{"id":27,"date":"2013-09-14T15:28:25","date_gmt":"2013-09-14T20:28:25","guid":{"rendered":"http:\/\/www.nano-blog.com\/?p=27"},"modified":"2022-09-02T13:19:38","modified_gmt":"2022-09-02T18:19:38","slug":"when-is-nano-really-nano","status":"publish","type":"post","link":"http:\/\/www.nano-blog.com\/?p=27","title":{"rendered":"When is \u201cnano\u201d really nano"},"content":{"rendered":"

The common definition of \u201cnano\u201d is when one dimension of a material is less than 100 nm.\u00a0 The definition from a Google search [1] on \u201cWhat is nanotechnology?\u201d yields the following: \u201cthe branch of technology that deals with dimensions and tolerances of less than 100 nanometers, esp. the manipulation of individual atoms and molecules\u201d.\u00a0 Wikipedia references [2] the National Nanotechnology Initiative\u2019s definition, which includes: \u201c\u2026which defines nanotechnology as the manipulation of matter with at least one dimension sized from 1 to 100\u00a0nanometers<\/a>.\u201c\u00a0 Since governmental regulations are based on this definition, let\u2019s consider if this is a realistic method of defining nanomaterials.\u00a0 There is a wealth of material to consider, but only the following properties will be considered in this blog: surface adhesion, color, melting point, conductivity, reactivity, and magnetic moments.<\/p>\n

SURFACE ADHESION:<\/b>\u00a0 There are a number of different ways to consider surface adhesion.\u00a0 The nano realm does not behave in ways we normally experience.\u00a0 The semiconductor industry requires extreme cleanliness.\u00a0 The issue of adhesion came to the forefront when the removal of 50 nm particles from imaging masks was an absolute necessity.\u00a0 The evaluation of the particle removal indicated that particles below 70 nm or 80 nm would adhere more strongly to surfaces.\u00a0 When the size of the material drops below 80 nm, van der Waals forces become the dominant mechanism for particle adhesion.\u00a0 Work in other areas have provided the ability to make glass that is self-cleaning by minimizing the ability of particles to the surface.\u00a0 Contrary to the perception that the flatter the surface, the harder it will be for particles to adhere is not a truism.\u00a0 The picture below shows a lotus leaf structure [3] which is the basis of the design of self-cleaning surfaces.\u00a0 By creating a surface that does not present a flat surface for materials to adhere to, the contaminate is naturally rejected.<\/p>\n

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COLOR:<\/b>\u00a0 As mentioned in a previous blog (August 30th<\/sup>, 2013), the application of nanomaterials has been employed for millennia.\u00a0 Nanoparticles of gold have been used to give glass a red color.\u00a0 The picture below is from a Smithsonian article [4] and references the pictures as being supplied by the British museum.\u00a0 The goblet appears to be green colored until light illuminates it from the rear.\u00a0 It then shows its reddish color. The effect is caused by particles about 50 nm imbedded in the glass.<\/p>\n

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MELTING POINT: <\/b>Over the centuries, one constant that people learned is that materials have a constant melting point.\u00a0 Gold melts at 1064.18o<\/sup>C, which has been determined experimentally.\u00a0 \u00a0In fact, the various melting points for different materials can be employed to remove impurities and obtain more pure amounts of the specific material desired.\u00a0 Recently, the ability exists to examine the behavior of smaller sized particles.\u00a0 What has been found is that below 50 nm the melting point of materials begins to diminish.\u00a0 The curve below [5] shows the decrease of the melting point of gold as the size is diminished.\u00a0 [A starting point for additional information on this effect is available in reference 6.]<\/p>\n

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CONDUCTIVITY: <\/b>In many respects, the conductivity issues is similar to the melting point issue.\u00a0 Conductivity is a bulk material property that is perceived as being a constant.\u00a0 Except that we are now able to work with very small material.\u00a0 Copper, a material valued for is conductivity, starts to have potential issues as the width of the conductors shrink below 50 nm.\u00a0 Effects of grain boundaries and crystal orientation can cause two similar sized conductors to have different conductivity.\u00a0 Consequently, precautions are required in semiconductor manufacturing processes to minimize the potential variance among conductors.<\/p>\n

