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The quest for new smart materials with engineered properties and desired functionalities has recently driven scientists into the domain of nanotechnology. Incorporation of functional nanoparticles (NPs) into polymeric materials is an appealing research topic to generate highly ordered NP-based functional materials, which can be specifically used for flexible sensors, tunable plasmonic nanostructures for surface-enhanced Raman scattering, ultrafast switches and organic memory devices, and advanced photovoltaic devices.
Janus-type NPs, that are defined as possessing different surface chemical/physical compositions on the two sides of the particles, are a specific kind of desired building blocks to be incorporated into polymeric matrices. Due to the unique combination of amphiphilicity and particle features, they are particularly promising in the precise organization of multicomponent NPs at the interface or surface of polymer matrices with a high degree of order.
In the research presented in this thesis, we established a feasible technique to prepare Janus particles from spherical polystyrene templates with the assistance of carbon dioxide. By utilizing this approach, various types of Janus particles were designed and fabricated, with different sizes, varied Janus balances and diverse surface functionalities. Following the fabrication of Janus particles, the distribution of Janus particles within block copolymer matrices was studied with the aim to achieve highly ordered structures.
Because of their chain-like architecture, blends of chemically different homopolymers are generally known to phase separate, similar to mixtures of water and oil. In block copolymers, however, two (diblock) or more (multiblock) of such macromolecules are covalently linked to each other, thereby making it impossible to phase separate macroscopically. Indeed, phase separation of block copolymers is confined to the molecular level. By changing the molecular weight or the composition of the copolymer, phase separation of diblock copolymers leads to spontaneous formation of numerous ordered structures with sizes ranging from approximately 10 up to 100 nm. Examples include lamellar, cylindrical and spherical structures.
Increasing the complexity of the macromolecular architecture usually leads to a more complex phase behavior. Structures formed by multiblock copolymers have for instance been thoroughly studied by both experimentalists and theoreticians. Since their synthesis is rather challenging, alternative, less demanding approaches are required for real-life technological applications. Supramolecular chemistry is one of these methods. By combining linear diblock copolymers and small organic surface active molecules, comb-shaped copolymers can be prepared by simply mixing both compounds. This often leads to the formation of multiblock-like hierarchical structures, i.e. structures within another structure.
The work described in this thesis is focused on the synthesis and self-assembly of a new class of supramolecular materials, so-called double-comb diblock copolymers. Microphase separation of such complexes resulted in several new, unique hierarchical morphologies that were not observed in block copolymer-based materials before. In addition, the general observed phase behavior was found to be in excellent agreement with previously developed theoretical models.
Our planet is expecting a population growth in the coming years and so a higher demand of food production (i.e., crops) that will require higher crop yields. The demand of fertilizers (chemical or natural) is going to increase as they contain one or more of the essential elements (nutrients) necessary for plant growth: phosphorus, nitrogen, and potassium.
Urine is considered as a possible source of such nutrients because of its composition. In urine, sodium (Na+), potassium (K+) and ammonium (NH4+) are competitive cations in separation and the recovery process as they have the same valence (+1), very similar hydrated radii and very similar diffusion coefficient which renders separation by charge, size, and mobility unsuitable.
This research is based on the development and characterization of membranes selective for the recovery of potassium and ammonium - two of the essential nutrients. A membrane-based technology was chosen due to its possibilities in continuous systems as well as the feasibility to incorporate selective phases (organic and inorganic) to the polymeric matrix. Polymers, selective inorganic and organic phases and additives were studied for their chemical effects on the transport of the target nutrients across the membranes. The research performed shows that membrane technology is a promising tool for the separation and recovery of potassium and ammonium from competitive cations and that the transport mechanism is key to understand the membrane performance.
Nowadays "green" is a hot topic almost everywhere, from retailers to universities to industries; and achieving green has become a universal perspective. However, polymers are commonly considered not to be “green”, being associated with massive energy consumption and severe pollution problems (e.g. the “Plastic Soup”) as a public stereotype.
