Observation of Nano‐Dewetting in Colloidal Crystal Drying

The drying of colloidal crystals is connected with a continuous shrinkage process. However, several minutes after starting the drying, the system seems to take a breath before it shrinks monotonously until its final state after about one day. This short period we call “v”‐event because of the shape of the curve characterizing the lattice constant: a decrease followed by a counter‐intuitive increase which ends after one hour. This event is found in time‐dependent optical spectra. It is assigned to the start of a nano‐dewetting process occurring at the colloidal particles.     

Ion-pairing and optical activity of diastereomeric zinc(II) 1, 10-phenanthroline,S-valinate systems

A series of S-valinatobis(1, 10-phenanthroline)zinc salts in methanolic solution have been prepared and their conductivities and ORD spectra measured. A positive linear correlation of optical rotation with conductance was found for salts of non-chelating counter anions. From the application of the Yoe-Jones method on the system Zn, phen, S-val^?, Cl^? it was concluded that the counter anion dependence of the optical activity is connected mainly with heterocyclic ligand counter anion exchange equilibria.     

The use of a bivalent counter anion to control the effective mobility of the hydrogen ion constituent in cationic isotachophoresis

The use of a bivalent counter anion for cationic isotachophoresis was studied both theoretically and experimentally. A mathematical model was proposed and solved to give the effective mobility of the hydrogen ion constituent, uH,H, in the respective electrolyte systems. The theoretical values agreed well with the experimental data in a series of electrolyte systems. The dependence of uH,H on such parameters as pH of the leading electrolyte, ionic mobilities of leading and counter ions, and dissociation constants was calculated and discussed. A bivalent counter anion will prove useful for the separation of low mobility cations and weak bases, as shown for the separation of substituted anilines in a succinate electrolyte system.     

Direct participation of counter anion in acid hydrolysis of glycoside

The mechanism of acid hydrolysis of glycoside has been investigated since the end of the 19th century accompanied by lots of literatures published on the mechanism, although little attention has surprisingly been paid to the action of counter anion of acid. In this paper, it was investigated whether or not counter anion of acid directly participates in acid hydrolysis of glycosides, methyl α- and β-d-glucopyranosides (MGP) in water, aqueous 74%, and 82% 1,4-dioxane systems. Because proton activity of a reaction system is the important rate-determining parameter in the universally acknowledged mechanism, it was carefully estimated in this study. The results suggested that bromide anion directly participates in the acid hydrolysis reaction of MGP in a water solvent system and the participation of bromide anion is further pronounced in aqueous 74% and 82% 1,4-dioxane solvent systems. It was also suggested that chloride anion directly participates in these dioxane solvent systems.     

Effect of the eluent pH and acidic modifiers in high-performance liquid chromatography retention of basic analytes

The retention of ionogenic bases in liquid chromatography is strongly dependent upon the pH of the mobile phase. Chromatographic behavior of a series of substituted aniline and pyridine basic compounds has been studied on C18 bonded silica using acetonitrile-water (10:90) as the eluent with different pHs and at various concentrations of the acidic modifier counter anions. The effect of different acidic modifiers on solute retention over a pH range from 1.3 to 8.6 was studied. Ionized basic compounds showed increased retention with a decrease of the mobile phase pH. This increase in retention was attributed to the interaction with counter anions of the acidic modifiers. The increase in retention is dependent on the nature of the counter anion and its concentration in the mobile phase. It was shown that altering the concentration of counter anion of the acidic modifier allows the optimization of the selectivity between basic compounds as well as for neutral and acidic compounds.     

Communication: A concerted mechanism between proton transfer of Zundel anion and displacement of counter cation

Ab initio path integral molecular dynamics simulation of M(+)(H(3)O(2)(-)) (M = Li, Na, and K) has been carried out to analyze how the structure and dynamics of a low-barrier hydrogen-bonded Zundel anion, H(3)O(2)(-), can be affected by the counter alkali metal cation, M(+). Our simulation predicts that the quantum proton transfer in Zundel anion can be strongly coupled to the motion of counter cation located nearby. A smaller cation can induce larger structural distortion of the Zundel anion fragment making the proton transfer barrier higher, and hence, lower the vibrational excitation energy. It is also argued that a large H∕D isotope effect is present.     

