Small Wonders

February 1, 2004
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Nanotechnology Offers New Innovations

Nanomaterials are emerging as one of the fastest growing segments of the chemical and materials industries. Nanomaterials (also known as nanoparticles, nanopowders, nanoscale materials, quantum dots, and nanocrystals) are inorganic or organic powders that have been precision manufactured at sizes less than 100 nanometers (1 nanometer equals 0.001 micron and corresponds to about 4 to 5 bonded atoms). In these size ranges, most compositions begin to show commercially useful novel properties and unusual performance in part because of size confinement effects, e.g., performance influenced by Newtonian and size-confined quantum physics.1



Figure 1. Nanoscale materials are the building blocks of nanotechnology. In this picture, each sphere represents an atom.
From a historical viewpoint, nanomaterials are not new. Catalysts, carbon black, sols, fumed silica and pigment industries have already commercialized several simple oxide nanopowders, nanoscale dispersion products, and nanoparticle manufacturing processes. These are already an integral part of the chemical industry and the global economy. What is new with the developing nanomaterials industry is the emergence of low-cost, high-volume novel processes and processing innovations. These processes and innovations offer complex compositions with precision and characteristics that were previously either too difficult to achieve or too expensive to be commercially useful. The continued development of processing technologies, availability of better instruments to measure quality and features at ever-shrinking dimensions, integration of computer-aided manufacturing, and a market demand for specialty chemicals and materials innovation are fueling the growth of nanomaterials and related nanotechnologies. Combined with chemical and environmental engineering expertise that already resides in industries such as catalysts, carbon black, and fumed silica, nanomaterials are beginning to offer a foundation for innovative, value-added products in the chemical and materials industries.

Adhesives are materials that can hold together two or more solid materials by means of surface attachment. Adhesives compete with many joining technologies such as mechanical fasteners (bolts, screws, rivets, nails). However, fasteners create holes in the items they join and these holes can act as stress concentrators. Fasteners can also be labor intensive. In joining dissimilar materials, fasteners can facilitate corrosion. Fasteners also add weight to joints and often fail to provide any sealing. Adhesives often address these limitations and are widely used in many industry sectors. Adhesives provide advantages over mechanical fastening techniques as a result of flexibility, versatility, weight reduction or labor savings.

Over time, adhesives have become essential to numerous value-added applications by offering functional capabilities in addition to bonding. Examples of functional capabilities include thermal and electrical conductivity, magnetic properties, and dielectric insulation. These capabilities often utilize advances in fillers and additives.

Recent developments in nanotechnology offer several opportunities to the adhesives and sealants industry. These opportunities are the result of a number of characteristics unique to nanoscale particles. Following are some of these opportunities.



Figure 2. Fillers enabled by recent developments in nanotechnology significantly expand the ability to modify rheology of adhesives and other formulations.
Rheology control. The manufacture of high-speed coating and adhesive products requires careful control of the rheology of adhesives and sealants formulations. It is well known that particle size and size distribution affect rheology. Historically, fillers such as fumed silica with agglomerated structures have been known to rapidly increase viscosity of formulations to unacceptable levels. Recent advances in nanotechnology offer non-agglomerated particles of silicates and other compositions that retain low viscosity even at very high loadings. Figure 2 presents data on the viscosity of a formulation where everything else is kept constant, except that one contains fumed silica (SiO2) and one contains PüreNanoTM silicates available in commercial quantities from NanoProducts. The rheology of silicate nanotechnology-derived formulation is over 100 fold lower in contrast with the rheology of fumed silica-based formulations.

Recently, innovative teams such as those from BASF have reported the use of bimodal powder additives at high loadings to minimize the high-shear viscosity while maintaining the highest possible solids content to reduce drying time and energy consumption, e.g., cost.2 Novel nanoparticles have been shown to achieve between 40-60% loadings without adverse impact on rheology. These nanoparticles in combination with submicron particles also offer multimodal packing formulations for highest possible solids loadings.

Improved Mechanical Properties. Several applications demand adhesives and sealants formulations with improved hardness, modulus and strength, mar resistance, chip resistance, and wear resistance. Nanoparticles-based formulations offer such characteristics. Several teams have reported excellent enhancements in mechanical properties with nanoscale complex silicates, aluminum oxides and other compositions.3 In certain applications, nano-platelets of clays and other compositions can be added to improve mechanical and gas barrier properties.

