The pH-responsive behaviour of poly(acrylic acid) in aqueous solution is dependent on molar mass

Abstract

Fluorescence spectroscopy on a series of aqueous solutions of poly(acrylic acid) containing a luminescent label showed that polymers with molar mass, Mn < 16.5 kDa did not exhibit a pH responsive conformational change, which is typical of higher molar mass poly(acrylic acid). Below this molar mass, polymers remained in an extended conformation, regardless of pH. Above this molar mass, a pH-dependent conformational change was observed. Diffusion-ordered nuclear magnetic resonance spectroscopy confirmed that low molar mass polymers did not undergo a conformational transition, although large molar mass polymers did exhibit pH-dependent diffusion.

The concept of entropic rectifier facing experiments

“…This pH is the isoelectric point of membranes. Results reported below were obtained at this pH, which is naturally obtained with polyacrylic acid (PAA) at a monomer concentration c  = 0.1 M, because its dissociation constant ( pK a  ≃ 4.528) is close to the one of acetic acid. Note that at this concentration only 1.8% of acid groups are dissociated.…”

“…In Fig. 7, τ B and τ L were computed from experimental D values28 for V  = 0.5 V, L  = 6  μ m, γ  ≃ 2 × 10 −2 (i.e. pK a  = 4.5 and c  = 0.1 M), B  = 200 nm and b  = 2 nm and plotted as a function of N .…”

“…Data points correspond to τ B and τ L calculated from data of ref. 28. Horizontal dashed lines indicate the time-scale (frequency range) of Fig.…”

Enhanced flocculation activity of polyacrylamide‐based flocculant for purification of industrial wastewater

“…The resulting surfactant/polyelectrolyte complexes form aggregate structures from the nano to micro scales. The structure and phase behavior of the resulting complexes can influence different parameters, such as charge density, molecular weight, hydrophobicity, concentration of the complex, and salinity of the wastewater, as well as the structure, polar head charge, hydrophobicity, and surfactant concentration …”

A self-healable fluorescence active hydrogel based on ionic block copolymers prepared via ring opening polymerization and xanthate mediated RAFT polymerization

“…These issues could be overcome by employing a functional organic polymer consisting of covalently bound fluorophore units 27 . Incorporation of covalently bound fluorescent labels has been shown to be a powerful way of studying both the internal conformational changes of stimuli responsive polymers 28,29 and the complexation of multiple polymers in solution 30,31 , and FRET analysis using two chromophores can provide additional information in both systems 32,33 . Recently Ma et.…”