Equilibrium and Kinetic Aspects of the Uptake of Poly(ethylene oxide) by Copolymer Microgel Particles of N-Isopropylacrylamide and Acrylic Acid

Abstract

The use of microgels for controlled uptake and release has been an area of active research for many years. In this work copolymer microgels of N-isopropylacrylamide (NIPAM) and acrylic acid (AAc), containing different concentrations of AAc and also cross-linking monomer, have been prepared and characterized. These microgels are responsive to pH and temperature. As well as monitoring the equilibrium response to changes in these variables, the rates of swelling/de-swelling of the microgel particles, on changing either the pH or the temperature, have also been investigated. It is shown that the rate of de-swelling of the microgel particles containing AAc is much faster than the rate of swelling, on changing the pH appropriately. This is explained in terms of the relative mobilities of the H(+) and Na(+) ions, in and out of the particles. It was observed that the microgels containing AAc, at pH 8, de-swelled relatively slowly on heating to 50 degrees C from 20 degrees C. This is attributed to the resistance to collapse associated with the large increase in counterion concentration inside the microgel particles. The swelling and de-swelling properties of these copolymer microgels have also been investigated in aqueous poly(ethylene oxide) (PEO) solutions, of different MW (2000-300 000). The corresponding absorbed amounts of PEO from solution onto the microgels have also been determined using a depletion method. The results, as a function of AAc content, cross-linker concentration, PEO MW, pH, and temperature, have been rationalized in terms of the ease and depth of penetration of the PEO chains into the various microgel particles and also the H-bonding associations between PEO and either the -COOH of the AAc moeities and/or the H of the amide groups (much weaker). Finally, the adsorption and desorption of the PEO molecules in to and out of the microgel particles have been shown to be extremely slow compared to normal diffusion time scales for polymer adsorption onto rigid surfaces.

Absorption Properties of Microgel‐PVP Composite Nanofibers Made by Electrospinning

“…We note that the high value of the swollen diameter most likely results from the lower crosslinker concentration of our particles compared to that often used in the literature. For example, Ramos et al [30] measured a size of 1 and of 1.4 mm for PNIPAM-AAc microgels with 10 and 6% crosslinker concentration at T ¼ 20 8C and pH 8, which also agrees with the values reported by Snowden et al [23] Absorption Properties of Microgel-PVP Composite Nanofibers . .…”

Preparation and Characterization of Novel Temperature and pH Sensitive (NIPAM-co-MAA) Polymer Microgels and Their Volume Phase Change with Various Salts

“…Effect of Temperature P(NIPAMco-MAA) Microgel Series: DLS measurements were used to judge the hydrodynamic radius in the temperature range of 20-70 o C of the polymer microgels at pH (3)(4)(5)(6)(7)(8)(9)(10)(11)(12). Hydrodynamic radius of the polymer microgel particles is dependent upon temperature.…”

“…A zeta plus zetameter (Brookhaven Instrument Corp., NJ) was used for the measurements of zeta potential. Polymer microgels surface charge density was determined from the electrophoretic mobility measurements at a temperature (20-55 o C) and pH (3)(4)(5)(6)(7)(8)(9)(10). The measurements were carried out as a function of pH (3)(4)(5)(6)(7)(8)(9)(10) at 25 o C. The measurements were performed in a background electrolyte concentration of 1×10 -3 mol dm -3 NaCl (In order to remove variability and to keep constant the length of electrical double layer, background electrolyte is used) solution.…”

“…E-mail: saleemkhan@upesh.edu.pk strength, and solvent composition. 4,5 Near human body temperature (physiological temperature), poly(N-isopropylacrylamide) (PNIPAM) polymer microgels which is temperature responsive undergo reversible volume phase transition (VPT). The temperature responsive PNIPAM-based temperature sensitive microgels makes it popular in various fields which need "smart" material responses to external stimuli, including drug delivery, 6 optical filtering 7 and bimolecular recovery.…”

Micromechanics of Soft Particles

“…In this paper we focus on the two simple methods schematically shown in Figure 1(C) and (D), osmotic compression [19][20][21][22] and capillary micromechanics, [23] respectively. These experimental methods also allow us to clearly separate the measurement of the compressive modulus from that of the shear modulus.…”