Nanotubos de Carbono (Carbon Nanotubes - CNTs) são nanoestruturas de carbono na forma de tubos cilíndricos que apresentam excelentes propriedades ópticas, elétricas, térmicas e mecânicas. A imobilização dos CNTs em conjunto com polieletrólitos condutores e naturais na forma de filmes ultrafinos, utilizando a técnica automontagem, apresenta uma nova alternativa para o desenvolvimento de nanocompósitos aplicados em dispositivos sensores e biossensores. Neste trabalho de mestrado foram construídos e estudados filmes automontados contendo CNTs funcionalizados com grupos ácidos carboxílicos e imobilizados com os polieletrólitos polianilina (PANI) e quitosana (QUIT). Também foram fabricados para comparação filmes de PANI e poliestireno sulfonado (PSS). O crescimento dos filmes de PANI/CNT e PANI/PSS revelou um crescimento linear com o número de bicamadas, conforme mostraram as medidas de espectroscopia UV-Vis e voltametria cíclica (CV), enquanto que para o filme de QUIT/CNT, as medidas de microbalança de cristal de quartzo (QCM) mostraram um crescimento exponencial. Análises de espectroscopias Raman e infravermelho com transformada de Fourier (FTIR) indicaram alterações nas bandas características dos filmes, comparadas com seus materiais precursores, indicando interação entre os componentes nas multicamadas dos filmes. Análises morfológicas obtidas por AFM mostraram um aumento da rugosidade com o aumento do número de bicamadas. O mapeamento Raman revelou que os filmes contendo CNTs apresentaram maior heterogeneidade química na superfície do que aos filmes somente com polieletrólitos. Foi observada uma queda na resistividade dos filmes, com o aumento do número de bicamadas, sendo esta, mais acentuada com a presença dos CNTs. Os eletrodos contendo os filmes automontados apresentaram alta estabilidade eletroquímica, a presença dos CNTs aumentou a intensidade das correntes de pico e tornou os sistemas mais reversíveis. Os eletrodos que se mostraram mais sensíveis à detecção de peróxido de hidrogênio foram selecionados para imobilização da enzima Glicose Oxidase (GOx). Foram investigados os seguintes sistemas biossensores: (PANI/CNT)7, (PANI/PSS)1 e (QUIT/CNT)5 apresentando na mesma ordem: valores de sensibilidades de 190 nA/(mmol/L), 36 nA/(mmol/L) e 220 nA/(mmol/L); Limite de detecção de 2,2 µmol/L, 67,5 µmol/L e 8,5 µmol/L, e valores deconstante de Michealis-Menten(\'K IND.M\'POT.APP\' ) de 2,2 µmol/L, 67,5 µmol/L e 8,5 µmol/L. Os resultados indicam que a utilização dos CNTs é bastante promissora para fabricação de dispositivos biossensores para aplicação em Nanomedicina, e além disso, a escolha dos componentes para formação dos nanocompósitos exerce grande influência no desempenho do dispositivo. / Carbon Nanotubes (CNTs) are cylindrical carbon nanostructures exhibiting excellent electrical, thermal, optical and mechanical properties. The immobilization of CNTs in nanostructured thin films in conjunction with polymers using the Layer-by-Layer (LbL) technique provides a new alternative for development of nanocomposites to be used as sensors and biosensors. In this study we report the fabrication of LbL films containing CNTs functionalized with carboxylic acid immobilized in conjunction with polyaniline (PANI) or chitosan (QUIT). Films comprising PANI and sulfonated polystyrene (PSS) were also produced for comparison. Film growth was monitored by UV-Vis spectroscopy, cyclic voltammetry (CV) and quartz crystal microbalance (QCM) and the results showed a linear increase with the number of bilayers in PANI films, and an exponential growth for QUIT/CNT films. FTIR and Raman analyses revealed changes in the bands of nanocomposites compared to their precursor materials, indicating the interactions between the components in the multilayers. Morphological analysis of the films obtained by atomic force microscopy (AFM) showed that the roughness of the films increased with the number of bilayers. Raman mapping showed that the presence of CNTs generated a high heterogeneity in film surface in comparison to a films formed only by polyelectrolytes. Electrical resistivity of the films decrease upon increasing the number of bilayers, especially for CNTs-containing films. Furthermore, electrodes containing LbL films exhibited high electrochemical stability, in which the presence of CNTs increased the intensity of response signal. The electrodes that exhibited best performance toward hydrogen peroxide detection were employed for immobilization of glucose oxidase (GOx) and used as glucose biosensors. The systems (PANI/CNT)7, (PANI/PSS) 1 and (QUIT/CNT)5 exhibited a sensitivity of 190 nA/(mmol/L), 36 nA/(mmol/L) and 220 nA/(mmol/L), respectively. The detection limit was estimated at 2.2 mmol/L, 67.5 mmol/L and 8,5 mmol/L, whereas the Michaelis-Menten constant ( \'K IND.M\'POT.APP\') values was found to be 2.2 mmol/L, 67.5 mmol/L and 8.5 mmol/L, respectively, to the three systems employed. The results indicated that the use of CNTs in Layer-by-layer thin films is promising for use as biosensors. Furhtermore, we showed that the choice of the polyelectrolyte is a crucial parameter to tailor specific, high performance sensors.

