Particles with designed different sized discrete pores
Polymeric porous particles have a continuous solid phase and at least two sets of discrete pores that are isolated from each other within the continuous phase and that have different average sizes. One set of discrete pores has a larger average size than another set of discrete pores by at least 50%. At least one set of discrete pores is free of detectably different marker materials. There porous particles can be prepared using evaporative limited coalescence techniques with especially chosen discrete pore stabilizing hydrocolloids to protect the pores during formation and to provide the different average sizes.
1. A porous particle comprising one or more organic polymers that provide a polymer that provides a continuous solid phase including an external particle surface, and at least first and second discrete closed pores that are isolated from each other and dispersed within the continuous phase, the first and second discrete closed pores having first and second average sizes,
wherein:
the second average size is greater than the first average size by at least 50%,
the first or second discrete closed pores are free of detectably different marker materials selected from the group consisting of colorants (dyes and pigments), metallic pigments, fluorescing materials, radioisotopes, metal oxides, metal hydroxides, metal sulfides, metal oxyhydroxides, and luminescing compounds,
the porous particle has a mode particle size of at least 2 μm and up to and including 50 μm, and
the first and second discrete closed pores comprise first and second discrete pore stabilizing hydrocolloids, respectively, which provide different osmotic pressures of at least 0.4 psi.
2. The porous particle of claim 1 , wherein second average size of the second discrete closed pores is greater than the first average size of the first discrete pores by at least 100%.
3. The porous particle of claim 1 , wherein the first discrete closed pores are predominantly nearer the external particle surface compared to the second discrete closed pores.
4. The porous particle of claim 1 , wherein the first and second discrete closed pores comprise first and second discrete pore stabilizing hydrocolloids, respectively, that are independently selected from the group consisting of carboxymethyl cellulose (CMC), a gelatin or gelatin derivative, a protein or protein derivative, a hydrophilic synthetic polymer, a water-soluble microgel, a polystyrene sulfonate, poly(2-acrylamido-2-methylpropanesulfonate), and a polyphosphate.
5. The porous particle of claim 1 , wherein the first discrete closed pores have a first average size of at least 0.3 μm and to and including 3 μm, and the second discrete closed pores have a second average size of at least 0.45 μm and to and including 10 μm.
6. The porous particle of claim 1 , further comprising at least a third discrete population of closed pores that have an average size that is different from both of the first and second average sizes.
7. The porous particle of claim 1 , wherein there are no detectably different marker materials in the first and second discrete closed pores.
8. The porous particle of claim 1 , wherein there are no detectably different marker materials in any of its closed pores.
9. The porous particle of claim 1 that has a porosity of at least 20% and up to and including 50% based on total porous particle volume.
10. The porous particle of claim 1 , wherein the continuous solid phase comprises one or more polymers selected from the group consisting of a polyester, styrenic polymer, mono-olefin polymer, vinyl ester polymer, α-methylene aliphatic mono-carboxylic acid ester polymer, vinyl ether polymer, and vinyl ketone polymer.
11. The porous particle of claim 1 further comprising a surface stabilizing material on the external particle surface.
12. An aqueous slurry of multiple porous particles as defined in claim 1 .