From: larry@kitty.UUCP (Larry Lippman)
Subject: Re: looking for thick liquids
Summary: Hydrophilic colloids & DIY fast food restaurant milk shakes...
Date: 27 Dec 90 04:05:23 GMT
Organization: Recognition Research Corp., Clarence, NY

In article <1990Dec26.214729.2334@ultra.com>, bob@ultra.com (Bob Beach)
writes:

> I am looking for a means of creating a very thick liquid. Ideally it
> should be clear, non toxic, not corrosive, and reasonably cheap to make.
> I would like to be able to create varying degrees of "thickness".

        You did not state the application, so I can't recommend any one
agent over another, but I will give you some general suggestions based
upon thickening agents used as food additives.  Such thickening agents
will obviously meet the conditions of being non-toxic and non-corrosive.
Consider using the following, all of which form hydrophilic colloids:

1.      Agar - a polysaccharide mixture of agarose and agaropectin derived
          from algae
2.      Arabic gum - carbohydrate polymer derived from acacia plants
3.      Bentonite - a colloidal clay largely comprised of aluminum silicate;
          this is indeed an FDA-approved food additive - scary, huh? :-)
4.      Carrageenan - a polysaccharide derived from seaweed
5.      Methylcellulose and carboxymethylcellulose - cellulose derivatives
6.      Polyethylene glycol (PEG) - a relatively inert condensation polymer
          of ethylene glycol
7.      Xanthan gum - a synthetic carbohydrate polymer, similar to natural
          gums

        There are various other agents, including numerous variations of
the above substances (e.g., ammonium alginate, calcium alginate, sodium
alginate, etc.).

        The hydrophilic colloidal properties of some of the above substances
are amazing.  Some years ago, I used to do a "party trick" that involved a
parody of a fast food restaurant milk shake.  I would take 12 ounces of
water, add a tablespoon of milk, a tablespoon of chocolate syrup and a
tablespoon of xanthan gum.  Mixed in a blender for a few minutes, the
result was virtually indistinguishable from a typical McShake.  So much
for the "milk" in "milk shake"... :-)

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
VOICE: 716/688-1231   {boulder, rutgers, watmath}!ub!kitty!larry
FAX:   716/741-9635                  {utzoo, uunet}!/      \aerion!larry





From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.chem
Subject: Re: looking for thick liquids
Summary: Thixotropy, mucilage & food additives
Message-ID: <4275@kitty.UUCP>
Date: 28 Dec 90 02:31:32 GMT

In article <00941CC5.04E18280@BINAH.CC.BRANDEIS.EDU>,
sommer@BINAH.CC.BRANDEIS.EDU writes:

> I seem to recall an article or Amateur Scientist column in Sci. Am. on
> thixotropic liquids a while back. Corn starch in water produces a
> thixotropic liquid but it's translucent, not clear.

	Is corn starch gel in fact thixotropic?  I don't believe so, but
I am not certain.  Many colloidal gels exhibit little or no thixotropy.
Most carrageenans and carboxymethylcellulose varieties, as examples, are
only slightly thixotropic.  One of the best examples of a colloidal gel
that is truly thixotropic is bentonite (clay, primarily containing
aluminum silicate).

> There are occasional articles in J. Chem. Educ. about classroom demos and I
> vaguely remember a few on polymers and gels. I think one of them involved
> aqueous solutions of boric acid and <cannot recall other ingredients>. That
> one was specifically for a hands-on grammar school chemistry demo, so I
> think it was pretty safe and non-toxic. (I think it was to make the "glop"
> used in children's toys.)

	Borax and sodium alginate will produce an "icky" gel.  A common
variety of mucilage can be produced from dextrin, borax, a small amount of
phenol, and water.

	BTW, when's the last time anyone bought a bottle of mucilage? :-)

> LL's shake recipe sounded delicious.

	Delicious, indeed. :-)  I always had to drink a sample to prove
than the xanthan gum was in fact harmless.

> BTW, some of those things are called
> THICK SHAKES because there isn't enough milk in them to be called MILK
> SHAKES legally.

	That's a good point!  One must be careful of USDA and FDA labeling
regulations when trying to deceive the public. :-)  A similar example is
found on many frozen dessert and snack products.  Instead of seeing the
label "ice cream", one finds "ice milk", "frozen confection containing
dairy products", etc.

> I have read that tiny plastic polymer beads are used to
> thicken some of them and other items in the food industry. (The beads just
> pass through undigested.)

	There is a series of carboxy vinyl polymers produced under the
tradename of Carbopol.  The Carbopols are used as thickening agents in
pharmaceutical and food products.  I have seen an effective demonstration
of Carbopol in which coarse sand was suspended with negligible settling.

	Low-density (branched chain) polyethylene is used as a chewing
gum base.  Makes it easier to re-chew after leaving it on the bedpost
overnight. :-)  Anyone remember the song?

> This IS an FDA approved use of the beads.

