Slit Height Research Articles

Shifting the Isotropic–Nematic Transition in Very Strongly Confined Semiflexible Polymer Solutions

We investigated how very strong confinement, smaller than the polymer persistence length lp, affects the isotropic–nematic transition for semiflexible polymer solutions using GPU-accelerated Langevin dynamics. Walls facilitate polymer alignment, and under strong quasi-two-dimensional slitlike confinement, the I–N transition is found to be a continuous transition occurring via capillary nematization. We found that the I–N transition in the slit is a second-order transition, and the transition volume fraction ϕcr decreases with decrease of the slit height H. For H < lp, the critical exponent of the order parameter is found to be β ≈ 0.3–0.5. β sharply increases for H higher than a critical height, indicating the onset of a different wall-induced phase transition. Higher ϕcr are found for larger H, which is associated with increased monomer packing near the walls and correspond to the partial wetting transition predicted by self-consistent field theory.

Self-assembly behavior of rod-coil-rod triblock copolymers within a planar slit

The self-assembly behavior of sphere-forming R5C30R5 triblock copolymers within a planar slit is studied by performing dissipative particle dynamics simulations. A sequence of novel structures which are not observed in bulk are formed within slits, including wetting layers, island-like structure, parallel cylinders, perpendicular cylinders and cross-cylindrical structures. Perpendicular cylinders are always formed before the increase in the layers of parallel cylinders. A phase diagram of the assembled structures with respective to the slit property and height is thus presented. The rod length is found to have a significant impact on the rod alignment, and a disordered-ordered transition of rod orientation occurs with an increase in the length of rod blocks. Some special structures, such as parallel half-cylinders and arrowhead-shaped morphology, are observed when the rod length increases to a certain extent. Our results show that the property and height of the slit and rod length all influence the self-assembly of rod-coil-rod triblock copolymers.

Effects of solvent and wall roughness on the dynamics and structure of a single polymer in a slit

The structure and dynamics of polymers in confinements (such as porous media, channels and slits) depend not only on the characteristic length scales of the confinements but also on solvent types and interactions between polymers and confinement constituents. In this study, we show by performing both molecular dynamics (MD) and Langevin dynamics (LD) simulations that the lateral diffusion of a single flexible polymer in a good solvent in a slit should be determined by a complicated interplay among the slit height (H), solvent types and slit wall roughness. The slit wall roughness is tuned by employing either corrugated walls or smooth walls. We find from simulations that only when solvent molecules are implemented explicitly in MD simulations, the wall roughness makes a qualitative difference in the lateral diffusion coefficient (D∥) of the polymer: as H is decreased, D∥ increases for smooth walls while D∥ decreases for corrugated walls. Such a qualitative difference in D∥ should be a solvent-mediated effect, which is not observed for implicit solvent models in LD simulations. The single polymer in the slit with the explicit solvent model follows Zimm dynamics while the polymer follows Rouse dynamics with the implicit solvent models. In the meantime, the wall roughness hardly affects the structure of the polymer in the slit. The density distribution functions of monomers (ρm(z)) and solvent molecules (ρs(z)) do not depend on whether the walls are corrugated or smooth. The radius of gyration (Rg) is also insensitive to the wall roughness. On the other hand, the solvent model gives rise to a qualitative difference in ρm(z) and Rg, especially when the height (H) of the slit is small. For sufficiently small values of H, ρm(z) depends on the size of solvent molecules used in the explicit solvent model. However, regardless of the solvent model and wall roughness, the scaling exponent (ν) of Rg and the degree of polymerization (N) (i.e., Rg∼Nν) changes gradually from 0.6 to 0.75 as H decreases.

Coil-globule transition of a single semiflexible chain in slitlike confinement.

