Papers by Author: Qamar Nawaz

Abstract: The effects of nanoconfinement on the dynamic and the glass transition (T_g) of polymers remains the focus of a lot of research since over a decade. Particularly, the glass transition temperature (T_g) and the dynamic of polystyrene (PS) were found to be altered by nanoconfinement in thin films and on the bulk free-surface. However, the dynamic of polymer nanoconfined in nanoparticles has not been investigated, even though the close-packed nanoparticle geometry is commonly used in many applications such as waterborne coatings. We investigate the dynamic of polystyrene in nanoparticles by monitoring the closure of voids (interstices) between PS nanoparticles in the close-packed structure. Void-closure during the passage from the close-packed particles to bulk PS is monitored using small angle neutron scattering at the bulk T_g (100 °C). The relaxation time (τ) and the apparent viscosity (η) of nanoconfined polystyrene estimated from the void-closure decay is found to decrease only by ~2 times for particle diameters between 93 nm and 42 nm. These results infer that dynamic of nanoconfined PS in nanoparticles at the bulk T_g is not different from that of bulk polystyrene.

Abstract: Frequent use of solid fuels as thrust generating energy source in modern day space vehicle systems has created a need to assess their serviceability for long term storage under various conditions. Solid fuel grain, the most important part of any solid fuel system, responds viscoelastically to any loading condition. For the assessment of the service life of any solid fuel system, the solid fuel grain has to be structurally evaluated in applied storage conditions. Structural integrity of the grain is exceptionally significant to guarantee the successful operation of the solid fuel system. In this work, numerical simulations have been performed to assess the mechanical stresses and strains induced in an HTPB based solid fuel grain during service life employing ABAQUS standard FEA software using 4-node bilinear quadrilateral elements. For finite element analysis (FEA), typical 2-D and π/n^th axisymmetric section of 5-point (n) star grain geometry is considered. Mechanical loads include the horizontal or vertical 1-g (solid fuel weight) storage condition. The simulation results are compared with the analytical results for the same grain geometry. Analytically measured slump deflections in grain segment at various storage times have been found in good relation with the FEA based simulation results. This proves the validity of the procedure adopted and is helpful in assessment of the service life of solid fuel systems.

Abstract: The impact of nanoconfinement on the dynamic and glass transition of polymers has been found altered in thin films and on the bulk free surface. Confined polymer in nanoparticles is an important system of application in water-borne environmental-friendly coatings. In this work, we discuss method to probe the large scale dynamic of nanoconfined polystyrene in close-packed structure of nanoparticles. We probe the deformation of polystyrene nanoparticles by applying stress at nano-scale level quantified via small-angle neutrons scattering technique. We extract information about the relaxation of the polystyrene confined in nanoparticles and compare it with the relaxation of the same polymer in bulk.