Unspecific interactions, at the interface between a synthetic material and an aqueous biological environment, leading to irreversible protein adsorption can cause to undesired consequences. These include fouling of a boat hull or a triggered immune response. Thus, stealthy materials are a topic that has generated a great deal of interest in the scientific community. This work deals with the design of networks, nanoparticles, and surfaces containing poly(ethylene glycol) (PEG), known for its resistance to protein adsorption and non-toxic nature. Initially, PEG-based networks, hydrogels, were synthesized using photoinduced thiol-ene chemistry in order to afford coatings targeted for marine antifouling applications. By varying the length of the PEG chain, curing chemistry, cross-linker as well as hydrolytical stability, a library of hydrogel coatings was produced. The coatings were subsequently characterized with respect to curing efficiency, thermal and mechanical properties, and aqueous stability. Furthermore, the antifouling properties of coatings were evaluated using in vitro tests with proteins, marine bacteria, and diatoms. As a final test the coatings were evaluated in a four month field test. It was found that coatings comprising longer PEG chains displayed enhanced antifouling performance, compared to shorter PEGs. In addition, the choice of cross-linker, curing chemistry, and hydrolytical stability also affected the properties to a great extent. This thesis further deals with the design of amphiphilic linear dendritic hybrids, with PEG as the hydrophilic block. Using non-toxic 2,2-bis(methylol) propionic acid (bis-MPA) based dendrons, bearing click functional cores (alkyne or allyl) and peripheral hydroxyl groups, as macrointitiators for ring-opening polymerization of ε-caprolactone, a library of star branched materials was afforded. As a final step, click functional (azide or thiol) PEGs were attached using copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) or thiol-ene click chemistry. The size of the dendrons was varied from generation 0-4, along with variation of both poly(ε-caprolactone) (PCL) length and PEG length. The materials were designed in order to allow a study of the impact of the dendron generation. Finally, the hybrid materials were used for the preparation of micelles, as well as for the formation of honeycomb membranes. The micelles critical micelle concentration, size and drug loading capacity were shown to be highly dependent on the generation of the dendron. The generation of the dendron also had a profound effect on the ability of the hybrid materials to form ordered honeycomb membranes, and hybrid materials of the 3rd generation yielded the most highly ordered membranes. / Ickespecifika interaktioner vid gränsytan, mellan ett syntetiskt material och en vattenbaserad biologisk miljö, kan leda till irreversibel adsorption av proteiner. Detta kan i sin tur leda till oönskade följdeffekter, såsom beväxning på båtskrov eller trigga en immunologisk reaktion. För att motverka dessa effekter har forskare utvecklat så kallade smygmaterial. Denna avhandling behandlar design av nätverk, nanopartiklar och ytor innehållande poly(etylenglykol) (PEG), som är känt för sina smygegenskaper och för att vara icke-toxiskt. Initialt behandlar avhandlingen PEG-baserade nätverk, hydrogeler, syntetiserade med fotoinitierad tiol-enekemi, för användning som beväxningsavvisande beläggningar för marina applikationer. Genom att variera olika parametrar, såsom längden på PEG-kedjan, härdningskemin, tvärbindaren samt den hydrolytiska stabiliteten, byggdes ett bibliotek av hydrogelbeläggningar upp. Hydrogelbeläggningarna karaktäriserades sedan med avseende på härdningseffektivitet, termiska och mekaniska egenskaper, samt hydrolytisk stabilitet. Vidare studerades beläggningarnas avvisande förmåga mot proteiner, bakterier samt kiselalger. Slutligen studerades ytbeläggningarna i ett fyra månader långt fälttest. Av testerna framgick att längre PEG-kedjor gav beläggningar med bättre avvisande förmåga. Dessutom framgick att valet av tvärbindare, härdningskemi samt hydrolytisk stabilitet var av betydelse för beläggningarnas effektivitet. Denna avhandling behandlar vidare design av amfifila linjära dendritiska hybridmaterial, med PEG som den hydrofila delen. Genom att använda icke-toxiska 2,2-bis(metylol)propionsyrabaserade dendroner, med en klickfunktionalitet i kärnan (alkyne eller allyl) och perifera hydroxylgrupper, som makroinitiatorer för ringöppningspolymerisation av ε-kaprolakton byggdes ett bibliotek av material upp. För att göra materialen amfifila, kopplades