I joined the Osuji lab as a postdoctoral associate
in March 2008 after completing my PhD in the lab of Prof. Dr. Christiane A.
Helm at Greifswald, Germany. Most of my experiments for my
PhD thesis were conducted at Helmholtz-Zentrum Berlin,
on Neutron reflectometer V6 instrument. My PhD thesis was focused
on the basic understanding of temperature and ionic effects on
the polyelectrolyte multilayer growth, hydration and layer interdigitation.
Basically, I am from India. My current research involves directed
self assembly of block copolymers, structure and phase behavior
of hydrogen bonded polymer-surfactant systems.
Magnetic Alignment of Li-Conducting Block Copolymers:
We are working on large area magnetic field alignment of PEO containing block copolymers which is an attractive polymer electrolyte for battery applications. High defect density and lack of long range order prevent continuous pathways for the ionic conduction and the subsequent utility of these materials as membranes for ion transport. We utilize strong magnetic fields to impose long range order in these soft materials.
We have accomplished large area domain alignment of poly(ethylene oxide-b-6-(4’-cyanobiphenyl-4-yloxy) hexyl methacrylate) (EO-MA/LC) block copolymer in high magnetic field (5T) while cooling from elevated temperatures through ODT of the system. The diamagnetic anisotropy provided by the LC ordering of the mesogens permit facile control of the alignment of the block copolymer superstructure over large length scales (>1 mm) by the application of magnetic fields. The orientation order is characterized by small angle X-ray scattering and polarized optical microscopy. The thermal behavior of the system is studied by DSC and impedance spectroscopy is utilized to measure the anisotropic thermal conductivity of the system. Small angle X-ray scattering demonstrated that lamellar and cylindrical PEO microdomains aligned with their interfaces along the applied field while the smectic layers of the liquid crystalline mesophase are perpendicular to the field in agreement with the positive diamagnetic anisotropy of the cyano-biphenyl mesogen and a homogeneous anchoring condition at the inter-material dividing surface (IMDS) between the two blocks. Doping with Li salt improves the microphase separation and orientation order in the system. We believe that facile control of PEO microdomains by magnetic fields will spur new developments in this area.
We continue to work on obtaining anisotropic Li conducting membranes from cylindrical material where the magnetic alignment is unique unlike the degeneracy associated with lamellar systems.
Figure 1: 2D scattering pattern of EO-MA/LC block copolymer: (a) no field (b) the field (vertical) (c) field normal to the plane.
Figure 2: : 2D scattering pattern of (a) EO-MA/LC:(20AA+1LiClO4) sample when the field was vertical (b) EO-MA/LC:(10AA) sample continuously rotated in the field at 4rpm (c) The aligned cylindrical sample obtained by swelling the LC block of EO-MA/LC:(10AA) by incorporating of 4'-(octyloxy)-4-biphenylcarbonitrile.
Figure 3: The transmitted intensity of the aligned EO-MA/LC:(10AA) sample under crossed polarized light shows periodic variation at every 90degrees indicating strong alignment of the mesogens along the field direction over large areas.
Supramolecular Polymer-Surfactant Complexes: Phase behavior and magnetic alignment:
Reversible hydrogen bonding between a surfactant and a polymer having complementary sites for the surfactant can lead to phase separation and block copolymer-like morphology. Our studies are focused on the structure and dynamics of polymer-surfactant complexes, with efforts paid to explicitly address the effect of the strength of the interaction between the polymer and surfactant. Above a critical stoichiometry, i.e. the ratio of ligand concentration to that of binding sites, these polymers may display liquid crystalline behavior in the melt state. The weak interaction between the ligands means that the binding equilibrium is dynamic, and so ligands are thought to change their sequence distribution along the polymer chain in response to changes in temperature, stoichiometry and the chemistry of the ligand. Characterizing this behavior is the central theme in our research. We study the thermal properties of the mesophases via DSC, and correlate this with polarized optical microscopy and small angle X-ray scattering studies in solution and in the melt. Figure2 depicts temperature dependent SAXS measurements on a melt sample showing the emergence of a bilayer liquid crystalline structure at elevated temperatures. The structure transitions back to a monolayer at lower temperatures.
