Cyclohexane Vapor Research Articles

Morphology response by solvent and vapour annealing using polystyrene/poly(methyl methacrylate) brushes

The aim of this work is to evaluate the switching behaviour of polymer brushes. Polystyrene (PS) and poly(methyl methacrylate) (PMMA) were grafted onto a silicon surface by radical polymerization where molecular weight of PMMA to be higher than molecular weight of PS. The morphology of polymer brushes was switched by modifying the surrounding environment using solvent and vapour annealing treatments. As selective solvent for PMMA acetic acid was chosen and cyclohexane at 55°C for PS. Using acetic acid as solvent or its vapours PS/PMMA brushes adopted dimple-like morphology composed mostly by PMMA chains resulting in contact angle values (~74° and 76°, respectively). In the case of cyclohexane, surface topography changed and the outermost layer was occupied by PS and PMMA chains. In this case, the topography adopted a slightly rough surface. In addition, PS/PMMA showed a smoother surface after treated with cyclohexane vapour annealing due to poor solubility of PS in cyclohexane at room temperature. Contact angle values changed from 85° with cyclohexane solvent annealing to 80° with cyclohexane vapour annealing suggesting that switching behaviour did not completed.

Derivation of the permeation equation for diffusion of gases and vapors in flat membrane by using Laplace transform

Generally, the model of forced diffusion of a penetrant through nonporous polymer membranes can be quantitatively described by a partial differential equation of parabolic type, which is known as Fick’s second law. In this article, the detailed explanation of application of the integral transform method (especially Laplace transform) for the solution of Fick’s second law at given initial and boundary conditions is presented. Obtained final expression for the concentration profile inside a flat membrane and the diffusion flux through a membrane were verified on permeability data of carbon dioxide and cyclohexane through low-density polyethylene membrane. While CO2 permeation data can be successfully fitted by obtained model, in the case of cyclohexane vapors, when the diffusion coefficient cannot be supposed to be constant due to strong polymer–penetrant interactions (swelling), the agreement between model and experimental data is lower.

A Porous 4-Fold-Interpenetrated Chiral Framework Exhibiting Vapochromism, Single-Crystal-to-Single-Crystal Solvent Exchange, Gas Sorption, and a Poisoning Effect

The synthesis and characterization of a 4-fold-interpenetrated pseudodiamond metal-organic framework (MOF), Co(II)(pybz)2·2DMF [pybz = 4-(4-pyridyl)benzoate], are reported. N,N-Dimethylformamide (DMF) of the channels can be removed to give the porous framework, and it can also be exchanged for methanol, ethanol, benzene, and cyclohexane. It is a rare example of a stable MOF based on a single octahedral building unit. The single-crystal structures of Co(II)(pybz)2·2DMF, Co(II)(pybz)2, Co(II)(pybz)2·4MeOH, and Co(II)(pybz)2·2.5EtOH have been successfully determined. In all of them, the framework is marginally modified and contains a highly distorted and strained octahedral node of cobalt with two pyridine nitrogen atoms and two chelate carboxylate groups. In air, the crystals of Co(II)(pybz)2·2DMF readily change color from claret red to light pink. Thermogravimetric analysis and Raman spectroscopy indicate a change in coordination, where the carboxylate becomes monodentate and an additional two water molecules are coordinated to each cobalt atom. In a dry solvent, this transformation does not take place. Tests show that Co(II)(pybz)2 may be a more efficient drying agent than silica gel and anhydrous CuSO4. The desolvated Co(II)(pybz)2 can absorb several gases such as CO2, N2, H2, and CH4 and also vapors of methanol, ethanol, benzene, and cyclohexane. If Co(II)(pybz)2 is exposed to air and followed by reactivation, its sorption capacity is considerably reduced, which we associate with a poisoning effect. Because of the long distance between the cobalt atoms in the structure, the magnetic properties are those of a paramagnet.

Thin Film Block Copolymer Assembly in Mixtures of Highly Selective Solvents

Perpendicular orientation of block copolymer (BCP) domains in thin films is generally preferred over parallel orientation for lithographic applications. [1] Thermal annealing can be used to promote this orientation, but often requires a top coat since one block will typically wet the air interface. [2] Solvent annealing is an attractive alternative for achieving perpendicular orientation of the domains by neutralizing the surface energy of the air interface. Many examples of using solvent annealing in BCP thin films exist in the literature, involving domain non-selective [3] and selective [4] solvents. Silicon-containing polymers are desirable for lithographic applications because their high chi-parameters and high etch selectivity allow them to self-assemble into small domains and be transferred easily into an underlying substrate by oxygen etching. [5,6] This paper describes the process used to solvent anneal a new silicon-containing polymer, poly(trimethylsilyl styrene-b-lactide) (PTMSS-b-PLA) using cyclohexane vapor, a solvent that preferentially swells the PTMSS domain.

