furthermore, a significant decrease in the viscosity of two PCL grades with different molecular weight (Mn ~ 10 kDa and 80 kDa) was also detected upon increasing the CO2 pressure to 300 bar. Experimental viscosity data were fitted to the Carreau model to quantify the extent of the plasticising effects on the zero-shear viscosity and relaxation time under different conditions. Similar analyses were conducted under high-pressure nitrogen, to compare the effects obtained in the presence of a non-plasticising gas

Development of biocompatible and “smart” porous structures using CO2-assisted processes

Dissertação apresentada para a obtenção do grau de Doutor em Engenharia Química, especialidade Engenharia da Reacção Química, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaOver the past three decades the use of supercritical carbon dioxide (scCO2) has received much attention as a green alternative in the synthesis and processing of polymers. The scope of this thesis is the development of biocompatible and “smart” porous structures using CO2-assisted processes. This thesis is organized in four main chapters. The first one reviews and highlights some potentialities of supercritical fluid technology and the following ones compile the experimental work developed. The work is divided in three main parts: in the first part (2nd chapter) a CO2-assisted phase inversion method was developed in order to prepare porous structures, namely membranes. In the second part (3rd chapter) the focus was the synthesis of “smart” polymers,especially thermo and pH sensitive polymers. Finally, these two areas were combined (4th chapter) for the preparation of “smart” porous structures. The common guide line was the preparation or processing of biodegradable and/or biocompatible materials with special emphasis on the preparation of porous matrices, namely membranes and scaffolds, with controlled morphology. For membrane preparation a new high pressure apparatus and a new high pressure cell were developed. Polysulfone membranes (a biocompatible polymer with numerous applications in the medical field) were prepared and the effect of the solvent affinity and depressurization rate in the morphology and in the performance in terms of pure water flux of the membranes was investigated. The incorporation of a foaming agent was also analyzed and the high pressure CO2 capability to swell and melt polycaprolactone (PCL) was used to produce and control the porosity and the properties of the membranes. Finally, a natural and water soluble polymer (chitosan) was processed. The presence of water in the casting solution introduced extraordinary difficulties due to the low affinity between water and CO2. To induce the phase inversion a co-solvent (ethanol)was introduced in the CO2 stream. The obtained devices (membranes and beads) were fabricated using moderate temperatures and “green” solvents (ethanol, water and CO2). The morphology and the three dimensional (3D) structures were controlled by altering the co-solvent (ethanol) composition in the CO2 non-solvent stream during the demixing induced process. Microarchitectural analysis by scanning electron microscopy identified the formation of particulate agglomerates when 10% of ethanol in the scCO2 stream was used and detected the development of porous membranes with different morphologies and mechanical properties depending on the programmed gradient mode and the entrainer percentage (2.5-5%) added to the scCO2 stream. These chitosan matrices exhibited low solubility at neutral pH conditions, with no further modifications, demonstrating their applicability in bioreactors as static (membranes) or stirred (beads) culture devices. It was also demonstrated that the current method is able to prepare, in a single-step, an implantable antibiotic release system by co-dissolving gentamicin with chitosan and the solvent. In addition, the cytotoxicity as well as the ability of these structures to support the adhesion and proliferation of human mesenchymal stem cells (hMSC) in vitro were also addressed. After 2 weeks in culture, a 9-fold increase was obtained (versus 6 of the control). More importantly, cells maintained their clonogenic potential and immunophenotype (>95% CD 105+ Cells after 7 days of culture). In this chapter, a hypothetical schematic ternary diagram for the systems polymer–solvent–CO2 is used to discuss and explain the results. Another goal of this thesis was the synthesis of “smart” polymers. Chapter 3, addresses the precipitation polymerization of a thermoresponsive hydrogel, poly(N-isopropylacrylamide)(PNIPAAm), in scCO2. This hydrogel has a transition temperature, hereinafter called low critical solution temperature (LCST), around 32 ºC in an aqueous solution, close to body temperature. A strategy of solvent-free impregnation/coating of polymeric surfaces with PNIPAAm was suggested, in order to further extend the applications of membranes or porous bulky systems. The in situ synthesis of PNIPAAm within a chitosan scaffold was tested as a proof of concept, in order to produce smart partially-biodegradable scaffolds for tissue engineering applications. The LCST was tuned by copolymerization or graft polymerization of NIPAAm with other monomers. Copolymerization with hydroxyethyl methacrylate (HEMA) was used to decrease the LCST temperature from 32.2 ºC to approximately 27.7 ºC. Cloud point measurements of CO2 + HEMA system were used to optimize the polymerization temperature. Experimental data were obtained at 40 ºC, 50 ºC and 65 ºC and pressures up to 21.1 MPa. Soave-Redlich-Kwong equation of state with Mathias-Klotz-Prausnitz mixing rule was used to model experimental results and a good correlation was achieved. To increase the LCST, polyethylene oxide (an hydrophilic polymer) was grafted to PNIPPAAm. Dual stimulus (thermo and pH responsive) hydrogels were also prepared by copolymerizing methacrylic acid with PNIPAAm. As a proof of concept fluorouracil was incorporated in the hydrogels network and their release was controlled by temperature and pH stimulus. In chapter 4 the concepts of the previous chapters were put together envisaging the preparation of“smart” functional polymeric devices with targeted physical and chemical properties namely: (i) chitosan-based dual stimulus scaffolds (temperature and pH responsive); (ii) polysulfone-based thermoresponsive membranes and (iii) polymethylmethacrylate-based membranes. The chitosan scaffolds (pH sensitive) were coated/impregnated with a thermoresponsive polymer,poly(N-isopropylacrylamide) (PNIPAAm), using scCO2 as a carrier to homogeneously distribute the hydrogels monomer within the chitosan scaffolds and as a solvent to perform the polymerization reaction.Fundação para a Ciência e Tecnologia através da bolsa de Doutoramento (SFRH/BD/16908/2004) e do projecto PTDC/CTM/70513/200

