Neste trabalho, utilizou-se a técnica de decaimento de fluorescência resolvida no tempo para estudar a dinâmica agregação intra-polimérica do [3,22]-ioneno e da interação destes agregados com co-íons e contra-íons. Brometo de [3,22]-ioneno apresenta supressão intra-polimérica da sonda fluorescente pireno, eliminada pela quaternização dos grupos amino terminais com cloreto de benzila e pela troca do contra-íon Br- por Cl-, obtendo-se o cloreto de NT-benzil-[3,22]-ioneno, viabilizando a realização de medidas fotofísicas. Medidas da dinâmica de formação de excímeros de pireno e seus derivados evidenciaram que, em contraste às micelas de cloreto de hexadeciltrimetilamônio, os agregados formados por NT-benzil-[3,22]-ioneno participam de um eficiente processo intra-polimérico de fusão/fissão que facilita a migração de sondas e supressores durante o tempo de vida da sonda excitada. A existência deste processo de migração intra-polimérica requer a presença de vários microdomínios ao longo da cadeia do ioneno. Medidas em temperaturas baixas (<15°C), onde o processo de fusão/fissão intrapolimérica torna-se mais lento que a supressão, forneceram uma estimativa do número de agregação dos microdomínios de 20,5. A constante de velocidade do processo de fusão/fissão (kfus) foi estimada a partir do estudo da dinâmica da formação de excímeros de pireno e derivados. Os dados para a dinâmica de saída de co-íons e de contra-íons supressores dos microdomínios de NTbenzil-[3,22]-ioneno foram tratados, levando em conta os dois mecanismos de migração, ou seja, pela fase aquosa e facilitada pelo processo de fusão/fissão. As constantes de velocidade de saída e de supressão para os microdomínios de NT-benzil-[3,22]-ioneno e micelas de CTAC1 apresentam dependências similares com o aumento da concentração de sal comum adicionado. / In this dissertation, the technique of time-resolved fluorescence quenching has been employed to investigate the dynamics of intrapolymeric aggregation of the [3,22]-ionene and the interaction of the resultant aggregates with coions and counterions. Undesirable quenching of the fluorescence of pyrene solubilized in [3,22]-ionene bromide was eliminated by quaternization of the amino terminal groups with benzyl chloride and by exchanging the counterion from Br- to Cl-, to give NT-benzyl-[3,22]-ionene chloride. Measurements of the dynamics of excimer formation by pyrene and its derivatives showed that, in contrast to cetyltrimethyanonium chloride (CTACl) micelles, the NT-benzyl-[3,22]-ionene aggregates undergoe an efficient intrapolymeric fusion/fission process that promotes the migration of probes and quencher between the aggregates. The existence of this intrapolymeric process requires that there be various microdomains distributed along the main ionene chain. At low temperature (<15°C), where the intrapolymeric fusion/fission process becomes much slower than quenching, an estimate of 20.5 ionene subunits is obtained for the aggregation number of the microdomains. The rate constant for the fusion/fission process (kfus) was estimated from the dynamics of excimer formation of pyrene and its derivatives. Data for the dynamics of exit of coions and counterions from the microdomains of NT-benzyl-[3,22]-ionene were analyzed by taking into account two simultaneous migration mechanisms: via the aqueous phase and via the fusion/fission route. The added common salt concentration dependences of the rate constants for exit and quenching are similar for both the NTbenzyl-[3,22]-ionene microdomains and CTACl micelles.

