PMMA Shell Research Articles

Preparation and Thermal Performance of Poly(Methyl Methacrylate)/Binary Alkane-Alcohol Organic Eutectic Microcapsules as Phase Change Materials for Cold Storage

In this study, the microcapsules containing binary alkane-alcohol organic eutectic of mixed n-tetradecane and 1-dodecanol (TD-DD) phase change materials as the core and poly (methyl methacrylate)(PMMA) as the shell were prepared by emulsion polymerization reaction. The microcapsules were characterized by using DSC, SEM, FT-IR and TG. The results of DSC test showed that melting and freezing temperatures of the microcapsules are-6.136 °C and 5.203 °C, and total latent heat value are-82.522 J/g and 77.632 J/g, respectively. The SEM and FT-IR analyses indicated that PMMA shell has successfully encapsulated TD-DD. The TD-DD and the microcapsules exhibited in spherical shape. Additionally, the TG test showed that the thermal stability of TD-DD was increased after encapsulation.

Segmental dynamics and rheology of miscible poly(vinylidene fluoride)/poly(methyl methacrylate) (70/30 by weight) blend filled with titania or poly(methyl methacrylate)-grafted titania

Titania (TiO2) or poly (methyl methacrylate) (PMMA)-grafted titania (TiO2-g-PMMA) were incorporated into miscible poly (vinylidene fluoride) (PVDF)/PMMA (70/30 by weight) blend by melt mixing. TiO2 particles exhibited aggregation in the composites as displayed by scanning electron microscopy observations and the storage modulus (G′) plateau in the low frequency (ω) region. This is accompanied with the restriction of molecular mobility and the elevation of glass transition temperature (Tg). Conversely, TiO2-g-PMMA nanoparticles with well-defined cross-linked PMMA shells of 5 nm in thickness are well-distributed in the matrix, without the influence on Tg and the appearance of low-ω plateau. The dispersion of TiO2 is not stable during the thermal annealing of the composite in the melt while the TiO2-g-PMMA nanoparticles demonstrate excellent dispersion stability. Broadband dielectric spectroscopies indicate that TiO2 influenced the molecular relaxations of αa and αc, while the effect of TiO2-g-PMMA was negligible. Furthermore, the core–shell structured TiO2-g-PMMA nanoparticles produced considerable smaller interfacial polarization than TiO2 in the composites.

LCST-Type Phase Separation of Poly[poly(ethylene glycol) methyl ether methacrylate]s in Hydrofluorocarbon.

Poly[poly(ethylene glycol) methyl ether methacrylate]s [poly(PEGMA)s] sharply and reversibly exhibited lower critical solution temperature (LCST)-type phase separation in 2H,3H-perfluoropentane (2HPFP). The cloud points decreased from 52 to 41 °C with increasing the PEG pendant length [-(CH2CH2O)mCH3: m = 4.5, 9, 19]. The cloud point was precisely controlled via the addition of perfluoroalkanes (e.g., perfluorooctane) to the 2HPFP solution: typically, it was inversely proportional to the amount of perfluorooctane in the mixture. The unique thermoresponsive solubility further afforded the temperature-mediated micellization of a block copolymer of PEG19MA and methyl methacrylate (MMA) in 2HPFP to uniquely give a PEG-core micelle with PMMA shell. Therefore, the LCST phase separation properties in the hydrofluorocarbon would open new vistas for thermoresponsive polymeric materials.

Achieving large dielectric property improvement in polymer/carbon nanotube composites by engineering the nanotube surface via atom transfer radical polymerization

High dielectric constant (high-k) polymer composites have many applications in electrical insulation and energy storage systems because of their ease of processing. An important route to high-k polymer composites is to introduce high-aspect-ratio conductive nanoparticles (e.g., carbon nanotubes, CNTs) into a dielectric polymer. However, it is difficult to tune the dielectric properties of the composites via only adjusting the nanoparticle loading, particularly when the conductive nanoparticle concentration is near the percolation threshold. In this work, by using surface-initiated atom transfer radical polymerization, poly(methyl methacrylate) encapsulated CNTs (PMMA@CNTs) were prepared and used to tune the dielectric properties of PMMA composites. It was found that the PMMA@CNTs can be well dispersed into the PMMA matrix, regardless of the thickness of the PMMA shell grafted onto the CNT surface. The electrical parameters of the composites, such as percolation threshold, electrical conductivity, dielectric constant and dielectric loss tangent, can be tuned by controlling the thickness of the PMMA shell on the CNT surface. High dielectric constant and low dielectric loss can be achieved by adjusting the loading of PMMA@CNTs and the thickness of the PMMA shell on the CNT surface.

