Octamethylcyclotetrasiloxane Research Articles

Nonlinear Rheology of a Nanoconfined Simple Fluid

We probe the rheology of the model liquid octamethylcyclotetrasiloxane (OMCTS) confined into molecularly thin films, using a unique surface force apparatus allowing us to explore a large range of shear rates and confinement. We thus show that OMCTS under increasing confinement exhibits the viscosity enhancement and the nonlinear flow properties characteristic of a sheared supercooled liquid approaching its glass transition. Besides, we study the drainage of confined OMCTS via the propagation of "squeeze-out" fronts. The hydrodynamic model proposed by Becker and Mugele [Phys. Rev. Lett. 91, 166104 (2003)] to describe such front dynamics leads to a conclusion in apparent contradiction with the dynamical slowdown evidenced by rheology measurements, which suggests that front propagation is not controlled by large scale flow in the confined films.

Study on the synthesis, structure, and properties of polydimethylsiloxane-acrylate/organophilic montmorillonite nanocomposite emulsions

Polydimethylsiloxane-acrylate/organophilic montmorillonite (PDMS-ACR/OMMT) nanocomposite emulsions were prepared by the copolymerization between ACR and PDMS/OMMT seeding emulsion, which was prepared beforehand by ring-opening in situ polymerization of octamethyl cyclotetrasiloxane (D4) intercalated into the interlayer of OMMT modified with dodecylbenzene sulfonate acid (DBSA). OMMT, PDMS/OMMT seeding emulsion, and PDMS-ACR/OMMT nanocomposite emulsions were characterized with X-ray diffraction, FTIR, laser particle size analysis, SEM, and TG; the physical properties of the of PDMS-ACR/OMMT latex films were also characterized including adherence, impact property, bend property, hardness, and water resistance. The results showed that DBSA was intercalated into the interlayer of montmorillonite, and ring-opening in situ polymerization of D4 could be carried out favorably in OMMT interlayer. The onset weight-loss temperature of PDMS-ACR/OMMT latex films was higher than that of polyacrylate latex film by 44°C. When the addition of the amount of OMMT was 2 wt % in PDMS-ACR/OMMT emulsions, OMMT had been peeled into layered structure and dispersed in the continuous polymer phase, the shape of OMMT was regular and its size was uniform, the physical properties of the latex films were improved obviously. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Unexpected Destructive Dealumination of Zeolite Beta by Silylation

Zeolite beta was silylated in a novel way, by chemical liquid deposition (CLD) of a cyclic organosiloxane, and characterized. Despite its large size, octamethyl-cyclotetrasiloxane (OMTS) did not provide a surface modification, as did the traditional tetra-alkoxysilanes (ethoxy, propoxy, and butoxy). OMTS treatment with minor Si deposition influenced the internal parts of the zeolite with destructive dealumination, as revealed by 27Al MAS NMR, IR, and XRD studies. Three types of AlO6 sites were found, (a) 17 ppm 27Al shift, (b) 0 ppm shift, 3782 cm−1 IR frequency, and (c) −20 ppm shift, exhibiting no Bronsted and Lewis acidity, respectively, toward pyridine. Apparently, OMTS’s low reactivity toward condensation with the less acidic external hydroxyl groups promoted ring-opening at pore-mouth sites. This allowed the resulting linear siloxane tetramer to penetrate the pores and cause dealumination during calcination. Catalysts modified with OMTS had the lowest amounts of AlO4 sites, Lewis acidity, large void...

Design of a Versatile Force Field for the Large-Scale Molecular Simulation of Solid and Liquid OMCTS

We developed a new, versatile force field for the molecular simulation of octamethylcyclotetrasiloxane (OMCTS) both in the solid and liquid phases. From a series of molecular dynamics simulations, we obtain good agreement with the experimental lattice constants, sublimation enthalphy, and molecular packing of the crystal. The experimental density, diffusion coefficient, and shear viscosity of this van der Waals liquid in the range 300−440 K are well reproduced as well. The new force field can be thus employed in the large-scale molecular simulation of liquid OMCTS where structural details are important in determining the collective properties of the system.