Neste trabalho foi estudada a influência da arquitetura molecular e das condições de fabricação de filmes sobre a birrefringência fotoinduzida em filmes automontados de um azopolímero comercial PS-119 ou do corante Brilliant Yellow (BY) como espécies fotorreativas. Os filmes automontados foram fabricados a partir de seis policátions, a saber, poli(alilamina hidroclorada) (PAH), poli(c1oreto de dodecildimetilamônio) (PDAC) (com 3 massas molares diferentes), poli(etileno imina) (PEI) e dendrímero poli(amidoamina) geração 4 (PAMAM-G4). No processo de fabricação o substrato era imerso alternadamente em solução aquosa de policátions e poliânions nos pHs 4, 6 e 8. O crescimento dos filmes foi monitorado por espectroscopia UV-VIS. após cada etapa de adsorção. Um aumento linear do pico em 480 nm, atribuído a transição , indicou que a mesma quantidade de material era adsorvida em cada passo de deposição. A birrefringência foi opticamente induzida usando-se um laser de 532 nm Nd-YAG. Dentre as propriedades dos filmes automontados, a que mais variou de um sistema para outro foi o tempo de escrita característico, definido como o tempo necessário para atingir 50% da birrefringência máxima. Este tempo dependia do polieletrólito e do pH da solução de partida. Os filmes PEI/PS-119 em pH 8 e PDAC(HMW)/PS-119, em pH 4, PAWBY em pH 8, e PDAC(HMW)/BY em pH 4, forneceram os seguintes tempos característicos: 34 min, 0,5 min, 10 min e 3 s, respectivamente. Estas grandes variações nos tempos de escrita estão relacionadas as diferenças nas estruturas dos policátions, que determinam a intensidade das interações entre os polieletrólitos. Os baixos tempos para PDAC, por exemplo, são atribuídos as menores interações com o poliânion, já que a carga do PDAC, um sal quaternário, sofre efeito de blindagem por grupos CH3. Mencione-se que o tempo de escrita para os filmes automontados de PDACIBY é o menor já relatado para filmes automontados, sendo da mesma ordem de grandeza dos filmes obtidos por spin-coating ou técnica de Langmuir-Blodgett (LB). A birrefringência residual, após o desligamento do laser de escrita, foi superior a 78% em todos os sistemas estudados, demonstrando a utilidade de filmes automontados para dispositivos de memória óptica permanente. / This work was aimed at investigating the influence of the molecular architecture and film fabrication on the photoinduced birefi-ingence of layer-by-layer (LbL) films containing the azopolymer PS 119® or the azodye Brylliant Yellow (BY) as photoreactive materials. The LbL films were produced with six polications, viz.: poly(allylamine hydrochloride) (PAH), poly(diallyldimethylammonium chloride) (PDAC) (with three different molecular weights), poly(ethy1eneimine) (PEI) and generation 4 dendrimer poly(amidoamine) (PAMAM-G4). They were prepared via the alternate immersion of a substrate into the polycationic and polyanionic aqueous solutions, at concentrations of 0.5 mg/mL at three pHs: 4, 6 and 8. The assembly of multilayers was monitored aRer each adsorption step by UV-VIS spectroscopy. A linear increase was observed in the peak at 480 nm, assigned to the transition of the azobenzene moiety, indicating that the same amount of material was deposited at each deposition step. Birefringence was optically induced in films using a 532 nm NdYAG laser. Among the LbL properties, the characteristic writing time - corresponding to the time to achieve 50% of maximum birefiingence - was the quantity that most varied with the materials and experimental conditions employed. The writing time was estimated as 34 min. for PEI/PS-119 with solution at pH 8 films, 0.5 min. for PDAC(HMW)/PS-119, pH 4 films, ca. 10 min. for PAWBY, pH 8 films and 3 s for PDAC(HMW)íBY, pH 4 films. These differences in writing times are probably related to the structural