Transient-thermal and isothermal studies of thermo-sensitive polymer solution with ultrasound resonator technology

How much weighs the swelling pressure

“…The average LCST value upon heating as determined by URT and AMM is 34.1±0.2 and 33.0±0.9 °C, respectively. The critical temperature extracted from the URT cooling cycles is slightly lower (33.2±0.2 °C) and confirms the known heating -cooling hysteresis for PNIPAM [32]. The difference of the LCST as determined with AMM and URT can have two possible causes.…”

“…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].…”

“…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]. Also upon cooling the initial behavior is dominated by the thermal property (this time shrinking) of the PTFE and only below a temperature of 28.7 °C, after the minimum in the m app -time curve, the swelling of the PNIPAM dominates the further changes in the apparent mass.…”

“…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.…”

Stabile, Thermoresponsive Colloidal Clusters: An Unusual Morphology of Polymer Dispersions

“…At the lower critical solution temperature of PNIPAM, the polymer becomes more hydrophobic, water is released, the overall compressibility of the sample solution increases and hence, the speed of sound decreases compared with pure water. With URT, we are tracking quantitatively changes in the adhering layer of water molecules . The data summarized in Figure clearly show the thermoresponsiveness of the polystyrene clusters.…”