Polymethylmethacrylate Structures Research Articles

Effect of graphene on the key electrical, optical, and magnetic properties of polymethylmethacrylate: a study based on molecular modeling.

In this work, a new polymeric structure was designed consisting of a nanometric sheet of graphene (G) and a polymethylmethacrylate (PMMA) repeat unit, which was designated as PMMA-G. Three degrees of polymerization of PMMA-G were considered: monomer (PMMA-G1), dimer (PMMA-G2), and trimer (PMMA-G3). The effect of incorporating a nanometric sheet of graphene into the molecular structure of PMMA on the modification of some of its main optical, magnetic, and electrical properties was investigated. Currently, the study presented here is of great relevance since various areas of technology require new materials with specific properties for the development of new devices. The results of our study reveal that the dielectric constant of PMMA is reduced when graphene is incorporated. However, a percentage increase of 14.48% in the refractive index of PMMA when graphene is inserted to form the nanocomposite is observed. It is found that the absolute value of molar magnetic susceptibility of PMMA increases considerably when reinforced with graphene. Finally, when reinforcing PMMA with graphene to obtain the PMMA-G nanocomposite, the electrical resistivity increases by almost an order of magnitude. We used computational tools under Materials Studio (MS) software. We built a PMMA molecule with three degrees of polymerization, graphene sheet, and polymethylmethacrylate-graphene composite (PMMA-G) was built also with three degrees of polymerization using a concentration of 50% graphene over the PMMA polymer. For each structure, we used computational code DMol3 of MS, which is based on the Density Functional Theory, and the geometry optimization process was carried out to obtain the most stable structures. Finally, using the connectivity indices method together with topological properties of the molecular structures, implemented in Synthia computational code of MS software, we calculated the dielectric constant, magnetic susceptibility, refractive index, and electrical resistivity, for pure PMMA and PMMA-G structures for their three degrees of polymerization. The results were analyzed, and the changes in these properties were discussed in terms of the effect of an electric and magnetic field on the molecular structures of PMMA-G with respect to PMMA.

Fatigue crack growth properties of PMMA material used in underwater transparent structures

ABSTRACT Polymethyl methacrylate (PMMA) is an ideal material used in underwater transparent structures such as submersible windows and the fully-transparent pressure chamber of the sightseeing submersibles. The failure of PMMA structures usually come from small crack-like defects. In this paper, the fatigue crack growth experiments were carried out on PMMA materials with different thicknesses (B = 3, 6, 12 mm) and stress ratios (R = 0.1, 0.3) as well as plane strain fracture toughness test for unstable crack propagation conditions. Thickness effect and dwell time effect are experimentally investigated in addition to load ratio effect. The applicability of an improved crack growth rate model on PMMA material is validated by test results. The application of this model for prediction of crack growth rates can greatly save experimental time under different working conditions and can be applied in fatigue assessment of full-transparent structures under random loading.

Thermal Reflow Simulation for PMMA Structures with Nonuniform Viscosity Profile.

This paper presents a new approach to the simulation of the thermal reflow of e-beam-exposed polymethyl methacrylate (PMMA) taking into account its nonuniform viscosity profile. This approach is based on numerical "soapfilm" modeling of the surface evolution, processed by the free software "Surface Evolver" in area normalization mode. The PMMA viscosity profile is calculated via the simulation of the exposed PMMA number average molecular weight distribution using the Monte-Carlo method and empirical formulas. The relation between the PMMA viscosity and the mobility of PMMA surface vertices was determined via the thermal reflow simulation for uniform PMMA gratings using analytical and numerical approaches in a wide viscosity range. The agreement between reflowed profiles simulated with these two approaches emphasizes the applicability of "soapfilm" modeling in the simulation of polymer thermal reflow. The inverse mobility of PMMA surface vertices appeared to be proportional to the PMMA viscosity with a high precision. The developed approach enables thermal reflow simulations for complex nonuniform structures, which allows the use of predictable reflow as a stage of 3D microfabrication.