differences of the polycations, which determine the degree of interactions between polycation and polyanion. Indeed, interactions between polyanion and PDAC are expected to occur to a lesser extent (in comparison to the other films) due to the hindering promoted by the dimethyl group in the quaternary ammonium salt, minimizing the interaction with sulfonated groups from PS-119 or BY. With less interaction the azobenzene groups are more mobile, thus causing the writing time to be shorter for PDACIpolyanion films. It should be stressed that the writing time for PDAC/BY is the shortest ever reported for LbL films, being of the same order of magnitude of writing times in cast and Langmuir-Blodgett (LB) films. The residual birefringence, aRer the writing laser was switched off, was at least 78% for all systems, indicating that these LbL films are suitable for long-term optical memories.

Orientador: Antonio Riul Júnior / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-02T19:37:47Z (GMT). No. of bitstreams: 1 Jimenez_MawinJavierMartinez_D.pdf: 7578838 bytes, checksum: def5bc65d8270856f55d63211e1e0f09 (MD5) Previous issue date: 2017 / Resumo: Para alcançar alto desempenho em dispositivos e aplicações faz-se necessário uma melhor compreensão do comportamento de materiais a base de grafeno em nanoescala para otimização de design e fabricação. A síntese química é uma excelente rota alternativa para produzir compósitos em nanoestruturas bem definidas de tamanhos semelhantes, garantindo propriedades elétricas reprodutíveis para aplicações confiáveis. O grafeno, na forma de pontos quânticos (QDs, do inglês quantum dots) em dimensão zero e nanofolhas (NPLs, do inglês graphene nanoplateletes) bidimensionais (2D), são materiais emergentes com funcionalidades únicas promissoras para novas aplicações. Neste trabalho apresentamos um estudo detalhado dos mecanismos de transporte em nanoestruturas formadas pela técnica de automontagem por adsorção física (LbL, do inglês Layer-by-Layer) na forma de multicamadas, com controle de espessura em nível molecular. Os filmes LbL foram formados por óxido de grafeno reduzido (rGO) funcionalizado com diferentes polieletrólitos tanto na forma de QDs quanto nanofolhas. As caracterizações elétricas indicaram corrente limitada pela carga espacial em algumas amostras, e em outras arquiteturas moleculares, mecanismo de condução via Poole-Frenkel seguindo a lei de Mott dominada por saltos variáveis. A flexibilidade da técnica LbL aliada à dimensão dos materiais utilizados foram favoravelmente exploradas como um ajuste fino para controle da mobilidade de portadores dentro das nanoestruturas formadas. Foi observado em alguns casos uma condução planar no interior da camada contendo rGOs na estrutura LbL com mobilidade eletrônica efetiva de ~ 35 cm² V^-1 s^-1. Em outros casos um mecanismo de condução 3D (interplanar ao longo de toda nanoestrutura LbL) com mobilidade eletrônica de ~ 151 cm² V^-1 s^-1. Medidas em função da temperatura indicaram alta probabilidade de saltos randômicos entre ilhas condutoras de rGO distribuídas ao longo da camada contendo os pontos quânticos, que contribui para um maior tempo de trânsito dos portadores e, consequentemente, mobilidades menores. O oposto ocorre para as nanofolhas de rGO, que requerem maiores energias de ativação devido ao tamanho e presença de defeitos, resultando em caminhos condutores maiores e com maiores mobilidades / Abstract: To achieve high-performance in devices and applications it is important a better comprehension of the behavior at nanoscale of graphene-based materials to promote a rational design and fabrication. The chemical synthesis is an excellent alternative route to optimize graphene-based composites in well-defined nanostructures of similar sizes, ensuring reproducible