Polydimethylsiloxane microspheres with poly(methyl methacrylate) coating: Modelling, preparation, and characterization

Polydimethylsiloxane (PDMS) microspheres are prepared by mixing homogeneous dispersions of vinyl‐functional PDMS and a curing agent using mechanical stirring in a series of aqueous solutions, and curing at 80 °C for 2 h. In order to verify the experimental diameter and size distributions of the PDMS microspheres, the Hinze‐Kolmogorov theory is applied to predict the mean diameter, and a population balance model as well as the maximum entropy formalism are used to describe the size distribution. Close agreement is found between experimental and theoretical results. Furthermore, vinyl functional PDMS microspheres were coated with poly(methyl methacrylate) (PMMA) by spin coating with different concentrations of PMMA solutions. The quality of the resulting PMMA shell is investigated using rheological measurements at 50 °C with a time‐sweep procedure. The results strongly suggest that PMMA‐coated PDMS microspheres react around 20 times slower than the uncoated ones, and that the PMMA shell significantly hinders the reaction between the PDMS microsphere and cross‐linker. Thus the thin PMMA shells are very efficient in protecting the reactive PDMS microspheres, since the PMMA shell forms an impermeable barrier up to 50 °C.

Synthesis of Self-Healing Thermosetting Resin Based Capsules and their Related Complexities

Microencapsulation forms an integral part in synthesizing bioinspired materials. This paper focuses on elaborating the problems faced in encapsulation of DGEBA microcapsules in PMMA and urea formaldehyde shell wall. The preparation process and the process parameters affecting the microcapsule property are discussed. The difference between the microcapsules prepared using emulsion polymerization and that by solvent evaporation has been discussed. The size, shape and morphology of the microcapsules was characterized using FESEM technique. It was observed that the agglomeration of the microcapsules can be prevented by changing the concentration of the emulsifier. However, in case of urea formaldehyde encapsulation chunks of pre-polymer resulted in agglomeration of the nanosized capsules even if higher concentration of emulsifier was implemented.

Controlled release in hard to access places by poly(methyl methacrylate) microcapsules triggered by gamma irradiation

Gamma irradiation was investigated as a triggering stimulus for the activation of poly(methyl methacrylate) (PMMA) microcapsules. PMMA was exposed to varying doses of irradiation and analyzed by differential scanning calorimetry, size‐exclusion chromatography, and nuclear magnetic resonance. It was found that the glass transition temperature (Tg) of the polymer decreases at low irradiation doses. Additionally, Tg can be physically adjusted by adding a plasticizer, and both kinds of microcapsules were successfully prepared with non‐plasticized and plasticized PMMA shell. Finally, impermeable microcapsules were shown to become permeable after irradiation and release an encapsulated cross‐linker, which enables the remotely controlled formation of polydimethylsiloxanes in traditionally unavailable places. Therefore, the activation method has significant implications for industrial application. Copyright © 2015 John Wiley & Sons, Ltd.

PMMA/PMMA core-shell particles with ellipsoidal, fluorescent cores: accessing rotational dynamics.