To achieve green polymers, three elements should be entailed:
(1) green raw materials, catalysts and solvents;
(2) eco-friendly synthesis processes; and
(3) sustainable polymers with a low carbon footprint, for example, (bio)degradable polymers or polymers which can be recycled or have a low environmental impact upon disposal.
By utilizing biobased monomers in enzymatic polymerizations, many advantageous green aspects can be fulfilled. For example, biobased monomers and enzyme catalysts are renewable materials which are derived from biomass feedstocks; enzymatic polymerizations are clean and energy saving processes; and no toxic residuals contaminate the final products.
Therefore, synthesis of renewable polymers via enzymatic polymerizations of biobased monomers provides an opportunity for achieving green polymers and a future sustainable polymer industry, which will eventually play an essential role for realizing and maintaining a green and sustainable society.
In recent decades, the hardware dimensions of electronic and storage devices for portable smart phones, laptops and cameras have scaled downwards, while their performance tremendously increased. To continue this trend in the near future, alternative materials need to be developed.
This research utilizes the intriguing nature of block copolymers to develop novel materials for data storage applications that are built into our everyday microelectronic devices. Block copolymers are large molecules composed of two different polymer blocks. Since both blocks are not compatible with each other (like water and oil), they phase separate on the nanoscale into domains of highly regular dots, lines or sheets, depending on the molecular architecture.
The precise self-assembly of block copolymers - used in this research - is a convenient way to build electronic devices, since the molecules arrange spontaneously into ordered structures and the dimensions and functionality can be tailored easily. In this research, we prepared block copolymers that include ferroelectric blocks.
The ability of ferroelectric materials to exist in different polarized states (“1” and “0”) and to switch the polarization in an electric field enables their application in storage devices. Our block copolymers were used to produce well-ordered ferroelectric nanofoams. Furthermore, we backfilled the polymer nanofoam with magnetic compounds to generate multiferroic materials composed of both ferroelectric and ferromagnetic domains. Potential coupling between the electric and magnetic properties will permit data to be written electrically and read magnetically.
Polymers are molecules, which consist of many repeating units (monomers). Starch and glycogen are natural polymers, and they are all around us. We use them on a daily basis but we do not understand them completely. Even though these sugars are simple concerning what they are made of (the repeating unit is glucose), they are hard to characterize. If there is a slight change in structure, polymers’ properties can vary a lot. For instance, a molecule of amylose consists of many glucose units that are connected via α-(1,4) linkages creating a long linear chain, which is insoluble in water. Whereas amylopectin actually represents a long amylose chain with many shorter chains (branches) connected to it with α-(1,6) linkages, and it is soluble in water.
In order to try to understand as much as possible about their structure and the relationship between molecular structure and the physical properties, the first steps are to create such polysaccharides. If you try to synthesize them via traditional organic chemistry, it is very hard and time consuming. Nevertheless if we copy nature and use enzymes as catalysts, the reaction is very easy. Enzymes catalyze specific things, like the formation of α-(1,4) or α-(1,6) linkages for synthetic amylose and amylopectin analogs respectively.
This thesis concentrates on the enzymatic synthesis of these analogs and their meticulous characterization with various techniques. Gathered information are used for unraveling parts of the synthesis mechanism and can be used in future for improved characterization and apprehension of natural polysaccharides.
Developments in enzymatic polymerization have been ongoing for decades. Various studies on the enzymatic synthesis of polyesters, polycarbonates, polysaccharides, polypeptides, and polyamides have been performed and some of them have been implemented on industrial scale. Lipases are the most used catalyst in the synthesis of polyesters and polyamides. Extensive studies on the kinetics and the mechanism of lipase-catalyzed synthesis of polyesters have been carried out already, but the enzymatic synthesis of polyamides has received less attention. Therefore, the current research aims to address this by focusing more on the enzymatic synthesis of polyamides in order to get a better understanding of its reaction mechanism.