electrical properties for reliable applications. Graphene as quantum dots (QDs) and nanoplatelets (NPLs) presents emerging zero- and two-dimensional (2D) materials with promising unique functionalities to novel applications. We present here a detailed study of the charge transport mechanisms in multilayered nanostructures formed by physical adsorption through the layer-by-layer (LbL) technique, with molecular level thickness control. The LbL films were formed by reduced graphene oxides (rGO) functionalized with different polyelectrolytes and processed either as QDs or nanoplatelets. The electrical characterizations indicated a space-charge-limited current (SCLC) in some samples, while in other molecular architectures it was found a Poole-Frenkel conduction mechanism dominated by a Mott-variable range hoping model. The LbL assembly together with the dimensionalty of the materials could be favorably used as a fine tuning to control the charge carrier mobility inside the formed nanostructures. The flexibility of the LbL technique together with the dimensionality of the materials were favorably explored as a fine tuning of the charge carrier mobility inside the nanostructures. It was observed in some cases a 2D intra-planar conduction within the rGO layer in the LbL films, with an effective charge carrier mobility of ~ 35 cm² V-1 s-1, and in other cases a 3D conduction mechanism (interplanar along with the LbL nanostructure) with electronic mobility of ~ 151 cm² V-1 s-1. Temperature measurements indicated a higher probability of random jumps between rGO conducting "islands" distributed along with the plane layer having quantum dots, which contributes for a longer transit time of the carriers and, consequently, lower mobility values. The opposite occurred for the rGO nanoplatelets that required higher activation energy due to size and presence of defects, resulting in larger conductive pathways and higher mobilities / Doutorado / Física / Doutor em Ciências / 1247719 / CAPES / FAPESP

Only in recent times has the true potential of cellulose as a high-end functional and sustainable material been realised. As the world’s most abundant resource cellulose has been utilised by man throughout history for timber, paper and yarns. It is found in every plant as a hierarchical material and can be extracted and converted into fibres which are of great use, especially in the form of nanofibrous materials. This thesis has focused on the utilisation and ability of cellulose nanocrystals (CNCs) to generate structural colour in fabricated thin films. This has been achieved in two ways: Firstly, the natural morphology of CNCs and their ability to form a suspension have been applied to a layer-by-layer (LbL) regime to produce tunable Bragg reflecting thin films. Secondly, a novel technique combining profilometry and spectroscopy has been developed to estimate the distribution of CNCs within EISA thin films and correlate this with the optical properties of the film. This thesis reports the successful fabrication of synthetic CNC LbL Bragg reflecting thin films. The film was compiled using an additive layer-by-layer technique which allowed the construction of a multi-layered thin film and control over individual layer thicknesses and refractive index. Also reported is the discovered reflection of both left and right handed circularly polarised light (CPL) from CNC EISA thin films. These reflections were found to correlate with CNC distribution within the thin films. The distribution of CNCs was estimated using a novel technique which combined spectroscopically measured film absorbance as a function of the volume of the film area under investigation. The specific volumes were calculated using profilometry measurements and the beam spot size used in the spectroscopy measurements.

