My research interests concern structure and dynamics at interfaces, in particular metal-soft matter interfaces, where the soft materials are amphiphiles, polymers and, recently, biomaterials. I want to correlate morphology, structure and bonding and explore the role of supramolecular interactions in complex matter dynamics. Phone: +91-33-2337-5347 Address: Surface Physics and Materials Science Division
Saha Institute of Nuclear Physics
1/AF Bidhannagar, Kolkata 700 064, India
We have explored morphology of DNA molecules bound with Cu-complexes of piroxicam molecules, a no... more We have explored morphology of DNA molecules bound with Cu-complexes of piroxicam molecules, a non-steroidal anti-inflammatory drug (NSAID), under one-dimensional confinement of thin films and have studied the effect of counterions present in a buffer. X-ray reflectivity at and away from the Cu K absorption edge and atomic force microscopy studies reveal that confinement segregates the drug molecules preferentially in a top layer of the DNA film, and counterions enhance this segregation.
A mixture of dodecanethiol-capped Au nanoparticles (AuNPs) and the amphiphilic fatty acid, steari... more A mixture of dodecanethiol-capped Au nanoparticles (AuNPs) and the amphiphilic fatty acid, stearic acid, spread as a monomolecular layer on water surface, is observed with Brewster angle microscopy (BAM) to form a two-dimensional network of AuNP clusters through demixing, at concentration of AuNPs by weight (ρ[over ¯])>10% and the surface pressure (π)≥10mNm^{-1}. For π=15mNm^{-1}, the number of nodes (n) remains unchanged till ∼2 hours and then changes over to a lower n state, where the pattern consists of almost perfect circles with greater in-plane thickness of the AuNP lamellae. For the higher n state the mean-square fluctuation of BAM intensity remains flat and then decays as f(ξ)=ξ^{2α} with α∼0.6 (correlated fluctuations) over the length scales of 400μm-6μm and below 6μm, respectively. For the lower n state the fluctuation decays almost over the entire length scale with α=0.3, indicating emergence of aperiodicity from quasiperiodicity and a changeover to anticorrelated fluctuations. These patterns can be looked at as two distinct chaotic trajectories in the I-I^{'} phase space of the system (I being the scattered light intensity at any position of the pattern and I^{'} its gradient) with characteristic Lyapunov exponents.
The aim of this study is to investigate the interaction of a drug (Piroxicam, 4-Hydroxy-2-methyl-... more The aim of this study is to investigate the interaction of a drug (Piroxicam, 4-Hydroxy-2-methyl-N-(2-pyridinyl)-2H-1,2-benzothiazine-3-carboxamide 1,1 dioxide) with a lipid (DMPC) monolayer used as a membrane-mime in terms of drug-induced changes in stability and compressibility with variation in temperature, surface-pressure, drug-dose and ionic states of the monolayers. Drug-induced fluidization is noticed in the $\pi-$A isotherms through increase in phase-transition pressure at constant temperature. The long-term dynamics of the lipid-monolayer is characterized by algebraic decays in surface-energy E with time t, $E\sim t^{-p_{1,2,3}}$, with an initial decay exponent $p_1$ that changes to $p_2$ after $\sim$ 1000s, and, at high surface pressures and/or drug-dose, to a third exponent $p_3$ after $\sim$ 3500s, suggesting structural reorganizations in the monolayer. With increasing drug-lipid ratio (D/L), $p_1$ shows a decrease ending at an almost constant value after 0.05, $p_2$ shows an almost negligible lowering while $p_3$ shows a monotonic and considerable increase. The reorganization is summarized by proposing two mechanisms: a) `charging-discharging' where drug-molecules sitting parallel to the interface increase headgroup separations and b) `discharging-charging' where drug-molecules sitting roughly perpendicular to the interface bring headgroups closer. Drug-induced softening of lipid-monolayers is characterized by the compressibilites of pure and mixed lipid monolayers. Compressibility-change (i.e. compressibility difference between drug/lipid and pure lipid monolayer) with pressure is maximum in the LE-LC transition zone and compressibility-change with drug-dose reveals an optimum dose of drug for maximum increase in compressibility. Molecular dynamics simulation shows that the ordering in the different parts of the lipid chains is changed to different extents in the presence of drugs with maximum change near the headgroups and again points to an optimum dose for maximum disorder.
