Memory effects in liquid crystal elastomers

Free-standing monodomain liquid crystal elastomer samples are shown to have a complete memory of the orientational configuration at the time of cross-linking. This memory is demonstrated through samples in which the parent polymer system is first aligned in a magnetic field prior to cross-linking. These films show reversible nematic-isotropic phase transitions and x-ray scattering patterns characteristic of nematic phases. The liquid crystal elastomer films exhibit a remarkable memory effect, in that the sample may be held at temperatures well above the nematic-isotropic transition for extended periods ( > 2 weeks), but on cooling into the liquid crystal phase region, both the original director alignment and the degree of preferred orientation are recovered. It is demonstrated that these novel memory effects are equilibrium in nature. The origins of this phenomena in terms of coupling between the mesogenic side-chains and the polymer network are discussed.

Desenvolvimento de redes de polímeros interpenetrantes (IPN) para a aplicação como eletrólito polimérico

Uma nova rede de polímeros interpenetrantes (IPN) baseada em poliuretana de óleo de mamona e poli(etileno glicol) e poli(metacrilato de metila) foi preparada para ser utilizada como eletrólito polimérico. Os seguintes parâmetros de polimerização foram avaliados: massa molecular do poli(etileno glicol) (PEG), concentração de PEG e concentração de metacrilato de metila. As membranas de IPN foram caracterizadas por calorimetria diferencial de varredura (DSC) e espectroscopia de infravermelho por transformada de Fourier (FT-IR). Os eletrólitos de redes de polímeros interpenetrantes (IPNE) foram preparados a partir da dopagem com sal de lítio através do inchamento numa solução de 10% em massa de LiClO4 na mistura de carbonato de etileno e carbonato de propileno na razão mássica de 50:50. As IPNEs foram caracterizadas por espectroscopia de impedância eletroquímica e Raman. As IPNEs foram testadas como eletrólito polimérico em supercapacitores. As células capacitivas foram preparadas utilizando eletrodos de polipirrol (PPy). Os valores de capacitância e eficiência foram calculados por impedância eletroquímica, voltametria cíclica e ciclos galvonostáticos de carga e descarga. Os valores de capacitância obtidos foram em torno de 90 F.g-1 e eficiência variou no intervalo de 88 a 99%. Os valores de densidade de potência foram superiores a 250 W.kg-1 enquanto que a densidade de energia variou de 10 a 33 W.h.kg-1, dependendo da composição da IPNE. As características eletroquímicas do eletrólito formado pela IPN-LiClO4 (IPNE) foram comparadas aos eletrólitos poliméricos convencionais, tais como poli(difluoreto de vinilideno)-(hexafluorpropileno) ((PVDF-HFP/LiClO4) e poliuretana comercial (Bayer desmopan 385) (PU385/LiClO4). As condutividades na temperatura ambiente foram da ordem de 10-3 S.cm-1. A capacitância da célula utilizando eletrodos de PPy com eletrólito de PVDFHFP foi de 115 F.g-1 (30 mF.cm-2) e 110 F.g-1 (25 mF.cm-2) para a célula com PU385 comparadas a 90 F.g-1 (20 mF.cm-2) para a IPNE. Os capacitores preparados com eletrólito de IPNE apresentaram valores de capacitância inferior aos demais, entretanto provaram ser mais estáveis e mais resistentes aos ciclos de carga/descarga. A interpenetração de duas redes poliméricas, PU e PMMA produziu um eletrólito com boa estabilidade mecânica e elétrica. Um protótipo de supercapacitor de estado sólido foi produzindo utilizando eletrodos impressos de carbono ativado (PCE) e o eletrólito polimérico de IPNE. A técnica de impressão de carbono possui várias vantagens em relação aos outros métodos de manufatura de eletrodos de carbono, pois a área do eletrodo, espessura e composição são variáveis que podem ser controladas experimentalmente. As células apresentaram uma larga janela eletroquímica (4V) e valores da capacitância da ordem de 113 mF.cm-2 (16 F.g-1). Métodos alternativos de preparação do PCE investigados incluem o uso de IPNE como polímero de ligação ao carbono ativado, estes eletrodos apresentaram valores de capacitância similares aos produzidos com PVDF. A influência do número de camadas de carbono usadas na produção do PCE também foi alvo de estudo. Em relação ao eletrólito polimérico, o plastificante e o sal de lítio foram adicionados durante a síntese, formando a IPNGel. As células apresentaram alta capacitância e boa estabilidade após 4000 ciclos de carga e descarga. As membranas de IPN foram testadas também como reservatório de medicamento em sistemas de transporte transdérmico por iontoforese. Os filmes, mecanicamente estáveis, formaram géis quando inchado em soluções saturadas de lidocaina.HCl, anestésico local, em propileno glicol (PG), poli(etileno glicol) (PEG400) e suas misturas. O grau de inchamento em PG foi de 15% e 35% em PEG400. Agentes químicos de penetração foram utilizados para diminuir a resistência da barreira causada pela pele, dentre eles o próprio PG, a 2-pirrolidinona (E1) e a 1-dodecil-2-pirrolidinona (E2). Os géis foram caracterizados por espectroscopia de impedância eletroquímica e transporte passivo e por iontoforese através de uma membrana artificial (celofane). O sistema IPN/ lidocaina.HCl apresentou uma correlação linear entre medicamento liberado e a corrente aplicada. Os melhores resultados de transporte de medicamento foram obtidos utilizando o PG como solvente.

