PMMA Micro Research Articles

Supercritical CO2‐assisted extrusion foaming: A suitable process to produce very lightweight acrylic polymer micro foams

AbstractA strategy of CO2‐assisted extrusion foaming of PMMA‐based materials was established to minimize both foam density and porosities dimension. First a highly CO2‐philic block copolymer (MAM: PMMA‐PBA‐PMMA) was added in PMMA in order to improve CO2 saturation before foaming. Then the extruding conditions were optimized to maximize CO2 uptake and prevent coalescence. The extruding temperature reduction led to an increase of pressure in the barrel, favorable to cell size reduction. With the combination of material formulation and extruding strategy, very lightweight homogeneous foams with small porosities have been produced. Lightest PMMA micro foams (ρ = 0.06 g cm−3) are demonstrated with 7 wt% CO2 at 130°C and lightest blend micro foams (ρ = 0.04 g cm−3) are obtained at lower temperature (110°C, 7.7 wt% CO2). If MAM allows a reduction of Tfoaming, it also allows a much better cell homogeneity, an increase in cell density (e.g., from 3.6 107 cells cm−3 to 2 to 6 108 cells cm−3) and an overall decrease in cell size (from 100 to 40 μm). These acrylic foams produced through scCO2‐assisted extrusion has a much lower density than those ever produced in batch (ρ ≥ 0.2 g cm−3).

Mechanical property and gas filtration behavior of porous reaction bonded Si3N4 with monodispersed PMMA as pore former

AbstractPorous Si3N4 ceramics were prepared by gel casting combined with a reaction bonding route using monodispersed PMMA as the pore former, and Isobam was used as a gel agent. With the PMMA addition varying from 0 to 20 wt.%, the bending strength was degraded from 94.0 to 39.1 MPa owing to the increased porosity and decreased bulk density. The β‐Si3N4 prismatic grains and round pores introduced by the monodispersed PMMA micro balls would endow the samples with high strength, and the permeability of the resulting samples was increased obviously with the increase of PMMA addition. Flue gas filtration test exhibited that the filtration efficiency of the porous ceramics filter was not degraded with introducing of the PMMA pore former, even though the permeability was increased obviously. The block type of the sample with 20‐wt.% PMMA additions during filtration was cake filtration, which indicates that the sample has the characteristic of being reusable after back‐blowing in flue gas filtration applications. Porous Si3N4 with high strength and permeability fabricated via the reaction bonding route exhibits great potential for low‐cost high‐performance ceramics filters.

Designer Core-Shell Nanoparticles as Polymer Foam Cell Nucleating Agents: The Impact of Molecularly Engineered Interfaces.

The interface between nucleating agents and polymers plays a pivotal role in heterogeneous cell nucleation in polymer foaming. We describe how interfacial engineering of nucleating particles by polymer shells impacts cell nucleation efficiency in CO2 blown polymer foams. Core–shell nanoparticles (NPs) with a 80 nm silica core and various polymer shells including polystyrene (PS), poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA), and poly(acrylonitrile) (PAN) are prepared and used as heterogeneous nucleation agents to obtain CO2 blown PMMA and PS micro- and nanocellular foams. Fourier transform infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy are employed to confirm the successful synthesis of core–shell NPs. The cell size and cell density are determined by scanning electron microscopy. Silica NPs grafted with a thin PDMS shell layer exhibit the highest nucleation efficiency values, followed by PAN. The nucleation efficiency of PS- and PMMA-grafted NPs are comparable with the untreated particles and are significantly lower when compared to PDMS and PAN shells. Molecular dynamics simulations (MDS) are employed to better understand CO2 absorption and nucleation, in particular to study the impact of interfacial properties and CO2-philicity. The MDS results show that the incompatibility between particle shell layers and the polymer matrix results in immiscibility at the interface area, which leads to a local accumulation of CO2 at the interfaces. Elevated CO2 concentrations at the interfaces combined with the high interfacial tension (caused by the immiscibility) induce an energetically favorable cell nucleation process. These findings emphasize the importance of interfacial effects on cell nucleation and provide guidance for designing new, highly efficient nucleation agents in nanocellular polymer foaming.

