Cross-Linked Hydrogels Based on PolyNIPAAm and Acid-Activated Laponite RD: Swelling and Tunable Thermosensitivity

Abstract

The effects of acid activation of Laponite RD (Lap) on the structure and properties of activated Lap nanoparticles (aLap) and the properties of polyNIPAA m hydrogels physically cross-linked by aLap have been studied. The acid activation of Lap by the sulfuric acid was done using the concentration of sulfuric acid within the interval C a = 0.525−14.58% for 10 h. For slightly activated samples (C a ≤ 1.25 wt %), the significant increase of the specific surface area (by ≈1.56 times) was accompanied with a significant decrease in both the values of the specific heat of immersion in water and n-decane. However, the hydrophilic properties of all samples S 0 −S 5 were still observed. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) data, Fourier transform infrared (FTIR) spectra, and X-ray diffraction (XRD) patterns demonstrated that the acid activation resulted in the destruction of the crystal lattice of Lap, leaching of magnesium and lithium, and formation of the amorphous phases. Moreover, the acid activation significantly affected aggregation and negative surface charges of the aLap faces in aqueous suspension. The effects of aLap on the swelling properties and cooperativity in the phase transitions of polyNIPAA m hydrogels cross-linked by aLap are also discussed. It was demonstrated that an increase in C a resulted in a significant increase in the equilibrium degree of swelling of the hydrogels and a decrease in the hydrogel phase-transition temperature from the swollen phase to the shrunken phase.

Temporary Actuation of Bilayer Polymer Hydrogels Mediated by the Enzymatic Reaction

“…Smart actuators constructed by stimuli-responsive polymers have deformational behaviors such as expansion and bending under specific stimuli such as light, − heat, − electricity, − and pH change. − They have wide application prospects in the fields of shape memory materials, , soft robotics, , artificial muscles, , microfluidics, , and drug delivery ,, and have attracted significant attentions. In the case of polymer hydrogels, it is the different swelling ratios of stimuli-responsive hydrogels under different circumstances that causes the deformational behaviors of the hydrogel actuators. ,, The most common way to achieve the bending of actuators is to construct an anisotropic structure, such as the bilayer structure. ,, For a bilayer hydrogel actuator, the shape change of the entire structure is usually caused by the different expanding/shrinking trends of each layer of the hydrogels under a certain stimulus. ,− Based on this principle, the hydrogel actuators normally exhibit a monotonic responsiveness, that is, there is only one response action after being stimulated once.…”

Foam Flotation of Clay Particles Using a Bifunctional Amine Surfactant

“…Adsorption of the protons from the nitric acid on the LRD plate surfaces first screened the negative charge, and at a high nitric acid concentration, it is likely to damage the crystalline structure of the tetrahedral silicate layers. 52,53 The ζ values for the Ethomeen−LRD solution showed a similar trend to those for the Ethomeen solution. The ζ values for the Ethomeen micelles hardly changed with the addition of LRD at pH > 6.…”

“…Moreover, nitric acid, which was added to adjust the pH during sample preparation, contributed to the decrease in the absolute value of ζ with decreasing pH. Adsorption of the protons from the nitric acid on the LRD plate surfaces first screened the negative charge, and at a high nitric acid concentration, it is likely to damage the crystalline structure of the tetrahedral silicate layers. , …”

Comparison of Structural, Water‐Retaining and Sorption Properties of Acrylamide‐Based Hydrogels Cross‐Linked by Physical and Chemical Methods

“…[36,37] Physical cross-linking by Laponite was also used to obtain thermoresponsible hydrogels, which are promis-ing for drug delivery. [38,39] Qiu et al prepared a nanocomposite of polyacrylamide (pAAm) and MMT and used it as an adsorbent of chromium(III). [40] Ma et al investigated the physicochemical properties of nanocomposite hydrogels composed of pAAm with MMT and their ability to bind and release ozone.…”

“…The combination of these properties made them promising for bone tissue engineering and development of biosensors for detection of body motion [36,37] . Physical cross‐linking by Laponite was also used to obtain thermoresponsible hydrogels, which are promising for drug delivery [38,39] . Qiu et al.…”