Poly Methyl Methacrylate Fibers Research Articles

Experimental study of light transmitting concrete with ultra-high content of polymethyl methacrylate

Light Transmitting Concrete (LTC) is an innovative material for crafting unique and sustainable architectural and civil structures. Previous studies primarily utilized optical fibers with diameters below 1.5 mm, which did not exceed 10 % of the volumetric content in concrete. This study aims to develop LTC with ultra-high light transmission capabilities while preserving its mechanical strength. An important innovation is the use of polymethyl methacrylate (PMMA) with larger diameters than normal optical fibers. Specifically, PMMA fibers of 2.0 mm diameter and PMMA tubes of 10–20 mm diameter were employed to increase the spacing between these materials when arranged in an ultra-high volumetric content within the concrete, facilitating easier compaction of the fresh concrete. Experiments of the material's mechanical properties, microstructure, and optical performance were conducted. The findings suggest that although the increased PMMA content might reduce the concrete’s mechanical strength due to a smaller effective cross-sectional area, the LTC still achieves compressive strength exceeding 40 MPa. This underscores the viability of LTC with a substantially higher content of light transmitting functional materials compared to previous studies, while still maintaining a mechanical strength greater than normal concrete. The light transmission efficiency of LTC is nearly directly proportional to its PMMA content, and able to reach up to 30 % of the light source's intensity. Additionally, LTC with PMMA fibers provides uniform light distribution across its surface because of scattering, while LTC with larger-diameter PMMA tubes focuses light around the core areas due to direct lighting.

Combining Polymer and Cyclodextrin Strategy for Drug Release of Sulfadiazine from Electrospun Fibers.

This study reports the fabrication of polymeric matrices through electrospinning using polymethyl methacrylate (PMMA) and poly(lactic-co-glycolic acid) (PLGA), biocompatible polymers commonly used in medical systems. These polymers were combined with an antibacterial drug, sulfadiazine sodium salt (SDS) or its supramolecular system formed with hydroxypropyl-β-cyclodextrin (HPβ/CD) at 1:1 molar ratio, aiming to assemble a transdermal drug delivery system. The formation of fibers was confirmed by scanning electron microscopy (SEM), and the fibers' surface properties were analyzed using contact angle and water vapor permeability techniques. Drug release tests and cell viability assays were performed to evaluate the potential toxicity of the material. SEM images demonstrated that the obtained fibers had nanoscale- and micrometer-scale diameters in PLGA and PMMA systems, respectively. The contact angle analyses indicated that, even in the presence of hydrophilic molecules (SDS and HPβCD), PMMA fibers exhibited hydrophobic characteristics, while PLGA fibers exhibited hydrophilic surface properties. These data were also confirmed by water vapor permeability analysis. The drug release profiles demonstrated a greater release of SDS in the PLGA system. Moreover, the presence of HPβCD improved the drug release in both polymeric systems and the cell viability in the PMMA SDS/HPβCD system. In terms of antibacterial activity, all membranes yielded positive outcomes; nevertheless, the PLGA SDS/HPβCD membrane exhibited the most remarkable results, with the lowest microbial load values. Additionally, the pseudo wound healing analysis demonstrated that the PLGA SDS/HPβCD fiber exhibited results similar to the control group. Consequently, these findings exemplify the substantial potential of the obtained materials for use in wound healing applications.

Incorporation and Deposition of Spin Crossover Materials into and onto Electrospun Nanofibers.

We synthesized iron(II)-triazole spin crossover compounds of the type [Fe(atrz)3]X2 and incorporated and deposited them on electrospun polymer nanofibers. For this, we used two separate electrospinning methods with the goal of obtaining polymer complex composites with intact switching properties. In view of possible applications, we chose iron(II)-triazole-complexes that are known to exhibit spin crossover close to ambient temperature. Therefore, we used the complexes [Fe(atrz)3]Cl2 and [Fe(atrz)3](2ns)2 (2ns = 2-Naphthalenesulfonate) and deposited those on fibers of polymethylmethacrylate (PMMA) and incorporated them into core-shell-like PMMA fiber structures. These core-shell structures showed to be inert to outer environmental influences, such as droplets of water, which we purposely cast on the fiber structure, and it did not rinse away the used complex. We analyzed both the complexes and the composites with IR-, UV/Vis, Mössbauer spectroscopy, SQUID magnetometry, as well as SEM and EDX imaging. The analysis via UV/Vis spectroscopy, Mössbauer spectroscopy, and temperature-dependent magnetic measurements with the SQUID magnetometer showed that the spin crossover properties were maintained and were not changed after the electrospinning processes.