klickfunktionella PEG-kedjor (azid eller tiol) till kärnan med koppar(I)-katalyserad azid-alkyn cykloadditionskemi alternativt tiol-enekemi. Storleken på dendronerna varierades från generation 0-4, dessutom varierades längden på både poly(ε-kaprolakton)- och PEG-kedjorna. Materialen designades så att inverkan av dendrongenerationen kunde studeras. Slutligen användes dessa hybridmaterial för att framställa miceller samt isoporösa filmer. Micellernas kritiska micellbildningskoncentration, storlek samt förmåga att laddas med läkemedel visade sig vara mycket beroende av dendrongenerationen. Dendrongenerationen visade sig vidare även ha stor inverkan i hybridmaterialens förmåga att självorganisera sig till en isoporös struktur och material av tredje generationen gav de mest välordnade filmerna. / QC 20101125

The environmental stability of a metal / polymer interface is essential for the durability and mechanical stability of constructions in several important areas such as the automotive, offshore, building and aerospace industries. The protective capability of a polymer film is strongly connected to its barrier properties, but the transport of water and corrosive constituents through the polymer and the subsequent processes at the metal surface are complicated to analyse in detail. The surface to be analysed is confined between two media that are impermeable to most probing particles used in conventional analytical techniques. Several methods exist to describe separate parts of the system, but few techniques work atambient pressure and have the capacity to conduct real-time analysis at relevant exposure conditions. In this work, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) in the Kretschmann geometry was successfully employed for systematic studies of metal / polymer interfaces. This technique requires the use of thin metal films deposited on an internal reflection element (IRE). Most studies were performed on aluminium, which is an important structural light-weight material, but also zinc was analysed, being frequently used for corrosion protection of steel. Upon exposure to water and electrolytes, the ATR-FTIR Kretschmann technique was found capable to monitor and to separate early deterioration related processes at the aluminium / polymer interface, including water sorption and transport of ionic species through the polymer film. Other main processes identified were the formation of corrosion products and swelling of the surface-near polymer network. To perform more comprehensive interpretations, a spectro-electrochemical method was further developed for in situ studies of the hidden metal / polymer interfaces. The ATR-FTIR Kretschmann technique was here combined with the complementary acting technique, Electrical Impedance Spectroscopy (EIS). The integrated set-up was able to provide complementary information, with ATR-FTIR Kretschmann being sensitive to the surface-near region and EIS to the whole system. For instance, metal oxidation and delamination processes can be difficult to distinguish by EIS, while on the other hand oxidation and hydration reactions on aluminiumcan be confirmed as IR bands at distinct positions. Delamination and swelling of a polymer both result in negative bands in an IR spectrum, but these processes may be distinguished by EIS as alterations in different frequency regions. While traditional chemical pre-treatments for enhanced hydrolytic stability perform excellent, they are being phased out from industrial applications due to environmental concerns and work health issues. Today there is an intense ongoing research regarding the mechanisms and performance of environmentally friendly pretreatments to develop systems of similar performance, and the analysis of the confined metal / polymer interface is crucial for this development. The capability of the integrated in situ ATR-FTIR Kretschmann and EIS set-up was therefore further applied to systems where a surface pre-treatment had been applied to the metal prior to the organic coating. Studies were first performed on vacuum-evaporated films of zinc treated with a titanium-based conversion coating and further coated with a UV-curing polymer. Alterations of the conversion layer could be detected upon exposure to the electrolyte. Also alkaline-cleaned aluminium coated with an amino-functional silane film and a thermo-curing epoxy top-coat was thoroughlycharacterized by both ATR-FTIR and IRRAS and further investigated upon exposure toelectrolyte and humid air. Changes at the hidden interface were detected upon thermal curingof the epoxy film and during exposure in electrolyte, and the in situ ATR-FTIR Kretschm annanalysis showed a high sensitivity towards alterations in the interfacial region. Complementary studies in the absence of metal could confirm a water uptake within the silane film and water-induced alterations of the siloxane network. / QC 20101222

