Thick Polymethyl Methacrylate Research Articles

Is digital mammography reducing radiation doses to women?

This study aims to investigate the impact of national quality programs in mammography and technological advances in digital mammography units on the radiation doses delivered to women in Brazil. Radiation dose assessments in mammography units were conducted through a mail-based dosimetric system. For each unit of facilities that applied to one of the two national quality programs, a postal dosimetric system is dispatched, comprising an optically stimulated luminescent dosimeter (OSL) attached to the surface of a 4.0 cm thick polymethyl methacrylate (PMMA) phantom, simulating a compressed breast with 4.5 cm thickness. Testing instructions to expose the dosimetric phantom for assessing the mean glandular dose (MGD) are provided. Between 2012 and 2023, the programs evaluated the MGD in 1,687 mammography units of computed radiography (CR) and direct digital radiography (DR) technologies from 1,399 facilities located in all Brazilian regions. A total of 1,660 (70.5%) evaluations were carried out on CR technology mammography units and 696 (29.5%) on DR units, totaling 2,356 MGD evaluations. The overall average MGD was 1.60 ± 0.80 mGy, with 1.68 ± 0.83 mGy for CR technology and 1.42 ± 0.68 mGy for DR technology. A comparison of average MGD between the periods 2012 - 2018 and from 2019 onwards shows a dose reduction of 8.6% for CR systems and of 26.0% for DR systems (p = 0.000). As CR systems use analog mammography units, which did not undergo technological advances between the two periods, the reduction in doses observed is due to the actions of national quality certification programs and by using image plates for dual-sided reading or needle-based image plates. The reduction observed in DR systems is due to both national quality programs and technological advances in mammography units, especially the use of radiation beams generated by X-ray tubes with tungsten targets.

Low-voltage organic field-effect transistors by using solution-processable high-κ inorganic-polymer hybrid dielectrics

Organic field-effect transistors (OFETs) incorporating hybrid high-κ inorganic Al2O3 and polymer dielectrics, including polyvinyl alcohol (PVA), polystyrene (PS), or polymethyl methacrylate (PMMA), through solution-processing techniques were fabricated. The analyses revealed that the high surface energy and hydrophilicity property of Al2O3 and PVA, and the relatively hydrophobic property of PS surface, hindered the performance of corresponding OFETs. The Al2O3/PMMA-based OFET achieved the optimized performance, with a threshold voltage of −2.7 V, a hole carrier mobility of 0.056 cm2/Vs, and a current on/off ratio of 1.0 × 104 at a low operating voltage of −5 V. Through analyzing the characteristics of leakage current, capacitance, contact resistance, and trap density of OFETs, we found that the PMMA-engaged films possessed the optimized electrical properties. The introduction of PMMA eliminated the interfacial trapping, thereby lowering the threshold voltage and enhancing the performance of the device. The COMSOL Multiphysics simulation was conducted to confirm the physical mechanism. The strategy of utilizing Al2O3/PMMA hybrid dielectric could simultaneously ensure the low operating voltage and good performance of OFET, while guaranteeing the low leakage current by the thick PMMA.

An experimental study of intensity‐phase characterization of femtosecond laser pulses propagated through a polymethyl methacrylate

AbstractThis article presents a comprehensive investigation into the intensity‐phase characteristics of ultrashort laser pulses propagated through a 10 mm thick polymethyl methacrylate (PMMA) using frequency‐resolved optical gating (FROG) and cross‐correlation frequency‐resolved optical gating (XFROG) techniques. The study focuses on discerning characteristic changes that are induced by the PMMA on the laser pulse. The results reveal that the phase variations exhibit a consistent trend and pattern. At the same time, the temporal full width at half maximum (FWHM) of both FROG and XFROG measurements displays only minor changes. The overall analysis indicates that PMMA induces no discernible modifications in the pulse, thus positioning it as a viable optical element. The analysis of reference FROG, FROG, and XFROG with PMMA is compared and discussed, showing that this analysis provides a foundation for optimizing PMMA's utilization in the optical components of ultrafast laser systems. This experimental study strongly affirms that PMMA could be a potential candidate as an optical element for laser pulses.

