Anomalous Transition in Aqueous Solutions of a Thermoresponsive Amphiphilic Diblock Copolymer

Abstract

The influence of shear flow on aggregation and disaggregation in aqueous solutions of the thermoresponsive methoxy-poly(ethylene glycol)-block-poly(N-isopropylacrylamide) (MPEG53-b-PNIPAAM113) copolymer that exhibits a lower critical solution temperature was investigated with the aid of turbidity, shear viscosity, and rheo small angle light scattering (rheo-SALS) methods. The turbidity results at quiescent conditions revealed a novel transition peak in the turbidity curve at intermediate temperatures, which reflects the delicate interplay between temperature-induced aggregation and shrinking of the species. A similar anomalous transition peak (located at the same temperature) was observed in the steady shear viscosity measurements at intermediate temperatures, and the amplitude of the peak was reduced with increasing shear rate as a consequence of breakup of interaggregate chains. At low temperatures (low sticking probability), enhanced shear rate generated interpolymer aggregates; whereas in the high-temperature domain (high sticking probability) association structures were broken up as the shear rate was increased. The rheo-SALS experiments disclosed growth of aggregates at low temperatures and destruction of association complexes at high temperatures. An increase of the cloud point temperature with rising shear rate is reported, which is interpreted as being a disruption of clusters under the influence of shear stresses.

Preparation and characterization of cross‐linked polymeric nanoparticles for enhanced oil recovery applications

“…20 The instrumentation for the rheo-SALS experiments was purchased from Physica-Anton Paar (Graz, Austria). In all measurements, a 10-mW diode laser operating at a wavelength of 658 nm was used as the light source; a polarizer was placed in front of the laser and an analyzer below the sample, making both polarized (polarizer and analyzer parallel) and depolarized (polarizer and analyzer perpendicular) experiments possible.…”

Self-assembly and drug delivery behaviors of a novel thermo-sensitive block glycopolymer

“…In particular, thermo-sensitive polymeric micelles have attracted much attention because of their potential application in the area of targeted drug delivery [3]. Because *Corresponding author (email: ceszhlm@mail.sysu.edu.cn) of the lower critical solution temperature (LCST) close to body temperature, poly(N-isopropylacrylamide) (PNIPAm) is one of the most studied polymer to prepared thermo-sensitive polymeric micelles [4][5][6][7][8][9][10][11]. However, there is another class of polymer that deserves attention with respect to the biocompatibility and biodegradability.…”

Temperature-induced intermicellization and contraction in aqueous mixtures of sodium dodecyl sulfate and an amphiphilic diblock copolymer

“…The uncharged diblock copolymer MPEG 53 -b-PNIPAAM 113 was synthesized via an atomic transfer radical polymerization (ATRP) in aqueous media according to a procedure described previously [13], and the weight-average molecular weight M w = 17,200 and the polydispersity index M w /M n = 1.1 of the sample were both determined by asymmetric flow field-flow fractionation (AFFFF) [13]. The composition of the diblock copolymer was determined with the aid of 1 H NMR and AFFFF methods, and the number MPEG groups is 53 and the number of repeating NIPAAM units in the PNIPAAM block is 113 [13].…”

“…The composition of the diblock copolymer was determined with the aid of 1 H NMR and AFFFF methods, and the number MPEG groups is 53 and the number of repeating NIPAAM units in the PNIPAAM block is 113 [13]. The SDS surfactant was supplied by Fluka Chemie AG, Buchs, Switzerland, and it was used without further purification.…”

“…In a recent study [13], we prepared a thermoresponsive methoxy-poly(ethylene glycol)-block-poly(N-isopropylacrylamide) (MPEG 53 -b-PNIPAAM 113 ) diblock copolymer (see Fig. 1) that exhibits a lower critical solution temperature.…”