Wave propagation is a common phenomenon in aircraft structures resulting from high velocity transient loadings like bird hit, gust etc. Apart from understanding the behavior of structures under such loading, wave propagation analysis is also important to gain knowledge about their high frequency characteristics, which have several applications. The applications include structural health monitoring using diagnostic waves and control of wave transmission for reduction of noise and vibration. Transient loadings with high frequency content are associated with wave propagation. As a result, the higher modes of the structure participate in the response. Finite element (FE) modeling for such problem requires very fine mesh to capture these higher modes. This leads to large system size and hence large computational cost. Wave propagation problems are usually solved in frequency domain using fast Fourier transform (FFT) and spectral finite element method is one such technique which follows FE procedure in the transformed frequency domain. In this thesis, a novel wavelet based spectral finite element (WSFE) is developed for wave propagation analysis in finite dimension structures. In WSFE for 1-D waveguides, the partial differential wave equations are reduced to a set of ODEs using orthogonal compactly supported Daubechies scaling functions for temporal approximation. The localized nature of the Daubechies basis functions allows finite domain analysis and imposition of the boundary conditions. The reduced ODEs are usually solved exactly, the solution of which gives the dynamic shape functions. The interpolating functions used here are exact solution of the governing differential equation and hence, the exact elemental dynamic stiffness matrix is derived. Thus, In the absence of any discontinuities, one element is sufficient to model 1-D waveguide of any length. This elemental stiffness matrix can be assembled to obtain the global matrix as in FE and after solution, the time domain responses are obtained using the inverse wavelet transform. The developed technique circumvents several serious limitations of the conventional FFT based Spectral Finite Element (FSFE). In FSFE, the wave equations are reduced to ODEs using FFT for time approximation. The remaining part of the formulation is quite similar to that of WSFE. The required assumption of periodicity in FSFE, however, does not allow modeling of finite length structures. It results in “wrap around” problem, which distorts the response simulated using FSFE and a semi-infinite (“throw-off”) element is required for imparting artificial damping. This artificial damping occurs as the “throw off” element allows leakage of energy. In some cases, a very high damping can also be considered instead of “throw off” element to remove wrap around effects. In either cases, the damping introduced is much larger than any inherent damping that may be present in the structure. It should also be mentioned that even in presence of the artificial damping, a larger time window is required for removing the distortions completely. The developed WSFE method is completely free from such problems and can efficiently handle undamped finite length structures irrespective of the time window considered. Apart from this, FSFE allows imposition of only zero initial condition and in contrary any initial conditions can be used in WSFE. Though FSFE has problem in modeling finite length undamped structures for time domain analysis, it is well suited for performing frequency domain study of wave characteristics, namely, the determination of spectrum and dispersion relations. WSFE is also capable of extracting these frequency dependent wave properties, however only up to a certain fraction of the Nyquist frequency. This constraint results from the loss in frequency resolution due to the increase in time resolution in wavelet analysis, where the basis functions are bounded both in time and frequency. A price has to be paid in frequency domain in order to obtain a bound in the time domain. The consequence of this analysis is to impose a constraint on the time sampling rate for the simulation with WSFE, to avoid spurious dispersion. WSFE for 2-D waveguides are formulated using Daubechies scaling functions for both temporal and spatial approximations. The initial and boundary conditions, however, are imposed using two different methods, which are wavelet extrapolation technique and periodic extension or restraint matrix respectively. The 2-D WSFE is bounded in both the spatial directions unlike 2-D FSFE, which is essentially unbounded in one spatial direction. Apart from