Silicone Microspheres Research Articles

Construction of silicone composite with controllable micro-nano structure via in-situ polymerization on fiber surface and study on SO2 adsorption performance

Micro-nano structure was constructed on the polyester fiber’s surface through in-situ polymerization by trialkoxysilane containing dicyano and zinc oxide, endowing the fabric with SO2 adsorption performance. The treating conditions, including the selection of solvent, water content in the solvent, and catalysts were investigated extensively. Therefore, three distinct first-order rough structures were fabricated, namely, triethylamine catalyzing coating (TEA@PET), triethylenediamine catalyzing coating (DTEA@PET), and tetraethylenepentamine catalyzing coating (TEPA@PET). Then, based on the primary structure DTEA@PET, the nano-zinc oxide was employed for secondary treatment, and the micro-nano structure (ZnO/CN@PET) with zinc oxide particles attached to the surface of silicone microspheres was fabricated. Combined with the surface’s chemical composition assessment and morphology investigation, it was demonstrated that the micro-nano surface consisted of inorganic nano-zinc oxide on the organopolysiloxane micron particles’ surface. When the roughness of DTEA@PET was 199 nm, ZnO/CN@PET increased to 229 nm. The SO2 adsorption capacity of DTEA@PET was 28.2 mL/g, while that of ZnO/CN@PET reached 38.6 mL/g, proving that the composite ZnO nanoparticles on micron roughened surface could offer remarkable SO2 adsorption capacity.

Preparation of refractive-index-controlled silicone microspheres and their application in polycarbonate light diffusing materials

ABSTRACTLight-diffusing materials (LDMs) are essential for diffusing indoor light-emitting diode (LED) illumination to soft light. The size and refractive index of the light-diffusing agent are the two main parameters that influence the light-diffusing properties of LDMs. Modulation of silicone microspheres’ refractive index and their influence on the light-diffusing properties of LDMs were systematically explored. An environmentally friendly, dispersant-free polymerization method carried out in an aqueous solution was developed for the preparation of silicone microspheres with different refractive indices. The prepared microspheres and LDMs were characterized by scanning electron microcopy (SEM), Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). Results showed that the refractive index of the prepared microspheres can be regulated by adjusting the copolymerization composition. Prepared silicone microspheres could be uniformly dispersed in a polycarbonate (PC) matrix, and the refractive index had a marked influence on the light-diffusing properties of the resulting LDMs. The silicone microspheres and LDMs both exhibited excellent thermal stabilities.

The Structure and Thermal Conductivity of Multicomponent Polymer Composites Filled with Hollow Ceramic and Silicone Microspheres

The structure of polymer composites has been investigated, and a procedure has been developed for calculating their effective thermal conductivity. Thermal conductivity measurements have been carried out, and the results of calculations have been compared with the authors' own experimental data and with independent experimental data, and also with manufacturers' data which are shown to be hundreds of percent too low.

Preparation and Properties of Cross-Linked Polysiloxane Microspheres for Light-Scattering

The narrow particle size distribution of poly (vinyl silicone) microspheres were prepared by the hydrolysis-polycondensation method with vinyl silane (VTMS) as raw materials. And the influences of pH value, oil/water ratio on the morphology, particle size and distribution of the microspheres were studied. The results shows that the particle size of microspheres decrease with the increasing of the PH value of polymerization, and the particle size has no specific linear relationship with the PH value of hydrolysis reaction, while the oil-water ratio is smaller, single particle size distribution is more narrow, more uniform distribution.

Lipase based static emulsions as efficient biocatalysts for biodiesel production

AbstractBACKGROUNDEnzymatic production of biodiesel is an alternative solution to circumvent the problems associated with chemical catalysis. However, the drawbacks, including lower stability and reusability of the lipase, often make this route unfeasible for industrial application.RESULTSA stable biocatalyst system was prepared by trapping an aqueous solution of Burkholderiacepacia lipase (BCL) in bead‐shaped silicone microspheres (named lipase‐based static emulsions). Compared with free BCL, lipase‐based static emulsions showed outstanding stability under vigorous shaking conditions and the thermal stability was improved. The lipase‐based static emulsions were employed to catalyze the transesterification of soybean oil with ethanol for biodiesel production. Under the optimum conditions, about 95.42% of FAEE yield was achieved in 30 h. In addition, the lipase‐based static emulsions presented good reusability, and the FAEE yield remained at more than 70.63% after 15 successive reaction cycles. The lipase‐based static emulsions were also used to catalyze the transesterification of jatropha oil and cottonseed oil with ethanol for biodiesel production, and the maximum FAEE yield was 96.10% and 90.39%, respectively.CONCLUSIONSLipase‐based static emulsions were developed as robust biocatalysts by trapping an aqueous solution of lipase in silicone microspheres. The lipase‐based static emulsions catalyzed process may be a suitable technique for biodiesel production. © 2016 Society of Chemical Industry

