Dynamics of Glass-forming Materials Gregory B. McKenna, Texas Tech University, DMR 0307084

1
Dynamics of Glass-forming MaterialsGregory B.
McKenna, Texas Tech University, DMR 0307084

• Structural Recovery after CO2 - jumps
• We have previously shown that the structural
  recovery of materials subjected to moisture-jumps
  (relative humidity) leads to different behavior
  in the glassy state than do simple temperature
  jumps. We have now demonstrated that this result
  is also observed when a carbon dioxide
  pressure-jump is used. The result is shown in
  Figure 1 where we compare the volume recovery
  after a temperature jump with that after a CO2
  pressure jump. We note that, though the excess
  volume in the CO2 jump condition is greater,
  the glass seems to be more stable (structural
  recovery times are longer).
• Importantly, this response is more dramatic than
  what was observed in the RH-jump conditions and
  is being further investigated.
• Dielectric Spectroscopy
• Time-domain dielectric spectroscopy is being
  developed to investigate the dynamic response of
  polymers subsequent to CO2 pressure jumps.
  Figure 2a shows master curves of the time-domain
  response of a model system of poly(vinyl
  acetate). Figure 2b shows the time-temperature
  superposition of the data and agreement with
  literature values. Dielectric spectroscopy is new
  to the PIs laboratories.
• The time-domain spectrometer is being adapted to
  perform dielectric hole burning experiments.

Figure 1. Comparison of structural
recovery after temperature jump and CO2
pressure jump to the same final state.
a)
b)
Figure 2. a) Time-temperature superimposed
time- domain dielectric responses for PVAc film.
b) Time- Temperature shift factors from 2a
compared with literature values showing
agreement between dielectric and mechanical from
literature and from present measurements.
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Dynamics of Glass-forming MaterialsGregory B.
McKenna, Texas Tech University, DMR 0307084
Broad Accomplishments

• Education and Outreach-June 2006-July 2007
• Project results presented at universities,
  companies and national and international meetings
• NIST, Gaithersburg, MD, July 2006 (invited talk
  by G.B. McKenna, PI)
• INSA, Lyon, France, June 2006 (invited seminar by
  G.B. McKenna, PI)
• Symposium honoring K..L. Ngai, Pisa, Italy,
  September 2006 (invited talk by G.B. McKenna, PI)
• Euromech Colloquium 487, Strasbourg France,
  October 2006 (invited talk by G.B. McKenna, PI)
• Dow Chemical Company, Freeport, TX, December 2006
  (invited talk by G.B. McKenna, PI)
• APS March Meeting, Denver, CO, March 2007
  (contributed talk by G.B. McKenna, PI)
• APS March Meeting, Denver, CO, March 2007
  (contributed talk by Q. Qin, Ph.D. student)
• E.S.P.C.I., Paris, France, May, 2007 (invited
  lecture by G.B. McKenna, PI)
• University of Bayreuth, Bayreuth, Germany, June
  2007 (invited talk by G.B. McKenna, PI)
• Project results presented at regional meetings
• Society of Plastics Engineers Polyolefins
  Conference, Houston, TX, February 2007 (poster by
  S. Kollengodu-Subramanian, graduate student)
• NATEX, Dallas, TX, April 2007 (poster presented
  by S. Kollengodu-Subramanian, graduate student)
• PhD students supported or partially supported-
  Duration of grant.
• Yong Zheng, Received Ph.D. in December 2003
  Xiangfu Shi, received Ph.D. in December 2004
• Anny Flory, received Ph.D. in December 2004
  Lameck Banda, received Ph.D. in December 2006.
• Qian Qin, current student, expected to defend
  Ph.D. thesis in spring 2008 Shankar Kollengodu-
• Subramanian, current student, expected to defend
  Ph.D. thesis summer 2008.