Hello, A change in allocation has been requested: Requester: sdeshmuk (Sanket Deshmukh) Project: MD_of_pnipam_brush Title: Structural and dynamic properties of thermo-sensitive polymer brushes: Molecular Dynamics study. Description: In this work we propose to use the Consistent Valence force field (CVFF) to understand the structural changes in the polymer brush at global as well as local level using an atomistic level model. The preliminary studies we carried out with CVFF on a single chain made up of 30 monomer units of PNIPAM in presence of pure water predicted the LCST close to 305K, which is in good agreement with experimentally observed value. To carry out MD simulations we will be using LAMMPS MD simulation package. Fully atomistic polymer chains with ~25 monomer units will be generated. Each chain will be end-grafted to form a 5 x 5 grid on flat surface, which will define the x-y plane of the system. Grafting density will be varied from 0.05 to 0.5 to study the structural changes with respect to grafting density. Depending upon the number of polymer chains TIP4P water molecules (~20,000 to ~100,000) will be added to simulation cell. To study the structural changes across the LCST o f PNIPAM, simulation system will then be equilibrated up to 40-50ns using LAMMPS at 278, 310 and 360K. To study the change in the LCST of PNIPAM in presence of another thermo-sensitive polymer, if any, we propose to use PNIPAM and PEO grafted and equilibrated in similar manner as mentioned above. The computational requirements for the proposed study will be substantial. To study the phase transition across the LCST in the case of single PNIPAM chain, simulations should be carried out for ~50ns. From preliminary results of the simulations we carried out on the CNM’s cluster Carbon, we observed a clear phase transition across the LCST, for polymer chains with 30 monomer units (572 atoms) in presence of 9,000 water molecules. This system with ~30,000 atoms required ~145 hrs of simulation time for 10ns on 96 cores. In the proposed work we plan to study, PNIPAM ~25 mer (475 atoms) brush made up of ~20 polymer chains (~9000 atoms) in presence of ~30,000 water molecules. Simulations will be carried out at 278, 310 and 360K for ~50ns (total simulation time = 150ns). We also propose to study PNIPAM ~25 mer (475 atoms) and PEO ~25 mer (150 atoms) polymer chains. In the initial stages of this project we plan to use 5 and 10 chains of both PNIPAM (2375 and 4750 atoms) and PEO (1500 and 3000 atoms) in presence of 30,000 water molecules. Total system will be consisted of ~100,000 atoms and simulations will be carried out at 278, 310 and 360K for ~50ns (total simulation time = 300ns). The estimated time to carry out the mentioned calculations in this particular work would be ~500,000 core hours. Current: undetermined amount Justification: To study the phase transition across the LCST in the case of single PNIPAM chain, simulations should be carried out for ~50ns. From preliminary results of the simulations we carried out on the CNM’s cluster Carbon, we observed a clear phase transition across the LCST, for polymer chains with 30 monomer units (572 atoms) in presence of 9,000 water molecules. This system with ~30,000 atoms required ~145 hrs of simulation time for 10ns on 96 cores. Requested: 500000 A specific reason has been given: I have already used the allocated time (450000 + 225000) for my calculations. I have finished the first step proposed in this proposal. Currently, I am conducting the simulations of polymer brush structures of PNIPAM and PEG. To carry out these simulations with different molecular weights of PNIPAM and PEG and with different grafting density I need more computational time. Based on the calculations I already carried out on Fusion, estimated time for these calculations would be around 500000 core-hours. This needs to be approved and the final allocation amount decided upon. Thank You, The LCRC Accounts System