Single polymer chains undergo a phase transition from coiled conformations to globular conformations as the effective attraction between monomers becomes strong enough. In this work, we investigated the coil-globule transition of a semiflexible chain confined between two parallel plates, i.e. a slit, using the lattice model and Pruned-enriched Rosenbluth method (PERM) algorithm. We find that as the slit height decreases, the critical attraction for the coil-globule transition changes non-monotonically due to the competition of the confinement free energies of the coiled and globular states. In wide (narrow) slits, the coiled state experiences more (less) confinement free energy, and hence the transition becomes easier (more difficult). In addition, we find that the transition becomes less sharp with the decreasing slit height. Here, the sharpness refers to the sensitivity of thermodynamic quantities when varying the attraction around the critical value. The relevant experiments can be performed for DNA condensation in microfluidic devices.

Single DNA Molecule Swollen and Trapped in Nanoslit

Single DNA Molecule Swollen and Trapped in NanoslitDirect visualization of individual DNA molecules confined within a nano/microfluidic geometry has provided a new route for the study of polymer physics. Molecular confinement has been utilized to evaluate theoretical predictions developed over several decades. Particularly, nanoslit confined DNA molecules are an interesting topic to show the conformational transition from 3D to 2D depending on nanoslit heights. Although several experiments have recently reported the dependence of DNA conformation on nanoslit confinement, a controversy still remains because the results have not been consistent with one another nor with theoretical predictions. Here we present nanoslit confined DNA conformations at various low ionic strength conditions down to 0.18 mM, which increase the repulsion between DNA−DNA and DNA−nanoslit. Moreover, we derived a new theoretical explanation for most measurements of single DNA molecule size under strong nanoslit confinement. Our findings demonstrates that very low ionic strength conditions not only increase the DNA persistence length dramatically, but also cause DNA molecules to swell to the extent that the effective diameter of DNA becomes larger than the nanoslit height (h < w), which can be considered as electrostatic trapping to confine molecules to geometry smaller than the physical boundaries. Consequently, by accounting for these effects, our results and theory provide a reasonable solution for a current controversy regarding the dependence of the DNA conformation on slit height (h), persistence length (p), and effective diameter (w).1. Lee J, Kim S, Jeong H, Jung GY, Chang R, Chen YL, Jo, K (2014) Nanoslit Confined DNA at Low Ionic Strengths. ACS Macro Letters 3(9): 926-930

Laser-Induced Spectroscopy of Graphene Ablation in Air

Carbon Swan spectra are observed following laser ablation of graphene in laboratory air. Previous experiments showed temperatures that ranged from 4500 to 7500 K for the Δv = 0 transition and 4200 to 4500 K for the Δv = −1 transition for time delays on the order of 1.6 μs to 70 μs. This experiment explored in greater detail time delays > 10 μs for both molecular bands. Temperatures were found to be similar, ranging from 4500 to 6700 K for the Δv = 1 transition and 3200 to 5500 K for the Δv = -1 transition. Investigation is also made into spatially resolving the plasma emissions along the slit height. In addition, efforts are made to investigate the applicability of the local thermodynamic equilibrium (LTE) assumption. Comparisons are discussed in view of previous work that utilized Stark broadening of the Hβ line, confirming LTE for delays < 10 μs, yet further research needed for later delays.

Nanoslit Confined DNA at Low Ionic Strengths.

We present nanoslit confined DNA conformations at very low ionic strengths and a theory to explain most measurements for single DNA molecule size under strong nanoslit confinement. Very low ionic strength conditions not only increase the DNA persistence length dramatically, but also cause DNA molecules to swell to the extent that the effective diameter of DNA becomes larger than the nanoslit height. By accounting for these effects, our results and theory provide a reasonable clue for a current controversy regarding the dependence of the DNA conformation on slit height (h), persistence length (p), and effective diameter (w).

Self-assembly of rod-coil diblock copolymers within a rod-selective slit: a dissipative particle dynamics simulation study.

