Micro-Fastening System and Method of Manufacture

TITLE

MICRO-FASTENING SYSTEM AND METHOD OF MANUFACTURE

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a micro-fastening system and, more
particularly, to a fastening system employing a plurality of mating
nanoscale fastening elements and a method of manufacturing a
micro-fastening system in accordance with the teachings of the present
invention.

2. Description of the Prior Art

Fastening systems, albeit on a macro-scale, have generally been in the
form of adhesive bonds or welds occurring between two distinct
components brought into relative contact. Numerous potential
disadvantages associated with employing adhesives are known such as
the irreversible nature of the bonds and the potential for degradation
at relatively high temperatures. Further, adhesives require smooth dry
interfaces which are free of impurities to effectuate high quality
bonds. Welding results in a physical deformation of the surfaces being
welded and cannot be used effectively for large interface areas. Thus,
there is a need for the mechanical micro-fastening system of the
present invention.

SUMMARY OF THE INVENTION

The micro-fastening system of the present invention employs a
plurality of mating nanoscale fastening elements which are obtained by
structurally modifying, i.e., functionalizing nanotubes generally and
carbon nanotubes particularly. Carbon nanotubes per se consist of a
graphite monolayer having the overall shape of a cylinder including
ordered pairs of hexagonal carbon rings disposed along the cylindrical
side walls which may be single or double walled as reported in Nature,
Vol. 354 (1991) pp. 56 -58. The ends of the tubes may generally be
closed by ordered pairs of pentagonal carbon rings. Carbon nanotubes
generally may range in diameter from one to about 50 nano-meters, and
may be as long as a fraction of a millimeter. While related to carbon
fibers, nanotubes are free of atomic scale defects, which accounts for
their high tensile strength, as compared to that of the strength of
individual graphite layers. Like graphite, carbon nanotubes exhibit
sp2 bonding which gives rise to a relatively high degree of
flexibility and resilience. Further, carbon nanotubes are structurally
stable nearly up to a the melting point of graphite, i.e., up to about
3,500 degrees Celsius.

By functionalizing the carbon nanotubes as will be described in
greater detail below, the generally cylindrical shape can be modified
to include bent portions. While it has been suggested generally that
carbon nanotubes can be readily functionalized, it has yet to be
reported that carbon nanotubes can be specifically functionalized so
as to obtain mating fastening elements as herein described.

Among the various applications for the micro-fastening system of the
present invention are the assembly of nano-robots useful for
micro-surgical procedures and surface coatings, by way of non-limiting
example.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1(a-c) are a series of views demonstrating the representative
closure forces for a generic micro-fastening system in accordance with
the teachings of the present invention.

Figures 1(d-f) are a series of views demonstrating the representative
opening forces for a micro-fastening system in accordance with the
teachings of the present invention.

Figure 2 is a schematic view illustrating the efficiency of the
micro-fastening system in accordance with the teachings of the present
invention.

Figures 3(a-c) are a series of views demonstrating the representative
opening and closure forces for a particular micro-fastening system
based on nanotubes functionalized to form a matching hook and loop
arrangement in accordance with the teachings of the present invention.

Figures 4(a-b) are illustrative of alternative mating nanoscale
micro-fastening system elements in accordance with the teachings of
the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The micro-fastening system of the present invention comprises a
plurality of mating nanoscale fastening elements manufactured by
modifying, i.e., functionalizing nanotubes which are substantially
linear in nature prior to functionalizing. Upon functionalizing the
nanotubes, fastening elements are obtained in a variety of forms such
as hooks, loops and spirals by way of non-limiting example, which
facilitates attachment to a corresponding fastening element. The
nanotubes employed may be composed of carbon, nitrogen, boron or other
elements which give rise to layered honeycomb lattice structures. For
simplicity, however, the present invention will generally be described
in terms of functionalizing graphitic carbon nanotubes.

By functionalizing graphitic carbon nanotubes, it is meant that a
specific number of pentagons and heptagons are added along the open
edge(s) of the core nanotube which comprise ordered pairs of hexagons.