this, 2-D WSFE is also free from “wrap around” problem similar to 1-D WSFE due to the localized nature of the basis functions used for temporal approximation. In this thesis, WSFE is developed for isotropic 1-D and 2-D waveguides for time and frequency domain analysis. These include elementary rod, Euler-Bernoulli and Timoshenko beams in 1-D modeling, and plates and axisymmetric cylinders in 2-D modeling. The wave propagation responses simulated using WSFE for these waveguides are validated using FE results. The advantages of the proposed technique over the corresponding FSFE method are also highlighted all through the numerical examples. Next part of the thesis involves the extension of the developed WSFE technique for modeling composite and nano-composite structures to study their wave propagation behavior. Due to their anisotropic nature, analysis of composite structures, particularly high frequency transient analysis is much more complicated compared to the corresponding metallic structures. This is due to the presence of stiffness coupling in these structures. Superior mechanical properties of composites, however, are making them integral parts of an aircraft and thus they often experience such short duration, high velocity impact Loadings. Very few literatures report the response of composite structures subjected to such high frequency excitations. Here, WSFE is formulated for a higher order composite beam with axial, flexural, shear and contractional degrees of freedom. WSFE is also formulated for composite plates using classical laminated plate theory with axial and flexural degrees of freedom. Simulations performed using these WSFE models are used to study the higher order and elastic coupling effects on the wave propagation responses. Carbon nanotubes (CNTs) and their composites are attracting a great deal of experimental and theoretical research world-wide. The recent trend in the literature shows a great interest in the dynamic and wave characteristics of CNTs and nano-composites because of their several applications. In most of these applications, CNTs are used in the embedded form as it does not requires precise alignment of the nano-tubes. In addition, the extraordinary mechanical properties of CNTs are being exploited to achieve high strength nano-composite. Apart from the experimental studies and atomistic simulation to study the mechanical properties of CNTs and nano-composites, continuum modeling is also receiving much attention, mainly due to its computational viability. In this thesis, a 1-D WSFE is formulated for multi-wall carbon nanotube (MWNT) embedded composite modeled as beam using higher order layer-wise theory. This theory allows to model partial interfacial shear stress transfer, which normally occurs due to improper dispersion of CNTs in nano-composites. The effects of different matrix materials and fraction of shear stress transfer on the wave characteristics are studied. The responses obtained using other beam theories are also compared. The beam modeling does not allow capturing the radial motions of the CNT, which are important for several applications. These can be effectively captured by modeling the CNT using a 2-D axisymmetric model. Hence, a 2-D WSFE model is constructed to capture the high frequency characteristics of single-walled carbon nanotubes (SWNTs). The response of SWNT simulated using the developed model is validated with experimental and atomistic simulation results reported in the literature. The comparison are done for dispersion relation and also radial breathing mode frequencies. The effects of geometrical parameters, namely the radius and the wall thickness of the SWNT on the higher radial, longitudinal and coupled radial-longitudinal vibrational modes are analyzed. These behaviors are studied in both time and frequency domains. Such time domain analyses of finite length SWNT are not possible with the Fourier transform based techniques reported in literature, although, such analyses are important particularly for sensor applications of SWNT. Spectral finite element method is very much suited for solution of inverse problems like force reconstruction from the measured wave response. This is because the technique is based on the concept of transfer function between the displacements (output) and applied forces (input). In the present work, WSFE is implemented for identification of impact force from the wave propagation responses simulated with FE and used as surrogate experimental results. The results show that WSFE can accurately reconstruct the impulse load applied to 1-D waveguides which include rod, Euler-Bernoulli