Phase separation in poly(<i>N</i>‐isopropyl acrylamide)/water solutions. II. Salt effects on cloud‐point curves and gelation

Yang, Yanyin; Zeng, Fang; Tong, Zhen; Liu, Xinxin; Wu, Shuizhu

doi:10.1002/polb.1064

Cited by 25 publications

(28 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…22 An alternative explanation is that the ions disrupt the hydration structure at the water-solute interface. 23 New theories, such as specific ion binding, have also been proposed to explain the Hofmeister series. 14,15 Although the effects of salt on some gelation systems, including MC, have been investigated in our earlier studies, 12,24,25 few reports have been made on the effects of salt on the gelation of HPMC, even though HPMC has more applications in pharmaceutics.…”

Section: Introductionmentioning

confidence: 99%

Effects of salts in the Hofmeister series and solvent isotopes on the gelation mechanisms for hydroxypropylmethylcellulose hydrogels

Liu

Joshi

Lam

2008

J of Applied Polymer Sci

View full text Add to dashboard Cite

The effects of various inorganic salts and isotopic solvents on the thermal gelation behavior of hydroxypropylmethylcellulose (HPMC) in aqueous solutions were examined by micro-differential scanning calorimetry and rheological measurements. It was found that salting-out salts, such as NaCl, promoted the sol-gel transition of HPMC at a lower temperature. An analysis of solvent isotope effects on the changes in the temperature at maximum heat capacity (T m ) with salt concentration showed that interchain hydrogen bonding (hydrogen bonding between the hydroxyl groups of different HPMC chains) was involved in the sol-gel transition, and its strength depended on the temperature and salt concentration. It was demonstrated that the effectiveness of anionic species in changing the T m of the HPMC solutions was in the sequence of the Hofmeister series. Anionic species play a role in reducing T m by their influence on the structure of the water, which in turn affects interactions between hydroxyl groups and water molecules, interchain hydrogen bonding, and the strength of the water cages prohibiting hydrophobic association. Rheological and microcalorimetric results indicated that the change in the thermodynamics of gelation of the HPMC aqueous solution was determined by the salt types and concentration, and the effect of monovalent salts was found to be more cooperative than that of multivalent salts on the sol-gel transition.

show abstract

Section: Introductionmentioning

confidence: 99%

Effects of salts in the Hofmeister series and solvent isotopes on the gelation mechanisms for hydroxypropylmethylcellulose hydrogels

Liu

Joshi

Lam

2008

J of Applied Polymer Sci

View full text Add to dashboard Cite

show abstract

“…According to the schematic description given in Figure 14, PNIPA sequences inserted between PDMA side-chains collapse above their transition temperature and form sticky globules that self-associate into a percolating 3D structure. This mechanism can be compared to the one reported with aqueous solutions of pure linear PNIPA as they also form physical networks during phase separation above some overlap concentration [52,53].…”

mentioning

confidence: 99%

Influence of topology of LCST-based graft copolymers on responsive assembling in aqueous media

Guo

Brûlet

Rajamohanan

et al. 2015

Polymer

View full text Add to dashboard Cite

This work, based on structure/properties relationships of associating polymers, aims to investigate the role of topology in the self-assembling behavior of responsive graft copolymers. For that purpose, two graft copolymers with inverse topologies were prepared with similar amounts of water-soluble chains (poly(N,N-dimethylacrylamide) = PDMA) and LCST polymer chains (poly(N-isopropylacrylamide) = PNIPA). In pure water, and above 3 wt%, PNIPA-g-PDMA and PDMA-g-PNIPA exhibit very similar macroscopic properties with a sol/gel transition above 35 °C related to the microphase separation of PNIPA sequences. From complementary experiments, performed by DSC, 1 H NMR and small angle neutron scattering, we show that the phase transition of PNIPA is more abrupt when NIPA units are located within the backbone, compared to side-chains. Nevertheless, well above their transition temperature, the two copolymers display very similar bicontinuous structures where PNIPA sequences self aggregate into concentrated percolating domains (about 70 wt% at 60 °C) characterized by a frozen dynamics. On the other hand, when salt or surfactant molecules are added into unentangled semi-dilute aqueous solution, the PNIPA-g-PDMA sample does not percolate anymore above the transition temperature while PDMA-g-PNIPA still demonstrate thermothickening properties that are correlated to the ability of water-soluble PDMA chains to bridge PNIPA aggregates.

show abstract

“…Moreover, if the salt concentration is decreased the collapse temperature increases proving that the solubility of PNIPAM in water is highly dependent on the temperature and the salt concentration. [26,30] The LCST of bulk and encapsulated PNIPAM with different ions is investigated with DSC and confocal microscopy, respectively. Capsules filled with PNIPAM were also measured with DSC, but due to the low sensitivity of the instrument the LCST of the encapsulated PNIPAM could not be observed.…”

Section: Taking CLmentioning

confidence: 99%

“…Yang et al have shown that objects which induce water structure, decrease the LCST by promoting hydrophobic interactions. [26] The difference between the LCST of pure PNIPAM in the bulk and inside the capsules arises from the increased order of the structure of the water inside the polyelectrolyte capsule wall. [27] The result is that either the capsule wall components or their complement are structuring the water, which brings about a 2 8C difference in the collapse temperature of the encapsulated and bulk PNIPAM.…”

mentioning

confidence: 99%

Behavior of Temperature‐Sensitive PNIPAM Confined in Polyelectrolyte Capsules

et al. 2006

View full text Add to dashboard Cite

Layer-by-layer assembled polyelectrolyte microcapsules are of great interest because they can possibly be used as microcontainers and they show interesting stimuli-responsive properties, which have been recently investigated. Here, we exploit capsules which are made temperature-sensitive by encapsulating poly(N-isopropylacrylamide) (PNIPAM). PNIPAM has a cloud point in water at about 32 degrees C, above which it collapses and is insoluble in water. Further this temperature responsiveness can be tuned by addition of various ions at various concentrations. Here, we present the encapsulation of PNIPAM inside polyelectrolyte microcapsules, and describe the dependence of the lower critical solution temperature (LCST) on the nature and the amount of different salts added. With this information, we demonstrate the ability to tune and finely control the collapse of encapsulated PNIPAM. In this light, this system could be used as a microsensor or drug- delivery system.

show abstract

Phase separation in poly(N‐isopropyl acrylamide)/water solutions. II. Salt effects on cloud‐point curves and gelation

Cited by 25 publications

References 21 publications

Effects of salts in the Hofmeister series and solvent isotopes on the gelation mechanisms for hydroxypropylmethylcellulose hydrogels

Effects of salts in the Hofmeister series and solvent isotopes on the gelation mechanisms for hydroxypropylmethylcellulose hydrogels

Influence of topology of LCST-based graft copolymers on responsive assembling in aqueous media

Behavior of Temperature‐Sensitive PNIPAM Confined in Polyelectrolyte Capsules

Contact Info

Product

Resources

About