The focus of this thesis is fundamental surface force and friction studies of silica and cellulose surfaces, performed mainly with the atomic force microscope (AFM). The normal interactions between model cellulose surfaces have been found to consist of a longer range double layer force with a short range steric interaction, the nature of which is extensively discussed. Both the surface charge and range of the steric force depend on the type of cellulose substrate used, as does the magnitude of the adhesion. Studies of friction on the same surfaces reveal that surface roughness is the determining factor for the friction coefficient, with which it increases monotonically. The absolute value, however, is determined by the surface chemistry. The above is illustrated by studies of the effect of adsorbed xyloglucan, a prospective paper additive, which is found in the cell wall of all plants. Xyloglucan is like cellulose a poly- saccharide but the effect of its adsorption was to reduce the friction significantly, while following the identical trend with surface roughness. Xyloglucan also increases the adhesion between cellulose surfaces in a time dependent manner, interpreted in terms of a diffusive bridging interaction. These facts combined provide a mechanistic explanation to contemporaneous findings about xyloglucans benefit in paper strength and formation. In air, the adhesion between e.g. particles or fibres, must be at least partially determined by the formation of capillary condensates. The dependence of capillary condensation on relative humidity is however not yet fully understood so studies have been performed to cast light on this phenomenon. Above about 60 % relative humidity the adhesion and friction increase dramatically due to the formation of large capillary condensates. The extent of the condensates depends both on the time the surfaces equilibrate, but also on the surface roughness. Harvesting of the condensate during shearing is also observed through hysteresis of the friction-load relationship. Measurements of surface forces and friction in surfactant systems show a clear relation between the adsorbed surfactant layer and the barrier force and adhesion, which in turn determine the friction. All of these interactions are critically dependent on the composition of the surfactant solution. A mixed surfactant system has been studied consisting of a trimethylammonium cationic surfactant and a polyoxyethylene nonionic surfactant. The results are interpreted in terms of current theories of adsorption and synergistic interactions. Finally, a novel technique for the in situ calibration and measurement of friction with the AFM is proposed. Comparison with lateral measurements show that the approach is successful. / QC 20100920

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Thesis (MTech. : Chemical Engineering.)--Tshwane University of Technology, 2010.

No description available.

Friction forces between protein / polyelectrolyte layers, adsorption properties of proteins, and conformational changes due to variation in electrolyte concentration have been investigated. The aim was to obtain better understanding of adsorbed layer properties, with focus on the relation between layer structure and lubrication capabilities. The major techniques used were AFM (atomic force microscope) with colloidal probe for normal force and friction measurements together with QCM-D (quartz crystal microbalance with dissipation) for measurement of adsorption and conformational changes of adsorbed layers. A comparison between some techniques for calibration of the AFM instrument for friction measurements was made to find the most suitably one for colloidal probe friction measurements in aqueous solutions. It is suggested that the normal and torsional Sader methods are preferred in combination with torsional detector sensitivity measurement, for which one new methodology has been proposed. Adsorption was studied for bovine serum albumin, cytochrome c, myoglobin and mucin, whereas conformational changes of the adsorbed layer were monitored only for mucin. It was found that it was essential to take into account bulk density and viscosity changes for correct interpretations of QCM data when studying the effect of changes in electrolyte type and concentration on preadsorbed layers of mucin, and also when