A Mathematical Model of Heat Transfer in Spheroplastic

Spheroplastics are composite materials composed of a polymer or organosilicate binder and hollow spherical inclusions (mostly, of glass, but there are also of carbon, phenol, and epoxy), which are called microspheres and have a diameter within a millimeter with the wall thickness of several micrometers. To reduce the material density in watercraft constructions sometimes are used so called macrospheres of up to 40 mm in diameter and shell thickness of 0,5--1,5 mm from spheroplastic with microspheres. Microspheres may contain inert gases such as nitrogen. Many countries have commercialised quartz microspheres. The USA, in particular, produces Q-Gel microspheres with density of 300 kg / m3, the bulk density - 100 kg / m3 and the average diameter of 75 microns, characterized by a high mechanical strength and low cost. Carbon microspheres having low mechanical properties can absorb radio waves in certain frequency ranges. Spheroplastic with silicone microspheres combine relatively high mechanical and dielectric properties. In virtue of low thermal conductivity spheroplastics are used in various heat-insulating structures. As the thermal insulation coatings, the spheroplastic covers the outer surface of the pipes, in particular oil and gas pipelines in the permafrost zones, regions of swampy ground, and underwater. The effective heat conductivity factor, primarily, determines the specific application of spheroplastic as a thermal insulation material. To quantify the value of this factor is necessary to have a mathematical model describing heat ransfer in spheroplastic. The paper presents a four-phase mathematical model of the heat transfer in a representative element of a spheroplastic structure placed in an unlimited array of homogeneous material, the thermal conductivity of which is to be determined as desired characteristics of spheroplastic. This model in combination with a dual variational formulation of stationary heat conduction problem in the inhomogeneous solid first is used to define the guaranteed two-sided boundaries of the parameter space in which there are the true values of effective thermal conductivity of spheroplastic, and then to calculate the dependences of this factor on the bulk concentration of microspheres. The paper conducts a quantitative analysis of the calculated dependences and determines the values of their greatest possible accuracy, which allow us to measure a reliability degree of the predicted effective thermal conductivity of the spheroplastic.

High-permeability functionalized silicone magnetic microspheres with low autofluorescence for biomedical applications

Functionalized magnetic microspheres are widely used for cell separations, isolation of proteins and other biomolecules, in vitro diagnostics, tissue engineering, and microscale force spectroscopy. We present here the synthesis and characterization of a silicone magnetic microsphere which can be produced in diameters ranging from 0.5 to 50μm via emulsion polymerization of a silicone ferrofluid precursor. This bottom-up approach to synthesis ensures a uniform magnetic concentration across all sizes, leading to significant advances in magnetic force generation. We demonstrate that in a size range of 5–20μm, these spheres supply a full order of magnitude greater magnetic force than leading commercial products. In addition, the unique silicone matrix exhibits autofluorescence two orders of magnitude lower than polystyrene microspheres. Finally, we demonstrate the ability to chemically functionalize our silicone microspheres using a standard EDC reaction, and show that our folate-functionalized silicone microspheres specifically bind to targeted HeLa and Jurkat cells.These spheres show tremendous potential for replacing magnetic polystyrene spheres in applications which require either large magnetic forces or minimal autofluorescence, since they represent order-of-magnitude improvements in each. In addition, the unique silicone matrix and proven biocompatibility suggest that they may be useful for encapsulation and targeted delivery of lipophilic pharmaceuticals.

Magnetic, Fluorescent, and Copolymeric Silicone Microspheres.

Silicone microspheres are exceedingly difficult to make. Here, polydimethylsiloxane microspheres (≈1 μm diameter) are synthesized using ultrasonic spray pyrolysis, the first demonstration of a scalable synthetic procedure for crosslinked silicone microspheres. This continuous, aerosol process is also used to directly produce fluorescent, magnetic, and copolymeric derivatives; the potential biomedical applications of these microspheres are explored.