Measurement and Analysis of Light Leakage in Plastic Optical Fiber Daylighting System

The daylighting systems via polymethylmethacrylate (PMMA) plastic optical fibers have obvious cost advantages and have been widely studied. However, there is light leakage when PMMA optical fibers transmit concentrated sunlight, resulting in a transmission efficiency lower than the theoretical value. This research aims to quantitatively study the light leakage effect of PMMA optical fibers. Concentrated sunlight was used as the sunlight source instead of a monochromatic laser. An adjustable diaphragm was used to adjust the angle of the incident light, and the infrared filter and heat-absorbing glass were used to solve the overheating problem of PMMA fibers. The results show that when the incident angle is greater than 13°, the relative transmission efficiency of the fibers drops rapidly, which means that the light leakage deteriorates. The data also show that the angle of the output beam of PMMA optical fibers is ±30°, which is independent of the angle of the incident beam. Based on this conclusion, a PMMA optical fiber daylighting system with an incident angle of 13° was developed, which has higher transmission efficiency than previously developed systems. This study indicates that the angle effect of light leakage should be considered in the design of a plastic optical fiber daylighting system.

Dynamic Rotational Sensor Using Polymer Optical Fiber for Robot Movement Assessment Based on Intensity Variation

A complex signal processing technique is usually required to process the data in most sensor design structures, and integration into real applications is also challenging. This work presents a dynamic rotational sensor using polymethyl methacrylate (PMMA) fiber for robot movement assessment. The sensor design structure is based on the coupling of light intensity, in which two PMMA fibers are twisted together. Both fibers are bent after twisting and attached on the linear translation stage, which is further attached to the robot. The variation in bending radius causes the bending loss, and that loss is coupled in the second fiber. The change in the macro-bend radius corresponds to the rotation of the robot. Experimental results indicate that the sensor can operate in full rotational cycle (i.e., 0°-360°) as well as for clock and anti-clockwise rotation. Moreover, different rotational speeds (2°/s, 3°/s, 5°/s, and 10°/s) were carried out. The hysteresis loss of the sensor was about 0.77% and the sensitivity was 8.69 nW/°. The presented dynamic rotational sensor is cost-effective and easily integrated into the robot structure to analyze the robot's circular motion.

Influence of UV Radiation on Mechanical Properties of Polymer Optical Fibers.

This paper presents an analysis of the mechanical properties of different polymer optical fibers (POFs) at ultraviolet (UV) radiation conditions. Cyclic transparent optical polymer (CYTOP) and polymethyl methacrylate (PMMA) optical fibers are used in these analyses. In this case, the fiber samples are irradiated at the same wavelength, pulse time and energy conditions for different times, namely, 10 s, 1 min, 2 min and 3 min. The samples are tested in tensile tests and dynamic mechanical thermal analysis (DMTA) to infer the variation in the static and dynamic properties of such fibers as a function of the UV radiation condition. Furthermore, reference samples of each fiber (without UV radiation) are tested for comparison purposes. The results show a lower UV resistance of PMMA fibers, i.e., higher variation in the material features in static conditions (Young's modulus variation of 0.65 GPa). In addition, CYTOP fiber (material known for its high UV resistance related to its optical properties) also presented Young's modulus variation of around 0.38 GPa. The reason for this reduction in the moduli is related to possible localized annealing due to thermal effects when the fibers are subjected to UV radiation. The dynamic results also indicated a higher variation in the PMMA fibers storage modulus, which is around 30% higher than the variations in the CYTOP fibers when different radiation conditions are analyzed. However, CYTOP fibers show a smaller operational temperature range and higher variation in the storage modulus as a function of the temperature when compared with PMMA fibers. In contrast, PMMA fibers show higher variations in their material properties when subjected to oscillatory loads at different frequency conditions. Thus, the results obtained in this work can be used as guidelines for the influence of UV radiation in POFs not only for the material choice, but also on the limitations of UV radiation in the fabrication of the grating as well as in sensor applications at UV radiation conditions.