beam and connected 2-D frame, even with highly truncated response. This is unlike FSFE, where the accuracy of the identified force depends largely on the time window of the measured responses. The detection of damage from the wave propagation analysis is another class of inverse problems considered in this thesis and is of utmost importance in the area of aircraft structural health monitoring. Here, the detection scheme is based on arrival time of the waves reflected from the damage. A novel detection technique based on wavelet filtering is proposed here and it is shown to work efficiently even in the presence of noise in the measured wave responses. Detection of damage requires an efficient damage model to simulate the mode of structural failure. In this regard, two spectrally formulated wavelet elements are proposed, one to model isotropic beam with through-width notch and the second to model composite beam with embedded de-lamination. In the first case, the response of the damaged beam is considered as the perturbation of the undamaged response and the linear perturbation analysis leads to a completely new set of dynamic stiffness matrix. In the second case, the delamination is modeled by subdividing the de-laminated region into separate waveguides and full damage model is established by imposing the kinematics. These models help to simulate wave propagation in such damaged beams to study the effect of damage on the wave response. Noise and vibration are often transmitted from the source to the other parts of the structure in the form of wave propagation. Thus, control of such wave transmission is essential for reduction of noise and vibration, which are the main cause of discomfort and in many cases cause failure of structure. Here, techniques for both passive and active controls of wave are proposed. For active control, a closed loop system is modeled using WSFE with magnetostrictive actuator for control of axial and flexural wave propagations in connected isotropic 1-D waveguides. The feedback is negative velocity and/or acceleration measured at different sensor points. A very new application of CNT reinforced composite for passive control of vibration and wave response is explored in this thesis. For this, a novel concept of nano-composite inserts is proposed. This insert can be made from CNTs dispersed in polymer. The high stiffness of the inserts helps to regulate the power flow in the form of wave propagation from the point of application of the loads to other parts of the structures. The length of the insert, volume fraction of CNTs and position are changed to achieve the required reduction in wave amplitudes. The entire thesis is split up into eight chapters. Chapter 1 presents a brief introduction, the motivation and objective of the thesis. Chapters 2 and 3 give a detail account of wavelet spectral finite element formulation for 1-D and 2-D isotropic waveguides, while Chapter 4 gives the same for composite waveguides. Chapter 5 brings out essential wave characteristics in carbon nanotubes and nano-composite structures, while Chapters 6 and 7 exclusively deal with application of WSFE to some real world problems. The thesis ends with summary and directions of future research. In summary, the thesis has brought out several new aspects of wave propagation in isotropic, composite and nano-composite structures. In addition to establishing wavelet spectral finite element as a useful tool for wave propagation analysis, several new techniques are presented, several new algorithm are proposed and several new concepts are explored.

Das Ziel der Promotionsarbeit ist es optisch transparente, nanoskalige Strontiumfluorid- und Ytterbiumfluorid-Sole hoher Konzentration für mögliche Anwendung in der Dentalmedizin zu synthetisieren. Über die fluorolytische Sol-Gel-Synthese ist es gelungen nanoskalige MFn-Sole (M=Sr, Yb) erfolgreich herzustellen. Die Umsetzung der Metallpräkursoren mit alkoholischer HF-Lösung im organischen Lösungsmittel führt zu transparenten, niedrig viskosen Solen. Mittels DLS, XRD und TEM wurden die Sole hinsichtlich ihrer Partikelgröße und ihres Alterungsverhaltens untersucht. Mittels WAXS-Messungen wurde das Alterungsverhalten der SrF2-Sole analysiert. Mit Hilfe der XRD und 19F-MAS-NMR-Spektroskopie wurde eine fluorhaltige, kristalline Spezies als Intermediat in der fluorolytischen Sol-Gel-Synthese des SrF2 nachgewiesen. DLS-Untersuchungen an Ytterbium-Solen zeigen eine Bildung von Partikeln im unteren Nanometerbereich sowie eine konzentrationsabhängige Partikelgrößenverteilung der Solpartikel. Die erhaltenen Xerogele sind röntgenamorph. Zudem