Poly(decamethylene oxide) single crystals from dilute solution

Summary A preliminary study on the morphology and chain orientation of four low molecular weight poly(decamethylene oxide) fractions crystallized from ethyl alcohol diluted solution is reported. The single crystals predominantly show the polyethylene orthorhombic unit cell projection although some also present the polytetrahydrofuran structure. The characteristic X-ray long periods obtained are indicative in all cases of a chain folded crystal surface.

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Zusammenfassung Eine vorläufige Studie der Morphologie und der Kettenorientierung von vier Polydecamethylenoxyd-Fraktionen niederen Molekulargewichtes, die aus verdünnter Methylalkohol-Lösung kristallisiert wurden, wird wiedergegeben.Die Einzelkristalle zeigen bevorzugt die orthorhombische Projektion der Einheitszelle, obgleich einige auch die Polytetrahydrofuranstruktur präsentieren. Die charakteristischen Röntgenstrahllangperioden deuten in allen Fällen auf eine kettengefaltete Kristalloberfläche hin.

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With 5 figures

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Thanks are due to Mr.J. Tinas Gálvez for the kind supply of the samples.     

Monte Carlo simulations of single crystals from polymer solutions

A novel "anisotropic aggregation" model is proposed to simulate nucleation and growth of polymer single crystals as functions of temperature and polymer concentration in dilute solutions. Prefolded chains in a dilute solution are assumed to aggregate at a seed nucleus with an anisotropic interaction by a reversible adsorption/desorption mechanism, with temperature, concentration, and seed size being the control variables. The Monte Carlo results of this model resolve the long-standing dilemma regarding the kinetic and thermal roughenings, by producing a rough-flat-rough transition in the crystal morphology with increasing temperature. It is found that the crystal growth rate varies nonlinearly with temperature and concentration without any marked transitions among any regimes of polymer crystallization kinetics. The induction time increases with decreasing the seed nucleus size, increasing temperature, or decreasing concentration. The apparent critical nucleus size is found to increase exponentially with increasing temperature or decreasing concentration, leading to a critical nucleus diagram composed in the temperature-concentration plane with three regions of different nucleation barriers: no growth, nucleation and growth, and spontaneous growth. Melting temperatures as functions of the crystal size, heating rate, and concentration are also reported. The present model, falling in the same category of small molecular crystallization with anisotropic interactions, captures most of the phenomenology of polymer crystallization in dilute solutions.     

Morphology and structure of nylon‐2,14 single crystals from dilute solution

A perfect single crystal of nylon‐2,14 was prepared from 0.02% (w/v) 1,4‐butanediol solution by a “self‐seeding” technique and isothermal crystallization at 120 and 145 °C. The morphology and structure features were examined by transmission electron microscopy with both image and diffraction modes, atomic force microscopy, and wide‐angle X‐ray diffraction (WAXD). The nylon‐2,14 single crystal grown from 1,4‐butanediol at 145 °C inhabited a lathlike shape with a lamellar thickness of about 9 nm. Electron diffraction and WAXD data indicated that nylon‐2,14 crystallized in a triclinic system with lattice dimensions a = 0.49 nm, b = 0.51 nm, c = 2.23 nm, α = 60.4°, β = 77°, and γ = 59°. The crystal structure is different from that of nylon‐6,6 but similar to that of other members of nylon‐2Y. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1913–1918, 2002     

Growth kinetics of polyethylene single crystals: (II) Growth of {110} faces of crystals from dilute solutions in decalin and in octane

Summary The lateral growth rates of the {110} faces of polyethylene single crystals from solutions in decalin and octane have been investigated, using fractionated polymer samples, as a function of crystallization temperature and concentration. The growth rate was found to vary with concentration raised to a power, the value of the power being a function of molecular weight, temperature and solvent. The variation of the growth rate and the concentration exponent with molecular weight and crystallization temperature are discussed in terms of the solvent properties and a recently proposed dilute solution theory of polymer crystal growth which incorporates a self-nucleation mechanism.

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Zusammenfassung Die laterale Wachstumsgeschwindigkeit der {110}-Flächen der Polyäthyleneinkristalle in Dekalin- und Oktanlösung sind mit fraktionierten Polymerproben als Funktion der Kristallisationstemperatur und der Konzentration untersucht worden. Die Wachstumsgeschwindigkeit veränderte sich exponentiell mit der Konzentration. Der Exponent ist eine Funktion des Molekulargewichts, der Temperatur und des Lösungsmittels. Die Anderung der Wachstumsgeschwindigkeit und des Konzentrationsexponenten mit dem Molekulargewicht und der Kristallisationstemperatur sind in Bezug auf die Eigenschaften des Losungsmittels und einer kürzlich vorgeschlagenen Theorie der verdünnten Lösung des Polymerkristallwachsums, die einen Selbstnukleationsmechanismus einbezieht, diskutiert worden.

