Cononsolvency of poly-N-isopropyl acrylamide (PNIPAM): Microgels versus linear chains and macrogels

Scherzinger, Christine; Schwarz, Annett; Bardow, André; Leonhard, Kai; Richtering, Walter

doi:10.1016/j.cocis.2014.03.011

Cited by 138 publications

(154 citation statements)

References 112 publications

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“…The position of the VPTT minimum and the depth of the minimum remain constant. The only slight difference is that in the etalon, a VPT could be observed up to 80 vol % of methanol, while in bulk [16,35] beyond 65 vol % no temperature effect could be detected. This might be a hint that there is a higher waterorganic solvent ratio in confinement than in the bulk, which is qualitatively in agreement with the present results.…”

Section: Shift In the Particle Size Minimum From Bulk To Adsorbed Parmentioning

confidence: 56%

“…It is worth to note that the reflectance not only change by the distance between the etalon surfaces but also by the increasing turbidity during the particle collapse within the etalon. There is also a mismatch in literature of cononsolvency data for PNIPAM microgels in bulk solution: Heppner et al found a VPTT minimum of −30 • C at 65 vol % methanol, while other studies report a VPTT minimum of −5 • C to −10 • C at 55 vol % methanol [16,35].…”

Section: Shift In the Particle Size Minimum From Bulk To Adsorbed Parmentioning

confidence: 94%

“…Thus, free and more movable organic solvent molecules are able to interact with the polymer network leading to a reswelling of the particle [20,21]. Beside the clathrate model, the assumption of the competitive absorption seems also to be a reasonable explanation of the the cononsolvency effect [16,22]. In this model, both solvents (water and organic solvent) compete to form H-bonds with the polymer network.…”

Section: Introductionmentioning

confidence: 91%

“…This phenomenon is called cononsolvency effect, which was first reported for linear PNIPAM chains by Winnik et al [15]. Several models are used to describe the cononsolvency effect ( [16] and references therein). Many studies explain the cononsolvency effect by a competition between solvent-solvent and solvent-polymer interactions.…”

Section: Introductionmentioning

confidence: 95%

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The impact of the cononsolvency effect on poly (N-isopropylacrylamide) based microgels at interfaces

2014

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The paper addresses the effect of solid interfaces on the cononsolvency effect for poly(N -iso propylacrylamide) based microgels containing different contents of the co-monomer allyl acetic acid (AAA). The cononsolvency effect is studied by dynamic light scattering (DLS) in solution and with atomic force microscopy (AFM) at surfaces against different mixtures of water and organic solvent (ethanol, iso-propanol, and tetrahydrofuran). For the studies at interfaces, the microgels are spin coated on silicon wafers that are precoated with poly(allylamine hydrochloride) (PAH). The minimum in particle volume due to cononsolvency shows a pronounced shift from 10-20 % of organic solvent to 40-50 % after deposition at the Si/PAH wafer. The strong shift indicates an increase of water to organic solvent ratio within the gel at the surface with respect to the bulk solution. In order to understand the increase of water to organic solvent ratio, shrinking/reswelling AFM experiments for different spincoating conditions and under ambient conditions are carried out. Spin coating from water instead from different solvent mixtures has no effect on the cononsolvency. In ambient conditions, the cononsolvency effect disappears

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Section: Shift In the Particle Size Minimum From Bulk To Adsorbed Parmentioning

confidence: 56%

Section: Shift In the Particle Size Minimum From Bulk To Adsorbed Parmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 95%

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The impact of the cononsolvency effect on poly (N-isopropylacrylamide) based microgels at interfaces

2014

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“…A typical example of environmentally sensitive polymer microgels that has received much attention is poly(Nisopropylacrylamide) (PNIPAM), which undergoes reversible hydrophilic/hydrophobic transitions in aqueous solution at a lower critical solution temperature (LCST) [30,31]. For example, the thermosensitive polystyrene (PS)-PNIPAM coreshell microgel has been applied as a nanoreactor for the immobilization of MNPs.…”

Section: Introductionmentioning

confidence: 99%

Amphiphilic polymer-Ag composite microgels with tunable catalytic activity and selectivity

et al. 2015

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Environmentally sensitive polymer microgels are increasingly being used to enhance the catalytic activity of supported metal nanoparticles. Herein, we synthesized composite polymer microgels composed of the core-shell structure poly(styrene-N-isopropylacrylamide)/poly(Nisopropylacrylamide-co-methacrylic acid) (P(St-NIPAM)/ P(NIPAM-co-MAA)). Ag nanoparticles (AgNPs) were loaded onto/into the network chains of the polymer microgels through a facile method. The prepared composite microgels were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, and ultraviolet-visible spectroscopy. The catalytic selectivity of P(St-NIPAM)/P(NIPAM-co-MAA)-Ag composite microgels for the reduction of hydrophilic 4-nitrophenol (4-NP) and hydrophobic nitrobenzene (NB) by NaBH 4 was investigated. The results indicated that the introduction of PMAA segments into the microgel networks caused the poly(N-isopropylacrylamide) (PNIPAM) chains to separate into a shell layer and prevented the aggregation of AgNPs. The separated PNIPAM segments not only favor the mass transfer, but also possess thermosensitive function to modulate the catalytic activity of AgNPs. These structural features of the prepared composite microgels could enhance the selectivity and mass transfer of the reactants for catalytic reduction of 4-NP and NB through temperature modulation.

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Dynamic Nanoparticle Assemblies for Biomedical Applications

et al. 2017

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Designed synthesis and assembly of nanoparticles assisted by their surface ligands can create "smart" materials with programmed responses to external stimuli for biomedical applications. These assemblies can be designed to respond either exogenously (for example, to magnetic field, temperature, ultrasound, light, or electric pulses) or endogenously (to pH, enzymatic activity, or redox gradients) and play an increasingly important role in a diverse range of biomedical applications, such as biosensors, drug delivery, molecular imaging, and novel theranostic systems. In this review, the recent advances and challenges in the development of stimuli-responsive nanoparticle assemblies are summarized; in particular, the application-driven design of surface ligands for stimuli-responsive nanoparticle assemblies that are capable of sensing small changes in the disease microenvironment, which induce the related changes in their physico-chemical properties, is described. Finally, possible future research directions and problems that have to be addressed are briefly discussed.

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Cononsolvency of poly-N-isopropyl acrylamide (PNIPAM): Microgels versus linear chains and macrogels

Cited by 138 publications

References 112 publications

The impact of the cononsolvency effect on poly (N-isopropylacrylamide) based microgels at interfaces

The impact of the cononsolvency effect on poly (N-isopropylacrylamide) based microgels at interfaces

Amphiphilic polymer-Ag composite microgels with tunable catalytic activity and selectivity

Dynamic Nanoparticle Assemblies for Biomedical Applications

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