Short Separation Research Articles

Advanced models for water simulations

Molecular simulations of water using classical, molecular mechanic potential energy functions have enjoyed a 50‐year history of development, and much has been learned regarding their parameterization and the essential physics that must be captured in order to reproduce water properties across the phase diagram and across system sizes, from the dimer to the condensed phase. While pairwise‐additive force fields using fixed, point charge‐based electrostatics have dominated this history owing to computational cost, their limitations in transferability are being recognized, owing particularly to the lack of many‐body effects, as well as an inherent difficulty in capturing quantum mechanical effects that become important at short intermolecular separation. This has spurred an impressive development of novel functional forms and parameterization schemes to account for such effects, especially the leading many‐body effect of polarization. This review discusses recent efforts in the development of advanced models of water, particularly with regard to important details of their parameterization from quantum mechanical or experimental data, the development of novel functional forms including machine learning‐based models, and algorithms that reduce the computational cost of polarization dramatically, permitting them to potentially become competitive with pairwise‐additive models as the standby of condensed‐phase simulation. These technical developments are appraised based on their ability to impact numerical calculations on water, particularly the condensed phase, and it is hoped that this article provides a clear connection between the essential physics captured by the model and their fitness across a range of environments. WIREs Comput Mol Sci 2018, 8:e1355. doi: 10.1002/wcms.1355This article is categorized under: Computer and Information Science > Computer Algorithms and Programming Molecular and Statistical Mechanics > Molecular Interactions Software > Simulation Methods

Ion-pairing reversed-phase chromatography coupled to inductively coupled plasma mass spectrometry as a tool to determine mercurial species in freshwater fish

Most of analytical community is focused on reversed phase high performance liquid chromatography (RP-HPLC) for mercury speciation by employing mobile phases comprising of high salts and moderate amounts of organic solvents. This study aims at rapid mercury speciation analysis by ion-pairing RP-HPLC with inductively coupled plasma mass spectrometry (ICP-MS) detection only using low salts for the sake of green analytical chemistry. Two ion-pairing HPLC methods were developed on individual usage of positively and negatively charged ion-pairing reagents (tetrabutylammonium hydroxide –TBAH and sodium dodecylbenzene sulfonate –SDBS), where sodium 3-mercapto-1-propysulfonate (MPS) and l-cysteine (Cys) were individually added in mobile phases to transform mercury species into negative and positive Hg-complexes for good resolution. Addition of phenylalanine was also utilized for rapid baseline separation in combination of short C18 guard columns. Optimum mobile phases of 2.0mM SDBS+2.0mM Cys+1.0mM Phe (pH 3.0) and 4.0mM TBAH+2.0mM MPS+2.0mM Phe (pH 6.0) both achieved baseline separation of inorganic mercury (Hg2+), methylmercury (MeHg), ethylmercury (EtHg) and phenylmercury (PhHg) on two consecutive 12.5-mm C18 columns. The former mobile phase was selected for mercury speciation in freshwater fish because of short separation time (3.0min). Detection limits of 0.015 for Hg2+, 0.014 for MeHg, 0.028 for EtHg and 0.042μgL−1 for PhHg were obtained along with satisfactory precisions of peak height and area (1.0-2.8% for 5.0μgL−1 Hg-mixture standard). Good accordance of determined values of MeHg and total mercury in certified reference materials of fish tissue (GBW 10029) and tuna fish (BCR-463) with certified values as well as good recoveries (91–106%) proved good accuracy of the proposed method. An example application to freshwater fish indicated its potential in routine analysis, where MeHg was presented at 3.7–20.3μgkg−1 as the dominate species.