A novel method for air assisted nanosecond pulsed fiber laser beam transmission micro-channelling on thick PMMA material

The demand for scaling up polymeric materials for mass production or scaling down for microscale applications is at its peak in the modern era. Laser beam technology enables the formation of micro-channels on polymers, specifically polymethyl methacrylate (PMMA). This study examines the viability and cost-effectiveness of employing the diode pump fiber laser transmission technique to create micro-channels on thick, transparent PMMA under air-assisted circumstances for biomedical engineering and micro-fluidics applications. The analysis has included process variables such as pulse frequency, power, and cutting speed, as well as machining parameters including depth of cut, kerf width, and heat-affected zone (HAZ) width. The results of multi-objective optimization indicate that the following parameters—a pulse frequency of 51.30 kHz, a working power of 13 % of 50 W, and a cutting speed of 0.60 mm/s—contribute to the desired microfluidics response values: 12.54 µm depth of cut, 24.05 µm kerf width, and 5.98 µm HAZ width.

Impact of vacuum ultraviolet photons on ultrathin polymethylmethacrylate during plasma etching

State-of-the-art extreme ultraviolet lithography requires the use of ultrathin photoresists (or resists) due to pattern stability concerns and reduced depth of focus of the extreme ultraviolet lithography scanners. Current resists for extreme ultraviolet lithography are less than 50 nm thick. These ultrathin resists further complicate pattern transfer as unintended plasma-induced damage during dry etching is more pronounced. A better understanding of the interaction of plasma species with ultrathin resists is critical for enabling pattern transfer of sub-10 nm features. Here, we study the impact of vacuum ultraviolet photons, argon ions, and argon plasma on a 40 nm thick polymethylmethacrylate film. Using a deuterium lamp, an industrial ion beam etch tool, and an industrial inductively coupled plasma etch tool, we exposed the polymer to photons, ions, and plasma, respectively. The exposed samples were then analyzed for chemical and physical changes using different characterization techniques. It was observed that the vacuum ultraviolet photons interact with the entire bulk of polymer film, while the ions only affect the surface and subsurface region. The photon exposed samples formed smaller polymer fragments at low exposure doses and further started to cross-link at high doses. In contrast, the ion modification leads to carbonization of only the top few nanometers of the polymer film, leaving the bottom bulk intact. The plasma exposed sample showed changes characteristic to both vacuum ultraviolet photons and ions and their synergism. It was stratified with a 1.34 ± 0.03 nm thick ion-caused carbonized layer on top of a 13.25 ± 0.12 nm photon-induced cross-linked layer. By studying the impact of plasma photons on ultrathin polymethylmethacrylate, we were able to establish a baseline for a testing methodology that can be extended to novel ultrathin resist platforms.

Effects of Confinement on Opposed-Flow Flame Spread over Cellulose and Polymeric Solids in Microgravity

Opposed-flow flame spread over solid materials has been investigated in the past few decades owing to its importance in fundamental understanding of fires. These studies provided insights on the behavior of opposed-flow flames in different environmental conditions (e.g., flow speed, oxygen concentration). However, the effect of confinement on opposed-flow flames remains under-explored. It is known that confinement plays a critical role in concurrent-flow flame spread in normal and microgravity conditions. Hence, for a complete understanding it becomes important to understand the effects of confinement for opposed-flow flames. In this study, microgravity experiments are conducted aboard the International Space Station (ISS) to investigate opposed-flow flame spread in different confined conditions. Two materials, cotton-fiberglass blended textile fabric (SIBAL) and 1 mm thick polymethyl methacrylate (PMMA) slab are burned between a pair of parallel flow baffles in a small flow duct. By varying the sample-baffle distance, various levels of confinement are achieved (H = 1–2 cm). Three types of baffles, transparent, black, and reflective, are used to create different radiative boundary conditions. The purely forced flow speed is also varied (between 2.6 and 10.5 cm/s) to investigate its interplay with the confinement level. For both sample materials, it is observed that the flame spread rate decreases when the confinement level increases (i.e., when H decreases). In addition, flame spread rate is shown to have a positive correlation with flow speed, up to an optimal value. The results also indicate that the optimal flow speed for flame spread can decrease in highly confined conditions. Surface radiation on the confinement boundary is shown to play a key role. For SIBAL fabric, stronger flames are observed when using black baffles compared to transparent. For PMMA, reflective baffles yield stronger flames compared to black baffles. When comparing the results to the concurrent-flow case, it is also noticed that opposed-flow flames spread slower and blow off at larger flow speeds but are not as sensitive to the flow speed. This work provides unique long-duration microgravity experimental data that can inform the design of future opposed-flow experiments in microgravity and the development of theory and numerical models.

