Sajjad Husain Mir

Ferroelasticity in an Organic Crystal: A Macroscopic and Molecular Level Study

Ferroelasticity has been relatively well-studied in mechanically robust inorganic atomic solids but poorly investigated in organic crystals, which are typically inherently fragile. The absence of precise methods for the mechanical analysis of small crystals has, no doubt, impeded research on organic ferroelasticity. The first example of ferroelasticity in an organic molecular crystal of 5-chloro-2-nitroaniline is presented, with thorough characterization by macro- and microscopic methods. The observed cyclic stress-strain curve satisfies the requirements of ferroelasticity. Single-crystal X-ray structure analysis provides insight into lattice correspondence at the twining interface, which enables substantial crystal bending by a large molecular orientational shift. This deformation represents the highest maximum strain (115.9u2009%) among reported twinning materials, and the associated dissipated energy density of 216u2005kJu2009m-3 is relatively large, which suggests that this material is potentially useful as a mechanical damping agent.

Development of Hierarchical Polymer@Pd Nanowire-Network: Synthesis and Application as Highly Active Recyclable Catalyst and Printable Conductive Ink.

Abstract A facile one‐pot approach for preparing hierarchical nanowire‐networks of hollow polymer@Pd nanospheres is reported. First, polymer@Pd hollow nanospheres were produced through metal‐complexation‐induced phase separation with functionalized graft copolymers and subsequent self‐assembly of PdNPs. The nanospheres hierarchically assembled into the nanowire‐network upon drying. The Pd nanowire‐network served as an active catalyst for Mizoroki–Heck and Suzuki–Miyaura coupling reactions. As low as 500u2005μmolu2009% Pd was sufficient for quantitative reactions, and the origin of the high activity is ascribed to the highly active sites originating from high‐index facets, kinks, and coalesced structures. The catalyst can be recycled via simple filtration and washing, maintaining its high activity owing to the micrometer‐sized hierarchical structure of the nanomaterial. The polymer@Pd nanosphere also served as a printable conductive ink for a translucent grid pattern with excellent horizontal conductivity (7.5×105u2005Su2009m−1).

Twinning ferroelasticity facilitated by the partial flipping of phenyl rings in single crystals of 4,4′-dicarboxydiphenyl ether

Evidence of ferroelasticity in a non-planar organic molecular crystal is presented for 4,4′-dicarboxydiphenyl ether. Ferroelasticity has been demonstrated by the micro- and macroscopic mechanical characterization of single crystals, including recording of a full hysteretic stress–strain cycle. The underlying mechanism involves the partial flipping of phenyl rings.

Carbon fiber doped thermosetting elastomer for flexible sensors: physical properties and microfabrication

We have developed conductive microstructures using micropatternable and conductive hybrid nanocomposite polymer. In this method carbon fibers (CFs) were blended into polydimethylsiloxane (PDMS). Electrical conductivities of different compositions were investigated with various fiber lengths (50–250u2009μm), and weight percentages (wt%) (10–60 wt%). Sample composites of 2u2009cmu2009×u20091u2009cmu2009×u2009500u2009μm were fabricated for 4-point probe conductivity measurements. The measured percolation thresholds varied with length of the fibers: 50u2009wt% (307.7u2009S/m) for 50u2009µm, 40u2009wt% (851.1u2009S/m) for 150u2009µm, and 30u2009wt% (769.23u2009S/m) for 250u2009μm fibers. The conductive composites showed higher elastic modulus when compared to that of PDMS.

Enhancement of dissipated energy by large bending of an organic single crystal undergoing twinning deformation

We demonstrate exceptional twinning deformation in a molecular crystal upon application of mechanical stress. Crystal integrity is preserved and the deformation is associated with a large bending angle (65.44°). This is a new strategy to increase the magnitude of the dissipated energy in an organic solid comparable to that seen in alloys. By X-ray crystallographic analysis it was determined that a large molecular rearrangement at the twinning interface preserves the crystal integrity. Drastic molecular rearrangement at the twinning interface helps to preserve hydrogen bonding in the molecular rotation, which facilitates the large bending angle. The maximum shear strain of 218.81% and dissipated energy density of 1 MJ m−3 can significantly enhance mechanical damping of vibrations.

Controllability of coercive stress in organoferroelasticity by the incorporation of a bulky flipping moiety in molecular crystals

The control of coercive stress in organoferroelasticity is demonstrated in single crystals of trans-1,4-cyclohexanedicarboxylic acid with bulky cyclohexane rings. Flipping difficulty, due to the bulkiness, increased coercive stress, which can improve mechanical damping. Crystals also undergo the spontaneous disappearance of a twinned domain upon unloading before the completion of domain formation.