Volume phase transition kinetics of smart N-n-propylacrylamide microgels studied by time-resolved pressure jump small angle neutron scattering

Abstract

The use of smart colloidal microgels for advanced applications critically depends on their response kinetics. We use pressure jump small angle neutron scattering with supreme time resolution to study the rapid volume phase transition kinetics of such microgels. Utilizing the pressure induced microphase separation inside the microgels we were able to resolve their collapse and swelling kinetics. While the collapse occurs on a time scale of 10 ms, the particle swelling turned out to be much faster. Photon correlation spectroscopy and static small angle neutron scattering unambiguously show, that the much slower collapse can be associated with the complex particle architecture exhibiting a loosely-crosslinked outer region and a denser inner core region. These insights into the kinetics of stimuli-responsive materials are of high relevance for their applications as nano-actuators, sensors or drug carriers. Moreover, the used refined pressure jump small angle neutron scattering technique is of broad interest for soft matter studies.

Supercrystal Formation of Gold Nanorods by High Pressure Stimulation

“…For the present solution, the data point to a crystallization pressure between 2000 bar (200 MPa) and 2050 bar (205 MPa), indicating a narrow transition range. Previous studies report a relaxation rate of such a deswelling process on the millisecond time scale, 43,51 suggesting that the PEG-ligands would be already collapsed immediately after the p−jump. After this deswelling transition, crystallization and growth is suggested to take place on a second time scale.…”

“…The pressure-jump method allows us to follow the kinetics of a temporal evolving system after a rapid change of pressure and has found recent applications for soft matter systems. [41][42][43][44] In our experiment, a set of 7500 images was collected with a exposure time per single frame of 4 ms, yielding a total collection time of 30 s. The pressure jumps were performed 1 s after the data collection had been started to ensure covering the full kinetics. Pressure-jumps are performed within 5 ms. 40 We carefully checked for radiation damage of the sample by using different absorbers to attenuate the X-ray photon flux on the sample.…”

Resolving the internal morphology of core–shell microgels with super-resolution fluorescence microscopy

“…9,10 At low temperatures the solution structure of microgel particles can be described by the "fuzzy-sphere" model, which exhibits a core-region with a constant density and a fuzzy shell where the density follows a sigmoidal decay. 11 Here, a more complex nanoscale architecture of the microgel particles is investigated: microgel particles based on N-isopropylmethacrylamide (NIP-MAM) (VPTT in water $42 C) 12 are used as seed particles for a second synthesis step, where N-n-propylacrylamide (NNPAM, VPTT of crosslinked homopolymer microgels in water: $22 C) 12,13 is polymerized in the presence of the collapsed seed particles leading to a core-shell structure. 14,15 A peculiar feature of these particles is the linear dependence of the particle size on the temperature.…”

Acrylamide precipitation polymerization in a continuous flow reactor: an in situ FTIR study reveals kinetics

“…The size of these colloidal gels ranges from a few tens of nm to approximately 1 µm. The ability to respond to an external stimulus, such as a change of temperature [6], pH value [7], pressure [8], solvent [9], or ionic strength [10], makes microgels interesting candidates for a broad range of applications. The response typically results in a change of the particles size, Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00396-020-04762-w) contains supplementary material, which is available to authorized users.…”

“…The best studied representative of thermoresponsive microgels is based on N-isopropylacrylamide (NIPAM), cross-linked with N, N -methylenebis(acrylamide) (BIS). Above a temperature of approximately 32 • C poly(Nisopropylacrylamide) (PNIPAM) microgels show a VPT in water by releasing solvent out of the polymer network, usually within some milliseconds [8]. Batch syntheses of PNIPAM-based microgels via precipitation polymerization are well established.…”