Measurement Method of the Thickness Uniformity for Polymer Films

Several methods for investigating the thickness uniformity of polymer thin films are presented as well as their measurement principles. A comparison of these experimental methods is given.The cylindrical lightwave reflection method is found to can obtain the thickness distribution along a certain direction.It is a simple and suitable method to evaluate the film thickness uniformity.

Adaptive Electrospinning System Based on Reinforcement Learning for Uniform‑Thickness Nanofiber Air Filters

Electrospinning is a simple and versatile method to produce nanofiber filters.However,owing to bending instability that occurs during the electrospinning process,electrospinning has frequently produced a non-uniform-thickness nanofiber filter,which deteriorates its air filtration.Here,an adaptive electrospinning system based on reinforcement learning(E-RL)was developed to produce uniform-thickness nanofiber filters.The E-RL accomplished a real-time thickness measurement of an electrospun nanofiber filter by measuring the transmitted light through the nanofiber filter using a camera placed at the bottom of the collector and converting it into thickness using the Beer–Lambert law.Based on the measured thickness,the E-RL detected the non-uniformity of the nanofiber filter thickness and manipulated the movable collector to alleviate the non-uniformity of the thickness by a pre-trained reinforcement learning(RL)algorithm.For the training of the RL algo-rithm,the nanofiber production simulation software based on the empirical model of the deposition of the nanofiber filter was developed,and the training process of the RL algorithm was repeated until the optimal policy was achieved.After the training process with the simulation software,the trained model was transferred to the adaptive electrospinning system.By the movement of the collector under the optimal strategy of RL algorithm,the non-uniformity of such nanofiber filters was significantly reduced by approximately five times in standard deviation and error for both simulation and experiment.This finding has great potential in improving the reliability of electrospinning process and nanofiber filters used in research and industrial fields such as environment,energy,and biomedicine.

Thickness Uniformity Adjustment of Inkjet Printed Light-emitting Polymer Films by Solvent Mixture

In this paper, thickness uniformity of poly（9,9-di-n-octylfluorene） films patterned by inkjet printing was im- proved by the use of solvent mixtures （a solvent with higher volatility, higher surface energy and lower viscosity, with another solvent with lower volatility, lower surface energy and higher viscosity）. The average thickness of inkjet printed poly（9,9-di-n-octylfluorene） films was increased from ca. 30 nm to ca. 100 nm when solvent mixtures were used instead of pure chlorobenzene. More flat PFO films were formed instead of the original films with con- cave-lens like cross-section formed by coffee ring effect. This improvement was explained by combination of in- tense Marangoni flow at early drying process and weak complementary flow at the later drying process formed in the solvent mixture. Patterned poly（9,9-di-n-octylfluorene） films were used for fabrication of electroluminescence devices with improved electronic property. Array of pixels with about 80% effective light-emitting area was ob- tained.

Investigation of spherical and concentric mechanism of compound droplets

Polymer shells with high sphericity and uniform wall thickness are always needed in the inertial confined fusion(ICF)experiments.Driven by the need to control the shape of water-in-oil(W1/O)compound droplets,the effects of the density matching level,the interfacial tension and the rotation speed of the continuing fluid field on the sphericity and wall thickness uniformity of the resulting polymer shells were investigated and the spherical and concentric mechanisms were also discussed.The centering of W1/O compound droplets,the location and movement of W1/O compound droplets in the external phase(W2)were significantly affected by the density matching level of the key stage and the rotation speed of the continuing fluid field.Therefore,by optimizing the density matching level and rotation speed,the batch yield of polystyrene(PS)shells with high sphericity and uniform wall thickness increased.Moreover,the sphericity also increased by raising the oil/water(O/W2)interfacial tension,which drove a droplet to be spherical.The experimental results show that the spherical driving force is from the interfacial tension affected by the two relative phases,while the concentric driving force,as a resultant force,is not only affected by the three phases,but also by the continuing fluid field.The understanding of spherical and concentric mechanism can provide some guidance for preparing polymer shells with high sphericity and uniform wall thickness.

Mechanical Properties of the Cured Laminates on the Hot-press Tackified Preforms in Vacuum Assisted Resin Transfer Molding

A hot-press tackified preform was used to improve the uniformity of the laminates thickness and the mechanical properties of the obtained laminates were studied using vacuum assisted resin transfer molding（VARTM）. Two modified preforms were prepared under 0.1 and 0.6 MPa in an autoclave and then were used to fabricate the laminates via VARTM. Permeability and thickness distribution of the laminates were obtained by using a special device. Moreover, the tensile and compressive strengths of the obtained laminates were studied and compared with the unmodified ones. Results show that the tackified laminates present a maximum and minimum thickness under 0.1 and 0.6 MPa, respectively. The thicknesses and in-plane permeability of the tackified laminates, with better thickness uniformity, are significantly decreased compared with that of the unmodified cases, while the tensile and compressive strengths of the tackified laminates are improved obviously. Results show that the mechanical property of the tackified laminates prepared by hotpressing at 0.1 MPa is better than that processed at 0.6 MPa.