Orientador: Luis Vicente de Andrade Scalvi / Banca: Maximo Siu Li / Banca: Aguinaldo Robinson de Souza / O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp / Resumo: Dióxido de estanho (Sn'O IND. 2') é um semicondutor do tipo n, que é transparente na região do ultravioleta/visível. Possui muitas aplicações como, por exemplo, eletrodos transparentes, sensores de gás, coletores solares e dispositivos eletro-ópticos. Quando dopado com íons terras-raras, Sn'O IND. 2' pode ser utilizado na confecção de dispositivos para comunicação óptica, principalmente na forma de filmes finos. Os íons terras-raras têm grande relevância devido às transições eletrônicas, que vão do ultravioleta ao infravermelho próximo. Outro aspecto importante está ligado às características físico-químicas da suspensão coloidal de onde são depositados os filmes. Filmes obtidos com pH elevado da suspensão apresentam alta resistividade elétrica e baixa cristalinidade em relação aos filmes obtidos com pHs das suspensões ácidas. O nível mais profundo de energia dos defeitos em Sn'O IND. 2' foi alterado da energia de 140eV até 67eV para variação do pHs 11, até 6, de acordo com a avaliação da energia de ativação. Os difratogramas destes filmes indicam aumento de cristalinidade com a diminuição do pH. Xerogéis de Sn'O IND. 2':Er2% com alteração do pH em relação a suspensão neutra apresentaram espectro de emissão mais intenso na região infravermelha para a amostra com pH7 e um pequeno alargamento dos picos de emissão para a amostra com pH4 e mais acentuado para a amostra com pH11, em bom acordo com medidas de Raman. Relatamos também a emissão na região visível de filme fino de Sn'O IND. 2' dopado com 'Er POT. 3+', que é um formato adequado da amostra para confecção de dispositivos. / Abstract: Tin dioxide (Sn'O IND. 2') is an n-type oxide semicondutor, which is transparent in the ultraviolet/visible range. It presents many types of applications, such as transparent electrodes, gas sensors, solar collectors and eletro-optical devices. When doped with rare-earth ions, Sn'O IND. 2' may be used to make optical communication devies, in the thin film configuration. Rare-earth ions have great relevance due to their electronic transitions, covering from ultraviolet to near infrared. Another important characteristic is related to the physical-chemical properties of the starting colloidal suspension to deposit the films. Films obtained with high pH of the suspension presents high electric resistivity and low crystallinity compared to films obtained with acid pH. The deepest energy level of the defects in Sn'O IND. 2' has been changed from the energy of 140 eV to 67 e V when the pH changes from 11 to 6. Diffractograms of these films show increase in the crystallinity with pH decrease. Sn'O IND. 2':Er2% xerogels with modified pH show more intense emission spectra in the infrared for sample with pH 7 and a low broadening of emission peaks for the sample with pH 4 and moer intense for pH 11, suggesting an "ideal" pH for higher emission samples, in good agreement with Raman shift spectra. We also report emission in the visible range from of an 'Er POT. 3+' -doped thin film, which is a very convenient form for devices fabrication. / Mestre

Orientador: Ines Joeks / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-10T13:30:49Z (GMT). No. of bitstreams: 1 Cardoso_AtiliodeOliveira_D.pdf: 4999395 bytes, checksum: 7096b1378702c52ba1881ec1b2449019 (MD5) Previous issue date: 2007 / Resumo: Crisotila é um silicato de magnésio de hábito fibroso, com fórmula ideal Mg6Si4O10(OH)8 e estrutura 1:1, intercalando camada tetraédrica de tridimita (sílica) com camada octaédrica de hidróxido de magnésio (brucita). Para haver coordenação entre os planos de tridimita e brucita as bicamadas se curvam e se enrolam sobre si mesmas, formando fibrilas cilíndricas com superfície constituída de brucita. As fibrilas se agregam dando origem a fibras que em meio aquoso, sob extensa faixa de pH, possuem potencial zeta positivo, em razão de haver cátions magnésio na superfície, originados por dissociação de ânions hidroxila, o que ocasiona pH de equilíbrio igual a 8,5. Apesar do potencial zeta essencialmente positivo, crisotila é um material sobre o qual aderem, espontaneamente, e em grande quantidade, materiais particulados de natureza negativa ou positiva. Visando compreender as causas do fenômeno, partículas de látex de poliestireno, com superfície negativa, PS-, e positiva, PS+, foram sintetizadas em meio aquoso, na ausência de surfactantes, e utilizadas