For several decades, nonaqueous dispersions of PMMA particles have played an important role in colloid research. They have found application as colloidal model systems, which are used to probe glassy dynamics or to explore crystal nucleation. To date, most research has focused on spherical particles, in which only translational motion can be investigated. Recently, however, there has been a surge of interest in analyzing also rotational dynamics. In this contribution, we introduce a new class of core-shell particles, which can be used as rotational probes. The colloids described herein are composed of shape anisotropic, fluorescent cores covered with nonfluorescent PMMA shells. The core-shell particles are built up in four steps. In a first step, we produce fluorescent and photo-cross-linkable PMMA colloids. In the second step, these particles are thermomechanically elongated and fixed in defined ellipsoidal shapes by photo-cross-linking. Subsequently, we cover the cross-linked, fluorescent core with a nonfluorescent PMMA shell. The shape of the resulting core-shell colloids is tunable between the initial anisotropic and perfect spherical shape. For shaping, we apply a simple solvent swelling procedure. As one option, this method yields perfect PMMA spheres with ellipsoidal, fluorescent centers. We also report morphological particle characterization using various fluorescence microscopy techniques. Finally, we demonstrate that the rotational dynamics of individual colloids can be tracked and analyzed.

Property improvement of plasticized poly(vinyl chloride) by nano‐TiO2 and poly(methyl methacrylate)–encapsulated nano‐TiO2

To improve the physical properties of plasticized poly(vinyl chloride) (p‐PVC), the p‐PVC nanocomposites filled with four loading levels (3, 5, 7, and 9 parts per hundred of PVC resin) of either nanosized titanium dioxide (nTiO2) or poly(methyl methacrylate)–encapsulated nTiO2 (PMMA‐nTiO2) were prepared by melt mixing on a two‐roll mill, followed by compression molding. The PMMA‐nTiO2 used in this study was synthesized via in situ differential microemulsion polymerization. The resulting PMMA‐nTiO2 exhibited core‐shell morphology (nTiO2 core and PMMA shell) with an average diameter of 42.6 nm. The effects of nTiO2 and PMMA‐nTiO2 on the tensile properties, hardness, morphology, and thermal stability of the as‐prepared p‐PVC nanocomposites were then investigated and compared. The inclusion of either nTiO2 or PMMA‐nTiO2 nanoparticles increased the tensile strength, Young's modulus, hardness, and thermal stability of the nanocomposites in a dose‐dependent manner and reduced the elongation at break. However, the elongation at break was still higher than that for the neat p‐PVC. Moreover, the PMMA‐nTiO2 nanocomposites had a higher enhancement of the tensile strength, Young's modulus, hardness, and thermal stability than the nTiO2 nanocomposites at a similar loading level. Hence, the PMMA grafted on the nTiO2 surface played an important role in toughening and increasing the thermal stability of the nanocomposites owing to the improved miscibility and interfacial adhesion between the encapsulated nanofiller and PVC matrix. J. VINYL ADDIT. TECHNOL., 22:433–440, 2016. © 2015 Society of Plastics Engineers

Fabrication of multicomponent polymer nanostructures containing PMMA shells and encapsulated PS nanospheres in the nanopores of anodic aluminum oxide templates.

Multi-component polymer nanomaterials have attracted great attention because of their applications in areas such as biomedicine, tissue engineering, and organic solar cells. The precise control over the morphologies of multi-component polymer nanomaterials, however, is still a great challenge. In this work, the fabrication of poly(methyl methacrylate)(PMMA)/poly-styrene (PS) nanostructures that contain PMMA shells and encapsulated PS nanospheres is studied. The nanostructures are prepared using a triple solution wetting method with anodic aluminum oxide (AAO) templates. The nanopores of the templates are wetted sequentially by PS solutions in dimethylformamide (DMF), PMMA solutions in acetic acid, and water. The compositions and morphologies of the nanostructures are controlled by the interactions between the polymers, solvents, and AAO walls. This work not only presents a feasible method to prepare multi-component polymer nanomaterials, but also leads to a better understanding of polymer-solvent interactions in confined geometries.

Incorporation of core–shell particles into methacrylate based composites for improvement of the mechanical properties

Core–shell particles (soft PBA core and hard PMMA shell) were incorporated into methacrylate based composites. By the incorporation of the polymer lattices the fracture toughness and E-modulus values were improved.