Electrospun PMMA fibers blended with core‐shell PCM/PS microspheres for thermal regulating applications

AbstractPhase changing materials (PCMs) have been widely investigated because of their unique properties and applications. In recent years, PCMs have been embedded into polymer fibers for thermal regulating purposes. The PCM‐containing polymer fibers, however, usually suffer the leakage problem because PCMs are not covered well by polymers in fibers. To solve this problem, in this study, we develop a facile strategy to fabricate PCM‐containing polymer fibers without the leakage problem. The PCM/polystyrene (PS) core‐shell microspheres are first prepared by suspension polymerization, in which n‐hexadecane is used as the PCM. By blending the PCM/PS microspheres into polymethyl methacrylate (PMMA) solutions, The PMMA fibers blended with core‐shell PCM/PS microspheres can be prepared via electrospinning. Acetic acid is chosen as the solvent, which can selectively dissolve PMMA and cannot dissolve PS. Therefore, the morphologies of the core‐shell PCM/PS microspheres can be maintained during the electrospinning processes. The microspheres and fibers are characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Thermal imaging results demonstrate that the PCM‐containing fibers can effectively regulate temperatures and fibers with higher contents of PCM exhibit better thermal regulating behaviors. Repeated thermal regulating experiments are also conducted for up to 4 cycles.

Stable Single‐Mode Lasing from a Hybrid Perovskite–Polymer Fiber

AbstractNanowire lasers are potential light sources that can be used in photonic integrated circuits (PICs) for inter‐chip optical communication. However, due to the size incompatibility between a nanoscale laser and a micrometer‐scale optical waveguide, their integration within a PIC remains challenging. Here, an in situ growth strategy to directly construct perovskite nanolasers inside the long polymethyl methacrylate (PMMA) fibers is explored. As the perovskite nanolasers are embedded inside the PMMA fibers, effective coupling of lasing light to the PMMA fibers is expected. Furthermore, due to the protection of PMMA coating, the perovskite nanolasers exhibit high robustness in water and demonstrate significant improvement in photostability. Stable single‐mode and polarization operations are obtained at room temperature from the lasers with a low excitation threshold. Hence, these results pave the way to realize ultra‐stable perovskite‐based PICs suitable for inter‐chip optical communication.

Gentamicin and fluconazole loaded electrospun polymethylmethacrylate (PMMA) fibers as a novel platform for the treatment of corneal keratitis

In this study, 10 mg fluconazole (10 FCZ) and 10 mg gentamicin (10 GEN) loaded with 40% polymethylmethacrylate (40% PMMA) fibers were fabricated by electrospinning and the performance of the formulations (40% PMMA, 40% PMMA/10 FCZ, 40% PMMA/10 GEN, and 40% PMMA/10 FCZ/10 GEN) was tested. 10 mg Gentamicin-loaded 40% PMMA fiber mat showed a more significant zone of inhibition against the S. aureus compared to the zone of 40% PMMA/10 GEN/10 FCZ fiber. The biocompatibility test using a human adipose-derived mesenchymal stem cell (MSCs) as a cell model proved that the amount of loaded and released GEN has no toxic effects on the MSCs.

POFBG-Based Humidity Detection Method for Insulating Gas in Electrical Equipment

The accumulation of moisture content undoubtedly threatens the safe operation of gas-insulated electrical equipment. On-line humidity monitoring of SF6 is an important way to check the insulation status of live equipment. This paper presents a direct optical measurement method based on a Polymethyl Methacrylate Fiber Bragg Grating (POFBG) sensor for the humidity detection requirement of SF6 gas with a very small water content. The experiments results show that this method is feasible with the sensitivity and resolution of the POFBG sensor studied being 14.3pm/%RH and 0.1%RH in the range of 8.4~30.4%RH. Additionally, the temperature variation can affect the relative humidity change of GIS and other sealed containers. Therefore, a reduction method of relative humidity centered on the initial baseline conditions under the condition of constant water content is also proposed. It can eliminate the error in relative humidity measurement caused by temperature variation.

Critical length reinforcement in core-shell electrospun fibers using composite strategies

An understanding of the reinforcement mechanism in composites is crucial for the development of novel materials where the application is limited by their mechanical properties. One of the methods used to obtain high performance composites is reinforcement with short fibers. Polymeric materials, such as electrospun polymethyl methacrylate (PMMA) fibers, have a very high tendency to fragment into regular short fibers after applying very low stress. This phenomenon was used to reinforce a polycarbonate (PC) core-shell structure (PMMA-PC) by using fragmented short PMMA fibers for reinforcement in the critical length limits. Mechanical testing revealed an increase of maximum stress and Young's modulus of almost 260% and 630%, respectively, for PMMA-PC fiber meshes. The observation of core-shell fibers after mechanical testing was confirmed by using confocal microscopy, showing very regular short fragments of PMMA fibers inside the PC shell. This work demonstrates a hierarchical approach that can be taken for reinforcement of a single fiber on the nanoscale and a composite on the macroscale.

