Unique rodlike surface morphologies in trisilanolcyclohexyl polyhedral oligomeric silsesquioxane films.

A trisilanol derivative of polyhedral oligomeric silsesquioxane (POSS), trisilanolisobutyl-POSS, has recently been reported to form stable monolayers at the air/water interface. This paper explores the mono- and multilayer properties of another POSS derivative, trisilanolcyclohexyl-POSS, with pi-A isotherm and Brewster angle microscopy measurements. Results show that with continuously increasing surface concentration via symmetrical compression, trisilanolcyclohexyl-POSS amphiphiles at the air/water interface undergo a series of phase transitions from traditional Langmuir monolayers (one-POSS-molecule thick) to unique rodlike hydrophobic aggregates in multilayer films (approximately eight-POSS-molecules thick) that are dramatically different from "collapsed" morphologies seen in other systems.

Phase behavior and viscoelastic properties of trisilanolcyclohexyl-POSS at the air/water interface.

A trisilanol polyhedral oligomeric silsesquioxane (POSS), trisilanolcyclohexyl-POSS (TCyP), has recently been reported to undergo a series of phase transitions from traditional Langmuir monolayers to unique rodlike hydrophobic aggregates in multilayer films that are different from "collapsed" morphologies seen in other systems at the air/water interface. This paper focuses on the phase transitions and morphology of films varying in average thickness from monolayers to trilayers and the corresponding viscoelastic properties of trisilanolcyclohexyl-POSS molecules at the air/water interface by means of surface pressure-area per molecule (Pi-A) isotherms, Brewster angle microscopy (BAM), and interfacial stress rheometry (ISR) measurements. The morphology studies by BAM reveal that the TCyP monolayer can collapse into different 3D structures by homogeneous or heterogeneous nucleation mechanisms.

Blends of amphiphilic poly(dimethylsiloxane) and nonamphiphilic octaisobutyl-POSS at the air/water interface.

Brewster angle microscopy (BAM) shows that a nonamphiphilic polyhedral oligomeric silsesquioxane (POSS) nanofiller, octaisobutyl-POSS, forms aggregates at all surface concentrations at the air/water interface. When amphiphilic poly(dimethylsiloxane) (PDMS) is blended with the octaisobutyl-POSS (>10 wt % PDMS), the degree of POSS aggregation dramatically decreases. Thermodynamic analyses and morphology studies through surface pressure-area per monomer isotherm data and BAM, respectively, exhibit three distinct composition regimes: (1) Blends with >70 wt % POSS have unstable isotherms whose shapes deviate from those of PDMS and form large rigid domains comparable to but smaller than pure, octaisobutyl-POSS films.

Polyhedral oligomeric silsesquioxane amphiphiles: isotherm and brewster angle microscopy studies of trisilanolisobutyl-POSS at the air/water interface.

A trisilanol derivative of polyhedral oligomeric silsesquioxanes (POSS), trisilanolisobutyl-POSS, has recently been reported to form stable monolayers at the air/water interface. Moreover, the trisilanolisobutyl-POSS monolayer undergoes a nonequilibrium structural transition (collapse) around a surface pressure of Rho approximately 18 mN.m(-1).

Blends of amphiphilic trisilanolisobutyl-POSS and phosphine oxide substituted poly(dimethylsiloxane) at the air/water interface.

Mixtures of a polyhedral oligomeric silsesquioxane, trisilanolisobutyl-POSS, and a polar silicone, poly(dimethyl-co-methylvinyl-co-methyl, 2-diphenyl phosphine oxide ethyl) siloxane (PDMS-PO), spread as Langmuir monolayers at the air/water interface are used to examine the surface phase behavior and aggregation of trisilanolisobutyl-POSS as a function of silicone composition. Analyses of the surface pressure-area per monomer (Pi-A) isotherms in terms of the collapse pressures and excess Gibbs free energies of mixing indicate the monolayers form slightly negative deviation mixtures. Direct observations of surface morphology with Brewster angle microscopy in the collapsed regime reveal that the governing factor for aggregation is the collapse Pi of the component with a stronger affinity for water.

Polyhedral oligomeric silsesquioxanes: a new class of amphiphiles at the air/water interface.

Insoluble films of trisilanolisobutyl-POSS and octaisobutyl-POSS at the air/water interface are investigated by means of surface pressure - area per molecule isotherm (Pi - A) and Brewster angle microscopy (BAM). Analysis of the experimental results shows the partial cage molecule, trisilanolisobutyl-POSS, is a surface-active molecule that self-assembles into uniform monolayer upon compression; but the fully condensed cage molecule, octaisobutyl-POSS, is nonamphiphilic.