Polymer coating/encapsulation of nanoparticles using a supercritical antisolvent process - Patents

Polymer coating/encapsulation of nanoparticles using a supercritical antisolvent process
#20050191491
09/01/05
Agent: Mccarter & English, LLP - Stamford, CT, US
Inventors: Yulu Wang, Robert Pfeffer, Rajesh Dave
Class: 428407000 (USPTO), B05D003/00 (Intl Class)
[0001] The present application claims the benefit of a co-pending provisional patent application entitled "Nanoparticle Coating Using a Supercritical Antisolvent Process," filed on Apr. 8, 2003 and assigned Ser. No. 60/461,506. The contents of the foregoing provisional patent application are incorporated herein by reference.
A process, method and/or system for preparing polymer-coated nanoparticles and/or other ultrafine particles utilizing a supercritical fluid, e.g., supercritical carbon dioxide (SC CO2), as an antisolvent that may be added to a solution of a polymer and an organic solvent in which insoluble nanoparticles or the like are suspended. The coating process occurs when the supercritical fluid (e.g., SC CO2) and the nanoparticle-containing suspension are combined to cause the suspended nanoparticles to precipitate as coated nanoparticles. Processing parameters for optimizing and/or enhancing the efficacy and/or efficiency of the coating process, method and/or system and for controlling the coating and/or agglomeration of coated particles are also described. The process, method and/or system has wide ranging applicability, e.g., for coating and/or encapsulation of pharmaceuticals, cosmetics, food products, chemicals, agrochemicals, pesticides, polymers, coatings, catalysts and the like.
SUMMARY OF THE DISCLOSURE
[0025] The present disclosure is directed to a method, process and system for producing polymer coated nanoparticles and/or other ultrafine particles through the use of a supercritical fluid, e.g., supercritical carbon dioxide, as an antisolvent. According to an exemplary embodiment of the present disclosure, a solution that includes a polymer and an organic solvent in which nanoparticles/ultrafine particles are suspended is added to the supercritical fluid. The nanoparticles/ultrafine particles are typically substantially insoluble in the organic solvent.
[0026] The polymeric coating of the nanoparticles/ultrafine particles is generally effected when the particle-containing suspension is added to the supercritical fluid or otherwise combined therewith. Combination of the particle-containing suspension with the supercritical fluid advantageously causes the suspended nanoparticles/ultrafine particles to precipitate as coated nanoparticles/ultrafine particles. The disclosed system/method is effective to coat or encapsulate ultrafine particles (sub-micron and nanoparticles) so as to modify their surface properties by using a supercritical fluid, e.g., supercritical carbon dioxide (SC CO.sub.2), in an enhanced supercritical antisolvent (SAS) process. In an exemplary embodiment of the present disclosure, SC CO.sub.2 is employed as the supercritical fluid to effect the desired coating/encapsulation, thereby benefiting from properties associated therewith, e.g., relatively mild critical conditions (T c=304.1 K, Pc=7.38 MPa), non-toxicity, non-flammability, recyclability and cost effectiveness.
[0027] The advantageous SAS process of the present disclosure generally employs principles associated with SC CO.sub.2 induced phase separation. Thus, according to the present disclosure, the solute precipitates due to a high super-saturation produced by the mutual diffusion of organic solvent into SC CO.sub.2 (and vice versa) when an organic liquid solution comes into contact with SC CO.sub.2. Of note, the organic solvent can be almost completely removed by simply flushing with a pure gas, e.g., pure CO.sub.2 in the case of a SC CO.sub.2-based method and/or system. Thus, dry particles may be produced after a CO.sub.2 extraction step (flushing) following feeding of the organic solution.
[0028] According to exemplary implementations of the present disclosure, submicron particles are successfully coated or encapsulated in the form of loose agglomerates. It was found that the polymer weight fraction and polymer concentration play a critical role in the agglomeration of the coated particles. A high polymer weight fraction favors agglomeration of the coated particles and an uneven distribution of the polymer coating. A low polymer concentration, e.g., on the order of 4.0 mg/ml, appears to prevent and/or minimize agglomeration among the coated particles. The operating pressure and temperature were also found to influence agglomeration. A higher pressure facilitates the agglomeration of coated particles due to sintering because the glass transition temperature of the polymer, T.sub.g, is depressed. The operating temperature appeared to have little effect on the agglomeration of the coated particles when the temperature is below the glass transition temperature; however, when the operating temperature is above T.sub.g, the polymer coating on the surface of particle appears to be sintered causing strong agglomeration. The flow rate of the polymer suspension was found to have little effect on agglomeration. The inclusion of a surfactant in the disclosed system (PFA, PFS, Krytox, PDMS, and Pluronic 25R2) did not function to suppress agglomeration and, in the case of PFA, PFS, and Krytox surfactants, agglomeration of the coated nanoparticles/ultrafine particles was promoted.
[0029] The system and method of the present disclosure is particularly useful in the field of pharmaceuticals, where controlled release systems in association with drugs, genes, and other bioactive agents provide multiple benefits, e.g., protection from rapid degradation, targeted delivery, control of the release rate, and prolonged duration of bioactive agents. Other fields utilizing nanoparticle technology also stand to benefit from the system and method of the present disclosure, including the food industry and food-related applications, the chemical industry and chemical-related applications, the pesticide industry and pesticide-related applications, the polymer industry and polymer-related applications, the coating industry and coating-related applications and the catalyst industry and catalyst-related applications.
[0030] A further exemplary application for the disclosed coating/encapsulation system and method of the present disclosure involves processing of conductive inks and/or coatings that contain metallic nanoparticles. Such nanoparticles generally require and/or benefit from passivation by a polymer film for protection, but when exposed to conventional heats of application, can melt away, allowing for a conductive sub-structure of the coatings. An additional exemplary application for the disclosed coating/encapsulation system and method of the present disclosure involves the processing of energetic materials (e.g., propellants and explosives) that employ or include nanosized metallic particle (e.g., aluminum or magnesium) that require and/or benefit from passivation to avoid oxidation.
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