Upon introducing pentagons and heptagons in a predetermined order, the
carbon nanotubes will exhibit a locally positive or negative Gaussian
curvature that results in a bend in the nanotube. By continuing to add
pentagons and hexagons in a specific manner, the bend of the nanotube
can be grown until the desired shape is obtained. As previously noted,
among the various fastening elements which can be manufactured are
hook structures as shown in Figures 3(a) and 4(a), loop structures as
shown in Figure 3(a) or spiral shaped structures as shown in Figure
4(b).

Upon growing the carbon nanotube to the desired length and shape, one
end of the tubule may be capped or terminated by introducing or
forming a fullerene half dome along the end to be terminated. By
providing a fullerene half-dome along an open end of the carbon
nanotube, the formed fastening element end becomes substantially
inert, i.e., non-bonding to other atoms or molecules.

The opposing end of the fastening element which is open, i.e.,
non-terminated, is bonded to a matrix or substrate which may be in the
form of various materials including metals, diamond and silicon to
name a few. Since the open end is highly reactive, it has a natural
affinity for bonding to the desired substrate. As a result of this
natural bonding affinity, the fastening element attaches to the
substrate in a manner whereby the element stands up along the
attachment surface, which in turn promulgates mating between
corresponding fastening elements.

While carbon nanotubes having pairs of pentagons and heptagons may
occur spontaneously to a limited extent during synthesis, in order to
design carbon nanotubes such that they can be used effectively in
micro-fastening systems, atomically dispersed catalysts may be
employed. For example, transition metals have been shown by the
inventors to convert pentagons into heptagons.

Additionally, it is theorized that spontaneous curving of relatively
straight carbon nanotubes may occur by employing a template in
proximity to a growing nanotube. In this regard, both on energetic and
entropic grounds, a horizontally growing nanotube, when approaching a
vertically positioned nanotube used as a template, has a higher
probability to form C5 and C7 carbon rings, i.e., pentagons and
heptagons which would cause the former to wrap around the latter. As
such, specifically functionalized carbon nanotubes useful as fastening
elements can also be prepared without employing catalysts.

As shown in Figs. 1 and 2, only a moderate force Fo is required to
close the gap and form a bond between component A and B. A much larger
force Fo is required to open this bond. The hatched area in Fig. 2
represents the work required to close and re-open the gap and
indicates the efficiency of a particular pair of mating nanoscale
fastening elements.

The strength of micro-fastening systems described herein relies on the
enormous stability of nanotubes, their structural rigidity, the
strength of nanotube-surface bonds and a large number of connections
possible on a limited surface area. In contrast to mechanical
fasteners which weaken the surfaces to be connected, there is no
apparent degradation of the opposing surfaces to be joined under the
present invention. Adhesives are typically weaker than most mechanical
fasteners and their strength is strongly diminished at higher
temperatures. Welding is not practicable for large interfaces, whereas
the fastening system of the present invention may be employed for both
large and microscopically small interfaces. Bonding technologies
excepting the micro-fastening system of the present invention leave
macroscopically large gaps at the interface. Unlike known bonds
between substrates, the micro-fastening system of the present
invention has an effective thickness of the gap at interface as small
as a few nanometers.

A further advantage of the present invention is that the surface bonds
based on microfastening, while extremely strong, may be re-opened and
re-closed, whereas the surface bonds generated by gluing or welding
are permanent. Thus, the micro-fastening system of the present
invention is selectively reversible which is considered to be highly
desirable, particularly for self-repair.

Still another advantage offered by the micro-fastening system is that
the conductivity of the fastening elements and their corresponding
substrates may be varied from metallic to insulating, depending
largely on the tubule diameter and chirality of the nanotubes.

ABSTRACT OF THE DISCLOSURE

The present invention relates to a micro-fastening system and, more
particularly, to a fastening system employing a plurality of mating
nanoscale fastening elements and a method of manufacturing a
micro-fastening system in accordance with the teachings of the present
invention. The mating nanoscale fastening elements are formed by
functionalizing nanotubes having ordered pairs of hexagons with both
pentagons and heptagons at a particular heterojunctions.

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