P 16 The implementation of Near-Infrared-Spectroscopy (NIRS) in sports science – a verification of suitability using the compound movement squat

Introduction Near - Infrared Spectroscopy (NIRS) serves as a promising tool to examine cortical activity in a sports-scientific context. The associated feasibility of said method remains to be validated as exercise - induced confounders such as increases in extracerebral blood flow have been postulated ( Tachtsidis and Scholkmann, 2016 ). Additionally, the relationship between force and cortical activity is yet to be investigated in compound movements. Both parameters show a linear relationship in isolated movements ( Shibuya et al., 2014 ) yet it remains unclear whether this relationship applies to compound movements. Here we assessed the feasibility of NIRS for the compound movement barbell squat (BS). Complementarily the relationship between force levels and cortical activity during the squat was examined. We hypothesized that the extracerebral blood flow superimposes the signal and can be eliminated. Furthermore, we hypothesized a linear relationship between force during BS and cortical activity in the leg area of bilateral primary motor cortex (M1). Methods Ten healthy young adults participated in this study (n = 10; age: 25.7 ± 2.214 years). All subjects performed the BS task, five 90° squats per activity block, on three separate days with varying NIRS - configurations to control for and eliminate extracerebral effects. The experimental setup corresponds to a block design with varying force levels (L0%, L20%, L40%) which were individually adjusted in succession to Maximum Strength Tests. Our standard NIRS - configuration (A) covered the cortical motor system. The second configuration (B) additionally covered bilateral auditory cortices, frontopolar areas, as well as primary visual cortex. A third configuration incorporated a short - distance - channel to use this channel in a short separation regression (C). Cortical activation was assumed to be reflected by increased oxyhemoglobin (HbO2) and a corresponding decline or unchanged deoxyhemoglobin (HHb). Results For (A) and (B), HbO2showed a significant increase in the entire detection range when comparing the varying force levels during BS ( p 0.0023 ). For (C), HbO2 showed a significant increase in bilateral superior parietal lobule (SPL) (L20%, L40%) when compared to L0% ( p 0.01 ). HbO2 showed no significant increase when comparing the different force levels to baseline values. HHb showed no regionally consistent, significant decline for all comparisons. Discussion Short separation regression potentially enables the disentanglement of extracerebral blood flow from cerebral blood flow. There is a relationship between force and cortical activity in the squat when comparing force levels, although in bilateral SPL as opposed to M1 as seen in isolated movements. This implies a different modulator for compound movements compared to isolated movements.

Numerical simulation of wavy surface effect on the stability of a hypersonic boundary layer

Generally the boundary layer transition is tripped by the surface roughness, while at certain circumstances, the surface roughness can delay the boundary layer transition. In this paper, by introducing the two-dimensional wall blow-suction upstream, high-order numerical method is used to simulate the Ma = 6 hypersonic boundary layer stability with a typical wavy-wall model. First, the mechanism of transition delay by the wavy wall is analyzed by comparison of the disturbance development in the flat-plate and wavy-wall boundary layer. Then the effects of the wavy-wall wave number, depth and streamwise location on the boundary layer stability are investigated. The results show that the disturbance development is closely related to the separation region. Compared with the flat plate, the wavy wall can suppress the second-mode instability via multiple separation regions, thus delaying the boundary layer transition. Concerning the wave number, the wavy wall with a single wave number has only a single short separation region, so the second-mode instability grows rapidly downstream; the wavy wall with multiple wave numbers means multiple separation regions and suppresses the second-mode instability sharply. As for the depth, the separation region grows with the increase of the wavy-wall depth and the second-mode instability is suppressed more evidently. Also as the location of the wavy wall moves downstream, the suppression on the second-mode instability is more obvious.