Figure 3. Fillers enabled by recent developments in nanotechnology offer the ability to modify the mechanical, electrical, thermal and other characteristics of a formulation. The data presented contrasts and illustrates the impact on the mechanical properties of a dental adhesive formulation.
Optically Clear and Colored Formulations. For applications that require transparent, low-haze finished product (particularly with excellent mechanical properties), nanotechnology enables something that is very difficult to achieve with coarse fillers. Visible wavelength of light is between 400-700 nanometers. Nanoparticles can now be manufactured where the discrete particle size is less than 1/10th of these visible wavelengths, e.g., less than 60 nanometers. When such nanoparticles are dispersed in a matrix, light interacts with the nanoparticles very differently than with coarser particles. Additionally, nanoparticles are now available wherein the refractive index of the particles can be matched to those of the cured resin formulation. These capabilities enable the ability to formulate adhesives and sealants that have high loadings of solids when cured and yet are translucent to optically clear with excellent mechanical properties.

In other applications, colored nanoparticles can be added to simultaneously improve mechanical properties and to provide a stable and lasting color to the adhesives and sealants formulation. Alternatively, nanoparticles of high or low refractive indices can be added into the formulation to modify the refractive index of the cured adhesive.

Electronics and Conductive Formulations. Adhesives used in the electronics industry need to meet demanding requirements. Properties of interest in these markets include thermal conductivity, electrical conductivity, coefficient of thermal expansion and shrinkage of adhesives in these products. Nanotechnology is now beginning to offer on a commercial basis a range of compositions with different particle shapes and sizes that impact these properties. While the increased interfacial area often lowers the conductivity, recent work shows that there are exceptions. To illustrate, carbon nanotubes and other high aspect ratio nanoparticles offer high conductivities and they percolate at significantly lowered loadings. With respect to other properties, nanoparticles can favorably impact the coefficient of thermal expansion and have been reported to significantly reduce shrinkage.

Anti-microbial properties. In biomedical, consumer and food applications, long-lasting and broadband anti-microbial characteristics are desired. Nanoparticles consisting of silver, zinc, copper and other elements offer anti-microbial properties. Silver has been known to be an anti-microbial for centuries. The benefit of nanotechnology is that the active elements such as silver are far more available and effective in nano-engineered form, are better distributed and can be engineered to be more affordable.

Figure 4. NanoProducts Corp.’s commercial process for manufacturing nanoscale powders of various compositions implemented in Colorado and Osaka, Japan.
Miniaturization and layer thickness reduction. The smaller domain size of nanoscale materials makes them attractive building blocks for coatings and films. In coating applications, part of the cost is a function of the total raw material used in the application which itself is a function of the coating or layer thickness. The thickness, in turn, is a function of the ingredients such as powder size used to prepare the coating or layer. The smaller the powder size in the formulation, the thinner the coating or layer can be. By reducing the powder size used to prepare a coating, the coating thickness can be reduced. Reduced coating thickness means reduced raw material usage and reduced costs for a given application. In the past, thinner coatings often led to sagging or poor coating uniformity. Recently available nanoparticles have already been shown to overcome these issues in commercial applications.4 These insights can be extended to adhesives and sealants applications where the raw material costs need to be reduced.

Security applications. With increasing interest in product traceability and tools to reduce logistics-related costs, there is a need for materials that can assist such efforts. Nanotechnology is enabling complex magnetic nanoparticles and phosphors that can be easily blended homogeneously with adhesives. The resulting magnetic or optically active adhesives can be easily and readily applied to products. Such magnetically and optically active adhesives offer means to identify, code, and trace products.

Ceramic adhesives. Adhesives that use polymers and resins as the primary formulation material are often not suitable for use in high-temperature and other extreme environments. Nanoparticles of calcium silicates and other ceramics offer the ability to provide thin or thick film bonding of parts that are rated for high-temperature applications. These ceramic nanoparticles bond faster, given their higher and more reactive surface areas. In other applications, cementing ceramic nanoparticles can be blended with resins to prepare nanocomposite adhesives.



The Future

There is a significant and emerging effort to produce and apply novel nanomaterials with unusual performance.5 These nanomaterials offer a number of opportunities to address demanding application requirements and create new products. In addition, the nanotechnology industry offers strategic growth opportunities to raw material suppliers, equipment manufacturers and product formulation companies.

It is likely that nanoparticles will first serve those applications in the adhesives and sealants industry where they offer added value and a compelling advantage. If cheaper micron-scale powders and specialty chemicals suffice for an application, they will continue to be used. As the nanomaterials industry develops and matures, nanomaterials will increasingly become more affordable and cost competitive with conventional materials while offering superior or novel performance. Even today, the volume and pricing of nanomaterials is already in the range where a number of commercial applications appear economically compelling. With the availability of such nanomaterials as building blocks and associated processing know-how, commercial applications enabled by nanotechnology are beginning to emerge.

For more information on nanomaterials, contact Tapesh Yadav, Ph.D., Chairman & Chief Executive Officer, NanoProducts Corp., 14330 Longs Peak Court, Longmont, CO 80504.

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