Octamethylcyclotetrasiloxane Research Articles

High-rate plasma-deposited SiO2 films for surface passivation of crystalline silicon

Si O 2 films were deposited by means of the expanding thermal plasma technique at rates in the range of 0.4–1.4μm∕min using an argon∕oxygen∕octamethylcyclotetrasiloxane (OMCTS) gas mixture. The film composition was studied by means of various optical and nuclear profiling techniques. The films deposited with a low OMCTS to oxygen ratio showed no residual carbon and a low hydrogen content of ∼2% with a refractive index close to thermal oxide. For a higher OMCTS to oxygen ratio a carbon content of ∼4% was detected in the films and the refractive index increased to 1.67. The surface passivation of the SiO2 films was tested on high quality crystalline silicon. The films yielded an excellent level of surface passivation for plasma-deposited SiO2 films with an effective surface recombination velocity of 54cm∕s on 1.3Ωcm n-type float zone crystalline silicon substrates after a 15min forming gas anneal at 600°C.

Determination of accurate surface tensions of maleimide copolymers containing fluorinated side chain from contact angle measurements

Surface energetics of two fluorinated maleimide copolymers containing fluorinated side chain, i.e., poly(ethene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ETMF) and poly(octadecene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ODMF), are studied by contact angle measurements with 10 liquids consisting of fairly bulky molecules. Because of the inertness of octamethylcyclotetrasiloxane (OMCTS) and decamethylcyclopentasiloxane (DMCPS) molecules, their contact angles are used to determine the surface tension of the two polymers. It is found that other liquids show specific interactions with the ETMF films, and their contact angles deviate from a smooth curve that represents the surface tension of ETMF, i.e., 11.00 mJ/m2. On ODMF surfaces, only OMCTS and DMCPS yield useful contact angles. Other liquids either dissolve the polymer film or show a slip-stick pattern. This finding is discussed in terms of interactions between segments of the polymer chains and the test liquids. OMCTS and DMCPS are suggested as the appropriate probe liquids, meeting specific criteria necessary for the determination of accurate surface tension of fluoropolymers.

Badanie zaleznosci czasu relaksacji podluznej w metodzie 1H NMR od struktury polidimetylosiloksanow i optymalizacja parametrow rejestracji widm

The results of investigations of the effects of size and shape of molecules of oligomers: hexamethyldisiloxane (HMDS) dimer, octamethylcyclotetrasiloxane (OMCTS) tetramer and polydimethylsiloxane, characterized by kineticviscosity ∼10 cSt (PDMS10), as well as of two linear polydimethylsiloxanes [one of viscosity about 300 cSt (PDMS300) the other of about 1000 cSt (PDMS1000)] on longitudinal relaxation time (T 1 ) in 1 H NMR method were presented. The samples were prepared by dissolution of the substances mentioned in the mixture of carbon tetrachloride with deuterated benzene (Table 2). It was found that T 1 time did not significantly depend on the analyte concentration in the sample and was practically independent on the mutual ratio of the solvents used. It was observed the increase in the chain length of PDMS caused T 1 decrease while cyclization of the molecule did not influence its value (Table 2). The investigations showed that to obtain credible results of quantitative PDMS determination it was necessary to use the optimal values of spectra registration parameters, especially delay time (t d ) and data acquisition time (t a ) which should be 15 s and 5 s, respectively.

Preparation and characterization of polysiloxane-poly(butyl acrylate–styrene) composite latices and their film properties

Gamma ray induced seeded emulsion co-polymerization of styrene and butyl acrylate was carried out in the presence of polymerizable polysiloxane seed latex which was obtained by the ring opening co-polymerization of octamethyl cyclotetrasiloxane (D 4) and tetramethyl tetravinyl cyclotetrasiloxane (VD 4) catalyzed by dodecylbenzene sulphonic acid (DBSA). A series of polysiloxane seed latices with different molecular weight, vinyl content, and particle size were used. The conversion–time curve showed that the polymerization rate was accelerated much by the seed latex. The obtained composite latices 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 microscope (TEM). The graft polymerization between polymerizable polysiloxane and butyl acrylate or styrene was confirmed by the Fourier transform infrared spectroscopy (FT-IR) and the graft efficiency was also studied. The influence of seed content, molecular weight, vinyl content of the polysiloxane and seed latex particles size to the mechanical performance, water absorption ratio, surface properties, transparency and UV resistance of the latex films, was also investigated.

