Ethylene Oxide Molecules Research Articles

Molecular Dynamics Study of Guest–Host Hydrogen Bonding in Ethylene Oxide, Trimethylene Oxide, and Formaldehyde Structure I Clathrate Hydrates

Molecular dynamics simulations are used to study the guest–host hydrogen bonding and guest dynamics in the clathrate hydrate phases of trimethylene oxide (TMO), ethylene oxide (EO), and formaldehyde (FA) as polar guests. Two water models, the SPC/E and TIP4P/ice, were used in the simulations. Binary hydrates are constructed with these guests in the large 14-sided cages and methane placed in the small 12-sided cages of the structure sI clathrate hydrates. The results of these simulations are compared with the nonpolar guests with analogous structures, cyclobutane (CB), cyclopropane (CP), and ethane, respectively, for TMO, EO, and FA. These simulations show that oxygen atoms of the cyclic ethers and carbonyl oxygen of formaldehyde form hydrogen bonds to differing degrees with cage water hydrogen atoms. The TMO size is larger than that of the EO and FA molecules and the closer proximity of the atoms of this large guest to the cage water molecule enhances the probability of guest–host hydrogen bonding in the ...

Effects of different sterilization methods on the physico-chemical and bioresponsive properties of plasma-treated polycaprolactone films

For most tissue engineering applications, surface modification and sterilization of polymers are critical aspects determining the implant success. The first part of this study is thus dedicated to modifying polycaprolactone (PCL) surfaces via plasma treatment using a medium pressure dielectric barrier discharge, while the second part focuses on the sterilization of plasma-modified PCL. Chemical and physical surface changes are examined making use of water contact angle goniometry (WCA), x-ray photoelectron spectroscopy and atomic force microscopy. Bioresponsive properties are evaluated by performing cell culture tests. The results show that air and argon plasmas decrease the WCA significantly due to the incorporation of oxygen-containing functionalities onto the PCL surface, without modifying its morphology. Extended treatment times lead to PCL degradation, especially in the case of air plasma. In addition to surface modification, the plasma potential to sterilize PCL is studied with appropriate treatment times, but sterility has not been achieved so far. Therefore, plasma-modified films are subjected to UV, H2O2 plasma (HP) and ethylene oxide (EtO) sterilizations. UV exposure of 3 h does not alter the PCL physico-chemical properties. A decreased wettability is observed after EtO sterilization, attributable to the modification of PCL chain ends reacting with EtO molecules. HP sterilization increases the WCA of the plasma-treated samples, presumably due to the scission of the hydrophilic bonds generated during the prior plasma treatments. Moreover, HP modifies the PCL surface morphology. For all the sterilizations, an improved cell adhesion and proliferation is observed on plasma-treated films compared to untreated ones. EtO shows the lowest proliferation rate compared to HP and UV. Overall, of the three sterilizations, UV is the most effective, since the physical alterations provoked by HP might interfere with the structural integrity when it comes to 3D scaffolds, and the chemical modifications caused by EtO, in addition to its toxicity, interfere with PCL bioactivity.

Density-functional investigation of the geometric and electronic structure of ethylene oxide adsorbed on Si(100)

The geometric and electronic structures of the ethylene oxide (EO) molecule adsorbed on Si(100)-[Formula: see text] surface were investigated by using the density-functional theory calculations. All possible adsorbed structures were considered and it was found that only four adsorption structures are stable. The calculations of the formation energy revealed the most stable conformation and demonstrated that the nature of Si–O bond significantly affects the stability of adsorption systems. The analysis of corresponding electronic structures showed that two adsorbed structures are still semiconductor compounds but the other two are not. In particular, the EO after adsorbing was found to be connected via a ring-opening reaction where the molecule forms a five-membered ring together with the surface of dimer silicon atoms, and the produced five-membered ring is almost perpendicular to the silicon surface.

