What a wonderful crossroad!

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  • M. Muthukumar

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    1. Polymer Science and Engineering Department, University of Massachusetts, Amherst, Massachusetts 01003
    • Polymer Science and Engineering Department, University of Massachusetts, Amherst, Massachusetts 01003
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What a journey our field has enjoyed! Only less than a century ago, mankind could not comprehend the possibility of stringing monomers together into polymer chains. Now we recognize polymers everywhere in genetic inheritance of life, material environments, emerging technologies, cures for diseases, and consciousness itself. Indeed, the advances made in our field, both technological and fundamental, in such a short period of time, are tantamount to the intellectual capacity of our species, and will soon be written by historians as an epic.

At this auspicious juncture, as we stand with the laurels for our understanding of universal aspects of homopolymers, it is inevitable to wonder about what the next challenge is. The very fact that we do understand that polymers are omnipresent in almost all fields of science is itself presenting a huge challenge to us in terms of what directions we would like to take. Too many choices! I think it is fantastic that each one of us can take steps in any direction in this wonderful field, and rewarding discoveries are guaranteed. My opinion given below is very personal, and I look forward to read other opinions.

Why did Mother Nature choose polymers as the theater to express Herself? Why is Life made of strings instead of, say, cubes or spheres? My belief is that this choice has to do with entropy. The great god Gibbs taught us that it is the free energy, ETS, which governs the physical processes in any system of many components. Yet, I must reckon with the fact that my body cannot sustain an error of 2% in the temperature T. For a finite T, in addition to rather marginal variations in the energy E, dramatic variations can be introduced through the entropy S. What can be a better candidate than polymer molecules, where the conformations can be wildly changed without losing their topological integrity? The beautiful micrographs that attract our minds, such as the chromosomal explosion out of a cell being lysed, attest to the dramatic variations in conformational entropy of single polymer molecules.

If I were to make everything in the Universe using polyethylene and their immediate relatives, simply because they are endowed with lots of conformational entropy, I quickly run into a great difficulty. Knowing the facts about the time scales involved in the transportation of uncharged polymer molecules in crowded environments, we can readily conclude that we must somehow design a way of making the macromolecular processes faster. I cannot imagine a child taking a week to exhibit a smile, or even worse, a mother taking a month to respond to that smile. I think that Evolution chose the design to make clocks faster through salts and by making the polymer molecules electrically charged. It is already clear from the experiments in our field that the small counterions swarm around gigantic polyelectrolytes and transport them with much faster speed than that if the polymers were to be left alone. In addition, the effective charge separation b along the chain contour (appearing through the electrostatic interaction strength, bT, and ε being the temperature-dependent local dielectric constant) modulates the local temperature.

So, my opinion is that the physics of polyelectrolytes is central to our field. It is the bridge between the past successes and future opportunities, independent of whether these are in life sciences or nanotechnology (translocation of macromolecules, polymer condensation, vesicular transport, encapsulation and gene therapy, drug delivery, hydrogels, ill-formed crystals behind neurological diseases, etc.). It is relatively easy to identify a key issue of great relevance. But the real challenge is to know what to do with this identification. In particular, the identification of questions, which are both answerable and at the same time relevant to physical reality, is exciting.

Given the context above, the immediate questions that come to my mind are the following:

  • 1For polyelectrolyte solutions, which have several major variables, it is necessary to cultivate useful analytical formulas to mirror the successes of Flory-type formulas for uncharged polymers, with a proper validation using experimental facts.
  • 2Structure of water in the vicinity of polyelectrolyte molecules, and a quantitative understanding of the dielectric function of aqueous solutions.
  • 3Organization of charged heteropolymers, both natural polymers (such as proteins) and synthetic hybrid polymers (such as brushes and multi-block copolymers) in crowded environments. The analogs of microphase separation, coil–globule transition, helix–coil transition, crystallization, and glassy behavior in these charged systems are very rich and challenging, and surely will keep many of us engaged for at least a decade. This area is in the heart of nanotechnology, which is currently being touted as new science.
  • 4Interface between charged membranes (2D) and polyelectrolytes (1D), as manifest in many delivery platforms. This question raises an opportunity to build a bridge between fundamental research in soft matter physics and biology/biotechnology.
  • 5Analog of ion pumps for macromolecular translocation—an example is the transport of mRNA through nuclear pores. An understanding of how small and big entities (for example, ion channels and polyelectrolyte channels) are coupled together in a hierarchy of length and time scales is needed to begin to explore the enigma of consciousness.

Naturally, the above list is subjective. I can easily imagine several other lists of creativity from synthetic polymer chemists. Finally I would like to conclude with a personal observation regarding the sociology in our community. We cannot really ask for a better time to be doing research in polymer physics. We have gained lots of confidence in dealing with such complex objects as stringy polymers, thanks to our great heroes, and the potential research projects for even greater accomplishments are conspicuously in front of us. However, it appears that the polymer community needs some sort of assurance that the field is not yet dead! Several polymer scientists seem to have the urge to do ‘biology’ or something else, which is imagined to be better. Of course, this perception is totally personal. I hope my arguments would persuade those pessimists that the polymer field is wonderful and the future of our Evolution is inside it. Yes, our field is indeed for mature scientists (due to the interdisciplinary nature) and don't we want to mature with Time? In addition, yes, there are “growing pains” within our community, because there are few scientists for such a vast area of research. The consequent frustrations have not helped to secure adequate research funding for our field. Some of us are either too critical or too pessimistic. I think we should collectively support our efforts and obtain more financial support for our dear meaningful inquiries.

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