Thermoresponsive Gold Nanoparticles with Positive UCST‐Type Thermoresponsivity

Liu, Fangyao; Agarwal, Seema

doi:10.1002/macp.201400497

Cited by 24 publications

(18 citation statements)

References 34 publications

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“…However, the reversibility of the multistep assembly process has not been exploited sufficiently. For the fabrication of sophisticated assemblies with dynamic structural changes, hierarchical structures composed of nanoparticles require controllable reversibility of assembly/disassembly in response to changes in the environment, such as temperature, pH, and light …”

Section: Introductionmentioning

confidence: 99%

Two‐Step Assembly of Thermoresponsive Gold Nanorods Coated with a Single Kind of Ligand

Iida

Mitomo

Niikura

et al. 2018

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Gold nanorods (GNRs) coated with a single kind of ligand show thermoreponsive two-step assembly to provide a hierarchical structure. The GNRs (33 nm in length × 14 nm in diameter) coated with a hexa(ethylene glycol) (HEG) derivative form side-by-side assemblies at 30 °C (T ) as a steady state through dehydration. By further heating to over 40 °C (T ), larger assemblies, which are composed of the side-by-side assembled units, are formed as hierarchical structures. The dehydration temperature of the HEG derivative varies depending on the free volume of the HEG unit, which corresponds to the curvature of the GNRs. Upon heating, dehydration first occurs from the ligands on the side portions with a lower curvature, and then from the ligands on the edge portions with a higher curvature. The different sized GNRs (33 × 8 and 54 × 15 nm) also show two-step assembly. Both the T and T are dependent on the diameter of the GNRs, but independent of their length. This result supports that the dehydration is dependent on the free volume, which corresponds to the curvature. Anisotropic assembly focusing on differences in curvature provides new guidelines for the fabrication of hierarchical structures.

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Section: Introductionmentioning

confidence: 99%

Two‐Step Assembly of Thermoresponsive Gold Nanorods Coated with a Single Kind of Ligand

Iida

Mitomo

Niikura

et al. 2018

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“…Both poly(NIPAM) and poly(AAm‐co‐AN) show non‐significant changes in cloud points with concentration for very dilute solutions (0.01–1 wt%), but cloud point increases for poly(AAm‐co‐AN) and decreases for poly(NIPAM) with an increase in concentration . Poly( N ‐acryloylglycinamide) (poly(NAGA)) is another interesting nonionic polymer showing phase transition of UCST type due to thermally controlled reversible H‐bonding interactions . The limitation of this system is the broad phase transition with hysteresis of more than 10 °C.…”

Section: Introductionmentioning

confidence: 99%

Tunable, concentration‐independent, sharp, hysteresis‐free UCST phase transition from poly(N‐acryloyl glycinamide‐acrylonitrile) system

Käfer

Lerch

Agarwal

2016

J. Polym. Sci. Part A: Polym. Chem.

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Poly(N‐acryloylglycinamide‐co‐acrylonitrile) (poly(NAGA‐AN)) copolymers were synthesized using reversible‐addition‐fragmentation transfer polymerization. In contrast to poly(NAGA) the thermoresponsive behavior of poly(NAGA‐AN) shows a narrow cooling/heating hysteresis in water with a tunable cloud point, depending on the acrylonitrile amount in polymer. Furthermore, we showed that there is no significant effect of the solution concentration on the cloud point and stable phase transition behavior in electrolyte solutions, which is presumable controlled by forming stable micellar like structures as a result of the block/graft‐copolymer structure. This is in contrast to poly(NAGA) which shows a strong concentration dependent cloud point in aqueous solution with a broad cooling/heating hysteresis. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 274–279

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“…bioseparation, drug delivery, sensors, membranes, etc., [5][6][7][8] have been achieved with poly(N-isopropyl acrylamide) (PNIPAAm) with phase separation of about 32°C. Nevertheless, non-ionic UCST systems have been progressing over the last few years not only with poly-(N-acryloylglycinamide) (PNAGA), [9][10][11] but also with copolymers, e.g. AAm with additional contents of hydrophobic AN or styrene (St) units.…”

Section: Introductionmentioning

confidence: 99%

pH dependent thermoresponsive behavior of acrylamide–acrylonitrile UCST-type copolymers in aqueous media

2016

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There are only a few non-ionic polymers known for showing thermoresponsivity of UCST-type. Copolymers of acrylamide (AAm) and acrylonitrile (AN) represent one of such thermoresponsive polymers.The present work shows pH-dependent UCST-transitions of this copolymer system. Herein, systematic studies were carried out to show hydrolytic stability and retention of UCST of the copolymer under various conditions. Regeneration of lost UCST-type transitions under extreme pH conditions could be achieved by changing pH, and by addition of electrolytes. Reversible addition fragmentation chain transfer (RAFT) was employed as a tool to synthesize copolymers of AAm and AN. Hydrolysis reactions were carried out intentionally under acidic and alkaline conditions, in order to analyze the chemical stability of the synthesized copolymers as well as to introduce carboxylic groups into the polymer structure. The obtained results showed high tolerance of poly(AAm-co-AN) samples under acidic conditions even after long periods of storage (25 days at pH 3) or after use of pH 0 and increased temperatures (40°C). In the case of base catalyzed hydrolysis, the thermoresponsive behavior was significantly influenced during hydrolysis in buffer solution of pH 9. Loss and regeneration of the phase transition temperature of these copolymers could be achieved by changing the pH from basic to acidic. Meanwhile, hydrolysis at pH 14 at 40°C influenced the thermoresponsive behavior and the chemical stability of the polymer, increasing the phase transition temperature over 30°C. Further, we observed that additives, e.g. formamide can act as a sacrificial agent for providing stable UCST-type transitions even under alkaline conditions as well as at high temperatures (85°C).

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Thermoresponsive Gold Nanoparticles with Positive UCST‐Type Thermoresponsivity

Cited by 24 publications

References 34 publications

Two‐Step Assembly of Thermoresponsive Gold Nanorods Coated with a Single Kind of Ligand

Two‐Step Assembly of Thermoresponsive Gold Nanorods Coated with a Single Kind of Ligand

Tunable, concentration‐independent, sharp, hysteresis‐free UCST phase transition from poly(N‐acryloyl glycinamide‐acrylonitrile) system

pH dependent thermoresponsive behavior of acrylamide–acrylonitrile UCST-type copolymers in aqueous media

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