konnten neue Yb(III)-Komplexe isoliert und strukturanalytisch charakterisiert werden. Die vorliegende Arbeit zeigt eine Möglichkeit, wie Kompositmaterialien auf Basis von nano-MFn (M=Sr, Yb) hergestellt werden können. Ausgehend von transparenten Solen konnten transparente Komposite mit einem großen Anteil an anorganischen Komponenten synthetisiert werden. Des Weiteren wurde die fluorolytische Sol-Gel-Synthese auf die Synthese von Nanopartikeln im System SrF2-YbF3 übertragen. Die Untersuchungen mittels DLS und TEM zeigen die Bildung von monodispersen Partikeln mit Partikelgrößen im unteren Nanometerbereich. Die nichtstöchiometrischen Phasen Sr1-xYbxF2+x sind durch einen weiten Homogenitätsbereich (bis ca. 50 mol-% Yb) charakterisiert und zeigen Anwendungspotential auf den Gebieten der Medizin, Zahnmedizin und Optik. / The focus of this thesis is the synthesis and characterization of nanoscopic metal fluorides for dental applications. Nanoscopic metal fluorides MFn (M = Sr, Yb) have been successfully synthesized via the fluorolytic sol-gel synthesis. The reaction of the metal precursors with alcoholic HF solution in organic solvents yields in transparent sols of high concentrations and low viscosity. DLS, TEM and XRD confirmed the formation of sol particles in the lower nm range and were used to characterize the particles as well as the aging behavior of the sols. Mechanistic insights were gained by following the reaction progress. A fluorine-containing crystalline species was detected by XRD and solid state 19F MAS NMR spectroscopy indicating the formation of an intermediate phase during the fluorolysis reaction. The investigation by DLS and TEM revealed the existence of ytterbium fluoride sol particles with diameter of approximately 5 nm. Additionally, DLS studies show a concentration dependency on particle size. XRD revealed total amorphousness of the product. In addition, new ytterbium(III) complexes were isolated and structurally characterized by X-ray analysis. Furthermore, the fluorolytic sol-gel synthesis has been modified for the preparation of transparent nanocomposite bulk materials. Large amounts of nanoscopic metal fluorides MFn (M=Sr, Yb) can be embedded in the organic polymer matrix commonly used in dentistry without facing loss of visual optical transparency. A new approach to prepare nanoparticles in SrF2-YbF3 systems via the fluorolytic sol-gel synthesis is presented. The investigations by DLS and TEM revealed the presence of monodisperse solid particles with sizes in the lower nm range. The Sr1-xYbxF2+x nonstoichiometric fluorite phases are characterized by a wide range of homogeneity (up to approx. 50 mol % Yb) and show promise of a wide range of applicability in the areas of medicine, dentistry and optics.

The search and research for high performance materials for aerospace applications is a continuous evolving process. Among several fibre reinforced polymers, carbon fibre reinforced polymer (CFRP) is well known for its high specific stiffness and strength. Though high modulus and high strength carbon fibre with structural resin systems have currently been established reasonably well and are catering to a wide variety of aerospace structural applications, these properties are generally directional with very high properties along the fibre direction dominated by fibres and low in other directions depending mainly on the resin properties. Thus, there is a need to enhance the mechanical properties of the resin systems for better load transfer and to improve the resin dominated properties like shear strength and properties in directions other than along the fibre. Use of carbon nanotubes (CNTs) with their extraordinary specific stiffness and strength apparently has great potential as an additional reinforcement in resin for development of CNT-CFRP nanocomposites. However, there are several issues that need to be addressed such as compatibility of a particular resin with CNTs, amount of CNTs that can be added, uniform dispersion of these nanotubes, surface treatment and curing process etc., for optimal enhancement of the required properties. Epoxy and cyanate ester resin systems are finding applications in aerospace structures owing to their desirable set of properties. Of these, bisphenol E cyanate ester (BECy) resin of low viscosity with its low moisture absorption, better dimensional stability, and superior mechanical properties can establish itself as potential structural resin system for these applications. BECy in particular has the advantage of being more suitable for out of autoclave manufacturing process such as Vacuum Assisted Resin Transfer