The primary focus of my work has been to prepare new solid adsorbents for solid phase microextraction (SPME) via sputtering of silicon. The orientation of the silica substrates/fibers and the sputtering pressure induced the formation of porous and columnar structures. Sputtering was performed for different times to yield fibers with different thicknesses. Piranha treatment of the surface increased the concentration of silanol groups, which underwent condensation with vapor deposited octadecyldimethylmonomethoxy silane to incorporate octadecyl chains onto the fiber surfaces. Silanized, sputtered fibers were preconditioned for 3 h at 320 °C to remove the unreacted chains. Comparison of the extraction efficiencies of 1.0 and 2.0 µm sputtered, silanized fibers with a commercial fiber (7 µm PDMS) for a series of analyte mixtures, which included alkanes, alcohols, aldehydes, esters, and amines, was demonstrated. The silanized, sputtered fiber performed better than the commercial fiber in extraction of most of the compounds. These fibers demonstrated long life as no degradation was seen even after 300 extractions. Carry-over between runs was not observed. The repeatability of the sputtered fibers was similar to commercial ones. The extraction of more than 50 compounds from a real world botanical sample using the 2.0 µm sputtered, silanized fiber was also demonstrated. In my second project, a facile method for the preparation of superhydrophobic surfaces (SHS) on glass and silicon surfaces was developed. A two-tier topography (needed for an SHS) was created in 60 min by the aggregation of nanosilica during in situ urea-formaldehyde polymerization. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrated rough topography. Vapor deposition of a low surface energy silane imparted hydrophobicity, which was confirmed by the presence of an F 1s signal in X-ray photoelectron spectroscopy (XPS). The prepared surfaces exhibited water contact angles (WCA) of greater than 150 °C with very low sliding angles. In my third project, a multilayer assembly of nitrilotris(methylene)triphosphonic acid, a corrosion inhibitor, and zirconium was constructed on alumina at room temperature. Attempts to prepare a layer-by-layer assembly at higher temperature (70 °C) was unsuccessful due to etching of the alumina surface. A suite of analytical techniques, XPS, AFM, time-of-flight secondary ion mass spectrometry, and spectroscopic ellipsometry was used to characterize these surfaces. This thesis also contains appendices of tutorial articles I wrote on modeling in ellipsometry, and data analysis tools (classical least squares and multivariate curve resolution).

Transparent electrodes made from metal oxides suffer from poor flexibility and durability. Highly transparent and electrically conductive thin films based on carbon nanotubes (CNTs) were assembled as a potential indium tin oxide (ITO) replacement using layer-by-layer (LbL) assembly. The ultimate objective of this dissertation work is to produce CNT-based assemblies with sheet resistance below 100 Omega/sq and visible light transmission greater than 85 percent. The alternate deposition of positively charged poly(diallyldimethylammonium chloride) [PDDA] and CNTs stabilized with negatively charged deoxycholate (DOC) exhibit linear film growth and thin film properties can be precisely tuned. Ellipsometry, quartz crystal microbalance, and UV-vis were used to measure the growth of these films as a function of PDDA-CNT bilayers deposited, while TEM, SEM, and AFM were used to visualize the nanostructure of these films. Following a literature review describing potential ITO substitutes and LbL technology, the influence of CNT type on optoelectronic performance of LbL assemblies is described. Three different types of nanotubes were investigated: (1) multiwalled carbon nanotubes (MWNTs), (2) few-walled carbon nanotubes (FWNT), and (3) purified single-walled carbon nanotubes (SWNTs). SWNTs produced the most transparent (>85 percent visible light transmittance) and electrically conductive (148 S/cm, 1.62 kOmega/sq) 20-bilayer films with a 41.6 nm thickness, while MWNT-based films are much thicker and more opaque. A 20-bilayer PDDA/(MWNT DOC) film is approximately 103 nm thick, with a conductivity of 36 S/cm and a transmittance of 30 percent. In an effort to improve both transparency and electrical conductivity, heat and acid treatments were studied. Heating films to 300 degree C reduced sheet resistance to 701 Omega/sq (618 S/cm conductivity, 38.4 nm thickness), with no change in transparency, owing to the removal of insulating component in the film. Despite improving conductivity, heating is not compatible with most plastic substrates, so acid doping was investigated as an alternate means to enhance properties. Exposing SWNT-based assemblies to HNO3 vapor reduced sheet resistance of a 10 BL film to 227 Omega/sq. Replacing SWNTs with double walled carbon nanotubes (DWNTs) provided further reduction in sheet resistance due to the greater metallic of DWNT. A 5 BL DWNT film exhibited the lowest 104 Omega/sq sheet resistance (4200 S/cm conductivity, 22.9 nm thickness) with 84 percent transmittance after nitric acid treatment. DWNT-based assemblies maintained their low sheet resistance after repeated bending and also showed electrochemical stability relative to ITO. This work demonstrates the excellent optoelectronic performance, mechanical flexibility, and electrochemical stability of CNT-based assemblies, which are potentially useful as flexible transparent electrodes for a variety of flexible electronics.