Dissipative particle dynamics simulations are performed to investigate the self-assembly of rod-coil diblock copolymers R(N(R))C(N-N(R)) within a rod-selective slit. The self-assembled structure of the confined system is sensitively dependent on the rigidity kθ and the fraction fR of the rod block and the slit height H. From the phase diagram of structures with respect to kθ and fR for N = 12 and H = 6, we observe four main structures including disordered cylinder (DC) structure, hexagonally packed cylinders (HPC) perpendicular to the slit surfaces, and lamellar structures parallel (L∥) and perpendicular (L⊥) to surfaces. And structure transitions can be achieved by tuning kθ. The effect of the slit height on the self-assembled structure is also studied for R6C6 and R7C5 copolymers with large kθ. For R6C6, different structures near surfaces and in the interior of slit are observed in relatively wide slits. Whereas for R7C5, L⊥ structure, whose lamellar domain spacing decays exponentially with H, is generally generated. Our results suggest an effective way to control the ordering of rod-coil diblock copolymers under nanoscale confinement.

Molecular simulation study of triangle-well fluids confined in slit pores

Grand canonical Monte Carlo simulations are used to study the behaviour of triangle-well (TW) fluids with variable well widths confined inside slit pores. The effect of individual factors influencing the properties of confined fluids such as fluid–fluid interactions, pore size and pore wall–fluid interactions are obtained using simulations as it is difficult to experimentally determine the same. An interesting observation of this study is that inside the narrow pore of slit height h* = 5 at the high-pressure condition of P* = 0.8, for the TW fluid with long-range attraction or for the fluid at a low temperature for even a short-range attraction, the density profiles show layering such that there is a sticking tendency of the particles at centre, while there is a depletion of particles near the wall (as the layers at the centre have higher density peak heights than near the walls).

Analiza pola magnetycznego w wibroizolatorze z cieczą magnetoreologiczną działającą w trybie ściskania

The present study investigates the behaviour of a magnetorheological (MR) vibroisolator operated in the squeeze mode. The structure design and operating principles of the vibroisolator are outlined and the results of numerical calculations of the magnetic field in the device are provided. The purpose of the numerical procedure was to find the magnetic field distribution for all considered design options of the device and to establish the dependence of the axial component of magnetic flux density and the inductance of the control coil on the slit height. The calculation procedure was supported by the program Opera-2d. Analysis of magnetic field in a magnetorheological vibroisolator in the squeeze mode

Conformational Transition of Nanoslit Confined DNA at Low Ionic Strengths

We investigate experimentally the effect of ionic strength on λ DNA molecule in glass/PDMS nanoslit by using fluorescence microscope. The radius of gyration Rg was measured as a function of slit height (250 ∼ 1049 nm), and ionic strength (0.183 ∼ 1.75 mM) as a result, we observed the Rg values increases as channel heights and ionic strengths decrease. Furthermore, based on Odijk's and de Gennes polymer physics theory, we interpret our experimental findings as a function of channel heights and ionic strengths. We also study the effect of EDTA concentration, radius of gyration of λ DNA change drastically in response to the varying EDTA concentration at low ionic strength condition. Our results are useful for understanding the manipulation of biomolecules in nanofluidic devices.

Simulation study on the structure of rod-coil-rod triblock copolymer and nanoparticle mixture within slit

Self-assembly structures of rod-coil-rod ABA triblock copolymer and nanoparticle mixture within a slit are simulated by dissipative particle dynamics method. Results show that the structures are dependent on the rigidity of the rod block kθ, the interaction between the rod block and slit a(wA), the fraction of rod block f(A), and the slit height H. With an increase in kθ, we observe a transition from parallel lamellae to hexagonal cylinders. While with the increase in a(wA), the parallel lamellae at small kθ and hexagonal cylinders at large kθ change to perpendicular lamellae at large a(wA) close to a(As). At last, we present a phase diagram of structure with respect to f(A) and H at large kθ.

Revisiting blob theory for DNA diffusivity in slitlike confinement.

