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1.
ACS Appl Mater Interfaces ; 13(37): 44460-44469, 2021 Sep 22.
Artigo em Inglês | MEDLINE | ID: mdl-34495628

RESUMO

A combined experimental and molecular dynamics (MD) simulation approach was used to investigate the effects of the nanoconfinement of a highly CO2/CH4-selective ionic liquid (IL), 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]), in porous poly(vinylidene fluoride) (PVDF) matrices on the gas separation performance of the resulting membranes. The observed experimental CO2/CH4 permselectivity increased by about 46% when the nominal pore diameter in PVDF, which is a measure of nanoconfinement, decreased from 450 to 100 nm, thus demonstrating nanoconfinement improvements of gas separation. MD simulations corroborated these experimental observations and indicated a suppression in the sorption of CH4 by [EMIM][SCN] when the IL nanoconfinement length decreased within the nonpolar PVDF surfaces. This is consistent with the experimental observation that the CH4 permeance through the IL confined in nonpolar PVDF is significantly less than the CH4 permeance through the IL confined in a water-wetting polar formulation of PVDF. The potential of mean force calculations further indicated that CO2 has more affinity to the nonpolar PVDF surface than CH4. Also, a charge/density distribution analysis of the IL in the PVDF-confined region revealed a layering of the IL into [EMIM]- and [SCN]-rich regions, where CH4 was preferentially distributed in the former and CO2 in the latter. These molecular insights into the nanoconfinement-driven mechanisms in polymer/IL membranes provide a framework for a better molecular design of such membranes for critical gas separation and CO2 capture applications.

2.
Langmuir ; 36(34): 10074-10081, 2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32787007

RESUMO

The literature clearly reports that magnetic surfactant systems respond to magnetic fields. This manuscript investigates if the responses are because the magnetic fields directly alter the interfacial properties or if the surface-active properties are independent of the paramagnetic fluid responses. It uses uniform and gradient magnetic fields to determine the magnetically induced changes to the surface tensions independent of bulk paramagnetic fluid effects for ionic magnetic surfactants. The magnetically induced decrease in surface tensions is small compared to the bulk paramagnetic fluid effects. The reported decrease in surface tensions is significantly smaller than those previously found in the literature, which reported a combined interfacial and bulk paramagnetic effect. The magnetically induced surface tension changes are a function of the degree of association, α, of the magnetic moiety with the surfactant's amphiphilic structure. Therefore, the proposed answer to the question is that as α approaches zero, the magnetic properties of the magnetic surfactant system approaches the behavior of an ordinary paramagnetic fluid. For magnetic surfactants with α approaching one, there is a measurable interfacial response. For example in this study, a magnetic surfactant with α = 0.92 had a 2.5 times greater magnetically induced change in surface tension compared to a magnetic surfactant with α = undetectable, even thought they had similar magnetic moments.

3.
Langmuir ; 35(36): 11843-11849, 2019 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-31408347

RESUMO

Predicting the behavior of magnetic surfactants in magnetic fields is critical for designing magnetically driven processes such as chemical separations or the tuning of surface tensions. The ability of magnetic fields to alter the interfacial properties of magnetic surfactant solutions may be dependent upon the strength of association between the magnetic and surfactant moieties of the surfactant molecules. This research shows that the stability of a magnetic surfactant in an aqueous environment is dependent upon the type of complex that contains the paramagnetic ion, and these findings provide valuable insight for the design of magnetic surfactants for applications in aqueous media. The surfactants investigated were ionic surfactants, which contained paramagnetic counterions. This investigation looked at both anionic and cationic surfactants; it utilized solution conductivity, cyclic voltammetry (CV), sampled current voltammetry (SCV), and solution pH measurements to qualitatively evaluate the stability of the magnetic counterions in aqueous solution. In addition, solution conductivity was used to quantify the degree of binding between the paramagnetic ions and surfactant micelles in solution. These results indicate metal halide-based cationic surfactants are unstable in aqueous solutions. We hypothesize that this instability results in the difference in the magnetic response of the anionic vs cationic surfactants examined in this study.