Interpretation of contact angle measurements on two different fluoropolymers for the determination of solid surface tension

Contact angle measurements with a large number of liquids on the semi-fluorinated acryl polymer EGC-1700 films are reported. The surface tension was determined to be γsv=13.84 mJ/m2 from contact angles of octamethylcyclotetrasiloxane (OMCTS) and decamethylcyclopentasiloxane (DMCPS). Inertness of these two liquids makes them ideal for determination of surface tension of low-energy fluoropolymers. On the other hand, contact angles of many other liquids deviated somewhat from a smooth contact angle pattern that represents the EGC-1700 surface tension. It is argued that noninertness of the molecules of these liquids gives rise to specific interactions with the polymer film, causing the deviations. Furthermore, contact angles of a series of n-alkanes (n-hexane to n-hexadecane) showed systematic deviations from this curve, similar to the trend observed for n-alkanes/Teflon AF 1600 systems studied earlier. Adsorption of vapor of short-chain liquids onto the polymer film caused their contact angles to fall above the γsv=13.84 mJ/m2 curve, and a parallel alignment of molecules of the long-chain n-alkanes in the vicinity of the solid was the explanation for the deviation of their contact angles below it. It is found that vapor adsorption effect is more significant in the case of Teflon AF 1600, while the alignment of liquid molecules close to the surface is more pronounced for EGC-1700.

Nanofluidics: Molecularly thin lubricant layers under confinement

Confined liquid films with a thickness in the range of a few molecular diameters exhibit different mechanical properties than in the bulk. With the technique of a 2-dimensional (2D) imaging surface forces apparatus (SFA) we investigated in detail the layer by layer thinning of a thin liquid film confined between two atomically smooth surfaces upon pressing them towards each other with increasing load. The dynamics of a series of subsequent squeeze-out processes of individual layers were analyzed. Using a simple hydrodynamic model, we extracted the thickness-dependence of the viscosity. For the system investigated here—the model lubricant Octamethylcyclotetrasiloxane (OMCTS) confined between ultraclean, recleaved mica surfaces—we found that the viscosity increased by a factor of 10 with decreasing the film thickness from 6 to 2 layers. We decomposed the friction into two components, one describing the sliding of liquid layers on top of the substrates, and the other describing liquid-on-liquid sliding. The latter contribution was found to agree closely with expectations based on the bulk viscosity, whereas the former was approximately 35 times higher for the present system.

Preparation and characterization of polysiloxane–polyacrylates composite latices and their film properties

AbstractGamma‐ray induced seeded emulsion polymerization of methyl methacrylate and butyl acrylate was carried out in the presence of a polymerizable polysiloxane seed latex, obtained by ring‐opening copolymerization of octamethyl cyclotetrasiloxane (D4) and tetramethyl tetravinyl cyclotetrasiloxane (VD4), catalyzed by dodecylbenzene sulfonic acid (DBSA). A series of polysiloxane seed latices with different molecular weights, vinyl contents and particle sizes was used. The conversion–time curve showed that the polymerization rate was accelerated significantly by the seed latex. The obtained composite latices also showed good storage stability, mechanical stability and high electrolyte resistance ability. By using transmission electron microscopy (TEM), the morphology of the composite latex particles was found to display a quite uniform fine structure. The graft polymerization reactions between the polymerizable polysiloxane and the acrylates were confirmed by Fourier‐transform infrared spectroscopy (FT‐IR) and the graft efficiencies were also studied. The influence of seed content, molecular weight, vinyl content of the polysiloxane and seed latex particles size on the mechanical performance, water absorption ratio, surface properties and transparency of the latex films was also investigated. It was found that the seed content and particles size greatly affect the mechanical performance, water absorption ratio and transparency of the latex films. Copyright © 2005 Society of Chemical Industry

How Confined Lubricants Diffuse During Shear

The translational diffusion of a fluorescent dye embedded at a dilute concentration in a confined fluid was compared at rest and during shear. The fluid, octamethylcyclotetrasiloxane (OMCTS), was confined between step-free muscovite mica to thickness 3-4 layers. Fluorescence correlation spectroscopy showed that the time scales of intensity-intensity autocorrelation functions were essentially the same during shear and at rest, except they were faster during shear by a factor of 2 to 5. This dynamical probe of how liquids order in molecularly thin films fails to support the hypothesis that shear produced a melting transition.

Contact angle measurements with liquids consisting of bulky molecules.