The surfactant is designed such that specific environmental stimuli such as temperature induces changes in the polymer chain-level structure by modifying the interaction strength. We use a combination of FTIR and Isothermal Calorimetry (ITC) measurements to carefully quantify the weak, reversible hydrogen bonding interactions between hydrophilic materials such as poly(acrylic acid) or poly(vinyl alcohol) and conjugate small molecular ligands.
In addtion to engineering novel polymer-surfactant systems through hydrogen bond interactions, our current work also encompasses utilizing simple non covalent interactions to obtain long range order in block copolymers by magnetic fields. We have succesfully obtained large area magnetic alignment of PS-b-AA polymer bearing mesogenic side chains interacting with AA backbone through intermolecular hydrogen bonding. We are also working on improving microphase separation and large area alignment of phase mixed block copolymers using simple non covalent interactions as well.
Figure 1: 2D scattering patterns (top) and the corresponding schematic representations of the possible arrangements of the mesogens (bottom) for S=0.75 recorded at 30 oC and 120 oC. At high T, the mesogens adopt a loosely packed bilayer structure. Upon cooling the sample, demixing occurs around 100 oC, scattering due to the large length scale (~110 Å) smectic demixed structure is clearly visible out to the third order reflection even at room temperature.
Figure 2: SAXS data as a function of temperature in a poly(acrylic acid)-surfactant complex for a stoichiometry of "0.75M".
Figure 3: IR spectra of PAA homopolymer, the imidazole mesogen and its blends at different compositions in the carbonyl stretching region (1800-1600 cm-1) recorded at 30 oC
Magnetic Field Alignment of a Diblock Copolymer Using a Supramolecular Route. M. Gopinadhan, P. W. Majewski, E. S. Beach, C. O. Osuji. ACS Macro Letters. Accepted (2011). doi:10.1021/mz2001059
Cholesteric Mesophase in Side-Chain Liquid Crystalline Polymers: Influence of Mesogen Interdigitation and Motional Decoupling." S.-K. Ahn, M. Gopinadhan, P. Deshmukh, R. K. Lakhman, C. O. Osuji, R. M. Kasi. Soft Matter. Accepted (2011).
Magnetic Field Alignment of Block Copolymers and Polymer Nanocomposites: Scalable Microstructure Control in
Functional Soft Materials. P. W. Majewski, M. Gopinadhan, C. O. Osuji. J. Polym. Sci. Part B: Polym. Phys. In press (2011). doi: 10.1002/polb.22382
Tailoring Crystallization Behavior of PEO Based Liquid Crystalline Block Copolymers through Variation in Liquid Crystalline Content. Y. Zhou, S-K. Ahn, R. K. Lakhman, M. Gopinadhan, C. O. Osuji, R. Kasi. Macromolecules.ASAP (2011). doi: 10.1021/ma102922u
Side-Chain Liquid Crystalline Polymer Networks: Exploiting Nanoscale Smectic Polymorphism to Design Shape Memory Polymers. S-K. Ahn, P. Deshmukh, M. Gopinadhan, C. O. Osuji, R. M. Kasi. ACS Nano5 (4), 3085 (2011). doi:10.1021/nn200211c
Anisotropic ionic conductivity in block copolymer membranes by magnetic field alignment. P. W. Majewski, M. Gopinadhan, W-S. Jang, J. L. Lutkenhaus, C. O. Osuji. Journal of the American Chemical Society132 (49), pp 17516-17522 (2010). doi:10.1021/ja107309p
Smectic demixing in the phase behaviour and self-assembly of a hydrogen bonded polymer with mesogenic side chains. M. Gopinadhan, E. Beach, P. Anastas, C. O. Osuji. Macromolecules43 (16) p.6646-6654 (2010). doi:10.1021/ma1006667
Facile Alignment of Amorphous Poly(ethylene oxide) Microdomains in a Liquid Crystalline Block Copolymer Using Magnetic Fields: Towards Ordered Electrolyte Membranes. M. Gopinadhan, P. W. Majewski, C. O. Osuji. Macromolecules, 43 (7) p. 3286-3293 (2010). doi:10.1021/ma9026349
Reflectivity of Polyelectrolyte Multilayers
My PhD work was focused on a detailed invesitigation of the the temperature effect and the hydrophobic (nonelectrostatic) interactions on the polyelectrolyte multilayer growth (X-ray reflection), surface structure (AFM, X-ray reflection), layer interpentration and hydration (neutron reflection).