Polyamides are widely used polymers in daily and industrial applications, due to their high mechanical strength and good thermal resistance. Synthesis of most polyamides involves the use of aggressive chemicals and high temperatures. Bio-catalytic approaches might be superior alternative synthesis routes, which can be performed under mild reaction conditions. In this research, the synthesis of aliphatic oligoamides (nylon-4,10, nylon-6,10, and nylon-8,10), aliphatic-aromatic oligoamides, and poly(ε-CL-co-β-lactam) was performed. These reactions were catalyzed by immobilized Fusarium solani pisi cutinase or Candida antarctica lipase B (CAL-B). Immobilized Fusarium solani pisi cutinase was prepared by two different methods: (1) physical adsorption on Lewatit (polymethyl methacrylate) beads and (2) cross-linked enzyme aggregates (CLEA).
Self-assembly of block copolymers results in intriguing nanoscale morphologies due to the repulsive interactions between the different blocks. These microphase-separated structures are of interest for possible applications in nanotechnology. Subtle changes in the chemical structure of the monomers and the copolymer architecture can lead to enhanced control of the morphologies formed or even result in exciting new morphologies. It is therefore very important to obtain a better understanding of these parameters available to access and fine-tune specific morphologies.
This research describes the investigation of several self-assembling polymer systems, focusing on binary block copolymers and supramolecular complexes using hydrogen bonding. The supramolecular complexes consist of low molecular weight amphiphiles connected to a polymer backbone.
The role of amylose-LPC inclusion complexation on the functional properties and digestibility of wheat starch(2013) Ahmadi-Abhari, Salomeh
Starch is the largest source of carbohydrates in human foods. It is a key component of staple foods like wheat, rice and potato. In addition, starch has been widely used in food products to modify texture, to control water mobility and to maintain the overall product quality during storage. Enzymatic degradation of starch results in glucose and due to this, starch in staple foods has been implicated in complications related to obesity, type II diabetes etc. Based on this, it becomes obvious that the rate of starch digestion is very important. A slow rate is considered positive since it leads to a lower metabolic stress. The present work studies wheat starch interactions with lysophosphatidylcholine (LPC) in great detail; starting with the effect on the functional properties, such as thermal properties and viscosity behavior of starch suspensions. The influence on the granular shape was observed by light microscopy, CLSM and SEM. The effect on the starch susceptibility to amylase hydrolysis was studied through a newly developed in-vitro method. The amount of reducing sugars after digestion were measured using DNSA reagent. The molecular size distribution of the starch molecules after digestion was analyzed by Size-Exclusion Chromatography. Suspensions with higher amount of LPC were more resistant to degradation at body temperature, due to higher amount of amylose-LPC inclusion complexes, as proven by a higher amount of amylose and a lower amount of reducing sugars. Iodine complexation with the digesta revealed the degree of amylose hydrolysis, proving lower digestibility of the inclusion complexes.
3D nanostructured inorganic materials appear as promising candidates for various practical applications. This thesis focuses on metal nanofoams, a novel class of 3D nanomaterials that combine the properties of metals and nanoporous materials. This unique combination allows nanoporous metal foams to be used as, for example, hydrogen storage materials, actuators, novel 3D structured batteries, substitutes for platinum group catalysts, etc.
Common approaches, such as dealloying, sol-gel synthesis, nanosmelting, combustion synthesis, etc., render metallic nanostructures with highly disordered architectures which might have adverse effects on their mechanical properties. In contrast, block copolymers have the ability to self-assemble into bicontinuous ordered nanostructures that can be applied as templates for the preparation of well-ordered metal nanofoams. The idea of block copolymer template-directed approach, relevant experimental results and future perspective will be described in this thesis. Additionally, the phase behavior of block copolymer-based supramolecular complexes, employed here as precursors to well-ordered metal nanofoams, is thoroughly examined.
Polyacrylates with pending saccharide groups (poly saccharide-acrylates) combine the properties of saccharides with the hydrophobic properties of polyacrylates. The polymers are synthesized from monofunctionalized saccharide-acrylates. The synthesis of these saccharide-acrylates is difficult or even impossible by conventional synthesis routes, because the saccharides possess multiple hydroxyl groups with more less the same reactivity. Using biocatalysts on the other hand, has the advantage of high selectivity towards the bond formation.
The goal of this PhD research is to find biocatalytic approaches that can be used for the synthesis of monofunctional saccharide-acrylates.