Well-measured contact angles with different solid-liquid systems fall approximately on smooth patterns when plotted versus liquid surface tension. However, there are deviations of 1 degrees -3 degrees , which are outside the error limits. It is the purpose of this paper to elucidate the reasons for such deviations. Two types of liquids were selected for advancing contact angle measurements on Teflon AF 1600 coated surfaces: a series of n-alkanes ranging from n-hexane to n-hexadecane and five liquids consisting of bulky molecules, octamethylcyclotetrasiloxane (OMCTS), methyl salicylate, tetralin, cis-decalin, and octamethyltrisiloxane (OMTS). It was found that contact angles of the liquids with bulky molecules fall on a perfectly smooth curve corresponding to a solid surface tension of 13.64 +/- 0.1 mJ/m2. However, contact angles of n-alkanes deviated from this curve by up to 3 degrees in a complicated fashion. The observed trend suggests that more than one mechanism is responsible for the deviations. Substrate-induced rearrangement of liquid molecules in the close vicinity of the surface in the case of long-chain n-alkanes and adsorption of vapor onto the solid surface in the case of short-chain n-alkanes are the most likely explanations. The results suggest that liquids with bulky molecules appear to be suitable for contact angle measurements to characterize energetics of polymeric surfaces.

Plasma-assisted growth of bilayer silicon-containing coatings for hardness and corrosion resistance

Hard corrosion-resistant bilayer coatings were grown in a high-density microwave electron cyclotron resonance discharge. The bilayer coatings consist of a relatively soft (0.6–1.5 GPa) polymer-like coating as the adherent bottom layer and a much harder (8–12 GPa) top layer. The polymer underlayers were grown from 100% octamethylcyclotetrasiloxane (OMCTS) while the hard top layer was either silicon dioxide grown from OMCTS in an oxygen plasma or silicon nitride grown from hexamethyldisiloxane in an ammonia plasma. The bilayer structures combined high surface hardness values with good corrosion resistance, surviving 1800–2600 h in an ASTM B117 salt-fog corrosion test.

Pulse-modulated plasma-enhanced chemical vapor deposition of SiO 2 coatings from octamethylcyclotetrasiloxane

Silicon dioxide coatings can be grown at low substrate temperatures in a pulse-modulated microwave electron cyclotron resonance (ECR) oxygen plasma with octamethylcyclotetrasiloxane (OMCTS) as the organosilicon precursor. The 2.45 GHz microwave power was pulse-modulated with repetition frequencies of 20 Hz–20 kHz, duty ratios (pulse on-time/pulse period) from 25 to 100%, and peak microwave power from 800 to 2400 W. The coatings are SiO 2-like with Si:O ratios of approximately 3:4 and carbon percentages of 20–25%. Pulsed plasma deposition significantly lowers the deposition substrate temperature as the peak power and duty ratio decrease. With 1600 W input continuous microwave power, substrate temperatures were 140–150 °C after 10 min of deposition, while with a 50% pulse duty cycle and 1600 W peak power the temperature decreased to 90 °C. The coating hardness decreased with pulsed operation compared to continuous operation, unless the average microwave power levels were made equivalent. Deposition growth rates depended only weakly on the pulse repetition frequency and duty ratio, but increased strongly as the pulse peak power was raised. Pulsed deposition at 800 W peak power and 50% duty ratio gave a growth rate of 0.5–0.6 μm/min for all frequencies between 20 Hz and 20 kHz, increasing to 0.8–0.9 μm/min at 1600 W peak power.

Comparison of silicon dioxide layers grown from three polymethylsiloxane precursors in a high-density oxygen plasma

We have compared the elemental composition, growth rates, and hardness of silicon dioxide layers grown from hexamethyldisiloxane (HMDSO), octamethylcyclotetrasiloxane (OMCTS), and tetramethylcyclotetrasiloxane (TMCTS) in a high-density electron cyclotron resonance oxygen plasma. Hard colorless coatings could be grown from each precursor; coating composition, growth rates, and hardness depended strongly on the ratio of oxygen to precursor flow. At the highest O2/precursor flow ratios (4:1 for HMDSO and 8:1 for OMCTS and TMCTS), the coatings were SiO2-like with oxygen-to-silicon ratios close to 2:1 and carbon percentages as low as 12% for HMDSO, 3.4% for OMCTS, and 1.4% for TMCTS. Growth rates were 0.7–1.1 μm/min, initially increasing with the O2/precursor flow ratio; final coating thicknesses after 5 min were 3.5 μm to 5.5 μm. Coating hardness values generally increased with increasing O2/precursor flow ratio, attaining 6 GPa, 7.4 GPa, and 8.7 GPa for HMDSO, OMCTS, and TMCTS, respectively.

