Crystallization Kinetics of Lamellar Crystals Confined in Polymer Thin Films

We used dynamic Monte Carlo simulations to investigate the crystallization kinetics of flat-on lamellar polymer crystals in variable thickness films. We found that the growth rates linearly reduced with decreasing film thickness for the films thinner than a transition thickness d_t , while they were constant for the films thicker than d_t . Moreover, the mean stem lengths (crystal thickness) we calculated decreased with film thickness in a similar way to the growth rates, and the intramolecular crystallinities we calculated confirmed the film thickness dependence of the crytsal thickness. Besides, the crystal melting rates in thin films were calculated and increased with decreasing film thickness. We proposed a new interpretation on the film thickness dependence of the crystal growth rate in thin films, suggesting that it is dominated by the crystal thickness in terms of the driving force term (l–l _min) expressed by Sadler, rather than the chain mobility based on experiments. The crystal thickness can determine whether a crystal grows or melts in a thin film at a fixed temperature, indicating the reversibility between the crystal growth and melting.     

The Spatial-Temporal Lamellar Structures in the Confined Ideal Polymer Blends

We consider the formation of self-organized spatial-temporal oscillating structures in symmetric binary polymer blends confined by two flat walls. An influence of these walls on the formation of the oscillating volume structures is studied. This phenomenon is simulated by an initial boundary-value problem for the conserved order parameter (or the concentration of one of the components in a binary mixture). Under a special choice the dynamical Puri-Binder’s boundary conditions these structures look like the lamellar structures. The behavior of the order parameter is described by the modified Cahn-Hilliard equation which models so-called the non-Fickian diffusion in the symmetric binary polymer blends. The nonlinear dynamical boundary conditions correspond to the process of adsorption-desorption on the walls. As a result, these nonlinear surface processes induce into the volume the spatial-temporal asymptotically periodic structures of relaxation, pre-turbulent or turbulent type with finite, countable or non-countable points of discontinuities on the period correspondingly. The frequency of oscillations on the period follows a power-law for the relaxation type and increases exponentially in the other cases.     

Growth Rates of Edge-on Lamellar Crystals Confined in Polymer Thin Films

The growth rates of edge-on lamellar polymer crystals in variable thickness films were investigated in terms of dynamic Monte Carlo (MC) simulations. The growth rates linearly decreased with decreasing film thickness for the thinner films and were nearly constant for the thicker films. The mean stem lengths (crystal thickness) were also constant in different thickness films. The crystal widths parallel to the film thickness increased more slowly with increasing film thickness in the thinner films than that in the thicker films, indicating they were restrained by the film thickness. We propose that the growth rate of edge-on lamellar crystals in thin films is dominanted by the crystal width in the thinner films and by the crystal thickness in the thicker films; the variation of the film thickness can change the three-dimensional shape of the crystal growth front, also affecting the growth rate of the edge-on lamellar crystal.     

Confined Crystallization in Polymer Blends: DSC Studies of the Behavior and Kinetics of Isothermal Crystallization of Polypropylene in Poly(cis-butadiene) Rubber Blends

Thermal properties of polypropylene with poly(cis-butadiene) rubber (iPP/PcBR) blends have been measured by differential scanning calorimetry (DSC), and the melting point T_m, crystallization temperature T_c, enthalpy Δ H (melting enthalpies and crystalline enthalpies), and equilibrium melting point T⁰ _m have been measured and calculated. The variation of T_m, T_c, Δ H and T⁰ _m with composition in the blends was discussed, showing that an interaction between phases is present in iPP/PcBR blends. The degree of supercooling characterizing the interaction between two phases in the blends and the crystallizability of the blends which bears a relationship to the composition of the blends was discussed. The kinetics of isothermal crystallization of the crystalline phase in iPP/PcBR blends was studied in terms of the Avrami equation, and the Avrami exponent n and velocity constant K were obtained. The Avrami exponent n is between 3 and 2, meaning that iPP has a thermal nucleation with two dimensional growths. The variation of the Avrami exponent n, velocity constant K, and crystallization rate G bear a relation to the composition of the blends, n increases with increasing content ofPcBR. K also increased with increasing content of PcBR. All of the K for the blends are greater than for pure iPP. The crystallization rate G (t_1/2) depends on the compositions in the blends; all G of the blends are greater than for iPP.     

Effect of Interaction upon Translocation of Confined Polymer Chain Through Nanopore

运用二维的键长涨落模型和蒙特卡洛方法研究高分子链从一个受限空间到自由空间穿孔过程中,链单体与纳米孔之间的相互作用.结果表明,在不同的链长和纳米孔交互作用下,高分子链成功穿越自由能能垒取决于链长和纳米孔长度,并且由于交互作用降低了自由能能垒,导致高分子链在纳米管的平均捕获时间缩短.     