Several enzymes of the glycosyl-hydrolase family are found to catalyze the reaction between hydroxyl functional acrylates and saccharides. The saccharide residues are obtained from cheap raw materials, like starch and cellulose (cotton).
As a result of the high selectivity of the enzymes used, the saccharide-acrylates contain only one acrylate group per saccharide. Furthermore, the selection of the appropriate enzyme can result in saccharide-acrylates containing one glucose group, one maltose group (two glucose residues) or a mixture of one to fourteen glucose residues.
Since the saccharide-acrylates contain only one functional group per saccharide, they can successfully be polymerized using (environmentally friendly) aqueous free radical polymerization in water. The resulting poly(saccharide-acrylates) are soluble in water. In the future, the novel kind of polymers can be used in applications like for instance dispersing agents in cosmetics, drug carriers and other biomedical applications.
Amylose is a linear polysaccharide having α-(1->4)-glycosidic linkages. The single helical V-amylose has a hydrophobic cavity that enables it to include guest polymers such as polytetrahydrofuran (PTHF). Amylose-PTHF complexes were prepared via direct mixing as it is more time- and cost-effective compared to the in situ complexation via “vine-twinning polymerization”. The complexes were formed immediately upon mixing of soluble amylose and emulsified PTHF. The degree of polymerization (DPn) and the end groups of the guest PTHF influence the complexation as the mechanism seems to proceed via insertion of the guest PTHF rather than wrapping around. The complexes are stable against storage, are yet reduced in organic solvents. Ethanol-washed complexes assembled as round spherulitic structures constructed of vertically stacked round lamellae.
The high melting temperature of the complexes (tm 125-145 °C) indicates a high crystallinity. Additionally, X-ray diffraction (XRD) demonstrates that the complexed amylose is in the form of V-amylose with 6 glucose residues per helix turn (V6-amylose), possibly a mixture or an intermediate between V6I- and V6II-amylose. This structure was also observed for complexation of low DPn PTHF with PTHF-b-amylose (tm complexes 120-139 °C). However, the V6II-amylose which indicates the presence of guest PTHF in between the amylose helices was observed in PTHF-b-amylose. This indicates that the structures of the corresponding PTHF-b-[amylose-PTHF complex] seems to be influenced by the organization of the block copolymer as well as by inclusion complex formation. Other polymers such as amylose-b-PTHF-b-amylose and three-arm PTHF-b-amylose were synthesized and are also expected to act as host molecules.
In this thesis it is shown that enzymes are essential laboratory tools for the in vitro synthesis of polysaccharides with control over macromolecular properties. Here we present a method to enzymatically polymerize hyperbranched polysaccharides with control over stereoregularity, degree of branching and molecular weight. Moreover, the possibility to construct hybrid materials consisting of a hyperbranched polyglucan part connected to a synthetic substrate (e.g. polymer, surface, etc) is shown.
Using an enzymatic catalyzed tandem polymerization in which the unique properties of the enzymes potato phosphorylase and glycogen branching enzyme (GBEDG; from Deinococcus geothermalis) are combined, a hyperbranched polyglucan was polymerized consisting of (1→4) linked alfa-D-glucose residues with branches at the glucose C6 hydroxy group. In this tandem polymerization, phosphorylase catalyzes the addition of (1→4) linked alfa-D-glucose residues from a short oligosaccharide, using glucose-1-phosphate (G-1-P) as donor substrate (monomer). GBEDG introduces in situ branch points at the growing polymer chain. More specifically, GBEDG catalyzes the formation of alfa(1→6) branch points by the hydrolysis of an alfa(1→4) linked glycosidic linkage and subsequent inter- or intra-chain transfer of the non reducing terminal fragment to the C6 hydroxyl position of an alfa-glucan.
A property of phosphorylase, essential for the research as outlined in this thesis, is the donor substrate (primer) dependency. Polymerization is impossible without an oligomeric alfa(1→4) linked D-glucose primer of at least 3 glucose residues. By taking advantage of this property hybrid materials were constructed by anchoring the oligomeric primer to a substrate prior to the enzymatic tandem polymerization with. This resulted in hyperbranched multi arm structures, diblock copolymers consisting of a hyperbranched polyglucan part and hyperbranched brush polymers anchored to Si wafers.
