Interfacial Properties of Fully Condensed Functional Silsesquioxane: A Langmuir Monolayer Study

Abstract

We have studied interfacial properties of fully condensed octakis[{2-(3,4-epoxy­cyclo­hexyl)­etyl}­dimethyl­silyloxy]­octa­silsesquioxane (OE-POSS). The surface pressure–area isotherm obtained in a Langmuir trough together with Brewster angle microscopy indicated formation of a stable, homogeneous liquid-like monolayer. For low molecular areas, the monolayer undergoes a stepwise collapse showing unusual multilayer morphology. A collapse mechanism is proposed to be a consequence of progressive decrease in the distance between silicon–oxygen cages after reorganization of side groups. Hysteresis experiment showed incomplete respreading of small aggregates and successive decrease in molecular areas. Relaxation measurements indicated a slight impact of desorption and molecular rearrangements on the monolayer stability. Interfacial rheology was investigated for compressional deformation of the air/water interface. Both components of surface dilational modulus (elastic, E′, and viscous, E″) were determined by the oscillating barriers method. With increasing frequency, E′ decreased while E″ increased almost linearly. The loss angle tangent indicated elastic response of the monolayer in the range of low deformation rates and viscous behavior when subjected to fast deformation. The rheological behavior of the monolayer is also strongly affected by the collapse mechanism that begins at 20 mN/m.

Controlled Ion Permeability of Ultrathin Nanoporous SiO2 Films from Silsesquioxane-Containing Polymer Nanosheets

“…The result indicates that pDDA is a good amphiphilic polymer to stabilize the monolayer. The limiting molecular occupied area ( A unit ), compression modulus ( C s –1 ), , and characteristic surface pressure (π*: defined as the surface pressure π when C s –1 reached the maximum point) were calculated from the π– A and C s –1 – A isotherms (Figures and S1). A unit was determined by extrapolating the linear portion of the condensed state in the π– A isotherm to zero pressure.…”

Synthesis of an Open‐Cage Structure POSS Containing Various Functional Groups and Their Effect on the Formation and Properties of Langmuir Monolayers

“…The ratio of E ′′ to E ′ is defined as the tangent of the loss angle, tan θ , where θ is the phase shift between the imaginary component and the real component of the dilatational modulus. A value of tan θ lower than 1 implies elastic properties of the monolayer, whereas a value of tan θ greater than 1 reveals a more viscous character …”

“…[37,39] The surface viscoelastic properties of the POSS monolayers spread on the air-water interface, as af unctiono ft he frequency of oscillations, were investigated at different surface states characterized by given values of the surface pressure. For ap erfectly viscousm onolayer,t he real part is equal to zero, whereas for ap erfectly elastic one, the imaginary parti sz ero.…”

“…The ratio of E'' to E' is defined as the tangent of the loss angle, tan q, where q is the phase shift between the imaginary component and the real component of the dilatational modulus.Avalue of tan q lower than 1i mplies elastic properties of the monolayer,w hereas av alue of tan q greater than 1r eveals am ore viscous character. [37,39] The surface viscoelastic properties of the POSS monolayers spread on the air-water interface, as af unctiono ft he frequency of oscillations, were investigated at different surface states characterized by given values of the surface pressure. The changes in the surfacee lastic modulus (E')a nd the viscous modulus( E") as af unction of the deformationr ate (i.e.,t he frequencyo fo scillations) are presentedi nF igure 8.…”

Interfacial behaviour of cubic silsesquioxane and silica nanoparticles in Langmuir and Langmuir–Blodgett films

“…In 2014 we reported the rst fully-condensed, multifunctional POSS, octakis[{2-(3,4epoxycyclohexyl)etyl}dimethylsilyloxy]octasilsesqui-oxane that forms stable Langmuir lm. 21 Recently, Paczesny et al demonstrated another fully-condensed, monofunctional POSS compounds bearing glycerol unit, maleamic acid and amino group which behave like typical amphiphiles. 22 On the other hand, POSS, especially uorinated derivatives, were recognized as excellent materials for fabrication of water-repellent surfaces.…”