Functional microporous polyimides based on sulfonated binaphthalene dianhydride for uptake and separation of carbon dioxide and vapors

A series of novel microporous polyimides (SMPIs) were synthesized from 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride (BTDA), 6,6′-disulfonic-4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride (SBTDA) and tetrakis(4-aminophenyl)methane (TAPM). The non-sulfonated SMPI-0 (SMPI-x, where “x” is the molar percent of SBTDA) exhibited a BET surface area of 574 m2 g−1 and a CO2 uptake of 2.53 mmol g−1, while sulfonated samples, i.e. SMPI-10, SMPI-50 and SMPI-100, possessed relatively low BET surface areas (from 23 to 112 m2 g−1) but high CO2 capture capacities (from 2.82 to 3.15 mmol g−1) and CO2/N2 selectivities (from 32 to 57). With the increase of sulfonation degree, the polymers were graded from hydrophobic to hydrophilic. Hydrophobic SMPI-0 and SMPI-10 adsorbed a large amount of non-polar benzene (134.7 wt% for SMPI-0 and 104.7 wt% for SMPI-10) and cyclohexane (42.5 wt% for SMPI-0 and 42.8 wt% for SMPI-10) vapor, whereas hydrophilic SMPI-50 and SMPI-100 adsorbed more polar methanol (68.5 wt% for SMPI-50 and 72.2 wt% for SMPI-100).

Stepwise Swelling of a Thin Film of Lamellae-Forming Poly(styrene-b-butadiene) in Cyclohexane Vapor

We investigated the swelling of a thin film of lamellae-forming poly(styrene-b-butadiene) in cyclohexane vapor. The vapor pressure and thus the degree of swelling of the film are increased in a ste...

Formation of a nanohybrid composite between mesostructured cellular silica foam and microporous copper trimesate

A metal-organic framework HKUST-1 or Cu3(BTC)2 was synthesized in mesopores of a COOH functionalized mesostructured cellular silica foam (MCF(M)-COOH), resulting in a hydrophobic nanocomposite. The Cu3(BTC)2 formed in the MCF(M)-COOH has been prepared by a microwave method with sequential incorporation of copper nitrate and 1,3,5-benzenetricarboxylic acid in a water/ethanol mixture containing the MCF(M)-COOH. The nanocomposite was characterized by XRD, BET, FT-IR, TEM and solid state 13C NMR. The nanocomposite had a higher hydrophobic property than pure Cu3(BTC)2 and MCF(M)-COOH as a result of their hybridization. Moreover, the formation of the nanocomposite increased the sorption rate of cyclohexane vapor as compared with those of pure Cu3(BTC)2 and MCF(M)-COOH due to the increased hydrophobicity.

Lanthanide homometallic and d–f heterometallic MOFs from the same tripodal ligand: structural comparison, one photon (OP) vs. two photon (TP) luminescence and selective guest adsorption behavior

In this paper, we report the design of a new functionalized tripodal ligand triCB-NTB (4,4′,4′′-(2,2′,2′′-nitrilotris(methylene)tris(1H-benzo[d]imidazole-2,1-diyl)tris(methylene))tribenzoic acid) and its assembly of Eu(III) homometallic or Zn(II)-Eu(III) heterometallic lanthanide-based metal–organic frameworks (MOFs). C3 symmetric Eu(III) center is achieved in the homometallic MOF, [Eu(triCB-NTB)]·DMAc·4H2O (1). The C3 axis of the three coordinated imino N atoms on the propeller-extended central triCB-NTB ligand coincides with the C3 axis that directs the three para-methyl carboxylic benzene arms on three surrounding ligands coordinating with the central Eu(III) simultaneously. Therefore, a (6, 3) pattern is formed in the framework with relatively large porosity. In the Zn-Eu heterometallic framework, [EuZn(triCB-NTB)(H2O)(Cl)2]·2DMAc·H2O (2), the N atoms on the triCB-NTB are coordinated with Zn(II) and the carboxylic O atoms are coordinated with Eu(III). A paddle-wheel linked Eu(III)2 cluster is formed and 1D loop-and-chain structure is obtained. Two ligands, two Zn(II) ions and two Eu(III)2 clusters constitute one box-like unit on the loop chain. Due to the non-inversion symmetry imposed on the central Eu(III) and the large polarizability of the ligand, both one photon (OP) luminescence based on the energy transfer from the ligand to Eu3+ and two photon (TP) luminescence based on the hypersensitive transition of the Eu3+ ions are observed in the two lanthanide-based MOFs. This satisfies the urgent needs of multi-mode luminescent lanthanide complex. Simultaneously, N2 gas and selective vapor adsorptions were also detected in the porous structure of complexes 1 and 2 due to their benzene-filled channels. The six-pointed-star like cavities in 1 can let the gas and vapor molecules go in and out smoothly subject to changes in the pressure, while the narrower and more irregular channels in 2 show irreversible adsorption behavior for benzene and cyclohexane vapor molecules in vacuum under room temperature.

