Direct Phase Equilibrium Simulations of NIPAM Oligomers in Water

Boţan, Vitalie; Ustach, Vincent D.; Faller, Roland; Leonhard, Kai

doi:10.1021/acs.jpcb.6b00228

Cited by 41 publications

(70 citation statements)

References 45 publications

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“…It is known that the chain length and concentration of the polymer can affect the process of LCST phase transition. For example, to observe a clear conformational transition in the case of computational studies of PNIPAAm, it was found that either the polymer chain length should be at least 30‐mer or the oligomer concentration should be high . In our single chain simulations, we observed a similar behavior for PMEO 2 MA that only 20‐ and 50‐mer polymers showed a LCST phase transition.…”

Section: Resultssupporting

confidence: 57%

Atomistic insights on the LCST behavior of PMEO₂MA in water by molecular dynamics simulations

Dalgakiran

Tatlipinar

2017

J Polym Sci B Polym Phys

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Fully atomistic molecular dynamics simulations of poly(2-[2-methoxyethoxy]ethyl methacrylate) (PMEO 2 MA) in water at temperatures below and above its lower critical solution temperature (LCST) were performed to improve the understanding of its LCST behavior. Atomic trajectories were used to calculate various structural and dynamic properties. Simulation results show that PMEO 2 MA undergo a distinct coil-to-globule transition above LCST. Detailed analyses of the number of first hydration shell water molecules around various atomic regions are revealed that the water solubility of PMEO 2 MA below LCST is mainly provided by the hydrophobic hydration around the side chain carbon atoms. This is achieved by the cage-like water network formations which are disrupted when the temperature is increased above LCST, accompanied by significant amount of water molecule release and local water-ordering reduction, which leads to the LCST phase transition. Furthermore, other analyses such as the number of hydrogen bonds and hydrogen bond lifetimes suggest that intermolecular hydrogen bondings between polymer and water molecules have little effect on the phase transition. Our results will contribute to a better understanding on the LCST phase transition of oligo(ethylene glycol) methyl ether methacrylate (OEGMA)based homopolymers at atomistic level that will be useful when designing homo-and co-polymers of OEGMAs with desired properties.

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Section: Resultssupporting

confidence: 57%

Atomistic insights on the LCST behavior of PMEO₂MA in water by molecular dynamics simulations

Dalgakiran

Tatlipinar

2017

J Polym Sci B Polym Phys

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“…Water content in the collapsed phase. To set up a system of collapsed PNIPAM polymers (20monomer-long atactic chains) above the LCST with the same chemical potential of water in as in bulk water, we first construct a system with two distinct phases [35,61]: a collapsed amorphous polymer phase in one part of the box, forming a membrane, and a polymer-free water reservoir in the other, as shown in Figure 1a. We use a novel, recently introduced, OPLS-based force field [62] for the PNI-PAM polymers, which better captures the thermoresponsiveness than the standard OPLS-AA [58].…”

Section: Resultsmentioning

confidence: 99%

“…For PNIPAM polymers we first tested the standard OPLS-AA [58] force field, which is among the most popular ones for PNIPAM simulations [27][28][29][30][31][32]35]. Since this force field did not yield satisfactory hydration results in the collapsed state (see Figure 1c) and also due to revealed issues with its thermo-responsive properties in the recent literature [61,96], we use its recent modification with recalculated partial charges by Palivec et al [62]. As has been demonstrated, the novel forcefield exhibits thermo-responsive properties of a single PNI-PAM polymer much closer to experimental observations.…”

Section: Atomistic Modelmentioning

confidence: 99%

Selective Molecular Transport in Thermoresponsive Polymer Membranes: Role of Nanoscale Hydration and Fluctuations

et al. 2018

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For a wide range of modern soft functional materials the selective transport of sub-nanometersized molecules ('penetrants') through a stimuli-responsive polymeric membrane is key to the desired function. In this study, we investigate the diffusion properties of penetrants ranging from non-polar to polar molecules and ions in a matrix of collapsed Poly(N-isopropylacrylamide) (PNIPAM) polymers in water by means of extensive molecular dynamics simulations. We find that the water distributes heterogeneously in fractal-like cluster structures embedded in the nanometer-sized voids of the polymer matrix. The nano-clustered water acts as an important player in the penetrant diffusion, which proceeds via a hopping mechanism through 'wet' transition states: the penetrants hop from one void to another via transient water channels opened by rare but decisive polymer fluctuations. The diffusivities of the studied penetrants extend over almost five orders of magnitude and thus enable a formulation of an analytical scaling relation with a clear non-Stokesian, exponential dependence of the diffusion coefficient on the penetrant's radius for the uncharged penetrants. Charged penetrants (ions) behave differently as they get captured in large isolated water clusters. Finally, we find large energetic activation barriers for hopping, which significantly depend on the hydration state and thereby challenge available transport theories.