Study on the influence of restricted distance on fixed-width discrete of discontinuous flame spread

This study investigates the impact of varying distances between vertical walls on the propagation of discrete flames in PMMA (Polymethyl Methacrylate) slabs. The primary objective is to analyze the dynamics of flame spread in confined spaces, with a particular focus on how the spacing between vertical walls and the number of PMMA slabs influence flame characteristics. Experimentally, flame spread rate, mass loss rate, heat release rate, and pyrolysis front dynamics are examined under different confined space distances ranging from 1 to 5 cm using thermally thick PMMA slabs. The findings reveal a significant influence of confined space distance on flame propagation. In narrower spaces (1 to 2 cm), a stack effect leads to a rapid increase in flame height and mass loss rate. As the confined distance increases, this effect gradually diminishes, resulting in a decrease in flame height and mass loss rate. Additionally, the flame spread rate initially rises with increasing confined distance, reaching a peak at 2 cm, before decreasing. Through the application of the law of conservation of energy, the dominant mechanisms of flame spread are deeply analyzed under various confined space conditions. These insights are crucial for understanding and predicting fire spread in confined spaces.

Prediction of quality characteristics of micro-channels by deep learning algorithm during laser transmission ablation of PMMA

Underwater laser transmission micro-channelling of thick transparent polymethyl methacrylate (PMMA) using a neodymium-doped yttrium aluminium garnet (Nd: YAG) laser is the focus of this study. Experiments are conducted to determine the effect of three significant variables, namely pulse frequency, lamp current, and cutting speed, on heat-affected zone (HAZ) width, cut depth, and kerf width. Experiments are designed systematically utilising the full factorial design method. The purpose of constructing empirical models, specifically non-linear ones, is to establish and clarify the relationship between control factors and corresponding responses. A feed forward backpropagation neural network (FF-BPNN) is employed for predicting the measured response. Additionally, an assessment is made between the FF-BPNN results and the values predicted by the model. On the basis of the anticipated results, it can be concluded that the FF-BPNN model is preferable in predicting both the depth of cut and kerf width. In contrast, when specifically contemplating the measurement of HAZ width, the application of a non-linear model is more advantageous. As a measure of accuracy, the mean absolute error is computed for both the feedforward backpropagation neural network (FF-BPNN) and the nonlinear modelling technique.

A numerical study on autoignition of finite thick polymethyl methacrylate (PMMA) subjected to thermal radiation and forced airflow

A 2D numerical model coupling condensed and gas phases is developed to investigate autoignition of finite thick PMMA heated by radiation in forced airflow. Six sample thicknesses (1–15 mm), four heat fluxes (30–60 kW/m2), and five airflow velocities (0–1.2 m/s) are considered to examine their effects. The model is first verified by measured surface temperatures in experiments. Then three boundary layers (BL), velocity, thermal and concentration BLs, are studied based on simulation results and BL theory. BL thickness, local and surface-averaged frication coefficients, convective heat and mass transfer coefficients at solid–gas interface are estimated and compared with analytical results. Meanwhile, Damköhler numbers (Da) in non-ignition cases are calculated to reveal their impact. The results show that the model predicts measured surface temperatures well despite some divergence for thin samples due to deformation. Simulated velocities and thermal BL thicknesses agree well with analytical ones, yielding a maximum error of 33 % for concentration BL. Numerical convective heat and mass transfer coefficients match analytical ones well, whereas large discrepancy exists for friction coefficient. Two types of Da evolution, corresponding to different controlling mechanisms of non-ignition cases, separated by 6 mm sample are identified.

Study the Effect of some Air Pollutants (Ammonium Sulfate - Cadmium Sulfate) on Thick Films PMMA Supported by Al2O3

In this research, the materials used are poly methyl methacrylate (PMMA) as base material with chloroform as pure solvent (99.8%) aluminum oxide (Al2O3) as support material as base material in percentages (25%, 50%, and 75%) several tests were carried out on the models, including X-ray diffraction (XRD), and the results showed the characteristic of crystallization through the characteristic peaks with a reinforcement percentage (75%) while scanning electron microscopy (SEM) images showed that the highest effect (ammonium sulfate, cadmium sulfate) in the form of nodular structures dimensions (84.45nm - 88.84nm) with a support reinforcement percentage (75%) representing gas liberation sites as a result of surface reactions with (ammonium sulfate, cadmium sulfate) atomic force microscopy (AFM) images showed that the thick film surface had a lower roughness with a reinforcement percentage (25%) which gave the highest stability of the thick film surface.