Influence of adsorption on the photocatalytic properties of TiO2/AC composite materials in the acetone and cyclohexane vapor photooxidation reactions

► A series of TiO 2 /AC photocatalysts with different TiO 2 contents were synthesized. ► Acetone and cyclohexane vapor photooxidation were studied in static and flow reactors. ► Adsorptivity of TiO 2 /AC catalysts was increased and activity decreased in the sequence TiO 2 , TiO 2 /AC, TiO 2 + AC. ► Reagents surface transfer is responsible for increase of TiO 2 /AC photoactivity. A series of TiO 2 /AC composite photocatalysts with various TiO 2 contents was prepared by thermal hydrolysis method of a TiOSO 4 water solution in the presence of activated carbon particles. XRD, SEM and BET methods revealed that in all cases deposited TiO 2 is an anatase with ∼170 m 2 /g specific surface area. All samples were tested in gaseous acetone and cyclohexane vapor photocatalytic oxidation in static and continuous flow reactors. Complete photocatalytic mineralization of both model pollutants without formation of gaseous intermediates was observed. Only TiO 2 /AC catalysts with TiO 2 content higher than 50% demonstrated good photocatalytic activity. The same amounts of individual TiO 2 and AC powders as in the case of 70%-TiO 2 /AC composite photocatalyst were placed separately in the static reactor and kinetic curves of the cyclohexane photocatalytic oxidation were compared for both cases. When TiO 2 and AC were used separately complete mineralization of cyclohexane was not observed even after 4 h of the PCO. Whereas in the case of 70%-TiO 2 /AC sample expected CO 2 level was almost achieved after 120 min. The most likely reason of this difference is the absence of reagents and intermediates surface transfer between separated individual TiO 2 and AC powders. L.-H. kinetic model was used to describe experimental data in the flow reactor. Obtained results demonstrated that effective adsorption constants for TiO 2 /AC photocatalysts were about 2 times higher than for pure TiO 2 . Model of TiO 2 /AC composite photocatalyst with increased photocatalytic and adsorption properties was suggested.

Detection of Pure Chemical Vapors in a Thermally Cycled Porous Silica Photonic Crystal

The condensation and evaporation of vapors of isopropanol, heptane, and cyclohexane in mesoporous silica photonic crystals are monitored by optical reflection spectroscopy as a function of sensor temperature. The spectral position of the stop band shifts to the red upon analyte adsorption, and it shifts to the blue as the sensor is heated and analyte evaporates from the porous nanostructure. The hysteresis of the optical response as the temperature of the sensor is cycled between 25 and 80 °C is characteristic of each analyte for partial pressures between 0 and 7.5 Torr. These characteristic hysteresis loops allow identification of the three analytes. The temporal response of the sensor is studied as a function of heating rate and analyte concentration in a flowing stream of analyte vapor, and it is compared with the equilibrium adsorption isotherms of the sensor. The ability of the temporal data to identify the analytes is attributed to differences in diffusion and adsorption properties of each analyte within the mesoporous silica sensor.

Transition between crystallization and microphase separation in PS-b-PEO thin film Influenced by solvent vapor selectivity

In this paper, the effect of solvent selectivity on the transition between crystallization and microphase separation of the semicrystalline diblock copolymer polystyrene-b-poly(ethylene oxide) (PS-b-PEO) thin films was investigated. Square-shaped crystals formed due to lower barrier of crystalline nucleation in both poor and good solvent vapor for PEO. However, in poor solvent (cyclohexane) vapor for PEO, crystalline structure changed to microphase separated structure in the square platelets due to the high mobility of PS blocks. Then breakout crystals dominated the morphology of the film. While, in good solvent (water) vapor for PEO, competition between nucleation and dissolution of crystallization caused the formation of imperfect crystals. Then imperfect crystals dissolved due to the high mobility of PEO blocks, and microphase separation dominated the morphology of the film. The gain of free volume of soluble block and the low swelling of crystalline block are keys for microphase separation and crystallization, respectively.