Thin layers with high barrier to oxygen and other gases are a key component to many packaging applications, such as flexible electronics, food, and pharmaceuticals. Vapor deposited thin films provide significant gas barrier, but are prone to cracking when flexed, require special, non-ambient processing environments, and can involve complex fabrication when layered with polymers. The addition of clay into polymers can enhance barrier properties relative to the neat polymer; however, these composites are subject to clay aggregation at high loadings, which leads to increased opacity and random platelet alignment that ultimately reduce barrier improvement. Layer-by-layer (LbL) assembly is capable of producing thin films that exhibit super gas barrier properties, while remaining flexible and completely transparent. Montmorillonite (MMT) clay and branched polyethylenimine (PEI) were deposited via LbL assembly to create gas barrier films that can be tailored by altering the pH of the PEI deposition solution or the concentration of the MMT suspension. Films grow linearly as a function of layers deposited, where increasing PEI pH increases spacing between clay layers and increasing MMT concentration increases thin film clay content. An oxygen transmission rate (OTR) below the detection limit of commercial instrumentation (< 0.005 cm3/m2•day•atm) is observed after 70 layers of 0.2 wt % MMT or 24 layers of 2 wt % MMT are deposited with pH 10 PEI onto 179 µm thick poly(ethylene terephthalate) (PET) film. Three-component films of PEI, poly(acrylic acid) (PAA), and MMT grow exponentially as a function of PEI/PAA/PEI/MMT quadlayers deposited. A transparent, ultrathin film of only four quadlayers deposited onto PET exhibits the lowest oxygen permeability ever reported for any thin film material, at only 51 nm thick. Finally, the first example of LbL assembly using large aspect ratio vermiculite (VMT) clay was performed. PEI/VMT films grow linearly as a function of layers deposited and exhibit 95 % light transmission with 97 wt % VMT. The barrier of these films is due to the highly aligned nanobrick wall structure that creates a tortuous path for permeating molecules. Coupling high flexibility, transparency, and barrier, these coatings are good candidates for a variety of packaging applications.

The present thesis focuses on the selection of polymers and methods to fabricate stable and stimuli responsive multilayer self-assembly via layer-by-layer (LbL) approach. The polymers utilized in this study are biodegradable and biocompatible such as hyaluronic acid, chitosan and poly(vinyl alcohol) (PVA). The thesis is comprised of six chapters and a brief discussion on the contents of the individual chapters is given below. Chapter I reviews the LbL self-assembly approach in the context of drug delivery. The various interactions such as electrostatic, hydrogen bonding and covalent bonding involved in preparation of stable multilayer assemblies via LbL approach are discussed. Stimuli responsive behaviour of these multilayer assemblies can be tuned by choosing suitable depositing materials and method. Preparation of hollow microcapsules using LbL approach and its application in drug delivery has also been described in this chapter. Chapter II deals with the LbL assembly of a neutral polymer, poly(vinyl alcholol) (PVA). The negative charge on PVA backbone was induced by physical cross-linking with borax. The PVA-borate can undergo electrostatic interaction with positively charged chitosan in LbL process to form multilayer thin film. The thin film of PVA-borate complex/chitosan was found be responsive towards glucose concentration; disintegration of the multilayer assembly was observed at a high glucose concentration. This finding was rationalized on the basis of strong interaction of glucose with borate ions leading to dissociation of PVA-borate complex and subsequent collapse of the assembly. Thus, this multilayer self-assembly is potent for glucose triggered drug delivery. Chapter III reports the construction of a stable hydrogen bonded multilayer self-assembly based on complementary DNA base pairs (adenine and thymine) interaction. The natural polymer such as chitosan was modified with adenine whereas hyaluronic acid was modified with thymine. These two modified polymers were sequentially deposited on flat substrate and melamine formaldehyde (MF) particles; wherein strong interaction among the DNA base pairs led to the formation of stable assembly without utilizing any external