Multi-response optimization and effect of tool rotation on micromachining of PMMA using an in-house developed µ-ECDM system

Poly-methyl methacrylate (PMMA) is a lightweight and transparent thermoplastic material which is commonly used as an alternative for high-cost and resilient glass. PMMA has potential applications in the fields of microfluidics because of its high strength, low weight, optical transparency, and biocompatibility. Therefore, in this study, in-depth experimentation was carried out to generate microchannels on PMMA using an in-house developed micro Electrochemical Discharge Machining (µ-ECDM) system. The µ-ECDM process parameters used for the experimentation include voltage (V), electrolyte concentration (wt%), and duty factor (DF) (%). Experiments were designed at three levels of process parameters for the parametric study. The microchannels were machined on a 2.5 mm thick PMMA workpiece using a titanium tool of diameter 0.7 mm. The optical microscope images, along with SEM images, are used to characterize the machined channels. The machining characteristics such as material removal rate (MRR), tool wear rate (TWR), channel width, surface roughness (SR), and depth of the channel were studied using the process parameters. Individual response optimization is carried out using S/N ratios, but confounding of factors at different factor level settings is observed for each response. Therefore, to overcome this problem, multi-response optimization using the JAYA algorithm coupled with the multi-attributed decision-making (MADM) R-method has been adopted for maximizing MRR and depth of the channel and minimizing TWR, channel width, and surface roughness at single factor level settings. The optimal process parameters are obtained by multi-response optimization are 51 V, 24 wt%, and 55% DF, and the MRR, TWR, channel width, surface roughness, and depth of the channel are found to be 21.5 µg/min, 5.5 µg/min and 804.33 µm, 5.2412 µm, and 238.22 µm, respectively that are in close pact with the predicted observations. Further, the optimal machining parameters have been used along with tool rotation (in RPM) to observe the effect on machining features. The findings show that with increment in tool rotation rate improved the MRR, TWR, and depth of the channel decreased the channel width and surface roughness.

Spin-casting of Micron-Scale Thick PMMA Films with Embedded Au Nanoparticles Formed by Laser Ablation in Liquid

Background: A Facile, scalable approach to fabrication of organic thin films with an embedded layer of nanoparticles in the ambient environment. The approach is based on step-bystep spin-coating of polymethylmethacrylate (PMMA) films and a nanoparticle layer. Objective: The goal of the present work is to fabricate a sandwich structure of the PMMA films for the top and bottom layers of a sandwich structure as well as a middle layer of nanoparticles formed in solution by the Laser Ablation in Liquid (LAL) method. Methods: First, a PMMA thin film was fabricated by spin-casting of PMMA solution in ethylacetate. Secondly, a solution of Au nanoparticles synthesized by laser ablation in ethanol was spin-cast on a prefabricated PMMA film. The distribution of Au nanoparticles and the morphology of the resulting film were analyzed using scanning electron microscopy (SEM), optical microscopy, and atomic microscopy (AFM). Finally, another PMMA layer was spin-cast on the nanoparticle-decorated film. Results: A hybrid organic film with the embedded layer of nanoparticles was fabricated using the spin-casting method for top and bottom layers as well as for the middle layer of Au nanoparticles fabricated by laser ablation in ethanol by a pulsed UV laser. Statistical and fractal analysis shows uniform distribution of nanoparticles on length scale above ten microns. Conclusion: Spin-cast-based layer-by-layer approach to fabrication of sandwich structures of organic films with embedded nanoparticlesis a facile and scalable method for hybrid organic - nanoparticle films. This approach can be extended for the fabrication of multi-layered hybrid structures.

The effect of electron dose on positive polymethyl methacrylate resist for nanolithography of gold bowtie nanoantennas

Plasmonic structures, such as bowtie nanoantennas, may be used in Surface Enhanced Raman Spectroscopy (SERS). Nanoantennas can be employed to amplify the biomolecular and chemical reactions, which is useful for biomedical applications. The electric field created by nanoantennas are optimized when the resonant wavelength of the probed laser light closely matches the resonant wavelength of the plasmonic structure. In this work, we fabricated several bowtie nanoantennas with varying geometric spacing for use with a 532 nm wavelength laser line in Raman Spectroscopy. The fabrication utilized nanolithography by electron beam lithography on a Raith Voyager, development, deposition, and metal lift-off. This study explored a specific bowtie nanoantenna geometry of 270 nm equilateral sides triangle pairs with 3 varying gap sizes, 50 nm, 20 nm, and 10 nm, and the effect of varying electron beam doses on the final structure of the nanoantenna. The results presented here, will show that the working dose factor range is 6.5–10.3 (650–10,300 μC/cm2) for 120 nm thick polymethyl methacrylate (PMMA), and with a 44.78% increase in dose, the footprint area increases between 5.9% and 10.7%.