Structural rearrangements in a lamellar diblock copolymer thin film during treatment with saturated solvent vapor.

We have investigated the structural changes in thin films of lamellar poly(styrene-b-butadiene) diblock copolymers during treatment with saturated cyclohexane vapor, a solvent slightly selective for polybutadiene. Using real-time, in-situ grazing-incidence small-angle X-ray scattering (GISAXS), the swelling and the rearrangement of the lamellae were investigated with a time resolution of a few seconds, and the underlying processes on the molecular level were identified. After a few minutes in vapor, a transient state with a more well-defined and more long-range ordered lamellar orientation was encountered. Additional parallel lamellae formed which we attribute to the increased degree of coiling of the polymers in the swollen state. Eventually, the film became disordered. These changes are attributed to the increased mobility of the swollen polymers and the gradually decreasing segment-segment interaction parameter in the film as solvent is absorbed.

Carbon Deposit Formation in Normal-Pressure Electrical Discharges in Hydrocarbons

The process of synthesis of carbon deposits from hydrocarbon vapours in low-current electrical-discharge plasma was investigated in the paper. The carbon deposits were effectively synthesised in discharge of positive polarity generated between a stainless steel needle and a plate made of nickel alloy, for the discharge current ranged from 0.1 mA up to 3 mA. The experiments were carried out at normal pressure in cyclohexane vapours with argon as carrier gas. The process of synthesis of carbon deposits was investigated using optical emission spectroscopy.

Carbon fiber formation in electrical discharges in hydrocarbons

The process of synthesis of carbon fiber from hydrocarbon vapours in low-current electrical-discharge plasma was investigated in the paper. The carbon fibers were effectively synthesised in discharge of positive polarity generated between a stainless steel needle and a plate made of nickel alloy, for the discharge current ranged from 1 mA up to 3 mA. The experiments were carried out at normal pressure in cyclohexane vapours with argon as carrier gas. The diameter of produced fibers varied from about 20 to 70 μm. The growth rate of the fiber was about 0.25 mm/s.

AFM Tip Hammering Nanolithography

Nanolithography at low cost and high speed is made possible by using a vibrating AFM tip in tapping-mode as a nanohammer to forge polystyrene-block-poly(ethylene/butylenes)-block-polystyrene triblock copolymer monolayer thin films after annealing to transform their microstructures from as-cast poorly ordered cylinders into well-ordered hexagonal spheres. Annealing is accomplished in cyclohexane vapor, a selective solvent for the majority poly(ethylene/butylenes) block. Experimental results demonstrate that such structure-tailored thin films enable macroscopic AFM tip writing to be performed in their surface; imprinted and embossed patterns can be generated with a sub-20-nm line-width resolution. In addition, it is found that the lithographic patterns generated can be erased within 5 min by thermal annealing at 70 degrees C, and if necessary the erasion process can be expedited by increasing the annealing temperature.

Solvent-Induced Morphology of the Binary Mixture of Diblock Copolymer in Thin Film: The Block Length and Composition Dependence of Morphology

A series of binary SB blend samples with various overall volume fraction of PS (Phi(PS)) and different discrete distribution of the block length (denoted as d(PS) or d(PB)) were prepared by mixing various asymmetric poly(styrene)-block-poly(butadiene) (SB) block copolymers with a symmetric SB block copolymer. The influences of the external solvent field, composition, and the block length distribution on the morphologies of the blends in the thin films were investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The experimental results revealed that after solvent annealing, the interface of the blend thin films depended mainly on the cooperative effects of the annealing solvent and the inherently interfacial curvature of the blends. Upon exposure to the saturated vapor of cyclohexane, which has preferential affinity for the PB block, a "threshold" of Phi(PS) (approximate 0.635-0.707) was found. Below such threshold, the influence of the annealing solvent played an important role on the interfacial curvature of the blend thin film. The morphologies of the thin films and the long-range order of the structures were related to the value of d(PS), regardless of the change of d(PB).