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With 9 figures and 5 tables     

Nanoscale calorimetry of isolated polyethylene single crystals

We used thin‐film differential scanning calorimetry to investigate the melting of isolated polyethylene single crystals with lamellar thicknesses of 12 ± 1 nm. We observed the melting of as few as 25 crystals. Over a wide number of crystals (25–2000 crystals), the heat of fusion was 40% larger than the bulk value. The melting temperature of the isolated single crystals was 123 ± 2 °C, 9 °C lower than that of the bulk material. We also measured the heat of fusion of quenched crystals (±15%) over a wide range of heating rates (20,000–100,000 K/s). Annealing the quenched crystals resulted in shifts in the endotherm peak by as much as 15 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1237–1245, 2001     

Crystallization of isotactic polystyrene from dilute solutions

The overall rate of crystallization of isotactic polystyrene from dilute solutions, 1% by weight, in trans-decalin and benzyl alcohol was studied as a function of temperature using dilatometry. These solvents were chosen because the dissolution temperatures of crystalline isotactic polystyrene are practically the same in both solvents. The overall rate of crystallization as a function of crystallization temperature showed a maximum in both solvents at about 50°C. At lower crystallization temperatures the rate of crystallization is much lower. The overall rate of crystallization of isotactic polystyrene in benzyl alcohol is far larger than in trans-decalin at the same undercooling throughout the temperature range, which is in apparent contradiction to present crystallization theories. At very large undercooling (T_c lower than about 0°C) the solutions of isotactic polystyrene in both solvents quickly become “rigid” gels. Surface replicas of freeze-etched gels indicate that a fringed micelle type of crystallization takes place at these low temperatures. The transition from folded chain crystallization to fringed micelle crystallization may be due to a stiffening of the polymer chain below about 50°C, with a reduced rotational mobility of the phenyl groups on the chain. If very dilute solutions, below 0.5% by weight, are crystallized at these low temperatures no gels were formed but fibrous crystals are produced which could be observed under the polarizing microscope.     

Spontaneous evaporation of dilute saturated solutions. Urea nitrate crystals from saturated solution in strong nitric acid

Summary Large, perfect crystals of urea nitrate were obtained by the addition of concentrated nitric acid to an aqueous solution of the salt, followed by spontaneous evaporation. The crystal angles have been measured.

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Zusammenfassung Große, gut ausgebildete Kristalle von Harnstoffnitrat erhält man bei Zugabe konz. Salpetersäure zu einer wäßrigen Lösung des Salzes und nachheriger Spontanverdampfung. Die Kristallwinkel wurden gemessen.

     

Thermotropic liquid crystals from a monosubstituted 2,2'-bipyridine

Unsymmetric functionalization of 5-bromo-2,2'-bipyridine and 5,5'-dibromo-2,2'-bipyridine with 4-n-alkoxyphenylethynyl leads to two new families of mesomorphic compounds. The smectic B, smectic A and nematic phases observed were studied by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. The structural parameters of the smectic phases were determined. The internal structure of the smectic phases, particularly the range of the in-layer ordering of the molecules, was investigated as a function of temperature.     

Thermotropic liquid crystals from a monosubstituted 2,2'-bipyridine

Unsymmetric functionalization of 5-bromo-2,2'-bipyridine and 5,5'-dibromo-2,2'-bipyridine with 4-n-alkoxyphenylethynyl leads to two new families of mesomorphic compounds. The smectic B, smectic A and nematic phases observed were studied by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. The structural parameters of the smectic phases were determined. The internal structure of the smectic phases, particularly the range of the in-layer ordering of the molecules, was investigated as a function of temperature.     

Solvent sublation of cerium ions from dilute aqueous solutions

The possibilities of using the adsorptive bubble process of separation (solvent sublation) for the removal of trace amounts of cerium were studied. The optimal conditions and kinetic regularities of the process in solutions containing cerium ions and a surfactant (sodium dodecyl sulfate) used as a collector were determined. The structure of the sublates extracted into the organic phase changes depending on the pH of the medium.     

Conformation analysis of freeze-dried isotactic polystyrene from dilute solutions

Fourier transform infrared spectra of freeze-dried samples of isotactic polystyrene (i-PS) from dilute solutions were analyzed. The 698, 1452, 1493 and 1601 cm⁻¹ bands increased in sharpness and intensity as the solution concentration decreased, indicating that the freeze-dried sample is in a more dilated state. When the freeze-dried i-PS was annealed at 100°C, all aforementioned bands broadened and their heights depressed, accompanied with a significant change of the bands at 981 and 906 cm⁻¹.     

