Polyelectrolyte and carbon nanotube multilayers made from ionic liquid solutions

Abstract

The inevitable contact of substrates with water during the traditional practice of layer-by-layer assembly (LBL) creates problems for multiple potential applications of LBL films in electronics. To resolve this issue, we demonstrate here the possibility of a LBL process using ionic liquids (ILs), which potentially eliminates corrosion and hydration processes related to aqueous media and opens additional possibilities in structural control of LBL films. ILs are also considered to be one of the best "green" processing solvents, and hence, are advantageous in respect to traditional organic solvents. Poly(ethyleneimine) (PEI) and poly(sodium styrenesulfonate) (PSS) were dispersed in a hydrophilic IL and successfully deposited in the LBL fashion. To produce electroactive thin films with significance to electronics, a similar process was realized for PSS-modified single-walled carbon nanotubes (SWNT-PSS) and poly(vinyl alcohol) (PVA). Characterization of the coating using standard spectroscopy and microscopy techniques typical of the multilayer field indicated that there are both similarities and differences in the structure and properties of LBL films build from ILs and aqueous solutions. The films exhibited electrical conductivity of 10(2) S m(-1) with transparency as high as 98% for visible light, which is comparable to similar parameters for many carbon nanotube and graphene films prepared by both aqueous LBL and other methods.

Simultaneous characterization of physical, chemical, and thermal properties of polymeric multilayers using infrared spectroscopic ellipsometry

“…Kotov and his group fabricated PEI multilayers (branched, Mw ≈ 25,000 Da)/PSS (Mw ≈ 1 × 10 6 Da), using LBL spin-coater [33, 60]. They found that the thickness of the multilayers linearly increases with a correlation coefficient of almost unity.…”

“…They found that the thickness of the multilayers linearly increases with a correlation coefficient of almost unity. They observed an average thickness per layer pair of 6.7 nm, as measured by ellipsometry, for multilayers constructed using spin-assisted LbL with polymers dissolved in water at pH 3.7, a concentration of 50 mg/mL, and using acetonitrile as rinsing solution [33]. …”

“…In our work, PEI and PSS are dissolved at 1 mg/mL a lower concentration as compared to the works of Kotov and Richards for the same polymeric system. The difference may arise in the concentration of the polymers used, the molecular weight of the polymers, the type of LbL methodology (dipping vs spin-coated), or the type of rinsing solution (water or acetonitrile vs acetate buffer) [21, 33]. Our work uses high molecular weight branched PEI (Mw ≈ 750,000 Da) which may lead to thicker films.…”

“…Two multilayered systems are evaluated: synthetic multilayers composed of polyethylenimine (PEI) and poly (sodium-p-styrene sulfonate) (PSS) and natural multilayers composed of collagen type I (COL) and heparin (HEP). PEI/PSS LbL films have been previously used as sorbents for CO 2 capture [21], adsorption of prussian blue colloids [32], and corrosion control [33]. The natural system of multilayers COL/HEP have been previously used to help promote the blood-compatibility of titanium implants [34][35][36][37], vascularization studies [38] and intravascular endothelialization with the functionalization of antibodies over the multilayers [39][40].…”

Controlled self-assembly of amphiphiles in ionic liquids and the formation of ionogels by molecular tuning of cohesive energies

“…5 Some recent studies also highlighted their use in inorganic synthesis, [6][7][8][9] hybridization with nanocarbons 10,11 and molecular self-assembly. [12][13][14][15] One of the advantageous features of ILs for their application in supramolecular chemistry is expressed in terms of solvent engineering, that is, the properties of ILs can be readily tuned based on their molecular structures. Traditionally, the structures and properties of amphiphilic molecular self-assembling systems have been tuned by designing the constituent molecules.…”