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“…The dissolution does not happen even for a slab of isotactic trimers in water (not shown), for both considered force fields, which is in agreement with simulations of trimers with several force fields. 22 The polymer regions at both sides of the central core (having half of the central density at the initial configuration) shrink along the run to produce larger densities (ρ s ) and thinner profiles (with width w). This shrinking process leads to the secondary maxima placed at the borders of the membrane, which are a consequence of the bending of the oligomer tips towards the central plane.…”

Section: B Membrane In Pure Watermentioning

confidence: 99%

“…A natural way of accounting for all these entangled effects together is by means of all-atom molecular simulations, with the price of strongly decreasing time scale and system size. This has been done mostly by considering an infinitely diluted oligomer chain in water for several force-fields 13,[19][20][21][22][23][24] and for different electrolyte solutions. 20 In particular, Tucker and Stevens have studied the T Θ dependence with the oligomer length for a syndiotactic chain, concluding that the large chain limit of T Θ is achieved with 30mers.…”

Section: Introductionmentioning

confidence: 99%

Conformation change of an isotactic poly (N-isopropylacrylamide) membrane: Molecular dynamics

Adroher‐Benítez

Moncho-Jordá

Odriozola

2017

The Journal of Chemical Physics

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In this work, isotactic Poly (N-Isopropylacrylamide)-PNIPAM-in neat water and in electrolyte solutions is studied by means of molecular dynamics simulations. This is done for an infinitely diluted oligomer and for an assembly of several PNIPAM chains arranged into a planar membrane configuration with a core-shell morphology. We employed two different force fields, AMBER (assisted model building with energy refinement) and OPLS-AA (all atom - optimized potentials for liquid simulations) in combination with extended simple point charge water. Despite the more water insoluble character of isotactic oligomers, our results support the existence of a coil to globule transition for the isolated 30-mer. This may imply the existence of an oligomer rich phase of coil-like structures in equilibrium with a water rich phase for temperatures close but below the coil to globule transition temperature, T. However, the obtained coil structure is much more compact than that corresponding to the syndiotactic chain. Our estimations of T are (308±5) K and (303±5) K for AMBER and OPLS-AA, respectively. The membrane configuration allows one to include chain-chain interactions, to follow density profiles of water, polymer, and solutes, and accessing the membrane-water interface tension. Results show gradual shrinking and swelling of the membrane by switching temperature above and below T, as well as the increase and decrease of the membrane-water interface tension. Finally, concentration profiles for 1M NaCl and 1M NaI electrolytes are shown, depicting a strong salting-out effect for NaCl and a much lighter effect for NaI, in good qualitative agreement with experiments.

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Direct Phase Equilibrium Simulations of NIPAM Oligomers in Water

Abstract: 2

Cited by 41 publications

References 45 publications

Atomistic insights on the LCST behavior of PMEO₂MA in water by molecular dynamics simulations

Atomistic insights on the LCST behavior of PMEO₂MA in water by molecular dynamics simulations

Selective Molecular Transport in Thermoresponsive Polymer Membranes: Role of Nanoscale Hydration and Fluctuations

Conformation change of an isotactic poly (N-isopropylacrylamide) membrane: Molecular dynamics

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Direct Phase Equilibrium Simulations of NIPAM Oligomers in Water

Abstract: 2

Cited by 41 publications

References 45 publications

Atomistic insights on the LCST behavior of PMEO2MA in water by molecular dynamics simulations

Atomistic insights on the LCST behavior of PMEO2MA in water by molecular dynamics simulations

Selective Molecular Transport in Thermoresponsive Polymer Membranes: Role of Nanoscale Hydration and Fluctuations

Conformation change of an isotactic poly (N-isopropylacrylamide) membrane: Molecular dynamics

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Product

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Atomistic insights on the LCST behavior of PMEO₂MA in water by molecular dynamics simulations

Atomistic insights on the LCST behavior of PMEO₂MA in water by molecular dynamics simulations