Friction and Capillary Forces at the Nanometer Scale

Frictional behaviors between mica surfaces have been investigated with the Surface Force Apparatus under various relative vapor pressures (rvp) of both water and cyclohexane. Stick-slip frictional behaviors were observed only under cyclohexane vapor. At rvp of 20%, stick-slip appeared but faded out with sliding time. At a rvp greater than 50%, the stick-slip pattern was stable without fading. Dependence of sliding velocity and applied load on stick-slip motions indicated that the mechanism of the stick-slips in the high rvp (stable stick-slip) region differs from that of the region of fading stick-slip. In the rvp range between 20% and 50%, where the fading stick-slip is observed, the condensate liquid seeps into the contact area under the influence of the applied tangential force and thus triggers the slip motion. Due to the small condensation volume, the liquid condensed around the contact area is exhausted in the process of repeating stick-slip. At a rvp greater than 50%, where stable sick-slip is observed, the stick-slip caused by essentially the same origin as that observed with mica surfaces sliding in bulk cyclohexane liquid. In vapor, the stick-slip is enhanced by the increase of the negative Laplace pressure in the capillary condensed liquid, thereby forcing the surfaces toward each other more strongly with decreasing rvp. [DOI: 10.1380/ejssnt.2009.137]

Two-Dimensional Ordering in Block Copolymer Monolayer Thin Films upon Selective Solvent Annealing

The morphology evolution of poly(styrene−ethylene/butylene−styrene) monolayer thin films upon “annealing” in the vapor of cyclohexane, a selective solvent for majority poly(ethylene/butylene) block, was investigated by atomic force microscopy (AFM). The pathway information on the two-dimensional ordering from poorly ordered short cylinders, to aligned long cylinders, and then to well-ordered hexagonal spheres was revealed by repeatedly taking images of the same marked area of 2 × 2 μm2 on the sample surface after ex-situ annealing treatments. It was found that the whole ordering process consists of (1) the cyclic transitions between poorly ordered cylinders and semidisordered phase via poorly ordered spheres, during which the orderliness of cylinders gradually improves, and (2) the pinching-off from enough-ordered cylinders into hex-spheres. It was noticed that part of the ordering takes place in the way of nucleation and growth, but it seems that the remaining part of ordering involves spinodal and decom...

Effect of the Nature of Annealing Solvent on the Morphology of Diblock Copolymer Blend Thin Films

The morphologies and structures for the thin film of blend systems consisting of two asymmetric polystyrene-block-polybutadiene (SB) diblock copolymers induced by annealing in the vapor of different solvents, namely, cyclohexane, benzene, and heptane, which have different selectivity or preferential affinity for a certain block, were investigated by tapping mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). The results revealed that even a slight preferential affinity of good solvent for one block would strongly alter the morphology of the blend thin film. An interesting structure of so-called “spheres-between-cylinders” (“sph-b-cyl”) was obtained when annealing the blend thin film with a weight fraction ratio of 50/50 of the two components in the saturated vapor of cyclohexane, which is a good solvent for PB and a (near) ϑ solvent for PS at 34.5 °C. The influence of the kinetic factors, such as the annealing time and vapor pressure of the solvent, together with the factors of ...

On the modified Tabor parameter for the JKR–DMT transition in the presence of a liquid meniscus

The JKR, DMT, Maugis models and Tabor parameter for contact under normal loading have been developed based mainly on solid-solid (van der Waals) interactions. In this case, the characteristic length scale for the adhesive forces in the Tabor parameter is the equilibrium interatomic spacing. However, for contact in humid environments, where a liquid meniscus may be present, capillary forces with a longer force range related to the Kelvin radius dominate. Fogden and White [J. Colloid Interface Sci. 138 (1990) 414] introduced a parameter that includes the Kelvin radius for the JKR-DMT transition. This topic was also addressed by Maugis and Gauthier-Manuel [J. Adhes. Sci. Technol. 8 (1994) 1311] who included capillary effects within the frame work that Maugis had previously established. The parameters introduced by Fogden and White and Maugis and Gauthier-Manuel can be viewed as a modified Tabor parameter for the JKR-DMT transition. In the present work, the Kelvin equation linking the Kelvin radius and the relative humidity was explicitly included in the modified Tabor parameter. This provided a quantitative description of the JKR-DMT transition in terms of the relative humidity. This parameter was examined via load and contact radius measurements, where the latter were obtained from Bowden and Tabor's assumption that the friction force f=tauA. The friction experiments were conducted at two different humidity levels using a newly-developed mesoscale friction tester (MFT), which provides a very wide range of contact radii. The modified Tabor parameter was used to reexamine data from pull-off experiments in water and cyclohexane vapor environments [L.R. Fisher, J.N. Israelachvili, Colloids Surf. 3 (1981) 303 and H.K. Christenson, J. Colloid Interface Sci. 121 (1988) 170]. Finally, guidelines are presented for the appropriate choice of contact mechanics models to be used in interpreting data from SFA and AFM experiments in humid environments.