Probing interactions between sphalerite and hydrophobic/hydrophilic surfaces: Effect of water chemistry

Due to the limited availability of fresh water sources, recycled water and sea water, generally with high salinity, have been widely used in mining industry in arid regions, which can significantly affect the interactions of mineral particles, chemical additives and air bubbles in mineral processing (e.g., flotation). In this work, the surface forces and interaction mechanism of Si3N4 tip and a model mineral (i.e. sphalerite) in various aqueous solution conditions have been studied using an atomic force microscope (AFM). The Si3N4 tip was functionalized with octadecyltrichlorosilane (OTS) to tune the surface hydrophobicity. The sphalerite substrate was either freshly cleaved or treated with conditioning solutions: activator (i.e. CuSO4) and collector (i.e. potassium amyl xanthate, PAX) in various background solutions (i.e., Milli-Q water, 0.46M NaCl, saline water to mimic diluted sea water/industrial process water). The force-separation profiles indicate that in addition to the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions, hydration interaction plays an important role for the surface interaction in saline water (with addition of divalent cations, Ca2+ and Mg2+) at short separation distance, while hydrophobic force dominates the interaction when Si3N4 tip and sphalerite are both hydrophobized. The surface force measurements further demonstrate that solution salinity and presence of divalent cations can significantly influence the adhesion between particles. The micro-flotation tests of sphalerite and silica mixtures of varying surface hydrophobicity can be well interpreted by the force measurements. This work provides useful insights into the fundamental interaction mechanisms of suspended particles possessing different hydrophilic and hydrophobic characteristics in complex aqueous media.

Enhanced treatment of dispersed dye-production wastewater by self-assembled organobentonite in a one-step process with poly-aluminium chloride

Organobentonite has been successfully applied in industrial wastewater treatment. However, the solid-liquid separation in wastewater treatment still needs improvement. This study presents an enhanced approach with high removal efficiency and short separation time for dispersed dye-production wastewater using self-assembled organobentonite in a one-step process with poly-aluminium chloride (PAC). The enhanced effects of PAC on wastewater treatment by organobentonite were comprehensively evaluated. Following the primary decontamination by the self-assembled organobentonite, the removal efficiency for dispersed dye-production wastewater was strengthened with PAC coagulation. The removal rates of TOC and organic pollutants were 55.0% and 63.5%, respectively, with the PAC-enhanced approach and were 1.3- and 1.6-fold higher, respectively, than those with the self-assembled organobentonite approach. The combination of PAC with self-assembled organobentonite was able to break the stability of the organobentonite suspension and enlarge the floc size, and thus reduce the solid-liquid separation time from 30 min to 10 min. Additionally, this enhanced approach could improve the biodegradability of wastewater with the BOD5/CODCr ratio increasing from 0.22 to 0.39, which was 4.1-fold higher than that of only organobentonite in a one-step process. Therefore, the PAC-enhanced approach could be a promising technology for wastewater pretreatment in practical industrial applications.

How to observe the giant thermal effect in the Casimir force for graphene systems

A differential measurement scheme is proposed which allows for a clear observation of the giant thermal effect for the Casimir force, that was recently predicted to occur in graphene systems at short separation distances. The difference among the Casimir forces acting between a metal-coated sphere and the two halves of a dielectric plate, one uncoated and the other coated with graphene, is calculated in the framework of the Dirac model using the rigorous formalism of the polarization tensor. It is shown that in the proposed configuration both the difference among the Casimir forces and its thermal contributioncan be easily measured using already existing experimental setups. An observation of the giant thermal effect should open opportunities for modulation and control of dispersion forces in micromechanical systems based on graphene and other novel 2D-materials.

Development of a New Method Based on Chiral Ligand-Exchange Chromatography for the Enantioseparation of Propranolol.

A new chromatographic procedure was proposed for the separation of propranolol (PRN) enantiomers based upon enantioselective chiral ligand-exchange chromatography. The separation was carried out on a short C8 column leading to considerably short separation time. L-alanine and Cu2+ were applied as chiral selector and central bivalent complexing ion, respectively. It was found that the kind of copper salt could influence the enantioseparation efficiency. The separation on the C8 stationary phase was more efficient than that on the C18 column. It was shown that the pH of mobile phase, organic modifier content of mobile phase, mole ratio of chiral ligand to bivalent ion and Cu (L-alanine) 2 concentration in the mobile phase were important in enantioseparation efficiency. Water/methanol (70:30) mixture containing L-alanine-Cu2+ (7:1) was found to be the best mobile phase condition for PRN enantioseparation. All effective parameters were optimized in order to improve the separation efficiency. The optimized HPLC method was utilized for analysis of propranolol enantiomers in spiked human blood plasma samples.