Influence of Solid-liquid Interaction and Temperature on the Dynamic Dewetting of a Thin Polymer Film:A Molecular Dynamics Study

Coarse-grained molecular dynamics simulations were carried out to investigate the dewetting behavior of a polymer thin film on partial wetting solid surface at the early stage of the dewetting process. Spontaneous dewetting is initiated by removing a band of strip from both the ends of the liquid polymer film which has achieved equilibrium. The solid-liquid interaction and temperature were varied to show their influence on the dewetting dynamics during dewetting as well as the shape evolution of the liquid ...     

Electrochemical Elucidation of the Facilitated Ion Transport Across a Bilayer Lipid Membrane in the Presence of Neutral Carrier Compounds

The ion transport facilitated by neutral carrier compounds (valinomycin, nonactin) has been investigated by cyclic voltammetry in the several electrolyte solutions (KF, KCl, KBr, KNO₃, KSCN, KClO₄), and we demonstrated the effect of the counter anions on the facilitated transport of K⁺ from the viewpoint of electroneutrality. Voltammograms for the ion transport were generated at steady state and the current density between W1 and W2, j_W1–W2, increased with the absolute value of the applied membrane potential, E_W1–W2. Then, the magnitude of j_W1–W2 at a certain E_W1–W2 increased with the hydrophobicity of the counter anion. It was proved that the logarithm of |j_W1–W2|at a certain E_W1–W2 is almost proportional to the hydration energy of the counter anion. This indicates that not only K⁺ but also the counter anion distributes into the BLM. Therefore, the magnitude of j_W1–W2 at a certain E_W1–W2 increased with an increase of pH, because the hydroxide ion was served as a counter anion. Based on the variation of the zero‐current potential in case of various asymmetrical ionic compositions, it is found that the amount of cation transport is much larger than that of anion transport.     

The surface morphology evolution of an ultrathin film of poly[styrene-b-(ethylene-co-butylene)-b-styrene] during its dewetting process

The dewetting process of an ultrathin film of a triblock copolymer, poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) was studied with an atomic force microscope. The surface morphology of the dewetting process exhibited two distinct dewetting processes of the 5.6 nm thick films: a slower dewetting for the polymer layer at the very vicinity of the substrate's surface, and a faster one for the polymer on top of this layer. The surface-induced difference in the kinetics of these two-step dewetting processes resulted in a special morphology evolution, including the absence of the dewetting rim, and a final unique network-like morphology.     

Dynamic instability of a sol-gel-derived thin film

We present a study on the dynamic instability of a sol-gel-derived (SG) thin film on a nonwettable substrate. Because of the structural instability accompanied by syneresis stress in a film deposited on the substrate, there exists a regular distribution of dewetting patterns required to relieve the in-plane stress, such as holes in the earlier stages, and droplets accompanying a regular polygonal distribution in the later stages of the dynamic instability. The characteristic length scales in each stage scaled linearly with the film thickness during the duration of dewetting. For the formation of holes during the earlier stages of rupture of the film, the dewetting velocity was analyzed with a viscous sintering theory of a SG thin film. In the earlier stages of the dynamic instability, the dewetting velocity decreases with increasing dewetting time and increases with increasing the initial film thickness, which indicates that the SG thin film behaves partially like a slipping polymer thin film. In the final times of the film rupture, the radius of the hole has a linear relationship with the film thickness, and the growth rate of the hole (dewetting velocity) is nearly constant, regardless of the film thickness. These dewetting behaviors indicate that the SG thin film in the final times of the rupture is somewhat similar to nonslipping film. From these observations, we found that the dewetting behavior of a SG thin film has ambivalent dewetting characteristics of slipping and nonslipping films and that a SG thin film is not a purely viscous film.     