Analyzing Microdomains in Biological Membranes Using Fluorescence Techniques

It is becoming increasingly clear that various lipids and proteins in the plasma membrane are not distributed homogeneously but are organized in compositionally and functionally variable microdomains. Fluorescence techniques have contributed significantly to our understanding of membrane structure and function. Here we review recent studies using fluorescence methods to detect membrane domains in intact cells. We also discuss the current limitations in the available techniques and the models used to interpret experimental data.     

Diffusing opinions in bounded confidence processes

We study the effects of diffusing opinions on the Deffuant et al. model for continuous opinion dynamics. Individuals are given the opportunity to change their opinion, with a given probability, to a randomly selected opinion inside an interval centered around the present opinion. We show that diffusion induces an order-disorder transition. In the disordered state the opinion distribution tends to be uniform, while for the ordered state a set of well defined opinion clusters are formed, although with some opinion spread inside them. If the diffusion jumps are not large, clusters coalesce, so that weak diffusion favors opinion consensus. A master equation for the process described above is presented. We find that the master equation and the Monte Carlo simulations do not always agree due to finite-size induced fluctuations. Using a linear stability analysis we can derive approximate conditions for the transition between opinion clusters and the disordered state. The linear stability analysis is compared with Monte Carlo simulations. Novel interesting phenomena are analyzed.     

Phase Self-Assembly Driven Inverse Kinetics of Mixing in Ternary Encapsulated Polymer Blends

The influence of mixing time on the evolution of phase morphologies in poly(methyl methacrylate)/polystyrene/poly(butylene terephthalate) (PMMA/PS/PBT) and PMMA/PS/ polycarbonate (PC) immiscible ternary blends with encapsulated dispersed phases was investigated. It was found that both systems demonstrate up to a sevenfold enlargement of the phase dimensions with mixing time, that is, display an inverse kinetics of blending. In addition, three different mixing sequences (MSs) used for preparation of the compositions resulted in pronounced differences in the domain sizes, especially, at intermediate mixing times. These differences decreased gradually with further blending. The phenomena observed are explained in terms of a transition from the nonequilibrium to equilibrium encapsulated morphologies driven by interfacial forces and phase self-assembly effects.     

Diffusing wave spectroscopy in Maxwellian fluids

We present a critical assessment of the diffusing wave spectroscopy (DWS) technique for obtaining the characteristic lengths and for measuring the loss and storage moduli of a reasonable well-known wormlike micelle (WM) system. For this purpose, we tracked the Brownian motion of particles using DWS embedded in a Maxwellian fluid constituted by a wormlike micellar solution made of cetyltrimethylam-monium bromide (CTAB), sodium salicylate (NaSal), and water. We found that the motion of particles was governed by the viscosity of the solvent at short times and by the stress relaxation mechanisms of the giant micelles at longer times. From the time evolution of the mean square displacement of particles, we could obtain for the WM solution the cage size where each particle is harmonically bound at short times, the long-time diffusion coefficient, and experimental values for the exponent that accounts for the broad spectrum of relaxation times at the plateau onset time found in the 〈Δr ²(t)〉 vs. time curves. In addition, from the 〈Δr ²(t) vs. time curves, we obtained G′(ω) and G″(ω) for the WM solutions. All the DWS microreological information allowed us to estimate the characteristic lengths of the WM network. We compare our DWS microrheological results and characteristic lengths with those obtained with mechanical rheometers at different NaSal/CTAB concentration ratios and temperatures.     

Water Desorption Kinetics of Polymer Composites with Cellulose Fibers as Filler

The water desorption kinetics of polymer composite systems with hydrophilic cellulose fibers from recycled paper (PSP) filler embedded in various polymer matrices (hydrophobic thermoset epoxy resin [EP] and thermoplastic polypropylene [PP], and hydrophilic thermoplastic poly[vinyl alcohol] [PVA]) was studied. Polymer composites test pieces containing 0, 3, 6, 9, and 30 wt. % of fibers were prepared. Adhesion between fibers and polymer matrices was improved by utilization of maleic anhydride grafted polypropylene (MAPP) coupling agent in the case of thermoplastic matrices (both PP and PVA). Water desorption tests were conducted after immersing test pieces in a distilled water bath at room temperature for 24 h. Study of the water desorption kinetics proved the expected enhanced absorption of the resulting composites after incorporation of cellulose fibers. A difference between two similar types of PVA by measurement of the desorption kinetics was found.     

Kinetics and Mechanism of in situ Simultaneous Formation of Metal Nanoparticles in Stabilizing Polymer Matrix

The kinetic peculiarities of the thermal transformations of unsaturated metal carboxylates (transition metal acrylates and maleates as well as their cocrystallites) and properties of metal-polymer nanocomposites formed have been studied. The composition and structure of metal-containing precursors and the products of the thermolysis were identified by X-ray analysis, optical and electron microscopy, magnetic measurements, EXAFS, IR and mass spectroscopy. The thermal transformations of metal-containing monomers studied are the complex process including dehydration, solid phase polymerization, and thermolysis process which proceed at varied temperature ranges. At 200–300°C the rate of thermal decay can be described by first-order equations. The products of decompositions are nanometer-sized particles of metal or its oxides with a narrow size distribution (the mean particle diameter of 5–10nm) stabilized by the polymer matrix.     

