Effect of Ionic Liquid on Diffusion in P123 Gel: Fluorescence Correlation Spectroscopy

Abstract

The effect of two room-temperature ionic liquids (RTILs) on the diffusion of three fluorescent dyes in the gel phase of a triblock copolymer, (PEO)(20)-(PPO)(70)-(PEO)(20) [Pluronic P123; poly ethylene oxide (PEO), poly propylene oxide (PPO)], was studied by using fluorescence correlation spectroscopy (FCS). We used three dyes, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), coumarin 480 (C480), and coumarin 343 (C343). By field-emission scanning electron microscopy (FESEM), it was observed that the macroscopic structure of the P123 gel remained unaffected upon addition of RTIL. In the absence of RTIL, the diffusion coefficient (D(t)) of the hydrophobic dye DCM (1 μm(2) s(-1) at the core) is smaller than that of the other two hydrophilic dyes (7 μm(2) s(-1) for C480 and C343). On addition of RTIL, the D(t) values of all of the dyes increase, indicating a decrease in local viscosity (η(eff)). The η(eff) of the core of the RTIL-P123 gel estimated from the D(t) of DCM is lower than that of both the P123 gel (at the core η=90 cP) and RTIL (η=110 cP). It is shown that the RTIL affects the structure of the gel by modifying the size of the micellar aggregates and by penetrating the core.

Single-molecule Spectroscopy: Exploring Heterogeneity in Chemical and Biological Systems

“…The distribution of D t of all three dyes (localized in different regions) in the P123 gel are quite narrow (Figure ) . This indicates that the dyes experience an almost homogeneous microenvironment around them.…”

“…Since the viscosities of both the RTILs are very high (∼ 100 cp), addition of RTIL to the P123 gel is expected to increase the viscosity of the medium, and hence, decrease the D t . Contrary to this expectation, addition of 1.5 M [pmim][Br] to P123 gel causes an increase in the D t of DCM by a factor of 10 . According to dynamic light scattering (DLS), addition of RTIL causes an increase in the size ( r H ) of the P123 micelle from 18 nm in 0 M [pmim][Br] to 560 nm in 1.8 M [pmim][Br] .…”

“…The different values of the D t of the three dyes indicate that the dye molecules are localized in different regions of the gel and follow different trajectories inside the P123 gel . The hydrophobic dye diffuses through the polymer chains, while the hydrophilic dye C343 diffuses through the periphery and the “void” region.…”

Effect of NaCl on ESPT‐Mediated FRET in a CTAC Micelle: A Femtosecond and FCS Study

“…[43] To fit the correlation function, we used a 3D diffusion model with a triplet contribution. The correlation function is expressed by Equation (7): [44] GðtÞ in which t D denotes the diffusion time in the confocal volume, t tr is the triplet lifetime of a dye molecule, T is the fraction of the number of molecules in the triplet state, t is the delay time, and N represents the average number of molecules in the confocal volume. The FCS experiments were performed at room temperature (20 8C).…”

“…Upon addition of 4 m NaCl to CTAC micelles, the viscosity of the system increases. To account for this viscosity correction, we used coumarin 480 (C480) as a reference molecule and the viscosity of the solution in 4 m NaCl (h 4m NaCl ) was obtained by using Equation (10): [44]…”