Molding (VARTM). Literature shows that, significant work has been carried out by various researchers reporting improvements using CNTs in epoxy resins along with various associated problems. However, studies on effects of addition of CNTs /fCNTs to BECy-CFRP composite system are not well reported. Thus, objective of this work is to study the effects of adding pristine and functionalized CNTs to low viscosity cyanate ester as well as epoxy resin systems. Further, to study the effects on mechanical properties of nanocomposites with carbon fibre reinforcement in these CNT dispersed resin system through a combination of experimental and computational approaches. Multiwall carbon nanotubes (CNTs) without and with different chemical functionalization are chosen to be added to epoxy and BECy resins. The quantity of these CNTs /fCNTs is varied in steps up to 1% by weight. Different methods of mixing such as shear mixing, ultrasonication and combined mixing cycles are implemented to achieve uniform dispersion of these nanotubes in the resin system. Standard test samples are prepared from these mixtures of nanotubes in resin systems to study the variation in mechanical properties. Further, these nanotubes added resin systems are used in fabricating CFRP laminates by VARTM process. Both uni-directional and bi-directional laminates are made with the above modified resin systems with CNTs/fCNTs. Series of experimental investigations are carried out to study various aspects involved in making of nanocomposites and the effects of the same on different mechanical properties of the nanocomposites. Standard specimens are cut out from these laminates to evaluate them for tension, compression, flexure, shear and interlaminar shear strength. The main parameters investigated are the effects of varied quantity of CNTs and functionalized CNTs in the resin mix and in CFRP nanocomposites, effect of different mixing / curing cycles etc. on the mechanical properties of the nanocomposites. The investigations have yielded very interesting and encouraging results to arrive at optimum quantity of CNTs to be added and also the effects of functionalization to achieve enhanced mechanical properties. In addition, correlation of mechanical property enhancements with failure mechanisms, dispersion behaviour and participation of CNTs / fCNTs in load transfer are explained with the aid of scanning electron microscope images. Computational studies are carried out through atomistic models using computational tools to estimate the mechanical properties, understand and validate the effects of various parameters studied through series of experimental investigations. An atomistic model is built taking into consideration the nanoscale effects of the single wall carbon nanotubes (SWCNTs) and its reinforcement in the BECy resin. Using these atomistic models, mechanical properties of individual SWCNT, BECy polymer resin, polymer with different quantities of added SWCNT, and the CFRP laminates with improved resin are computed. As the interaction of CNT with the polymer is only at the outermost layer and the mechanical properties of either MWCNTs or SWCNTs are too high compared to resin systems, it is not expected to have any difference in the final outcome whether it is MWCNT or SWCNT. Hence, only SWCNTs are considered in computational studies as it helps in reducing the complexity of atomistic models and computational time when coupled with polymer resin. This is valid even for functionalized CNT as functionalization is also a surface phenomenon. To start with, the mechanical behaviour of SWCNT is studied using molecular mechanics approach. Molecular mechanics based finite element analysis is adopted to evaluate the mechanical properties of armchair, zigzag and chiral SWCNT of different diameters. Three different types of atomic bonds, i.e., carbon-carbon covalent bond and two types of carbon-carbon van der Waals bonds are considered in the carbon nanotube system. The stiffness values of these bonds are calculated using the molecular potentials, namely Morse potential function and Lennard-Jones interaction potential function respectively and these stiffness values are assigned to spring elements in the finite element model of the SWCNT. The importance of inclusion of Lennard-Jones interactions is highlighted in this study. Effect of these non-bonded interactions is studied by making the numerical stiffness of these bonds to negligible levels and found that they significantly reduce the mechanical properties. The effect of non-bonded Lennard-Jones atomic interactions (van der Waal interactions) considered here is a novelty