Suresh K. Ahuja

Electrostatic control of flow-induced smearing in the transfer of liquid ink images

Abstract Electrophotographic images developed from liquid inks are occasionally subject to a defect called transfer smearing. This defect is most noticeable on solid area patches as a shift of the trailing edge of the image onto the adjacent clear area, and can be eliminated by the application of an electric field. Measurements of the theology of the image and estimates of the viscous and electric forces in the transfer nip indicate that the suppression of the defect results from the electrorheological nature of the developed image.

Interface and Dynamic Indentation of Crosslinked Polyester Films

Nano-indentation is increasingly used to estimate the mechanical properties of polymeric films of nanometer-scale thickness. Hardness and modulus, as obtained on indentation are parameters that are strongly dependent upon tip geometry, elastic and inelastic material behavior, and specimen boundary conditions. The objective of this study was to analyze the mechanical response of nano-indentation loading on surfaces and interfaces of polymer films both linear and cross-linked. Polymer films on nano-indentation show confinement effect on their modulus and hardness. Reduced modulus and hardness in polyester and polycarbonate show strain softening that is associated polymer chain flexibility. The spatial constraints imposed to the plastic flow of the interface layer by the rigid indenter and substrate surfaces produce a dynamic effect, demonstrated by the loading rate dependence of the deformation response. In nano-indentation of cross-linked polymers, entanglements physical and chemical affect reduced modulus and hardness dependence on strain. Strain softening and strain hardening as well as dynamic frictional response are applied to indented polymer films consisting of surface, intermediate, and interface layers.Copyright

Flow of Nano and Micron Size Particles in a Cylindrical Cavity

Flow of particles is analyzed by considering driving force from applied shear energy (rotating augers). against constraints of extrinsic constraints (consolidation, boundary) and intrinsic constraints (cohesion, compressibility and inter-particle forces). Both Discrete Element Method (DEM) and Continuum Models are used to analyze powder flow with DEM uses models at particle level and is therefore requires costly computation where as Continuum Models are less accurate for complicated geometries and free surfaces. The cohesive (tensile) stress for an assembly of cohesive particles is an increasing function of volume fraction but depends only weakly on shear rate. As the particle volume fraction is decreased, the dependence of the tensile stress on shear rate grows, but for all volume fractions, this dependence is much weaker than that of the total stress. Empirical correlations are costly to obtain for predicting developer flow from frequent bench experiments (Freeman tester, Jenike shear cell and Seville tester) and tests in fixtures and housings. A rheological equation can be used to analyze shear stress, normal stress, cohesive stress and dynamic coefficient of friction in a shear cell. Experimental results are compared with the existing models.Copyright

Visco-Elastic Modulus and Intercalation of Polymer Chains in Epoxy Nano-Composites

Polymer nano-composites (PNC) are polymers which are reinforced with less than 5% by volume of nano-sized particles with high aspect ratios (L/h > 300). Compared to conventional composites, where the reinforcement is on the order of microns, the nano-composites are reinforced on the order of a few nanometers with advantages in processing and toughness. Nano-composites of epoxy clay have been studied where epoxy is mixed at high shear rates with clay. In our method of making nano-composites, an epoxy, Diglycidyl ether of bisphenol (DGEBA) A was mixed under high shear with organically modified mica type silicate (OMTS) either of benzyl dimethyl stearyl ammonium (BDSMA) or of methyl bishydroxyethyl stearyl ammonium chloride ion exchange with sodium montmorillonite. Nano-composites of epoxy cured with hexahydrophthalic anhydride (70%) with polyether polyol (25%) were made also under high shear both at 90C and 120C. Heat of reaction and transition temperature of epoxy nano-composite was compared with cured epoxy nano-composite. Analysis by X-Ray Diffraction was used to determine peaks, spacing and interfacial region. Dynamic visco-elastic measurements were used to distinguish between the nano-composites from two organically modified mica type silicates. Effect of increase in concentration and temperature on visco-elastic modulus of nano-composites was analyzed in terms of intercalation of polymer chains.© 2007 ASME

Effect of Interface and Depth on Hardness and Viscoelastic Modulus in Polycarbonate and Polyester Films

Hardness and modulus of a polymer is known to depend on its structure, molecular weight and number of segments between entanglements. Nano-indentation is used increasingly as a powerful tool to determine hardness and visco-elastic modulus of polymer surfaces linear, cross-linked or composites. Hysitron Nanoindenter was used in our investigation of contact deformation of surfaces of polyester and polycarbonate supported on an aluminum substrate. Bar coatings of polymer films were made from solutions and dried all at 110C for half an hour. The coatings were subjected to indentation including sinusoidal deformation at various contact depths and hardness as well as modulus is computed. The results show that hardness of surface of polycarbonate on polyester is higher than hardness of surface of polycarbonate, which in turn is higher than polyester surface. It appears that diffusion of polyester chains into compatible polycarbonate chains results in higher modulus of the surface than the modulus of either of the two polymers. Hardness and modulus of polycarbonate is found to decrease with contact depth and reaches a plateau around 600nm while that of polyester keeps on decreasing. Differences in contact deformation including the one arising from dynamic deformation between polycarbonate from that of polyester is analyzed in terms of morphology, molecular weight and entanglements.Copyright

Effect of Additive on Hardness and Brittleness in Polycarbonate Films

Hardness and modulus of a polymer composite is known to depend on its structure, molecular weight, number of segments between entanglements and additives (filler). Nano-indentation is used increasingly as a powerful tool to determine hardness and visco-elastic modulus of polymer surfaces linear, cross-linked or composites. Hysitron Nanoindenter was used in our investigation of contact deformation of surfaces of filled polycarbonates supported on aluminum substrate. Bar coatings of polymer films were made from solution and dried all at 110C for half an hour. The results show that filled polycarbonate gives higher hardness than unfilled polycarbonate, which can give significantly different temperature dependence depending on molecular weight of the polycarbonate and structure of the filler. Depending on the type of filler and its concentration, the polycarbonate composite exhibits brittle-ductile transition at different strains. This behavior is analyzed in terms of chain mobility and free volume in the composite.Copyright