Temperature dependent phase behavior of PNIPAM microgels in mixed water/methanol solvents

Abstract

Temperature dependent phase behavior of poly(N‐isopropylacylamide) (PNIPAM) microgels in water/methanol mixtures of different composition was studied with dynamic light scattering (DLS) and small‐angle neutron scattering (SANS). Using DLS, it is possible to measure the diffusion coefficient, and thus the size of particles exactly and directly; the variation of the phase transition temperature in the different solvents is also easy to detect by this method. With SANS measurements in D2O/MeOD mixtures, some of the DLS results were confirmed. Moreover, SANS measurements give valuable information on the particle structure in different solvents. The experiments were compared with the theory of competitive hydration introduced by Tanaka et al. We found a good agreement of theory and experiment, and obtained the theoretical predictions: around the transition temperature, the composition of the bound methanol along the chains is higher than that of the outer solution, while the whole methanol composition inside the gel is lower. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2013, 51, 1100–1111

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

“…At a certain water to methanol ratio, a minimum in VPTT occurs. This behavior is well-known for microgel particles in bulk solution [14,35]. In contrast to the present paper, Heppner et al have not observed any influence of the confinement on the cononsolvency effect.…”

“…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.…”

“…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].…”

Cononsolvency of mono- and di-alkyl N-substituted poly(acrylamide)s and poly(vinyl caprolactam)

“…While the VPTT decreases strongly, the shape of the R h (T) curve in these two mixtures is still similar to the one in pure water [41]. With increasing x MeOH the phase transition of PNIPAM becomes broader and the VPTT decreases further.…”

“…Due to the cononsolvency effect, even low molar methanol fractions of x MeOH ¼ 0.05 and 0.10 influence the phase behaviour and VPTT of PNIPAM significantly [41]. While the VPTT decreases strongly, the shape of the R h (T) curve in these two mixtures is still similar to the one in pure water [41].…”