In the past decades enzymes have become part of the chemists’ toolbox and they have proven to be effective in different organic reactions. Polymers produced by enzymes include polysaccharides, polyesters and even vinyl polymers. The synthesis of polyamides by enzymatic pathways is however not extensively studied. This project was started to synthesize polyamides by enzyme catalysis.
The enzymatic (Candida antarctica lipase B) ring-opening polymerization of b-propiolactam a 4-membered lactam ring in toluene is introduced. Optimally, the enzyme is dried for 24 hours over P2O5. A reaction at 55 °C yields enzyme with the highest DP.
Enzymatic catalysis can also be applied to the polycondensation of diesters and diamines. The polycondensation diesters and diamines is followed with ATR-FTIR spectroscopy over time. A comparison is made between the rate of amide formation by the uncatalyzed reaction and by the enzymatic reaction. At 60 °C the enzymatic reaction is slower than the non-catalyzed reaction.
Papain, a protease, catalyzes the homopolymerization and copolymerization of amino acid esters. Four hydrophobic amino acids were used, tyrosine, leucine, phenylalanine and tryptophan. A detailed analysis of the composition is done by MALDI-ToF mass spectrometry. When the chains grow longer in general more leucine is present and less tryptophan is incorporated in the chains. Tyrosine is slightly more reactive than phenylalanine. Phenylalanine produces short chains with apparently a low solubility.
Papain is able to synthesize amide bonds between amino acids and diamines. A series of monoamides based on protected glycine, phenylalanine and leucine and aromatic diamines can be synthesized catalyzed by papain.
This thesis deals with an immobilization of the most widely used lipase, Candida antarctica lipase B (Cal-B), on different types of carriers. To this end, as starting carrier, a highly porous epoxy-containing copolymer was synthesized: poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) [poly(GMA-co-EGDMA)]. The properties of immobilized enzymes are highly influenced by the copolymer properties, in particular, porosity characteristics.
The use of poly(GMA-co-EGDMA) was motivated by the presence of epoxy rings in its structure that makes this copolymer highly reactive. Hence, various modifications of epoxy-containing copolymer were carried out. The influence of the type of immobilization on enzyme loading and enzyme activity is assessed.
After modifying the starting epoxy-containing copolymer, we turned our attention to Cal-B itself and tried to develop carrierless immobilization methods. Since, it was proved that Cal-B may successfully react with epoxy groups from the poly(GMA-co-EGDMA), modification and cross-linking with epoxy-containing compounds were chosen. With these treatments, in most of cases, activity and thermal stability of the Cal-B derivatives were significantly improved.
The standard procedure to evaluate the surface topography of immobilized enzyme and to characterize the architecture down to the molecular level is enzyme immobilization on flat surfaces. In order to immobilize Cal-B on silicon surfaces, pre-treatments with aminopropyltriethoxysilane and subsequently with glutaraldehyde were performed. Final enzyme properties are strictly determined by the structure and architecture of the aminopropyltriethoxysilane film, and all subsequent steps cannot significantly change the immobilization protocol. We have found the reaction conditions that favour creation of the perfect fully-covered aminopropyltriethoxysilane monolayer.
Block copolymers spontaneously assemble into nanoscale structures (10-9 m), which makes them suitable for applications in nanotechnology. The more complex the self-assembly, the greater the number of possible applications.
In this research, the phase behaviour of triblock copolymers (three blocks) and their supramolecular complexes with the amphiphile pentadecylphenol was addressed. Both the triblock copolymers as well as the complexes form very well ordered structures indeed.
Due to the fact that the amphiphile is attached to the triblock copolymer through hydrogen bonds, it is easily washed away after structure formation, thus creating a porous structure.
A 3D network structure was found for the first time for this type of block copolymer complexes. The networks were subsequently rendered porous by washing the material with ethanol. Such nanoporous networks stretch through the entire material by definition, a property which is very important for the possible applications. It can be used as a membrane material, but also the possibility to make nanoactuators out of it will be tested soon.
|Laatst gewijzigd:||26 juli 2016 16:06|