Nonsolvent-induced dewetting of thin polymer films

The process of nonsolvent-induced dewetting of thin polystyrene (PS) films on hydrophilic surfaces at room temperature has been studied by using water as a nonsolvent. It is observed that the process of nonsolvent-induced dewetting is greatly different from other previous dewetting processes. The PS film is found in nonviscous state in our study. A mechanism of nonsolvent-induced dewetting is deduced in an order of penetration, replacement, and coalescent, and it is different from other previous dewetting mechanisms. The results of experiments are analyzed from thermodynamics and dynamics to support the hypothetical mechanism.     

Dewetting Kinetics of Thin Polymer Films with Different Architectures: Effect of Polymer Adsorption

We have investigated the influence of the adsorption process on the dewetting behavior of the linear polystyrene film(LPS),the 3-arm star polystyrene film(3 SPS) and the ring polystyrene film(RPS) on the silanized Si substrate.Results show that the adsorption process greatly influences the dewetting behavior of the thin polymer films.On the silanized Si substrate,the 3 SPS chains exhibit stronger adsorption compared with the LPS chains and RPS chains; as a result,the wetting layer forms more easily.For LPS films,with the decrease of annealing temperature,the kinetics of polymer film changes from exponential behavior to slip dewetting.As a comparison,the stability of 3 SPS and RPS films switches from slip dewetting to unusual dewetting kinetic behavior.The adsorbed nanodroplets on the solid substrate play an important role in the dewetting kinetics by reducing the driving force of dewetting and increase the resistant force of dewetting.Additionally,Brownian dynamics(BD) simulation shows that the absolute values of adsorption energy(ε) gradually increase from linear polymer(-0.3896) to ring polymer(-0.4033) and to star polymer(-0.4264),which is consistent with the results of our adsorption experiments.     

Autophobic dewetting of Z-tetraol perfluoropolyether lubricant films on the amorphous nitrogenated carbon surface

The thermodynamic stability of thin films of the perfluoropolyether (PFPE) Z-Tetraol, as a function of molecular weight, on amorphous nitrogenated carbon, CNx, is investigated. An optical surface analyzer is used to image the autophobic dewetting of the Z-Tetraol films. Film dewetting results when the PFPE film thickness applied to the CNx surface exceeds a critical value. This critical dewetting thickness is identified as the monolayer thickness of the adsorbed PFPE film via measurements of the changes in the surface energy as a function of lubricant film thickness. The observed dewetting coincides with the film thickness at which the disjoining pressure goes to zero. The critical dewetting thickness is dependent on the PFPE molecular weight.     

Remarkable effects of counter ions on scandium ion-promoted electron transfer reactions

Scandium ion-promoted electron transfer reactions of p-benzoquinone are remarkably accelerated when tetrakis(pentafluorophenyl)borate anion is used instead of trifluoromethanesulfonate anion as the counter anion of scandium ion. Only a catalytic amount of scandium borate salt (Sc[B(C6F5)4]3) accelerates significantly the Diels-Alder reaction of 9,10-dimethylanthracene with p-benzoquinone, which proceeds via Sc(3+)-promoted electron transfer from the anthracene to p-benzoquinone.     

RUPTURING OF POLYMER FILMS WITH RUBBING-INDUCED SURFACE DEFECTS

It has been a long-standing question whether dewetting of polymer film from non-wettable substrate surfaceswherein the bicontinuous morphology never forms in the dewetting film is due to spinodal instability or heterogeneousnucleation. In this experiment, we use a simple method to make the distinction through introduction of topographical defectsof the films by rubbing the sample surface with a rayon cloth. Spinodal dewetting is identified for those films that dewet by acharateristic wavevector, q, independent of the density of rubbing-induced defects. Heterogeneous nucleation, on the otherhand, is identified for those with q increasing with increasing density of defects. Our result shows that PS films on oxidecoated silicon with thickness less than ≈ 13 nm are dominated by spinodal dewetting, but the thicker films are dominated bynucleation dewetting. We also confirm that spinodal dewetting does not necessarily lead to a bicontinuous morphology in thedewetting film, contrary to the classic theory of Cahn.     

Conformation of 1,4-dineopentyl-2,5-cis-diphenylpiperazine and its diammonium salts: remarkable change in conformation depending upon the counter anion

The free base of 1,4-dineopentyl-2,5-diphenylpiperazine takes a chair conformation in CDCl3, while the conformation of its diammonium salts changes depending upon the counter anion.     

