Thank you for your interest in my work. Unfortunately due to constraints I was unable to outline all the cool applications of NOHMs, such as desalination.

One thrust to improving membranes is to add a reactive barrier (such as a reactive nanoparticle) in addition to the selective barrier (size selective pores). Zero valent iron, Titanium dioxide and silver are examples of such nanoparticles that can react with and destroy contaminants. However, conventional methods of incorporating these nanoparticles present a fabrication challenge as they can alter the morphology, porosity, and mechanical properties of the membrane.


Previous work has shown that these challenges can be overcome through NOHMs. With a silver core and a corona of polyethylene imine (PEI) molecules that link to the membrane, we can bind a high concentration of these biocidal (an inherent property of silver nanoparticles) NOHMs to the surface of polysufone ultrafiltration (UF) membranes. Thus, we have an active reactive barrier on the surface without modifying the inherent properties of the original membrane.


The benefits of this approach include the wide range of available properties through different NOHM designs, ease of manufacturing, and reduction of costs by using a more efficient membrane.

I hope that answers your question.

Also, I’d like to add that NOHMs can be used to help keep the selective barrier clean of fouling organic species. Often times the membranes have organic species bind to them and this reduces the flux and performance. Recent work has shown that by adding polyamide-silica based NOHMs on to the membrane surface, we can drastically improve the hydrophilicity of the membrane. This hydrophilicity means that water can displace the organic foulants and keep membrane performance high.

The reason why NOHMs are preferred to simply functionalizing the membrane itself with amide groups is the fact that this method decreases the performance of the membrane (similar to above). Additionally, in this case, the amide groups can be removed from the surface of the membrane where as they are more rigidly held to the nanoparticle in the case of the NOHM.

Reference: Tiraferri, A., Kang, Y., Giannelis, E., and Elimelech, M. “Superhydrophilic Thin-Film Composite Forward Osmosis Membranes for Organic Fouling Control: Fouling Behavior and Antifouling Mechanisms”, Environmental Science & Technology, Volume 46, October 2012, pages 11135–11144.

Thanks for taking an interest in my project.

The image at the top of the poster depicts GNR that are coated with the surfactant CTAB as a result of the synthesis. These particles were originally in water and then drop casted on a TEM grid. The assembly you see is a result of the evaporation process and the interaction between the particles and surfactant. CTAB is comprised of long non-polar alkyl chains. It is my understanding that the particle alignment you notice stems from a CTAB bilayer forming between the two adjacent particles. Our microscopy has also shown that the distance between these adjacent gold particles to be relatively constant at about 4nm.

A closer inspection of the poster will show a distinct difference in the particle alignment of that TEM image and the following TEM image of the GNR after the corona has been attached. This is because the organic molecules in the corona displace the CTAB and exhibit a different set of interactions. These particles were also dispersed in THF and not water so the evaporation process is different as well.

Hi Dr. Ludwick,
I am not sure I fully understand your question.

In the video I mention the all the changes we can make to the corona “hairs” such as the grafting density, the length of the polymer, etc. I can illustrate an example about how varying one of these design parameters will affect the resulting NOHMs material.

Say we were to have a low grafting densities (less than the root of the polymer hair’s radius of gyration). Here the polymers would not have many neighbors and would be able to fold on itself and form a loose coil. Now as we increase the grafting density, the polymer chains in the corona would start to encroach upon eachother and the steric hindrance would force the chains to extend out. We could also attach a polymer with an ionic group at the end, this would add an electrostatic interaction to the above situation. These low to moderate grafting densities can be modeled like a polymer brush.

Structurally these corona interactions have a lot of importance, particularly with regards to the dispersion state of the material. The steric repulsion at high grafting densities mentioned above can provide stabilization of the nanoparticles as it can keep the cores from agglomerating and phase separating. This is one of the key advantages of NOHMs over other organic-inorganic nanocomposites. By directly attaching the polymer to the inorganic core the only way to “demix” is by physically breaking this bond.

A labmate of mine has recently studied the effect of corona design on the dispersion state of Silica-PEG NOHMs particles in a PEG matrix by systematically varying the grafting density on the particles. He found that at significantly high grafting densities, the polymers in the corona become significantly compressed and can actually jam the system. This is shown through a transition in the viscosity of the material. I highly recommend that you consult his work listed below. He also did a study on how the grafting density affects the structure factor, S(q).

I hope the sufficiently answers your question and if I missed the mark, please let me know.

Hi Dr. Gannett,

Thank you for taking the time to review my presentation.

You are correct that the notion of grafting polymers onto nanoparticles can be traced as far back as the 1950s and has been a growing area of research for the past few decades. I did not mean to imply that Cornell “invented the wheel” when it comes to organic-inorganic nanocomposites. I sincerely apologize if you feel my phrasing did not properly credit the appropriate researchers for their groundbreaking work in this field. However, to my knowledge, the concept of self-suspended nanoparticle-organic hybrid systems can be correctly attributed to Cornell university scientists (see reference below). I would say it is this solventless aspect that truly distinguishes the materials I’m talking about when I say “NOHMs” from the other materials you mentioned.

There were a few reasons why I chose to use the term “recent.” First, I started my video with a reference to adobe bricks from thousands of years ago. With that time scale in mind, these nanocomposites can be considered “recent.” Further, I wanted to convey the sentiment that the full range of possible material properties in NOHMs are not fully known and additional research (like mine) is necessary. And as a consequence of this incomplete fundamental understanding, there exists a still greater potential for this class of materials to impact future technology. This motivates the work and conveys its importance to society as whole.

Perhaps there is a better way to express these ideas than the phrase you quoted. Again, I apologize if you feel I misrepresented this work.

Please feel free to ask any additional questions,
T.J. Wallin

Reference: A. B. Bourlinos, S. R. Chowdhury, R. Herrera, D. D. Jiang, Q. Zhang, L. A. Archer and E. P. Giannelis, Adv. Funct. Mater., 2005, 15, 1285.

Further, the viscoelastic behavior of other nanoparticle-organic hybrids (star polymers, colloidal suspensions and granular particles) does not completely describe the viscoelastic behavior seen in our NOHMs. This points to NOHMs being a truly unique materials platform.

OK, thanks. I actually knew pretty much nothing about plasmon resonance, but your explanation was excellent.

Thanks Dr. Opilia. I felt this medium lent itself well to actually illustrating some of the examples.

Thanks Tony! My goal was to make the material accessible to everyone and I’m glad someone from another field could understand it.

I am in no way the discoverer of this class of nanoparticle-organic composite materials (that happened before my arrival in the 2000s). However, I mentioned in the video there is a wide range of possible properties in NOHMs because of the many ways in which we can modify the design. So in this regard, my research can still be considered important.

For example, my particles have an unusual shape (rods). How self-suspended rod-shaped NOHMs flow and how different factors affect their flow behavior is unknown in the field. My research, in addition to the shear sensor application, looks to probe this behavior on a fundamental level.

Another unknown variable my research looks to study from a fundamental standpoint is the type of bond that attaches the hairs to the core. I am using a thiol-gold bond which is a different type of covalent bond than the previous studied NOHMs materials by my group.

Finally, the cool optical properties are a result of an intrinsic feature of gold nanoparticles called localized surface plasmon resonance. There has been little work done on NOHM cores that have this feature, so my work can be considered somewhat cutting edge in that regard.

I really think the strength of NOHMs lies in their tunability-we don’t know the limit of the possible properties this class of materials can exhibit. So while I am far removed from the discovery, I still feel this work is necessary and innovative (but I’m a little biased).