in this work which has not been considered in previous research works. The finite element model of the SWCNT is constructed, appropriate boundary conditions are applied and the behaviour of mechanical properties of SWCNT is studied. It is found that the longitudinal tensile strength and maximum tensile strain of armchair SWCNTs is greater than that of zigzag and chiral SWCNTs and its value increases with increasing SWCNT diameter. The estimated values of the mechanical properties obtained agree well with the published literature data determined using other techniques. As the systems become more complicated with the inclusion of polymers, molecular dynamics (MD) method using well established codes is more adoptable to study the effect of SWCNTs on BECy. Hence, it is used to model and solve the nanosystems to generate their stress-strain behavior. Further, MD approach followed here can effectively include interfacial interaction between polymer and the CNTs as well. Mechanical properties of SWCNT functionalized SWCNT (fSWCNT), pure BECy resin and that of the CNT nanocomposite consisting of specific quantity of SWCNT / fSWCNT in BECy are estimated using MD method. Atomistic models of SWCNT, fSWCNT, BECy, BECy with specific quantities of CNT / fSWCNT are constructed. A monomer of BECy is modelled and stabilized before its usage as a building block for modelling of BECy resin and to compute its properties. A cell of specific size containing monomers of BECy and another cell of same size with SWCNT at centre surrounded by BECy monomer molecules are built. The appropriate quantity of SWCNT in resin is modelled. This model captures the required density of the composite resin. The models so constructed are subjected to geometric optimization satisfying the convergence criteria and equilibrated through molecular dynamics to obtain a stable structure. The minimized structure is subjected to small strain in different directions to calculate the Young’s modulus and other moduli of the CNT-BECy resin composite. The process is repeated for different quantities of SWCNT in BECy resin to obtain their moduli. Further, tensile and shear strengths of CNT-BECy are obtained by subjecting the equilibrated structure to a series of applied strains from 0 to 10% in steps of 1%. The stress values corresponding to each strain are obtained and a stress – strain curve is plotted. From the stress- strain curve, the strengths of the CNT -BECy which is the stress corresponding to the modulus after which the material starts to soften are determined. Effects of functionalization on mechanical properties of SWCNT are observed. Further, effects of functionalization of SWCNT are studied with a specific quantity of fSWCNT on different moduli and strengths of BECy are investigated. The properties of enhanced CNT–BECy nanocomposite resin with different quantities of added CNT obtained through MD are used to estimate the mechanical properties of the CNT-BECy-CFRP nanocomposite using micromechanics model. Further, validation with experimental results is attempted comparing the trends in enhancement of properties of the CNT-BECy resin and CNT-BECy-CFRP nanocomposite system. The outcome of this research work has been significantly positive in terms of i) Development of an appropriate process establishing different parameters for dispersing CNTs in the resin system, mixing, curing cycle for making of nanocomposites demonstrating significant and consistent enhancement of mechanical properties of BECy based resin system and CFRP nanocomposites using optimum quantity of CNTs /fCNTs through a series of well planned and executed experimental investigations. Evaluation of mechanical properties for each of the cases has been carried out experimentally. ii) Establishing a computational methodology involving intricate atomistic modelling and molecular dynamics of nanosystems for estimation of mechanical properties of BECy polymer resin and to study the effects by addition of SWCNT / functionalized SWCNT on the properties. Results obtained through series of experimental investigations have been validated through this computational study. This could be an important step towards realising the potential of this resin system for high performance aerospace applications. Thus, in brief, detailed experimental work combined with computational studies performed as presented in this thesis resulted in achieving structurally efficient cyanate ester based nanocomposites which is unique and not reported in open literature.

