Rheological Control of Aqueous Dispersions by Thermoresponsive BAB* Copolymers of Different Architectures

Abstract

Temperature control of rheological properties of aqueous solutions can be achieved by the addition of amphiphilic polymers that show temperature-dependent self-assembly. For this purpose, we explored three sets of acrylamide-based block copolymers with BAB*-, B 2 AB*-, and B(AB*) 2 -type architectures, where "B" represents a permanently hydrophobic unit, "A" is a permanently hydrophilic block, and "B*" is a thermoswitchable block, which undergoes a phase transition of the lower critical solution temperature (LCST) type. Depending on the specific polymer architecture and choice of the thermoresponsive block, the viscosity of their aqueous solutions can augment substantially with increasing temperature. The macroscopic rheological changes were correlated with the results of static and dynamic light scattering (SLS, DLS) and small-angle neutron scattering (SANS) experiments, showing a clear correlation with the mesoscopic organization of the respective systems. Complementary studies with the fluorescence probe Prodan also revealed a clear correlation of the enhanced viscosity to the formation of hydrophobic domains of the thermoresponsive block. Accordingly, the appropriate design of such "smart" copolymer thickeners enables the tuning of the viscoelastic properties of aqueous solutions.

Modifying the Properties of Microemulsion Droplets by Addition of Thermoresponsive BAB* Copolymers

“…In this way, we can markedly enhance the hydrophobicity of the components, either by doubling the permanently hydrophobic segment B (in B 2 AB*), or by doubling the TR block B* (in B­(AB*) 2 ). The structural and rheological behaviors of the pure copolymer systems in aqueous solution as a function of concentration and temperature have been reported by us recently …”

“…In addition, we varied the copolymer architecture, studying in addition to linear BAB* also aqueous solution as a function of concentration and temperature have been reported by us recently. 38 ■ EXPERIMENTAL METHODS Chemicals. The surfactant Tween 20 [polyethylene glycol (20) sorbitan monolaurate, Tw20, Sigma-Aldrich], the cosurfactant 2ethylhexylglycerol (EHG, 3-[(2′-ethylhexyl)oxy]-1,2-propanediol, Clariant Produkte, Germany), the oils isopropyl palmitate IPP (≥90%, Sigma-Aldrich) and n-decane (≥98%, Fluka) were used as received.…”

“…The used polymers were synthesized and characterized in detail previously. 38 Their key parameters are summarized in the Supporting Information, Table S2.…”

Multitunable LCST and UCST Behaviors of Y-Junction-Bearing Polyacrylamides

“…To date, some methods have been developed to monitor thermoresponsive behaviors. Among them, turbidity, fluorescence, − and dynamic light scattering (DLS) analyses are popular methods to determine the cloud point or critical aggregation temperature, and temperature-variable FT-IR ,, and 1 H NMR analyses using a deuterium reagent can reflect the evolutions of solvation status and hydrogen bonding interactions with increasing temperature at the molecular level. However, it remains a challenge to efficiently reveal the phase transition process as the solvent isotope effect is pronounced. ,,,, Owing to different stability of HBs in deuterium and nondeuterium reagents (e.g., D 2 O and H 2 O), the phase transition temperatures are dramatically distinct, , and even a variable number and type of phase transition may emerge during solvent switch.…”

“…The emergence of nontraditional intrinsic luminescence (NTIL) − may hold great promise in addressing the challenge. Different from traditional fluorescence analysis using a conjugated fluorescence moiety to determine the critical aggregation temperature by monitoring variations of the hydrophobic/hydrophilic microenvironment, − the clustering of nonconventional chromophores with lone pairs (n) and/or π electrons is liable to extend electron delocalization and rigidify conformations via through-space electronic communications. − Consequently, NTIL-type polymers can exhibit remarkable emissions as monitored by fluorometry. Among them, the amide group has been recognized as a promising luminogen in polyamides, , polyacrylamides, and polymethacrylamides with NTIL features.…”