Fundamental properties, self-assembling behavior, and their temperature and salt responsivity of ionic amphiphilic diblock copolymer having poly(N-isopropylacrylamide) in aqueous solution

Matsuoka, Hideki; Moriya, Shotaro; Yusa, Shin‐ichi

doi:10.1007/s00396-017-4217-3

Cited by 4 publications

(1 citation statement)

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“…An example of a relatively well-established area is the temperature- and salt-induced assembly of poly( N -isopropylacrylamide)pNIPAM, − in which a coil-to-globule transition (CGT) is observed at the lower critical solution temperature (LCST), , the latter being highly sensitive to the presence of ions in solution. pNIPAM is said to resemble the cold denaturation of globular proteins, and for this reason, pNIPAM is considered a model for understanding the effects of specific ions on a number of biologically relevant reactions, ranging from the solubility and stability of proteins to enzymatic action in crowded macromolecular environments, to creating smart devices incorporating pNIPAM and DNA functionalities. ,− The CGT in pNIPAM is often viewed by utilizing a combination of theoretical approaches devised to rationalize the occurrence and the mechanism of cold protein denaturation, using an assumption that the effective size of bound vs loose water molecules depends on the temperature. , This theoretical effort is complemented by a growing number of experimental studies, with the general consensus that the globular collapse transition is “entropy-driven” by decreasing the solvent-excluded polymer shell to maximize the translational entropy of water molecules and ions and minimize the hydrophobic interactions. − The reduction in the solvent-excluded volume plays a major role when a polymer chain passes from a swollen conformation to a collapsed one, which corresponds to an increase in the translational entropy of water molecules.…”

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confidence: 99%

Salt-Induced Liquid–Liquid Phase Separation and Interfacial Crystal Formation in Poly(N-isopropylacrylamide)-Capped Gold Nanoparticles

et al. 2021

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We report on the dynamic response of aqueous solution containing poly(N-isopropylacrylamide)-capped gold (pNIPAM-capped Au) nanoparticles to the introduction of NaCl. The addition of NaCl increases the density of the solution and prompts the liquid–liquid phase separation process, confining the polymer to a lower-density salt-deficient aqueous phase. As the pNIPAM-occupied aqueous phase becomes excluded from the higher-density NaCl-rich bulk solution, the pNIPAM-capped Au nanoparticles follow liquid–liquid phase separation and reside on the surface of the formed pNIPAM-filled globes at the interface between the NaCl-rich bulk solution and the pNIPAM-containing solution, exhibiting a hexagonal packing with interparticle distance of ∼23 nm. Driven by the minimization of hydrophobic interactions, the buoyant Au-decorated globular assemblies filled with aqueous pNIPAM solution escape to the air/water interface, collapse at the interface, and form planar hexagonal crystalline domains of different sizes, depending on NaCl concentration. At low NaCl concentrations, the collapse of the Au-decorated aqueous pNIPAM-filled globes at the air/water interface produces an interfacial two-dimensional (2D) hexagonal lattice of pNIPAM-capped Au nanoparticles with an interparticle distance of 25–27 nm. The increase in NaCl concentration leads to a formation of smaller globes escaping to, and collapsing at the air/water interface and yielding smaller two-dimensional hexagonal domains.

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