Numerical Simulation of PMMA Impact Based on the J–C Constitutive and Damage Models under Hydrostatic Pressure Loading

Polymethyl methacrylate (PMMA) polymer is widely used in various fields today. In order to reveal the structural impact performance of PMMA materials in underwater engineering thoroughly, this paper firstly proposed a simplified plate model for a spherical shell hull under concentrative impact loading. Then, to simulate the hyper-elastic material properties of PMMA in the impact process, the Johnson–Cook constitutive model and damage failure model were adopted. And the least squares method was used to confirm accurately the J–C constitutive and damage failure model parameters of PMMA through material test data. Moreover, the dynamic process of the steel bullet impacting the PMMA plate structure was analyzed by the finite element software ABAQUS. The calculation results show that the numerical simulation results in this paper have a good convergence, and the residual velocities at different initial velocities and thicknesses of plates are in good agreement with the experimental test data. Therefore, the feasibility and accuracy of the impact analysis of PMMA structures based on J–C constitutive and damage failure models in this paper are verified accordingly. Finally, based on the presented finite element model, the structure response and the variation of residual velocity of the bullet with the PMMA plate thickness was analyzed in depth; that is, the results show that the residual velocity of the bullet has a certain linear relationship with the thickness, even in an underwater environment, and even in an underwater environment will increase both with a thicker structure or a higher pressure.

Biomimetic Moth-eye Anti-reflective Poly-(methyl methacrylate) Nanostructural Coating

This study reports a simple imprinting method for the fabrication of biomimetic moth-eye antireflective polymethyl methacrylate (PMMA) nanostructures on the surface of the substrate. The antireflection structured silicon was obtained by Reactive Ion Etching (RIE) method. By using the antireflection structured silicon substrate as the imprinting stamp, the biomimetic moth-eye polymer structures showed tapered holes, whose depth and periodicity were around 780 nm and 580 nm, respectively. The reflectance of the resulting PMMA structures was reduced from 10% to less than 1% in the wavelength range from 300 nm to 1600 nm. This simple methodology can be scaled up via self-loading and nanoimprinting, which may have a promising application in optoelectronic devices and solar cells.

High fidelity 3D thermal nanoimprint with UV curable polydimethyl siloxane stamps

A two-step replication process chain is developed for a microlens array structure with deep three dimensional (3D) reliefs and sharp features enabling the transfer of a photocured acrylic resist patterns into thermoplastic poly-methyl methacrylate (PMMA) with the same structural polarity via an intermediate stamp. By using ultraviolet (UV)-curable polydimethyl siloxane (PDMS), high fidelity negatives were cast from the original microstructures made by two-photon-polymerization and subsequently replicated into PMMA using thermal imprint. The mechanical properties of the new UV-PDMS (X-34-4184, Shin-Etsu Chemical Company, Ltd.), along with its nearly zero process shrinkage, proved to be highly suitable to replicate both 50 μm high concave features and sharp tips with an apex diameter of 500 nm. The results prove that silicone rubber, despite its elasticity, has specific advantages in thermal imprint in structures where both tall microstructures and submicron surface structures have to be replicated. This way, high fidelity PMMA structures with low defects could be prepared by the optimized processing found in this work to have a replication of 3D masters for further upscaling.

Polymer microspheres with structured surfaces

Microspheres from polymethyl methacrylate (PMMA) and Eudragit FS 30D (a commercial copolymer of poly(methyl acrylate- co-methyl methacrylate- co-methacrylic acid) 7:3:1) were prepared using microsieve emulsification. A mixture of these polymers in dichloromethane (DCM) was dispersed into water, leading to extraction of DCM in water and the formation of microspheres with a PMMA core and a partially demixed Eudragit shell. With a higher ratio of Eudragit to PMMA, more and bigger pores can be seen on the surface of the microspheres. Eudragit can be removed from the shell of the microspheres under alkaline conditions. Depending on the initial Eudragit to PMMA ratio, PMMA microspheres with different surface morphologies are obtained. At low Eudragit concentrations microspheres with a crumpled surface are formed, while at higher Eudragit concentrations microspheres are formed with a core to which dendritic PMMA structures are attached. At even higher Eudragit concentrations the microspheres obtained after dissolving the Eudragit show a nanorough surface.