While monolayer area fraction versus time ($A_{n}-t$) curves obtained from surface pressure-area ... more While monolayer area fraction versus time ($A_{n}-t$) curves obtained from surface pressure-area ($\pi-A$) isotherms for desorption-dominated (DD) processes in Langmuir monolayers of fatty acids represent continuous loss, those from Brewster Angle Microscopy (BAM) also show a 2D coalescence. For nucleation-dominated (ND) processes both techniques suggest competing processes, with BAM showing 2D coalescence alongside multilayer formation. $\pi$ enhances both DD and ND with a lower cut-off for ND, while temperature has a lower cut-off for DD but negligible effect on ND. Hydrocarbon chain length has the strongest effect, causing a cross-over from DD to ND dynamics. Imaging Ellipsometry (IE) of horizontally transferred films onto Si(100) shows Stranski-Krastanov (SK) like growth for ND process in arachidic acid monolayer resulting in successive stages of monolayer, trilayer, multilayer islands, ridges from lateral island-coalescence and shallow wavelike structures from ridge-coalescence on the film surface. These studies show that lipophilic attraction between hydrocarbon chains is the driving force at all stages of long term monolayer dynamics.
Abstract Surface pressure versus Specific Molecular Area (Pi-A) Isotherms for Langmuir Monolayers... more Abstract Surface pressure versus Specific Molecular Area (Pi-A) Isotherms for Langmuir Monolayers of stearic acid (StA), and stearic acid containing 10% and 50%(by mass) of dodecanethiol-capped Au nanoparticles (StAu10 and StAu50, respectively), have been recorded. The isotherms show a decrease in the magnitude of the slopes in both the'liquid'L2 and L2. phases and the'solid'S phase, as well as a decrease in the differences between slopes of all the adjacent phases, indicating a change from a complex to a ...
We have explored morphology of DNA molecules bound with Cu-complexes of piroxicam molecules, a no... more We have explored morphology of DNA molecules bound with Cu-complexes of piroxicam molecules, a non-steroidal anti-inflammatory drug (NSAID), under one-dimensional confinement of thin films and have studied the effect of counterions present in a buffer. X-ray reflectivity at and away from the Cu K absorption edge and atomic force microscopy studies reveal that confinement segregates the drug molecules preferentially in a top layer of the DNA film, and counterions enhance this segregation.
A mixture of dodecanethiol-capped Au nanoparticles (AuNPs) and the amphiphilic fatty acid, steari... more A mixture of dodecanethiol-capped Au nanoparticles (AuNPs) and the amphiphilic fatty acid, stearic acid, spread as a monomolecular layer on water surface, is observed with Brewster angle microscopy (BAM) to form a two-dimensional network of AuNP clusters through demixing, at concentration of AuNPs by weight (ρ[over ¯])>10% and the surface pressure (π)≥10mNm^{-1}. For π=15mNm^{-1}, the number of nodes (n) remains unchanged till ∼2 hours and then changes over to a lower n state, where the pattern consists of almost perfect circles with greater in-plane thickness of the AuNP lamellae. For the higher n state the mean-square fluctuation of BAM intensity remains flat and then decays as f(ξ)=ξ^{2α} with α∼0.6 (correlated fluctuations) over the length scales of 400μm-6μm and below 6μm, respectively. For the lower n state the fluctuation decays almost over the entire length scale with α=0.3, indicating emergence of aperiodicity from quasiperiodicity and a changeover to anticorrelated fluctuations. These patterns can be looked at as two distinct chaotic trajectories in the I-I^{'} phase space of the system (I being the scattered light intensity at any position of the pattern and I^{'} its gradient) with characteristic Lyapunov exponents.
The aim of this study is to investigate the interaction of a drug (Piroxicam, 4-Hydroxy-2-methyl-... more The aim of this study is to investigate the interaction of a drug (Piroxicam, 4-Hydroxy-2-methyl-N-(2-pyridinyl)-2H-1,2-benzothiazine-3-carboxamide 1,1 dioxide) with a lipid (DMPC) monolayer used as a membrane-mime in terms of drug-induced changes in stability and compressibility with variation in temperature, surface-pressure, drug-dose and ionic states of the monolayers. Drug-induced fluidization is noticed in the $\pi-$A isotherms through increase in phase-transition pressure at constant temperature. The long-term dynamics of the lipid-monolayer is characterized by algebraic decays in surface-energy E with time t, $E\sim t^{-p_{1,2,3}}$, with an initial decay exponent $p_1$ that changes to $p_2$ after $\sim$ 1000s, and, at high surface pressures and/or drug-dose, to a third exponent $p_3$ after $\sim$ 3500s, suggesting structural reorganizations in the monolayer. With increasing drug-lipid ratio (D/L), $p_1$ shows a decrease ending at an almost constant value after 0.05, $p_2$ shows an almost negligible lowering while $p_3$ shows a monotonic and considerable increase. The reorganization is summarized by proposing two mechanisms: a) `charging-discharging' where drug-molecules sitting parallel to the interface increase headgroup separations and b) `discharging-charging' where drug-molecules sitting roughly perpendicular to the interface bring headgroups closer. Drug-induced softening of lipid-monolayers is characterized by the compressibilites of pure and mixed lipid monolayers. Compressibility-change (i.e. compressibility difference between drug/lipid and pure lipid monolayer) with pressure is maximum in the LE-LC transition zone and compressibility-change with drug-dose reveals an optimum dose of drug for maximum increase in compressibility. Molecular dynamics simulation shows that the ordering in the different parts of the lipid chains is changed to different extents in the presence of drugs with maximum change near the headgroups and again points to an optimum dose for maximum disorder.