having different (high) concentrations of proteins in the measuring solution. The adsorbed amount of proteins appears to depend on the strength of the surface attachment, in such a manner that a too high affinity reduces the adsorbed amount. Friction properties in aqueous solution have been studied for adsorbed layers of PEO45MEMA:METAC co-polyelectrolytes, with varying density of grafted PEO45 side chains and varying charge density, as well as for a naturally occurring polyelectrolyte (chitosan) and the glycoprotein mucin. These polymers were used to cover a wide range of different types of adsorbed layers and interactions to gain a better understanding of friction mechanisms and demands on layer properties for achieving favourable lubrication. It was found that the common features of low friction layers are that no attractive forces are present, and that excluded volume and / or electrostatic forces counteract chain interpenetration under load. / QC 20100903

Starch is a mixture of two polysaccharides, amylose (AM) and amylopectin, which occurs naturally in the form of microscopic granules that are abundantly found in tubers, roots, cereal grains and fruits. In order to bring out their functional properties as thickeners and texture enhancers, starch granules are often disrupted by heating in excess water. This process, which is referred to as gelatinisation, causes the granules to swell and exude a fraction of the starch polysaccharides, resulting in a dramatic increase in the viscosity of the starch suspension. Surfactants are known to affect the different aspects of the gelatinisation process and, in particular, the swelling properties of starch. Surfactants are also known to form helical inclusion complexes with AM, the formation of which plays an important role in many of the instances in which starch and surfactants interact. This work was carried out in order to gain insight into how the surfactant structure (head group and chain length) influences the swelling properties of starch and the molecular mechanisms behind these effects. The investigations involved the study of the temperature-induced gelatinisation of starch in the presence of surfactants as well as studies on the association of surfactants to AM in solution and the solubility of the resulting AM-surfactant complexes. Information on the extent of granule swelling upon heating was indirectly obtained by means of viscometry while insight on the molecular events taking place during gelatinisation was sought by means of differential scanning calorimetry (DSC) and confocal laser scanning microscopy (CLSM). Viscometric studies revealed that, with the exception of the cationic surfactants (alkyl trimethyl ammonium bromides), short-chain (C10, C12) surfactants induce an early swelling (swelling at lower temperatures than the control sample) in normal wheat starch granules, whereas their longer chain counterparts (C14, C16) have the opposite effect. Contrary to this finding, the effect of surfactants on the swelling of waxy wheat starch granules, an AM-free starch variety, is not influenced by the surfactant chain length but by the head group charge of the surfactant. The enhancing/restricting effect of surfactants on the swelling of normal wheat starch is not correlated to their effect on the early aspects of gelatinisation (onset of the gelatinisation transition) but is, in most cases, associated with the dissociation temperature of AM-surfactant complexes formed simultaneously as the granules gelatinise. CLSM studies revealed that, compared to a longer-chain surfactant (C16), a short-chain (C12) surfactant has the ability to penetrate further into the granule matrix during gelatinisation, which may favour its availability for interacting with different starch granule components during gelatinisation. Studies on the interactions between AM and surfactants with different chain length (C12 vs. C16) and head group (sodium sulphates vs. maltosides) revealed that the presence of a charged head group favours the water solubility of the resulting AM-surfactant complexes. However, this effect can be counteracted by the effect of the surfactant chain length: an increase in the chain length (C12 vs. C16) decreases the solubility of the complex. / QC 20100913