Synthesis and Characterization of Functionalized Polyorganosiloxanes Containing Amino and Fluorocarbon Side Chains

A series of functional polyorganosiloxanes containing fluorocarbon side chain and amino groups had been synthesized by ring-opening polymerization. The raw materials used were Octamethyl cyclotetrasiloxane (D4), dodecafluoroheptyl-propyl-trimethoxylsilane (502) and γ-aminopropyltriethoxylsilane (550), respectively. FTIR, 1H-NMR, 13C-NMR, and 19F-NMR were used to characterize the copolymer structures. The surface properties of the functional polyorganosiloxanes emulsions were discussed. The results showed that the functional polyorganosiloxanes containing fluorocarbon and amino side chains had low surface tension and excellent water repellency.

Volatile Organic Compounds Emanating from Indoor Ornamental Plants

A broad cross-section of volatiles emanating from four species of popular indoor ornamental plants (Spathiphyllum wallisii Regel, Sansevieria trifasciata Prain, Ficus benjamina L., and Chrysalidocarpus lutescens Wendl.) was identified and categorized based on source. Volatile organic compounds from individual plants were obtained using a dynamic headspace system and trapped on Tenax TA during the day and again at night. Using short-path thermal desorption and cryofocusing, the volatiles were transferred onto a capillary column and analyzed using gas chromatography–mass spectroscopy. The volatiles originated from the plants, media/micro-organisms, pot, and pesticides. A total of 23, 12, 13, and 16 compounds were identified from S. wallisii, S. trifasciata, F. benjamina, and C. lutescens, respectively. The night emanation rate was substantially reduced (i.e., by 30.1%, 69.5%, 73.7%, and 63.1%, respectively) reflecting in part the regulation of biosynthesis and the greater diffusion resistance when the stomata were closed. S. wallisii had the highest emanation rate, releasing 15 terpenoid compounds [e.g., linaloloxide, linalool, (Z)-β-farnesene, farnesal, (+)-δ-cadinene, (+)-β-costol] into the surrounding air. Alpha-farnesene (90.3%) was quantitatively the dominant volatile present followed by (Z)-β-farnesene (1.4%), (+)-β-costol (1.4%), and farnesal (1.1%). Substantially fewer terpenoids (i.e., two, nine, and eight) emanated from S. trifasciata, F. benjamina, and C. lutescens, which quantitatively emitted fewer volatiles than S. wallisii. Most terpenoids from the four species were sesquiterpenes rather than monoterpenes. Methyl salicylate, a plant-signaling compound, was emitted by all four species. Certain volatiles (e.g., 2-chlorobenzonitrile, 1-ethyl-3,5-dimethylbenzene) were released from growth media and/or micro-organisms therein; other sources included the plastic pot (e.g., 2-ethyl-1-hexanol, octamethyl cyclotetrasiloxane) and pesticide ingredients [e.g., 2-(2-methoxy- ethoxy)ethanol, 2-ethylhexyl salicylate, homosalate].

Carbon-free SiOx films deposited from octamethylcyclotetrasiloxane (OMCTS) by an atmospheric pressure plasma jet (APPJ)

The deposition of carbon-free, silicon oxide (SiOx) films with a non-thermal, RF capillary jet at 27.12 MHz at normal pressure is demonstrated. The gas mixture for film deposition is constituted of argon, oxygen and small admixtures of octamethylcyclotetrasiloxane (Si4O4C8H24, 0.4 ppm). Surface analysis of the deposited films reveals their exceptionally low carbon content. The XPS atom percentage stays at 2% and less, which is near detection limit. The parametric study reported here focuses on the optimization of the deposition process with regard to the chemical and morphological surface properties of the coating by varying oxygen feed gas concentration (0–0.2%) and substrate temperature (10–50 °C).

