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Phase Transitions in Colloidal Suspensions of Disks

Zhengdong Cheng, Texas Engineering Experiment Station, DMR 1006870

Despite their natural abundance and wide industrial applications, such as red blood cells and clay, disks are the least studied colloidal systems compared to geometries like spheres and rods. In our project, we established methods to fabricate and control the size, aspect ratio, and polydispersity of organic and inorganic disks and platelets, respectively. The phase behavior of charged disk suspensions displays a strong dependence on ionic strengths, as the interplay between excluded volume and electrostatic interactions determines the formation of gels and liquid crystal states.A systematic variation in the aspect ratio in the low aspect ratio region (0.001 < ξ < 0.01), showed that the I-N transition volume fraction increases with the aspect ratio. We also demonstrate the fabrication of amphiphilic nano-sheets, which are either surface- or edge-modified plates with thickness at the atomic scale, one of the thinnest amphiphilic particles reported so far. 

Disks & liquid crystals. (a) Fabri-cation: surface control of low aspect ratio wax disks. (b) Poly-dispersity-dependent phase transition of high. (c) gelation via ion exchange.

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(d) Dependence of I-N transition on aspect ratio and polydispersity. (e) Fabrication of thin amphiphilic nano-sheets.

Phase Transitions in Colloidal Suspensions of Disks

Zhengdong Cheng, Texas Engineering Experiment Station, DMR 1006870

1.      “Surface-controlled shape design of discotic micro-particles” A. F. Mejia, P. He, M. Netemeyer(undergraduate), D. Luo, M. Marquez and Z. Cheng, Soft Matter, 6, 2010,4885-4894.2.       “Oscillatory swelling behavior of hydrogels incorporated with ion-exchange nanoparticles” Q. Wang, G. Wang and Z. Cheng, Drug Delivery Letters, 1, 2011, 58-61.3.       “Gelation via Ion Exchange in Discotic Suspensions” Y. Chang, A.F. Mejia, Z. Cheng, D. Di, and G.B. McKenna, Phys. Rev. Lett. 108, 2012, 247802.

Publications from NSF-DMR-1006870: Educational outreach. (a) International student A. Guiza-Vargas visualizes nematic droplets using a crossed-polarized optical microscope. (b) High school student C. Xie performs experiment with R. Ng. (c) Under graduate students R. Ng and M. Simonnetty discuss measurements. (c) Xie is observing a sample with graduate student M. Shuai.

Education: This research project has involved three graduate students (one Hispanic student A.F. Mejia, and two female students Y. Chang and M. Shuai), five undergraduate students from TAMU (P. Nguyen, R. Ng, M. Simonnetty, S. Greer, and E. Risinger), one summer REU student, (X. Zhang, Univ. Michigan), two international students from Colombia (Juan S. Guevara and Alexis Guiza-Vargas), and three high school students (Sarah Akbani, C. Xie and A. Gawande).

Outreach: The PI was invited by the Guangdong University of Engineering, Sichuan University & Hongkong University to lecture on “Colloidal crystals and liquid crystals”. The PI was invited to Mary Kay O’Connor Process Safety Center Steering Committee meeting to deliver talk “Nanoplates for industrial applications” to industrial safety leaders. Collaborations have been established with scientists in Spain and China.

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4.       “Aspect Ratio and Polydispersity Dependence of Isotropic-nematic Transition in Discotic Suspensions” A.F. Mejia, Y. Chang, R. Ng (undergraduate), M. Shuai, M.S. Mannan, and Z. Cheng, Physical Review E 85, 2012, 061708. Figure selected as part of PRE kaleidoscope images, June 2012.5.      “Pickering Emulsions Stabilized by Amphiphilic Nano-sheets” A. F. Mejia, A. Diaz, S. Pullela, Y. Chang, M. Simonetty (undergraduate), C. Carpenter, J. D. Batteas, M. S. Mannan, A. Clearfield, and Z. Cheng, Soft Matter, DOI:10.1039/C2SM25846C, (2012), In press.