Simulation of electron beam lithography of nanostructures

The authors report a numeric simulation tool that they developed for the modeling and analysis of electron beam lithography (EBL) of nanostructures employing a popular positive tone resist polymethylmethacrylate (PMMA). Modeling and process design for EBL fabrication of 5–50 nm PMMA structures on solid substrates is the target purpose of the simulator. The simulator is functional for exposure energies from 1 to 50 keV with arbitrary writing geometries. The authors employ a suite of kinetic models for the traveling of primary, secondary, and backscattered electrons in the resist, compute three-dimensional (3D) distributions of the yield of main-chain scission in PMMA, and convert these into the local volume fractions of fragments of various sizes. The kinetic process of development is described by the movement of the resist-developer interface with the rate derived from the mean-field theory of polymer diffusion. The EBL simulator allows the computation of detailed 3D distributions of the yield of main-chain scission in PMMA for various conditions of exposure, the corresponding volume fractions of small fragments, and the clearance profiles as functions of the development in time and temperature. This article describes the models employed to simulate the EBL exposure and development, reports examples of the computations, and presents comparisons of the predicted development profiles with experimental cross-sectional resist profiles in dense gratings.

Fused deposition modeling of patient‐specific polymethylmethacrylate implants

PurposeThe purpose of this paper is to investigate the use of medical‐grade polymethylmethacrylate (PMMA) in fused deposition modeling (FDM) to fabricate porous customized freeform structures for several applications including craniofacial reconstruction and orthopaedic spacers. It also aims to examine the effects of different fabrication conditions on porosity and mechanical properties of PMMA samples.Design/methodology/approachThe building parameters and procedures to properly and consistently extrude PMMA filament in FDM for building 3D structures were determined. Two experiments were performed that examined the effects of different fabrication conditions, including tip wipe frequency, layer orientation, and air gap (AG) (or distance between filament edges) on the mechanical properties and porosity of the fabricated structures. The samples were characterized through optical micrographs, and measurements of weight and dimensions of the samples were used to calculate porosity. The yield strength, strain, and modulus of elasticity of the samples were determined through compressive testing.FindingsResults show that both the tip wipe frequency (one wipe every layer or one wipe every ten layers) and layer orientation (transverse or axial with respect to the applied compressive load) used to fabricate the scaffolds have effects on the mechanical properties and resulting porosity. The samples fabricate in the transverse orientation with the high tip wipe frequency have a larger compressive strength and modulus than the lower tip wipe frequency samples (compressive strength: 16±0.97 vs 13±0.71 MPa, modulus: 370±14 vs 313±29 MPa, for the high vs low tip wipe frequency, respectively). Also, the samples fabricated in the transverse orientation have a larger compressive strength and modulus than the ones fabricated in the axial orientation (compressive strength: 16±0.97 vs 13±0.83 MPa, modulus: 370±14 vs 281±22 MPa; for samples fabricated with one tip wipe per layer in the transverse and axial orientations, respectively). In general, the stiffness and yield strength decreased when the porosity increased (compressive strength: 12±0.71 to 7±0.95 MPa, Modulus: 248±10 to 165±16 MPa, for samples with a porosity ranging from 55 to 70 percent). As a demonstration, FDM is successfully used to fabricate patient‐specific, 3D PMMA implants with varying densities, including cranial defect repair and femur models.Originality/valueThis paper demonstrates that customized, 3D, biocompatible PMMA structures with varying porosities can be designed and directly fabricated using FDM. By enabling the use of PMMA in FDM, medical implants such as custom craniofacial implants can be directly fabricated from medical imaging data improving the current state of PMMA use in medicine.