Synthesis and characterization of cobalt-supported catalysts on modified magnetic nanoparticle: Green and highly efficient heterogeneous nanocatalyst for selective oxidation of ethylbenzene, cyclohexene and oximes with molecular oxygen

In this study, a new supported cobalt nanocatalyst has been described. The Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) modified by SiO2/aminopropyl trimethoxy silane/cyanuric chloride (Fe3O4@SiO2-APTMS/CC) utilized for anchoring metformin-cobalt complex (Fe3O4 Ms@SiO2-APTMS/CC/Met@Co(II)). The structure of novel complex well defined by elemental analysis, ICP, AAS, BET, FT-IR, EDX, SEM, TEM, DLS, XRD, TG-DTG, VSM and XPS. The catalytic efficiency of the synthesized cobalt nanocatalyst was studied in the oxidation of ethylbenzene (EB), cyclohexene (CYHE) and various oximes using molecular oxygen as ecofriendly oxidant and high catalytic activity and selectivity toward oxidation is observed. Selective aerobic oxidation of EB and CYHE and various oximes catalyzed by the cobalt nanocatalyst without any reducing agent by using N-hydroxyphthalimide (NHPI), gave acetophenone (AcPO), 2-cyclohexene-1-one and corresponding carbonyl compounds respectively, as major products. To achieve high level of efficiency of heterogeneous nanocatalyst, various parameters such as the ratio and amount of nanocatalyst/NHPI, reaction time, temperature and solvents were evaluated. The easily preparation from inexpensive and commercially available reagent, thermal stability, suitable performance in reusability, high efficiency and selectivity in oxidation reactions, short reaction time, easy recovery and separation from reaction mixture, are advantages of this novel catalyst.

THE TWINS' SITUATION IMPACT ON THE PERSONALITY DEVELOPMENT

Since the moment of their birth between the twins develop a relationship that differs from the brother and sister relationships. Two children of the same age, growing under the same conditions, promote and develop their personalities. The twins' connections are so close that at a short time separation from each other, the twins suffer the same as been separated from their mother. The aim of the research: to research the twins' situation impact on the child's personality development. The research involves the analysis of the scientific pedagogical and psychological literature, structured interviews are used in the empirical research. The obtained data from the parents interviews of 37 twins' pairs have been analyzed. Results: the role distribution, the twins bilateral/reciprocal competitiveness, speech-therapist's necessity, self-contentedness inside the pair, communication with other children, amount of vocabulary at an early age are clarified in the twins pair, presence of cryptophasia, emphasizing of similarity, difference, difficulty to formulate thoughts and emotions by words. Conclusions: twins' situations impact essentially differs, depending on the type of twins: MZ, DZ or different gender. Their bilateral/reciprocal interrelation indexes are different: the role distribution in the pair, desire to competitiveness, be closely self-contained inside their pair and disallow to let others into their dyad or to be open to communication with other people.

An Examination of Bias in SODA Interferometry

Second-order difference array (SODA) interferometry provides unambiguous high-accuracy direction of arrival (DOA) estimation of RF signals. A low-resolution unambiguous DOA estimate is formed by interferometry with a receiver pair having short separation. This is then used to select from a number of high-resolution DOA estimates formed with a receiver pair of large separation. In this study, SODA is applied to DOA estimation of close sources for which the planewave approximation does not hold well. Expressions for bias in SODA estimates are determined. The conditions under which the bias is large enough to prevent successful disambiguation are explored. Implications for the design and deployment of SODA interferometers are inferred.