The controlling mechanisms of horizontal flame spread over thick rods in upward cross flow

This work studies the flame spread over horizontal thick PMMA (polymethyl methacrylate) rods with three radii under different oxygen concentrations and upward cross flow velocities. The flame spread rate and the limit oxygen concentration are measured. Far away from the extinction limit, the flame spread rate increases with the flow velocity but decreases with radius. Near the extinction limit, the flame spread rate is insensitive to the flow velocity and radius. The flame spread rate can be correlated by the stretch rate, and it is found that the flame spread rates for different radii are close at the same stretch rate. A scaling analysis shows that the flame spread rates are approximately square-root dependent on the stretch rate. Prior to the extinction, the flame has entered the regressive burning regime where the flame leading edge will not spread forwardly but continuously retreat. The flame extinction is dependent on the local stretch rate and in-depth heat conduction. For a given radius, the limit oxygen concentration increases with the stretch rate. For a given stretch rate, the smaller cylinder can sustain at lower oxygen concentration due to the less solid-phase heat loss.

Composite auto-ignition criterion for PMMA (Poly methyl methacrylate) exposed to linearly declining thermal radiation

This contribution experimentally studies auto-ignition of thermally thick PMMA (Poly methyl methacrylate) subjected to linearly declining heat flux (HF) radiated from a cone heater. Thermogravimetric tests (TGA) were conducted to derive the kinetics of PMMA by model fitting method. A numerical model dealing with heat transfer and pyrolysis is utilized to simulate the experimental measurements. Results show that auto- and no-ignition regions are separated by a critical decreasing rate of HF which is quantitively determined by numerical results. Measured surface temperatures are compared with the analytically and numerically estimated ones, and it is found both ignition time and critical decreasing rate are sensitive to critical temperature. These senilities are also confirmed by numerical model through parametric study. In no-ignition region near the critical condition, the maximum mass flux is higher than the measured critical value, 4.26 g/m2s, indicating critical mass flux is not a credible ignition criterion. Measured critical temperature increases with higher initial HF and yields an average value of 641 K. A composite auto-ignition criterion combining both critical mass flux and critical temperature is found valid in estimating ignition time. Meanwhile, the different affecting mechanisms of decreasing HF on auto-ignition between this work and literature is reasonably interpreted.

Injection-rolling nozzle in an imprint system with continuous injection direct rolling for ultra-thin microstructure guide light plate

A novel Injection-rolling Nozzle (IRN) in an imprint system with continuous injection direct rolling (CIDR) for ultra-thin microstructure polymer guide light plates was developed to achieve uniform flow velocity and temperature at the width direction of the cavity exit. A novel IRN cavity was designed. There are eight of feature parameters of cavity were optimized by orthogonal experiments and numerical simulation. Results show that the flow velocity at the width direction of the IRN outlet can reach uniformity, which is far better than that of traditional cavity. The smallest flow velocity difference and temperature difference was 0.6 mm/s and 0.24 K, respectively. The superior performance of the IRN was verified through a CIDR experiment. Several 0.35-mm thick, 340-mm wide, and 10-m long microstructural Polymethyl Methacrylate (PMMA) guide light plates were manufactured. The average filling rates of the microgrooves with the aspect ratio 1:3 reached above 93%. The average light transmittance is 88%.

