Atomistic Molecular Dynamics Simulations of the Lower Critical Solution Temperature Transition of Poly(N-vinylcaprolactam) in Aqueous Solutions

ABSTRACTPoly(N-isopropylacrylamide) (PNIPAM), a classic thermo-sensitive polymer, has a lower critical solution temperature (LCST) at ∼32°C. In this work we have used molecular dynamics simulations to understand the origin of the LCST and agglomeration of PNIPAM chains of 5 and 30 monomer units (5-mer and 30-mer). Experimentally, when the concentration of PNIPAM is >1 ppm, polymer chains after undergoing coil-to-globule transition above the LCST aggregates to yield a stable colloidal dispersion.In our study two PNIPAM chains, consisting of 30 monomer units each, were placed in a cubic simulation cell and were subsequently solvated. Simulations were carried out below and above the LCST, namely at 278 and 310K for 10ns. Simulated trajectories were analyzed for structural and dynamical properties of both PNIPAM and water. We observe coil-to-globule transition in PNIPAM above the LCST. We also find that the PNIPAM chains agglomerate above the LCST. We also observe entanglement in PNIPAM chains below the LCST. We also study agglomeration of 5 PNIPAM chains each consisting of 5 monomer units. There was no significant difference in polymer agglomeration behavior across the LCST for these short chain oligomers. The agglomeration behavior is thus strongly correlated to the size of the polymer chains. These results provide fundamental insight into the atomistic scale mechanism of PNIPAM agglomeration across the LCST.

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Combined Salt Concentration and Degree-of-Ionization Effect on the Structure of Poly(methacrylic acid) in Aqueous Solutions as Revealed by Molecular Dynamics Simulations

Industrial & Engineering Chemistry Research ◽

10.1021/acs.iecr.1c00492 ◽

2021 ◽

Author(s):

Abhishek Kumar Gupta

Keyword(s):

Molecular Dynamics ◽

Aqueous Solutions ◽

Molecular Dynamics Simulations ◽

Methacrylic Acid ◽

Salt Concentration ◽

Degree Of Ionization ◽

Ionization Effect ◽

Dynamics Simulations

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Aqueous solutions of ionic liquids: study of the solution/vapor interface using molecular dynamics simulations

Physical Chemistry Chemical Physics ◽

10.1039/b806205f ◽

2008 ◽

Vol 10 (37) ◽

pp. 5765 ◽

Cited By ~ 44

Author(s):

Jan Picálek ◽

Babak Minofar ◽

Jiří Kolafa ◽

Pavel Jungwirth

Keyword(s):

Molecular Dynamics ◽

Ionic Liquids ◽

Aqueous Solutions ◽

Molecular Dynamics Simulations ◽

Vapor Interface ◽

Dynamics Simulations

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UNDERSTANDING DIFFERENT LCST LEVELS OF POLY(N-ALKYLACRYLAMIDE)S BY MOLECULAR DYNAMICS SIMULATIONS AND QUANTUM MECHANICS CALCULATIONS

Journal of Theoretical and Computational Chemistry ◽

10.1142/s0219633611006505 ◽

2011 ◽

Vol 10 (03) ◽

pp. 359-370 ◽

Cited By ~ 7

Author(s):

JUAN PANG ◽

HU YANG ◽

JING MA ◽

RONGSHI CHENG

Keyword(s):

Molecular Dynamics ◽

Quantum Mechanics ◽

Aqueous Solutions ◽

Molecular Dynamics Simulations ◽

Steric Effect ◽

Conformational Transition ◽

Methyl Group ◽

Branched Chain ◽

Dynamics Simulations ◽

Different Levels

Poly(N-alkylacrylamide) is a group of thermo-sensitive polymers that include poly (N-isopropylacrylamide), poly(N-n-propylacrylamide), poly(N-isopropylmethacryl-amide), and so on. The polymers exhibit different levels of lower critical solution temperatures (LCST) in aqueous solutions. In this article, their monomers and oligomers with 10 repeating units are selected, respectively, to demonstrate the cause of different LCST levels of the polymers in aqueous solutions using molecular dynamics simulations and quantum mechanics calculations. The monomers have functional groups of different steric volume that greatly affect the conformational transition of chains and LCST levels of the polymers. A branched chain of N-propyl group in N-isopropylacrylamide and an additional methyl group at α-carbon in N-isopropylmethacrylamide both increase the steric effect, making it more difficult for monomers to draw closer and resulting in higher LCST levels of the polymers. In addition, the simulated results from their corresponding oligomers exhibit the similar trend to those from the monomers.

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