pkrebaum
10th July 2008, 01:36
Ionic vs Colloidal, and Nanoparticles
An atom is ionic when it has either gained or lost an electron, acquiring a charge. Table salt (sodium chloride) is an ionic compound. When elemental sodium and chlorine are combined, the sodium atom loses an electron (becomes oxidized) while the chlorine gains an electron (is reduced). The product of this rather spectacular reaction is sodium chloride... along with a lot of heat and light. The mutual attraction of the oppositely charged ions binds the two tightly together, which becomes the crystalline lattice you see as cubic grains of salt. Silver chloride is an ionic compound.
A substance is colloidal when particles of that substance are so small that they will not settle out of solution. Note here that we are talking about discrete particles... they can be seen with the aid of a microscope (either a light microscope or an electron microscope)... we are not talking about individual atoms or ions, such as is table salt when dissolved in water. Colloidal particles are kept suspended by Brownian Motion, which is due to the random thermal movements of the atoms in the solution surrounding the particles.
Many colloidal particles have a tendency to aggregate together into larger particles and settle out over time. Opposite charges on particles (e.g. thru friction) and VanDer Walls forces are operative here. Often the key to a stable colloidal suspension is a stabilizer, which is often a surfactant (detergent) or a water-soluble polymer. These agents surround and "coat" the particles, preventing them from approaching one another too closely and sticking together. Homogenized milk is a colloidal suspension of cream (oil) in skim milk. The protein in the milk acts as the stabilizer.
If you dilute up homogenized milk and shine light through it it has a haziness to it, which is called the Tyndale effect. Basically, the particles are so small that they are around the same wavelength as light and that causes the light to scatter. Or to put it simply, dilute colloidal solutions look milky. This is in contrast to a true solution (salt or sugar dissolved in water).... true solutions are not hazy. True solutions are solutions at the atomic or molecular level.... these species are much too small to scatter light. The upper particle size limit for a colloidal suspension varies, but in general it becomes very difficult if the particle is more than a micron or two in diameter.
Can something which is ionic be colloidal ????
Yes, in fact many are. Silver chloride is ionic. It is also virtually insoluable in water. In fact, chemists assay the silver content of something by dissolving it in nitric acid to form silver nitrate, which is very water soluable. They then add a solution of sodium chloride, which forms soluable sodium nitrate and insoluable silver chloride. By weighing the silver chloride the silver content of the original sample can be computed. Here's the catch.... before you can weigh the silver chloride you have to filter it from the solution, wash it with water, and dry it. The initial precipitate formed upon addition of the sodium chloride is impossible to filter... much of it is colloidal and too small a particle size for filter paper to catch. So, the solution is briefly boiled. The boiling aggregates the colloidal particles into a granular precipitate which is easily filtered. If you omitted the boiling and added a stabilizer you would have a colloidal suspension of ionic silver chloride.
What are nanoparticles ??? What's Nano-Silver ???
Nanoparticles are discrete particles in the nanometer size range. A nanometer is (10)-9 (ten to the negative power of nine) meters, or one billionth of a meter. Remember we mentioned "microns" a few paragraphs ago ? A micron is (10)-6 meter, or a millionth of a meter. A millimeter is (10)-3 meter, one-thousandth of a meter, or about 1/25 inch. There's 1,000 nanometers in a micron, 1,000 microns in a millimeter, 1,000 millimeters in a meter. A human hair might be around 50 microns in diameter.
Some nanoparticles in common use include fumed silica (thickener), carbon black (tires, ink), zinc oxide and titanium dioxide (transparent sunscreens). Micron-sized zinc oxide is used in non-transparent sunscreens and diaper-rash ointment. Ruby-red glass from Medieval times owes its color to gold nanoparticles dispersed within the glass.
Most nanoparticles in use today have a size between 10 and 200 nanometers, or .01 to .2 micron. These particles could have between 20,000 and 200,000,000 atoms in them. Most nanoparticles will quickly agglomerate without some sort of stabilizing or dispersing agent. Because of their extremely high surface area many nanoparticles have very unique physical properties. Bulk Silver, for example, has a melting point in excess of 1700 degrees F., nanosilver particles can melt at under 400 degrees F. One curent application is the printing of conductive circuit traces with nanosilver-based ink, then fusing the particles together into a solid conductor in a simple oven.
Silver nanoparticles are made simply in the lab by mixing silver nitrate solution with sodium citrate and a stabilizer, usually polyacrylic acid (PAA) or polyvinylpyrrolidinone (PVP). It is then warmed on the hotplate overnight and in the morning.... presto...nanosilver ! The size of the nanoparticles produced can be changed by adjusting the experimental conditions. Some of these stabilizers, like PAA, are charged (PAA is acidic), so some confusion may exist about neutral, metallic Silver nanoparticles which are "ionically stabilized" and "ionic silver". The lack of uniform nomenclature, and deliberate obfuscation by some manufacturers, only adds to the confusion.
Silver surfaces are toxic to bacteria and viruses. Nanoparticles have a huge surface area... 15 to 1,500 square meters per gram are common. Ten grams might cover a football field if evenly distributed. Thus nanosilver kills many viruses and bacteria, including HIV, at least in a test tube. How you would use it in a live animal without it attacking the good (host's) cells is currently a topic of hot research.
My personal idea for nanosilver would be to fight an epidemic of bird flu (H5N1) virus, if this virus ever becomes contageous in man. Since this virus primarily exists (and does most of its damage) in the lungs, treatment would consist of putting a dilute solution of silver nanoparticles into an ultrasonic humidifier and breathing the resulting nanosilver fog. You read it here first !!!