Wetting of Hydrophilic Electrospun Mats Produced by Blending SEBS with PEO–PPO–PEO Copolymers of Different Molecular Weight

The interaction of electrospun mats with water is critical for many possible applications, and the water contact angle on the surface is the parameter usually measured to characterize wetting. Although useful for hydrophobic surfaces, this approach is limited for hydrophilic mats, where wicking also has to be considered. In this case, it is still unclear how the fiber surface chemical composition and morphology will affect the wetting behavior of electrospun mats. In this work, wetting was studied with different hydrophilic membranes produced by blending thermoplastic elastomer poly(styrene)-b-poly(ethylene-butylene)-b-poly(styrene) (SEBS) with amphiphilic poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) molecules. Three different types of PEO-PPO-PEO, with different molar masses, PEO content, and physical form were used. The effect of these differences on the wetting behavior of the electrospun mats was evaluated by contact angle goniometry, wicking measurements, and different imaging techniques. X-ray photoelectron spectroscopy was used to characterize the surface chemical composition. The smaller molecules quickly saturated the surface at low concentrations, making the mats hydrophilic. The sheath of PEO-PPO-PEO also resulted in fast absorption of water, when comparing the saturated and nonsaturated surfaces. Longer PEO chain-ends seemed to hinder complete segregation and also led to a higher activation time when in contact with water. Liquid PEO-PPO-PEO was easily leached by water.

Intermolecular potential energy surface and thermophysical properties of ethylene oxide

A six-dimensional potential energy hypersurface (PES) for two interacting rigid ethylene oxide (C2H4O) molecules was determined from high-level quantum-chemical ab initio calculations. The counterpoise-corrected supermolecular approach at the MP2 and CCSD(T) levels of theory was utilized to determine interaction energies for 10178 configurations of two molecules. An analytical site-site potential function with 19 sites per ethylene oxide molecule was fitted to the interaction energies and fine tuned to agree with data for the second acoustic virial coefficient from accurate speed of sound measurements. The PES was validated by computing the second virial coefficient, shear viscosity, and thermal conductivity. The values of these properties are substantiated by the best experimental data as they tend to fall within the uncertainty intervals and also obey the experimental temperature functions, except for viscosity, where experimental data are insufficient. Due to the lack of reliable data, especially for the transport properties, our calculated values are currently the most accurate estimates for these properties of ethylene oxide.

Conformational Properties of a Polymer in an Ionic Liquid: Computer Simulations and Integral Equation Theory of a Coarse-Grained Model.

We study the conformational properties of polymers in room temperature ionic liquids using theory and simulations of a coarse-grained model. Atomistic simulations have shown that single poly(ethylene oxide) (PEO) molecules in the ionic liquid 1-butyl 3-methyl imidazolium tetrafluoroborate ([BMIM][BF4]) are expanded at room temperature (i.e., the radius of gyration, Rg), scales with molecular weight, Mw, as Rg ∼ Mw(0.9), instead of the expected self-avoiding walk behavior. The simulations were restricted to fairly short chains, however, which might not be in the true scaling regime. In this work, we investigate a coarse-grained model for the behavior of PEO in [BMIM][BF4]. We use existing force fields for PEO and [BMIM][BF4] and Lorentz–Berthelot mixing rules for the cross interactions. The coarse-grained model predicts that PEO collapses in the ionic liquid. We also present an integral equation theory for the structure of the ionic liquid and the conformation properties of the polymer. The theory is in excellent agreement with the simulation results. We conclude that the properties of polymers in ionic liquids are unusually sensitive to the details of the intermolecular interactions. The integral equation theory is sufficiently accurate to be a useful guide to computational work.

Threading of Ring Poly(ethylene oxide) Molecules by Linear Chains in the Melt.

We report results from an atomistic molecular dynamics simulation study of ring-linear poly(ethylene oxide) (PEO) melts followed by a topological reduction to ensembles of primitive paths and a detailed geometric analysis using vector calculus, which reveals considerable cyclic threading by the linear chains. The simulations have been conducted using ring-linear PEO blends of the same size, over a series of molecular lengths and compositions. For PEO melts characterized by molecular weight (MW) greater than 10044 g/mol, in particular, our computations reveal the occurrence of multiple threading events (penetrations). We further find that the time it takes a linear molecule that threads a cyclic one to fully pass through the latter can be more than 1 order of magnitude larger than the corresponding relaxation time of the ring in its own melt. Our analysis implies that dynamics in ring-linear polymer blends is highly heterogeneous, with many of the threadings being long-lived and with the linear chains (even when present in small amounts) dramatically obstructing the mobility of rings.