Drainage of a nanoconfined simple fluid: Rate effects on squeeze-out dynamics

We investigate the effect of loading rate on drainage in molecularly thin films of a simple fluid made of quasispherical molecules [octamethylcyclotetrasiloxane (OMCTS)]. We find that (i) rapidly confined OMCTS retains its tendency to organize into layers parallel to the confining surfaces, and (ii) flow resistance in such layered films can be described by bulklike viscous forces if one accounts for the existence of one monolayer immobilized on each surface. The latter result is fully consistent with the recent work of Becker and Mugele, who reached a similar conclusion by analyzing the dynamics of squeeze-out fronts in OMCTS [T. Becker and F. Mugele, Phys. Rev. Lett. 91, 166104 (2003)]. Furthermore, we show that the confinement rate controls the nature of the thinning transitions: layer-by-layer expulsion of molecules in metastable, slowly confined films proceeds by a nucleation-growth mechanism, whereas deeply and rapidly quenched films are unstable and undergo thinning transitions akin to spinodal decomposition.

Synthesis of N‐β‐aminoethyl‐γ‐aminopropyl polydimethyl‐co‐polydiphenylsiloxane and its film morphology and orientation

AbstractA fabric softener, N‐β‐aminoethyl‐γ‐aminopropyl polydimethyl‐co‐polydiphenylsiloxane (PASO), was synthesized by the polymerization of octamethyl cyclotetrasiloxane with an amino‐functional silane and dimethyldiphenylsilane. The chemical structure of the synthesized polysiloxane was characterized by Fourier transform infrared and 1H‐NMR spectra. The morphology, composition, and hydrophobic properties of the PASO film were investigated by X‐ray photoelectron spectroscopy, atomic force microscopy, contact angle measurement, and other measurements. The experimental results indicate that on the silicon wafer surface, PASO formed a hydrophobic, nonhomogeneous structural film. In addition, the atomic force microscopy results show that the PASO film deposited on the silicon wafer seemed to be slightly rougher than the film of the control, the N‐β‐aminoethyl‐γ‐aminopropyl polydimethylsiloxane. As a result, an orientation model of PASO is proposed on the basis of the characterization of the PASO film properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Polysiloxane nanoparticles prepared by emulsion polymerization under microwave irradiation

AbstractEmulsion polymerization of octamethyl cyclotetrasiloxane (D4) under microwave irradiation (MI) was studied. The polysiloxane (PSi) nanoparticles via cationic ring-opening polymerization of D4 were obtained by using the dodecylbenzene sulphonic acid (DBSA), sodium dodecylbenzene sulphate (SDBS) and poly(ethylene glycol) monooctylphenyl ether (OP-10) as the catalyst and the emulsifiers respectively. The particle size analyzer and transmission electron microscope (TEM) were used to determine the particle size of PSi emulsions. The results show that, the particle size of PSi emulsions prepared under MI is substantially smaller and the particle distribution is narrower compared with that under conventional heating (CH). With the aid of MI, the polymerization rate and the equilibrium conversion are enhanced. The polydispersity index (PDI) and molecular weight (Mw) measured by GPC indicate that under MI, PDI of PSi is narrower and Mw of PSi at high temperature is lower than those under CH.

Microwave-Irradiated Ring-Opening Polymerization of Octamethylcyclotetrasiloxane in the Presence of Water

α, ω-dihydroxyl polydimethylsiloxane (DHPDMS) was prepared via anionic ring-opening polymerization of octamethyl cyclotetrasiloxane (D4) under microwave irradiation (MI) in the presence of water. The conversion and polymerization rate were calculated by the gravimetric method. The effect of microwave power on the polymerization was investigated. FTIR was used to verify the DHPDMS prepared at different irradiation times. The results show that the conversion is the highest when the initial microwave power is preset at 700 W. Compared with conventional heating (CH), the polymerization rate and equilibrium conversion are both enhanced by the introduction of microwave irradiation. The species and concentration of the cyclosiloxane mixture caused by backbiting reaction were determined by gas chromatography/mass spectrometry (GC/MS). The lower concentration of cyclosiloxane in the polymer prepared under MI indicates that side reactions have been reduced and a pure polymer obtained. The molecular weight and polydispersity index (PDI) measured by GPC show that under MI, the molecular weight of DHPDMS is lower and PDI is narrower than those under CH.