Application Development for Ag Plated PMMA Micro Powder

Application Development for Ag Plated PMMA Micro Powder

Experimental Evaluation for Macrophage Responses Stimulated by PMMA Micro Particles for Immune Therapy

Experimental Evaluation for Macrophage Responses Stimulated by PMMA Micro Particles for Immune Therapy

Permeability of the porous Al2O3 ceramic with bimodal pore size distribution

Porous Al2O3 ceramics with bimodal pore size distribution were fabricated by partial sintering with monodispersed PMMA micro balls as pore agent. The porosity of the fabricated porous Al2O3 is increased with content of the pore agent increase, the bulk density and bending strength are decreased, accordingly. Relations between pressure drop and flow velocity of the air through the porous Al2O3 fit the Forchheimer's equation well for compressible fluid. Due to pores introduced by the pore agent, the Darcy permeability and inertial permeability of the porous Al2O3 are increased obviously. For given flow velocity, with increase of the PMMA content, the Forchheimer's number of the fluid through the porous Al2O3 is decreased, which results in decrease of the inertial resistance ratio to the total pressure drop. The porous Al2O3 ceramics with pores introduced by the monodispersed PMMA micro balls show higher permeability while the filtration selectivity is not deteriorated.

Polymer microfiber bridging Bi-tapered refractive index sensor based on evanescent field

A PDMS/graphene enhanced PMMA micro optical waveguide sensor is reported in terms of fabrication method and optical characteristics. The micro optical waveguide with a diameter of 6μm and a length of 800μm is used as the sensing probe to realize refractive index (RI) measurement suspended in NaCl solutions with different concentrations. Experimental results show that the refractive index sensing sensitivity can reach 2027.97 nm/RIU within the refractive index ranging from 1.3333–1.3426. Research results show that PMMA/graphene micro optical waveguide doped with PDMS is an excellent high sensitive sensing technology in refractive index detection field.

Silica-Assisted Nucleation of Polymer Foam Cells with Nanoscopic Dimensions: Impact of Particle Size, Line Tension, and Surface Functionality

Core–shell nanoparticles consisting of silica as core and surface-grafted poly(dimethylsiloxane) (PDMS) as shell with different diameters were prepared and used as heterogeneous nucleation agents to obtain CO2-blown poly(methyl methacrylate) (PMMA) nanocomposite foams. PDMS was selected as the shell material as it possesses a low surface energy and high CO2-philicity. The successful synthesis of core–shell nanoparticles was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy. The cell size and cell density of the PMMA micro- and nanocellular materials were determined by scanning electron microscopy. The cell nucleation efficiency using core–shell nanoparticles was significantly enhanced when compared to that of unmodified silica. The highest nucleation efficiency observed had a value of ∼0.5 for nanoparticles with a core diameter of 80 nm. The particle size dependence of cell nucleation efficiency is discussed taking into account line tension effects. Complete engulfment by the polymer matrix of particles with a core diameter below 40 nm at the cell wall interface was observed corresponding to line tension values of approximately 0.42 nN. This line tension significantly increases the energy barrier of heterogeneous nucleation and thus reduces the nucleation efficiency. The increase of the CO2 saturation pressure to 300 bar prior to batch foaming resulted in an increased line tension length. We observed a decrease of the heterogeneous nucleation efficiency for foaming after saturation with CO2 at 300 bar, which we attribute to homogenous nucleation becoming more favorable at the expense of heterogeneous nucleation in this case. Overall, it is shown that the contribution of line tension to the free energy barrier of heterogeneous foam cell nucleation must be considered to understand foaming of viscoelastic materials. This finding emphasizes the need for new strategies including the use of designer nucleating particles to enhance the foam cell nucleation efficiency.

基于X光移动光刻技术的PMMA微透镜阵列制备

基于X光移动光刻技术的PMMA微透镜阵列制备

Preparation and Investigation of Quantum-Dot-Loaded Hollow Polymer Microspheres

In this work, hollow poly(methyl methacrylate) (PMMA) microspheres loaded with CdSe/CdS core−shell quantum dots (QDs) were fabricated onto hydrophilic glass substrates using a spray-drying method. The PMMA micro- spheres were investigated using scanning electron microscopy, confocal microscopy, and fluorescent lifetime imaging microscopy (FLIM) to investigate the morphology of the spheres and confirm their hollow structure. The QDs were used as fluorophores in confocal microscopy to observe the central cavity of the microspheres and in solid-state photo- luminescence spectroscopy to observe whispering gallery modes (WGMs), demonstrating the high optical quality of the hollow microspheres and their potential application as optical microresonators.