em experimentos de heterocoagulação com crisotila, variando: i) o grau de desfibrilamento da crisotila, em meio aquoso, através de ação mecânica e através de hidrofobicidade causada por metilação da superfície das fibras usando Si(CH3)2Cl2; ii) o potencial zeta de crisotila através de lavagem com HCl, variação do pH do meio de dispersão usando NaOH e lavagem com solução aquosa de silicato de sódio; iii) a quantidade adicionada de partículas de poliestireno por mg de crisotila; iv) o potencial zeta das partículas de poliestireno através da adsorção de surfactante catiônico brometo de cetil-trimetil-amônio (CTAB). Resultados de análise microscópica via MEV mostraram que a formação de heterocoágulos ocorre preferencialmente sobre fibras de crisotila mais finas e portanto flexíveis, havendo expressiva formação de homocoágulos de látex a partir de aproximadamente 10 partículas por mg de crisotila. De acordo com resultados de medidas de densidade óptica residual de sobrenadantes, os procedimentos que diminuem o grau de desfibrilamento e o potencial zeta de crisotila diminuem a velocidade inicial de formação de heterocoágulos com partículas de PS-. A adsorção de CTAB inibe a adesão de partículas PS- e não interfere na adesão de partículas PS+ sobre crisotila. A heterocoagulação de látex PS- é completamente revertida com a adição de silicato de sódio ao meio de dispersão. Em meio aquoso, silicato de sódio extrai impurezas da crisotila, detectadas por aumento da densidade óptica do meio de dispersão. Partículas de látex PS+ praticamente não aderem sobre crisotila lavada com silicato de sódio. Os resultados indicam que a adesão de partículas negativas sobre crisotila ocorre preferencialmente sobre sítios positivos oriundos de magnésio dissociado de hidroxila, enquanto a adesão de partículas positivas ocorre sobre sítios negativos, ocasionados pela pré-adesão de impurezas durante a etapa de lavagem da crisotila com água. A densidade superficial de sítios positivos é significativa em fibras mais finas e flexíveis, sobre as quais a heterocoagulação ocorre preferencialmente. Sugerese que a homocoagulação seja dependente principalmente da mobilidade de heterocoágulos préformados, que sob agitação do sistema colidem entre si com energia mecânica suficiente para causar a adesão entre as partículas de látex / Abstract: Chrysotile is a magnesium silicate with fibrous habit and ideal formula Mg6Si4O10(OH)8, having 1:1 layered structure of tetrahedral tridimite (silicate) with octahedral brucite (magnesium hydroxide). The layers are curved and rolled, resulting in cylindrical fibrils with brucite in the external surface and tridimite in the hollow internal surface. The fibrils aggregate giving rise to bundles, or fibers, which have a positive zeta-potential in aqueous medium. This results from the Mg occurrence after dissociation of the surface hydroxyl groups. Despite its positive zeta potential, the surface of chrysotile attaches colloidal particles of negative or positive nature. Aiming to understand this phenomenon, polystyrene latex particles, with negative (PS-) and positive (PS+) surface charge, were synthesized in aqueous solution, in the absence of surfactants, and used in experiments of heterocoagulation with chrysotile. The aggregation of the fibers was controled through mechanical action or improved hidrofobicity by metilation of the surface using Si(CH3)2Cl2. The zeta potential of chrysotile was modified by washing with HCl or adding NaOH or sodium silicate aqueous solution. The amount of polystyrene particles was varied and its surface charge adjusted adding cetyl trimethylammonium bromide cationic surfactant (CTAB). Results of microscopic analysis (MEV) showed that the formation of heteroaggregates occurs preferentially on disaggregated fibers, or fibrils, which are the most flexible. Also, an expressive quantity of homoaggregates of latex with approximately 10 particles/mg of chrysotile are formed. According with the results of optical density of the supernatants, procedures that reduce the disaggregation and the zeta-potential of chrysotile decrease the initial rate of formation of heteroaggregates with particles of PS-. The adsorption of CTAB inhibits the adhesion of PS- particles and does not interfere in the adhesion of PS+ particles on chrysotile. The heterocoagulation of PS- latex is completely reverted with the addition of sodium silicate to the dispersion. In aqueous suspension, sodium silicate removes impurities of the chrysotile surface, as detected by the increase in