An atom is ionic when it has either gained or lost an electron, acquiring a charge. Table salt (sodium chloride) is an ionic compound. When elemental sodium and chlorine are combined, the sodium atom loses an electron (becomes oxidized) while the chlorine gains an electron (is reduced). The product of this rather spectacular reaction is sodium chloride... along with a lot of heat and light. The mutual attraction of the oppositely charged ions binds the two tightly together, which becomes the crystalline lattice you see as cubic grains of salt. Silver chloride is an ionic compound.
A substance is colloidal when particles of that substance are so small that they will not settle out of solution. Note here that we are talking about discrete particles... they can be seen with the aid of a microscope (either a light microscope or an electron microscope)... we are not talking about individual atoms or ions, such as is table salt when dissolved in water. Colloidal particles are kept suspended by Brownian Motion, which is due to the random thermal movements of the atoms in the solution surrounding the particles.
Many colloidal particles have a tendency to aggregate together into larger particles and settle out over time. Opposite charges on particles (e.g. thru friction) and VanDer Walls forces are operative here. Often the key to a stable colloidal suspension is a stabilizer, which is often a surfactant (detergent) or a water-soluble polymer. These agents surround and "coat" the particles, preventing them from approaching one another too closely and sticking together. Homogenized milk is a colloidal suspension of cream (oil) in skim milk. The protein in the milk acts as the stabilizer.
If you dilute up homogenized milk and shine light through it it has a haziness to it, which is called the Tyndale effect. Basically, the particles are so small that they are around the same wavelength as light and that causes the light to scatter. Or to put it simply, dilute colloidal solutions look milky. This is in contrast to a true solution (salt or sugar dissolved in water).... true solutions are not hazy. True solutions are solutions at the atomic or molecular level.... these species are much too small to scatter light. The upper particle size limit for a colloidal suspension varies, but in general it becomes very difficult if the particle is more than a micron or two in diameter.
Can something which is ionic be colloidal ????
Yes, in fact many are. Silver chloride is ionic. It is also virtually insoluable in water. In fact, chemists assay the silver content of something by dissolving it in nitric acid to form silver nitrate, which is very water soluable. They then add a solution of sodium chloride, which forms soluable sodium nitrate and insoluable silver chloride. By weighing the silver chloride the silver content of the original sample can be computed. Here's the catch.... before you can weigh the silver chloride you have to filter it from the solution, wash it with water, and dry it. The initial precipitate formed upon addition of the sodium chloride is impossible to filter... much of it is colloidal and too small a particle size for filter paper to catch. So, the solution is briefly boiled. The boiling aggregates the colloidal particles into a granular precipitate which is easily filtered. If you omitted the boiling and added a stabilizer you would have a colloidal suspension of ionic silver chloride.
What are nanoparticles ??? What's Nano-Silver ???
Nanoparticles are discrete particles in the nanometer size range. A nanometer is (10)-9 (ten to the negative power of nine) meters, or one billionth of a meter. Remember we mentioned "microns" a few paragraphs ago ? A micron is (10)-6 meter, or a millionth of a meter. A millimeter is (10)-3 meter, one-thousandth of a meter, or about 1/25 inch. There's 1,000 nanometers in a micron, 1,000 microns in a millimeter, 1,000 millimeters in a meter. A human hair might be around 50 microns in diameter.
Some nanoparticles in common use include fumed silica (thickener), carbon black (tires, ink), zinc oxide and titanium dioxide (transparent sunscreens). Micron-sized zinc oxide is used in non-transparent sunscreens and diaper-rash ointment. Ruby-red glass from Medieval times owes its color to gold nanoparticles dispersed within the glass.
Most nanoparticles in use today have a size between 10 and 200 nanometers, or .01 to .2 micron. These particles could have between 20,000 and 200,000,000 atoms in them. Most nanoparticles will quickly agglomerate without some sort of stabilizing or dispersing agent. Because of their extremely high surface area many nanoparticles have very unique physical properties. Bulk Silver, for example, has a melting point in excess of 1700 degrees F., nanosilver particles can melt at under 400 degrees F. One curent application is the printing of conductive circuit traces with nanosilver-based ink, then fusing the particles together into a solid conductor in a simple oven.
Silver nanoparticles are made simply in the lab by mixing silver nitrate solution with sodium citrate and a stabilizer, usually polyacrylic acid (PAA) or polyvinylpyrrolidinone (PVP). It is then warmed on the hotplate overnight and in the morning.... presto...nanosilver ! The size of the nanoparticles produced can be changed by adjusting the experimental conditions. Some of these stabilizers, like PAA, are charged (PAA is acidic), so some confusion may exist about neutral, metallic Silver nanoparticles which are "ionically stabilized" and "ionic silver". The lack of uniform nomenclature, and deliberate obfuscation by some manufacturers, only adds to the confusion.
Silver surfaces are toxic to bacteria and viruses. Nanoparticles have a huge surface area... 15 to 1,500 square meters per gram are common. Ten grams might cover a football field if evenly distributed. Thus nanosilver kills many viruses and bacteria, including HIV, at least in a test tube. How you would use it in a live animal without it attacking the good (host's) cells is currently a topic of hot research.
My personal idea for nanosilver would be to fight an epidemic of bird flu (H5N1) virus, if this virus ever becomes contageous in man. Since this virus primarily exists (and does most of its damage) in the lungs, treatment would consist of putting a dilute solution of silver nanoparticles into an ultrasonic humidifier and breathing the resulting nanosilver fog. You read it here first !!!