Molecular modeling the microstructure and thermodynamic properties of complex fluids

The accurate prediction of a complex fluid's equilibrium microstructure and corresponding thermodynamic properties relies on the capability to describe both the molecular level architecture and specific governing physics. This thesis makes key contributions to furthering the application and understanding of molecular models for complex bulk and inhomogeneous fluids with a specific interest in mixtures involving trace components. Such developments have potential for wide-ranging application to fields from consumer goods and medicine to energy and targeted specialized material design. In the bulk, the perturbed-chain statistical associating fluid theory (PC-SAFT), an equation of state based on Wertheim's first order thermodynamic perturbation theory (TPT1) is used to demonstrate the robustness and performance of intrinsic molecular parameters determined for a complex fluid (water) with a new fitting strategy. Experimental solubility data at ambient conditions was used to find the PC-SAFT parameters for water which where capable of reproducing water content for binary mixtures with liquid and vapor n -alkanes under a myriad of physical conditions. The model gave excellent qualitative and very good quantitative agreement without the need of a binary interaction parameter. For inhomogeneous fluids, the application of a density functional theory (DFT) also based on TPT1, is extended to model the self-assembly of amphiphilic molecules at a liquid-liquid interface. This DFT, interfacial SAFT ( i SAFT), is validated against molecular simulation results for the microstructure and interfacial tension of a simple diatomic surfactant based on the continuum oil-water-surfactant model of Telo da Gama and Gubbins. A comprehensive systematic study is conducted for characterizing the affects of part of the vast parameter space governing the fluid microstructure and observed interfacial tension. The role of surfactant structure, oil structure, surfactant concentration, nonionic cosurfactant mixtures, and temperature play in altering molecular level phenomena such as surfactant aggregation, solvent depletion, and surfactant chain conformation as a result of the balance between enthalpic and entropic driving forces are described

