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Nanoparticles

Notes

From 04/14/2015 thorugh 4/27/2012

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Notes

1. Definition

2. Compounding

3. Nanoparticle Toxicity

4. Grafted Nanoparticles

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1. Definition:

 “In nanotechnology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. Particles are further classified according to size in terms of diameter, coarse particles cover a range between 10,000 and 2,500 nanometers. Fine particles are sized between 2,500 and 100 nanometers. Ultrafine particles, or nanoparticles are sized between 100 and 1 nanometers. The reason for this double name of the same object is that, during the 1970-80's, when the first thorough fundamental studies were running with "nanoparticles" in the USA (by Granqvist and Buhrman) and Japan, (within an ERATO Project).  They were called "ultrafine particles" (UFP). However, during the 1990s before the National Nanotechnology Initiative was launched in the USA, the new name, "nanoparticle" had become fashionable (see, for example the same senior author's paper 20 years later addressing the same issue, lognormal distribution of sizes.  Nanoparticles may or may not exhibit size-related properties that differ significantly from those observed in fine particles or bulk materials. Although the size of most molecules would fit into the above outline, individual molecules are usually not referred to as nanoparticles.”

“Nanoclusters have at least one dimension between 1 and 10 nanometers and a narrow size distribution. Nanopowders are agglomerates of ultrafine particles, nanoparticles, or nanoclusters. Nanometer-sized single crystals, or single-domain ultrafine particles, are often referred to as nanocrystals.”

(Wikipedia, Nanoparticles, 9/28/2011)

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2. Compounding Problems

“Over the past several years, polymer nanoparticles have attracted increased attention not only in the technical fields such as catalysis, combinatorial chemistry, protein supports, magnets, and photonics, but also in the manufacture of rubbery products such as tires. For example, nanoparticles can modify rubbers by uniformly dispersing throughout a host rubber composition as discrete particles. The physical properties of rubber such as moldability and tenacity can often be improved through such modifications. Moreover, some polymeric nanoparticles may serve as a reinforcement material for rubber. For example, polymer nano-strings are capable of dispersing evenly throughout a rubber composition, while maintaining a degree of entanglement between the individual nano-strings, leading to improved reinforcement over traditional reinforcing fillers.

However, an indiscriminate addition of nanoparticles to rubber may cause degradation of the matrix rubber material. Rather, very careful control and selection of nanoparticles having suitable architecture, size, shape, material composition, and surface chemistry, etc., are needed to improve the rubber matrix characteristics. For example, properties of polymeric nanoparticles made from diblock copolymer chains are controlled by the thermodynamics of diblock copolymers in a selected solvent. The thermodynamic phase diagram of those systems usually depends on two factors, the volume fractions of the componentsand the miscibility between them . Therefore, for a given system, i.e., when the parameters between components are fixed, the formation of micelle structures depends primarily on the volume fraction of each component  In order to obtain a micelle nanoparticle of desired structure, the concentration or the volume fraction must be controlled. Flexibility of concentration adjustment is usually small due to the underlying thermodynamic laws and the phase diagrams. As such, it cannot provide high flexibility in concentration variations. This could raise unwelcome constraints in industrial processes”.

[Wang et al, US Patent 8,288,473 (10/16/2012)]

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3. Nanoparticle Toxicity

The rapidly growing nanotechnology requires understanding and measurement of potential nanoparticle toxicity.  Materials not normally toxic or carcinogenic may be toxic due to quantum effects in the 1-100 nm particle sizes.  These have increased surface/mass ratios with different shapes on the molecular level.  Biomarkers whose gene expression profiles change upon exposure to nanomaterials can be reliable indicators of nanoparticle effects. 

Chen  developed in-vitro assays of biomarkers detecting toxicity, stress response and DNA damage as a result of nanomaterial exposure in any cell type, especially human epithelial cells, normal human keratinocytes  and human fibroblasts.   Each assay is first calibrated against nanomaterials with toxic, stress and/or DNA damage responses.  Cytotoxic thresholds are indicated when 1% of the total genes are changed more than two-fold.  Carbon nanotubes show inflammatory response, and titanium dioxide induces DNA damage.  Nanoparticles in general do demonstrate toxicity, especially at higher concentrations.  Both size and shape of the particles affect toxicity levels. In fact, carbon nanoonions show potential cancer treatment because of its cytotoxicity.

US Patent 8,785,505 (July 22, 2014), “Toxicology and Cellular Effect of  Manufactured Nanomaterials,” Fanqing Chen (University of California, Oakland, California, USA).

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4. Grafted Nanoparticles

Nanoparticles such as semiconductor nanoparticles are being used in the fabrication of nanostructured electronic devices.  In many instances, grafting or passivation of molecules to nanoparticles is needed to fine tune the most critical properties.  The usual thermal grafting of these particles while avoiding agglomeration, is limited to small particle concentrations, severely limiting application. 

Mangolini et al improved passivation efficicncy by grafting Group IV nanoparticles in the gas phase flowing through specially designed plasma chambers.  The plasma causes the organic molecules to break into active groups which bond to the suspended nanoparticles.   The nanoparticles are activated in the first plasma chamber and grafted in a second plasma chamber without agglomeration in milliseconds compared to minutes and hours by the conventional grafting method.

US Patent 8,945,673  (February 3, 2015), “ Nanoparticles with Grafted Organic Molecules,” Lorenzo Mangolini, Uwe Kortshagen, Rebecca J. Anthony, David Jurbergs, Xuegeng Li, and Elena Rogojina (University of Minnesota, Minneapolis, Minnesota and Innovalight, Inc., Sunnyvale, California, USA).

 

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Roger D. Corneliussen
Editor
www.maropolymeronline.com

Maro Polymer Links
Tel: 610 363 9920
Fax: 610 363 9921
E-Mail: cornelrd@bee.net  

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Copyright 2012 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen
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* Date of latest addition; date of first entry is 4/27/2012.

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