Blob theory has been widely applied to describe polymer conformations and dynamics in nanoconfinement. In slit confinement, blob theory predicts a scaling exponent of 2/3 for polymer diffusivity as a function of slit height, yet a large body of experimental studies using DNA produce a scaling exponent significantly less than 2/3. In this work, we develop a theory that predicts that this discrepancy occurs because the segment correlation function for a semiflexible chain such as DNA does not follow the Flory exponent for length scales smaller than the persistence length. We show that these short length scale effects contribute significantly to the scaling for the DNA diffusivity, but do not appreciably affect the scalings for static properties. Our theory is fully supported by Monte Carlo simulations, quantitative agreement with DNA experiments, and the results reconcile this outstanding problem for confined polymers.

Investigation of the Nucleation During Extrusion Cooking of Corn Starch by A Novel Nucleation Die

In this paper, a novel method for the investigation of nucleation in expanding starch-based melts is introduced. Therefore, corn starch was extruded by a twin screw extruder. A long slit die, which facilitated the formation of a nucleation area to extend nucleation, was mounted at the exit of the extruder. The temperature of the nucleation die (160–190 °C), the moisture content of the starch melt (17–27 %), and the slit height (4 and 10 mm) were varied to investigate the effect of pressure profile and shear rates on nucleation. The pore size distributions of the samples were determined by image analysis of the cross-sections. The influence of temperature, moisture content, and slit height on nucleation was investigated by analysis of the resulting pore size distribution. We found two totally different types of product: a product with few big pores and a product with small and evenly distributed pores. In general, small pores were achieved when the vapor pressure was reached already at the earlier stages of the nucleation die. The addition of nucleating agents, such as droplets or solid particles did not change the appearance of the products significantly. Applying a nucleation area such as introduced in our study enables further investigation of the mechanisms of nucleation.

Force-fluctuation physics of confined DNA: probing the breakdown of the Marko-Siggia law

&#x0D; &#x0D; &#x0D; Introduction: The study of polymers in nanofluidic systems such as nanopores and nanochannels is an important avenue of research in the physical and life sciences today. Complex nanofluidic devices containing varying topography are ideal for quantifying the behaviour of polymers under confinement. This study investigates the Marko-Siggia force-extension relationship under confinement. We measure the transverse fluctuations of deoxyribonucleic acid (DNA) confined between two pits in a nanofluidic slit to measure the potential breakdown of this model.&#x0D; Methods: We took images of fluorescently tagged single DNA molecules in the nanopit array with video- fluorescence microscopy and analyzed the standard deviation of the peak position along the direction of the molecular extension.&#x0D; Results: We were able to measure the parabolic relation between position and the strength of transverse fluctuations. By examining the peak variance as a function of slit height, our results indicate that the two dimensional version of the force-fluctuation relationship may be appropriate in the limit of strong confinement. However, we could not consistently measure the absolute length of the DNA stretched between two pits, which prevented us from fully exploring the force-extension and force-fluctuation relationships of confined DNA.&#x0D; Conclusions: These experiments further demonstrate that nanofluidic confinement serves as a useful tool for testing the extreme properties of polymers, and our results suggest further investigation into the breakdown of the Marko-Siggia force law.&#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D;

Separation of Ions in Nanofluidic Channels with Combined Pressure-Driven and Electro-Osmotic Flow

Separation of ionic species with the same electrophoretic mobility but different valence in electrolyte systems can occur within nanometer-scale channels with finite electrical double layers (EDLs). This is because EDL thicknesses are a significant fraction of slit height in such channels and can create transverse analyte concentration profiles that allow for unique separation modalities when combined with axial fluid flow. Previous work has shown such separation to occur using either pressure-driven flow or electro-osmotic flow separately. Here, we develop a Poisson-Boltzmann model to compare the separation of such ions using the combination of both pressure-driven and electro-osmotic flow. Applying a pressure gradient in the opposite direction of electro-osmotic flow can allow for zero or infinite retention of analyte species, which we investigate using three different wall boundary conditions. Furthermore, we determine conditions in fused silica nanochannels with which to generate optimal separation between two analytes of different charge but the same mobility. We also give simple rules of thumb to achieve the best separation efficacy in nanochannel systems.

