NMR evidence of the formation of surfactant micelles inside spherical poly(<i>N</i>-isopropylacrylamide) microgels

Gao, Yibing; Au-Yeung, Steve C. F.; Zhou, Shuiqin; Wu, Chi

doi:10.1080/00222349708212394

Cited by 14 publications

(4 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The state of the gelation of the polymer particles was governed by the initial amount of cross-linker introduced into the latex recipe. NMR has also been used to provide evidence for the formation of surfactant micelles inside spherical poly(NIPAM) microgels . In addition, solid-state NMR has also been used for the characterization of polystyrene−poly( tert -butyl acrylate) core and inverse core−shell particles .…”

Section: Resultsmentioning

confidence: 99%

Calorimetric Investigation of the Influence of Cross-Linker Concentration on the Volume Phase Transition of Poly(N-isopropylacrylamide) Colloidal Microgels

et al. 2003

View full text Add to dashboard Cite

A series of poly(N-isopropylacrylamide) microgels were prepared, by a surfactant-free emulsion polymerization method, incorporating varying cross-linker concentrations (0.25−30.0% of N,N‘-methylenebisacrylamide). Turbidimetric, light scattering, and differential scanning calorimetric (DSC) analyses of aqueous dispersions of these microgels show that the temperature and the half-width of the overall volume phase transition (VPT) of the colloidal dispersions increase with increasing cross-linker concentration. DSC analysis also reveals a decrease in the overall calorimetric enthalpy of the VPTs with increasing cross-linker concentration. The DSC thermograms have been deconvoluted into two component transitions; one is asymmetric and attributed to aggregation of “free” N-isopropylacrylamide monomers/oligomers, and a second, two-state conformational transition, is associated with the cross-linked microgels. Pulsed-gradient spin−echo NMR diffusion measurements show that the diffusion of water within the particles can be estimated and this diffusion rate decreases with increasing cross-link concentration. Complementary fluorescence studies show an increased hydrophobicity as the cross-linker density increases.

show abstract

Section: Resultsmentioning

confidence: 99%

Calorimetric Investigation of the Influence of Cross-Linker Concentration on the Volume Phase Transition of Poly(N-isopropylacrylamide) Colloidal Microgels

et al. 2003

View full text Add to dashboard Cite

show abstract

“…In contrast, anionic surfactants, such as sodium dodecyl sulfate (SDS), bind to the microgels at micro- to millimolar concentrations due to the hydrophobic effect on the hydrocarbon chain and thus convey their electric charge to the microgels. This charging leads to a strong increase in size of the microgels and shifts the VPTT to higher temperatures. ,,, …”

Section: Resultsmentioning

confidence: 99%

“…This charging leads to a strong increase in size of the microgels and shifts the VPTT to higher temperatures. 4,32,76,77 PW and SiW seemingly cause intermediate swelling effects between the anionic surfactants and salts. Exclusively at low POM concentration, the electric charging effect of pNiPAMpolymer segments upon binding of the anionic POMs seems to dominate and induce an increase in the mean mesh size of the polymer network that is reflected as an increase in the overall microgel size.…”

Section: Resultsmentioning

confidence: 99%

Nonionic Microgels Adapt to Ionic Guest Molecules: Superchaotropic Nanoions

Simons,

Hazra,

Petrunin

et al. 2024

ACS Nano

View full text Add to dashboard Cite

Microgels are commonly applied as solute carriers, where the size, density, and functionality of the microgels depend on solute binding. As representatives for ionic solutes with high affinity for the microgel, we study here the effect of superchaotropic Keggin polyoxometalates (POMs) PW 12 O 40 3− (PW) and SiW 12 O 40 4− (SiW) on the aqueous swelling and internal structure of nonionic poly(N-isopropylacrylamide) (pNiPAM) microgels by light scattering techniques and smallangle X-ray scattering. Due to their weak hydration, these POMs bind spontaneously to the microgels at millimolar concentrations. The microgels thus become charged and swell at low POM concentration, surprisingly without strongly increasing the volume phase transition temperature, and deswell at higher POM concentration. The swelling arises because of the osmotic pressure of dissociated counterions of the POMs, while the deswelling is due to POMs acting as physical cross-links in the microgels under screened electrostatics in NaCl or excess POM solution. This swelling/deswelling transition is sharper for PW than for SiW related to the lower charge density, weaker hydration, and stronger binding of PW. The POMs elicit qualitatively and quantitatively different swelling effects from ionic surfactants and classical salts. Moreover, the network softness and topology govern the swelling response upon POM binding. The softer the microgel, the stronger is the swelling response, while, inside the microgel, regions of high polymer density swell/contract more upon electric charging/cross-linking than regions with low polymer density. POM binding thus enables fine-tuning of microgel properties and highlights the role of network topology in microgel swelling. Because POMs decompose at an alkaline pH, these POM/microgel systems also exhibit pH-responsive swelling in addition to the typical temperature responsiveness of pNiPAM microgels.

show abstract

“…Negatively charged co-monomers promote expansion of the macromolecule owing to the repulsion from electron-rich amide groups and are expected to hinder thermoprecipitation more than positively charged co-monomers; the latter have attraction to the amide groups and stabilize to some extent the compact conformation needed for thermoprecipitation to take place. This rationale was used to explain the effect of negatively and positively charged detergents on the thermoprecipitation of poly-NIPAM and the collapse of poly-NIPAM-based latexes (Gao et al, 1997).…”

Section: Nipam Copolymers With Metal Chelates For Affinity Precipitationmentioning

confidence: 99%

Affinity precipitation of proteins: design criteria for an efficient polymer

1998

View full text Add to dashboard Cite

Affinity precipitation is fast emerging as a successful technique for the purification of proteins which can be introduced at an early stage of downstream processing. The technique applies the use of reversibly soluble-insoluble polymers which have either natural or synthetic origin. Apart from the successful use of some natural polymers, such as chitosan and alginate, the vast application of the technique depends upon the design of efficient synthetic polymers. In this laboratory, N-isopropylacrylamide (NIPAM) copolymers have been developed for metal chelate affinity precipitation of proteins. The copolymers of 1-vinylimidazole (VI) and iminodiacetic acid (IDA) with NIPAM were synthesized. The copolymers were thoroughly characterized with a view to designing an efficient soluble-insoluble polymer for metal chelate affinity precipitation of proteins.

show abstract

NMR evidence of the formation of surfactant micelles inside spherical poly(N-isopropylacrylamide) microgels

Cited by 14 publications

References 9 publications

Calorimetric Investigation of the Influence of Cross-Linker Concentration on the Volume Phase Transition of Poly(N-isopropylacrylamide) Colloidal Microgels

Calorimetric Investigation of the Influence of Cross-Linker Concentration on the Volume Phase Transition of Poly(N-isopropylacrylamide) Colloidal Microgels

Nonionic Microgels Adapt to Ionic Guest Molecules: Superchaotropic Nanoions

Affinity precipitation of proteins: design criteria for an efficient polymer

Contact Info

Product

Resources

About