|Current Research Areas|
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|Understanding crystallization of diblock copolymer|
|Diblock copolymers consist of two chemically different blocks of repeat units (covalently bonded), which are in most of the cases, incompatible (viz. immiscible). This mutual immiscibility leads to the formation of respective domain via microphase separation. Diblock copolymer demonstrates a wide variety of phase and morphological behavior depending on the relative composition of the blocks and their mutual miscibility (viz. block incompatibility). The self-assembly characteristics of such polymer control the richness of the phase and morphological behavior. They are widely used in template fabrication, nanotechnology and biomedical applications etc. In most of the cases, both the blocks are non-crystalline in nature. An interesting scenario happens when one or both the blocks are crystalline in nature. In the presence of crystalline blocks, there is interplay between microphase separation and crystallization. Usually, the block with higher melting point or longer block length crystallizes first followed by the phase transition (crystallization) of the block with lower melting point or shorter block length. The crystalline block upon crystallization, creates confinement for the phase transition of the second block. If the second block is non-crystalline, it will remain in the glassy, amorphous state. On the other hand, if both the blocks are crystalline in nature, the crystallization of the second block is slowed down due to the presence of the already crystalline first block. Second block has to crystallize in the presence of the hard confinement created by the first block. As a result, a dramatic change in the morphology of the material occurs. The modification of the morphology alters the properties which enable to prepare tailored-made material for potential applications. Understanding the crystallization behavior of diblock copolymer is of fundamental interest and has the implications on their numerous applications in various fields. There are a growing interest on the thermodynamics, kinetics and morphological behavior of such crystalline diblock copolymer. Crystalline diblock copolymers such as PLLA-b-PE, PLLA-b-PCL, PLLA-b-PEO etc. are of great importance due to their potential application in biomedical field. PLLA has been in use in biomedical application for a long time. Incorporating another polymer (e.g., PDLA, PEO, and PEG etc.) would change the property of the parent polymer. The current research project is aiming to understand the fundamental mechanism behind the interplay between the crystallization and the microphase separation of crystalline blocks, and the effect on the thermodyanics and kinetic of crystallization, morphological evolution, and to correlate with the macroscopic behavior of the material. In addition, crystallization of diblock copolymers represents the model for studying polymer phase transition in the presence of nano-scale confinement, which is relevant in nano science and nano technology.|
|Crystallization of model ionomer (associating polymer)|
Ionomers are the copolymer with less than 15% co-units content. These co-monomers either are ionic in nature or are linked with ionic groups. In the solution, they dissociate and behave like a polyelectrolyte. In the melt, in the absence of any solvent (hence no salvation energy), they cannot dissociate. Rather, the ionic groups associate and form ionic clusters via aggregation. Upon cooling from the high temperature melt state to the crystalline state, the already formed ionic clusters inhibit the crystallization and as a result, a less crystalline material with completely different morphology is obtained. How the ionic aggregation does affect the crystallization thermodynamics and kinetics is the key question. How does it affect in the nucleation in polymer crystallization. In some cases, it has been reported that the presence of the ionic aggregate accelerates the nucleation - they behave like a heterogeneous nucleating agent. The molecular mechanism behind this observation is not well understood. In the current work, we will focus on (i) general understanding on the crystallization of polymer in the presence of ionic aggregate; (ii) the sequence of events, which occurs first - aggregation or crystallization and the consequences on the crystallization; (iii) nucleation of polymer crystallization in the presence of ionic aggregate; (iv) application to real ionomer, such as Na-salt of sulphonated polystyrene.
Folding, unfolding and misfolding of prion protein
There are certain classes of diseases which are caused by the misfolding of protein molecules. These diseases are known as the neurodegenerative disease. Examples are: Alzheimer, Perkinson, Mad Cow etc. Protein molecules are active in the native (or folded) state and they lose their activity on going from the native state to the denatured state. While going from the denatured to the native state, some of the protein molecules follow a different pathway and misfolded. Understanding the detail kinetic pathway is extremely important to address the issue: what are the factors which motivates the proteins to get misfolded, what physiological condition is responsible for the misfolding of proteins, the role of the primary structure of the protein molecules, how can we control or eliminate the possibility of misfolding of such protein molecules. The misfolded protein induces other protein molecules to be misfolded and they form a fibril structure (via aggregation of protein molecules) and cause the disease. Detail study is necessary to understand the pathway for the fibril formation, how can we prevent the aggregation of misfolded protein molecules and fibril formation. It is believed that the protein aggregation proceeds via nucleation and growth mechanism, but the details are poorly understood.
Ashok Kumar Dasmahapatra
Key Research Areas : Complex fluids, Phase transition in polymeric systems, Structure-property relations,
Molecular simulations, Biological physics, Solar cells, Polymer nano-composites.
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