Viscoelastic and Thermal Properties of Collagen-Xanthan Gum and Collagen-Maltodextrin Suspensions During Heating and Cooling

The purpose of this work was to investigate the viscoelastic properties of aqueous suspensions of crude collagen powder extracted from bovine hides and nonsubmitted to the hydrolysis reaction that leads to gelatin. The studied variables included the collagen concentration and the addition of xanthan gum or maltodextrin at varied concentrations during heating/cooling of the mixtures. Differential scanning calorimetry thermograms showed that the addition of polysaccharides decreased the endothermic peak areas observed at the denaturation temperature of collagen. The rheological properties of the pure collagen suspensions were highly dependent on concentration: 4% and 6% collagen suspensions presented a great increase in the storage modulus after heating/cooling, whereas for concentrations of 8% and 10% G' decreased during heating and did not recover its original value after heating/cooling. The frequency sweeps showed that the thermal treatment was responsible by the strengthening of the interactions that formed the polymer network. Addition of 0.1% xanthan gum to collagen suspensions increased the gel strength, especially after heating/cooling of the system, whereas increasing gum concentration to 0.3% resulted in a weaker gel, which could indicate thermodynamic incompatibility between the biopolymers. Mixtures of collagen and maltodextrin resulted in more fluid structures than those obtained with pure collagen at the same collagen concentration and the range of temperatures in which these mixtures behaved as a gel decreased with increasing concentrations of both collagen and maltodextrin, suggesting incompatibilities between the biopolymers.

Defects in thermosensitive colloidal crystals

Poly-N-Isopropylacrylamide (PNIPAM) colloidal particles form crystal phases that show a thermosensitive behaviour and can be used as atomic model systems. This polymer has both hydrophilic and hydrophobic character and has interesting stimuli-responsive properties in aqueous solution, of which the most important is the temperature response. Above a certain temperature, called Lower Critical Solution Temperature (LCST), the system undergoes a volume phase transition (VPT). Above the LCST, the water is expelled from the polymer network and the swollen state at low temperature transforms into a shrunken state at high temperature. The thermoresponsive behaviour of PNIPAM can be influenced by pH and ionic strength, as well as by the presence of copolymers, such as acrylic acid. In a system formed both by particles of PNIPAM and PNIPAM doped with acrylic acid, one can control the size ratio of the two components by changing the temperature of the mixture, while keeping particle interactions relatively the same. It is therefore possible to obtain thermoresponsive colloidal crystal in which temperature changes induce defects whose formation processes and dynamics can be analysed in an optical microscope at a convenient spatial and temporal scale. The goal of this thesis project was to find the conditions in which such a system could be formed, by using characterization techniques such as Static Light Scattering, Dynamic Light Scattering and Confocal Laser Scanning Microscopy. Two PNIPAM-AAc systems were available, and after characterization it was possible to select a suitable one, on the basis of its low polydispersity and the lack of a VPT, regardless of the external conditions (system JPN_7). The synthesis of a PNIPAM system was attempted, with particles of dimensions matching the JPN_7 system and, unlike JPN_7, displaying a VPT, and one suitable candidate for the mixed system was finally found (system CB_5). The best conditions to obtain thermoresponsive crystal were selected, and the formation and healing of defects were investigated with CLSM temperature scans. The obtained results show that the approach is the correct one and that the present report could represent a useful start for future developments in defect analysis and defect dynamics studies.

