This study was conducted in order to develop damping materials for practical applications, such as insulators for compact disk players and hard drive disks. Three types of styrene-based triblock copolymers and various paraffinic oils were selected to produce physical gels with low modulus. These polymer gels can be shaped by injection moulding to reduce the total cost for mass production. The miscibility and the morphology of the systems were examined by modulated-temperature differential scanning calorimetry (M-TDSC), dynamic mechanical thermal analysis (DMTA), transmission electron microscopy (IEM) and small angle X-ray scattering (SAXS). The experimental results showed that the glass transition temperatures of the mid blocks of the block copolymers swollen with the high Mw paraffinic oils obeyed the Fox equation. This means that the added paraffinic oil is selectively miscible with the mid blocks. However, it was also found by TEM that the polystyrene domains were also swollen by the low Mw paraffinic oil.

An NMR technique has recently been developed to determine the crosslink density in each phase of a polymer blend. This work uses the NMR method to study natural rubber (NR)/acrylonitrile butadiene rubber (NBR) blends, in order that the cure system used to vulcanize such blends can be optimized. A standard injection moulding cure system for NR/Perbunan N1807 (18% acrylonitrile content) gave much more crosslinking in the NBR phase. To reduce this imbalance a less polar analogue of the accelerator was used, resulting in a more even distribution of crosslinks but still with a bias towards the NBR.

The research evaluated the means in which mild variations in the polymer properties could be modified during the mixing process so that the final mixed compound met the desired rheological parameters. The initial work developed a model to measure the viscosity of the material in the internal mixer during the mixing process. The model assumed the mixer could be treated as two concentric rotary viscometers. The model had a rotor speed dependence which was caused by the assumption not being valid. However, this led to the work continuing in a modified form. It was felt that at a given rotor speed and temperature the torque measured on the rotors would be proportional to the viscosity of the material. This was found to be correct and therefore work continued using this principle. Programs were developed for internal mixers with variable speed rotors and fixed speed rotors. The programs were evaluated using natural rubber with different viscosities and were found to be capable of modifying the polymers to obtain a final mixed compound to a target viscosity. The control program was also used to mix a series of batches at different processing conditions. The rheological properties of these batches were compared to a similar group mixed to a specification based on unit work. The result was the control system gave more rheologically uniform material.

This study is to investigate the fabrication of filled polyurethane elastomer tiles by the reaction injection moulding (RIM) process. The base matrix is composed of a crosslinked polyurethane elastomer formed by the reaction between a diisocyanate (MDI) and a polyol (polytetramethylene glycol) and crosslinked by trimethylol propane (TMP). The two fillers investigated were barium sulphate and Expancel which were used to dissipate and scatter sonic waves in acoustic damping applications.

Thermoplastic rubbers have been shown to have unusual solid state properties which must derive from the structure of the melt prior to solidification. The melt phase has been studied in some detail. The molecular architecture of these block copolymers comprises of hard segments (usually polystyrene) connected by a flexible rubbery chain (polybutadiene or polyisoprene) in a linear or radial structure. Their flow characteristics have been studied and the results correlated with measurements in the solid state. They have been modelled mathematically based on two particular theoretical models. A liquid phase transition was recorded for both models, with appreciable reduction in the apparent activation energy of flow above this temperature. The quality of the domain structure depends on the continuity of the polystyrene phase and has been measured by the stress at yield and by the optical birefringence. A change in response was associated with the liquid-liquid transition.

Fatty diamine cationic surfactants are a recent entrant into the rubber mix formulation and have significant effects on the processing and properties of rubber compounds. Six new fatty diamine cationic surfactants, based on oleic acid, linoleic acid, rubber seed oil, 1,2-ethane diamine and 1,6-hexane diamine, were synthesised; and a simple method of their isolation and purification was developed. The effects of the experimental surfactants as combined activator and accelerator in rubber compounds were investigated. The rubber compounds containing them exhibited high activation energy of vulcanisation; and the surfactants functioned effectively as both activator and accelerator in SBR mixes. One of the new salts (l,2-ethane diamine dioleate, EDDO) and two commercial materials (EN444 and Duomeen TDO) were applied in standard NR and SBR mixes, and their effects on vulcanisation, rheological and vulcanisate properties investigated. Mixes containing the multi functional additives processed better, cured faster and had improved physical/mechanical properties over control mixes containing the same level of fillers. NRJEDDO mixes containing Si69 require a twostage mixing technique for further improvement in vulcanisate properties; similar SBR mixes were only slightly affected. Compounds were prepared in a Farrel (BR model) Banbury and a Francis Shaw KI Intermix internal mixers. Cure measurements were made on a Wallace Precision Cure Analyser and Monsanto (ODR) curemeter. Tensile properties were measured with a Hounsfield electronic tensometer (model SOOL). Filler dispersion was measured by SEM and "dark field" image analysis. Carbon black (N330)-filled NR compounds containing EDDO exhibited higher shear viscosity, higher activation energy of viscous flow and higher extrudate swell than a control compound which contained the same level of RAF black. Silica-filled mixes containing the MF A exhibited higher extrudate swell but lower shear viscosity than the control mixes containing the same level of silica filler. Melt flow measurements were carried out using a Davenport Capillary Rheometer and a Negretti TMS Rheometer. The effects of temperature and die length on shear viscosity, extrudate swell, melt flow behaviour index, n', and extrudate defonnation were investigated. The combined effect of MFA (EN444) level and mixing energy on properties of carbon black (N330)-filled natural rubber compounds was investigated by a factorial design experiment. No dependence of vulcanisation rates and elastic modulus on mixing energy was observed. Vulcanisation rates, mixing time and modulus (M300) showed a decrease with increase in MF A level. Other vulcanisate properties, including tensile strength, tear strength and j hardness, are optimised at MF A level of 2phr and above this level suffered significant deterioration.

