Abrupt Shear Thickening of Aqueous Solutions of Hydrophobically Modified Poly(N,N′-dimethylacrylamide-co-acrylic acid)

Abstract

We report some new and interesting observations on the abrupt and large shear-induced thickening of aqueous solutions of hydrophobically modified poly(N,N′-dimethylacrylamide-co-acrylic acid). High molecular weight copolymer was prepared by free radical copolymerization of N,N′-dimethylacrylamide [DMA] and acrylic acid [AA] and was subsequently modified to different extents using a hydrophobic compound, namely, 3-pentadecylcyclohexylamine [3-PDCA], which is derived from a renewable resource material, cashew nutshell liquid [CNSL]. The structural elucidation of the base copolymer and the hydrophobically modified copolymers was performed by 1H and 13C NMR spectroscopy. The zero shear viscosities [η0] of the hydrophobically modified polymers were lower than that of the precursor poly(N,N′-dimethylacrylamide-co-acrylic acid) until some critical polymer concentration, which increased with increase in hydrophobic modification. Above the critical concentrations, the η0 of the hydrophobically modified copolymers surpassed that of the precursor at the same concentration. At moderate shear rates some of these hydrophobically modified copolymers exhibited an abrupt shear-induced thickening in which the viscosity of the samples increased severalfold. We show here from creep experiments that thickening occurs only when the shear rate reaches a critical value, γ̇crit, and that the thickened samples can be trapped in different metastable states by controlling the applied stress. Interestingly, the shear thickened samples showed further thickening upon decreasing the applied stress. Eventually, the metastable samples revert to their equilibrium states at characteristic time that depends on (small) probe stress.

Thermo-reversible sol–gel transition of aqueous solutions of patchy polymers

“…The synthesis of hydrophobically modied copolymer (HMCP) was carried out as per procedures given by Lele et al 69 and Cadix et al, 70 which involves two steps: (a) synthesis of precursor copolymer (PCP) viz. poly(N,N-dimethylacrylamide-co-acrylic acid), and (b) modication of some of the acrylic acid units in the precursor co-polymer with n-dodecyl amine.…”

“…The rate of polymerization of DMA is higher than that of AA, and this is expected to result in the formation of a blocky structure of the PCP backbone. 68,69,74 The weight-average molecular weight of PCP, as determined by GPC, was found to be M w $ 5 Â 10 6 g mol À1 (polyacrylamide standard) with a dispersity of 2.7 as shown in Fig. S1 of ESI.…”

“…61 Besides thermally induced gelation, shear induced gelation has also been observed in polymeric systems having a few localized, energetically favored interactions such as in ionomers, [62][63][64] worm-like micellar solutions, 65,66 colloidal solutions 67,68 and aqueous solutions of hydrophobically modied polymers (HMPs). 64,[69][70][71] The molecular cause for shear thickening phenomenon in polymer solutions was suggested to be a shear induced transformation of intramolecular to intermolecular interactions. 69,72 The present work reports a sol-gel transition under quiescent or near quiescent conditions upon cooling an aqueous solution of a hydrophobically modied poly(N,N-dimethylacrylamide-co-acrylic acid).…”

“…64,[69][70][71] The molecular cause for shear thickening phenomenon in polymer solutions was suggested to be a shear induced transformation of intramolecular to intermolecular interactions. 69,72 The present work reports a sol-gel transition under quiescent or near quiescent conditions upon cooling an aqueous solution of a hydrophobically modied poly(N,N-dimethylacrylamide-co-acrylic acid). The transition is manifested as a large and abrupt non-Arrhenius increase in low shear viscosity of the polymer solution when cooled below a transition temperature, which decreases with decrease in copolymer concentration.…”

Synthesis and Swelling Behavior of SiO2-HA/PNIPAm Core-shell Structured Thermoresponsive Microgels

“…这一现象可以通过瞬态晶格理论 模型来解释 [28,29] . 该理论认为, 含有疏水基团的聚合物, 在静态条件下, 彼此之间发生相互作用是有限的, 随着 剪切应力的增加, 高分子链内与链间的相互作用得到加 强, 且主要体现后者的作用力 [30] . ,0 3 shell shell core shell shell,0 P shell core 3 3 shell core 3 3 shell core 4π / 3 4π / 3 4π …”