The Advanced Photon Source
a U.S. Department of Energy Office of Science User Facility

Soft Matter Interest Group

Type Of Event
Meeting
Sponsoring Division
APS
Location
Virtual
Start Date
03-08-2021
Start Time
10:00 a.m.
Description

SPEAKER: Christine DeWolf (Professor, Department of Chemistry and Biochemistry, Concordia University, Canada)

TITLE: Pi-interactions in Langmuir Films:  A Tale of Structured Monolayers and Multilayers (and Their Interconversion)

ABSTRACT: It has long been known that strong headgroup interactions will influence lipid and surfactant molecular self-assembly.  In Langmuir films their influence is observed as changes to film structure, organization, morphology and rheology.  In this seminar, our recent work probing the balance of competing pi-stacking and hydrogen bonding interactions will be presented with two systems, namely surfactants containing aminobenzoquinones and phenolic headgroups. In both cases, the presence of pi-stacking interactions yields strong directional interactions that dominate the phase behaviour and lead to highly rigid films with unusual film morphologies. Grazing incidence x-ray diffraction (GIXD) revealed that these were associated with the formation of crystalline headgroups, a feature not often observed for lipids or surfactants with small headgroups. The long-range ordering of the headgroups is not only evident from the diffraction patterns but also supported by computational studies. This pi-stacking driven headgroup organization then leads to the formation of molecular superlattices and crystalline 3-D structures. The latter, observed with the dialkylaminobenzoquinones, were observed to co-exist with both tilted and untilted monolayers and, despite the heterogeneity, was found to be a highly reversible and reproducible process. In the case of the phenols, the relative strength of the pi-interactions can be observed via the invariance of the unit cell parameters, despite compression, deprotonation and/or addition of an w-thiol. The latter, which creates a bola amphiphile, also induces controlled and regular multilayer formation. While the utility of introducing pi-stacking to control ordering is well known in liquid crystals, there are relatively fewer reports of the use for creating and controlling long-range ordering in monolayer films. 


LINK: https://uchicago.zoom.us/j/94220080385?pwd=b0VpcUFUOFNDT0pITk5WeTg4YjAw…
Meeting ID: 942 2008 0385
Password: 013444

  1. Please turn off your video to save bandwidth. 
  2. We will mute your audio during the seminar to avoid any interfere. 
  3. If you have any question during the seminar, please keep the question to the end of the meeting. We will have 5-10 minutes at the end of the seminar for Q&A.
  4. We will record the presentation and turn the recording off during the discussion session.
  5. The meeting will start (10 am) and end (11 am) on time.
  6. Please feel free to forward this seminar announcement to others who are interested in soft matter topic.
     
03.01.2021

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