Adsorption of polyalkyl glycol ethers and triblock nonionic polymers on PET

Surface modification enables fiber lubrication and processing but little is known about the extent and dynamics of adsorption of typical adsorbates applied for such purposes, which often includes water-soluble block nonionic amphiphilic polymers. In this work we used quartz crystal microgravimetry (QCM) to investigate the adsorption on poly(ethylene terephthalate) (PET) of polyalkyl glycol ethers and triblock molecules of ethylene oxide and propylene oxide. The adsorption from aqueous solution of the block nonionic amphiphilic polymers strongly correlated with the self-association driven by the chain length of the respective hydrophobic blocks. This was demonstrated for the different adsorbing polymers using hydrophobic numbers calculated from simple group contribution methods. Hydrophobic and van der Waals interactions explain the affinity of the nonionic polymers with PET, which lead to adsorption isotherms that follow Langmuir-based and one-step empirical adsorption models.

Light-Induced Organic Monolayer Modification of Iodinated Carbon Electrodes

We report the modification of carbon electrodes formed from pyrolyzed photoresist films (PPF) via plasma iodination followed by the organic monolayer modification of these surfaces. The iodinated surfaces were characterized using cyclic voltammetry, atomic force microscopy, and X-ray photoelectron spectroscopy to enable the optimization of the iodination while preserving the stability and smoothness of the carbon surface. Subsequently, the C-I surface was further modified with molecules that possess an alkene or alkyne at one end through light activation with low energy (visible range λ 514 nm). The versatility of the modification reaction of the C-I surfaces is shown by reactions with undecylenic acid, 1,8-nonadiyne, and S-undec-10-enyl-2,2,2-trifluoroethanethioate (C11-S-TFA). Modification with 1,8-nonadiyne allows further modification via "click" chemistry with azido-terminated oligo(ethylene oxide) molecules demonstrated briefly to alter the hydrophilicity of the surface after attachment of ethylene oxide moieties. Furthermore, patterning of C11-S-TFA was demonstrated using a simple photolithography technique. Deprotection of the C11-S-TFA gave a free thiol allowed patterning of gold nanoparticles on the surface as verified using scanning electron microscopy (SEM). These results demonstrate that plasma iodination to form C-I is a versatile, simple, and modular approach to functionalize the carbon surface.

Fourier Transform Microwave Spectrum of the Nitrogen Molecule–Ethylene Oxide Complex: Intracomplex Motions

The rotational spectra of the N2-ethylene oxide (EO) complex were measured in the frequency region from 4 to 27 GHz by Fourier transform microwave spectroscopy, paying particular attention to intracomplex motions. The isotopologues with enriched (15)N2 or (15)NN as a moiety were also investigated. We have observed spectra of a strong/weak pair for each of the ortho and para states of the (14)N2-EO and (15)N2-EO species, which indicated that the complex existed in four distinct states. We interpreted, on the basis of the observed relative intensities, that these states were generated primarily by the exchange of the nitrogen atoms of the N2 moiety, followed by that of the two CH2 groups in the EO molecule. The (15)NN-EO species was found to consist of two isomers, one with the (15)N in the inner expressed as N(15)N-EO and the other in the outer position designated as (15)NN-EO, and the spectra of both isomers were accompanied by one weak set of satellites. The observed spectra were rotationally assigned by using sum rules and were analyzed by the asymmetric-rotor program of S-reduction, with the standard deviation of less than 10 kHz. We have found some of the molecular parameters like A, D(JK), and D(K) to be correlated between the two pairs of the spectra, and also, to much less extent, between the strong and weak members. The differences in these molecular parameters between the four sets were explained by the first-order Coriolis interaction between the "ground" and "excited" states generated by a combination of the two internal motions corresponding to the exchanges of the equivalent atoms and/or groups in the N2 and EO constituents of the complex. These internal motions were simulated by the 2-fold internal rotations of the two moieties. We have carried out ab initio molecular orbital calculations at the level of MP2 with basis sets 6-311++G(d,p), aug-cc-pVDZ, and aug-cc-pVTZ, to complement the information on the intracomplex motions obtained from the observed rotational spectra.