Nanoscale self-assembly of conjugated polyelectrolytes

Ph.DDOCTOR OF PHILOSOPH

Complex Coacervate-based Materials for Biomedicine

There has been increasing interest in complex coacervates for deriving and trans- porting biomaterials. Complex coacervates are a dense, polyelectrolyte-rich liq- uid that results from the electrostatic complexation of oppositely charged macroions. Coacervates have long been used as a strategy for encapsulation, par- ticularly in food and personal care products. More recent efforts have focused on the utility of this class of materials for the encapsulation of small molecules, pro- teins, RNA, DNA, and other biomaterials for applications ranging from sensing to biomedicine. Furthermore, coacervate-related materials have found utility in other areas of biomedicine, including cartilage mimics, tissue culture scaffolds, and adhesives for wet, biological environments. Here, we discuss the self- assembly of complex coacervate-based materials, current challenges in the intel- ligent design of these materials, and their utility applications in the broad field of biomedicine

Structural studies of supramolecular host-guest systems

Abstract This research work details a systematic study of the structure and function of supramolecular host-guest systems. Host-guest inclusion complexes were formed between β-Cyclodextrin (β-CD) and its copolymers (as hosts), with several types of guest molecules both in aqueous solution and the solid state. The research is divided into two themes; (1) structural characterization and dynamic properties of the inclusion compounds of β-CD with various guest systems in aqueous solution and the solid phase, and (2) heterogeneous adsorption and structural studies of β-CD based copolymers with various guest systems in aqueous solutions. The guest systems include alkyl and perfluoroalkyl carboxylates, perfluoroalkyl sulfonate, and p-nitrophenol (PNP) at variable experimental conditions. In the first theme (chapter 2-5), host-guest complexes in the solid state were prepared using dissolution and slow cool methods at variable host/guest mole ratios (i.e., 1:1 and 2:1). The complexes were further characterized using 19F/13C DP/MAS and CP/MAS solid-state NMR spectroscopy. The solution state complexes were prepared in D2O for structural characterization using 1H/19F NMR spectroscopy. The NMR studies were complemented using FT-IR, thermal analyses (DSC, and TGA), and powder X-ray diffraction (PXRD). Evidence for the formation of host-guest inclusion compounds (ICs) was provided using CP/MAS solids NMR spectroscopy and complexation-induced chemical shift (CIS) values of 1H/19F nuclei in aqueous solution. The β-CD/PFC ICs displayed variable guest geometry and hydration states as determined by the host-guest stoichiometry and the conformation of the guest. PFOA and SPFO form 1:1 and 2:1 ICs with β-CD, wherein the guest adopts a range of gauche and trans conformations, respectively. 1:1 host-guest complexes were concluded for short perfluorocarbon chains (i.e., PFBA) where the gauche conformation of the PFC guest in the bound state was favoured. In the second theme (chapters 6–8), β-CD based copolymers were used as host materials. The structural characterization of a soluble poly-CD material (known as HDI-1) revealed that the solution behaviour of such polymeric hosts are sensitive to the presence of guest compounds such as p-nitrophenol (PNP) (i.e. chemo-responsive), as well as temperature variations (i.e. thermo-responsive). The host-guest chemistry of the soluble poly-CD material, as studied by 2-D solution NMR and induced circular dichroism (ICD) spectroscopy, indicates that PNP was bound within the cavity sites of β-CD and the interstitial domains of the copolymer (cf. Scheme 1.6 and chapter 6). The observed responsive nature of such polymeric host materials to temperature variation and chemical potential resembles behaviour characteristic of ‘smart materials’. Herein, ‘smart materials’ refer to systems which are responsive to external stimuli (e.g. temperature and chemical). The adsorption properties of the soluble (HDI-1) and insoluble (HDI-3 and -6) poly-CD adsorbents with octyl and perfluorooctyl carboxylate and sulfonate anions were estimated using the Sips and BET models. The hydrocarbon (HC) and fluorocarbon (FC) anions form monolayer and multilayer structures at the surface of the polymeric adsorbents, respectively. The formation of layered structures was controlled by the relative hydrophobicity of the alkyl/perfluoroalkyl chains and their mutual miscibility with the adsorbent surface. Other factors include the inductive effects of the alkyl/perfluoroalkyl head groups and their interactions with aqueous solvent or dipolar domains of the adsorbent surface. The adsorbed species at the liquid-solid interface were characterized using FT-IR spectroscopy, thermal analyses, and contact angle