Utilization of Silicone Microspheres: Improving Color Uniformity and Reducing the Amount of Phosphor Used in White Light-Emitting Diodes

The aim of this paper is to improve the color temperature uniformity per view angle of a white light-emitting diode (LED) by utilizing silicone microspheres (SMSs). The view angle is 97.5 ° when using silicone encapsulant alone, and it increases to 108 ° with the use of 0.1 wt% SMSs. With 0.3 wt% SMSs added to a silicone encapsulant that contains 7 wt% phosphor, the color temperature deviation improves from 1300 to 167 K. A design of experiments is used to quantitatively analyze the effect of SMSs on the reduction of the amount of phosphor required, and actual samples are fabricated based on the results to compare their characteristics. To fabricate a white LED with a correlated color temperature (CCT) of 5500 K, 9.5 wt% phosphor is used when using phosphor only, whereas 6.7 wt% phosphor is used after adding 2.3 wt% SMSs. When a combination of phosphor and SMSs is used to fabricate an LED with the same color temperature, the luminous flux decreases by 4.6%, the CCT deviation improves from 502 to 106 K, and the amount of phosphor needed by is reduced to 30%.

Silicone microspheres for pH-controlled gastrointestinal drug delivery

Silicone microspheres containing pH-sensitive hydrogels are prepared, characterized and evaluated for their potential pH-controlled gastrointestinal (GI) drug delivery. The pH-sensitive hydrogels are semi-interpenetrating polymer networks (semi-IPN(s)) made of varying proportions of poly(methacrylic acid-co-methylmethacrylate) (Eudragit (EUD) L100 or EUD S100) and crosslinked polyethylene glycol 8000 (P8000C). Up to 35 wt% hydrogel particles of mean volume diameters from 89 to 123 μm, medicated with 15 wt% prednisolone (PDN), are encapsulated, with 100% efficiency, into morphologically acceptable silicone microspheres in the 500–1000 μm size range, by a modified emulsion vulcanization method. Microspheres are eluted for 9 h with isotonic fluids at pH values increasing from 1.2 to 7.4, to simulate transit across the GI regions. PDN release depends on dissolution medium pH and on hydrogel composition, which determines hydrogel pH-sensitivity. With the P8000C–EUD L100 (1:2) semi-IPN, the release shows a marked peak at pH 6.8. The P8000C–EUD S100 (1:2) semi-IPN causes a gastroprotection and an almost uniform distribution of released drug between media at pH 6.8 and 7.4. With the P8000C–EUD S100 (1:1) semi-IPN, the dose fraction released to gastric fluid increases to match the values for the media at pH 6.8 and 7.4. With the pH-insensitive, highly swelling, P8000C, the largest dose fraction is released to the gastric medium and release is of Fickian type. With semi-IPNs, release depends weakly on the buffer molarity of the dissolution medium, a reduction from 0.13 to 0.032 of which renders the release rate to the media at pH 6.8 and 7.4 more uniform.

Preparation of silicone microspheres by emulsion polymerization: Application to the encapsulation of a hydrophilic drug

The objective of this work was to evaluate the ability of appropriate silicone elastomers to encapsulate hydrophilic compounds in microspheres prepared according to a multiphase emulsion-polymerization process. The particle size of the microspheres can be modified by controlling the usual emulsification parameters, such as the viscosity of the different phases, shear rates and surface activity properties of additives. The encapsulation efficiencies of a hydrophilic drug, propranolol hydrochloride, were very high but its release rates were very slow. Osmotic agents such as glycerol and propylene glycol did not enhance the release rate, whereas it was slightly increased by both sodium chloride addition and higher drug loading.

Mechanism of drug release from silicone microspheres containing Polycarbophil

The possibility of a pH-controlled drug release mechanism applying to silicone microspheres containing nicotinamide (NAM) and Polycarbophil (PCP), a pH-sensitive hydrogel, is evaluated. NAM-medicated PCP in the 4:1 PCP-NAM wt ratio is dispersed, at the 20% or 40% concentration, in silicone in the form of osmotically active particles of around 15 μm mean volume diameter, and encapsulated in microspheres in the 105–710 μm size range by a modified emulsion vulcanization technique, with a 100% entrapment efficiency. The external and internal morphology of microspheres, and the size distribution of PCP-NAM particles dispersed therein are evaluated by scanning electron micrography. Microspheres are eluted 9 h with simulated GI fluids (pH 1.2–7.4). Assessment of the time exponent characterizing the release kinetics, together with release and swelling data from planar matrices of same formulation as the microspheres, substantiate the following release mechanism. Due to their small size, the osmotically active particles have a limited ability to crack the silicone polymer and interconnect upon swelling, so the hydrogel route of release is of a minor relevance, and so is the hydrogel pH-sensitivity. Drug release is mainly governed by partitioning-diffusion in the silicone continuum of microspheres, therefore it is pH-independent and the time exponent is close to the value typical of Fickian release. It is concluded that encapsulation of hydrogel particles of larger size is a necessary condition for a pH-controlled release pattern.