Optimum design of the surface plasmon resonance sensor based on polymethyl methacrylate fiber

A novel type of polymethyl methacrylate (PMMA) fiber refractive index sensor based on surface plasmon resonance (SPR) is proposed in this work, which is applied to measure the refractive index of liquid. The performance is investigated by the SPR theory and the structural properties of the side-polished D-type fiber. In order to obtain the optimized parameters of SPR sensor, the effects of metal film material, the metal film thickness and the length of the sensing zone on spectral characteristics of the sensor are studied. The fiber SPR sensor is manufactured and applied to the preparation experiment. The change of refractive index of glycerol solution is detected and analyzed at a constant temperature of 20 ​°C. Experimental results indicate that the proposed fiber SPR sensor exhibits refractive index sensitivity up to 3328.1 nm/RIU in the range of 1.334–1.388, which can be utilized as the alternative material for bio-sensing studies.

Characterization of optical components for the ESS Target Imaging System

At the European Spallation Source (ESS), a Target Imaging System (TIS) has been proposed to monitor the integrity of the target wheel. The TIS signal will be provided by the gamma decay photons from the activated tungsten bricks of the target. To collect the photons, a linear array of 500 scintillators is mounted on a collimator and the imaging is achieved via a push-broom method. Scintillation light will be carried by optical fibers to an intensified sCMOS camera.This study presents a characterization of the performance of the full detector chain: emission from crystals, attenuation in optical fibers and response of the camera optics. The behaviour of both unirradiated and irradiated optical fibers is also evaluated for γ-only irradiations up to 15kGy.Among the tested crystals (LuAG:Ce, YAG:Ce and BGO), LuAG:Ce is the preferred choice both in terms of radiation hardness and photon yield.Losses induced by Poly methyl methacrylate (PMMA) and quartz optical fibers are ~65% and ~45%, respectively. In ESS conditions, over half-year of continuous operations, PMMA fibers are estimated to lose an additional 3%, compared to 2% for quartz fibers. Both PMMA and quartz fibers represent a potentially viable choice: the former suffer a more serious radiation damage than the latter, but formation of permanent defects in quartz can impair the efficiency of quartz fibers in the 580−620nm range. Mix-and-match of PMMA and quartz fibers may represent a cost-effective compromise for the final TIS design.Two different fibers-camera coupling optics are compared. The measured difference in transmittance is 3%.

Performance Enhancement of a Quartz Tuning Fork Sensor Using a Cellulose Nanocrystal-Reinforced Nanoporous Polymer Fiber

A cellulose nanocrystal (CNC)-reinforced polymethylmethacrylate (PMMA) fiber was obtained via electrospinning, and then attached between the two tines of a quartz tuning fork (QTF). The change in the resonance frequency of the CNC/PMMA composite fiber-coated QTF (CP-QTF) was measured upon being exposed to various concentrations of ethanol vapor. The frequency decreased as the ethanol vapor concentration increased, because the modulus of the composite fiber decreased due to the adsorption of the ethanol vapor. The composite fiber obtained at a high relative humidity (RH; 60% RH, CP60 fiber) produced a highly porous structure as a result of the moisture adsorption-induced phase separation of PMMA. The porosity of the CP60 fiber was higher than that of a CNC/PMMA composite fiber obtained at 30% RH (CP30 fiber) or that of a plain PMMA fiber obtained at 60% RH (P60 fiber), because hygroscopic CNCs promote moisture adsorption. The CP60 fiber-coated QTF (CP60-QTF) exhibited a greater frequency change and faster response time than P60-QTF and CP30-QTF upon exposure to ethanol vapor at the same concentration. The enhanced performance of CP60-QTF was attributed to its higher surface area and larger fiber modulus.

Self-assembled template-confined growth of ultrathin CsPbBr3 nanowires

Fabrication of ultrathin (e.g., ∼2 nm) CsPbBr3 nanowires is still challenging for existing methods, for the extremely fast crystal growth process of CsPbBr3. Here, we developed a self-assembled nanotemplate-confined growth concept to prepare ultrathin CsPbBr3 nanowires. During electrospinning using the N,N-dimethylformamide (DMF) solution composed of polymethyl methacrylate (PMMA), PbBr2, CsBr, and capping agents, PMMA chains would assemble into nanochannels acting as nanotemplates within the electrospun PMMA fibers. Owing to the very limited amount of precursors within the nanochannels, ultrathin CsPbBr3 nanowires were prepared after DMF evaporation. The CsPbBr3 nanowires within the PMMA fibers or dispersed in toluene showed bright blue luminescence. The structure of the CsPbBr3 products could be adjusted by the stirring time, as well as the amount of PMMA, PbBr2, and CsBr in DMF. Overall, we developed a new method towards engineering ultrafine CsPbBr3 nanostructure through self-assembled template-confined growth concept during electrospinning, which may find potential applications in blue light emitting diodes and other optoelectronic devices.