Quantum chemical study of the mechanism of the catalytic oxyethylation of ethylene glycol on phosphorus-doped titanium dioxide: The role of the surface phosphoryl and hydroxyl groups of the catalyst

DFT calculations of the oxyethylation pathways of monoethylene glycol (MEG) and diethylene glycol (DEG) were performed on a model fragment of phosphorus-doped titanium dioxide (anatase). It was shown that the surface hydroxyl group of titanium dioxide, whose proton initiates C-O bond cleavage in the ethylene oxide molecule, plays the key role in the activation of the molecule. At the same time, the phosphoryl group -P(OH)2O activates the reactant molecule R (MEG, DEG, etc.) and carries out the synchronous proton transfer from R to the hydroxyl oxygen atom of titanium dioxide, thus restoring the catalyst structure and closing the catalytic cycle. This restructuring occurs synchronously in one step. The substitution of the catalyst hydroxyl groups by alkoxyl groups can influence oxyethylation occurring via the bimolecular nucleophilic substitution mechanism and can poison the catalyst in some cases.

Approximate inclusion of four-mode couplings in vibrational coupled-cluster theory

The vibrational coupled cluster (VCC) equations are analyzed in terms of vibrational Mo̸ller-Plesset perturbation theory aiming specifically at the importance of four-mode couplings. Based on this analysis, new VCC methods are derived for the calculation of anharmonic vibrational energies and vibrational spectra using vibrational coupled cluster response theory. It is shown how the effect of four-mode coupling and excitations can be efficiently and accurately described using approximations for their inclusion. Two closely related approaches are suggested. The computational scaling of the so-called VCC[3pt4F] method is not higher than the fifth power in the number of vibrational degrees of freedom when up to four-mode coupling terms are present in the Hamiltonian and only fourth order when only up to three-mode couplings are present. With a further approximation, one obtains the VCC[3pt4] model which is shown to scale with at most the fourth power in the number of vibrational degrees of freedom for Hamiltonians with both three- and four-mode coupling levels, while sharing the most important characteristics with VCC[3pt4F]. Sample calculations reported for selected tetra-atomic molecules as well as the larger dioxirane and ethylene oxide molecules support that the new models are accurate and useful.

Role of the surface hydroxyl groups of modified titanium oxide in catalytic ethylene oxide hydration

A quantum-chemical study of the mechanism of ethylene oxide hydration on titanium oxide (anatase) modified with phosphorus additives was performed. It was demonstrated that the hydroxyl groups of the anatase surface are of importance for the activation interaction of ethylene oxide with the catalyst surface. The activation of the ethylene oxide molecule and proton transfer occur with the participation of these hydroxyl groups. It was found that the modification of the titanium oxide surface with phosphorus additives plays a crucial role in proton transfer.

On the Structure of Poly-(Ethylene Oxide) When Immersed in Water

It can be shown that poly-(ethylene oxide) in its monomeric form, at molecular weights greater than about 1,000, cannot be soluble in water. Nonetheless, in actual practice poly-(ethylene oxide) is widely used for its hydrophilicity and for its unlimited aqueous solubility. The explanation for this apparent contradiction lies in the fact that poly-(ethylene oxide) molecules form a nonionic surfactant of a novel category, with its hydrophilic and hydrophobic chains attached to each other over their entire length so that its hydrophilic ethylene oxide side is exposed to the water interface while the hydrophobic poly-(ethylene) side remains hidden thanks to the formation of micelles.

Monte Carlo study of sI hydrogen hydrates

In this study, we perform grand canonical Monte Carlo simulations to evaluate the hydrogen storage capacity of structure I (sI) hydrogen hydrates at pressures up to 500 MPa. Initially, we calculate the upper limit of H2 content of sI hydrates by studying the hypothetical sI hydrate, where H2 is the single guest component. It is found that the storage capacity of the hypothetical pure H2 sI hydrate could reach 3.5 wt% at 500 MPa and 274 K. Depending on pressure, the large cavities of the pure H2 hydrate can accommodate up to three H2 molecules while the small ones are singly occupied at most, even at pressures as high as 500 MPa, without any double occupancy being observed. Subsequently, the binary H2–ethylene oxide (EO) hydrate is examined. In this case, the large cavities are occupied by a single EO molecule while the small cavities can accommodate at most a single H2 molecule. Such configuration results in a maximum H2 content of only 0.37 wt%. The hydrogen storage capacity does not improve significantly even in case when EO is replaced by a component with smaller molecular weight.

