NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/sci/nanotech/712

Internet Message Format | 1992-12-20 | 5.5 KB

Path: sparky!uunet!spool.mu.edu!yale.edu!qt.cs.utexas.edu!cs.utexas.edu!rutgers!igor.rutgers.edu!planchet.rutgers.edu!nanotech
From: [e-mail] (Ralph Merkle)
Newsgroups: sci.nanotech
Subject: Re: Some questions re "Nanosystems".
Message-ID: <[e-mail]>
Date: 18 Dec 92 01:24:13 GMT
Sender: [e-mail]
Lines: 93
Approved: [e-mail]

> Topic   6:  Nanosystems - New Drexler Book - Critique
> By: Hudson Hayes Luce (hluce) on Sun, Nov 15, '92


>   For starters, let's look at p259, figs. 9.2a-e. Drexler terms these
>  structures
>   "diamondoid" and ascribes the properties of diamond to them. Diamond
>   is made up of carbon atoms covalently bonded to each other, and except
>   for the surface, all bonds are single bonds. All of the three-atom C-C-C bond
>   angles are 109.5 degrees, and all of the C-C-C-C bond dihedral angles are
>   + or - 120 degrees. This conformation minimizes strain energy. Moreover,
>   all of the rings in the structure are six-membered.
>
>   However, in structure 9.2c, there are fused 3- and 4-membered rings, which
>   have bond angles of 60 degrees and 90 degrees, respectively, and whose
>   C-C-C-C dihedral angles, in some cases, are 0 degrees. This structure is
>   highly strained due to bond angle deformation and non-bonded steric
>   interactions. Compound 9.2c can thus be assumed to be highly unstable
>   at room temperatures, and is probably subject to thermodynamically-
>   driven rearrangement.

To quote from "Molecular Mechanics," by Burkert and Allinger, ACS Monograph 177,
page 117, "There are a substantial number of relatively simple, cyclopropane-
containing molecules with known structures, or known heats of formation,
or sometimes both.  We exclude from consideration here a number of relatively
large molecules containing a cyclopropane ring (in steroids, for example),
for which crystallographic structures are available.  These are not really
suitable for parameterization of the cyclopropane part of a molecule, because
there are too many other kinds of interactions present to complicate matters.
The compounds examined (174) are shown below."

There follows illustrations of 13 compounds which contain 3-member rings.
Note that cyclopropane has 3 carbon atoms located at the corners of a triangle.

The hexagonal form of carbon, which involves torsional angles of 0 degrees,
exists in nature.  To quote from "Modified Phases of Diamond Formed under
Shock Compression and Rapid Quenching" by Hisako Hirai and Ken-Ichi Kondo,
Science Vol. 253, page 772, August 16 1991:  "Crystalline forms of pure
carbon, such as diamond, lonsdaleite (hexagonal diamond), graphite, and
carbynes have long been recognized.  Diamond and hexagonal diamond have
been synthesized by both static and dynamic high-pressure techniques."

>   On p265 Drexler states "acquiring and processing molecules from solution.."
>   in reference to a possible use of nanosystems, but on p5 he states that "The
>   operating environment assumed for the nanomechanical and mechano-
>   synthetic systems discussed in Part II is high vacuum"
>
>   Describe a high-vacuum/solvent interface.

This is illustrated on page 374, figure 13.1.  There is a diamondoid wall
between the liquid external environment and the high-vacuum internal
environment.  Figure 13.4 illustrates a multi-staged cascade which will
produce an output with a contaminant fraction of less than 10^-15.


>   On p 196 it is stated, "In solution-phase chemistry, when molecular
>  potential
>   energy is transformed into mechanical energy, this promptly appears as heat
>   Reactions that reduce potential energy are accordingly termed exothermic,
>   those that increase it, endothermic. In mechanochemical systems, however,
>   potential energy released by a reaction can often be stored elsewhere in the
>   mechanical system, either as potential energy or as kinetic energy in the
>  form
>   of orderly motion"
>
>   Potential energy can be transformed into kinetic energy. True.
>   Kinetic energy can be stored in the form of orderly motion. True.
>
>   Kinetic energy can also be dissipated as heat, as random vibrational,
>  rotationl, or translational motion.
>
>   Analyse Drexler's statement in light of the 2nd Law of Thermodynamics. If
>  this
>   statement is true, perpetual motion is possible.

The second law is safe, and Drexler's statement in no way implies that
violation of the second law is feasible.  For a specific example of a
mechanosynthetic process that converts chemical energy into energy elsewhere
in the system, consider the analysis on page 223 (figure 8.6) of the
cleavage of a C-C bond.  Figure 8.7 illustrates the energies involved.
The reaction is reversible, so mechanical energy can be converted either to
or from chemical energy.  The exact efficiency of this conversion will vary
depending on the specific design.

If we broaden the definition of "mechanochemical" to include biological
muscles (which is reasonable in this case, as the underlieing principles
governing energy conversion and dissipation in biological muscles are the
same as the principles involved in systems that comply with the more
specific definition of "mechanochemical" adopted by Drexler for "Nanosystems"),
then Drexler's statement also applies to a person lifting a weight.  Some
fraction of the chemical potential energy that is released in the muscles
is used to lift the weight, thus converting chemical energy into a mechanical
form.  Lifting weights does not violate the second law of thermodynamics.