REACTIVTY: <\/b>The increase of surface area provides for an increase in reactivity.\u00a0 This is one of my favorite points when someone wants to include all material under 100 nm as being nano and should be considered the same regardless of the size.\u00a0 Consider a jar of 80 nm aluminum particles.\u00a0 How carefully should it be handled?\u00a0 There is the obvious concern about opening it and having some of the dust inhaled or possible attached to one clothing.\u00a0 It is advisable to be cautious, but there is nothing obviously dangerous about the container and its contents as long s proper handling is observed.<\/p>\n

According to the desire to create one classification of all 100 nm or smaller similar material, in this case aluminum, it makes no difference as regard to the size of the material.\u00a0 Consider a jar of 30 nm aluminum.\u00a0 Obviously, the same precautions need to be taken as the 80 nm material.\u00a0 BUT, and this is a key difference, 30 nm aluminum particles react when exposed to air (oxygen).\u00a0 Chemists classify the reaction as being very energetic.\u00a0 To the lay person, it is an explosion! \u00a0Yet some regulation agencies want to classify both sizes as being identical.\u00a0 Really?\u00a0 There is some effort in France to include exposed surface area in the classification of nanomaterial.<\/p>\n

MAGNETIC MOMENTS:<\/b>\u00a0 There are a limited number of materials that are considered to have magnetic properties.\u00a0 The nano realm always provides surprises.\u00a0 \u201cThere are a number of materials that are known to have magnetic properties, and they do not include either silver or platinum.\u00a0 However, 13 atoms of silver have been shown theoretically to have a magnetic moment, and 13 atoms of platinum has been shown experimentally to have a magnetic moment. [8 & 9]\u00a0 This is a new property<\/span><\/b> for these metals.\u201d[7]<\/p>\n

THOUGHTS:<\/b> Establishing a standard or regulation based on a simple property as 100 nm or less does not guarantee that the issued document appropriately addresses the concerns.\u00a0 Material Safety Data Sheets (MSDS) become questionable at best.\u00a0 A nano-MSDS that is 17 pages long will not be effective, nor are there enough resources to produce an MSDS for each 1 nm variation of particle size..\u00a0 The effort of DuPont and the Environmental Defense Fund to develop the Risk Framework is an excellent starting point.\u00a0\u00a0 But, how does one really know what the material properties are.\u00a0 If there are a distribution of particles, and there are always some size differences, how does one quantify the material properties?\u00a0 Our experience is that we can go to a table and find a property, but at the nano scale the properties are changing with size.\u00a0 Does a distribution of 10 nm gold particles (0.5 nm half-width) have the same properties as a similarly sized distribution with a half-width of 3 nm?\u00a0 Will they melt the same way?\u00a0 What happens when one looks at the impact of multiple effects on the nanoparticles?\u00a0 Currently, bulk material properties have two-dimensional curves for the properties, e.g., the boiling point of water is a function of temperature and pressure.\u00a0 Does this imply that the proper description of nanoparticles will need to be three-dimensional? Or multi-dimensional?\u00a0\u00a0 More on this topic in a later blog.\u00a0 Please feel free to submit comments and\/or questions.<\/p>\n

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References:<\/b><\/p>\n

    \n
  1. https:\/\/www.google.com\/#q=what+is+nanotechnology<\/a> Google<\/li>\n
  2. http:\/\/en.wikipedia.org\/wiki\/Nanotechnology<\/a> Wikipedia<\/li>\n
  3. http:\/\/phys.org\/news2730.html<\/a><\/li>\n
  4. http:\/\/www.smithsonianmag.com\/history-archaeology\/This-1600-Year-Old-Goblet- Shows-that-the-Romans-Were-Nanotechnology-Pioneers-220563661.html<\/a><\/li>\n
  5. http:\/\/www.carolina.com\/teacher-resources\/Interactive\/what’s-so-unusual-about-nanomaterial-melting-points%3F\/tr23010.tr<\/a> Carolina site<\/li>\n
  6. http:\/\/en.wikipedia.org\/wiki\/Melting-point_depression <\/a><\/li>\n
  7. Chapter 14 Nano Risk Assessment, W. Trybula and D. Newberry, Nanotechnology Safety, Ramazan Asmatulu editor, Elsevier Publisher 2013\/4<\/li>\n
  8. NanoTechWeb.org, May 30, 2006 posting http:\/\/nanotechweb.org\/cws\/article\/tech\/24983<\/a><\/li>\n
  9. NanoTechWeb.org, January 10, 2007 posting on University of Stuttgart report<\/li>\n<\/ol>\n

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