PENGARUH PREHEAT DAN TEMPERING TERHADAP KEKERASAN DAN STRUKTUR MIKRO HASIL PENGELASAN BAJA JIS SS 400

JIS steel SS 400 is one of the most common types of steel used for hot rolling steel structures general. This steel is excellented to the weldability and machinability properties. This study aimed to determine the effect of heat treatment with preheating without tempering (PTT), with preheating and tempering (PT), without preheating and without tempering (TPTT), and without preheating tempering (TPT). The test results are then compared with the raw material specimens. Method of forming specimens using welding SMAW (Shielded Metal Arc Welding) DC reverse polarity using E7018 type electrode diameter of 4 mm. Type of seam used is V open seam with slit width and height of 2 mm and the width of the root angle 70o. This studied used a low alloy steel (JIS steel SS 400) which contain high levels of 0.20% C, maximum 0.005% S, maximum 0.005% P with repetitions each variation three times. Tests conducted it has testing the tensile strength, brinell hardness testing, and microstructure photo shoot. Value of the brinell hardness of welded joints highest in the tempering specimens without preheating, amounting with 163,911 HB hardness value. The structure of cementite and pearlite formed. While the lowest hardness values of specimens owned by raw material is 120,498 HB hardness values that form the microstructure of pearlite and ferrite.

Discrete Frequency Noise Generated by Air Jet between Flat Plate and Wedge

Aerodynamic noise with discrete frequencies is generated in an unexpected way from a slit between a flat plate, which is placed in parallel to the main flow, and a wedge that is placed normal to the flow. To study this phenomenon, we examined the discrete frequency noise generated by a subsonic air jet flow from a slit. It was found that the slit height and the plate length have considerable effects on the noise generation. In addition, the discrete frequency noise was generated only when the values of these parameters are within a limited range. Furthermore, it was found that the noise frequency is proportional to the jet velocity and is inversely proportional to the plate length. Finally, it was made clear from the present study that the interaction of the vortex, which is generated from the shear layer due to a wedge, with the wake of a flat plate is a major cause for the discrete noise due to a slit.

Experimental study of planar opposed jets with acoustic excitation

Oscillation behaviors of planar opposed jets with acoustic excitation were experimentally investigated. The flow regimes of planar opposed jets at various exit air velocities, nozzle separations, excitation frequencies, and excitation amplitudes have been identified by a flow visualization technique combining with a high-speed camera. Results show that planar opposed jets exhibit horizontal instability at L/H ≤ 4 (where L is the nozzle separation and H is the slit height of the planar nozzle) and deflecting oscillation at L/H ≥ 6. The deflecting oscillation is originally started by the antisymmetric structures in the planar jets and is self-sustained by the periodic changes of the velocity field and the pressure field. At L/H ≤ 4, the acoustic excitation results in the horizontal periodic oscillation, whose frequency is equal to the excitation frequency. The acoustic excitation of oscillation amplitude less than 10% has negligible influence on the deflecting oscillation; for synchronous or asynchronous excitation with higher amplitude, the transition from the deflecting oscillation to a steady state or horizontal oscillation occurs.

A multiple-step slit die rheometer for rheological characterization of extruded starch melts

Extrusion cooking is a very important process in the field of cereal and snack manufacturing. The rheological properties of the starch based matrix strongly influence this process. A newly developed online rheometer was mounted on a twin screw extruder in order to measure these properties. It was possible to obtain viscosity of wheat flour and corn grits at typical extrusion cooking conditions over a shear rate range of three decades. Flow curves for varying screw speed and water content at a constant thermomechanical history of the starch were measured. Also the temperature dependence of the apparent viscosities could be determined showing activation energies in the range found for synthetic polymers. Furthermore, additional pressure drops that occur at step changes of the slit height were detected. Thus, it was possible to evaluate visco-elastic properties of extruded starch melts at different extrusion cooking conditions.