The number of poorly water-soluble drug substances in the pharmaceutical pipeline is increasing, and thereby also the need to design effective drug delivery systems providing high bioavailability. One favourable formulation approach is preparation of solid dispersions, where dispersing a poorly water-soluble drug in a water-soluble polymer matrix improves the dissolution behaviour and the bioavailability of the drug. However, in order to take full advantage of such formulations the impact of material properties on their performance needs to be investigated.   An experimental toolbox has been designed, and applied, for analysing the processes which govern the behaviour of solid pharmaceutical formulations in general, and that of solid dispersions in particular. For the purpose of monitoring multifaceted phenomena in situ during tablet dissolution, nuclear magnetic resonance (NMR) spectroscopy and NMR imaging are superior to many other techniques, both on macroscopic and molecular levels. The versatility of NMR with its isotope and chemical selectivity allows one to follow the influence of the original tablet properties on polymer mobilisation, drug migration and water penetration selectively. Mapping these processes on relevant time scales in dissolving tablets highlighted the gel layer inhomogeneity below the originally dry tablet surface as a key factor for drug release kinetics.   Furthermore, NMR relaxometry has been shown to provide novel information about the particle size of the drug and its recrystallisation behaviour within swelling solid dispersions. The NMR experiments have been complemented and supported by investigation of the crystalline state, the powder morphology and the surface composition of the dry solid dispersions. These experiments have been performed by X-ray photoelectron spectroscopy (XPS),  scanning electron microscopy (SEM), powder X-ray diffraction (pXRD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and dynamic contact angle (DAT) measurements.   The methods presented in this thesis provide a new avenue towards better understanding of the behaviour of solid dispersions, which in turn may result in more effective distribution of promising drug candidates despite their low water-solubility. / En allt större andel av de läkemedelssubstanser som idag är av intresse för den farmaceutiska industrin är svårlösliga i vatten. För att trots detta erhålla hög biotillgänglighet måste man utveckla beredningsformer som medger effektiv frisättning av den aktiva substansen. En lovande sådan beredningsform utgörs av fasta dispersioner, där den svårlösliga substansen finfördelas i en vattenlöslig polymer. För att utnyttja dessa dispersioners potential fullt ut måste dock materialegenskapernas inverkan på deras beteende kartläggas i större utsträckning än vad som tidigare gjorts.   En uppsättning experimentella metoder har i detta arbete utvecklats och använts för att analysera de processer som styr beteendet hos fasta läkemedelsberedningar i allmänhet, och fasta dispersioner i synnerhet. För observation av sådana processer in situ, under pågående tablettupplösning, är NMR-spektroskopi (kärnmagnetisk resonans-spektroskopi) och NMR-avbildning överlägsna många andra tekniker, både på makroskopisk och på molekylär nivå. NMR är en mångsidig metod med både isotop- och kemisk selektivitet. Genom att utnyttja dessa möjligheter kan de enskilda sambanden mellan den ursprungliga tablettens materialegenskaper och polymermobilisering, vatteninträngning och den aktiva substansens migrering följas separat. Kartläggning av dessa processer, på relevanta tidsskalor i tabletter under upplösning, påvisar att gellagrets inhomogenitet inuti den ursprungliga tabletten har stor betydelse för frisättningskinetiken.   Vidare visar sig NMR-relaxometri ge värdefull information om den aktiva substansens partikelstorlek och dess omkristallisationsbeteende i fasta dispersioner under svällning och upplösning. NMR-experimenten kompletteras med oberoende karakterisering av det kristallina tillståndet, pulvermorfologin och ytsammansättningen hos de torra fasta dispersionerna. Dessa experiment utförs med hjälp av XPS (röntgen-fotoelektronspektroskopi), SEM (elektronmikroskopi), pXRD (pulver-röntgendiffraktion), DCS (differentiell kalorimetri), FTIR (infraröd Fourier transform spektroskopi) och DAT (dynamisk kontaktvinkel) mätningar.   De metoder som presenteras i den här avhandlingen pekar mot nya vägar att nå djupare förståelse för beteendet hos fasta dispersioner, vilket i sin tur kan leda till att fler lovande läkemedelssubstanser kan distribueras effektivt trots begränsad vattenlöslighet. / QC 20100915