4.
J Phys Chem B ; 121(29): 7163-7172, 2017 07 27.
Artigo em Inglês | MEDLINE | ID: mdl-28677969

RESUMO

A number of proposed applications for ionic liquids (ILs) involve IL/water interfaces, such as chemical separations or drug delivery. Therefore, an understanding of the solubility and micellar behavior ILs in aqueous environments is critical. The anion, bis(trifluoromethanesulfonyl)imide (Tf2N) promotes water stability and forms water immiscible ILs. This study, therefore, paired the Tf2N-anion with three different classes of IL cations. The three classes examined were 1-alkyl-3-methylimidazoliums (Rmim), alkyl-trimethylammoniums (CTA), and bulky ammoniums (BAM). CTAs can be synthesized from inexpensive ammonium surfactants; however, large CTAs are solids at ambient conditions. In contrast, large BAMs remain in the liquid state at ambient conditions. We used total organic carbon (TOC) analysis to determine the IL content in IL saturated water. Surface tension measurements of IL containing water determined if micelles existed in the IL saturated water. We used linear free energy relationship (LFER) semiempirical models to correlate the IL water solubility to the molecular volume and IL cation structure. The reported LFERs can predict the IL solubility in water before the IL is synthesized. Combining the LFER results with surface tension measurements and thermodynamic calculations allowed us to determine that micelle formation is not significant for the tested ILs with molecular weights ≤510.

5.
J Colloid Interface Sci ; 428: 16-23, 2014 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-24910029

RESUMO

HYPOTHESIS: Magnetic Ionic Liquid (MILs), novel magnetic molecules that form "pure magnetic liquids," will follow the Ferrohydrodynamic Bernoulli Relationship. Based on recent literature, the modeling of this fluid system is an open issue and potentially controversial. EXPERIMENTS: We imposed uniform magnetic fields parallel to MIL/air interfaces where the capillary forces were negligible, the Quincke Problem. The size and location of the bulk fluid as well as the size and location of the fluid/air interface inside of the magnetic field were varied. MIL properties varied included the density, magnetic susceptibility, chemical structure, and magnetic element. FINDINGS: Uniform tangential magnetic fields pulled the MILs up counter to gravity. The forces per area were not a function of the volume, the surface area inside of the magnetic field, or the volume displacement. However, the presence of fluid/air interfaces was necessary for the phenomena. The Ferrohydrodynamic Bernoulli Relationship predicted the phenomena with the forces being directly related to the fluid's volumetric magnetic susceptibility and the square of the magnetic field strength. [emim][FeCl4] generated the greatest hydraulic head (64-mm or 910 Pa at 1.627 Tesla). This work could aid in experimental design, when free surfaces are involved, and in the development of MIL applications.

6.
J Colloid Interface Sci ; 238(2): 230-237, 2001 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-11374916

RESUMO

This work develops models for calculating the disjoining pressures of a cylindrical fluid "plug", specifically in submicrometer cylindrical pores. This modeling produces closed-form, cylindrical-pore disjoining pressures for London/van der Waals and solute/pore-wall adsorption interactions, which are the slit-pore models with the characteristic pore size replaced by the radius and multiplied by 6, resulting in a 48-fold or more increase in magnitude. In addition, this work contains a numerical solution for electrostatic interactions. The result of the numerical solution was a 9-fold increase in the modeled disjoining pressure compared to that in the slit-pore model. The cylindrical models may apply to the chemical coating of the interior walls of cylindrical pores or to the thermodynamics within droplets after the breakup of a fluid coating a surface. However, the application used as the base case in this paper is the extension of transport and thermodynamic laws for porous media, previously developed with capillary pressure models, to fully saturated porous media with submicrometer-sized pores. As such, the models could apply to mass transport in ultrafiltration, nanofiltration, and reverse-osmosis membranes. Copyright 2001 Academic Press.

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