cross-linking agent. The modified polymers are non-cytotoxic as proved from MTT assay. Further the multilayer assembly was used for pH responsive anticancer drug doxorubicin hydrochloride (DOX) release. In Chapter IV, glutaraldehyde mediated LbL self-assembly of single polymer multilayer thin films on flat and colloidal substrate by covalent bonding is described. A comparitive study between the native polymer (chitosan) and adenine modified polymer in the growth of thin film is performed. It is established from the study that the conformation of polymer and the availability of cross-linking points on the polymer play a crucial role in controlling the growth of these multilayer assemblies. Chapter V is divided into two parts (A and B). Part A describes a simple and unique protocol for fabrication of water dispersed chitosan nanoparticles (CH NPs). The method utilized in this work is based on the fast desolvation technique without using any additional stabilizer or any sophisticated instrumental setup. Furthermore, the CH NPs prepared from the mentioned protocol were proved to be cell-viable and are found to be responsive towards pH of the solution. In part B of this chapter, the LbL self-assembly of the responsive CH NPs is fabricated via electrostatic interaction with hyaluronic acid (HA). The growth of the multilayer thin film was found to be linear as function of number of bilayers. The morphology of thin film was characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The microscopic images reveal the uniform film morphology devoid of any phase separation of nanoparticles and polymers. Subsequently, the film was loaded with an anticancer therapeutic, doxorubicin hydrochloride (DOX). The release dynamics of encapsulated drug from the self-assembly are tunable and pH responsive. Chapter VI deals with the general and versatile method for the encapsulation of hydrophobic model drugs into polymeric multilayer assembly by using LbL approach. Electrical charge was induced on the surface of pyrene (uncharged organic substance) using an amphiphilic surfactant, sodium dodecyl sulfate (SDS) by micellar solubilization. The SDS micellar solution of pyrene was utilized to grow LbL multilayer thin film on a planar substrate and colloidal particles along with chitosan as a polycation. The LbL self-assembly of pyrene loaded SDS micelles/chitosan is additionally able to encapsulate hydrophobic or hydrophilic model therapeutics, thus providing an opportunity for dual-drug delivery. The desorption kinetics of the two model drugs from the thin film is found to follow a second order rate model.

Multi-walled carbon nanotubes (MWCNTs) were successfully coated with two different pseudocapacitive polyoxometalates (POMs) (SiMo12O40-4 (SiMo12) and PMo12O40-3 (PMo12)) via “Layer-by-Layer” deposition. Even with merely a “single-layer” of POM, the modified nanotubes exhibited more than 2X increase in capacitance compared with that of bare nanotubes. To further improve their electrochemical performances, the deposition sequence of the POM layers was adjusted to form “alternate layer” coating to modify MWCNT. A synergistic effect on the capacitance and kinetics was observed with the alternate layer coatings. X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM) also proved the successful coating of POMs on MWCNTs. The potential-pH relationship provided important insights in terms of the deposition mechanism and suggested that the bottom layer close to the electrode substrate was the dominating layer in alternate layer coated MWCNT electrodes.

Multi-walled carbon nanotubes (MWCNTs) were successfully coated with two different pseudocapacitive polyoxometalates (POMs) (SiMo12O40-4 (SiMo12) and PMo12O40-3 (PMo12)) via “Layer-by-Layer” deposition. Even with merely a “single-layer” of POM, the modified nanotubes exhibited more than 2X increase in capacitance compared with that of bare nanotubes. To further improve their electrochemical performances, the deposition sequence of the POM layers was adjusted to form “alternate layer” coating to modify MWCNT. A synergistic effect on the capacitance and kinetics was observed with the alternate layer coatings. X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM) also proved the successful coating of POMs on MWCNTs. The potential-pH relationship provided important insights in terms of the deposition mechanism and suggested that the bottom layer close to the electrode substrate was the dominating layer in alternate layer coated MWCNT electrodes.