the optical density of the dispersion. Particles of PS+ latex practically will not attach on chrysotile washed with sodium silicate. The results indicate that the adhesion of negative particles on chrysotile occurs preferentially at positive surface sites, while the adhesion of positive particles occurs at the negative surface sites, probably caused by the pre-adhesion of impurities on the chrysotile when washing with water. The surface density of positive sites is more significant in flexible and disaggregated fibers, on which the heterocoagulation occurs preferentially. The homoaggregation of the latex particles seems to be dependent mainly on the mobility of the preformed heteroaggregates, which, under stirring, collide among themselves with enough mechanical energy to cause the adhesion between the latex particles / Doutorado / Físico-Química / Doutor em Ciências

Here we present direct investigation of the lasing behaviour by performing gain spectroscopy of solution-based CQDs enabled via in-situ tuning of the feedback wavelength of an open-access hemispherical microcavity. The investigation is performed on two different types of CQDs, namely spherical CdSe/CdS core-shell CQDs and nanopletelets (NPs). The lasing threshold and the differential gain/slope efficiency of the fundamental cavity mode are measured as a function of their spectral position over a spectral range of ∼ 32 nm and of ∼ 42 nm for the spherical CQDs and NPs, respectively. The results of the gain spectroscopy are described using theoretical models, providing insights into the mechanism governing the observed lasing behaviour. Furthermore, the open-access cavity architecture provides a very convenient way of producing in-situ tunable lasing, and single-mode lasing of the fundamental cavity mode over a spectral range of ∼ 25 nm and ∼ 37 nm is demonstrated using spherical CQDs and NPs, respectively. In addition, the stability of laser emission is investigated, with the lasing intensity of the fundamental cavity mode remaining constant over a time period of almost 6 mins. It is hoped that the results will provide a detailed understanding of the lasing behaviour of CQDs. This information can be fed back into the design of CQDs in which the lasing threshold can be reduced to the point where useful devices can be constructed, and in the design of resonant optical feedback structures for which the appropriate wavelength must be carefully selected.

In this thesis type II colloidal quantum dots (CQDs) with zinc blende crystal structure were investigated. The optical properties were characterized by steady state absorption and photoluminescence (PL) spectroscopy for all the samples, and the PL quantum yield was measured for selected samples by using both absolute and relative methods. Exciton dynamics and interactions were investigated by time-resolved PL (TRPL).The exciton-exciton interaction energy for CdSe, CdSe/CdTe and CdSe/CdTe/CdS CQDs was investigated using TRPL spectroscopy, an established method. The TRPL results were compared with previous results from ultrafast transient absorption (TA) measurements and theoretical predictions. The discrepancies between the TRPL and TA results and the theoretical calculations suggest that TRPL data has been misinterpreted in the literature. The single exciton recombination dynamics for CdSe, CdSe/CdTe and CdSe/CdTe/CdS CQDs were investigated. The effects of non-radiative recombination were identified from the PL transients by using a theoretically-calculated radiative lifetime as a fitting parameter. The combined rate of the non-radiative processes thus found was consistent with the localisation of holes into shallow traps by an Auger-mediated process. A rate equation analysis also showed how shallow trapping can give rise to the tri-exponential PL dynamics observed experimentally. Chloride passivation of CdTe CQDs resulted in a near-complete suppression of surface traps, producing a significant enhancement of the optical properties. PL quantum yield (PLQY) and PL lifetime in particular benefit from the chloride treatment. The radiative recombination rate that now could be extracted from PL transients for chloride treated samples was used to calculate the non-radiative recombination rate for the untreated samples. In addition, a study of the effects of air exposure on the PL, observed for both treated and untreated samples was undertaken and revealed the importance of the influence of the dielectric environment surrounding the traps states on recombination dynamics.