We found that above a critical salt concentration, the polyelectrolyte multilayer thickness increases, indicating that attenuation of the electrostatics (range 1nm) is necessary to allow secondary forces to contribute. The thickness of PAH/PSS bilayers from 1 M NaCl or KCl solution increases on increase in the temperature of the deposition solution (5 to 60 °C) by a factor of 3. We found that the bilayer thinkness is independent of the kind of salt, yet different composition (hydration). On heating the preparation solution, eventually the amount of bound water decreases. We also found a correlation between the amount of bound water and the layer interdigitation (less bound water leads to roughening of the interfaces). i.e, the interdigitation is higher at high temperatures. We also observed that the onset of roughening depends on the size of the ion (50 or 35 °C for films made from 1 M NaCl or KCl, respectively). on increase of temperature, the hydrophobic force dominates the changes in polyelectrolyte multilayer growth and composition.
Figure 1: Top: Neutron reflectivity curves normalized relative to the Fresnel reflectity of polyelectrolyte multilayers with selectively deuterated layers. The films are prepared from 1 M NaCl solution at the temperatures indicated. Bottom: The deduced scattering length density profiles.
Figure 2: Schematic of contrast decrease due to larger layer interpenetration caused by polyelectrolytes adsorbing in a pearl-necklace or a partly globular structure.
Figure 3: Box modeling of reflectivity data. Each layer is parametrized by thickness, electron density and multiplied by error functions at the interfaces.
Aggregation and Rearragement within a Silver Nanoparticle Layer during Polyelectrolyte Multilayer Formation, Langmuir 26 (19), 15219 (2010). DOI:
O. Soltwedel, O. Ivanova, Matthias Höhne, M. Gopinadhan and C. A. Helm
Immobile Light Water and Proton-Deuterium Exchange in Polyelectrolyte Multilayers, Macromolecules, 2008, 41 (19), pp 7179–7185 DOI:10.1021/ma800456z
O. Ivanova, O. Soltwedel, M. Gopinadhan , R. Kohler, R. Steitz and C. A. Helm
Influence of Secondary Interactions during the Formation of Polyelectrolyte Multilayers: Layer Thickness, Bound Water and Layer Interpenetration, J. Phys. Chem. B, 111 (29), pp 8426–8434, 2007 DOI:10.1021/jp067402z M. Gopinadhan , O. Ivanova, H. Ahrens, J.U. Gnther, R. Steitz, C. A. Helm
Energy Barrier Distributions of Maghemite Nanoparticles, Nanotechnology, 18 115709 (8pp), 2007 DOI:10.1088/0957-4484/18/11/115709
E. Romanus, T. Koettig, G. Glckl, S. Prass, F. Schmidl, J. Heinrich, M. Gopinadhan, D. V. Berkov , C. A. Helm, W. Weitschies, P. Weber and P. Seidel
Close Approximation of Two Platelet Factor 4 Tetramers by Charge Neutralization Forms the Antigens Recognized by HIT Antibodies, Arterioscler Thromb Vasc Biol, 26, 2386 - 2393, 2006 DOI: 10.1161/01.ATV.0000238350.89477.88
A. Greinacher, M. Gopinadhan , J.-U. Gnther, M. A. Omer-Adam, U.
Strobel, T. E. Warkentin, G. Papastavrou, W. Weitschies, C. A. Helm
Structral Deformation, Melting Point and Lattice Parameter Studies of Size Selected Ag Clusters, European physical journal D, 37, 409-415, 2006 DOI: 10.1140/epjd/e2005-00319-x
I. Shyjumon, M. Gopinadhan , O. Ivanova, M. Quass, C. A. Helm, R. Hippler
Deposition of Ti/Ti Oxide clusters produced by magnetron sputtering, Thin Solid Films, 500, 41-51, 2006 DOI: 10.1016/j.tsf.2005.11.006
I. Shyjumon, M. Gopinadhan , C. A. Helm, B. M. Smirnov, R. Hippler
Approaching the Precipitation Temperature of the Deposition Solution and the Effects on the inter-nal Order of Polyelectrolyte Multilayers, Macromolecules, 38 (12), 5228 -5235, 2005 DOI: 10.1021/ma047552c M. Gopinadhan, H. Ahrens, J.U. Gunther, R. Steitz, C. A. Helm