Research work has been carried out to critically study parameters affecting peroxide-cured conductive silicone rubbers, using various carbon blacks as the conducting phase.

Polyurethane elastomers have demonstrated unusually excellent physical and mechanical properties, but these advantages are considerably diminished at elevated temperatures.

Active nematic elastomers are a class of active materials that possess the elasticity of a rubber, and the orientational symmetry of a liquid crystal. Their constituent elements are typically elongated, cross-linked and active. The cross-linking of the elements leads to an elasticity that prevents the material to ow like a liquid. These elements are active in a sense that they continuously consume and dissipate energy, creating a state that is far-from-equilibrium. Active nematic elastomers may be a good physical model for biological systems such as the metaphase spindle, a complex biological machine that is made of an integrated assembly of microtubules and molecular motors. These motors not only cross-link the microtubules, but also actively slide them against each other, creating a highly dynamic, non-equilibrium state. The metaphase spindle, like other non-equilibrium structures in biology, has important functions to perform. During mitosis, the spindle is responsible for (1) capturing the sister chromatids, (2) bringing all the sister chromatids to the equator of the mother cell, and (3) segregating the daughter chromosome to the opposite poles of the cell. Thus, a fundamental challenge to biological physics is to understand the complex dynamics of the spindle, and similar systems, using the tools of non-equilibrium statistical mechanics. In this Thesis, we develop and explore a phenomenological model for an active nematic elastomer. We formulate the dynamics of this phenomenological model by incorporating the contribution of the active elements to the standard formulation of the hydrodynamic equations of a passive system. In a coarse-grained picture, the activity is taken into account as an extra active stress, proportional to the alignment tensor, added to the momentum equation of an otherwise passive nematic elastomer. Having obtained the equations of motion of an active nematic elastomer, we then investigate the response of the system to an external field by means of examining the structure and the stability of the modes. An active nematic elastomer has eight modes, in which six modes are propagating and two modes are massive. Out of the six propagating modes, two modes are in the longitudinal direction, linked to the density waves, and the other four modes are in the transverse direction, linked to the shear waves. The nature of these propagating modes transitions from dissipative and oscillatory, and vice versa, depending on the length scales. In particular, their stability is largely determined in the hydrodynamic limit, by a competition between the stabilizing effect of the elasticity and the destabilizing effect of the activity. In fact, the activity renormalizes the elastic coefficients down to even a negative value in some cases and thus, rendering the system linearly unstable. This is in contrast to the well-known instability of an active nematic liquid crystal, which is always linearly unstable. We then map out and discuss the stability phase diagram of the active nematic elastomer. Next, we compute and study various equal-time correlation functions of an active nematic elastomer, assuming that the noise spectra are thermal in origin. We find that they can be conveniently arranged into two terms. The first term has the exact mathematical structure of the equal-time correlation functions of a passive nematic elastomer, albeit with certain coefficients renormalized by activity. The second term, which is proportional to the activity, represents the non-equilibrium nature of an active nematic elastomer, and manifestly breaks the Fluctuation-Dissipation Theorem. We also find that (1) the displacement-displacement correlation function decays inversely with the square of the wave number for both the compressible and incompressible nematic elastomer, similar to that of a passive nematic elastomer, with elastic coefficients renormalized by the activity. (2) The density-density correlation function approaches a constant at the long wave-length limit, since the conservation of mass links the density to the rate of changes of the displacement in the longitudinal direction. (3) The director-displacement correlation function is purely imaginary, and thus the director is locked to the displacement with a (π/2) phase-shift. (3) The director-director correlation function approaches a constant value in the long-wavelength limit, instead of decaying inversely with the square of the wave number, like it would for a liquid crystal. This is because of the massive mode stems from the coupling energy, and it indicates that director in the large length scale is locked to a specific angle. These theoretical results are in qualitative agreement with the experimental measurements of the spindle. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

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