Thermal Behaviour of Microgels Composed of Interpenetrating Polymer Networks of Poly(N-isopropylacrylamide) and Poly(acrylic acid): A Calorimetric Study

Abstract

Stimuli-responsive microgels have recently attracted great attention in fundamental research as their soft particles can be deformed and compressed at high packing fractions resulting in singular phase behaviours. Moreover, they are also well suited for a wide variety of applications such as drug delivery, tissue engineering, organ-on-chip devices, microlenses fabrication and cultural heritage. Here, thermoresponsive and pH-sensitive cross-linked microgels, composed of interpenetrating polymer networks of poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAAc), are synthesized by a precipitation polymerization method in water and investigated through differential scanning calorimetry in a temperature range across the volume phase transition temperature of PNIPAM microgels. The phase behaviour is studied as a function of heating/cooling rate, concentration, pH and PAAc content. At low concentrations and PAAc contents, the network interpenetration does not affect the transition temperature typical of PNIPAM microgel in agreement with previous studies; on the contrary, we show that it induces a marked decrease at higher concentrations. DSC analysis also reveals an increase of the overall calorimetric enthalpy with increasing concentration and a decrease with increasing PAAc content. These findings are discussed and explained as related to emerging aggregation processes that can be finely controlled by properly changing concentration, PAAc content an pH. A deep analysis of the thermodynamic parameters allows to draw a temperature– concentration state diagram in the investigated concentration range.

Keratin–PNIPAM Hybrid Microgels: Preparation, Morphology and Swelling Properties

“…This behavior suggests that the presence of the protein renders the system more rigid and hydrophobic, likely due to hydrogen bonding complexation. A similar reduction in swelling ability was previously reported for hybrid PNIPAM-keratin hydrogels at different crosslinking degrees [54] and for IPN microgels made of PNIPAM and poly(acrylic acid) [102,103].…”

“…Conversely, the s ing ratio was smaller than that of pure PNIPAM at all investigated pH values (Figur with a lesser decrease observed at acidic compared to neutral and basic pH values behavior suggests that the presence of the protein renders the system more rigid an drophobic, likely due to hydrogen bonding complexation. A similar reduction in sw ability was previously reported for hybrid PNIPAM-keratin hydrogels at different linking degrees [54] and for IPN microgels made of PNIPAM and poly(acrylic [102,103]. The HYB-M sample, produced by simply mixing preformed PNIPAM microgel the protein, maintained the temperature responsiveness of PNIPAM, with a VPTT parable to that of pure PNIPAM at both pH 6 and 8.5 (Figure 6a).…”

Water-Recyclable Chitosan-Based Ion-Imprinted Thermoresponsive Hydrogel for Rare Earth Metal Ions Accumulation

“…The peaks of the C-H stretching vibration of -CH 3 , -CH 2 -and CH in NIPAM appeared at 2974, 2934 and 2876 cm −1 , respectively [27]. The strong adsorption peak at 1661 cm −1 was the C=O stretching vibration peak of the amide group, and the N-H bending vibration superimposed with the C-N stretching vibration showed an absorbance at 1549 cm −1 [28]. The strong absorption peaks at 3447 cm −1 and 2934 cm −1 in the CS spectrum were the N-H and O-H stretching vibration peak and C-H absorption peak, respectively [29].…”

Peculiarities of Emulsions Stabilized by Stimuli-Responsive Interpenetrating Polymeric Network Microgels

“…This imposes restrictions on the selection of oil–water pair and the fractions of liquid phases at which they could be stabilized . A fine solution can be found in applying a stepwise polymerization, which will result in the formation of physically entangled interpenetrating polymeric networks (IPNs). ,− Recently, our group has conducted an extensive research on microgels of such architecture based on poly­( N -isopropylacrylamide) (PNIPAM) and poly­(acrylic acid) (PAA) and explored their various applications. − In particular, we have shown that the physical entanglement provides the colloidal stability of IPN particles upon the collapse either of PNIPAM or PAA subnetworks with simultaneous induction of the microphase separation in the microgel interior . Regarding the liquid interface, one can expect that independent response of two networks to external stimuli will expand the possibilities for stabilizing emulsions and tuning their properties.…”