Formation of Microcapsulated Aluminium Potassium Sulfate Dodecahydrate by Phase Separation Method

The aim of this study was to produce microencapsulated phase change materials (PCMs) by simple coacervation method. For PCM KAl(SO4)2.12H2O (Alum) and for coating ethyl cellulose (EtC) and poly(methyl methacrylate) (PMMA) were selected. The spherical core particles of 1.25 – 2 mm size were prepared by pan granulation of Alum-water wet pellets. Shell coating was carried out by two different types of coacervation variants. Process I: EtC polymer coacervation was induced from cyclohexane solution reducing the temperature from 81 °C to 25 °C. The polymer shell on the Alum particles surface was incomplete, because during hardening the polymer coatings was shrunken. Process II: Formation of EtC and PMMA shell coating was induced on Alum core surface by solvent change method. The polymer shell was coacervated from their dichloromethane solution by hexane. The water permeability, i. e. the release of Alum was investigated by conductivity measurements.

The functional separator coated with core–shell structured silica–poly(methyl methacrylate) sub-microspheres for lithium-ion batteries

To improve the safety of lithium-ion batteries (LIBs), a functional ceramic-coated separator (FCC separator) is developed by coating core–shell structured silica–poly(methyl methacrylate) (SiO2–PMMA) sub-microspheres on one side of a conventional porous polyethylene (PE) separator. The FCC separator possesses multi-functional properties of better separator thermostability and higher electrolyte stability by combining the advantages of both the ceramic-coated separator and the gel polymer electrolyte (GPE). The heat-resistant SiO2 core particles effectively protect the FCC separator from thermal shrinkage. Meanwhile, the PMMA shells form a gel after swelling and activation by the liquid electrolyte, which endows the FCC separator with the functional properties of the GPE to stabilize the electrolyte. As a result, the FCC separator shows considerable wettability for the liquid electrolyte and outstanding electrolyte retention ability at elevated temperature. Moreover, the FCC separator with the coating layer improves the safety performance of cells by preventing cells from experiencing internal short circuits at high temperature. Meanwhile, the cells assembled with such separators demonstrate superior cycle performance and C-rate capability. Therefore, the FCC separator provides LIBs with greater security and better electrochemical performance.

SU‐E‐J‐138: An IGRT QA Device for Measuring with Tenths‐Millimeter Accuracy KV and MV Isocenter Congruence, Couch Travel and Laser Alignment of Accelerators Used for SRS and SBRT

Purpose:To develop a practical device having sufficient accuracy for daily QA tests of accelerators used for SRS and SBRT.Methods:The UAB (Universal Alignment Ball) consists of a 6.35 mm (1/4 inch) diameter tungsten sphere located concentrically within a 25.4 mm (1 inch) diameter acrylic plastic (PMMA) sphere. The spheres are embedded in polystyrene foam, which, in turn, is surrounded by a cylindrical PMMA shell. The UAB is placed on the couch and aligned with wall lasers according to marks that have known positions in relation to the center of the spheres. Using planar and cone beam images the couch is shifted till the surface of the PMMA sphere matches Eclipse‐generated circular contours. Anterior and lateral MV images taken with small MLC openings allow measurement of distance between kV and MV isocenter, laser and MLC alignment. Measurements were taken over a one‐month period.Results:Artifacts from the tungsten sphere were confined within the PMMA sphere and did not affect cone beam localization of the sphere boundary, allowing 0.1 mm precise alignment with a computer‐generated circle centered at kV isocenter. In tests extending over a one‐month period, the distance between kV and MV isocenters along the vertical, longitudinal and lateral directions was 0.125 +/−0.06, 0.19 +/−0.08, and 0.02 +/−0.08 mm, respectively. Laser misalignment along these directions was 0.34 +/‐ 0.15, 0.74 +/−0.29, and 0.49 +/−0.22 mm. Automated couch shifts moved the spheres to within 0.1 mm of the selected position. The center of a 1cmx1cm MLC‐defined field remained within +/−0.2 mm of the tungsten sphere center as the gantry was rotated.Conclusion:The UAB is practical for daily end‐to‐end QA tests of accelerator alignment. It provides tenths‐mm accuracy for measuring agreement of kV and MV isocenters, couch motions, gantry flex and laser alignment.