Effect of molecular weight on the quality of poly(alpha-methylstyrene) mandrel

Hollow poly(alpha-methylstyrene)(PAMS)shows application in inertial confinement fusion experiments as the degradable mandrels of glow plasma polymer shells.However,the molecular weight of PAMS has great influence on the quality of mandrels.In this work,this influence was systematically studied using several PAMS samples with different molecular weights.For PAMS shells with 900 mm inner diameter and different wall thickness,when the molecular weight of PAMS is in the range of 300e500 kg·mol^(-1),perfect sphericity and good wall thickness uniformity can be obtained.In contrast,when increasing molecular weight to 800 kg·mol^(-1),the sphericity and the wall thickness uniformity become worse.Moreover,compared with the wall uniformity,the sphericity of PAMS shells was much less sensitive to the molecular weight.The results also showed that the stability of W1/O compound droplets of PAMS shells were less affected by the molecular weight.It was revealed that the wall uniformity and the sphericity of the PAMS shells were associated with the diffusion rates of fluorobenzene(FB).

Improvement of thickness uniformity and elements distribution homogeneity for multicomponent films prepared by coaxial scanning pulsed laser deposition technique

In conventional pulsed laser deposition （PLD） technique, plume deflection and composition distribution change with the laser incident direction and pulse energy, then causing uneven film thickness and composition distribution for a multicomponent film and eventually leading to low device quality and low rate of final products. We present a novel method based on PLD for depositing large CIGS films with uni- form thickness and stoichiometry. By oscillating a mirror placed coaxially with the incident laser beam, the laser＇s focus is scanned across the rotating target surface. This arrangement maintains a constant re- flectance and optical distance, ensuring that a consistent energy density is delivered to the target surface by each laser pulse. Scanning the laser spot across the target suppresses the formation of micro-columns, and thus the plume deflection effect that reduces film uniformity in conventional PLD technique is eliminated. This coaxial scanning PLD method is used to deposit a CIGS film, 500 nm thick, with thickness uniformity exceeding ±3% within a 5 cm diameter, and exhibiting a highly homogeneous elemental distribution.

Study on thickness uniformity of Ta_(2)O_(5) film evaporated on the inner-face of a hemispherical substrate

Theoretical analysis and experimental study on the thickness distribution of Ta_(2)O_(5) film evaporated on the inner-face of a hemispherical substrate are demonstrated. It is derived that the value of n/R and L/R influence the film thickness distribution(where R is the radius of the hemisphere, n and L are the horizontal distance and vertical height between the evaporation source and the center of the hemisphere, respectively). The whole hemispherical substrate can be coated when n≤L+R, otherwise there is a "blind area" on the substrate when the substrate is self-rotating. A hemispherical composite substrate with a radius of 200 mm is coated with Ta_(2)O_(5) protective film under a certain configuration, the thickness of Ta_(2)O_(5) film at the edge is 0.372 times the film at the vertex which shows that the evaporation characteristics of Ta_(2)O_(5) tend to be a point source.

A Model of Spray Tool and a Parameter Optimization Method for Spraying Path Planning

The digital camouflage spraying of special vehicles carried out by robots can greatly improve the spraying efficiency, spraying quality, and rapid adaptability to personalized patterns. The selection of spray tool and the accuracy of the adopted mathematical spray tool model has a great impact on the effectiveness of spray path planning and spraying quality. Since traditional conical spray tool models are not suitable for spraying rectangular digital camouflage, according to the characteristics of digital camouflage, the coating thickness cumulative distribution model of strip nozzle spray tool for 2 D plane spraying and 3 D surface spraying is derived, and its validity is verified by simulation. Based on the accumulation velocity model of the coating thickness(AVCT) on the curved surface and aiming at spraying path planning within the same surface and different surfaces, a path parameter optimization method based on coating uniformity evaluation of adjacent path overlapping area is proposed. Combined with the vehicle surface model, parameters such as path interval, spray tool angle and spray tool motion velocity can be calculated in real-time to ensure uniform coating. Based on the known local three-dimensional model of vehicle surface and the comprehensive spraying simulation, the validity of the purposed models: the coating thickness on the adjacent path area(CTAPA), the coating thickness on the intersection of two surfaces(CTITS), the coating thickness on the intersection of a plane and a surface(CTIPS), and the optimization method of path parameters are verified. The results show that compared with the traditional spray tool, the strip nozzle can better ensure the uniformity of the coating thickness of digital camouflage spray. Finally, according to a practical spraying experiment, the results prove that the proposed models not only are effective but also meet the practical industrial requirements and are of great practical value.