Colloidal copolymer microgels of N-isopropylacrylamide and acrylic acid: pH, ionic strength and temperature effects

Abstract

Aqueous colloidal microgels have been prepared, based on poly(N-isopropylacrylamide) [poly(NIPAM)], cross-linked with bisacrylamide, containing 5% w/w acrylic acid (AAc) as a comonomer. Transmission electron micrographs of the microgels show that the copolymer microgels are monodisperse spheres. The size of the microgel particles containing 5% AAc has been studied, using dynamic light scattering, as a function of pH (3-lo), ionic strength (10-4-10-' M NaC1) and temperature (20-75°C). The hydrodynamic diameter of the copolymer microgels decrease both with increasing ionic strength (at pH 6 and 25°C) and reversibly with increasing temperature at pH values of 2.6, 3.4 and 6.5. However, under isothermal conditions in M NaCl at 25 "C, the hydrodynamic diameter increases in going from pH 3.3-9.4. In addition, the temperature-induced conformational changes in the polymer chains have been followed using high-sensitivity differential scanning calorimetry (HSDSC). A comparison is made with the behaviour of poly(N1PAM) microgel particles, not containing AAc. Explanations are offered to account for the pronounced difference in the physico-chemical properties observed.

Clusters of Superparamagnetic Iron Oxide Nanoparticles Encapsulated in a Hydrogel: A Particle Architecture Generating a Synergistic Enhancement of the T2 Relaxation

“…However, the poly(NIPAM-AA) hydrogel is weakly hydrated due to the hydrophilicity of the NIPAM moieties. 18 As the pH increases, the acrylic acid moieties begin to deprotonate, generating electrostatic repulsion within the polymer network thus causing it to swell with water. A steep increase in the diameter of the particles occurs near the pk a of acrylic acid between a pH of 4.3 to 4.7.…”

“…14 Other recent studies reported that relaxivity values are nearly independent of polymer coatings for large magnetic particles (100 nm), while the relaxation rates of smaller particles (10 nm) were dramatically reduced when coated with silica. 18,19 Another report showed that increasing the hydrophilicity of the particle coating leads to enhanced interactions between the protons with the magnetic core thereby increasing the relaxivity. 13 Recently, Monte Carlo simulations illustrated that some of these discrepancies in effects are attributed to differences in particle size (or dephasing mechanism) and coating composition.…”

“…The volume fraction of hydrogel at various pH values was first determined by using data previously reported on colloids of the same composition. 18 For this calculation, the TEM diameter was used to calculate the volume of the colloid in a dehydrated state while the hydrodynamic diameters were used to calculate the water content at various pH values (here the hydration layer at the colloid surface is assumed to be negligible in comparison to the size of the colloid …”

Morphing in nature and beyond: a review of natural and synthetic shape-changing materials and mechanisms

“…This decreases the space between them, ejecting solvent and losing volume. The temperature at which this occurs may be adjusted by the temperature of processing [145], blending [146] and microstructure [147], in addition to the inclusion of composites which may adjust temperature response through density changes [148], or Joule or surface plasmon resonance heating (see later sections on light, electricity and magnetism for these mechanisms).…”

Thermosensitive Nanoparticles Conjugating With Cd34 Antibody and Its Solution Peroperties

“…The codes and detail ingredient of the NIPAAm-AA nanoparticles was shown in Table . From Table , high conversion (>95%) of all the linear polymers (data not shown) and nanoparticles were measured. In typical free radical polymerization reaction, high conversion (>90%) are easily achieved within two hours [15,18]. The transmission electron micrograph of the LPIA5 nanoparticle was shown in Figure 1.…”