A perspective on the Langmuir adsorption model applied to molecular liquid crystals containing ions and nanoparticles

Abstract

Electrical properties of molecular liquid crystals doped with nanomaterials have been extensively studied over the past two decades. In general, nanoparticles in liquid crystals can play a dual role acting as either ion capturing agents or ion generating objects. An interplay between ions and nanomaterials in liquid crystals can result in a great variety of nontrivial ionic effects. This perspective discusses the Langmuir adsorption model applied to describe ionic phenomena in molecular liquid crystals doped with nanoparticles. The applicability and limitations of this model are emphasized. Within a range of its applicability, the Langmuir adsorption model can be used to obtain a wealth of information about nanoparticle-induced ionic effects in molecular liquid crystals. In addition, this model also offers important improvements to standard experimental procedures for evaluation of electrical properties of advanced liquid crystal materials.

Eliminating Ambiguities in Electrical Measurements of Advanced Liquid Crystal Materials

“…An analysis of the reported experimental results [38,52,110] was performed in the framework of the Langmuir adsorption model applied recently to molecular liquid crystals containing ions and nanoparticles [109]. An essential feature of this model is the consideration of the possibility of ionic contamination of the cell substrate and/or nanoparticles [109]. The details of this approach, its limitations, and its applicability to describe molecular liquid crystals with ions and nanomaterials can be found in recent papers [109,113].…”

“…An essential feature of this model is the consideration of the possibility of ionic contamination of the cell substrate and/or nanoparticles [109]. The details of this approach, its limitations, and its applicability to describe molecular liquid crystals with ions and nanomaterials can be found in recent papers [109,113]. An analysis of the reported experimental results [38,52,110] was performed in the framework of the Langmuir adsorption model applied recently to molecular liquid crystals containing ions and nanoparticles [109].…”

Nanoparticle-Induced Ionic Effects in Liquid Crystal Devices

“…Another important factor is the ability of nanoparticles to capture ions quantified by the parameter K NP = k a NP /k d NP . In general, the value of this empirical parameter depends on the type of nanomaterials, the nature of ions, and the dielectric constant of liquid crystals [11][12][13]. Greater values of K NP will result in higher values of the electrical resistivity, as evidenced from Figure 2 (K NP = 10 −23 m 3 ) and Figure 3 (K NP = 10 −22 m 3 ).…”

“…We assume a spherical nanoparticle of a surface area A NP . n NP is the volume concentration of nanoparticles, σ NP S is the surface density of surface sites on a surface of nanoparticle, and Θ NP is the fractional surface coverage of a nanoparticle [13].…”

“…where n 0 represents the initial concentration of mobile ions in molecular liquid crystals (prior to mixing them with nanoparticles), and ν NP is the contamination factor accounting for the possibility of ionic contamination of nanoparticles [13]. By solving Equations ( 1) and (2), the concentration of mobile ions in liquid crystals doped with nanoparticles can be found.…”