Pyrolysis and piloted ignition of thermally thick PMMA exposed to constant thermal radiation in cross forced airflow

Impact of cross forced airflow on pyrolysis and piloted ignition of PMMA (Poly methyl methacrylate) under constant heat flux is experimentally, analytically and numerically addressed in this study. Experimental setup consisting of a heating and blowing units was employed to provide the target constant heat flux and airflow velocity. Surface temperature and ignition time were measured in tests to examine the combined effect of forced airflow and heat flux. No ignition was observed when the heat flux and air velocity were 11.53 kW/m2 and 1.43 m/s combined, indicating a critical airflow velocity dominates ignition. An analytical model and a solid phase numerical model were developed to predict and validate the experimental measurements. Both surface and in-depth absorption of thermal radiation were considered in the models. The results showed both the critical temperature and ignition time increase with airflow velocity. Radiation reducing was found to be enhanced by increasing airflow velocity. Both the analytically and numerically predicted results employing either pure surface or in-depth absorption of thermal radiation matched the experimental measurements at acceptable levels, but the agreement between the calculations of in-depth absorption and measurements was better.

Optimization of a continuous hot embossing process for fabrication of micropyramid structures in thermoplastic sheets

Reported is the manufacture and optimization of inverted micropyramid cavity structures into thermoplastic sheets using roll-to-roll (R2R) embossing. To manufacture the master, an ultraprecision diamond machining method was applied to create seamless surface structures into a copper-coated hot embossing roller. Using the hot embossing process, the roller features were successfully transferred to 2 mm thick polymethyl methacrylate (PMMA) sheets. Optimization of the R2R control process variables was conducted using Taguchi's numerical methods, which showed the importance of the roller temperature for a successful pattern transfer. The work presents a novel fabrication technique that allows microstructures to be manufactured into thick PMMA sheets in a continuous process.

Effects of backwall on inner thermal structure in opposed-flow horizontal flame spread of thick PMMA panel

Flame spread on solid fuel is an important aspect of fire safety engineering. In this work, an unsteady numerical model was developed to investigate the opposed-flow horizontal flame spread mechanism of thick polymethyl methacrylate (PMMA) on backwall with different thermal properties. The temperature fields in both the condensed fuel and backwall material, the fuel gas distribution and the pyrolysis profiles along the fuel bed were analysed in detail. The results showed that the thermal properties of the backwall play an important role in the structure of the melting interface of the PMMA flame front. The molten layer will not penetrate the sample obviously for the case of gypsum backwall. However, the molten liquid penetrates the PMMA sample with more molten liquid generated on the aluminium backwall, thus resulting the higher possibility of molten droplets. It is also indicated that the heat accumulation at the preheated region was enhanced by the heat transfer through the aluminium backwall from the flame and pyrolysis region. On the other hand, the aluminium wall behind the flame tip normally remain at relatively high temperatures, which in turn improved the pyrolysis rate, and lead to higher gas temperature. Therefore, the flame spread of polymer would be accelerated obviously for the case of metal backwall. This work provides important information for the acceleration mechanism of metal backwall on the opposed-flow horizontal flame spread of polymer and the design of polymer components, and also provides an important basis for engineering application to evaluate the fire risk of materials by considering the thermal performance of the backwall.

Limiting condition for auto-ignition of finite thick PMMA in forced convective airflow

This contribution experimentally addresses the auto-ignition of finite thick PMMA (polymethyl methacrylate) subjected to parallel forced convective airflow. 1–15 mm thick samples, 30–60 kW/m2 heat fluxes (HF) and 0–1.2 m/s airflow velocities (u) were utilized to examine the auto-ignition mechanism and the limiting condition of non-ignition cases. Critical temperature, surface temperature evolution and ignition time were recorded. A modified numerical model, considering both PMMA and thermal insulation layers, and theoretical correlations developed for thermally intermediate solid were employed to analyze the experimental data. Results show that three regimes corresponding to different controlling mechanisms are identified: (1) solid-dominant regime, u ≤ 0.4 m/s, where auto-ignition is primarily determined by the heat transfer and pyrolysis in solid; (2) transitional regime, 0.4 m/s < u < 1.0 m/s, where both solid and gas phases have nonnegligible contributions; (3) gas-dominant regime, u ≥ 1.0 m/s, where gas phase chemical kinetics is responsible for the observed non-ignition phenomenon. Critical temperature is reliable only in the solid-dominant regime. In all the ignition scenarios, critical temperature increases with increasing sample thickness and u, but it barely changes with varying HFs. In the gas-dominant regime, surface temperature measurement suffers greatly from the generated large bubbles, worsening the agreement with numerical predictions. Based on the simulated in-depth temperature, estimated Biot number and thermal penetration depth, 1 mm PMMA is not thermally thin, whereas 15 mm sample is approximately thermally thick. Furthermore, thermal diffusivity of PMMA and the critical HF are estimated by fitting the measured ignition times.