Realization of high flux daylighting via optical fibers using large Fresnel lens

Due to energy saving and flexible installation, the daylighting system via optical fibers for indoor illumination has attracted a lot of research attention. However, in applications, it is hard to adopt large aperture lens to improve sunlight collection due to the overheating problem caused by high sunlight concentration. The optical fibers generally adopted, Polymethylmethacrylate (PMMA) fiber, often suffers from overheating, and cannot work under a temperature exceeding 70 °C (Ashby, 2005). To solve this problem, this study tested three measures, infrared light filter (Sedki and Maaroufi, 2017), flux homogenization and fiber facet polishing, respectively to control thermal load caused by a large lens with a diameter of 1 m. The experimental data shows that the infrared light filter can reflect infrared light (740–1100 nm) efficiently, meanwhile keeping highly transparent for the visible spectrum (400–700 nm), which produces the cold incident light. A homogenizer was also designed to produce a uniform flux distribution by reflection in a mirror cavity. Analysis based on Monte Carlo rays-tracing method (MCRT) showed that the homogenizer could supply a flat flux distribution of 1500 suns by eliminating the flux peak. Microscopy experiments revealed that fine polish could effectively remove dust off the surface of the PMMA fiber, so to avoid heat spot to protect PMMA fiber. A long time daylighting test on Beijing (40°05′23″N, 116°17′45″E, 97 klux outdoor) demonstrated the feasibility of the large lens with an aperture of 1 m for daylighting via optical fibers, which offered an illumination level of 180 lx on an area of 36 m2. A comparison test on Lhasa, Tibet (29°39′52″N, 91°06′26″E) has also carried out under a higher outdoor illuminance of 125 klux, which showed a daylighting efficiency of 15.1%. The research showed that, as long as there was good thermal load control, PMMA optical fibers can work well and it is feasible to adopt large lens into daylighting system via plastic optical fibers.

Doxycycline release and antibacterial activity from PMMA/PEO electrospun fiber mats.

Objective:To investigate the use of polymethyl methacrylate (PMMA) electrospun fiber mats containing different amounts of polyethylene oxide (PEO) as a doxycycline delivery system and to test antibacterial activity against an oral pathogen.Methodology:PMMA powders or PEO (mol wt 200 Kd) (10,20,30% w/w/) were dissolved in N, N-dimethylformamide (DMF) to obtain a final polymer concentration of 15% in DMF (w/v). 2% Doxycycline monohydrate was added to the solutions and submitted to vortex mixing. The solution was transferred to a plastic syringe and fit into a nanofiber electrospinning unit. The parameters applied were: voltage at 17.2 kV; distance of 20 cm between the needle tip and the collector plate; target speed at 2 m/min; and transverse speed at 1cm/min. Syringe pump speed was 0.15 mm/min. The drug release analysis was performed by removing aliquots of the drug-containing solution (in PBS) at specific periods. Doxycycline release was quantified using RP-HPLC. Fiber mats from all groups had their antibacterial action tested against S. mutans based on inhibition halos formed around the specimens. The experiments were performed in triplicate. Gravimetric analysis at specific periods was performed to determine any polymer loss. Morphological characterization of the electrospun fibers was completed under an optical microscope followed by SEM analysis.Results:The addition of PEO to the PMMA fibers did not affect the appearance and diameter of fibers. However, increasing the %PEO caused higher doxycycline release in the first 24 h. Fibers containing 30% PEO showed statistically significant higher release when compared with the other groups. Doxycycline released from the fibers containing 20% or 30% of PEO showed effective against S. mutans.Conclusion:The incorporation of PEO at 20% and 30% into PMMA fiber mat resulted in effective drug release systems, with detected antibacterial activity against S. mutans.