<p>In the research presented in this licentiate thesis the surface specific technique Vibrational Sum Frequency Spectroscopy, VSFS, combined with the Langmuir trough has been utilized to investigate Langmuir monolayers and Langmuir-Blodgett (LB) deposited mono- and bilayers of phospholipids. Their molecular structure, stability, and hydration were probed to gain additional understanding of important properties aiming at facilitating the use of such layers as model systems for biological membranes.</p><p>VSFS was applied to <em>in situ</em> studies of the degradation of Langmuir monolayers of 1,2-diacyl-phosphocholines with identical C-18 chains having various degrees of unsaturation. The time-dependent change of the monolayer area at constant surface pressure as well as the sum frequency intensity of the vinyl-CH stretch at the C=C double bonds were measured to monitor the degradation. It was shown that a rapid degradation of the monolayers of unsaturated phospholipids occurred when exposed to the laboratory air compared to the fully saturated lipid, and that the degradation could be inhibited by purging the ambient air with nitrogen. The degradation was attributed to oxidation mediated by reactive species in the air.</p><p>The molecular structure and order of Langmuir monolayers of 1,2-distearoyl-phosphocholine (18:0 PC) and their hydrating water were investigated at different surface pressures using VSFS. The spectroscopic data indicated a well ordered monolayer at all surface pressures with a more intense signal at higher pressures attributed to the subsequent increase of the number density and more ordered lipid molecules due to the tighter packing. Water molecules hydrating the headgroups or being in contact with the hydrophobic parts were observed and distinguished by their vibrational frequencies, and found to have different average orientations.</p><p>Additionally, monolayers of 18:0 PC, its fully deuterated analogue, and 1,2-distearoyl-phosphoserine (18:0 PS) were Langmuir-Blodgett (LB) deposited on CaF₂ substrates and VSFS was used to investigate the structure and order of the films as well as the hydrating water. The CH-region, water region, and lower wavenumber region containing phosphate, ester, carboxylic acid, and amine signals were probed to obtain a complete picture of the molecule. The data indicates that all deposited monolayers formed a well ordered and stable film and the average orientation of the aliphatic chains was determined using the antisymmetric methyl stretch.</p> / <p>I forskningen som presenteras i denna licentiatavhandling har den ytspecifika vibrationssumfrekvensspektroskopin, VSFS, använts tillsammans med Langmuirtråget för att studera Langmuir-monolager och Langmuir-Blod-gett (LB) deponerade monolager och bilager av fosfolipider. För att utvidga förståelsen av egenskaper som är viktiga för att underlätta användandet av dem som modellsystem för biologiska membran undersöktes såväl deras molekylära struktur som stabilitet och hydratisering.</p><p>VSFS användes för att genomföra <em>in situ</em>-studier av nedbrytningen av Langmuir-monolager av 1,2-diacyl-fosfokoliner med identiska 18 kolatomer långa sidokedjor med varierande antal omättade kol-kol-bindningar. För att övervaka nedbrytningen mättes såväl den tidsberoende förändringen av monolagernas area vid konstant yttryck som sumfrekevensintensiteten från dubbelbindningarnas CH-vibration. När monolagerna bestående av omättade fosfolipider utsattes för laboratorieluften bröts de ner hastigt jämfört med det helt mättade monolagret. Denna nedbrytning som sannolikt orsakades av reaktiva ämnen i luften kunde inhiberas fullständigt genom att ersätta den omgivande luften med kvävgas.</p><p>Den molekylära strukturen och ordningen hos Langmuir-monolager av 1,2-distearoyl-fosfokolin (18:0 PC) och deras hydratiseringsvatten undersöktes vid olika yttryck med VSFS. Den spektroskopiska datan visar att monolagerna är välordnade vid alla yttryck samt att sumfrekvenssignalens styrka ökar med ökande yttryck på grund av såväl det större antalet molekyler per ytenhet som den högre ordningen då molekylerna packas tätare. Vattenmolekyler som hydratiserar huvudgrupperna eller är i kontakt med hydrofoba delar och har olika medelorientering observerades och kunde identifieras genom sina vibrationsfrekvenser.</p><p>Vidare deponerades monolager av 18:0 PC, dess fullt deuterade analog och 1,2-distearoyl-fofsfoserin (18:0 PS) på substrat av CaF₂ och VSFS användes för att undersöka filmernas struktur och ordning såväl som hydratiseringsvattnet. CH- och vattenregionerna samt lågvågtalsområdet som innehåller fosfat-, ester-, karboxylsyra- och aminsignaler undersöktes för att få en fullständig bild av den molekylära strukturen. Data visar att alla deponerade monolager bildade en välordnad och stabil film och kolvätekedjornas medelorientering bestämdes med hjälp av signalen från den antisymmetriska metylvibrationen.</p> / QC 20100924