Fabrication of Prototype of Artificial Retina Adapted to a Curved Image Plane Based on Arrayed PMMA Microfibers

The traditional visual prosthesis combines both a camera and an electrode array implanted on the visual neural networks. Here, we introduce a new design of artificial retina which integrate the transmission of image and the electrical stimulation of cortical neurons on a single PMMA micro fiber. It is comprised of multiple PMMA microfibers with both ends connected with one flexible and one rigid substrates. The flexible one is a PDMS mold of microrods and ready to conform to a curved image plane. The rigid one is in the form of a silica plate coated with a PMMA thin film and could be attached to a CMOS image sensor for the evaluation of its optical performance. The multiple PMMA microfibers were directly drawn from liquid PMMA thin film with PDMS rods. With arrayed PMMA microfibers, the image planes could be transferred from the flexible to rigid substrate. Each PMMA microfiber delivers a part of the image the PDMS mold transmits. Incorporated with O/E convertors, each micro fiber could function as an unit of electrical stimulation in accordance with part of the image the artificial retina delivered and is ready to function as a cortical neural prosthesis in the future application.

Ultrahydrophobic PMMA micro- and nano-textured surfaces fabricated by optical lithography and plasma etching for X-ray diffraction studies

Polymeric (PMMA) ultrahydrophobic surfaces with contact angles up to about 170° have been fabricated and used in the context of synchrotron radiation experiments on biological droplets. The different microfabrication processes included either an optical lithography phase followed by a plasma texturing one or a single step deep reactive ion etch attack.The drying of several biological solution droplets has been monitored. Room temperature evaporation experiments (lysozyme, lactalbumin, cytochrome C, doxorubicin and synthesized peptides) finally result in the formation of easily detachable hollow residuals because of the low interaction between the ultrahydrophobic substrate and the aqueous droplet while pilot experiments (bovine insulin) in a sitting-drop environment bring to the formation of well defined crystals. Recent results about in situ X-ray diffraction experiments by SAXS & WAXS (Small and Wide Angle X-ray Scattering) μ-beam techniques confirm that the presence of such surfaces influences the formation of crystal or fibril structures. These substrates represent indeed a suitable support to study biological and inorganic droplets in a near contact-free environment exploiting the homogeneous evaporation rate induced by the ultrahydrophobicity of the system.

Microscopic and Spectroscopic Studies of Thermally Enhanced Electrospun PMMA Micro- and Nanofibers.

Carbon nanofibers (CNFs) have been incorporated into poly(methyl methacrylate) (PMMA) through electrospinning. The resulting micro- and nanofibers have been characterized by Scanning Electron Microscopy (SEM), which confirmed fiber formation and demonstrated a core-sheath structure of the PMMA fibers. Thermogravimetric Analysis (TGA) was used to obtain the thermal properties of the materials, indicating an enhancement in the thermal properties of the composite fibers. In addition, Fourier Transform Infrared Spectroscopy (FTIR) was utilized to investigate the interactions of PMMA micro- and nanofibers with CNFs, demonstrating the preferred sites of intermolecular interactions between the polymer matrix and the filler.

Surface modification of poly(methyl methacrylate) for improved adsorption of wall coating polymers for microchip electrophoresis

The development of rapid and simple wall coating strategies for high-efficiency electrophoretic separation of DNA is of crucial importance for the successful implementation of miniaturized polymeric DNA analysis systems. In this report, we characterize and compare different methods for the chemical modification of poly(methyl methacrylate) (PMMA) surfaces for the application of wall coating polymers. PMMA surfaces coated with 40 mol% diethylacrylamide and 60 mol% dimethylacrylamide are compared to the PMMA surfaces first oxidized and then coated with hydroxypropylmethyl-cellulose or poly(vinyl alcohol) (PVA). PMMA oxidation was accomplished with UV/ozone or an aqueous solution of HNO(3) to yield hydrogen-bond donors for the spontaneous adsorption of the coating polymers. Contact angle measurements of UV/ozone exposed PMMA surfaces indicate increase in hydrophilicity, and polymer coated surfaces show a strong dependence on the coating polymer and the oxidation method. Fast and repeatable electrophoretic separations of a 10-base and 20-base DNA ladder were performed in PMMA micro CE devices. All analyses were completed in less than 10 min, resulting in the number of theoretical plates as high as 583 000 in a 7.7 cm long separation channel. The duration of UV/ozone treatment was found to have a considerable impact on separation performance. The microchips irradiated with UV for 10 min and coated with PVA as well as the microchips treated with HNO(3) and coated with HPMC were found to have the best separation performance. These results demonstrate facile and robust methods for the surface modification of PMMA enabling low-cost single use devices for electrophoretic DNA separations.

