Enhancement in Elastic Bending Rigidity of Polymer Loaded Reverse Microemulsions

Abstract

Elastic bending rigidity of the surfactant shell is a crucial parameter which determines the phase behavior and stability of microemulsion droplets. For water-in-oil reverse microemulsions stabilized by AOT (sodium 1,4-bis(2-ethylhexoxy)-1,4-dioxobutane-2-sulfonate) surfactant, the elastic bending rigidity is close to thermal energy at room temperature (kT) and can be modified by the presence of hydrophilic polymers. Here, we explore the influence of two polymers polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP), both having nearly same size (radius of gyration, R) but different dipole moment, on elastic bending rigidity of water-AOT-n-decane reverse microemulsions via estimating the percolation temperatures (T) and droplet radii using dielectric relaxation spectroscopy (DRS) and small-angle neutron scattering (SANS) techniques. Notably, an increase in T is observed on introducing PEG and PVP polymers and is attributed to the adsorption of polymer chains onto the surfactant monolayer. The stability of the droplet phase of microemulsion after the incorporation of PEG and PVP polymers is confirmed by contrast matching SANS experiments. An enhancement in elastic bending rigidity of AOT surfactant shell amounting to ∼46% is observed upon incorporation of PVP into the droplet core, whereas for PEG addition, a smaller increase of about 17% is recorded. We conjecture that the considerable increase in elastic bending rigidity of the surfactant monolayer upon introducing PVP is because of the strong ion-dipole interaction between anionic AOT and dipoles present along the PVP polymer chains. Scaling exponents extracted from the temperature dependent electrical conductivity measurements and the frequency dependent scaling of conductivity at percolation indicate the dynamic nature of percolation for both pure and polymer loaded reverse microemulsions. The decrease in activation energy of percolation upon incorporating PEG and PVP polymer molecules also reflects the increased stability of microemulsion droplets against thermal fluctuations.

Scanning Electron Microscopy Imaging of Large DNA Molecules Using a Metal‐Free Electro‐Stain Composed of DNA‐Binding Proteins and Synthetic Polymers

“…The linear polymer PVP weighs 40 kDa and has an R g of 3.8 nm based on a reference value. [ 22 ] Thus, the external diameter of the PVP was ≈9.8 nm, as deduced from $${{d}_{out}} = \ 2\sqrt {5/3} {{R}_g}$$, assuming a spherical shape. This figure closely aligns with the 9.4‐nm FWHM in Figure 2b.…”

Combined Small-Angle Neutron Scattering/Small-Angle X-ray Scattering Analysis for the Characterization of Silver Nanoparticles Prepared via Photoreduction in Water-in-Oil Microemulsions

“…p micelles (11) where I p (q) is the scattering intensity of Ag NPs. Here, it is assumed that the structure of microemulsion droplets (composed of a water core and an AOT shell) is not significantly affected by the formation of Ag NPs, and the intensity of the microemulsion droplets after the photoreduction is approximately equal to that before the reduction; I p (q) calculated using eq 11 is plotted as a function of q in the logarithmic scale (Figure 2a).…”

“…The structural changes in the adsorbed organic ligands underline the mechanism of the steric stabilization of microemulsion droplets. 10,11 Small-angle X-ray scattering (SAXS) has been employed as one of the most powerful techniques to provide detailed information regarding the NP size and particle interactions in solutions. 13−19 Suitable structural models have been developed by fitting SAXS data to a form factor for the size/shape determination, and particle−particle interactions are described using a structure factor.…”

“…Several studies have been conducted on the state of water and aqueous solutions confined in AOT reverse micelles, , providing a quite complete structural and dynamic picture of w/o microemulsions. Recently, some issues regarding the chemical synthesis and stability of metal nanoparticles (NPs) have been addressed. − In particular, for colloidal metal NPs stabilized by organic ligands, − controlling the size of metal NPs in solution and gaining a good knowledge of the stabilization mechanisms are important. The adsorbed structure of organic ligands in w/o microemulsions can also be studied.…”

“…The adsorbed structure of organic ligands in w/o microemulsions can also be studied. The structural changes in the adsorbed organic ligands underline the mechanism of the steric stabilization of microemulsion droplets. , …”