Structure and magnetic susceptibility of (PhCH 2 NEt 3 ) 2 Cu 2 Br 6 : Unprecedented similarity to the Haldane state with potential competing interactions

Abstract The synthesis, crystal structure and magnetic susceptibility of a new binuclear Cu(II) complex templated by benzyltriethylammonium as a counterion, are reported. The X-ray crystal structure reveals that this compound is composed of an anionic dimer and organic cation. The complex, (PhCH2NEt3)2Cu2Br6 crystallizes in the triclinic space group P 1 ¯ with two molecules in the unit cell. In the crystal structure, the inorganic layer, built up by the independent anionic binuclear moiety [Cu2Br4-(μ-Br)2]2−, is connected to the organic layers through C H⋯Br hydrogen bonding to build a three-dimensional network. Each copper ion exhibits an intermediate geometry between square planar and tetrahedral. The Cu2Br2 structural core is characterized by a bridging Cu Br Cu angle of 91.335° and a short Cu Cu separation of 3.487 A. Magnetic interactions in the binuclear copper(II) material were studied with the aim of elucidating magneto-structural correlations. The magnetic susceptibility data (1.8–300 K) show a maximum in χ near 8 K with a significant decrease in susceptibility at lower temperatures. The best fit was obtained using the strong-rail ladder model which resulted in exchange values of −14.2(1) K for the rail and +3.6(2) K for the rung. The existence of ferromagnetic exchange across the rungs of this system may induce a transition from an S = ½ ladder-like system to an S = 1 Haldane system at low temperatures.

Short path length pQCD corrections to energy loss in the quark gluon plasma.

Recent surprising discoveries of collective behaviour of low-pT particles in pA collisions at LHC hint at the creation of a hot, fluid-like QGP medium. The seemingly conflicting measurements of non-zero particle correlations and RpA that appears to be consistent with unity demand a more careful analysis of the mechanisms at work in such ostensibly minuscule systems. We study the way in which energy is dissipated in the QGP created in pA collisions by calculating, in pQCD, the short separation distance corrections to the well-known DGLV energy loss formulae that have produced excellent predictions for AA collisions. We find that, shockingly, the large formation time (compared to the 1/μ Debye screening length) assumption that was used in the original DGLV calculation, results in a highly non-trivial cancellation of correction terms. We investigate the effect of relaxing the large formation time assumption in the final stages of the calculation and find that, not only is the effect of the small separation distance correction important even in large (~ 5 fm) systems, but also that the correction term dominates over the leading term at high energies.

The effect of like-charge attraction on aerosol growth in the atmosphere of Titan

The formation of aerosols in the atmosphere of Titan is based extensively on ion-neutral chemistry and physical condensation processes. Herein it is shown that the formation of aerosols may also occur through an alternative pathway that involves the physical aggregation of negatively charged particles, which are known to be abundant in the satellite’s atmosphere. It is shown that, given the right circumstances, like-charged particles with a dielectric constant characteristic of nitrated hydrocarbons have sufficient kinetic energy to overcome any repulsive electrostatic barrier that separates them and can subsequently experience an attractive interaction at very short separation. Aerosol growth can then unfold through a charge scavenging process, whereby nitrated aggregates preferentially grow by assimilating smaller like-charged particles. Since hydrocarbon aerosols have much lower dielectric constants, it is shown that a similar mechanism involving hydrocarbon particles will not be as efficient. As a consequence of this proposed growth mechanism, it is suggested that the lower atmosphere of Titan will be enriched in nitrogen-containing aerosols.

Hemibonding between Water Cation and Water.

