Alpana Nayak K. A. Suresh Santanu Kumar Pal Sandeep Kumar

Cite this: J. Phys. Chem. B 2007, 111, 38, 11157–11161Publication Date:August 31, 2007 https://doi.org/10.1021/jp073196z

Abstract

Discotic molecules are known to form highly anisotropic structures at the air−water (A−W) interface. We have studied two novel ionic discotic mesogenic molecules, viz., pyridinium tethered with hexaalkoxytriphenylene with bromide counterion (Py-Tp) and imidazolium tethered with hexaalkoxytriphenylene with bromide counterion (Im-Tp) at A−W and air−solid interfaces. The monolayer phases were investigated at the A−W interface employing surface manometry and Brewster angle microscopy techniques. They indicate a uniform monolayer phase which shows negligible hysteresis on expanding and compressing. Also, in both the systems the collapsed state completely reverts to the monolayer state. These monolayer films transferred at different surface pressures by Langmuir−Blodgett technique were studied by employing atomic force microscopy. The topographies of these films transferred at the low and high surface pressure region of the isotherm indicate a transformation of the monolayer from face-on to edge-on structure.

The post Films of Novel Mesogenic Molecules at Air−Water and Air−Solid Interfaces appeared first on Nanoarchitectonics Lab.

• Alpana Nayak^‡
• K. A. Suresh^*§

View Author Information Cite this: J. Phys. Chem. B 2009, 113, 12, 3669–3675Publication Date:February 16, 2009https://doi.org/10.1021/jp806600g

Abstract

We have studied the mechanical properties of films of a novel ionic discogen, pyridinium tethered with hexaalkoxytriphenylene (PyTp) and its complex with DNA (PyTp−DNA) using atomic force microscope (AFM). The PyTp and PyTp−DNA complex monolayer films were first formed at air−water interface and then transferred onto silicon substrates by Langmuir−Blodgett (LB) technique. For the mechanical properties, particularly to obtain elastic modulus, we have carried out nanoindentation measurements on the LB films of PyTp and also PyTp−DNA complex. The load versus indentation curves from the nanoindentation measurements were analyzed quantitatively using Hertz model. Our analysis yields Young’s modulus values of 54 and 160 MPa for the PyTp and PyTp−DNA complex films, respectively. In addition, the LB films were imaged in the tapping mode AFM to obtain topography and phase images simultaneously. The energy dissipation maps were constructed from the phase images to determine qualitatively the variation in stiffness on the film surfaces. We find that the complex film exhibits a nonuniform surface with varying stiffness while the pure film exhibits a uniform surface.

The post Mechanical Properties of Langmuir−Blodgett Films of a Discogen−DNA Complex by Atomic Force Microscopy appeared first on Nanoarchitectonics Lab.

• Alpana Nayak
• K. A. Suresh

View Author Information Cite this: J. Phys. Chem. B 2008, 112, 10, 2930–2936Publication Date:February 19, 2008 https://doi.org/10.1021/jp710084q

Abstract

We have studied films of an ionic discogenic (discotic mesogenic) molecule (pyridinium salt tethered with hexaalkoxytriphenylene (PyTp)) and DNA complex at air−water (A−W) and air−solid interfaces. We have formed an PyTp monolayer on an aqueous subphase containing a small amount of DNA to obtain a PyTp−DNA complex at the A−W interface. Compared to the pure PyTp monolayer, the PyTp−DNA complex monolayer exhibits a higher collapse pressure and lower limiting area, indicating condensation and better stability. A Brewster angle microscope was used for in situ observation of the morphology of the film at the A−W interface. The PyTp−DNA complex films on silicon wafers were prepared using the Langmuir−Blodgett (LB) technique. We find that several tens of layers of the PyTp−DNA complex monolayer can be transferred with good efficiency. Fourier transform infrared spectroscopy studies confirm the presence of DNA in the LB films of the PyTp−DNA complex. Nanoindentation measurements using atomic force microscope reveal that the PyTp−DNA complex films are about two times harder as compared to the pure PyTp films.

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