Thermodynamic Free Energy Behavior of Diblock Copolymer Chains Confined Between Planar Surfaces Having End-Tethered Flexible Polymer Molecules

A molecular model for the free energy of a confined system of diblock copolymer chains within a 2D slit with the interior surfaces having end-tethered chains is presented, based on a combined lattice and scaling theory approach. The thermodynamics of a model system, based on a constrained minimization of free energy, is explored as a function of the intermolecular energy parameters for interaction between the segments of block copolymer chains, end-tethered chains, and the surfaces. The effects of chain length and the block length ratio are investigated over a wide range of values. The results obtained are qualitative in nature; however, the model can be implemented to real systems provided appropriate parameterization of the model parameters to real systems can be performed. The phase diagrams obtained here provide ways for designing thermodynamically stable systems within the physical parametric variable space.     

Frequency-Domain Measurements of Diffusing Photon Propagation in Solid Phantoms

Photon propagation in a highly scattering medium such as living tissue is well described by the photon diffusion equation. In a homogeneous and isotropic case, the equation has analytically been solved for a medium with a simple geometrical shape. We report frequency-domain measurements using slab-shaped solid phantoms. Comparison of the results with computer simulations proves the validity of extrapolated boundary conditions.     

CP MAS Kinetics Study of Ionic Liquids Confined in Mesoporous Silica: Convergence of Non-Classical and Classical Spin Coupling Models

The high data point density measurements of ¹H→¹¹B cross-polarization (CP) kinetics upon magic-angle spinning (MAS) of [bmim][BF₄] confined in mesoporous SBA-15 and MCM-41 were carried out. The complex shaped ¹¹B CP MAS signals were observed in both silica and decomposed into two Lorentz components. This points towards the possibility of bimodal distribution of [bmim][BF₄] in the studied confinements. The convergence of classical and non-classical spin coupling models was deduced processing CP kinetic curves. A good fit of the theoretical curves to the experimental data was achieved using both models without any non-random deviations between theory and experiment to appear. The convergence of spin coupling models was discussed in terms of relatively high mobility of BF₄ ^? anion respect to the cation and the dynamics of anions in pores. These factors delete the borders between spin clusters. The spin diffusion along the pore surfaces in MCM-41 is more than twice faster than in SBA-15.     

Harmonically Confined, Semiflexible Polymer in a Channel: Response to a Stretching Force and Spatial Distribution of the Endpoints

We consider an inextensible, semiflexible polymer or worm-like chain which is confined in the transverse direction by a parabolic potential and subject to a longitudinal force at the ends, so that the polymer is stretched out and backfolding is negligible. Simple analytic expressions for the partition function, valid in this regime, are obtained for chains of arbitrary length with a variety of boundary conditions at the ends. The spatial distribution of the end points is also analyzed.     

Synthesis of a Cationic BODIPY-Containing Conjugated Polymer for Detection of DNA and Cellular Imaging

A water-soluble cationic conjugated polyelectrolyte (P1) containing fluorene, BODIPY and diacetylene moieties was synthesized and characterized. P1 showed two main absorption bands with maxima at 360 and 574 nm as well as fluorescence maxima at 648 nm due to the incorporation of BODIPY into the polymer backbone. Addition of CT DNA can quench the emission of P1 because of the formation of a P1/CT DNA complex, which was demonstrated by UV–vis spectra and dynamic light scattering (DLS) analyses. Cellular imaging results indicated P1 could be utilized as cellular imaging of HeLa cells, where red fluorescence was observed in the partial cytoplasm. Moreover, CCK-8 assay showed P1 had a low cytotoxicity.     

Confined phonons in glasses

The European Physical Journal E - We have applied nuclear inelastic absorption (NIA) to the molecular glass former dibutyl phthalate/ferrocene, both in bulk and in nanoporous matrices having pore...     

Confined subdiffusion in three dimensions

Three-dimensional （3D） Fick＇s diffusion equation and fractional diffusion equation are solved for different reflecting boundaries. We use the continuous time random walk model （CTRW） to investigate the time-averaged mean square dis- placement （MSD） of a 3D single particle trajectory. Theoretical results show that the ensemble average of the time-averaged MSD can be expressed analytically by a Mittag-Leffler function. Our new expression is in agreement with previous formu- las in two limiting cases： （^-δ2） ~ △1 in short lag time and （^-δ2} ~ △1 -α in long lag time. We also simulate the experimental data of mRNA diffusion in living E. coli using a 3D CTRW model under confined and crowded conditions. The simulation results are well consistent with experimental results. The calculations of power spectral density （PSD） further indicate the subdiffsive behavior of an individual trajectory.