Hydrogen bonding of single acetic acid with water molecules in dilute aqueous solutions

In separation processes, hydrogen bonding has a very significant effect on the efficiency of isolation of acetic acid (HOAc) from HOAc/H₂O mixtures. This intermolecular interaction on aggregates composed of a single HOAc molecule and varying numbers of H₂O molecules has been examined by using ab initio molecular dynamics simulations (AIMD) and quantum chemical calculations (QCC). Thermodynamic data in aqueous solution were obtained through the self-consistent reaction field calculations and the polarizable continuum model. The aggregation free energy of the aggregates in gas phase as well as in aqueous system shows that the 6-membered ring is the most favorable structure in both states. The relative stability of the ring structures inferred from the thermodynamic properties of the QCC is consistent with the ring distributions of the AIMD simulation. The study shows that in dilute aqueous solution of HOAc the more favorable molecular interaction is the hydrogen bonding between HOAc and H₂O molecules, resulting in the separation of acetic acid from the HOAc/H₂O mixtures with more difficulty than usual.     

Distribution of single DNA molecule electrophoretic mobilities in semidilute and dilute hydroxyethylcellulose solutions

The distribution of center of mass electrophoretic mobility mobilities and normalized migration time of up to 1080 lambda DNA molecules per experiment were measured in both semidilute hydroxyethylcellulose HEC/0.5 x Tris-borate-EDTA (TBE) solutions and dilute HEC/0.5 x TBE solution by high-speed video microscopy. Measurements were made microscopically over a short migration distance in homogeneous DNA HEC/0.5 x TBE solution and after electrophoretic migration of a plug of DNA through 7 cm. Video at 120 frames/s (semidilute HEC solution) and 236 frames/s (dilute HEC solution) allowed visualization with adequate resolution for single molecule mobility measurements. The electrophoretic migration times and band shapes predicted from the measurements corresponded well with those measured by conventional capillary electrophoresis (CE) in both semidilute and dilute HEC. In semidilute solution, the band width predicted by a square root of time scaling is in good agreement with the results of conventional CE. However, in dilute solution the precision of the measurements was not good enough to allow scaled estimates of band widths.     

稀醋酸/水溶液中单个醋酸与水分子的氢键结构

在醋酸/水体系的工业分离中,溶液中的氢键对分离效率有很大影响.本文采用两种第一性原理方法,即从头算分子动力学模拟(AIMD)和量子化学计算(QCC),对由单个醋酸和不同水分子所组成聚合体的氢键相互作用进行了研究,采用极化统一模型和自洽反应场模型计算得到了聚合体在水溶液中的热力学数据.从QCC计算的气相和水溶液中的聚合自由能表明六元环在两种状态下都为最优结构,热力学数据反映出的各种结构的相对稳定性与AIMD模拟的环分布符合得相当一致.研究表明,由于存在醋酸和水分子间的氢键作用,稀醋酸/水溶液中的醋酸分离要比在浓醋酸溶液中困难得多.     

Formation of manganese solid solutions in single crystals of ZnGeP2

Process of the solid-phase diffusion of manganese into single crystals ZnGeP² are investigated by electron paramagnetic resonance and X-ray element microanalysis. Conditions for formation of a solid solution with Mn²⁺ concentration of 10¹⁸ cm^-3 were found. A diffusion coefficient of manganese in single crystal of ZnGeP² at a diffusion annealing temperature was determined.     

Jetting of dilute polymer solutions

Light emitting devices containing conjugated polymers are conveniently fabricated using ink-jet printing. A common problem in the processing of these materials is that the Newtonian viscosity of the polymer solution is not sufficient to describe the jetting performance because the molecular weights and concentrations employed are such that the resulting solutions are elastic. These differences in fluid elasticity levels cannot be measured using traditional techniques like dynamic mechanical experiments or the first normal stress difference in shear, but strongly impact the jetting behavior of the liquid. In this study, a variety of polystyrene solutions in DECALIN having a shear viscosity of ~5 mPa s but different elasticity levels were examined for their jetting behavior. The jetting behavior of these solutions was studied visually using drop-on-demand jetting equipment and their rheology was characterized using a custom extensional rheometer designed for measuring the elasticity of such low viscosity liquids. If elasticity effects are absent as in Newtonian liquids (corresponding to a Trouton ratio of 3) satellite drops are formed resulting in loss of liquid and poor positioning. On the other hand, if elasticity effects are very large (Trouton ratios ≫4) separation problems occur at the nozzle with undesirable “tailing.” The optimum range for stable, efficient jetting occurs at Trouton ratios in a narrow band between 3 and ~5. A very slight degree of elasticity corresponding to a Trouton Ratio around four thus seems to be optimum for the jetting process. This appears to be the first time that such a design criterion has been outlined for this process. Such an approach complements thermal techniques for elucidating the role of molecular and flow properties on the processing behavior of polymeric systems.     

TheLangmuir-Freundlich equation in adsorption from dilute solutions on solids

Correlation between parameters obtained from the signle-solute and bisolute adsorption data by means of theLangmuir-Freundlich equation has been studied.