TY - JOUR
T1 - Interfacial microrheology of DPPC monolayers at the air-water interface
AU - Kim, Kyuhan
AU - Choi, Siyoung Q.
AU - Zasadzinski, Joseph A.
AU - Squires, Todd M.
PY - 2011/9/7
Y1 - 2011/9/7
N2 - We present systematic measurements of the surface rheology of monolayers of liquid-condensed (LC) dipalmitoylphosphatidylcholine (DPPC) at the air-water interface. Using microfabricated, ferromagnetic 'microbuttons' as new microrheological probes, we measure the linear viscoelastic moduli of LC DPPC monolayers as both surface pressure and frequency are varied. Visualization of this interface reveals that the interlocked liquid crystalline domains that comprise an LC-DPPC monolayer give rise to a viscoelastic solid response. Two distinct behaviors arise as surface pressure is increased: for low surface pressures (8 mN m-1 ≤ Π ≤ 12-14 mN m-1), the monolayer behaves like a two-dimensional emulsion, with a surface elastic modulus G′s that is relatively constant, as would be expected from a line tension-mediated elasticity. The surface viscosity increases exponentially with Π, as would be expected for a condensed liquid monolayer. Above 12-14 mN m-1, however, both moduli increase exponentially with Π, albeit with a weaker slope - a response that would not be expected from line-tension-mediated elasticity. This transition would be consistent with a second-order phase transition between the LC and solid-condensed phase, as has been observed in other phospholipid monolayers. Finally, we employ a controlled-stress (creep) mode to find a stress-dependent viscosity bifurcation, and thus the yield stress of this monolayer.
AB - We present systematic measurements of the surface rheology of monolayers of liquid-condensed (LC) dipalmitoylphosphatidylcholine (DPPC) at the air-water interface. Using microfabricated, ferromagnetic 'microbuttons' as new microrheological probes, we measure the linear viscoelastic moduli of LC DPPC monolayers as both surface pressure and frequency are varied. Visualization of this interface reveals that the interlocked liquid crystalline domains that comprise an LC-DPPC monolayer give rise to a viscoelastic solid response. Two distinct behaviors arise as surface pressure is increased: for low surface pressures (8 mN m-1 ≤ Π ≤ 12-14 mN m-1), the monolayer behaves like a two-dimensional emulsion, with a surface elastic modulus G′s that is relatively constant, as would be expected from a line tension-mediated elasticity. The surface viscosity increases exponentially with Π, as would be expected for a condensed liquid monolayer. Above 12-14 mN m-1, however, both moduli increase exponentially with Π, albeit with a weaker slope - a response that would not be expected from line-tension-mediated elasticity. This transition would be consistent with a second-order phase transition between the LC and solid-condensed phase, as has been observed in other phospholipid monolayers. Finally, we employ a controlled-stress (creep) mode to find a stress-dependent viscosity bifurcation, and thus the yield stress of this monolayer.
UR - http://www.scopus.com/inward/record.url?scp=84855417065&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84855417065&partnerID=8YFLogxK
U2 - 10.1039/c1sm05383c
DO - 10.1039/c1sm05383c
M3 - Article
AN - SCOPUS:84855417065
SN - 1744-683X
VL - 7
SP - 7782
EP - 7789
JO - Soft Matter
JF - Soft Matter
IS - 17
ER -