Late postoperative opacification of hydrogel intraocular lenses: analysis of 13 explanted lenses

PURPOSE: We report the clinical, morphological, and ultrastructural findings of 13 consecutively explanted opacified Hydroview(R) (hydrogel) intraocular lenses (IOLs). Our purpose was to provide a comprehensive account on the possible factors involved in late postoperative opacification of these IOLs. PATIENTS AND METHODS: Thirteen consecutive opacified hydrogel IOLs (Hydroview H 60 M, Bausch ; Lomb) were explanted due to the significant visual impairment they caused. The IOLs underwent macroscopical examination, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electrophoresis for protein detection. Three unused control Hydroview IOLs served for comparison. RESULTS: Macroscopical examination showed a diffuse or localized grey-whitish opacification within the IOL optic. TEM confirmed the presence of lesions inside the optic in all the explanted IOLs and revealed 3 patterns of deep deposits: a) diffuse, thick, granular, electron-dense ones; b) small, thin, lattice-like ones, with prominent electron-lucent areas; and c) elongated electron-dense formations surrounded by electron-lucent halos. SEM showed surface deposits on four IOLs. EDS revealed oxygen and carbon in all IOLs and documented calcium, phosphorus, silicon and/or iron in the deposits. Two of the patients with iron in their IOLs had eye surgery prior to their phacoemulsification. Iron correlated well with the second TEM pattern of deep lesions, whereas calcium with the third TEM pattern. No protein bands were detected on electrophoresis. Control lenses did not show any ultrastructural or chemical abnormality. CONCLUSIONS: The present study supports the presence of chemical alterations inside the polymer of the optic in late postoperative opacification of Hydroview IOLs. This opacification does not follow a unique pathway but may present under different ultrastructular patterns depending on the responsible factors. Mechanical stress during surgery may initiate a sequence of events where ions such as calcium, phosphorus, silicon, and/or iron, participate in a biochemical cascade that leads to gradual alteration of the polymer network. Intraocular inflammation due to previous operation may be a factor inducing opacification through increase of iron-binding capacity in the aqueous humour. Calcification accounts only partially for the opacification noted in this type of IOL.

Molecular architecture of basement membranes

Basement membranes are specialized extracellular matrices with support, sieving, and cell regulatory functions. The molecular architectures of these matrices are created through specific binding interactions between unique glycoprotein and proteoglycan protomers. Type IV collagen chains, using NH2-terminal, COOH-terminal, and lateral association, form a covalently stabilized polygonal framework. Laminin, a four-armed glycoprotein, self-assembles through terminal-domain interactions to form a second polymer network, Entactin/nidogen, a dumbbell-shaped sulfated glycoprotein, binds laminin near its center and interacts with type IV collagen, bridging the two. A large heparan sulfate proteoglycan, important for charge-dependent molecular sieving, is firmly anchored in the basement membrane and can bind itself through a core-protein interaction to form dimers and oligomers and bind laminin and type IV collagen through its glycosaminoglycan chains. Heterogeneity of structure and function occur in different tissues, in development, and in response to different physiological needs. The molecular architecture of these matrices may be regulated during or after primary assembly through variations in compositions, isoform substitutions, and the modifying influence of exogenous macromolecules such as heparin and heparan sulfate.

Novel imprinted polymers as artificial enzymes

Derivatives of L-histidine were investigated as suitable models for the Asp-His couple found in the catalytic triad of serine proteases. A combination of molecular dynamics and IH NMR spectroscopy suggested that the most populous conformations of N-acetyl-L-histidine and the N-acetyl-L-histidine anion were predominated by those in which the carboxylate group was gauche to the imidazole ring overcoming steric and electrostatic repulsion, suggesting there is an interaction between the carboxylate group and the imidazole ring. Kinetic studies, using imidazole, N-acetyl-L-histidine and the N-acetyl-L-histidine anion showed that in a DMSO/H20 9: 1 v/v solution, the N-acetyl-L-histidine anion catalysed the hydrolysis of p-nitrophenyl acetate at a greater rate than using either imidazole or N-acetyl-L-histidine as catalyst. This indicates that the carboxylate group affects the nucleophilicity of the unprotonated imidazole ring. 31P MAS NMR spectroscopy was investigated as a new technique for the study of the template molecule environment within the polymer networks. It was found that it was possible to distinguish between template associated with the polymer and that which was precipitated onto the surface, though it was not possible to distinguish between polymer within imprinted cavities and that which was not. Attempts to study the effect of the carboxylate group/imidazole ring interaction in the imprinted cavity of a molecularly imprinted polymer network were hindered by the method used to follow the reaction. It was found though that in a pH 8.0 buffered solution the presence of imprinted cavities increased the rate of reaction for those polymers derived from L-histidine. Some preliminary investigations into the design and synthesis of an MIP which would catalyse the oxy-Cope rearrangement were carried out but the results were inconclusive.