PH-controlled silicone microspheres for controlled drug delivery

Several types of controlled drug release microspheres has been developed. In this study, we describe a new type of microspheres that control drug release with changing inner core pH. In the microspheres, micronized model drug, timolol maleate and pH-adjusting agents (mono, di, and trisodium phosphate or Tris buffer) were either dry blended by mixing or coprecipitated by spray drying, and encapsulated in X7-3012 silicone microspheres using emulsion vulcanization technique. Upon water influx into microspheres, buffer dissolves and adjusts the inner pH. Thus, the fraction of unionized drug is increased by higher pH and, consequently, partition-driven release of basic drug from the microspheres is accelerated. Scanning electron micrographs showed that spray dried materials were completely encapsulated by the elastomer, and the drug was homogenously distributed in silicone micromatrices. An amine resistant silicone elastomer could be used to make microspheres incorporating up to 30 wt% of solid particles. Typical size range of the pH-controlled microspheres was 150–200 μm. Timolol release from the microspheres followed square root of time kinetics, and it was proportional to wt% loading level of drug in the micromatrices. In vitro release of timolol from microspheres can be controlled over a wide range of rates by selecting a suitable pH adjusting agent and by varying its amount in the microspheres. Spray drying of the drug and buffer together was the most effective in controlling the drug release since, in this case, buffer was in the same microcompartment inside silicone and thus buffering effect was maximal. Drug release from pH-controlled microspheres was independent of pH of dissolution medium.

Tantalum loaded silicone microspheres as particulate emboli

Chloroform solutions of medical grade silicone resin were cured in an aqueous dispersion medium containing poly(vinyl alcohol) (PVA) as the drop stabilizer at 40-60 degrees C to generate smooth, spherical, elastic microspheres. The microspheres were encapsulated with tantalum powder to render them radiopaque. Tantalum loaded microspheres having diameter more than 1.00 mm could be prepared by this technique. Incorporation of radiopaques such as barium sulphate and methyl iothalamate resulted in the instability of the suspension giving rise to an agglomerated product. Microspheres were grafted with hydrophilic monomers such as 2-hydroxyethyl methacrylate (HEMA) and N-vinyl pyrrolidone (NVP) using ionizing radiation from a 60Co source in an effort to make their surfaces hydrophilic. While the graft yield was very little when HEMA alone was used for grafting, a combination of HEMA/NVP in a 1:1 ratio produced better graft yields resulting in improved surface hydrophilicity. The tantalum loaded microspheres were found to be very resistant to surface modification. Microspheres could be dispersed in water with the aid of small quantities of surfactants such as Tween 20. These microspheres may find use in particulate embolization.

The MR appearance of endovascular embolic agents in vitro with clinical correlation

A spectrum of embolic agents including PVA, avitene, gelfoam, ethanol, IBCA, silicone microspheres, metal and platinum coils, and balloons containing contrast of HEMA were imaged in vitro at 0,3 Tesla using spin echo, gradient echo, and inversion recovery sequences. Signal intensities associated with these agents and changes created by addition of blood are presented. The in vitro model is also correlated with clinical MR material. Recognition of embolic materials is important to avoid confusion with persistent flow void, hemorrhage, or thrombus.

Ferromagnetic Silicone Necrosis of Hypernephromas by Selective Vascular Occlusion to the Tumor: A New Technique

Arterial vascular occlusion of hypernephromas may be performed by obstructiing the tumor vascular tree with the injection of ferromagnetic silicone microspheres. The powerful superconducting electromagnet confines the embolized iron-silicone compound to the neoplastic target organ. Radioactive material may or may not be added to the iron-silicone compound to give local direct radioactive radiation therapy to the tumor area. In experimental dogs up to 70,000 rad of beta radiation from the P32 source had been delivered homogeneously within the kidney when mixed with the ferrosilicone. This technique may well be used in cases in which a major operation is contraindicated or when preoperative necrosis of the tumor is advisable. Since the entire procedure can be done with the patient under local anesthesia in a radiology department it may be a valuable new technique in the future management of urological tumors, unilateral renal hypertension, solitary kidney pathology and so forth. Ferrosilicone material has not been found to be toxic. The application of a powerful superconducting electromagnet to the technique provides a means of confining the embolized iron-silicone compound to the target organ.