Thermal property changes of poly(N-isopropylacrylamide) microgel particles and block copolymers

Abstract

Investigation of the thermo-reversible properties of different poly(N-isopropyl acrylamide) samples, including microgels and block copolymers, with a combination of methods such as electron microscopy, dynamic light scattering, analytical ultracentrifugation, electrophoresis and ultrasound resonator technology allows comprehensive characterisation of the phase transition. By the combination of methods, it was possible to show that the precipitated polymer phase contains at 40°C between 40 and 50 vol.% of water. Besides free bulk water, there is also bound water that strongly adheres to the N-isopropyl acrylamide units (about 25 vol.%). Ultrasound resonator technology, which is a non-sizing characterisation method, revealed for the microgel particles two more temperatures (at about 35 and between 40°C and 50°C depending on the chemical nature) where characteristic changes in the ultrasound attenuation take place. Moreover, the experimental data suggest that the phase transition temperature is related to surface charge density of the precipitated particles.

Synthesis of hybrid microgels by coupling of laser ablation and polymerization in aqueous medium

“…Electronic mail: pich@dwi.rwth-aachen.de microgels with their unique properties can enhance. Recently, numerous reports on the nanogel/microgel synthesis, 10 characterization, 11-13 modification 14,15 and application in drug delivery, 16,17 design of biomaterials, 18 development of sensors 19 are emerging, thereby illustrating the potential of the crosslinked polymer colloids in a wide range of applications (and fundamental research).…”

How much weighs the swelling pressure

“…This happens about 8 degrees below the LCST which is quite an astonishing result because so far, only moderate changes in the PNIPAM solution state have been described in this temperature range [24][25][26][27][28][29][30]. Moreover, 25 °C is frequently used as starting or reference temperature for deswelling studies [26,[29][30][31][32][33]. Long-time changes in the interaction between PNIPAM and water after passing the LCST towards higher temperatures have been known already for a few years [32].…”

“…URT evaluates the temperature dependence of the difference in the speed of sound (U) between a solution and pure water and belongs to the methods with an extremely high resolution in measurements of physical parameters of solutions and colloidal suspensions [34]. Recently this technique has also been successfully applied to study the thermoreversible properties of PNIPAM [35] and PNIPAM-b-PSS block copolymers solutions [32,33].The speed of sounds (U) depends in fluids on the compressibility and density of the medium. With increasing temperature PNIPAM becomes more hydrophobic and water molecules are released and the speed of sound decreases compared with pure water in the reference cell.…”

Heterophase Polymerization as Synthetic Tool in Polymer Chemistry for Making Nanocomposites

“…% of water. [20,21] In this line, if as secondstage monomer styrene, VTMeOS, or MTMeOs is used dispersions and triblock copolymers are obtained only if a PNIPAM middle block is present. In the absence of the PNIPAM middle block hydrolytic condensation takes place but not the formation of block copolymers.…”