The Creation and Evaluation of Novel Canine Training Aids for Cocaine Using Molecularly Encapsulated Sol-Gel Polymers and an Investigation of Canine Field Accuracy

Biological detectors, such as canines, are valuable tools used for the rapid identification of illicit materials. However, recent increased scrutiny over the reliability, field accuracy, and the capabilities of each detection canine is currently being evaluated in the legal system. For example, the Supreme Court case, State of Florida v. Harris, discussed the need for continuous monitoring of canine abilities, thresholds, and search capabilities. As a result, the fallibility of canines for detection was brought to light, as well as a need for further research and understanding of canine detection. This study is two-fold, as it looks to not only create new training aids for canines that can be manipulated for dissipation control, but also investigates canine field accuracy to objects with similar odors to illicit materials. It was the goal of this research to improve upon current canine training aid mimics. Sol-gel polymer training aids, imprinted with the active odor of cocaine, were developed. This novel training aid improved upon the longevity of currently existing training aids, while also provided a way to manipulate the polymer network to alter the dissipation rate of the imprinted active odors. The manipulation of the polymer network could allow handlers to control the abundance of odors presented to their canines, familiarizing themselves to their canine’s capabilities and thresholds, thereby increasing the canines’ strength in court. The field accuracy of detection canines was recently called into question during the Supreme Court case, State of Florida v. Jardines, where it was argued that if cocaine’s active odor, methyl benzoate, was found to be produced by the popular landscaping flower, snapdragons, canines will false alert to said flowers. Therefore, snapdragon flowers were grown and tested both in the laboratory and in the field to determine the odors produced by snapdragon flowers; the persistence of these odors once flowers have been cut; and whether detection canines will alert to both growing and cut flowers during a blind search scenario. Results revealed that although methyl benzoate is produced by snapdragon flowers, certified narcotics detection canines can distinguish cocaine’s odor profile from that of snapdragon flowers and will not alert.

The creation and evaluation of novel canine training aids for cocaine using molecularly encapsulated sol-gel polymers and an investigation of canine field accuracy

Biological detectors, such as canines, are valuable tools used for the rapid identification of illicit materials. However, recent increased scrutiny over the reliability, field accuracy, and the capabilities of each detection canine is currently being evaluated in the legal system. For example, the Supreme Court case, State of Florida v. Harris, discussed the need for continuous monitoring of canine abilities, thresholds, and search capabilities. As a result, the fallibility of canines for detection was brought to light, as well as a need for further research and understanding of canine detection. This study is two-fold, as it looks to not only create new training aids for canines that can be manipulated for dissipation control, but also investigates canine field accuracy to objects with similar odors to illicit materials. ^ It was the goal of this research to improve upon current canine training aid mimics. Sol-gel polymer training aids, imprinted with the active odor of cocaine, were developed. This novel training aid improved upon the longevity of currently existing training aids, while also provided a way to manipulate the polymer network to alter the dissipation rate of the imprinted active odors. The manipulation of the polymer network could allow handlers to control the abundance of odors presented to their canines, familiarizing themselves to their canine’s capabilities and thresholds, thereby increasing the canines’ strength in court.^ The field accuracy of detection canines was recently called into question during the Supreme Court case, State of Florida v. Jardines, where it was argued that if cocaine’s active odor, methyl benzoate, was found to be produced by the popular landscaping flower, snapdragons, canines will false alert to said flowers. Therefore, snapdragon flowers were grown and tested both in the laboratory and in the field to determine the odors produced by snapdragon flowers; the persistence of these odors once flowers have been cut; and whether detection canines will alert to both growing and cut flowers during a blind search scenario. Results revealed that although methyl benzoate is produced by snapdragon flowers, certified narcotics detection canines can distinguish cocaine’s odor profile from that of snapdragon flowers and will not alert.^

Development and chemo-mechanical characterization of eco-compatible extenders containing REOB and recycled tyres’ rubber for the production of greener bituminous binders