	It is amazing what the FDA approves.  Bentonite as a thickening
agent is a good example.  Good lord, this stuff is *clay*!  I really have
mixed emotions when it comes to some of these food additives.  Wearing
my "chemist's hat", I know the material is inert and harmless.  Wearing
my "consumer's hat", I have to ask: isn't anything *real* and *wholesome*
 anymore?

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
VOICE: 716/688-1231   {boulder, rutgers, watmath}!ub!kitty!larry
FAX:   716/741-9635                  {utzoo, uunet}!/      \aerion!larry





From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.chem
Subject: Re: looking for thick liquids
Summary: Some rheolly :-) complex issues & thixotropy in religious ceremonies
Keywords: non-newtonian fluids,pseudoplastic,dilatent,thixotropic,rheopectic
Date: 30 Dec 90 18:37:11 GMT

In article <1990Dec28.150032.12455@kodak.kodak.com>,
ornitz@kodak.kodak.com (Barry Ornitz) writes:

	Barry Ornitz gives a good capsule summary of the four most common
categories of viscous fluids, to which I will add a few additional comments.

	Barry used the term non-Newtonian fluid, which should probably be
defined for the benefit of some readers.  A Newtonian fluid is one in
which the viscosity is independent of the shear rate, alternately expresed
that the ratio of shear rate (flow) to shear stress (force) is constant.
A Newtonian fluid represents an "ideal" fluid whose viscosity and flow
characteristics are readily predictable.  Behavior of non-Newtonian fluids
is not so easy to predict.

	In many process industries such as food, soap, cosmetics, paint,
polymers, etc. the majority of all end products are non-Newtonian in their
fluid characteristics.

	Most hydrocolloids lose viscosity over time, for reasons including
but not limited to: (1) depolymerization; (2) degradation due to hydrolysis;
and (3) cleavage of cross-linkages.  These mechanisms are all accelerated
by heat and repeated exposure to mechanical shear.

	Some hydrocolloids in solution exhibit interesting behavior with
temperature change.  Consider methylcellulose, which is soluble in cold
water but insoluble in hot water.  If one heats an aqueous solution of
methylcellulose it will first result in a viscosity decrease proportional
to increasing temperature *until* about 50 deg C where dehydration occurs.
Such dehydration produces a rather rapid gel formation, which then reverses
upon cooling.

> Having said all of this, I should now give some examples of each. But
> this is the problem. Some materials exhibit one form of non-newtonian
> behavior at low concentrations and other forms at high concentrations.
> So maybe Larry is not really wrong after all. ;-)
> ...
> Like I said, it gets complicated. Drilling mud is usually bentonite
> clay, for example. Starch shows up in more than one list too.

	It sure does get complicated!  Bentonite is commonly considered as
thixotropic when in a gel state, but when in a sol state it is rheopectic.

	I made a general statement about starch not being thixotropic, but
I gave no qualification as to concentration or whether the starch was in the
form of a sol (suspension) or gel (colloidal solution).  While I stand by my
statement in characterizing the most common behavior of starch in solution, 
the situation is really more complex than that.

> If you want to see an extreme case, make up a very thick paste of
> cornstarch and water. Stir rapidly. It almost behaves as a solid. Let it
> sit and it flows easily. If you get the proportions right, you can make
> a starch ball and roll it around in your hands. Stop rolling and it will
> flow through your fingers.

	Obviously Barry's example above is not one of thixotropic behavior!

	It is not easy to obtain a good understanding of rheology and
behavior of non-Newtonian fluids.  Such an understanding requires good
background in physical chemistry, colloid chemistry and fluid mechanics.
Most undergraduate courses in physical chemistry have a brief discussion
of colloids, but do not even mention such topics as thixotropy.  Most
undergraduate courses on fluid mechanics have only a brief discussion
of non-Newtonian fluid behavior and usually do not mention colloids.
Courses in colloidal chemistry (often graduate level) cover such topics
as thixotropy, but usually lack good discussion of fluid mechanics
necessary for full understanding in a process environment.

	Many people who have worked with colloids and non-Newtonian fluids
have pieced their knowledge together from multiple sources, and have in some
cases learned a lot about the topic The Hard Way.  Much of my own knowledge
falls into this latter category, largely the result some early experiences
working with soap and cosmetic products.

	In closing, here is an interesting "application" of thixotropy.
It has been speculated that certain religious reliquaries that purport to
show "liquefaction of blood" are in fact thixotropic gels of ferric oxide.
Such a ferric oxide gel appears reddish-brown in the rest state, but when
shaken will become more red and somewhat transparent as the contents
change to a sol state.  There is indeed evidence that such ferric oxide
is of volcanic origin, and is readily found in places like as Naples, Italy.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
VOICE: 716/688-1231   {boulder, rutgers, watmath}!ub!kitty!larry
FAX:   716/741-9635                  {utzoo, uunet}!/      \aerion!larry