Talk:Colloid

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In Netscape Communicator 4.79, this table overlaps the frames in the standard skin, rendering the whole an unreadable mess. -- April 12:06 Aug 6, 2002 (PDT)

So I'm reading about asphalt when I see a link to a page on colloids, and as I click it I wonder out loud, "What's a colloid?" The first words that load are in the caption for the picture : "milk is a colloid." Problem solved! I didn't even have to wait for the rest of the page to load! Love it how things sometimes work out. --Ye Olde Luke (talk) 05:08, 18 April 2008 (UTC)

Contents

[edit] Merging with colloidal suspension

Should we perhaps merge this article with colloidal suspension?

[edit] Typo Correction

Made a typo correction (changed 'is' to 'are') --fixman88 01:36, Jun 12, 2005 (UTC)

[edit] Question

[edit] Shoe polish a colloid?

Most shoe polishes consists of a wax base with pigment particles. The viscoelasticity (i.e. "semisolidness") of shoe polish is a result of the behavior of the hydrocarbon chains that form the wax, which entangle to form a solid at rest, but can disentangle with applied shear, resulting in "liquid-like" behavior (for example, wiping the polish on a cloth). Therefore, while there may be some small particles present in the shoe polish that contain the pigment, the viscoelatic behavior of shoe polish is not due to colloidal interactions.

That being said, cream shoe polish is an emulsion, and therefore would be considered a colloidal suspension. The viscoelastic properties of cream shoe polish (or hand cream for that matter) ARE due to colloidal interactions betwen emulsion droplets.

[edit] Nature claims 6 errors

Nature disputes the accuracy of this article; see http://www.nature.com/news/2005/051212/multimedia/438900a_m1.html and Wikipedia:External_peer_review#Nature. We're hoping they will provide a list of the alleged errors soon. —Steven G. Johnson 01:54, 15 December 2005 (UTC)

[edit] Errors ID'd by Nature, to correct

The results of what exactly Nature suggested should be corrected is out... italicize each bullet point once you make the correction. -- user:zanimum

  • 'In general, a colloid or colloidal dispersion is a two-phase system of matter'; No, a uniform dispersion of particles in a liquid is a one-phase system of two or more components, no matter how large the particles are. A two-phase system requires there to be two distinct phases separated by an interface. If all the colloidal particles coalesced into one large particle, only then would it be a two-phase system, and the original colloid would be considered to have been in a meta-stable state
  • In a phase colloid, small droplets or particles of one substance, are dispersed in another substance, the continuous phase. In a molecular colloid, macromolecules are dispersed in a continuous phase (or dispersion medium). I’ve never heard of this division of colloids into phase colloids and molecular colloids.
  • Colloids can be classified as follows: ß Inconsistency: What follows is a very different classification than given in the opening two paragraphs. à


   Dispersed phase material           
        Gas     Liquid droplets Solid particles    

   Gas     None: all gases are mutually soluble    Liquid aerosol,

Examples: fog, mist Solid aerosol, Examples: Smoke, dust

   Liquid  Foam,

Examples: Whipped cream Emulsion, Examples: Micelles, milk, mayonnaise, hand cream, vesicles, blood Sol, Examples: Paint, pigmented ink

   Solid   Solid foam,

Examples: Aerogel, Styrofoam, Pumice Gel, Examples: Gelatin, jelly, cheese, Opal Solid sol, Examples: Cranberry glass, Ruby glass

  • Misconception: van der Waals forces: These are due to dipole-dipole interactions (permanent and/or induced). Even if the particles don't have a permanent dipole there could be are always quantum mechanical fluctuations of the electron gas giving rise to an instantaneous a temporary dipole. So these types of forces are always present.
  • Omission in 'interactions' section: * Steric forces between polymer-covered surfaces or in solutions containing non-adsorbing polymer can modulate interparticle forces, producing an additional repulsive steric stabilization force or attractive depletion force between them.
  • The charge on the dispersed particles can be observed by applying an electric field: all particles migrate to the same electrode ß Only if the sign of their charge (positive or negative) is the same and therefore must all have the same charge. ß The same sign, not necessarily the same charge. The logic of this sentence is backwards.

