The sol‐gel approach towards thermo‐responsive poly(N‐isopropyl acrylamide) hydrogels with improved mechanical properties

Abstract

A new type of thermo‐responsive hydrogels based on the polymer poly(N‐isopropyl acrylamide) (PNIPAA) has been synthesized with the sol‐gel technology. For the preparation of this type of nano‐structured hydrogels, the inorganic silica phase was synthesized by the sol‐gel process in the presence of an aqueous solution of high molecular weight PNIPAA. This combination of the organic and inorganic phases forms hybrid hydrogels with a semi‐IPN morphology. The unique structure of these hydrogels improves the mechanical stability to a great extent as compared to conventional PNIPAA‐hydrogels. This was shown by stress‐strain experiments and the capability to absorb and desorb large amounts of water. The silica only slightly influences the transition temperature of the hydrogels but allows us to vary the thermo‐responsive properties of the materials to a great extent.

Perspectives for the mechanical manipulation of hybrid hydrogels

“…In this case, the interaction between the inorganic component and the gel matrix is dominated by physical forces, that may comprise electrostatic interactions, van-der-Waals forces, and surface complex or hydrogen bond formation. 106 Examples of such hybrid hydrogels are realized by the introduction of poly(vinyl pyridine) segments 107 that attach to many metal nanoparticles, 108,109 or the use of hydroxyethyl methacrylates co-monomers in combination with metal oxide nanoparticles. 101 In the latter example, hydrogen bridges are formed between the polymer matrix and the particle surface.…”

Nanoscale Polyacrylamide Copolymer/Silica Hydrogel Microspheres with High Compressive Strength and Satisfactory Dispersion Stability for Efficient Profile Control and Plugging

“…With decreasing the particle size, the oscillation energy increased, resulting in better nanofluid diffusion at the interface between the oil drop and the solid matrix. − Apparently, the increase in elasticity of microspheres and the inhibition of rapid swelling of the microspheres would be beneficial for efficient profile control and plugging. As inorganic particles generally have high thermal stability and rigidity while organic components have good flexibility, the combination of PAM and inorganic nanoparticles may endow PAM-based hydrogels with improved mechanical properties and enhanced resistances to temperature and salt. , Shamlooh and Hamza prepared SiO 2 –PAM composite hydrogels by combining PAM with SiO 2 and triamine silica, respectively. Silica nanoparticles are suitable for adding into hydrogel microspheres as profile control agents because of their rigidity and resistances to salts and temperatures …”

Highly active, thermo‐responsive polymeric catalytic system for reuse in aqueous and organic CuAAC reactions

“…Reversible addition fragmentation chain transfer (RAFT) polymerization has allowed the preparation of a wide range of stimuli‐responsive polymers in a controlled fashion 1–3. Among them the thermo‐responsive polymer poly( N ‐isopropyl acrylamide) (PNIPAM) has gained a significant interest because aqueous solutions of PNIPAM exhibit a lower critical solution temperature transition (LCST) in the range of 28–32 °C, depending on the aqueous solution composition 4–6. When heated in water above this LCST‐value, PNIPAM undergoes a reversible LCST‐phase transition from a swollen hydrated state to a shrunken dehydrated state.…”

“…[1][2][3] Among them the thermo-responsive polymer poly(N-isopropyl acrylamide) (PNIPAM) has gained a significant interest because aqueous solutions of PNIPAM exhibit a lower critical solution temperature transition (LCST) in the range of 28-32 C, depending on the aqueous solution composition. [4][5][6] When heated in water above this LCST-value, PNIPAM undergoes a reversible LCST-phase transition from a swollen hydrated state to a shrunken dehydrated state. This very sharp transition (over ca.…”