Rapid mold temperature variation for assisting the micro injection of high aspect ratio micro-feature parts using induction heating technology

Hot embossing and injection molding are popular methods to duplicate micro features formed during polymer micro-fabrication of MEMS devices. However, both methods face challenges in filling the polymer melt completely into a micro-featured geometry of a high aspect ratio. In this study, electromagnetic induction heating combined with water cooling is used to achieve rapid mold surface temperature control during the micro-feature injection molding process. A CAE simulation was also developed through integration of both thermal and electromagnetic analysis modules of ANSYS, and its capability and accuracy were verified experimentally. Efficiency evaluations of induction heating and the uniformity of mold temperature control were conducted on a micro-featured mold. This mold was designed with a micro channel array of 30–50 µm in width and 120 and 600 µm in depth, corresponding to aspect ratios ranging from about 2.4 to 12. The accuracies of the micro channels in molded PMMA parts can be used to evaluate the effect of mold temperature on replication accuracy. It was found that rapid mold surface heating with temperature rising from 60 °C to between 100 °C and 140 °C by induction heating requires 2–3.5 s, while the mold temperature returns to 60 °C in about 70–110 s. The simulated mold surface temperature results are consistent with measured results. Achieving the same temperature variation by switching circulation coolants of different temperatures requires at least 7 min. The simulation also reveals that the electromagnetic wave can penetrate into the bottom of the micro channel and results in only about a 2 °C difference in temperature uniformity. For mold temperatures of 100 °C, 120 °C and 140 °C, the molded channel depths were 94.9 µm, 105.4 µm and 116.0 µm, respectively, when the ideal channel depth was 120 µm. When the channel depth is 600 µm, the mold temperature must exceed 120 °C, so that reasonable accuracy in micro-feature replication can be achieved. Our results to date indicate that the aspect ratio for molded PMMA micro channels can be as high as 12. Efficient mold temperature variation by induction heating to improve the replication accuracy in molding micro features is successfully illustrated.

Fabrication of PMMA micro- and nanofluidic channels by proton beam writing: electrokinetic and morphological characterization

The fabrication of microfluidic channels in poly(methylmethacrylate) (PMMA) by proton beam writing and the characterization of their electrokinetic behavior are reported. Microchannels down to 200 nm width have been fabricated in high-molecular-weight, thick PMMA sheets and a surface smoothness of 2.45 nm for the sidewalls of the channels was measured using atomic force microscopy. The polymeric channels were sealed using thermal bonding. The methods of digital video microscopy and current monitoring were used for characterization of the electrokinetic phenomena. The electrokinetic properties of the PMMA rectangular microchannels were measured in 20 mM buffered solutions of phosphate (pH 7.20), tris (pH 8.00) and borate (pH 9.05) at different voltages. In addition, particle image velocimetry was used to determine the electroosmotic flow profile and the electrophoretic mobility of 600 nm polystyrene microspheres. A theoretical model was developed to predict the bulk electroosmotic flow of phosphate buffer solution in the PMMA microchannels and this model showed good agreement with the measured electroosmotic mobilities.

Fabrication of PMMA micro CE chip using IPA assisted low-temperature bonding

Fabrication of PMMA micro CE chip using IPA assisted low-temperature bonding

Colour mixing LEDs with short microsphere doped acrylic rods

The output colour distributions from red, green and blue (RGB) LEDs mixed with cross linked PMMA micro particle doped PMMA mixing rods is compared to output from a plain PMMA mixing rod. Distinctive patterns with clear colour separation result with the undoped rod. These are homogenised by our mixers, resulting in white light. Light output has been photographed, measured and computer simulated at a distance of 10 cm from the output end of the rods.