Synthesis and characterization of hybrid silica/PMMA nanoparticles and their use as filler in dental composites

The effect of hybrid silica/poly(methylmethacrylate) (PMMA) nanoparticles on the properties of composites for dental restoration was evaluated. Hybrid nanoparticles with silica as core and PMMA as shell were obtained by a seeded emulsion polymerization process. Fourier transform infrared spectrum of the hybrid nanoparticles shows an intense peak at 1730cm−1, corresponding to carbonyl groups (CO) of the ester. The thermal stability of the hybrid particles decreases with increasing amounts of PMMA and the residual mass at 700°C corresponds to the silica content in the hybrid particles. Composites were obtained by dispersing nanoparticles (silica or hybrid), as fillers, in a resin—bis glycidyl dimethacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) (40%/60% (w/w)). The paste was then placed in a mold and polymerized under light irradiation. During the preparation of the composites, with the hybrid nanoparticles, the monomers swell the PMMA shell and after photo-curing, a semi-interpenetrating network (semi-IPN) is obtained around the silica core. The properties of the composites, obtained using the hybrid nanoparticles, depend on the filler content and the amount of PMMA in the semi-IPN matrix. For composites with similar inorganic filler contents, the composites with low amounts of PMMA shell had higher modulus than those in which silica was used as the filler.

Shape-Tunable Core–Shell Microparticles

Colloidal polymer particles are an important class of materials finding use in both everyday and basic research applications. Tailoring their composition, shape, and functionality is of key importance. In this article, we describe a new class of shape-tunable core-shell microparticles. They are composed of a cross-linked polystyrene (PS) core and a poly(methyl methacrylate) (PMMA) shell of varying thickness. In the first step, we prepared highly cross-linked PS cores, which are subsequently transferred into a nonpolar dispersant. They serve as the seed dispersion for a nonaqueous dispersion polymerization to generate the PMMA shell. The shape of the particles can subsequently be manipulated. After the shell growth stage, the spherical PS/PMMA core-shell colloids exhibit an uneven and wrinkled surface. An additional tempering procedure allows for smoothing the surface of the core-shell colloids. This results in polymer core-shell particles with a perfectly spherical shape. In addition to this thermal smoothing of the PMMA shell, we generated a selection of shape-anisotropic core-shell particles using a thermomechanical stretching procedure. Because of the unique constitution, we can selectively interrogate molecular vibrations in the PS core or the PMMA shell of the colloids using nonlinear optical microscopy techniques. This is of great interest because no photobleaching occurs, such that the particles can be tracked in real space over long times.

POSS end-capped diblock copolymers: Synthesis, micelle self-assembly and properties

Polyhedral oligomeric silsesquioxane (POSS) end-capped diblock copolymers are synthesized using aminopropylisobutyl POSS (ap-POSS-Br) to initiate atom transfer radical polymerization (ATRP) of methylmethacrylate (MMA) and methacrylisobutyl POSS (MA-POSS). Their chemical structures are confirmed as ap-POSS–PMMA152.0-b-P(MA-POSS)4.3, 4.8, 10.0 with 19,840–24,770gmol−1 by 1H NMR and SEC. In tetrahydrofuran (THF) solution, the obtained diblock copolymers could self-assemble into 150–300nm core–shell micelles as ap-POSS/MA-POSS core and PMMA shell, or 164nm core–shell–crown micelles as P(MA-POSS) core, PMMA shell and ap-POSS crown when P(MA-POSS) content is increased. These micelles can produce typical films with lower surface roughness (0.816–1.690nm), lower water absorption and lower viscoelasticity, but higher hydrophobicity (112–126° water contact angle) and higher thermostability in glass transition temperature Tg>110°C and decompose temperature Td>380°C than pure POSS–PMMA film. In this study, the results strongly support the potential application of the POSS end-capped diblock copolymers as the coatings.

