scholarly journals Entropy Rules: Molecular Dynamics Simulations of Model Oligomers for Thermoresponsive Polymers

Entropy ◽  
2020 ◽  
Vol 22 (10) ◽  
pp. 1187
Author(s):  
Alexander Kantardjiev ◽  
Petko M. Ivanov
Keyword(s):  
Entropy Change ◽  
Atomic Scale ◽  
Solution Temperature ◽  
Water Molecules ◽  
Thermoresponsive Polymers ◽  
Simulation Data ◽  
Critical Solution Temperature ◽  
Extended Conformation ◽  
Dynamics Simulations ◽  
Experimental Findings

We attempted to attain atomic-scale insights into the mechanism of the heat-induced phase transition of two thermoresponsive polymers containing amide groups, poly(N-isopropylacrylamide) (PNIPAM) and poly(2-isopropyl-2-oxazoline) (PIPOZ), and we succeeded in reproducing the existence of lower critical solution temperature (LCST). The simulation data are in accord with experimental findings. We found out that the entropy has an important contribution to the thermodynamics of the phase separation transition. Moreover, after decomposing further the entropy change to contributions from the solutes and from the solvent, it appeared out that the entropy of the solvent has the decisive share for the lowering of the free energy of the system when increasing the temperature above the LCST. Our conclusion is that the thermoresponsive behavior is driven by the entropy of the solvent. The water molecules structured around the functional groups of the polymer that are exposed to contact with the solvent in the extended conformation lower the enthalpy of the system, but at certain temperature the extended conformation of the polymer collapses as a result of dominating entropy gain from “released” water molecules. We stress also on the importance of using more than one reference molecule in the simulation box at the setup of the simulation.

Thermoresponsive polymers with lower critical solution temperature: from fundamental aspects and measuring techniques to recommended turbidimetry conditions

2017 ◽  
Vol 4 (2) ◽  
pp. 109-116 ◽  
Author(s):  
Qilu Zhang ◽  
Christine Weber ◽  
Ulrich S. Schubert ◽  
Richard Hoogenboom
Keyword(s):  
Lower Critical Solution Temperature ◽  
Temperature Behavior ◽  
Solution Temperature ◽  
Thermoresponsive Polymers ◽  
Critical Solution Temperature ◽  
Measuring Techniques

This focus article addresses fundamental and practical aspects of investigating polymers with lower critical solution temperature behavior.

scholarly journals Constrained thermoresponsive polymers – new insights into fundamentals and applications

2021 ◽  
Vol 17 ◽  
pp. 2123-2163
Author(s):  
Patricia Flemming ◽  
Alexander S Münch ◽  
Andreas Fery ◽  
Petra Uhlmann
Keyword(s):  
Phase Transition ◽  
Current Knowledge ◽  
Polymer Chains ◽  
Switching Behavior ◽  
Solution Temperature ◽  
Miscibility Gap ◽  
Underlying Structure ◽  
Thermoresponsive Polymers ◽  
Critical Solution Temperature ◽  
Stimuli Responsive Polymers

In the last decades, numerous stimuli-responsive polymers have been developed and investigated regarding their switching properties. In particular, thermoresponsive polymers, which form a miscibility gap with the ambient solvent with a lower or upper critical demixing point depending on the temperature, have been intensively studied in solution. For the application of such polymers in novel sensors, drug delivery systems or as multifunctional coatings, they typically have to be transferred into specific arrangements, such as micelles, polymer films or grafted nanoparticles. However, it turns out that the thermodynamic concept for the phase transition of free polymer chains fails, when thermoresponsive polymers are assembled into such sterically confined architectures. Whereas many published studies focus on synthetic aspects as well as individual applications of thermoresponsive polymers, the underlying structure–property relationships governing the thermoresponse of sterically constrained assemblies, are still poorly understood. Furthermore, the clear majority of publications deals with polymers that exhibit a lower critical solution temperature (LCST) behavior, with PNIPAAM as their main representative. In contrast, for polymer arrangements with an upper critical solution temperature (UCST), there is only limited knowledge about preparation, application and precise physical understanding of the phase transition. This review article provides an overview about the current knowledge of thermoresponsive polymers with limited mobility focusing on UCST behavior and the possibilities for influencing their thermoresponsive switching characteristics. It comprises star polymers, micelles as well as polymer chains grafted to flat substrates and particulate inorganic surfaces. The elaboration of the physicochemical interplay between the architecture of the polymer assembly and the resulting thermoresponsive switching behavior will be in the foreground of this consideration.