Effect of Tip Size on Force Measurement in Atomic Force Microscopy

An atomic force microscope (AFM) has been used to study solvation forces at the solid-liquid interface between highly oriented pyrolytic graphite (HOPG) and the liquids octamethylcyclotetrasiloxane (OMCTS), n-hexadecane (n-C16H34), and n-dodecanol (n-C11H23CH2OH). Oscillatory solvation forces (F) are observed for various measured tip radii (Rtip=15-100 nm). It is found that the normalized force data, F/Rtip, differ between AFM tips with a clear trend of decreasing F/Rtip with increasing Rtip.

Freezing of Fluids Confined between Mica Surfaces

Using grand ensemble simulations, we show that octamethyl-cyclo-tetra-siloxane (OMCTS) confined between two mica surfaces can form a variety of frozen phases which undergo solid-solid transitions as a function of the separation between the surfaces. For atomically smooth mica surfaces, the following sequence of transitions 1[triangle up] --> 1[triangle up]b --> 2B --> 2 square --> 2[triangle up] are observed in the one- and two-layered regimes, where n[triangle up], n[square], and nB denote triangular, square, and buckled phases, respectively, with the prefix n denoting the number of confined layers. The presence of potassium on mica is seen to have a strong influence on the degree of order induced in the fluid. The sequence of solid-solid transitions that occurs with the smooth mica surface is no longer observed. When equilibrated with a state point near the liquid-solid transition, a counterintuitive freezing scenario is observed in the presence of potassium. Potassium disrupts in-plane ordering in the fluid in contact with the mica surface, and freezing is observed only in the inner confined layers. The largest mica separations at which frozen phases were observed ranged from separations that could accommodate six to seven fluid layers. The extent of freezing and the square-to-triangular lattice transition was found to be sensitive to the presence of potassium as well as the thermodynamic conditions of the bulk fluid. The implications of our results on interpretation of surface force experiments as well as the generic phase behavior of confined soft spheres is discussed.

Chaotic behavior appearing in dynamic motions of nanoscale particles

The case of one-directional motion, under which graphite and mica flakes are driven on an octamethylcyclotetrasiloxane (OMCTS) liquid surface, is presented. The dynamical forces needed to move these bodies increase linearly with the logarithm of scanning velocity, which are typical energy dissipation process. A transition from quasi-periodic to chaotic motions occurs in the dynamics of a graphite flake when its velocity is increased. The dynamics of graphite flakes pulled by the nanotip on an OMCTS liquid surface can be treated as that of a nanobody on a liquid. On the other hand, there do not appear chaotic motions in the dynamics of a mica flake because the contact area between a mica flake and an OMCTS liquid surface is larger than that between a graphite flake and an OMCTS liquid surface.

Structure Characterization of HSQ Films for Low Dielectrics Uses D4 as Sacrificial Porous Materials

Hydrogensilsesquioxane (HSQ) (low-k) films were prepared by spin-on deposition using D4 (octamethyl cyclotetrasiloxane) as a sacrificial porous material. The dielectric constant of silica films significantly changed from 3.0 to 2.2. Fourier transform infrared spectroscopy was used to identify the network structure and cage structure of the Si–O–Si bond and other bonds that may appear. We studied the structural and electrical properties of the spin-coated films prepared by mixing HSQ and D4 films after oxygen plasma exposure for 5 min, and studied the structural recovery of the damage by annealing at 350°C for 1.5 h in a nitrogen (N2) ambient. This structure results in significant lowering of the dielectric constant (k) on annealing at 350°C for 1.5 h in an N2 ambient and improvement in the leakage current density.

