Investigation of the Poly(N-isopropylacrylamide)-Sodium Dodecyl Sulfate Complexation with Viscosity, Dialysis, and Time-resolved Fluorescence-Quenching Measurements

Abstract

Interaction of poly(N-isopropylacrylamide) (PNIPAM) with sodium dodecyl sulfate (SDS) has been studied by viscometry, time-resolved fluorescence-quenching (TRFQ), and dialysis measurements. The reduced viscosity of PNIPAM in SDS aqueous solutions presents an abrupt increase in the low SDS concentration region, lower than the surfactant critical micelle concentration, whereas TRFQ measurements show the formation of an increasing number of polymer−surfactant aggregates in the same SDS concentration region. The aggregation number of these aggregates, determined by combining TRFQ with dialysis data, remains constant and equal to 7−8 surfactant molecules per polymer-bound surfactant aggregate. Moreover, the values of the inverse of the intramicellar quenching rate constant, expressing the effective microviscosity of the aggregates, indicate that these microdomains, formed in the low SDS concentration region, are very rigid. After saturation of the PNIPAM chain with these aggregates, a further quantity of surfactant is adsorbed on the polymer, and this is reflected in an increase of their aggregation number. However, the aggregation number of these polymer−surfactant aggregates remains much lower than that of free surfactant micelles.

Mechanically Driven Reorganization of Thermoresponsive Diblock Copolymer Assemblies in Water

“…Upon cooling our spherical particle mixture (at a polymer weight fraction of 8 wt %, see Reaction 1 in Table S1 in the Supporting Information) rapidly over 5 min from 70 to 25 °C below the LCST of PNIPAM the transmission electron microscopic images display the change from spheres to long rods (Figure 1 B). Cooling the reaction mixture below the LCST of the PNIPAM block results in swelling of the PNIPAM chains, supported by strong binding of SDS to PNIPAM,15 which induces a mechanical strain to reorganize the spheres into rodlike structures. The core of the rod most probably consists of the hydrophobic PSTY, and the corona as well as the surface of the rod consists of the hydrophilic PNIPAM stratified by strong binding to SDS.…”

Interplay between Hydrogen Bonding and Macromolecular Architecture Leading to Unusual Phase Behavior in Thermosensitive Microgels

“…[1] Poly-N-isopropylacrylamide (PNIPAM) undergoes a reversible transition at 32 8C attributed to the formation of intra-and intermolecular hydrogen bonds. The coil-to-globule transition of linear PNIPAM has been investigated by calorimetry, [2] fluorescence spectroscopy, [3] light scattering, [4] and infrared spectroscopy. [5] Computer simulations show that the folding process is strongly influenced by the polymer structure.…”

Thermodynamic Characterization of Humic Acid-surfactant Interaction: New Insights into the Characteristics and Structure of Humic Acids

“…After HA saturation (saturation concentration, C 2 ), further addition of surfactant (increase in R s/ha ) promotes micelle formation in the bulk solution (Niemiec and Loh, 2007). Previous studies, using other surfactant molecule interaction systems, have corroborated the molecular processes described above, including surface tension measurements (Peron et al, 2008), conductivity (Nichifor et al, 2008), dialysis (Mylonas et al, 1999), viscosity (Lof et al, 2009), dye solubilization (Dubin et al, 1992), microcalorimetry (Lof et al, 2007), and scattering techniques (Dai and Tam, 2006). The topic has also been studied in several book chapters (Goddard and Anathapadmanabhan, 1993) and review articles (Tam and Wyn-Jones, 2006).…”