N-Ester-substituted polyacrylamides with a tunable lower critical solution temperature (LCST): the N-ester-substitute dependent thermoresponse

2016 ◽  
Vol 7 (21) ◽  
pp. 3509-3519 ◽  
Author(s):  
Shengli Chen ◽  
Yuan Zhang ◽  
Ke Wang ◽  
Heng Zhou ◽  
Wangqing Zhang
Keyword(s):  
Lower Critical Solution Temperature ◽  
Great Influence ◽  
Solution Temperature ◽  
Thermoresponsive Polymers ◽  
Solution Property ◽  
Critical Solution Temperature

New thermoresponsive polymers ofN-ester-substituted polyacrylamides were discovered, and theN-ester-substitute exerting a great influence on the solution property was demonstrated.

MOLECULAR DYNAMICS SIMULATIONS OF DMPC/DPPC MIXED BILAYERS

2007 ◽  
Vol 18 (01) ◽  
pp. 73-89 ◽  
Author(s):  
ARMEN H. POGHOSYAN ◽  
HRANT H. GHARABEKYAN ◽  
ARAM A. SHAHINYAN
Keyword(s):  
Md Simulation ◽  
Orientational Order ◽  
Hydrocarbon Chain ◽  
Water Molecules ◽  
Hydrocarbon Chains ◽  
Racemic Mixtures ◽  
Area Per Lipid ◽  
Dynamics Simulations ◽  
Experimental Findings ◽  
Good Agreement

We have performed the atomistic MD simulation of dimyristoylphosphatidylcholine(DMPC)/dipalmitoylphosphatidylcholine(DPPC) mixed bilayers, consisting of various fraction of lipids, i.e., with fraction 0.25, 0.5 and 0.75 and hydration level 33 water molecules per lipid. The simulations were performed using NAMD code.The area per lipid, densities, orientational order parameters and tilt angle of hydrocarbon chain and also the interdigitation of chains were calculated. It has been established that the interdigitation degree of hydrocarbon chains is increased as the DPPC fraction is decreased. It has been also stated that the area per lipid value in case of racemic mixtures is about 0.72 nm2, which is in good agreement with experimental estimations. The hydrocarbon thickness is increased as the DPPC fraction increased. The DMPC/DPPC mixtures behave as almost ideally mixtures.The diffusion coefficients were also calculated and the results are in agreement with experimental findings.All the calculated parameters were compared with values obtained either from experimental data of DPPC or DMPC depending on the fraction of compound. The reason is that there are no experimental findings on DMPC/DPPC mixtures.

High-throughput physicochemical analysis of thermoresponsive polymers

2018 ◽  
Vol 9 (15) ◽  
pp. 1934-1937
Author(s):  
S. J. M. C. Bou ◽  
A. R. Connolly ◽  
A. V. Ellis
Keyword(s):  
Critical Micelle Concentration ◽  
High Throughput ◽  
Lower Critical Solution Temperature ◽  
Physicochemical Analysis ◽  
Solution Temperature ◽  
Thermoresponsive Polymers ◽  
Critical Solution Temperature ◽  
Critical Micelle Temperature

A novel high-throughput approach to rapidly measure the lower critical solution temperature, critical micelle concentration and critical micelle temperature of thermoresponsive polymers was developed and utilized to generate a physicochemical ‘MAP’ of a polymer series.

scholarly journals Water Infiltration in ZSM-5 Zeolites: Effect of Pore Volume and Water Structure

2012 ◽  
Author(s):  
Shalabh C. Maroo ◽  
Tom Humplik ◽  
Tahar Laoui ◽  
Evelyn N. Wang
Keyword(s):  
Water Structure ◽  
Water Desalination ◽  
Water Infiltration ◽  
Water Molecules ◽  
Geometric Approximation ◽  
Dynamics Simulations ◽  
Experimental Findings ◽  
Nano Crystal ◽  
Infiltration Behavior ◽  
Zeolite Crystals

This study investigates the infiltration of water in ZSM-5 zeolite crystals via molecular dynamics simulations and experiments. A zeolite nano-crystal is constructed in the simulations and is surrounded by water molecules which enter and saturate the pores. The average number of water molecules per unit cell of the zeolite is determined along with the radial distribution function of water inside the zeolites. A geometric approximation of the zeolite pores and intersections is proposed and verified. Partial charge on the zeolite atoms is found to be a crucial parameter which governs the water infiltration behavior. ZSM-5 zeolite crystals were also synthesized and water infiltration experiments were conducted using an Instron. The simulation and experimental findings are compared and discussed. The understanding gained from these studies will be important for the development of zeolite based reverse osmosis membranes for water desalination.

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