Raman Scattering from Confined Liquid Films in the Sub-Nanometre Regime

Raman spectroscopy has been used to study the confinement of octamethylcyclotetrasiloxane (OMCTS) and n-hexadecane between a prism and a lens at contact pressures of 40 MPa. Both lens and prism surfaces were optically smooth but not atomically flat. A total internal reflection geometry was employed to provide the sensitivity needed to detect liquid films of sub-nanometre thickness. For both liquids, the thickness of the residual film under load corresponded to less than a monolayer of liquid. The Raman spectra of the confined liquids were identical or very similar to that of the bulk liquid. Similar results were obtained for hexadecane confined between two surfaces coated with a Langmuir-Blodgett monolayer of a fatty acid. We infer that the liquids do not form a boundary layer under these conditions but rather they are squeezed out of the contact under the modest pressure applied. We ascribe the residual signal to liquid trapped in scratches or other defects on the surfaces.

Properties of Siloxane Coatings Deposited in a Reel-to-Reel Atmospheric Pressure Plasma System

techniques. The requirement forthe vacuum process however limits the exploitation ofthis technology to batch processing. As a result, there hasbeen an increasing interest in the use of atmosphericpressure plasmas for continuous processing. In this study,silicon-containing coatings were deposited from four typesof liquid siloxane precursors, with varying molecularstructures, as follows: poly(dimethylsiloxane) (PDMS),tetraethylorthosilicate (TEOS), octamethylcyclotetrasilox-ane (OMCTS) and hexamethyldisiloxane (HMDSO). Theobjective of this study was to evaluate both the influenceof siloxane precursor structure and the level of exposure ofthe precursor to the plasma, on the properties of thedeposited coatings. Amongst the properties evaluatedwere deposited coating thickness, surface energy, mor-phology and coating siloxy chemistry and elementalcomposition.

Surface Melting of Octamethylcyclotetrasiloxane Confined in Controlled Pore Glasses: Curvature Effects Observed by 1H NMR

We have measured the thickness of the pre-molten surface layer that appears at the interface of octamethylcyclotetrasiloxane (OMCTS) to the matrix in controlled pore glasses with pore diameters ranging 7.5-73 nm. Except for the glass with the largest pores, the layer thickness data for different pore diameters fall on a single master curve when plotted versus Tm - T, where Tm is the size-dependent volume melting point of the pore-confined OMCTS. Hence, at a single temperature, the surface layer thickness depends strongly on the curvature of the pore wall and therefore that of the solid-liquid interface. For temperatures where it exceeds two monolayers, the layer thickness depends logarithmically on Tm - T; for the glass with the largest pores, this turns into a power law with the exponent -1/2. The results are interpreted in terms of a continuous model of the solid-liquid interface with an arbitrary curvature. Because OMCTS is a weakly polar molecule with close to spherical shape, our data also lend themselves to Lennard-Jones type simulations.

Dynamics of graphite flake on a liquid

One-directional motion, where graphite flakes are driven by a nanotip on an octamethylcyclotetrasiloxane (OMCTS) liquid surface, is presented. A transition from quasiperiodic to chaotic motions occurs in the dynamics of a graphite flake when its velocity is increased. The dynamics of graphite flakes pulled by the nanotip on an OMCTS liquid surface can be treated as that of a nanobody on a liquid.

Preparation and characterization of polysiloxane–polyacrylates composite lattices by two seeded emulsion polymerization and their film properties

AbstractGamma ray‐induced seeded emulsion polymerization of methyl methacrylate and butyl acrylate was carried out in the presence of polymerizable polysiloxane seed latex, which was obtained by the ring‐opening copolymerization of octamethyl cyclotetrasiloxane (D4) and tetramethyl tetravinyl cyclotetrasiloxane(VD4) catalyzed by dodecylbenzene sulfonic acid (DBSA). After the first seeded polymerization, 3‐methacryloxylpropyltrimethoxylsilane (MPS) was added for the second seeded polymerization. The conversion–time curve showed that the first seeded polymerization rate was accelerated much by the polysiloxane seed latex. The final composite lattices also showed good storage stability, mechanical stability, and high electrolyte resistance ability. The morphology of the composite latex particles was found to be a quite uniform fine structure by transmission electron microscopy (TEM). The graft of polyacrylates onto polysiloxane and hydrolysis of MPS were confirmed by Fourier transform infrared (FT‐IR) spectroscopy. The mechanical performance, water absorption ratio, surface properties, and transparency of the latex films were also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1406–1411, 2007