In this thesis we have studied systems that driven by mechanisms broadly known as phoresis. More specifically, in the second chapter we calculate the excess noise in electrophoresis of a colloid due to microion fluctuations. In the next three chapters we study in detail a system of self-phoretic colloids, propelled by the energy released when an ambient fuel molecule makes contact with a catalytic region on the particle’s surface. We start with the behaviour of a single particle in a linear substrate gradient, then go on to study interactions between two particles due to their diffusion clouds, and finally obtain the collective equations of motion by a systematic coarse-graining of the microscopic Langevin dynamics. To understand the role of nonequilibrium fluctuations in an electrophoretic system we have theoretically analyzed the dynamics of a single colloidal particle in an externally applied electric field. We have studied the colloidal dynamics in two scenarios: a particle free to move in an unbounded fluid and a colloid near a wall which is stationary due to a balance between gravity and the electric field. The thermal motions of microions lead to an anisotropic, nonequilibrium noise, proportional to the field, in the effective Langevin equation for the colloid. The fluctuation-dissipation ratio depends strongly on frequency, in contrast to an equilibrium system, and the colloid if displaced from its steady-state position relaxes with a velocity not proportional to the gradient of the logarithm of the steady-state probability. Other measurable effects of this noise are a superdiffusive peak at short times and an enhanced diffusity at long times. We have then studied the effective potential and obtained a non-dimensional measure of the size of the excess noise. Possible extensions of this study to include the behaviour of the mean and fluctuation properties in the case of an applied alternating potential, and the effect of the excess noise on electrohydrodynamic aggregation of colloids. We next turn to a phoretic system that has been much studied in the recent years – active Janus colloids . On one hand these colloids are an important contribution to the general class of problems on self-propulsion at low Reynolds number. On the other hand since their behaviour can be tuned at the level of single particle we can ask how their collective behaviour depends on the swimmer design. This makes it a very rich field with lots of challenging questions. We first study the single particle behaviour of an active Janus colloid in an imposed substrate gradient, then build the two-particle interactions and ultimately the collective equations of motion by a generalisation of these results. Our work presents a new approach to active matter. We show theoretically how to design particles that are not only motile but can reorient in response to gradients, thus mimicking chemotaxis. We outline the collective behaviour emerging from these single-particle properties, including colloidal realisations of gravitational collapse, plasma oscillations and spontaneously ringing states, and present a phase diagram, in terms of single particle parameters, that can be tested in experiments. This provides a template to design collective behaviours of interest by tuning the surface properties of the colloids. We can also control the range of the interaction by varying the concentration of reactant. Our coarse-grained equations of motion for the polar orientation and number density fields for a collection of colloids propelled by and interacting through long-ranged dif-fusion fields are novel in a number of ways. This is the first example in active matter literature of a microscopic derivation of collective dynamics for particles interacting via long-ranged diffusion fields. The instabilities and possible phases that we predict are different from those in traditional flocking models, which consider only short-ranged aligning interactions. The long-ranged interactions of interest here cannot produce a globally polar ordered state, and we work in a concentration regime where steric and collisional interactions are not important. Instabilities towards flocking, and the advective nonlinearities of the Toner-Tu model, although not ruled out by the symmetries of our model, do not play a significant role in our system. The collective behaviour we predict will not be seen in purely locally interacting active-particle systems. The mechanisms at work in the “saturated” case where reactant is abundant cannot be viewed as totally generic features of collections of self-driven particles; they require interactions mediated by the production or consumption of long-ranged diffusing solute fields. Earlier work on saturated systems resolved neither interactions mediated by the polarity of the objects nor chemotactic effects. Their treatment truncated the equations at the level of the concentration [1]. In the “unsaturated” case more than one mechanism operates. One is related to the motility-induced phase separation discussed phenomenologically in refs. [2,3] (for which our system provides an important microscopic realisation). The other is due to chemo-taxis and phoresis which we report for the first time. Our expression of the various coefficients in the equaions of motion in terms of the single particle properties can also be used to design systems in which one or the other of these mechanisms dominate. We are now planning to study a collection of these particles in a fluid and examine the diffusion of a tracer particle as was done by