“The joy of discovery is certainly the liveliest that the mind of man can ever feel”

- Claude Bernard -

Investigating physical properties of polymer chains and networks

June 2014 - July 2014 (Summer internship)

Advisor: Prof. S. Ramakrishnan, Department of Inorganic & Physical Chemistry, Indian Institute of Science

I gained exposure to research in Polymer Science through three mini-projects:

Volume phase transitions: Synthesised a cross-linked polyelectrolyte (polyacrylic acid) gel, and observed the volume phase transition on increasing the pH. Devised a method to make the gel porous, to increase the rate of swelling. This project was motivated by the idea of a 'self-walking gel'[1].

Shear-thickening polymer: Attempted synthesis of an amphiphilic shear-thickening polymer[2], by functionalising poly (4-vinylpyridine) with long chain alkyl groups.

Template polymerisation: Conducted a polymerisation reaction using another polymer as a template. To do this, we synthesised a cationic polymer, and polymerised an anionic monomer in presence of the cationic polymer.

Figure 3: Template polymerisation using 1:1 cation-anion ratio. When the reaction is conducted under low

concentration (1% w/v, left), the polymerisation occurs along individual template chains and a

clear solution is obtained. When the reaction is conducted under high concentration (5% w/v, right),

polymerisation occurs along multiple template chains leading to an opaque white gel.

A detailed report of the project can be found here.

Skills gained:

Organic synthesis, drying of solvents, rotary evaporation.
Polymerisation synthesis techniques: solution polymerisation, precipitation polymerisation.
Polymer characterisation by NMR.

References:

Self-Walking Gel: Maeda, S. et. al. Adv. Mater. 2007, 19, 3480-3484
Shear-thickening polymer: Bokias, G.; Hourdet, D.; Iliopoulos, I. Macromolecules 2000, 33, 2929-2935

Design of Ruthenium-based catalyst for asymmetric transfer hydrogenation

June 2015 - July 2015 (Summer internship)

Advisor: Prof. A. G. Samuelson, Department of Inorganic & Physical Chemistry, Indian Institute of Science

Asymmetric Transfer hydrogenation (ATH) is a class of reduction reactions that show promise due to their strong selectivity, high enantioselectivity and mild conditions. Noyori[1][2] has pioneered the usage of Ruthenium-based half-sandwich complexes as catalysts for ATH, for which he was awarded the 2001 Nobel Prize in Chemistry. We have synthesised amino-acid based thiazolidinethione ligands as chiral auxiliaries. Using the ligands, we have synthesised chiral Ruthenium-based complexes to catalyst reduction of acetophenone using isopropanol (Image 1). The complex had an unusual NMR spectrum and had an unusually low enantiomeric excess. To explain the anomalies, we have proposed the presence of a strong Cl-H hydrogen bond in the complex. Due to this hydrogen bond, the catalyst can exist in two diastereomeric forms in solution (Image 2), explaining the unusual spectrum and low enantiomeric excess. We have used X-Ray diffraction and low temperature NMR spectroscopy to test the presence of diastereomers.

Figure 1: Asymmetric transfer reduction of acetophenone using Ruthenium catalyst with Leucine-auxiliary

Figure 2: Proposed mechanism of diastereomerisation of the catalyst. In absence of the Cl-H hydrogen bond, the

two molecules are identical (conformers).

A detailed report of the project can be found here.

Skills gained:

Drying of solvents and organic synthesis.
Conducting inert atmosphere reactions using Schlenk line.
Conducting catalysis reactions.
Crystallisation of complexes for X-Ray diffraction.
Exposure to low temperature NMR spectroscopy.

References:

Noyori, R.; Hashiguchi, S.; Acc. Chem. Res. 1997, 30, 97-102
Hashiguchi, S.; Fujii, A.; Takehara, J.; Ikariya, T.; Noyori, R.; J. Am. Chem. Soc. 1995, 117, 7562-7563

Determination of Mark-Houwink parameter for PEO in the ionic liquid [BMIM][BF4]

June 2016 - July 2016 (Summer internship)

Advisor: Prof. Timothy P. Lodge, Department of Chemistry, University of Minnesota

Project supported by S. N. Bose Fellowship

Polymers in ionic liquids are a new class of composite materials. Though they display a great potential for applications, little work has been done to understand the nature of polymer-ionic liquid interactions. Recent simulation studies[1][2] have determined the Flory exponent for poly (ethylene oxide) (PEO) in the ionic liquid [BMIM][BF4], but report contradictory values using different simulation techniques. Our project aims to experimentally determine the Flory exponent for PEO in [BMIM][BF4]. We have used a parallel plate rheometer to conduct intrinsic viscosity measurements. Through intrinsic values measured for two molecular weights, we have obtained a rough estimate for the Mark-Houwink parameter. Through further measurements, the Mark-Houwink parameter and Flory exponent can be determined.

An abstract of the project can be viewed on the University of Minnesota MRSEC REU page. A detailed summary of the project can be found here.

Skills gained:

Purification of polymers by precipitation and ionic liquids by column chromatography.
Characterization of polymers by NMR and SEC.
Drying of samples in vacuum oven.
Viscosity measurement using AR G2 parallel plate rheometer.
Using the data analysis software TA Rheology Advantage.
Using the reference management software Mendeley.
Work organization and maintaining of records.
Giving research presentation in oral format.

References:

Mondal, J.; Choi, E.; Yethiraj, A. Macromolecules 2014, 47, 438−46
Choi, E.; Yethiraj, A. J. Phys. Chem. B 2015, 119, 9091-9097

Study of electronic structure & optical properties in metallic nanoparticles

Aug 2016 - Apr 2017 (Bachelor's thesis)

Advisor: Prof. Anshu Pandey, Solid State & Structural Chemistry Unit, Indian Institute of Science

The Mie Theory uses the classical theory of electromagnetism to explain scattering of light by small particles. The predictions of Mie Theory are quantitatively accurate for a wide range of particle sizes and light wavelengths. By its virtue of being a classical theory, Mie Theory is inaccurate at size regimes where quantum mechanical effects begin to dominate. Recent studies [1][2] on metallic nanoparticles report systems where electron tunneling and spill-out effects are significant, and deviations from the classical theory are observed. Our project aims to computationally study the electronic structure in metallic nanoparticles and study optical properties of the electron gas. I am building coarse-grained DFT programs for the purpose. I am working in collaboration with an experimentalist studying non-Mie like behaviour in certain metallic systems.

Skills gained:

Methods for electronic structure calculation.
Study of optical properties of metallic nanoparticles.
Programming in Mathematica.

References:

Halas, N. J.; Lal, S.; Change, W.; Link, S.; Norlander, P. Chem. Rev. 2011, 111, 3913-3961
Scholl, J. A.; Koh, A. L.; Dionne, J. A. Nature 2012, 483, 421-427