Scanning Probe Microscope Study of Mixed Chain-Length Phase-Segregated Langmuir-Blodgett Monolayers

Abstract

Using a scanning probe microscope, the influence of adhesion on measured film height of mixed-chain-length fatty acid Langmuir-Blodgett monolayers was investigated. A 1:1 mixture of CH3[CH2]22COOH and CH3[CH2]14COOH, was deposited in which the long chain-length acid, C24, was segregated from the short chain-length acid, C16. Two experiments were performed, contact scanning and force curve mapping. From both experiments, the film height difference measured between the C16 and C24 regions was larger than expected. Adhesion of the tip was 20% larger over the C16 acid regions. Using a compressional modulus derived from film pressure vs. area isotherms of the pure components, the adhesion difference and apparent filmheight difference over the two regions can be understood.

Scanning Probe Microscopy

“…3.10. For example, lateral force contrast has been found on films of molecules with varying length but the same chemical endgroup [180] . A further source of friction contrast is the local variation of tip-sample forces on inhomogeneous surfaces, usually referred to as material-specific contrast.…”

Surface morphology studies of in situ polycondensation microcomposites using atomic force microscopy

“…5b). To explain the different adhesion forces, the contact mechanics relationships governing the tip-surface interaction should first be examined [6]. The adhesion force represents the difference in surface energies [6].…”

“…To explain the different adhesion forces, the contact mechanics relationships governing the tip-surface interaction should first be examined [6]. The adhesion force represents the difference in surface energies [6]. Since PHB and PBT-PTMG are two components of the composite they should have the same surface energy, as they are dissolved with chloroform and dispersed on the mica surface.…”

“…* Corresponding author In recent years, great developments have been seen in the field of scanning force microscopy (SFM), also known as atomic force microscopy (AFM) [5]. In addition to topographic imaging, the force between the AFM tip and the surface can also provide unique localized chemical and physical information about the sample surface on the nanometer scale which could not readily be obtained by other techniques [6]. By using the force-distance curve [7], one can directly measure the surface force, elasticity, friction and adhesion, which are dependent on the probe, contact surface and surrounding medium.…”

“…Analysis of the adhesion forces can thus produce localized chemical information about the sample-liquid interface, such as the nature of the surface functional group. However, the complexity of the structure of surfaces and the interaction between the AFM tip and the surface (such as contact area, surface/tip compliance) [6], has limited AFM identifying unknown chemical specimens on the surface.…”