The role of polymer structure on water confinement in poly(N-isopropylacrylamide) dispersions

In-situ study of the impact of temperature and architecture on the interfacial structure of microgels

“…We note that the main effect of selective deuteration and of using deuterated solvents is to shift the VPTT of pNIPAM to a higher temperature 61 – 64 . However, at the lowest and highest temperatures measured, the microgels are in the fully swollen and collapsed state (see Supplementary Figs.…”

Impact of the Environment on the PNIPAM Dynamical Transition Probed by Elastic Neutron Scattering

“…In pure PNIPAM at 1 h (panel a), a drastic intensity decrease is observed at ≈270 K. The sharpness of the drop suggests the occurrence of a structural phase transition such as melting of D 2 O rather than a dynamical effect. Indeed, calorimetric studies on hydrated PNIPAM , and, in particular, recent investigations on D 2 O-hydrated PNIPAM chains with the same molecular weight of those considered herein showed that, in samples with h = 1, a fraction of water molecules undergoes cold crystallization on heating and subsequently melts at ≈270 K. A smaller fraction of molecules undergoes crystallization upon cooling and melts at ≈277 K on heating with the total amount of crystalline water however being quite low . In the context of hydrated polymers, cold crystallization is associated with “weakly-bound” water, i.e., a population of water molecules forming with polymer chains an interaction of intermediate strength between that of free bulk molecules, which crystallize upon cooling, and bound hydration molecules, which never crystallize. − Upon further heating such cold-crystallized molecules eventually melt, but the melting temperature is lower than that in the bulk because of the confining effect due to the interaction with polymer chains. , The intensity drop around 270 K in our PNIPAM 1 h sample can therefore be ascribed to the coupling of the polymer dynamics with melting of weakly bound water molecules.…”

“…In PNIPAM 1 h , a dynamical transition clearly takes place at T d ≈ 220 K (see Table ), similarly to hydrated biomolecules. ,,, A close value of about 225 K has been previously reported for PNIPAM chains at 0.67 h , suggesting that T d remains substantially unaffected when the hydration level increases from 0.67 h to 1 h . This allows one to separate the dynamical transition from the glass transition of hydrated PNIPAM, reported by calorimetric investigations. , Contrary to T d , the glass transition temperature T g of PNIPAM shows a strong dependence on h , and in particular, it shifts from 243 K at 0.67 h to 230 K at 1 h . A distinction between glass and dynamical transitions has also been pointed out for hydrated proteins, where the former is reflected in a mild slope change in the MSDs at T g ≈ 200 K followed by a more marked change at T d due to the dynamical transition .…”

“…This allows one to separate the dynamical transition from the glass transition of hydrated PNIPAM, reported by calorimetric investigations. 67,69 Contrary to T d , the glass transition temperature T g of PNIPAM shows a strong dependence on h, and in particular, it shifts from 243 K at 0.67h to 230 K at 1h. A distinction between glass and dynamical transitions has also been pointed out for hydrated proteins, where the former is reflected in a mild slope change in the MSDs at T g ≈ 200 K followed by a more marked change at T d due to the dynamical transition.…”

In-situ study of the impact of temperature and architecture on the interfacial structure of microgels

“…We note that the main effects of selective deuteration and of using deuterated solvents is to shift the VPTT of pNIPAM to a higher temperature. [61][62][63][64] However, at the lowest and highest temperatures measured, the microgels are in the fully swollen and collapsed state (see Supplementary Figs. 1c and 2a-d), respectively, allowing for an appropriate comparison of the different architectures.…”