I believe I've fixed the errors now (at least, I've done what I would do if that was the referee report on my own paper) and have removed the naturedispute tag. Sdedeo (tips) 23:51, 5 January 2006 (UTC)

[edit] Nature Review: possible misunderstandings

the article should probably state "all gases are soluble" in the classification table instead of "all gases are soluble", as suggested, because "all gases are soluble" does not imply they are mutually soluble, which is the relevant property in this context. In addition, I would recommend to replace the word "medium" in the column head by "material", as suggested, because "medium" usually refers to the solvent in which the other substance is solved, "medium" impies that the material is of greater quantity than the other.

[edit] Identifying Colloids

How would I go about identifying a colloid? Say a textbook gives you a series of substances which you have to identify as colloid, suspension, or solution, how would you do it? (other than the Tyndall effect - you can't pull that off everywhere) Are people just supposed to memorize what are colloids?

Welll, off the top of my head, a suspension will settle out whereas a colloid will stay suspended. That's a start, anyway. Gzuckier 18:31, 3 October 2006 (UTC)

[edit] Isn't milk more properly a sol and not an emulsion?

I believe milk is an emulsion when stored about 32 degrees celsius, but I hope for your health that you are storing it at a temperature below that. So, I'm editting the page to classify milk as a sol rather than as a emulsion. - 63.107.91.99 17:01, 27 August 2007 (UTC)

Regardless of storage temperature, milk comes out of the teat at a somewhat higher temperature than normal storage. It is perfectly healthy to drink at this point. How, then, do you classify it? Water could be classified as a solid, because, when stored below 0 Celsius, it is a solid, if we go by storage temperatures Fiddle Faddle 17:02, 4 October 2007 (UTC)
How about we just go with how people actually encounter milk the vast majority of the time? No question milk is an emulsion coming out of the teat, but at 4 celsius it's a sol. - 63.107.91.99 17:41, 6 November 2007 (UTC)
Okay, someone modified milk back to being an emulsion rather than a sol, without commenting here. Butter was left listed as a gel, rather than an emulsion, though, which is inconsistant in an unexplained way. - 63.107.91.99 (talk) 19:32, 24 March 2008 (UTC)
User:Epastore had a discussion on his talk page, but not here, about the reasoning behind his change. In any case, I just removed milk and butter from the table; if the purpose of the table is to inform people of examples of various colloids, there's no need to include confusing edge cases like butter and milk. - 63.107.91.99 (talk) 19:39, 24 March 2008 (UTC)

[edit] Second paragraph of lead section

The second paragraph lists 7 books on the subject of colloids. The referencing format is distracting and should be replaced. I suggest creating a separate section at the end of the article for "further reading", and listing the books there. Shalom (Hello • Peace) 00:58, 30 October 2007 (UTC)

[edit] Colloid: State of matter?

On the bottom of the page there is a list of phases of matter; in the list is a colloid. Does this, as it suggests make a colloid a phase?

[edit] Smoke and whipped cream are suspensions, not colloids.

If you are using this Wikipedia page for a project for Chemistry class you should find your informaition elsewhere- most of the information here is in-correct. Colloids are heterogeneous. Smoke and whipped cream are suspensions, not colloids. Whipped cream if left over time gets watery, smoke once dispersed leaves ash behind, these are signs of suspensions, not colloids. (this editorial comment by User:142.227.15.1 moved to talk page from article) -- Paleorthid (talk) 16:29, 14 December 2007 (UTC)

[edit] Homogeneous?

The article says that, "In some cases, a colloid can be considered as a homogeneous (not heterogeneous) mixture."

I don't see how this can be correct. A homogeneous mixture is a solution, not a colloid, right? If you look at the solution article, it defines a solution as "a homogeneous mixture composed of two or more substances". Deepfryer99 (talk) 15:23, 9 April 2008 (UTC)