The hemibonding interaction in the water dimer cation is studied using coupled cluster electronic structure methods. The hemibonded dimer cation geometry is a local minimum structure characterized by the two participating monomers having both a very short separation and a near parallel relative orientation. It is shown that the vertically ionized dimer at its optimum neutral geometry can convert to the hemibonded dimer cation structure with essentially no energetic hindrance. Direct conversion to the hemibonded structure is therefore an energetically facile alternative to the minimum energy path that connects the vertically ionized neutral water dimer to the global minimum proton-transferred structure. A substantial barrier must be surmounted to convert the hemibonded dimer cation to the proton-transferred structure. The optical absorption spectrum of the hemibonded dimer cation is characterized by three excited near-UV states, two of which have very large oscillator strengths. Relative resonance Raman intensities are estimated for the hemibonded dimer cation vibrational modes, finding the intermolecular stretching mode to be the most strongly enhanced when in near resonance with each of the near-UV excited states, and the anharmonicity and overtones of this mode are estimated. These results provide guidance for the possible observation of hemibonded cations in irradiated liquid water.

Dynamic pre-BCR homodimers fine-tune autonomous survival signals in B cell precursor acute lymphoblastic leukemia.

The pre-B cell receptor (pre-BCR) is an immature form of the BCR critical for early B lymphocyte development. It is composed of the membrane-bound immunoglobulin (Ig) heavy chain, surrogate light chain components, and the signaling subunits Igα and Igβ. We developed monovalent quantum dot (QD)-labeled probes specific for Igβ to study the behavior of pre-BCRs engaged in autonomous, ligand-independent signaling in live B cells. Single-particle tracking revealed that QD-labeled pre-BCRs engaged in transient, but frequent, homotypic interactions. Receptor motion was correlated at short separation distances, consistent with the formation of dimers and higher-order oligomers. Repeated encounters between diffusing pre-BCRs appeared to reflect transient co-confinement in plasma membrane domains. In human B cell precursor acute lymphoblastic leukemia (BCP-ALL) cells, we showed that frequent, short-lived, homotypic pre-BCR interactions stimulated survival signals, including expression of BCL6, which encodes a transcriptional repressor. These survival signals were blocked by inhibitory monovalent antigen-binding antibody fragments (Fabs) specific for the surrogate light chain components of the pre-BCR or by inhibitors of the tyrosine kinases Lyn and Syk. For comparison, we evaluated pre-BCR aggregation mediated by dimeric galectin-1, which has binding sites for carbohydrate and for the surrogate light chain λ5 component. Galectin-1 binding resulted in the formation of large, highly immobile pre-BCR aggregates, which was partially relieved by the addition of lactose to prevent the cross-linking of galectin-BCR complexes to other glycosylated membrane components. Analysis of the pre-BCR and its signaling partners suggested that they could be potential targets for combination therapy in BCP-ALL.

Challenges to the Pair Bond: Neural and Hormonal Effects of Separation and Reunion in a Monogamous Primate.

Social monogamy at its most basic is a group structure in which two adults form a unit and share a territory. However, many socially monogamous pairs display attachment relationships known as pair bonds, in which there is a mutual preference for the partner and distress upon separation. The neural and hormonal basis of this response to separation from the adult pair mate is under-studied. In this project, we examined this response in male titi monkeys (Callicebus cupreus), a socially monogamous New World primate. Males underwent a baseline scan, a short separation (48 h), a long separation (approximately 2 weeks), a reunion with the female pair mate and an encounter with a female stranger (with nine males completing all five conditions). Regional cerebral glucose metabolism was measured via positron emission tomography (PET) imaging using [18F]-fluorodeoxyglucose (FDG) co-registered with structural magnetic resonance imaging (MRI), and region of interest (ROI) analysis was carried out. In addition, plasma was collected and assayed for cortisol, oxytocin (OT), vasopressin (AVP), glucose and insulin concentrations. Cerebrospinal fluid (CSF) was collected and assayed for OT and AVP. We used generalized estimating equations (GEE) to examine significant changes from baseline. Short separations were characterized by decreases in FDG uptake, in comparison to baseline, in the lateral septum (LS), ventral pallidum (VP), paraventricular nucleus of the hypothalamus (PVN), periaqueductal gray (PAG), and cerebellum, as well as increases in CSF OT, and plasma cortisol and insulin. Long separations differed from baseline in reduced FDG uptake in the central amygdala (CeA), reduced whole brain FDG uptake, increased CSF OT and increased plasma insulin. The response on encounter with a stranger female depended on whether or not the male had previously reproduced with his pair mate, suggesting that transitions to fatherhood contribute to the neurobiology underlying response to a novel female. Reunion with the partner appeared to stimulate coordinated release of central and peripheral OT. The observed changes suggest the involvement of OT and AVP systems, as well as limbic and striatal areas, during separation and reunion from the pair mate.