Yeomans et al. [4] for hydrodynamic interactions. The Levy flights obtained in [4] is due to the long-ranged nature of the hydrodynamic fields, which cause effects like entrainment leading to interesting tracer dynamics. In this thesis we have considered colloids in which the symmetry axis of the colloid and the catalytic coat coincide. It might be of interest to consider cases when the axes are at an angle making the swimmer biaxial, or more complicated arrangements leading to chirality and thus rotation. Collective dynamics and two particle interaction between such swimmers can also be interesting. The formalism developed for the study of interaction between two active colloids through their diffusion fields and hydrodynamics can be extended to study their interaction with extended passive surfaces like walls or spheres. The collective dynamics of this class of active systems when it is confined between parallel walls is also of interest. Work in progress includes studies of the motion of the swimmer in a periodic array of passive colloids. In this study of collective dynamics, we have ignored the role of hydrodynamics, as the slowest decay of the field is 1/r3, which is subdominant to the decay of the chemical fields and in the dilute limit is expected to change things only qualitatively. However their role would be more important when we consider the stability of ordered structures like an aster in the saturated case. Another effect of hydrodynamics is to stir the fluid. It might be interesting to study the finite-P´eclet number regime [5, 6] of our system particularly in the unscreened region when advection of the scalar fields s and p by the velocity can affect clustering. We have derived the form of the nonlinear equations of motion in both the saturated and the unsaturated regimes. It will be interesting to investigate their relevance in the dynamics and phases that this extremely rich system can form. Even in the overdamped limit where we obtain an effective density equation it is not clear that the dynamics will resemble that of the Keller-Segel model due to the presence of the interesting nonlinear terms. Also, in this thesis, we have only looked at the fluid-like state of the system. We have just started exploring the high concentration regime where we can check the propensity of the system to develop crystalline order. In the screened limit where we obtain a condensation due a negative squared sound speed, it is posssible to study the condensation phenomenon in greater detail. In future we also plan to examine whether the tendency to condense at nonzero wavenumber (See Fig 5.1), i.e., microphase separation, can lead to liquid-crystalline phases like smectics. The systems described in this thesis are extremely rich and the few ideas mentioned above form just a small subset of the plethora of exciting theoretical and experimental explorations that can be performed with them. Since they can be “designed”, unlike biological substances, they can also become a test-bed for testing theoretical predictions of the nonequilibrium statistical mechanics of self-propelled systems.

External thermal insulation composite system (ETICS) is a widespread method appearance of the facades of existing and new civil and industrial buildings. With its frequent application becomes engaged his durability issues and possible rehabilitation and more topical. Influences affecting durability ETICS is still under investigation, as well as systematic and practical way to usable redevelopment. The main theme of this work is to summarize knowledge in ETICS issue, particularly from the viewpoint adhesive and leveling materials based on Portland cement and final finishes. The theoretical part is discussed ETICS composition, the composition of its components, technical requirements and factors affecting durability. The experimental part focuses on the redevelopment of ETICS and verification using colloidal silica for modification of construction materials, which are part of the ETICS.

In the construction of buildings and infrastructures, high resistance materials are used due to current design requirements, concrete being one of the main materials used in the execution of these projects whose cement content is limited to obtaining an economic concrete and of minimum retraction. This limitation requires the use of new additions such as Nano Silica (NS), which due to its nanometric structure is used as a partial replacement for cement, producing an increase in strength in concrete. The present investigation studies the partial replacement of the NS in the cement to determine its behavior in compressive strength, diametric compressive strength, water permeability coefficient. The results indicate that with an addition of 0.225% of NS the compressive strength and splitting tensile strength are increased and the water permeability coefficient decreases, all of them compared to a conventional concrete.

No description available.

Silver-polymer composite material containing highly dispersed silver nanoparticles (AgNPs) of 20-100. nm diameter can be obtained from bare nanosilver. The synthesis consists of three steps. The first step is modification of AgNPs by 2-aminoethanethiol. Second, polyacrylic acid is bonded to the silver 2-aminoethanethiolate by the carbodiimide method. Then esterification of the remaining carboxyl groups of the product by methanol results in formation of a stable colloidal dispersion of AgNPs in the polymer matrix. The method allows obtaining of nanocomposites with silver contents up to 1.4. wt%.