While monolayer area fraction versus time ($A_{n}-t$) curves obtained from surface pressure-area ... more While monolayer area fraction versus time ($A_{n}-t$) curves obtained from surface pressure-area ($\pi-A$) isotherms for desorption-dominated (DD) processes in Langmuir monolayers of fatty acids represent continuous loss, those from Brewster Angle Microscopy (BAM) also show a 2D coalescence. For nucleation-dominated (ND) processes both techniques suggest competing processes, with BAM showing 2D coalescence alongside multilayer formation. $\pi$ enhances both DD and ND with a lower cut-off for ND, while temperature has a lower cut-off for DD but negligible effect on ND. Hydrocarbon chain length has the strongest effect, causing a cross-over from DD to ND dynamics. Imaging Ellipsometry (IE) of horizontally transferred films onto Si(100) shows Stranski-Krastanov (SK) like growth for ND process in arachidic acid monolayer resulting in successive stages of monolayer, trilayer, multilayer islands, ridges from lateral island-coalescence and shallow wavelike structures from ridge-coalescence on the film surface. These studies show that lipophilic attraction between hydrocarbon chains is the driving force at all stages of long term monolayer dynamics.
Abstract Surface pressure versus Specific Molecular Area (Pi-A) Isotherms for Langmuir Monolayers... more Abstract Surface pressure versus Specific Molecular Area (Pi-A) Isotherms for Langmuir Monolayers of stearic acid (StA), and stearic acid containing 10% and 50%(by mass) of dodecanethiol-capped Au nanoparticles (StAu10 and StAu50, respectively), have been recorded. The isotherms show a decrease in the magnitude of the slopes in both the'liquid'L2 and L2. phases and the'solid'S phase, as well as a decrease in the differences between slopes of all the adjacent phases, indicating a change from a complex to a ...
Role of Interfaces in Growth Dynamics of Nanostructures
Alokmay Datta1,2, Natsuki Iguchi1,Keni... more Role of Interfaces in Growth Dynamics of Nanostructures
Alokmay Datta1,2, Natsuki Iguchi1,Kenichi Yoshikawa1, Smita Muhkerjee2 and Sudeshna Chattopadhyay1,3
1Department of Physics, Kyoto University, JAPAN
2Surface Physics Division, Saha Institute of Nuclear Physics, INDIA
3Department of Physics and Astronomy, Northwestern University, USA
Figure 1
Figure 2
Figure 3
Interfaces between nanostructures and the respective matrices have multiple roles in the growth dynamics and stability of the nanostructures. They can serve as confining barriers deciding the structure and orientation of growth, as in the case of air-water interfaces (Figure 1). They can redistribute the excess free energy, generated through different processing protocols, and give rise to specific growth centres (Figure 2). They can also play the role of exchanging energy (and material) between a nano-domain and a bulk, as seen in microscopic phase transitions (Figure 3). These different aspects of interfaces in relation to nanoscale dynamics will be presented.
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Papers by Alokmay Datta
Alokmay Datta1,2, Natsuki Iguchi1,Kenichi Yoshikawa1, Smita Muhkerjee2 and Sudeshna Chattopadhyay1,3
1Department of Physics, Kyoto University, JAPAN
2Surface Physics Division, Saha Institute of Nuclear Physics, INDIA
3Department of Physics and Astronomy, Northwestern University, USA
Figure 1
Figure 2
Figure 3
Interfaces between nanostructures and the respective matrices have multiple roles in the growth dynamics and stability of the nanostructures. They can serve as confining barriers deciding the structure and orientation of growth, as in the case of air-water interfaces (Figure 1). They can redistribute the excess free energy, generated through different processing protocols, and give rise to specific growth centres (Figure 2). They can also play the role of exchanging energy (and material) between a nano-domain and a bulk, as seen in microscopic phase transitions (Figure 3). These different aspects of interfaces in relation to nanoscale dynamics will be presented.