Specific Ion Effects and pH Dependence on the Interaction Forces between Polystyrene Particles.

Colloidal interactions have been extensively studied due to the wide number of applications where colloids are present. In general, the electric double layer force and the van der Waals interaction dominate the net force acting between two colloids at large separation distances. However, it is well accepted that some other phenomena, especially those acting at short separation distances, might be relevant and induce substantial changes in the force profiles. Within these phenomena, those related to the surface contact angle, the hydration degree of the ions, or the pH, may dominate the force profiles features, not only at short distances. In this paper, we analyzed the effect of the pH and counterion type on the long-range as well as short-range forces between polystyrene colloidal particles by using the colloidal probe technique based on AFM. Our results confirm that the features of the force profiles between polystyrene surfaces are strongly affected by the pH and hydration degree of the counterions in solution. Additionally, we performed a study of the role of the pH on the wettability properties of hydrated and nonhydrated polystyrene sheets to scan the wettability properties of this material with pH. Contact angle measurements confirmed that the polystyrene surface is hydrophobic in aqueous solutions over the entire range of pHs investigated. These results are in good agreement with the features observed in the force profiles at low pH. At high pH, a short-range repulsion similar to the one observed for hydrophilic materials is observed. This repulsion scales with the pH, and it also depends on the hydration degree of the ions in solution. This way, the short-range forces between polystyrene surfaces may be tunable with the pH, and its origin does not seem to be related to the hydrophobicity of the material.

Crystal structure of 3,5-di-methyl-pyridine N-oxide dihydrate.

In the title compound, also known as 3,5-lutidine N-oxide dihydrate, C7H9NO·2H2O, the N-O bond is weakened due to the involvement of the O atom as an acceptor of hydrogen bonds from the two water mol-ecules of crystallization present in the asymmetric unit. Fused R35(10) ring motifs based on O-H⋯O hydrogen bonds form chains in the [010] direction, which are further connected by weak C-H⋯O inter-molecular contacts. As a result, the lutidine mol-ecules are stacked in an efficient manner, with π-π contacts characterized by a short separation of 3.569 (1) Å between the benzene rings.

Effect of solvent quality and chain density on normal and frictional forces between electrostatically anchored thermoresponsive diblock copolymer layers

Equilibration in adsorbing polymer systems can be very slow, leading to different physical properties at a given condition depending on the pathway that was used to reach this state. Here we explore this phenomenon using a diblock copolymer consisting of a cationic anchor block and a thermoresponsive block of poly(2-isopropyl-2-oxazoline), PIPOZ. We find that at a given temperature different polymer chain densities at the silica surface are achieved depending on the previous temperature history. We explore how this affects surface and friction forces between such layers using the atomic force microscope colloidal probe technique. The surface forces are purely repulsive at temperatures <40°C. A local force minimum at short separation develops at 40°C and a strong attraction due to capillary condensation of a polymer-rich phase is observed close to the bulk phase separation temperature. The friction forces decrease in the cooling stage due to rehydration of the PIPOZ chain. A consequence of the adsorption hysteresis is that the friction forces measured at 25°C are significantly lower after exposure to a temperature of 40°C than prior to heating, which is due to higher polymer chain density on the surface after heating.