Control of dispersion state of silsesquioxane nanofillers for stabilization of polystyrene thin films

The influence of the dispersion states of the nanofillers on the dewetting behavior of the polymer thin film was investigated. Polyhedral oligomeric silsesquioxanes (POSS) with various substituents were added into polystyrene (PS) thin films as the nanofillers. The dewetting rate of the films drastically changed with the surface substituents of POSS additives. Neutron reflectivity measurements indicated that the difference of the dewetting rate was associated with the dispersion state of POSS additives in the films. POSS with phenethyl groups (PhPOSS), which homogeneously dispersed into the films, resulted in the decrease of the glass transition temperature of PS and the enhancement of the dewetting of the films. POSS with a fluoroalkyl group (CpPOSS-R f) segregated to the film surface and showed the retardation of the dewetting by the decrease of the surface energy of the film. POSS with hydroxyl groups (CpPOSS-2OH) segregated to the film surface and film-substrate interface and led to the elimination of the dewetting, suggesting the importance of the interfacial segregation for the inhibition of dewetting. These results revealed the strong relationship between the dispersion state of the nanofillers and the dewetting of the nanofilled films.     

Synthesis and solid state characterization of hexacoordinated 1:1 ionic gallium(III) complexes

The coordination of the N,N ligands 2,2-bipyridine (bipy) and 1,10-phenanthroline (phen) to Ga(III) has been investigated via the formation of new ionic hexacoordinated complexes of general formula [Q'(2)Ga(N,N)][X], where HQ' stands for 2-methyl-8-hydroxyquinoline and the counter anion X(-) is nitrate (NO(3)(-)) or hexafluorophosphate (PF(6)(-)). All synthesized complexes were characterized by single-crystal X-ray diffraction analysis. The geometry of the Ga(III) cations is octahedral and a single geometric isomer (all N, N trans conformation) has been obtained in all cases. The role of both the N,N ligand and the counter anion has been investigated in the formation of the crystal supramolecular motifs occurring in the 3D-crystal networks of these new class of ionic Ga(III) derivatives. A full investigation of the photophysical properties of the new synthesized ionic species is reported and discussed in relation to their crystalline packing and the degree of crystallinity of thin solid films as well as the nature of the N,N ligand and the counter anion.     

Acid-catalyzed deprotection mechanism of tert-butyloxycarbonyloxy polymers in chemically amplified resists

A mechanism of acid-catalyzed deprotection of poly(4-tert-butyloxycarbonyloxy-styrene), PBOCST, in chemically amplified resists has been elucidated in terms of elementary processes by means of semiempirical molecular orbital calculations. It is concluded that the overall deprotection of tert-butyloxycarbonyl (t-BOC) group proceeds stepwise; i.e., (a) the first products are an acid carbonate and a tert-butyl cation; (b) a phenolic compound is the secondary and final product from the acid carbonate, which is realized by assistance with a counter anion accompanied by acid; (c) the counter anion also assists acid regeneration from the tert-butyl cation to produce isobutylene. The yield rate of the phenol is proportional to the product of concentrations of the polymer, the catalytic acid, and the counter anion. The activation energy (21 kcal/mol) calculated for the rate-determining step (a) is in good agreement with an experiment. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1035–1042, 1998     

Dynamic (de)wetting properties of superhydrophobic plasma‐treated polyethylene surfaces

Superhydrophobic surfaces present properties of self‐cleaning and unwetting that could be applied in the optics field. The wetting and dewetting of these superhydrophobic surfaces are compared to that of only hydrophobic polyethylene. The contact angle of such a surface varies from 170° to 130–140°. The dewetting is studied using two techniques of dynamic dewetting measurements. The behaviors of surfaces, dried or prewetted with water vapor, are different. The dewetting of the dried surface previously prewetted is discontinuous, and slower than that of the dry one. This specific behavior is interpreted as a roughness effect on trapped water. However, its dewetting is still faster than a corresponding hydrophobic surface like polytetrafluoroethylene (PTFE). Copyright © 2006 John Wiley & Sons, Ltd.