A fluorescence probe study on the effects of surfactants on cloud points in aqueous poly(N-isopropylacrylamide) solutions

Abstract

Fluorescence probe methods were used to investigate micelle formation of poly(N-isopropylacrylamide) (PNIPA) with two types of surfactants, anionic sodium n-dodecyl sulfate (SDS) and cationic n-dodecyltrimethylammonium chloride (DTAC), in aqueous solutions using pyrene or 1-pyrenecarboxaldehyde as a fluorescence probe. Two PNIPA samples, one having a hydrophobic chain-end group and the other having a negatively charged hydrophilic chain-end group, were used to investigate the effects of the chain-end group on the formation of the micelles. The critical aggregation concentration, at which surfactant molecules begin to bind to PNIPA chains to form micelles, was observed to be much lower for PNIPA solutions containing SDS than for solutions containing DTAC. This is consistent with previous results showing that the cloud point in PNIPA solutions containing SDS begins to increase from its value in surfactant-free solutions at a much lower concentration of added surfactant than that in solutions containing DTAC. It was also observed that there is a discrepancy in the emission spectra of solutions containing SDS between the two PNIPA samples but not for solutions containing DTAC, indicating that the chain-end groups of PNIPA may affect the microenvironmental polarity in the micelles composed of PNIPA and the surfactants.

Fluorescent Nanoassembly of Tetrazole-Based Dyes with Amphoteric Surfactants: Investigation of Cyanide Sensing and Antitubercular Activity

“…This might be due to the hydrogen bonding interaction between the tetrazole and hydroxyl functional groups of the surfactants. On the other hand, at a higher concentration zone (50–250 μM), we could observe turn-on fluorescence with a significant broadening (or even the presence of a small hump) at a higher wavelength region . Such kind of improvement of fluorescence response along with red-shifted λ max values indicates a lowering of conformation flexibility of dye molecules inside the micellar or vesicular cavity .…”

“…On the other hand, at a higher concentration zone (50−250 μM), we could observe turn-on fluorescence with a significant broadening (or even the presence of a small hump) at a higher wavelength region. 40 Such kind of improvement of fluorescence response along with red-shifted λ max values indicates a lowering of conformation flexibility of dye molecules inside the micellar or vesicular cavity. 41 The restricted conformation could promote the extent of intramolecular charge transfer.…”

Self-Assembled Multifunctional Nanoreactors for Dephosphorylation Reactions

“…The polymer/surfactant complexation leads to the formation of hydrophobic microenvironments for [CTAB] > CAC, even below the CMC. These can be characterized using pyrene as a fluorescent polarity probe through the intensity ratio of bands I and III (I I /I III ). , The profiles of I I / I III obtained for PAA/CTAB in the absence and presence of ImR are shown in Figure . In the presence of PAA (1.0 × 10 –4 mol L –1 ) and absence of CTAB and ImR, the I I / I III value was 1.55.…”