Silica-diblock fluoropolymer hybrids synthesized by surface-initiated atom transfer radical polymerization

Silica/diblock fluoropolymer hybrids SiO2-g-PMMA-b-P12FMA for coatings were synthesized by the silica surface-initiating atom transfer radical polymerization (SI-ATRP) of methylmethacrylate (MMA) and dodecafluoroheptyl methacrylate (12FMA). Silica surface initiator (SiO2-initiator) was obtained by 10–25 nm fumed silica particles grafted hydrosilylated undec-10-enyl, 2-bromo-2-methyl propionate with a density of 0.573 mmol g−1. The SI-ATRP approach in this paper displays the diagnostic criteria of controlled radical polymerization by the analysis of 1H NMR, 19F NMR and SEC-MALLS analysis, after comparing with the conventional initiator of ethyl 2-bromoisobutyrate (EBiB) for the E-PMMA-b-P12FMA diblock copolymer. Three mass ratios of SiO2-initiator/MMA/12FMA as 1/72.50/18.15, 1/72.50/45.38 and 1/181.26/18.15 were used to obtain the SiO2-g-PMMA-b-12FMA hybrids. The hybrids show 25–30 nm core–shell particles in CHCl3 solution composed of a P12FMA core and PMMA shell, but densely twined together as agglomerated particles. The PMMA-b-P12FMA shell grafted onto silica particles obviously increases the surface roughness of the film (50–500 nm), more than the E-PMMA-b-12FMA film (30 nm), and thereby contributes to the hydrophobic (112–118°) and oleophobic (45–78°) properties of the films. Increasing the P12FMA concentration (1/72.50/45.38) could result in stronger migration of the P12FMA segments onto the film surface, and therefore led to a lower surface free energy (10.97 mN m−1), increased advancing and receding for water contact angles (112° and 108°) and the highest cetane contact angles (74° and 70°), the lower water absorption and viscoelasticity, but a high thermostability at 420–450 °C.

Advanced dielectric polymer nanocomposites by constructing a ternary continuous structure in polymer blends containing poly(methyl methacrylate) (PMMA) modified carbon nanotubes

A nanocomposite with ultra-low percolation threshold and high dielectric performance is prepared by controlling the localization of multiwalled carbon nanotubes (MWNTs) in one phase of a ternary continuous polymer blend system through melt processing. Polystyrene (PS), poly(vinylidene fluoride) (PVDF), and poly(methyl methacrylate) (PMMA) can form a ternary continuous structure when the volume fractions of PS, PVDF and PMMA are 70 vol%, 20 vol%, and 10 vol%, respectively. The PS is a continuous matrix (sea-phase) whereas the other two phases are interconnected threads (the PVDF is situated as the core while the PMMA is the shell, and the thickness of the PMMA shell is about 1 μm). Adding PMMA could improve the compatibility between the PS and PVDF components. Selective distribution of MWNTs in the PMMA shell is achieved through a combination of PMMA modified MWNTs and appropriate processing procedures. The composite shows an ultra-low percolation threshold of ca. 0.3 wt%. When the weight fraction of PMMA modified MWNTs is 0.4 wt%, the dielectric constant of the composite is as high as 182 (at 100 Hz), which is about 60 times higher than that of a pure PS matrix. The composite’s dielectric properties have excellent temperature stability. This approach can provide a new and low-cost route to design high-performance dielectric materials with ultra-low percolation thresholds.

Physicochemical and Thermal Study of a MPCM of PMMA Shell and Paraffin Wax as a Core

The present work studies a Phase Change Slurry (PCS) as a proposed Thermal Energy Storage (TES) medium. Microencapsulation is an advanced technology to implement PCMs (Phase Change Material) avoiding leakage from building materials. The morphology and physicochemical properties of this Microencapsulated Phase Change Material (MPCM) sample were analyzed using some analytical techniques like Scanning Electron Microscopy (SEM), Infrared Spectroscopy (FT-IR), Thermogravimetrical Analysis (TGA), Differential Scanning Calorimeter (DSC), and Atomic Force Microscopy (AFM). The results showed that Micronal® DS 5007 is a suitable candidate to be used as slurry in active systems due to their studied mechanical properties.