The present Doctoral Thesis focuses on the investigation, characterization and influence of polyacrylic materials in different scientific and technological disciplines via a detailed computer simulation using the Molecular Dynamics (MD) technique, in conjunction with the very accurate, all-atom Dreiding force-field. The main research concepts and objectives are discussed and analyzed in three separate parts. In the first part, atomistic configurations of two model pressure-sensitive acrylic adhesives (PSAs), the atactic homopolymer poly(n-BA) [poly(n-butyl acrylate)] and the atactic copolymer poly(n-BA-co-AA) [poly(n-butyl acrylate-co-acrylic acid)] in the bulk phase or confined between two selected substrates, glassy silica (SiO2) and metallic α-ferrite (α-Fe), were built and simulated by MD in the NPT statistical ensemble. First, an equilibration cycle consisting of temperature annealings and coolings was followed, in order to generate well-equilibrated configurations of the PSA systems. Detailed results from the atomistic simulations are presented concerning their volumetric behavior, glass transition temperature, conformational, structural, viscoelastic and dynamic properties. Particular emphasis was given to the analysis and characterization of the hydrogen bonds that form in the poly(n-BA-co-AA) system. By analyzing the MD trajectories, poly(n-BA-co-AA) was found to exhibit a higher density than poly(n-BA) by about 7% at all temperatures, to be characterized by smaller-size chains for a given molecular weight (MW), to exhibit significantly slower terminal and segmental dynamics properties, and to be characterized by a glass transition temperature that was approximately 40% higher than that of poly(n-BA). We also examined the type and degree of adsorption of the two acrylic systems on the selected substrates by analyzing the MD results for the local mass density as a function of distance from the solid plane and the distribution of adsorbed chain segments in train, loop, and tail conformations, and by computing the work of adhesion at the two substrates. The results revealed a stronger adsorption for both acrylics on the SiO2 surface due to highly attractive interactions between polymer molecules and substrate atoms, and as a consequence a higher value for the work of adhesion compared to that on the α-Fe surface. Furthermore, we have developed a generalized non-equilibrium molecular dynamics (NEMD) algorithm to simulate the mechanical response of the two adhesives under a uniaxial stretching deformation. In the second part of the Thesis, results have been obtained from a hierarchical simulation methodology that led to the prediction of the thermodynamic, conformational, structural, dynamic and mechanical properties of two polymer nanocomposites based on syndiotactic poly(methyl methacrylate) or sPMMA. The first was reinforced with uniformly dispersed graphene sheets and the second with fullerene particles. How graphene functionalization affects the elastic constants of the resulting nanocomposite has also been examined. The phase behavior of the nanocomposite (in particular as we varied the relative size between the sPMMA chains and the diameter of fullerene molecules) has also been studied as a function of fullerene volume fraction. The simulation strategy entailed three steps: 1) Generation of an initial structure, which was then subjected to potential energy minimization and detailed molecular dynamics (MD) simulations at T = 500K and P = 1atm to obtain well relaxed melt configurations of the nanocomposite. 2) Gradual cooling of selected configurations down to room temperature to obtain a good number of structures representative of the glassy phase of the polymer nanocomposite. 3) Molecular mechanics (MM) calculations of its mechanical properties following the method originally proposed by Theodorou and Suter. By analyzing the results under constant temperature and pressure, all nanocomposite systems were found to exhibit slower terminal and segmental relaxation dynamics than the pure polymer matrices. The addition of a small fraction of graphene sheets led in all cases to the enhancement of the elastic constants; this was significantly more pronounced in the case of functionalized graphene sheets. We further mention that, for all polymer/fullerene nanocomposites addressed here, no phase separation or variation of polymer chain dimensions was observed as a function of fullerene size and/or fullerene volume fraction. In the third part of the Thesis, and motivated by the use of acrylic polymers for the design of membranes with aligned carbon nanotubes (CNTs) for several separation technologies (such as water desalination and wastewater treatment), we report results from