NIL processes and material characterization on transparent substrates for optical applications

Several nanoimprint lithography polymers have been investigated for optical applications. The objective was to establish which materials can be used as a permanent polymer coated on top of a glass substrate to provide nanostructures imprinted by nanoimprint lithography. 400 and 600nm dots were realized in polystyrene, polymethylmethacrylate (PMMA), mr-I T85, and mr-I6000. The adhesion study shows that PMMA and mr-I6000 materials are the best candidates for demolding issues. Scanning electron microscopy characterization confirmed that PMMA structures are well defined, whereas dots printed in other polymers exhibit defects due to sticking issues which lead to local pattern deformation. Finally, optical characterization showed that the nonperfect profiles are a benefit in terms of light extraction. Polycarbonate sheets were also imprinted on one or two sides in order to study the influence of a double side patterning. It was also concluded that a double side imprinted device leads to an increase in the external efficiency.

Process conditions in X-ray lithography for the fabrication of devices with sub-micron feature sizes

This article describes the fabrication of polymer structures with lateral dimensions in the sub-micron regime using hard X-rays (λc ≈ 0.4 nm) from the electron storage ring ANKA. Spincoated polymethylmethacrylate (PMMA) grades have been analyzed with respect to development rates and contrast. The contrast has been determined to be constant over a wide dose regime but rapidly decreases for dose values below 1 kJ/cm3. Films with a thickness from 2 to 11 μm have been patterned using a high resolution X-ray mask consisting of 2 μm thick gold absorbers on a suspended 1 μm thick silicon nitride membrane. The fabrication of sub-micron X-ray lithography structures with feature sizes down to 400 nm is confined by the mechanical parameters of the resist material and the process conditions. Surface tension after development limits the achievable aspect ratio of isolated pillars and walls, depending on the actual resist height. PMMA structures have been successfully used as template for electroplating of 1 μm thick gold to demonstrate the fabrication capability of sub-micron scale metal parts.

Modeling and Design of Polymer-Based Tunneling Accelerometers by ANSYS/MATLAB

A prototype design of an inexpensive polymer-based tunneling accelerometer is described in this paper. Instead of silicon, polymethyl methacrylate (PMMA) is used as the mechanical material. By using silicon molds fabricated by conventional lithography and wet-etching techniques in hot embossing, PMMA structures can be replicated within 20 min. The performance of the tunneling sensor can be estimated and improved based on mechanical-level analysis by ANSYS and system-level analysis by MATLAB. The nonlinear tunneling mechanism and electrostatic actuation are linearized using small-signal approximation. To enhance the stability and broaden the bandwidth of the tunneling accelerometer system, a feedback control system with one zero and two poles is designed. The dynamic range of the system is greatly enhanced. The bandwidth of the closed-loop system is approximately 15 kHz.

Use of polymethylmethacrylate for pattern transfer by ion beam etching: Improvement of etching homogeneity and patterning quality

We have studied the peculiar defects that appear on the surface of polymethylmethacrylate (PMMA) during ion beam etching. The quantity of defects and their type can be strongly influenced by a preparatory treatment before ion beam etching. Electron irradiation in a wide range of doses and a development procedure were used as the treatment. We have shown that high dose electron irradiation of PMMA structures before ion beam etching can noticeably improve pattern transfer. The improved homogeneity of the PMMA etching is the main reason for the effect. The obtained result is explained by a specific mechanism of ion beam etching of PMMA.

Replication of 175-Å lines and spaces in polymethylmethacrylate using x-ray lithography

A new technique for fabricating high contrast x-ray masks with simple patterns of lines and spaces less than 50 Å in width is described. The successful replication of 175-A lines and spaces in polymethylmethacrylate (PMMA) using the carbon K (45-Å) x-ray is reported. It was found that PMMA structures smaller than 150 Å in width lost their physical integrity and would not adhere to SiO2 substrates.