Dynamics of Partial Wetting and Dewetting of an Amorphous Fluoropolymer by Pure Liquids

We report velocity dependencies of dynamic contact angles for CCl4 and tert-butyl alcohol on the amorphous fluoropolymer AF 1600 and compare them with our previous results for octamethylcyclotetrasiloxane (OMCTS) on the same substrate. The molecules of these liquids have well-defined form and the solid surface is almost smooth and homogeneous, which enables checking the assumptions of the main theories of wetting dynamics. We find that the molecular-kinetic theory well represents the data for CCl4 in the characteristic cos ϑ/V scale but qualitatively disagrees with the experiment for tert-butyl alcohol and OMCTS at high velocities. The CCl4 data do not fulfill the requirement of the hydrodynamic theory for symmetric advancing and receding branches. For the other two systems, the hydrodynamic theory works better at high velocities, but the nonlinear initial sections of the ϑ3/V plots require consideration of the velocity dependence of the microscopic dynamic contact angle ϑc(V). This is done by the molecular-hydrodynamic theory accounting for both contact line and bulk viscous friction. This theory shows agreement with the experimental data in the entire velocity range for all systems compared. It fits the receding and advancing ϑ/V branches simultaneously, yielding unique values of the microscopic dynamic parameters λ, Ko,s, and Lc,max that do not depend on direction of the contact line motion. Only this theory describes the wetting−dewetting asymmetry observed for tert-butyl alcohol and OMCTS. However, it yields inadequately large values of λ and too small hopping frequencies Ko,s for CCl4 and tert-butyl alcohol. Such results, also reported previously, might mean that not λ and Ko,s but their combinations better serve for description of wetting dynamics. Here we analyze the characteristic molecular-kinetic velocity Vo,s = λKo,s and the coefficient of friction of a unit contact line length ξc = kT/Ko,sλ3 and find a significant difference between the studied systems.

Synthesis of Polyethylene Magnetic Nanoparticles

ABSTRACT Very low molecular weight polyethylene (average MW 700 g/mole) magnetic nanocomposite particles were synthesized by nonsolvent and temperature induced crystallization along with ultrasonication. The particles are further coated with poly dl-lactic acid to functionalize the polyethylene particles for biomedical applications. A solvent-nonsolvent emulsion was made with polyethylene and surface modified iron oxide and was raised to very high temperature followed by rapid cooling. Decalin and octamethylcyclotetrasiloxane (OMCTS) were used as solvent and tetraglyme as nonsolvent. The synthesized particles were found to have two different types of morphology. Particles sizes can be varied depending on the choice of solvent, polymer concentration and amplitude of ultrasonication. The composite particles were characterized by scanning transmission electron microscopy. Magnetic properties of the composite particles were also studied.

In-Situ Mass Spectrometry Analyses of the Fragmentation of Linear and Cyclic Siloxanes in a Glow Discharge Compared with Ex-Situ FTIR Analyses of the Deposits

Mass Spectrometry (MS) analyses, up to 300 amu, were performed on linear hexamethyldisiloxane (HMDSO) and cyclic octamethylcyclotetrasiloxane (OMCTSO) vapors in low frequency plasmas (40 kHz). The fragmentation rates of the precursors, and possible oligomerization in the gas phase, depend on the plasma power. Two extreme plasma power conditions were compared: a high plasma power density and a low plasma power density, corresponding to silica-like and polymer-like film deposition conditions, respectively. The results of ex-situ Fourier transform infrared spectroscopy (FTIR) analyses can be explained by the plasma composition analyzed by MS.

Solvation Forces Using Sample-Modulation Atomic Force Microscopy

Oscillatory solvation forces in liquid were studied using off-resonance, low-amplitude, sample-modulation atomic force microscopy (AFM). Experiments were carried out with as-purchased tips and with tips modified by the attachment of 10-μm-sized glass beads on a highly oriented pyrolytic graphite (HOPG) substrate submerged in octamethylcyclotetrasiloxane (OMCTS). The sample-modulation response curves allow us to make a direct measurement of the interaction stiffness (force gradient) as a function of tip−sample distance, and we show how this technique is capable of measuring both repulsive and attractive solvation potentials in a single approach with the correct selection of cantilever stiffness. We calculate the solvation force by integrating the stiffness over the tip−sample distance, from which we see clear oscillatory behavior. Normalizing the force with the tip radius allows comparisons to be made between these results and previous surface force apparatus (SFA) data, which sometimes agree with SFA data...