a detailed computer simulation study for the nano-sorption and mobility of four different small molecules (water, tyrosol, vanillic acid, and p-coumaric acid) inside smooth single-wall CNTs (SWCNTs). Most of the results have been obtained with the molecular dynamics (MD) method, but especially for the most narrow of the CNTs considered, the results for water molecule were further confirmed through an additional Grand Canonical (μVT) Monte Carlo (GCMC) simulation using a value for the water chemical potential μ pre-computed with the particle deletion method. Issues addressed in the Thesis include molecular packing and ordering inside the nanotube for the four molecules, average number of sorbed molecules per unit length of the tube, and mean residence time and effective axial diffusivities, all as a function of tube diameter and tube length. In all cases, a strong dependence of the results on carbon nanotube diameter was observed, especially in the way the different molecules are packed and organized inside the CNT. For water for which predictions of properties such as local structure and packing were computed with both methods (MD and GCMC), the two sets of results were found to be fully self-consistent for all types of SWCNTs considered. Water diffusivity inside the CNT (although, strongly dependent on the CNT diameter) was computed with two different methods, both of which gave identical results. For large enough CNT diameters (larger than about 13 Å), this was found to be higher than the corresponding experimental value in the bulk by about 55%. Surprisingly enough, for the rest of the (phenolic) molecules simulated in this Thesis, the simulations revealed no signs of mobility inside nanotubes with a diameter smaller than the (20, 20) tube. This has been attributed to strong phenyl-phenyl attractive interactions, also to favorable interactions of these molecules with the CNT walls, which cause them to form highly ordered, very stable structures inside the nanotube, especially under strong confinement. The interaction, in particular, of the methyl group (present in tyrosol, vanillic acid, and p-coumaric acid) with the CNT walls seems to play a key role in all these compounds causing them to remain practically immobile inside nanotubes characterized by diameters smaller than about 26 Å. It was only for larger-diameter CNTs that tyrosol, vanillic acid, and p-coumaric acid were observed to demonstrate appreciable mobility. / Η παρούσα Διδακτορική Διατριβή εστιάζει στη μελέτη της σχέσης μεταξύ δομής και μακροσκοπικών φυσικών ιδιοτήτων υλικών από πολυακρυλικά μέσω μίας λεπτομερούς προσομοίωσης στον υπολογιστή με τη μέθοδο της Μοριακής Δυναμικής (ΜΔ), σε συνδυασμό με ένα πολύ επακριβές πεδίο δυνάμεων (το Dreiding) σε ατομιστική λεπτομέρεια. Οι κύριες ερευνητικές έννοιες καθώς και οι στόχοι συζητιούνται και αναλύονται σε τρία ξεχωριστά μέρη. Στο πρώτο μέρος, ατομιστικές απεικονίσεις δύο προτύπων πίεσο-ευαίσθητων συγκολλητικών υλικών (acrylic pressure sensitive adhesives ή PSAs), του ατακτικού πολυ-βουτυλικού-ακρυλικού εστέρα (poly(n-BA)) και του συμπολυμερούς του με ακρυλικό οξύ (poly(n-BA-co-AA)), τόσο μακριά όσο και κοντά σε υποστρώματα σίλικας (SiO2) και α-φερρίτη (α-Fe), μελετήθηκαν στη βάση ενός φάσματος ιδιοτήτων (θερμοδυναμικές, δομικές, ιξωδοελαστικές, δυναμικές, και συγκολλητικές), όπως και η μηχανική τους απόκριση υπό συνθήκες μονοαξονικής εκτατικής παραμόρφωσης. Στο δεύτερο μέρος παρουσιάζονται τα αποτελέσματα που εξήχθησαν από μία ιεραρχική μεθοδολογία προσομοίωσης που οδήγησε στην πρόβλεψη της φασικής συμπεριφοράς και των μηχανικών ιδιοτήτων νανοσύνθετων πολυμερικών υλικών (polymer nanocomposites ή PNCs) βασισμένων στο συνδιοτατκτικό πολυ-μεθακρυλικό μεθυλεστέρα (syndiotactic poly(methyl methacrylate) ή sPMMA), ενισχυμένο με ομοιόμορφα διεσπαρμένα φύλλα γραφενίου (graphene sheets) ή σωματίδια φουλερενίου (fullerene particles). Στο τρίτο μέρος, υποκινούμενοι από τη χρήση των ακρυλικών πολυμερών στο σχεδιασμό μεμβρανών με ενσωματωμένους ευθυγραμμισμένους νανοσωλήνες άνθρακα (ΝΑ, carbon nanotubes ή CNTs) σε διάφορες τεχνολογίες διαχωρισμού μορίων (με έμφαση στον καθαρισμό του νερού), παρουσιάζουμε αποτελέσματα από προσομοιώσεις, για τη νανο-ρόφηση και την κινητικότητα τεσσάρων διαφορετικών μικρών μορίων (water, tyrosol, vanilic acid, και p-coumaric acid) στο εσωτερικό λείων μονο-στρωματικών ΝΑ (single-wall CNTs ή SWCNTs). Τα θέματα που εξετάζονται περιλαμβάνουν τη μοριακή διευθέτηση και τη διάταξη στο εσωτερικό Ν.Α. των τεσσάρων μορίων, το μέσο χρόνο παραμονής τους, καθώς και τους αξονικούς συντελεστές διάχυσής του, συναρτήσει της διαμέτρου και του μήκους των ΝΑ.