Associative telechelic polymers – application as mist-control additives, dynamics and thermodynamics
Jeremy Wei, Boyu Li
Liquid fuels, such as gasoline, diesel and kerosene, are the world's dominant power source, representing 34% of global energy consumption. Transportation relies on such liquids, presenting the risk of explosive combustion in the event of impact, such as the 1977 Tenerife airport disaster—an otherwise-survivable runway collision that claimed 583 lives in the post-crash fireball. The UK and the U.S. responded with a multi-agency effort to develop polymeric fuel additives for “mist control.” Ultra-long, associative polymers (e.g., ICI’s “FM-9,” >3•106 g/mol copolymer, 5 mol% carboxyl units) increased the drop diameter in post-impact mist1,2, resulting in a relatively cool, short-lived mist fire. However, the polymers interfered with engine operation3, and their ultra-long backbone—essential for mist control—degraded upon pumping4. They were abandoned in 1986. A quarter century later, the post-impact fuel fireball involved in the collapse of the World Trade Center motivated us to revisit polymers for mist control. Building on recent advances in supramolecular assembly as a route to emergent functional materials5-9, particularly assembly of complex polymer architectures10,11, we discovered an unexplored class of polymers that is both effective and compatible with fuel systems. Long (>4•105g/mol) end-associative polymers form “mega-supramolecules” that control post-impact mist without adversely affecting power, efficiency or emissions of unmodified diesel engines. They also reduce turbulent drag, hence, conserving energy used to distribute fuel. The length and end-association strength of the present polymers were designed using statistical mechanical considerations. In comparison with ultra-long polymers for mist control4, the present polymers are an order of magnitude shorter; therefore, they are able to resist shear degradation. In contrast to prior randomly-functionalized associative polymers3, these end-associative polymers also avoid chain collapse12. We found simple carboxylic-acid/tertiary-amine end-association to be effective, and the unprecedented length10 of these telechelic polymers to be essential for their potent rheological effects.
Apparatus for impact/flame propagation experiments. An aluminum canister (outer diameter = 23 mm, height = 100 mm) was used as a miniature fuel tank to hold ~30 mL of a test sample. The cap was tightly sealed with superglue and electrical tape. A stainless steel cylinder (diameter = 24 mm, length = 50 mm) was used as a projectile to impact the sample canister and disperse the fuel. To the left of this image: Compressed air at 6.89×105 Pa was used to propel the projectile through a 1.66 m-long barrel (inner diameter = 25.4 mm), resulting in a muzzle speed of 63 m/s measured by time of flight between two flush-mounted sensors in the barrel. An array of three continuously burning propane torches was placed in the path of the ejected fuel. To prevent the torches from being extinguished by the burst of air from the gun, a shield was placed between the torch tip and the gun. The impact, misting, subsequent ignition and flame propagation were captured using a high-speed camera (Photron SA1.1, frame rate 10 kHz). Image acquisition was triggered by a laser-motion detector attached to the end of muzzle.
Movie 1 High-speed impact movie for pure Jet-A.
Movie 4 High-speed impact movie for Jet-A treated with 430k TA (0.3% wt) “unsheared”
Movie 5 High-speed impact movie for Jet-A treated with 430k TA (0.3% wt) “sheared”
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Mixed Matrix Polymer Films for Sustainable Chemistry
Polymeric membranes are critical for applications in sustainable chemistry, engineering and materials (SusChEM)1–2. The Diallo Group at KAIST1–3 has made major advances in the preparation of mixed matrix porous membranes that combine the durability of polyvinylidene fluoride (PVDF) with the fouling resistance and diverse functionality of neutral, hydrophilic polymers (e.g., polyethylene glycol). The Diallo Group recently discovered a new class of membranes—PVDF membranes with embedded polymeric particles (Figure 1)—and these materials show broad potential applications.
In collaboration with Prof. Diallo, we seek to understand the relationship between the preparation conditions and the resulting structure of these membranes, using small-angle neutron scattering (SANS), electron microscopy, x-ray photoelectron spectroscopy, and permporometry. Two exciting applications of the membrane will also be explored. The first one is water purification, particularly desalination of seawater. Our goal is to develop ultrafiltration and nanofiltration membranes for the pretreatment of seawater. Furthermore, we will exploit a few key features of these membranes for use in electrochemical cells. One such feature is the functionality of the embedded polymeric particles; this functionality enables them to bind metal ions and encapsulate metal clusters. We are utilizing this chelating ability to develop novel copper-containing electrode materials for the electrochemical reduction of carbon dioxide.
Preparation of mixed matrix polyvinylidene fluoride (PVDF) membrane with in-situ synthesized polyethyleneimine (PEI) particles. Particles are made by crosslinking hyperbranched PEI with epichlorohydrin (ECH).4
1) Kotte, M. R.; Hwang, T.; Han, J-I. and Diallo, M. S. J. Memb. Sci. 2015, 474, 277–287.
2) Kotte, M. R., Cho, M. and Diallo, M. S. J. Memb. Sci. 2014, 450, 93–102.
3) Kotte, M. R., Kuvarega, A., Mamba, B. B, Cho, M. and Diallo, M. S. Mixed Matrix PVDF Membranes With In-Situ Synthesized Dendrimer-Like PAMAM Particles: A New Class of Sorbents for Cu(II) Recovery from Aqueous Solutions by Ultrafiltration. Environ. Sci. Technol. Accepted.
4) Figure 4B from Diallo, M. S.; Kotte, M. R.; and Cho, M. Mining Critical Metals and Elements from Seawater: Opportunities and Challenges. Environ. Sci. Technol. [Article ASAP]. DOI: 10.1021/acs.est.5b00463. Published Online: April 20, 2015.