Effect of interfacial liquid structuring on the coherence length in nanolubrication.

The degree of interfacial structuring of n-hexadecane and octamethylcyclotetrasiloxane (OMCTS) was measured within a nanometer boundary regime to silicon surfaces. Boundary-layer effects on lubricating sliding (in terms of a thermodynamic stress activation parameter) and the layer thickness were determined by scanning force microscopy. A 2.0+/-0.3 nm thick, entropically cooled layer was found for n-hexadecane. Measurements on spherically shaped OMCTS molecules exhibited only an interfacial "monolayer," and identified the molecular shape of n-hexadecane responsible for augmented interfacial structuring. Interfacial liquid structuring was found to reduce friction.

Phase behavior of low molecular weight polyethylenes from homogeneous and heterogeneous solutions

The pseudophase diagrams of solutions of low molecular weight polyethylene (PE) (number-average molecular weight < 1500 g/mol) in octamethyl cyclotetrasiloxane (OCTS) and isododecane (IS) were determined by direct observation of cloud points and optical microscopy. In addition, melting temperatures were also determined by differential scanning calorimetry. In the range of single liquid–solid transitions, the data conformed to the classical melting temperature composition relation as a result of the formation of extended crystallites. The melting data were used to determine the interaction parameter of the PE in OCTS (1.4 ± 0.1) and IS (0.22 ± 0.05). The structural and thermal properties of the gels formed by a competing liquid–liquid and liquid–solid phase separation, under nonequilibrium conditions, contrast with the properties of the crystals formed from a single liquid–solid transition. Coarsening within the liquid phases was evidenced by optical microscopy, and insights about the mechanism of the kinetics of the coarsening process are given. The temporal changes of the melting temperature of crystallites formed from the heterogeneous phase (OCTS) reveal dynamics within a nonequilibrium state. In contrast, the crystallites formed from a homogeneous solution (IS) showed negligible melting-temperature changes with time. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 878–889, 2002

The effect of liquid properties to contact angle hysteresis

Low-rate dynamic advancing and receding contact angles of 21 liquids from two homologous series (i.e. n-alkanes and 1-alcohols) and octamethylcyclotetrasiloxane (OMCTS) on FC-732-coated silicon wafer surfaces were measured by an automated Axisymmetric Drop Shape Analysis-Profile (ADSA-P). The receding contact angle was found to decrease with time, suggesting surface swelling and sorption. An initial receding angle ( θ ri), which theoretically represents the receding angle before sorption starts, was extrapolated back to time of zero contact ( t 0) by least-squares regression in each experiment. The contact angle hysteresis, i.e. the difference between advancing contact angle and θ ri, was found to decrease with increasing chain length of the liquid molecules for both the alkane and alcohol series. Contact angle hysteresis was found to vanish when the chain length was extrapolated to infinity. These results are plausible in terms of liquid sorption by the solid surface: very large molecules are unlikely to penetrate into the solid film. In order to reconfirm that contact angle hysteresis depends on molecular size of the liquid, contact angles of OMCTS, which is a bulky and quasi-spherical molecule, were measured. The hysteresis was found to be 4.1°, which is smaller than for any alkane or alcohol system. The molecular size-dependent hysteresis suggests that contact angle hysteresis phenomena are mainly due to liquid penetration and surface swelling, or at least liquid retention, even on this very hydrophobic surface. The fact that receding contact angles reflect liquid retention by the solid and are therefore not a property of the solid alone, supports the widespread practice of using only the advancing contact angles in studies of surface energetics of solids and disregarding the receding contact angles.

The mica slit-pore as a tool to control the orientation and distortion of simple liquid monolayers

Grand canonical ensemble Monte Carlo computer simulations have been used to study mono-layer octamethylcyclotetrasiloxane (OMCTS) and cyclohexane films confined between mica-like surfaces to determine the effect of the mica surfaces on the orientation and distortion of the films at different surface alignments. The film molecules are packed as a highly ordered lattice. The orientation of the lattice is fixed relative to the mica surfaces and depends on the size of the film molecule. Registry shifts distort the film lattice by effectively stretching it along a particular direction that depends on the size of the film molecule. For a particular registry, OMCTS and cyclohexane monolayers are stretched in perpendicular directions. Coupling between the monolayers and the mica surfaces generates a nonzero shear stress when the surfaces are out of alignment, but the film does not become disordered or melt. It is possible that precisely controlled solid surfaces could be used to create packed arrays of film molecules with desired orientation and degree of distortion that may be useful in nanotechnological applications.