The concepts of circular economy and sustainability are the basis of the present experimental research that seeks to reduce the environmental impact of traditional road construction materials. This study mainly focuses on the development and the chemo-mechanical characterization of bitumen extenders containing rubber (R) from end-of-life tyres (ELTs) and re-refined engine oil bottoms (REOBs) for the production of innovative and eco-friendly extended bitumens (i.e. bituminous binders containing 25%wt. of recycled products) and asphalt mixtures. In order to create more sustainable asphalt mixes, also recycled aggregates are used for partial replacement of virgin natural aggregates in the aggregate skeleton. The experimental program encompassed five successive steps: (i) the evaluation of physicochemical properties of R and REOB, (ii) the definition of the optimal extenders by the development of a new protocol and their characterizations, (iii) the realization and investigation of the chemo-rheological responses of the extended bitumens at different boundary conditions, (iv) the assessment of the effectiveness of analytical method to predict the rheological parameters of extended bitumens and, finally, (v) the analysis of the mechanical performances of the corresponding asphalt mixtures. A standard 50/70 penetration grade bitumen was chosen as a reference material and the main constituent of the innovative bituminous products. The results of this study underlined the importance of material characterization. The incorporation of R-REOB extenders strongly affects the chemo-rheological responses of the resulting extended bitumens and asphalt mixtures overall the boundary conditions. While the presence of R and the consequent formation of a polymer network improves the elasticity of the final products, especially at high test temperatures; the addition of REOB, softens the bituminous binders and asphalt mixes increasing their response at low test temperatures. Nonetheless, the use of recycled products increased the susceptibility of bituminous material under damaging conditions, which would need further investigations.

Evolution of network structure in polymer-stabilised liquid crystals

Experiments were performed to investigate the evolution of structure and morphology of the network in polymer-stabilised liquid crystals. In situ optical microscopy revealed that the morphology was significantly altered by extraction of the LC host, while scanning electron microscopy showed that the network morphology was also dependent on the polymerisation conditions and closely related to the depletion of monomer, as monitored by high performance liquid chromatography. Transmission electron microscopy allowed observation of internal structure, resolving microstructure on the order of 0. 1 μm.

A novel study of the polymerisation process involved in the formation of the network component of polymer-stabilised liquid crystals within electro-optic cells using high performance liquid chromatography

Polymer-stabilised liquid crystals are systems in which a small amount of monomer is dissolved within a liquid crystalline host, and then polymerised in situ to produce a network. The progress of the polymerisation, performed within electro-optic cells, was studied by establishing an analytical method novel to these systems. Samples were prepared by photopolymerisation of the monomer under well-defined reaction conditions; subsequent immersion in acetone caused the host and any unreacted monomer to dissolve. High performance liquid chromatography was used to separate and detect the various solutes in the resulting solutions, enabling the amount of unreacted monomer for a given set of conditions to be quantified. Longer irradiations cause a decrease in the proportion of unreacted monomer since more network is formed, while a more uniform LC director alignment (achieved by decreasing the sample thickness) or a higher level of order (achieved by decreasing the polymerisation temperature) promotes faster reactions.

A 2D coordination polymer with brick-wall network topology based on the [Cu(NCS)(2)(pn)] monomer

The new complex [Cu(NCS)(2)(pn)] (1) (pn = 1,3-propanediamine) has been synthesized and characterized by elemental analysis, infrared and electronic spectroscopy. Single crystal X-ray diffraction studies revealed that complex 1 is made up of neutral [Cu(NCS)(2)(pn)] units which are connected by mu-1,3,3-thiocyanato groups to yield a 2D metal-organic framework with a brick-wall network topology. Intermolecular hydrogen bonds of the type NH...SCN and NH...NCS are also responsible for the stabilization of the crystal structure. (c) 2007 Elsevier B.V. All rights reserved.

Characterization of a polymer-infiltrated ceramic-network material

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Surface plasmon resonance of gold nanoparticles formed by cathodic arc plasma ion implantation into polymer

Shallow subsurface layers of gold nanoclusters were formed in polymethylmethacrylate (PMMA) polymer by very low energy (49 eV) gold ion implantation. The ion implantation process was modeled by computer simulation and accurately predicted the layer depth and width. Transmission electron microscopy (TEM) was used to image the buried layer and individual nanoclusters; the layer width was similar to 6-8 nm and the cluster diameter was similar to 5-6 nm. Surface plasmon resonance (SPR) absorption effects were observed by UV-visible spectroscopy. The TEM and SPR results were related to prior measurements of electrical conductivity of Au-doped PMMA, and excellent consistency was found with a model of electrical conductivity in which either at low implantation dose the individual nanoclusters are separated and do not physically touch each other, or at higher implantation dose the nanoclusters touch each other to form a random resistor network (percolation model). (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3231449]