An optical fiber daylighting system with large Fresnel lens

Because of flexible installation and natural spectrum, the concentrated sunlight transmission systems via PMMA (Polymethyl methacrylate) fibers for indoor illumination are concerned widely in areas of building energy saving. Due to the long-term indoor work, the daily working population in cities lacks of natural light and is susceptible to various diseases. Therefore, from the health point of view, it is necessary to develop deep indoor daylighting. In this work, a sunlight concentration and transmission system was developed and tested, which uses a Fresnel lens with a diameter of 1m to achieve large flux collection. A reflection design of light path was adopted to resolve the problem of long focal length of the Fresnel lens. A hot mirror and a homogenizer were used to protect the optic fiber bundle from burned by high temperature. The results showed that the daylighting efficiency is about 11%-13%. The operability of the equipment was verified through experiments, proving that the equipment can be combined with buildings for daylighting. It is hoped that this research will be of some reference value to the design of optical fiber daylighting systems in buildings.

Wavelength Dependent Ammonia Sensing Characteristics of SnO2 based Fiber Optic Sensor

SnO2 nanoparticles were synthesized by co-precipitation technique. The synthesized SnO2 nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and UV-visible diffused reflectance spectrometer (DRS). The XRD results addressed that the SnO2 nanoparticles was crystallized in rutile tetragonal structure. The SEM analysis confirms that the prepared nanopowder is composed of nanoparticles. Analysis of the DRS UV-Vis spectrum showed that the band gap of the synthesized SnO2 is to be ∼3.4 eV. The small cladding portion of the optical fiber was replaced with the synthesized nanoparticles. The ammonia sensing characteristics of the prepared SnO2 nanoparticles were analyzed for different wavelength ranges (red, yellow and blue) using polymethyl methacrylate fiber. It has been found that the synthesized SnO2 nanoparticles shows high sensitivity (∼23) in yellow wavelength range compared with red and blue wavelength ranges at room temperature.

Characterization of spectral and intensity changes with measurement geometry in various light guides used in scintillation dosimetry.

To characterize response changes of various light guides used in megavoltage (MV) photon beam scintillation dosimetry as a function of irradiation conditions. Particular emphasis was placed on quantifying the impact of response changes on the Čerenkov light ratio (CLR). Intensity and spectral response measurements as a function of dose, depth, and fiber-beam angle were performed with a commercial scintillation detector stripped of its scintillation material and five different custom-made light guides. The core materials of the light guides investigated consisted of polymethyl methacrylate (PMMA), low- and high-hydroxyl content silica, and polystyrene. Dose levels ranging from 50monitor units (MU) to 1000MU, depths ranging from 1 to 20cm, and fiber-beam angles ranging from 10° to 90° were investigated. All measurements were performed at a photon beam energy of 6MV. The CLR was calculated by taking the ratio of the responses in the blue to green spectral regions. There was no significant change in the CLR measured with the modified commercial scintillation detector as a function of delivered dose. In addition, increases in the CLR as functions of depth and fiber-beam angle were observed where the maximum changes were 4.2% and 3.6%, respectively. The spectrum measurements showed no observable changes in spectral shape with depth except for the low-hydroxyl content silica fiber. Variations in the measured spectral shape with fiber-beam angle were observed for all fibers investigated. The magnitude of the changes in the spectral shape varied with fiber type, where the silica fibers exhibited the largest changes and the plastic fibers exhibited the smallest changes. Increases in the CLR were observed for the silica fibers with depth and for all fibers with fiber-beam angle. The plastic fibers showed no significant change in the CLR as a function of depth. Increases of 3.1% and 9.5% in the CLR were observed for the high- and low-hydroxyl content silica fibers, respectively, over the range of depths investigated. Variations of 2.3%, 6.1%, 5.1% and 11.9% were observed for the PMMA, polystyrene, high-hydroxyl, and low-hydroxyl content silica fiber CLR values as a function of fiber-beam angle, respectively. The insignificant change in the CLR with delivered dose indicates that a single CLR value over the investigated dose range is sufficient for accurate Čerenkov subtraction. Variations in the stem-effect spectrum shape can occur with changes in irradiation geometry. The magnitude of the changes are governed by the fiber construction and the optical properties of the fiber. The observed spectral shape changes can be explained by a combination of variations in optical path length through the fiber and the fiber fluorescent signal contribution to the stem-effect. These spectral shape variations directly influence the calculated CLR values. This work confirms that careful characterization of scintillation detectors is important as changes in the stem-effect spectrum can cause changes in the CLR. If the CLR changes between the reference and measurement conditions, this could result in an incorrect stem-effect subtraction and reduced measurement accuracy.