Biomedical subjects

Mohit Singh

Publications and source records attributed to Mohit Singh.

7 recordsLinked to original sources

PubMed2005

Use of a self-assembling organogel as a reverse template in the preparation of imprinted porous polymer films.

The concept of reverse templating of an organogel to form imprinted porous divinylbenzene polymer films with submicrometer channels is demonstrated. The organogel comprising a 1:1 molar ratio of two organogelators, that is, bis(2-ethylhexyl) sodium sulfosuccinate and 4-chlorophenol, was formed in divinylbenzene. The gel was cast as a thin film before UV polymerization of the solvent, and the organogelators were later removed by simple washing with water and isooctane. The integrity of the fiber bundles of the organogel was preserved during polymerization, and an exact hollow replica was obtained after the organogelators were leached away. It is easily possible to imprint gel fiber bundle structures into polymeric films through this technique. The gel can also be formed on macroporous substrates to yield supported thin porous polymeric films. With the incorporation of functional nanoparticles in AOT inverse micelles and hence the organogel, nanoparticle-containing porous polymer films exhibiting luminescence or magnetic properties are envisioned.

Chlorophenols↗

PubMed2004

Biocatalysis in the development of functional polymer-ceramic nanocomposites.

Fluorescent silica/polymer nanocomposites have been synthesized by condensing tetramethyl orthosilicate (TMOS) around fluorescent polymer strands of poly(2-naphthol). The polymer is biocatalytically synthesized via peroxidase catalyzed polymerization in micelles of the cationic surfactant, cetyltrimethylammonium bromide (CTAB). Silica condensation at the micelle-water interface results in encapsulation of the polymer. Fluorescence spectroscopy and fluorescent light microscopy provide critical evidence that the polymer luminescence properties are conferred to the composite material. The fabrication of polymer entrapped in ordered, mesoporous materials represents a viable step toward the development of functional polymer-ceramic nanocomposites.

Catalysis↗

PubMed2004

Structural evolution in cationic micelles upon incorporation of a polar organic dopant.

Micelles of cetyltrimethylammonium bromide (CTAB), when doped with increasing levels of 4-ethylphenol, show microstructural transitions from spherical micelles to elongated wormlike micelles, disks, and subsequently to globular and then to tubular vesicles. Wormlike micelles are observed at a dopant-to-CTAB molar ratio of 1:3. At higher dopant ratios (1:1), globular vesicles are observed which transition to tubular vesicles when the dopant becomes the predominant species at a ratio of 3:1. These transitions are reflected in small-angle neutron scattering analysis and, interestingly, can be directly observed through cryo-transmission electron microscopy. The para-substituted phenol is interfacially active and modulates interfacial curvature of the micelles. The observations of microstructure modifications have relevance to the synthesis of mesoporous materials using CTAB as the template.

Journal Article↗

PubMed2004

Structural evolution of a two-component organogel.

Dry reverse micelles of AOT in isooctane spontaneously undergo a microstructural transition to an organogel upon the addition of a phenolic dopant, p-chlorophenol. This microstructural evolution has been studied through a combination of light scattering, small-angle neutron scattering (SANS), NMR, and rheology. Several equilibrium stages between the system of dry reverse micelles of AOT and a 1:1 AOT/p-chlorophenol (molar ratio) gel in isooctane have been examined. To achieve this, p-chlorophenol is added progressively to the dilute solutions of AOT in isooctane, and this concentration series is then analyzed. The dry micelles of AOT in isooctane do not undergo any detectable structural change up to a certain p-chlorophenol concentration. Upon a very small increment in the concentration of p-chlorophenol beyond this "threshold" concentration, large strandlike aggregates are observed which then evolve to the three-dimensional gel network.

Chlorophenols↗

PubMed2004

Shear-induced orientation of a rigid surfactant mesophase.

An optically clear, crystalline, gel-like mesophase is formed by the addition of water to a micellar solution consisting of a mixture of 0.85 M anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and a 0.42 M zwitterionic surfactant phosphatidylcholine (lecithin) in isooctane. At 25 degrees C and water to AOT molar ratio of 70, the system has a columnar hexagonal microstructure with randomly oriented domains. The shear-induced orientation and subsequent relaxation of this structure were investigated by rheological characterization and small-angle neutron scattering (SANS). The rheological response implies that the domains align under shear, and remain aligned for several hours after cessation of shear. Shear-SANS confirms this picture. The sheared gel mesophase retains its alignment as the temperature is increased to 57 degrees C, indicating the potential to conduct templated polymer and polymer-ceramic composite materials synthesis in aligned systems.

Journal Article↗

PubMed2004

Shear-induced alignment and nanowire silica synthesis in a rigid crystalline surfactant mesophase.

Highly aligned stringlike silica nanostructures are obtained through templated synthesis in the columnar hexagonal structure of a rigid crystalline surfactant mesophase. A two-step procedure is used to first shear-align the surfactant mesophase and then conduct synthesis under quiescent conditions in the mesophase. The mesophase retains its alignment for extended periods, allowing materials synthesis to be decoupled from the application of shear. The observations have significant implications in the control of ceramic microstructure morphology and transitions from nonaligned to aligned nanowire type structures.

Journal Article↗

PubMed2004

Freeze fracture direct imaging of a viscous surfactant mesophase.

Freeze fracture direct imaging (FFDI) has been used to image microstructures present in a highly viscous four-component mesophase containing water, isooctane, AOT [bis(2-ethylhexyl) sodium sulfosuccinate], and lecithin. As water is added to a fixed amount of a ternary solution of isooctane and the two surfactants, the microstructure evolves from a water-in-oil microemulsion, to a highly viscous columnar hexagonal, and then to multilamellar vesicles. Each of these microstructures is imaged directly. Previous small-angle neutron scattering measurements have identified the lamellar phase, but the FFDI technique demonstrates that these are onionlike curved multilamellar structures rather than planar bilayers. Freeze fracture direct imaging expands the range of cryo-transmission microscopy to highly viscous, high-organic-content systems that typically have been difficult to visualize.

Freeze Fracturing↗