Microgels with controlled network topologies by photocrosslinking-assisted continuous precipitation polymerization.

In this study, we present a new synthesis methodology based on photo-crosslinking-assisted continuous precipitation polymerization which allows controlling the distribution of crosslinks in microgels. In our approach we substituted conventional crosslinking agent by a comonomer carrying photo-crosslinkable 4-oxocyclopent-2-en-1-yl group. Microgel size, morphology, distribution of crosslinks and packing density of the polymer chains are studied as a function of retention time (Rt) in the flow reactor. Dynamic and static light scattering (DLS and SLS) as well as small angle X-ray scattering (SAXS) proved an excellent level of control over the distribution of crosslinks in microgels during the polymerization process. These results were confirmed by atomic force microscopy (AFM), indicating a difference in microgel stiffness and arrangement of the polymer network as resulting from increased Rt.

Multicompartment polymeric colloids from functional precursor Microgel: Synthesis in continuous process.

Raspberry-like poly(oligoethylene methacrylate-b-N-vinylcaprolactam)/polystyrene (POEGMA-b-PVCL/PS) patchy particles (PPs) and complex colloidal particle clusters (CCPCs) were fabricated in two-, and one-step (cascade) flow process. Surfactant-free, photo-initiated reversible addition-fragmentation transfer (RAFT) precipitation polymerization (Photo-RPP) was used to develop internally cross-linked POEGMA-b-PVCL microgels with narrow size distribution. Resulting microgel particles were then used to stabilize styrene seed droplets in water, producing raspberry-like PPs. In the cascade process, different hydrophobicity between microgel and PS induced the self-assembly of the first formed raspberry particles that then polymerized continuously in a Pickering emulsion to form the CCPCs. The internal structure as well as the surface morphology of PPs and CCPCs were studied as a function of polymerization conditions such as flow rate/retention time (Rt), temperature and the amount of used cross-linker. By performing Photo-RPP in tubular flow reactor we were able to gained advantages over heat dissipation and homogeneous light distribution in relation to thermally-, and photo-initiated bulk polymerizations. Tubular reactor also enabled detailed studies over morphological evolution of formed particles as a function of flow rate/Rt.

Bistability, Remanence, Read/Write-Memory, and Logic Gate Function via a Stimuli-Responsive Polymer.

Stimuli-responsive materials change their state in response to external triggers. Switching between different states enables information to be written, stored, and read, if the transition between the states exhibits hysteresis. Thermally responsive polymers exhibit an intrinsic hysteresis for the volume phase transition between the swollen and de-swollen solution state. Here, it is shown that this hysteresis can be used to realize bistability, remanence, and reversible write/read information storage. This is demonstrated for the simplest and most widely used thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM), as well as for PNIPAM block copolymers, which widens the hysteresis window. The hysteresis is shown to be related to cluster domain assembly/disassembly during the phase transition. Information can be written thermally using a laser, or using heated or cooled pen tips on a thin-film backscattering display. The bistable state can additionally be switched by pH, enabling an AND logic gate function. Furthermore, an unusual memory state is discovered, where information is visible in the hysteresis window and invisible at higher temperatures, allowing encoded information to be hidden. Since hysteresis is a very common intrinsic phenomenon for responsive materials, this principle to encode and store information is potentially applicable to a broad range of responsive materials.