Hindering of rotational motion of guest molecules in the Type I clathrate hydrate

Guest–host interactions in the Type I mixed clathrate hydrate with ethylene oxide and carbon monoxide guest molecules at temperature below 110 K are studied. By means of both molecular dynamics simulations and FTIR spectroscopy we investigate the hindering of rotational motion of guests molecules, the origin of this hindering, and the spectroscopically measurable consequences. Steric effects are responsible for restriction of rotational displacements of carbon monoxide. For ethylene oxide the rotational hindering is caused predominantly by van der Waals interactions between oxygen atom of guest and hydrogen atoms of water molecules. Creation of host–guest hydrogen bonds was not observed.

Self-Assembled Block Copolymer Thin Films as Water Filtration Membranes

Nanoporous membranes containing monodisperse pores of 24 nm diameter are fabricated using poly(styrene-b-lactide) block copolymers to template the pore structure. A 4 mum thin film of the block copolymer is cast onto a microporous membrane that provides mechanical reinforcement; by casting the copolymer film from the appropriate solvents and controlling the solvent evaporation rate, greater than 100 cm(2) of a thin film with polylactide cylinders oriented perpendicular to the thin dimension is produced. Exposing the composite membrane to a dilute aqueous base selectively etches the polylactide block, producing the porous structure. The ability of these pores to reject dissolved poly(ethylene oxide) molecules of varying molecular weight matches existing theories for transport through small pores.

Letter to the Editor: The Molecular Distribution and HLB Value of Nonionic Polioxiethylenated Surfactants

In 1940, Flory deducted that the molecular distribution of ethylene oxide polymers, obtained by reaction of ethylene oxide with ethylene glycol, is represented by Poisson's distribution law. This mathematical equation was subsequently used by other authors for calculating the fractions molars of the products of the reaction of ethylene oxide with alcohols and phenols, without taking into account to be used as quantity of units of ethylene oxide to x instead of x − 1. In this article, it is theoretically demonstrated that if the equation obtained by Flory is modified in this way, it gets that the hydrophilic-lipophilic balance of non ionic polioxiethylenated surfactants can be calculated from the mean number of molecules of ethylene oxide that reacts with one molecule of alcohol or phenol.

Study on anionic polymerization of ethylene oxide initiated by ammonium/triisobutylaluminum

In this paper, ammonium/triisobutylaluminum was used as an initiating system for anionic polymerization of ethylene oxide (EO). When the amount of triisobutylaluminum versus ammonium was in excess, a fast polymerization rate was achieved at room temperature and allowed polyethylene glycol synthesized with a high molecular weight and narrow molecular weight distribution. It was found that triisobutylaluminum may play two roles during the polymerization, one is that it can react with ammonium to form “ate” complex as an efficient initiator for EO polymerization, and the other is that it exerts a significant activating effect on the monomer. The catalytic effect of triisobutylaluminum in EO polymerization was elucidated by using quantum chemical calculations at density functional theory level, involving thermo-chemistry parameters. The studies show that EO homopolymerization cannot be conducted without the aid of catalyst due to the big energy difference of bonding orbitals. The interaction between EO and trialkylaluminum makes the electron cloud distribution and energy gap of EO molecule change, which indicates trialkylaluminum can activate the monomer. In addition, because of the lower enthalpy of formation, the formation of “ate” complex is prior to the interaction of trialkylaluminum and EO.

Ethylene epoxidation in low-temperature AC corona discharge over Ag catalyst: Effect of promoter

In this work, the epoxidation of ethylene using a low-temperature corona discharge system was investigated with various reported catalytically active catalysts: Ag/α-Al 2O 3, Cs–Ag/α-Al 2O 3, Cu–Ag/α-Al 2O 3, and Au–Ag/α-Al 2O 3. It was experimentally found that the investigated catalysts could improve the ethylene conversion and the ethylene oxide (EO) yield and selectivity for the corona discharge system, particularly 1 wt.% Cs–12.5 wt.% Ag/α-Al 2O 3 and 0.2 wt.% Au–12.5 wt.% Ag/α-Al 2O 3. The power consumption per EO molecule produced in the corona discharge system, combined with the superior bimetallic catalysts, was much lower than that of the sole corona discharge system and that of the corona discharge system combined with the monometallic Ag catalyst.